Secondary Injector Not Firing - Have Tried All Probable Causes I Know Of

[Jayton]

Sorry for the long post in advance, but I’ve read through all posts pertaining to the secondary injector not firing and have covered all probable causes I could find in all of the previous posts to no avail. So here’s my situation that I’m hoping you guys can help me figure out:

 

First My Engine Mods:

- Block was boiled, balanced, blueprinted and bored .30 over and deck was milled

- Crankshaft was index ground, micro-polished and all oil holes were chamfered for increased flow

- Balance shafts are eliminated

- Connecting rods were race prepped - shot peened, beam polished, resized on the big ends, small ends bushed for floaters, new rod bolts installed, magnafluxed and balanced.

- JE forged pistons with Total Seal rings.

- ARP hardware was used where applicable in the re-assembly.

- An Ajusa head gasket with ARP head studs.

- A new M6 non-jet valve head - ported and polished with a 3-angle valve job on stainless steel valves with performance valve retainers, keepers, springs and a stock cam.

- A custom tubular, equal length header w/ external wastegate mount

- A Mitsubishi TD05 - 20G 'Frankenstein Stage 4' turbocharger

- HKS 40mm external wastegate

- HKS EVC IV.

- HKS blow off valve

- Custom mandrel bent intercooler piping and OVCP

- Intake manifold match ported

- Throttle body enlarged to 52mm

- Crane Cams Hi-6 ignition amplifier

- Magnecor 10mm wires

- Custom 2 ½" downpipe and straight through exhaust.

- Custom Griffin 3-row aluminum radiator

- Bosch Hi-Performance fuel pump with all new stainless fuel lines.

 

The car had been running great and I sent it to my good friends performance shop where he sorted out all of the final punch-list nonsense that remained after a complete ground-up restoration/modification process that I performed off and on over the course of the past 15 years or so. The sorting out the car needed had nothing to do with the way it ran, but more with the annoyances of stuff like no power steering, tachometer not working, suspension noises, no heat and the like. He was able to successfully complete everything on my list and everything seemed to be great until suddenly, out of nowhere, the car just started running like complete crap.

 

After checking through all of the basics we believed that possibly one or both of the injectors were clogged or going bad (I was still running the 25 year old OEM units at that time) and so I had the injectors and several other pairs I had lying around sent out for cleaning/repair and all were deemed as unrepairable. Left with no other option we purchased and installed aftermarket Delphi units using a 650 Primary with 950 Secondary, but the problem persisted and even got worse. Knowing how the TBI does not always react favorably to aftermarket injectors I decided that we should try to tune the car using the Greddy eManage Ultimate engine management system that I had installed years before, but had never actually used. The car had run great prior to this situation and so the eManage had yet to be needed. I had originally installed the eManage with the purpose of one day fine tuning the car on a dyno for optimal A/F ratio.

 

So we had the car street tuned in NY by a reputable tuner during which it was driven approximately 20-30 miles in different heat cycles and varied loads with no problems. The car ran strong with the only issue being that the boost level was not able to be limited by the HKS EVC IV (later found a melted plastic T-fitting on the silicone hoses running to/from the external wastegate which has since been replaced with a brass fitting). After the tune the car was run another 7 – 10 times and ran like a champ every time. With everything in good order I had the car shipped to NC (where I recently relocated to) in an enclosed 18-wheel car transporter. After receiving the car in NC I took it out for a test drive and it did not run good at all. It was falling flat on its face at about 3000 rpms so I limped it back home and ran it in the driveway for a while.

 

In my driveway the car idled perfectly, all temps and pressures were good and solid, but romping on the gas would cause it to break up bad. However, by gently giving it gas I was able to get it to rev past 3000 RPM’s and into the 4000 – 5500 range and hold it there with only very minor sputtering. I tried to drive it a few more times and nothing changed and I was at a loss because it had been running great in NY right before being loaded on the trailer so I don’t know what could have gone wrong between here and there.

 

Since tuning had proven to be successful in solving the running issues we experienced in NY I located a mechanic/tuner here n NC who came out to my home this past Sunday to try to sort things out via the eManage. I had heard about cars ‘losing their tune’ unexpectedly with the eManage and so figured it was a good place to start. Here is what transpired:

 

We began to tune the car using the eManage Ultimate software and the wideband O₂ sensor (located in the downpipe). The tuning went well, holding 14.2-14.6 AFR up until about 2400 RPM, where any changes made did not have any effect at all and the engine continued to severely stutter, acting as if fuel starvation or REV cut was occurring. We then removed the MAS and replaced with a MAS unit I modified/hacked to retain only the Air Intake Temperature (AIT) sensor in the stock location. We then switched to the Greddy MAP sensor by connecting a vacuum line to it from the #4 port on the intake manifold. (I had pre-installed the MAP sensor with this intent when originally installing the eManage years prior). We then made the necessary changes in eManage to read the MAP sensor accordingly. The theory behind the switch to the MAP sensor was that with no way to really test the MAS and no good replacements units available, I’d rather do away with it altogether than to play a guessing game with whether or not it was operating properly. Not to mention the additional airflow gained from removing all that clutter from the air intake path. The car did not run any better after the switch and the car idled oddly, wanting to die at times when warm.

 

After some diagnostics and consulting by phone with the previous tuner, we determined that the secondary injector was not pulsing and so we performed the following tests to try and determine why:

1. Swapped Primary injector pigtail to the Secondary to confirm that the Secondary injector does in fact work; Confirmed Working.

2. Checked continuity from ECU through eManage harness; Confirmed Good.

3. Checked continuity through OEM harness to new injector pigtails; Confirmed Good.

4. Checked continuity from either ECU pin crossing to either harness pin; Confirmed Good (but suspect bad injector resistor)

5. Diagnostic on injector resistor revealed 12v on single post in both connectors; Confirmed Good, however, we are still suspect of this.

Is this truly a solid test of the resistor?

Could there still be something wrong with it even though it passes this test?

I believe I have another one laying around I can swap in just to be sure.

Are these resistors still available new OEM or aftermarket?

6. Swapped ECU with a spare to confirm that the injector driver in the ECU was not faulty. Problem persisted and so I’m assuming the ECU drivers are good, but I still have other spare ECU’s that can be swapped in just to be certian.

7. Removed custom eManage harness from between factory harness and ECU and plugged the factory harness directly into ECU. The car ran poorly (as to be expected because MAS was removed in favor of the MAP sensor) and problem persisted.

8. Injectors Ohms:

@ Primary: 2.7

@ Secondary: 2.5

Compensation for the injectors within the eManage does nothing because it will not recognize or drive low impedance injectors and so they are still being driven by the stock ECU.

Any help on something we have missed in the injector driver path?

 

Any additional sensors that trigger the secondary injector?

 

From what I understand the injectors are driven via RPM signal into the ECU? Could the aftermarket ignition system, the tach sensor for it or the actual factory tachometer wiring be a culprit here?

I was unable to get the tachometer to work with the Crane Cams Hi-6 through the wiring harness and so a jumper wire was installed on the circuit board on the back of the cluster to give it its signal.

 

You can respond here or contact me directly at jtilt25@yahoo.com

 

Thanks in advance to all for reading my lengthy post and for any advice or clues you might be willing to offer.

[scott87star]

From what I understand the injectors are driven via RPM signal into the ECU?

 

It will be both RPM and MAF frequency (airflow rate).

[Jayton]

OK thanks.

 

So given that information, are there any additional signal paths that should be checked to this effect that we have not covered already?

Or have I potentially disturbed any of these signals with the mods that have been made?

 

Also, is there any way to read or diagnose what the ECU is seeing in terms of these signals?

 

What's still the most puzzling to me is that the car was running real strong prior to being shipped and nothing was changed or altered between here and there. Having now performed the diagnostics as listed in my original post I'm simply at a loss for what else could have caused the secondary injector to stop firing between here and there. I understand that certain parts are 25+ years old at this point and can go bad at any point, but it seems that we have confirmed that the known causes for this condition are all sound and in working order.

 

Finally, the injectors are from Fuel Injector Clinic (650cc Primary / 950cc Secondary found here: http://fuelinjectorclinic.com/starion-conquest/IS6595). Has anyone had known problems with injectors from this vendor or with this cc combo? I don't believe the injector to be dead due to the pigtail swap test we performed, but can't rule out that it may be faulty to some effect. I'm confident that the the injector connections and wiring are all in good order as per the tests we've performed.

[scott87star]

I didn't read it above, this car is an 87-89? And what are you doing for fuel pressure control? Is that loggable?

[Jayton]

Yes the car is an '87 (with 88/89 ECU).

 

I have the Trilogy RRFPR that mounts in the stock location to control pressure.

For monitoring fuel pressure I have a 1 1/2" fuel pressure gauge mounted on the TB as well as a cockpit mounted gauge.

 

I don't have any way to monitor the fuel pressure via the eManage (that I am aware of) if that's what your mean when you ask if it's 'loggable'.

[scott87star]

Yeah, are you watching the pressure gauge when its not running well? I assume the pressure is rising appropriately and holding appropriately?

[Jayton]

Due to how poorly it runs over 2500 RPM's, I haven't been able to drive it enough or been able to get it into boost under load to be able to truthfully answer that. All testing and diagnostics we have performed thus far have been with the car in neutral in my driveway and with no load on it or the ability to build boost in neutral the fuel pressure has remained rock solid at 40psi (which is what I have it set at) even when it starts breaking up.

[scott87star]

Rock solid at 40 is the wrong place for it to be when it starts breaking up. That's probably why it starts breaking up. I assume you're into boost by then, most are, and it should be climbing at least 1:1 with boost psi. If its not then you have your problem. Edited November 8, 2014 by scott87star

[StarquestRescue]

Tps, isc nose switch, bad secondary, wiring or ecu. till the injector has been tested on a flow bench it has not been tested. And even that is not a 100%. You can not tune a piggy back system in neutral for much more then idle.

 

The transition from the primary to both the primary and secondary is controlled first and for most by the airflow meter and secondly by tps movement. Rpm seems to have nothing to do with it. X amount of rpm will result in Y amount of airflow, which is why the engine can only be nursed so far on the primary by easing on the gas.

 

Go back to the mas for now. You should be able to see the airflow signal and the modified airflow signal with the emanage software. The secondary comes in at 390 hz, or sooner if you mash the gas and off at 290 hz. You should be able to see the hz signal generated by the emanage in speed density mode as well.

[Jayton]

Rock solid at 40 is the wrong place for it to be when it starts breaking up. That's probably why it starts breaking up. I assume you're into boost by then, most are, and it should be climbing at least 1:1 with boost psi. If its not then you have your problem.

 

I hope I didn't confuse you. To clarify, it's rock solid at 40 psi while revving the engine in neutral without any load on the motor. Not while driving the car and with the engine under a load.

 

Otherwise, are you saying that I should be able to build boost and see fuel pressure adjust in neutral? If you would please clarify I would appreciate it because as far as I understand this is not possible.

 

However, if what you're saying is that I should be building boost by 2500 RPM with the engine under load while driving and that the fuel pressure should be rising 1:1 accordingly I understand and agree that it should, but unfortunately cannot verify this at this time because the car is barely drive-able.

Edited November 8, 2014 by Jayton

[Jayton]

Tps, isc nose switch, bad secondary, wiring or ecu. till the injector has been tested on a flow bench it has not been tested. And even that is not a 100%. You can not tune a piggy back system in neutral for much more then idle.

 

The transition from the primary to both the primary and secondary is controlled first and for most by the airflow meter and secondly by tps movement. Rpm seems to have nothing to do with it. X amount of rpm will result in Y amount of airflow, which is why the engine can only be nursed so far on the primary by easing on the gas.

 

Go back to the mas for now. You should be able to see the airflow signal and the modified airflow signal with the emanage software. The secondary comes in at 390 hz, or sooner if you mash the gas and off at 290 hz. You should be able to see the hz signal generated by the emanage in speed density mode as well.

 

TPS & ISC were checked prior to the original tuning when the poor running condition originally started. The TPS checked out fine. A broken wire was found on the ISC and repaired to test out good. Given their age, however, I know I can't rule out the possibility that either one of these parts could have gone bad since then and so I will need to re-test each.

 

Also wanted to mention that the vacuum advance checked out good, but the mechanical advance has not been checked. From what I have read in other posts, this could cause timing issues that could cause the symptoms I'm having? So just to clarify, if the distributor is not able to advance the timing does this effect the secondary injector from firing or coming on when it's supposed to or does it simply cause the engine to run poorly and to break up badly? I'm not 100% clear on the correlation between the engine timing and the secondary injector if there is one?

 

So, if I understand correctly, what you're saying is that the air flow meter and TPS are largely in charge of when the secondary injector comes on and that it may not come on at all if the signal from either of these sensors is not being read properly by the ECU?

 

So if I go back to the MAS (which is easy enough to do) and I'm able to read the airflow signal from it in hz with the eManage and the secondary is not coming on at 390 hz and going of at 290 hz like it's supposed to, what will this confirm?

Edited November 8, 2014 by Jayton

[StarquestRescue]

So, if I understand correctly, what you're saying is that the air flow meter and TPS are largely in charge of when the secondary injector comes on and that it may not come on at all if the signal from either of these sensors is not being read properly by the ECU?

Yes

 

 

So if I go back to the MAS (which is easy enough to do) and I'm able to read the airflow signal from it in hz with the eManage and the secondary is not coming on at 390 hz and going of at 290 hz like it's supposed to, what will this confirm?

That the problem occurs at the point that the ecu switches to both injectors.

 

Depending on the emanage settings, it may be modifying the airflow signal (hz) sent to the ecu. This is the signal the ecu will respond to.

 

Your symptoms do seem to point to a secondary not supplying the fuel the ecu thinks it will. (flow issues with the injector it's self).

Since the duty cycle of the primary drops when the secondary comes on line. The car goes on it face lean if the secondary does not supply the fuel it should. At that point the airflow drops, the ecu switches back to the the primary, the engine recovers, air flow increases and the cycle repeats when the ecu switches to both injectors again. Once the sputtering starts the wide band afr reading is pretty much use less.

Edited November 8, 2014 by StarquestRescue

[StarquestRescue]

There are factors that shut the injectors off or greatly reduce them when the engine is decelerating. The main one being the the isc nose switch. But that shuts both injectors off compleatly.

 

Air flow will drop if the throttle is opening is reduced or closed. The tps may play a role here, but i do not really know. But there have been cases of the ecu doing strange things with the injectors. and the problem went away when the tps was replaced. Even though the tps tested "good"

 

For example, on my car mega squirt picks up a negaitive voltage spike when i stab the throttle sometimes. My stock ecu does not seem to notice, and i can not see it on a volt meter. But a oscilloscope show the negative spike is there.

[StarquestRescue]

A good logworks picture of the change in duty cycle when the ecu switches from the primary to both injectors and back again. Stock oem injectors. If i doubled the primary size the transition would be pushed higher into the rpm range, as i would have to reduce the modified air flow signal the afc is sending tp the ecu to attain the desired afr. In terms of boost the difference would be about zero boost vs 3-4 psi for the engine running a primary twice the size at the transition point.

 

http://i237.photobucket.com/albums/ff45/StarquestRescue/Data%20logs/Secondaryonsetatlightthrottle.jpg

Edited November 8, 2014 by StarquestRescue

[Jayton]

Great information. I truly appreciate all of it.

I'm just tying to absorb it all to determine the most logical plan of attack to try and pinpoint the root of the issue.

 

If you don't mind me asking, what would your approach be in terms of the order in which you would test things?

For example; Would you start by switching back to the MAS and checking the hz signal the ECU is or is not seeing or start with something like the TPS?

 

I'm just trying to be as logical as possible about things by going after the most probable causes first and working my way down from there. While I'm comprehending all of the information that has been offered so far I'm still unclear as to which of it points to the most probable cause given what I've described and what has already been tested.

 

My concern with switching back to the MAS is that the problem existed prior to switching to the MAP sensor and so it would seem that the issue is independent of the change. It's also my understanding that airflow is not metered with a MAP sensor, but then there must be an alternate method within the eManage to be able to provide the ECU with the signal it needs to drive the secondary injector? If the eManage was capable of driving low impedance injectors then I could just relieve the ECU of this responsibility, but from what I have been told it can only drive high impedance injectors.

[StarquestRescue]

If you don't mind me asking, what would your approach be in terms of the order in which you would test things?

For example; Would you start by switching back to the MAS and checking the hz signal the ECU is or is not seeing or start with something like the TPS?

 

 

I would go back to what i know the car should decently idle, cruze and run under low boost on. That would be a stock or 1g mas, the emanage settings zeroed out or with the airflow wire by passing the emanage. And since it has the after market 650/950 i would bump the base fuel pressure to 45 psi. It should run like that, buy may go to rich if you get to far into boost. At some point you would run out of injector capacity to support that turbo, but that is a topic for later.

 

If it still appeared that the problem occurred when the secondary should come in, then i would install a 1050 secondary i happen to have laying around and see what happens. I do not have a 950 right now.

 

If there was no real improvement i would recheck the things that the last guy "checked and ruled out" Even if i was the last guy.

 

At some point i would verify what the airflow signal was that the ecu is being sent and take a good look at the tps signal and swap it with spare used ones if i could find nothing wrong any where.

 

The emanage is just a glorified afc, air flow correction computer. What these gismos do is intercept the airflow signal and modifies it based on your tune settings, and then send it on to the cars ecu. For example if the car is running to rich at 3000-4000 rpm you would set the afc to reduce the airflow signal by say 10% in that range.

 

To run speed density with the emanage, A table would have to be created that would generate a airflow hz signal based on rpm and the map signal. This hz signal would them be sent to the cars ecu via it airflow in put wire. It is unlikely that table is good enough to drive the car on yet.

 

It has been a long time since i have looked in to the emanage system.

Edited November 9, 2014 by StarquestRescue

[mikec]

The injector ballast resistors are just a few ohms each. if one has failed a bit - say it now is a few hundred ohms - you'll still read around +12volts on the injector + pin since voltmeters, by design, put no load into a circuit. (technically the voltmeter is a very high resistance now in series with the 6 ohms or so of the ballast resistor... voltage divides relative to the ratio of resistances so 6 ohms vs. thousands or millions of voltmeter ohms means only a teeny fraction of battery voltage will be "lost" accross the resistor, the voltmeter will see almost the entire +12volts)

 

Directly measuring the resistance is a better test. Engine off, key out of the ignition, disconnect the two injector clips. Set your multimeter to "ohms" or "resistance" mode on the least sensitive scale (usually marked "x1" on analog meters, and "200" on digital meters). Measure the two ballast resistors together - in series - by touching the meter leads to the yellow+white and yellow+green wires on the injector clips. If you read somewhere between 10 and 20 ohms then the resistors are okay. If higher than that... let's test each resistor individually. They're hard to access - bolted to the bodywork bulkhead between the air filter canister and headlight. But we can access the resistor wires using other wires at the throttle body: the two injector clip wires already tested and the black+red wire going to the EGR control solenoid... or the red wire at the secondary air filter control solenoid. Hook one multimeter lead to either of those solenoid wires (this is the +12volt line that powers the injectors and other stuff by the way) and then test the yellow+white injector clip wire. Note the resistance, it ought to be around 6 ohms if I remember correctly. Then move that meter wire to the yellow+green injector wire and you should read about the same thing. If they differ a lot, then one of the two resistors in the case is shot... if the yellow+green one is the bad one that'll explain your secondary injector issues.

 

I'd also look at the ECU connector with the injector wires. Really examine the contact ends - maybe the pin has busted off or is corroded. On 87-earlier cars, water leaks around the windshield caused water to flow down the passenger side "A" pillar and then dump onto the ECU connectors. 88-later cars flipped the ECU around (connectors now on the bottom) to mitigate this issue... but a flooded passenger footwell let water splash onto the ECU.

 

The other thing that'll make a StarQuest act like the secondary injector is dead is a bad coolant temp sensor. This is the 2-prong one in the intake manifold (points upwards) and is different from the dash gauge sensor. The ECU uses this sensor to know if the engine is warmed up or not... when cold, the ECU runs the engine over-rich in choke mode. This leads to high RPM bucking especially when boost pressure is present. Warmed up the engine to normal temps, then shut it off. Unplug the electrical connector (squarish shape) and measure the resistance of the sensor. It should be lower than 300 ohms. If it's above 1000 ohms, it is shot or you don't have engine coolant flowing through the manifold.

 

mike c.

[Jayton]

And since it has the after market 650/950 i would bump the base fuel pressure to 45 psi.

OK, is 45psi what has been determined by most to be the optimal baseline fuel pressure with the aftermarket 650/950 combo?

 

If it still appeared that the problem occurred when the secondary should come in, then i would install a 1050 secondary i happen to have laying around and see what happens. I do not have a 950 right now.

I don't quite understand what switching to a larger secondary would do or tell us if the problem still persists? If the injector is not coming on what difference will a different size injector make?

And are you offering to lend me the 1050 you have for testing purposes? If so I appreciate it and will let you know if we get to the point that it seems necessary to swap it out.

 

If there was no real improvement i would recheck the things that the last guy "checked and ruled out" Even if i was the last guy.

Agreed. I completely trust the quality of work that has been performed, but it never hurts to recheck things. Especially when certain parts are as old as they are.

 

At some point i would verify what the airflow signal was that the ecu is being sent and take a good look at the tps signal and swap it with spare used ones if i could find nothing wrong any where.

Agreed on the airflow signal and actually am thinking we should start here. And to confirm my understanding, without the correct signal in hz (390 on / 290 off) as you described earlier, the ECU will not activate/terminate the secondary correct?

Am I asking for trouble (in the form of future issues) by continuing to rely on the used TPS's that are available? I just hate the notion of using unreliable old parts that could potentially fail prematurely. I have read the positive reviews on the Mazda TPS conversion kit that is being offered by another member here http://www.starquest...pic=136410&st=0 and wouldn't mind splurging on a brand new Mazda TPS if it means longer term reliability.

 

To run speed density with the emanage, A table would have to be created that would generate a airflow hz signal based on rpm and the map signal. This hz signal would them be sent to the cars ecu via it airflow in put wire. It is unlikely that table is good enough to drive the car on yet.

Understood. So essentially, if we can get the airflow table created properly in eManage to provide the correct airflow signal to the ECU in hz then the MAS can be eliminated and the MAP sensor can be used in its place.

[Jayton]

The injector ballast resistors are just a few ohms each. if one has failed a bit - say it now is a few hundred ohms - you'll still read around +12volts on the injector + pin since voltmeters, by design, put no load into a circuit. (technically the voltmeter is a very high resistance now in series with the 6 ohms or so of the ballast resistor... voltage divides relative to the ratio of resistances so 6 ohms vs. thousands or millions of voltmeter ohms means only a teeny fraction of battery voltage will be "lost" accross the resistor, the voltmeter will see almost the entire +12volts)

 

Directly measuring the resistance is a better test. Engine off, key out of the ignition, disconnect the two injector clips. Set your multimeter to "ohms" or "resistance" mode on the least sensitive scale (usually marked "x1" on analog meters, and "200" on digital meters). Measure the two ballast resistors together - in series - by touching the meter leads to the yellow+white and yellow+green wires on the injector clips. If you read somewhere between 10 and 20 ohms then the resistors are okay. If higher than that... let's test each resistor individually. They're hard to access - bolted to the bodywork bulkhead between the air filter canister and headlight. But we can access the resistor wires using other wires at the throttle body: the two injector clip wires already tested and the black+red wire going to the EGR control solenoid... or the red wire at the secondary air filter control solenoid. Hook one multimeter lead to either of those solenoid wires (this is the +12volt line that powers the injectors and other stuff by the way) and then test the yellow+white injector clip wire. Note the resistance, it ought to be around 6 ohms if I remember correctly. Then move that meter wire to the yellow+green injector wire and you should read about the same thing. If they differ a lot, then one of the two resistors in the case is shot... if the yellow+green one is the bad one that'll explain your secondary injector issues.

Understood regarding readings at the + terminal on the injector clips not being fully accurate and good to know. We have been somewhat skeptical about this so thank you for confirming. Actual readings at the injector + pin were just under 12volts at like 11.8 and 11.9 respectively. We will need to directly measure the resistance as you have described to be certain.

I do have a spare resistor pack that can be used. Is there a way to bench test it? Also are new OEM units still available if needed?

 

I'd also look at the ECU connector with the injector wires. Really examine the contact ends - maybe the pin has busted off or is corroded. On 87-earlier cars, water leaks around the windshield caused water to flow down the passenger side "A" pillar and then dump onto the ECU connectors. 88-later cars flipped the ECU around (connectors now on the bottom) to mitigate this issue... but a flooded passenger footwell let water splash onto the ECU.

A quick visual inspection last weekend didn't show anything to be concerned about in terms of corrosion on the contacts, but I agree that these should be thoroughly examined and proved good. Thank you for suggesting.

 

The other thing that'll make a StarQuest act like the secondary injector is dead is a bad coolant temp sensor. This is the 2-prong one in the intake manifold (points upwards) and is different from the dash gauge sensor. The ECU uses this sensor to know if the engine is warmed up or not... when cold, the ECU runs the engine over-rich in choke mode. This leads to high RPM bucking especially when boost pressure is present. Warmed up the engine to normal temps, then shut it off. Unplug the electrical connector (squarish shape) and measure the resistance of the sensor. It should be lower than 300 ohms. If it's above 1000 ohms, it is shot or you don't have engine coolant flowing through the manifold.

OK. I have been assuming that the coolant temp sensor has been working because the dash gauge has been reading accurately (I now realize that these are 2 different sensors :/ )

Judging by the color of the brass on it, it appears that the CTS that's currently installed is an older piece and so we will need to test this for sure. Should I be getting an OEM unit if it proves to be faulty (and are they still available) or are the aftermarket sensors OK?

[mikec]

The ballast resistor box is just two resistors inside one metal case. One input wire (gets +12volts from the ECI relay) and two output wires. The input wire goes to both resistors, the outputs come from individual resistors. You'll see 3 pins on the connector. The "by itself" pin is the input, the other two are outputs. Hook one end of your ohmmeter on the input lead. Hook the other meter lead to either output pin and note the resistance - it should be just a few ohms. Now test the other output lead and look for a similar low resistance reading. I have no idea if OEM replacements are still available. If not, I'll bet the metal box can be opened up easily and I'll bet you'll see two sandy brown rectangular resistors in there. Any real electronics supplier (yellow pages, Google, etc) should be able to get replacements; resistors are generic parts. Bring both resistors to the store so they can read the values (resistance and wattage) directly off the resistor body.

 

ECU coolant temp sensor: OEM or certain aftermarket ones are known to work. Other folks have posted brands and part numbers; I don't have a list myself. For testing, you can buy a 270 ohm half-watt resistor from Radio Shack, Frys, or a real electronics supplier. Connect its two wires to the connector normally going to the sensor; this 270 ohm resistor (a common & standard value so it'll be just a few cents) simulates a fully warmed-up engine reading to the ECU. See if the engine runs better with this test resistor in place of the sensor.

 

mike c.

[Tim_C.]

I think you are probably on to something with the resistors, but if not: I know this is the hack method, but I discovered a bad ingniter caused my secondary injector to open fully. The injector signal literally maxed out. I swapped igniters, and the problem went away. Also, I wouldn't rule out harness issues just yet. Continuity proves connection, but says nothing about another signal or ground being shorted to it. You can try by-passing the harness with your own separate wires from close to the ECU connector, to rule out a short. Cut the wires and run your own around the A-Pillar, or through the window, etc.. Or take the whole harness apart to make sure nothing is melted or shorted in it.