MAF sensor testing methods?

[avenger89]

Well After much much testing I am running out of ideas! First off I posted A topic A bout my 88 Quest About A month ago Titled "Plug in the MAF car runs like crap" Well that's not the problem anymore One day it miraculously reverted to only running with the MAF plugged in! But all those post can help to explain some of the testing that has been covered. I have done alot more tests, And keep coming back to the maf. I have replaced the ECU and the MAF with one I got here Off the board. First I want to explain why I replaced the ECU. After using my old analog And testing for codes, it would give me the code for the MAF after start up and attempting to drive the car. And then my meeter would peg out randomly at 12 volts and not resume giving codes until Ignition was cycled off then on. And according to trusty old Alldata, If this happens "Replace ECU". Easy enough, But to no avail. Same results with my replacement ECU. Now I have tried both of the MAF's I have With the new ECU, And no change. I have tested The Both MAF's according to Alldata's procedures With include, Using a thermometer and testing the MAF at room temperature [i used A laser thermometer for this part] Install MAF in car and start and run up to operating temp and test resistance At the MAF side. It should change value at hotter temps, And both MAF's are in spec. I have "chased" all six wires from the MAF harness to the ECU and all have continuity. I have had my injectors cleaned and are in good stock working shape. using my radiator tester pump and some fabricated adapters I have tested my inter cooler and all plumbing for leaks. I have replaced a ton of vacuum lines and believe that system to be leak free And is in stock configuration. The car runs well up until introduction of boost, then all hell breaks loose. At the first sign of positive boost the car bogges down MAF code sets and It is back to the drawing board.

Thanks in advance

E.

Edited August 27, 2009 by avenger89

[ovenfresh]

I have been having very similar problems and have seen this issue all over the forums. After lurking around a lot, this is probably one of my first posts, sorry. I've tryed alot of the things everyone has suggested. Replaced coolant temp sensor, tps replaced and set it and isc. replaced oxygen sensor, cuz i was getting that code, replaced vac advance, thats what most people where saying would cause this issue. spark plugs are good, gaped properly. Has new plug wires, cap and rotor. going to the junkyard this weekend to try and find a maf, or the one from an eclipse, cuz i'm getting that code as well. I also had the same thing happen where it will throw the code for maf or o2 sensor, then go 12 volts steady, turn car on and off and back to normal, then throws codes again.

I've been fighting this issue for a couple months with still no problem solved. It does get better when the car warms up. and once I start to boost past about 5-7 psi it clears up and goes like mad. But issue is still there. And seems to come and go. Thought maybe it was fpr or maf, so will try those this weekend and let you know if I find anything. I've got 2 other friends who are mechanics and are just as baffled as me and everyone else. Hope we can figure this out soon.

[cyberquest]

sounds like a bad secondary injector, could be dumping too little fuel, or it could also be dumping too much. we traced a similar problem down on a friends quest by unplugging the secondary and found no real change in the way the car acted. i had a spare primary and hes running on two primarys right now till his new injectors get here this weekend.

 

this is where he got his injectors from.

http://starquest.i-x.net/viewtopic.php?t=1200

 

and are you sure there are no cracks in the accordian inlet turbo hose.

[avenger89]

sounds like a bad secondary injector, could be dumping too little fuel, or it could also be dumping too much. we traced a similar problem down on a friends quest by unplugging the secondary and found no real change in the way the car acted. i had a spare primary and hes running on two primarys right now till his new injectors get here this weekend.

 

this is where he got his injectors from.

http://starquest.i-x.net/viewtopic.php?t=1200

 

and are you sure there are no cracks in the accordian inlet turbo hose.

 

Well I am sure it's not the injectors, they were tested and cleaned. the accordion inlet appears to be in serviceable shape. I have not seen any cracks/tears. would A small crack or something I might have missed set the MAF code?

[cyberquest]

if its sucking air from the inlet boot and not thru the mass can cause it to run rough cause its not metering the air, not sure if it would be enough to trip the code. but its odd that it trips the code for the mass when the turbo starts to spool.

[mikec]

The 87-later ECUs trip the airflow sensor error code if the sensor output frequency is really low while the idle/nose switch indicates "engine is at idle." So having the code flip ON during on-boost driving is, in theory, impossible. What it really means is really bad stuff is happening. My guess:

It's not flipping on during on-boost driving, I'll bet it's happening just AFTER you get off boost. Imagine this scenario:

* driving along... with boost pressure.

* You lift off the throttle completely to shift. This closes the throttle plates almost completely; there is thus very little air going into the engine. At the same time, the idle/nose switch is now closed.

 

If there are any air leaks between the airflow sensor (including bad/missing cork gaskets between the sensor and the lid, or a bad gasket between the lid and canister) you'll have even less air going through the sensor than normal (for lift-throttle deceleration) and the idle/nose switch is in the "idle" position --> ergo the exact conditions to "trip" the ECU's MAS error code. A horribly mis-adjusted ISC/MPS/TPS (the idle adjustment stuff, the procedures to do this adjustment are detailed in the FAQ) will leave the throttle plates too-closed (if your lift-off idle RPMs are below 900 RPM then you have this problem) and that means the engine draws in almost no air - leading to a MAS error code.

 

An 87-later car that chugs, bucks or dies when boost pressure builds means:

* if it has problems at high boost, you probably have TOO MUCH boost and are feeling detonation which means ENGINE DAMAGE IS HAPPENING! The dash boost gauge is not accurate above about 10 psi... you could be running 20 psi and the gauge might read "only 12psi."

 

* if it happens at normal boost levels, and seems to get even worse if the engine is warmer, then the coolant temp sensor that feeds the ECU (a different sensor from the one that drives your dash temp gauge) is probably crap. When this sensor goes bad, it tells the ECU "cold engine" which makes the ECU think "need to run in over-rich 'choke mode' while the engine warms up." Under boost, this "choke mode" is too rich and it floods the engine leading to a bucking.

 

* Leaks in ANY air hose, the intercooler, etc. let boost pressure OUT instead of that pressure getting into the pistons... the MAS has "measured" that air and the ECU expects 100% of it to reach the engine - it's commanding fuel for that much air. If boost pressure makes a split/torn rubber hose open up and leak... then some air is going "overboard" (bad "blow-off valves" do this too) instead of into the cylinders; there will be way too much fuel when this happens leading to bogging. And probably black exhaust smoke.

 

To inspect the fat hoses from the turbo to the engine inlet, you pretty much have to remove them and eyeball them in bright sunshine. Just looking at them in the engine compartment isn't enough.

 

Dying fuel injectors cause all sorts of problems too.

 

mike c.

 

[Indiana]

You shouldn't pay much attention to these lame "codes" this ECU puts out. If the car isn't getting fuel from a dirty injector or a dirty connection or it has an air leak then its going to throw that MAF code and that has nothing to do with a bad MAF MAS ECU or anything. There is something else wrong with the car. Maybe the head is cracked and its just starting to leak coolant you need to start looking elsewhere.

[ovenfresh]

Went to the junk yard today and not a single starquest was there. Also no mas from any other mitsu either. Will try and get some new parts when I get some moneys.

[Shelby]

testing costs nothing

[avenger89]

Well everybody I am back with some updates. O.k. first off looks like part of my problem was a short in the ICS plug/harness. soldered it up and it helped, But still not right. fabricated a coupler from the turbo to the accordion Just to make sure it was totally air tight. Before installing the accordion I plugged all the holes and pressurized it, all good there. still not running right. performed the ICS,TPS adjustments as found in the FAQ section [Hence finding the short in the ICS plug] now, when adjusting the TPS rotating it as far as i could The closest i could get it was 4.80 volts. It is only .20 off, but sometimes an inch is a mile. Do you think this is to big of a variance? settled for 4.80, buttoned it up and gave it a shot. still not right. I took the advice of my parts supplier and got some autolite plugs, and from what i have read NGK plugs are the only way to go. Gonna slap a set in in a few days, after i get the injector seal kit i have on order. I broke one of the isolator/sealer bushings on the primary, so she is dead in the water until Friday. one step forward two steps back! it's alot better but still not right.

I will keep yall informed

E.

 

[Indiana]

when adjusting the TPS rotating it as far as i could The closest i could get it was 4.80 volts. It is only .20 off, but sometimes an inch is a mile. Do you think this is to big of a variance? settled for 4.80,

 

I took the advice of my parts supplier and got some autolite plugs

 

I broke one of the isolator/sealer bushings on the primary

 

You are adjusting the TPS wrong, you do not adjust it in any way to read 4.8 volts. Is this on upside down? What side do the wires poke out from, top or bottom? At idle cold it should read just above .5volts. Warmed up idle should be, it MUST be below .5volt or the idle motor won't work. When you floor it, WOT=wide open throttle, it must go to 4.5 or greater there is no set it at 4.8 whatever you meant by that. If its on upsidedown, and I'm just guessing that the Tab isn't in between the two arms on the TPS that move it. Unless you were holding the pedal down and saw 4.8 there isn't any way to get that. You don't adjust for the WOT that is going to be there because of the pedal range and throttle rotation when you set the IDLE value. You then just check the WOT value after the idle is set and I've never seen one of these that couldn't reach 4.5 or above after the idle was set. Maybe you TPS has something broken. Have you removed it and looked to see that the two plastic parts aren't broken? They can't be sloppy on the shafts either and I meanioned this is the past week or so just don't remember who I was responding to. You have to be careful if you set the TPS at some way off value and mash the pedal and thoat plastic parts aren't in their correct positions you wull bust them.

 

Autolite? aahhhhh NO its the DESIGN of that plug not the "brand". ALL these fancy plugs with those tiny arse electrodes in the center like a pin point SUCK all that big gap around there is just a place for them to very easily foul out. The air fuel ratio on this motor just way up and way down all the time. Those plugs are meant for hot running cars with STABLE air fuel ratios.

 

That doesn't mean the injector will leak, many are cracked down worry about it.

 

 

First thing to do is to never again look at those damn "codes". Go get a $12 pressure gauge and screw that into the throttlebody. Get a hand pump, bicycle if you have to just something that can pump up about 10psi and no more. You get a jumper wire and run it from the + battery cable to the fuel pump test connector which is a single female terminal over by the cruise actuator and that will activate the fuel pump. You watch the gauge you put in the throttlebody and it must be 36-38psi and be STABLE. Now slowly using your air pump which is attached to the fuel pressure regulator where its vacuum hose was, increase pressure and for the pressure you add with the pump, the fuel pressure regulator is to raise the fuel pressure you'll see in the throttlebody gauge the same amount. Listen to the fuel pump does it start to whine? You should be able to easily add 10-15 or a little more and get the fuel pressure to raise but much past 10psi and that stock regulator isn't designed for that as the stock boost wasn't much past that. If that fuel pressure can't remain stable you have that problem to fix. The return line clogged, the supply line mashed, the filters clogged or the pump is just dying.

 

Next thing, unhook all that, put a volt meter - on the battery, turn the key "on" then put the + from the meter on one of the terminals of the injector clip, one of those much read same voltage as the battery, do that for both clips. Now using that meter check continuity from the other wire in each clip back to the ECU. The ECU makes the ground path that fires the injector. This could all just simply be a BAD connection from old or replaced clips as attached to the nasty corroded stock wiring harness when it was crimped to a black corroded end of the new clips and htat accomplished NOTHING. You have to keep cutting back to find good clean wire to attach to and it might take 12" to do that.

 

There are three you replace and two you may clean. One in the tank, one in the inlet of the pump, one under the hood and one each in the upper portion of the throttlebody (screens) This is what I mean when ignore those retarded codes. The next thing I'd consider is pulling out the ECU harness, unwrapping it and inspecting all the splices you may have a short where voltage is getting to the other sensors and screwing things up.

 

It sounds like classic non working secondary injector that has been made complicated from trying to use those "error codes". Those codes ASSUME that some things are working, like injector clips and injectors and 02 sensors and corroded wires giving back the correct resistance readings to the ECU when the harness is full of green gooey crimp connections all wrapped up along the entire length of the harness you can't see, if you couldn't unwrap the harness you'd see all of those they are just laughable when you see them. I guess that's all you got in the 80s for wiring but time, heat and moisture have did their part.

 

 

[ovenfresh]

Not sure if anyone is still on this post, but my timing was advanced 8 degress past spec. should be 10 degrees btdc. I set the timing and the problem is gone. So maybe try timing if you haven't allready. Also need to set tps/isc after setting timing back to spec. Hope that helps.