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TPS and O2 sensor error codes and no spark.


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#1 JMartinez

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Posted 07 April 2019 - 02:48 PM

Hi All,  Iím new to the site.  I bought an 87 to work on it with my kid.  The older man that I bought it from had it suiting for 12 yrs in the garage.  He said that it died on him one day and just wonít start.  Currently there is no spark.  He changed the coil, spark plugs and cables.  Still no spark.  I replaced the knock box per other postings... still no spark.  I did the led to the behind the globe box controller and I got two error codes.  One is the TPS which according to some it can only be adjusted while running.  The other error is the O2 sensor.  Iím lost.... any help is much appreciated.





#2 croquest87

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Posted 07 April 2019 - 03:36 PM

Is there any spark on the coil itself or on the wire that goes from coil to distributor? Check all the fusible links ? I would start volt meter testing to what is and what is not getting power.
Knock box seems to be # 1 suspect on 87s but these cars are getting old and wiring becomes all corroded and green so it could be a few things involved.

Volt meter and service manual is a must have when you own one of these things.

Edited by croquest87, 07 April 2019 - 04:10 PM.


#3 JMartinez

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Posted 07 April 2019 - 05:08 PM

Thanks for that.  I just bough the mechanics manual and a volt meter.  Does this car has fuses only under the steering wheel?

#4 croquest87

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Posted 07 April 2019 - 05:17 PM

View PostJMartinez, on 07 April 2019 - 05:08 PM, said:

Thanks for that.  I just bough the mechanics manual and a volt meter.  Does this car has fuses only under the steering wheel?
Fuses under the steering wheel  yes mostly for accessories and such.

If you look on the right side of the battery  there is a small block w 4 small wires( they are fusible links or old school version of fuses) clearly marked on that little box what they are.Color identifies how many amps before they burn and wire inside them is properly sized for that.Just like fuses you have to use correct one.
Also behind that black metal cover there is bunch of relays and all. I suggest you get familiar  to what is what first and what it does.  Any questions? On particular stuff  just ask  someone will respond to you to help.

Edited by croquest87, 07 April 2019 - 05:26 PM.


#5 mikec

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Posted 07 April 2019 - 07:02 PM

I'll assume the engine is turning over with the starter motor...

Think of StarQuest fuel and ignition systems as "electronic carburetor" and "conventional electronic ignition."  They pre-date today's cars where everything is ECU-controlled to the nth degree.

Some basics:
1.  croquest87 mentioned the fusible links by the battery.  Fusible links are basically slow-acting fuses.  With the annoyance that the section that "blows" is covered by normal wire insulation so you can't readily tell by eyeballing them if they are healthy or not.  Even if they've never been overloaded (i.e. never had a reason to "blow out" doing their fuse job) they do degrade with time.  Being close to the corrosive battery fumes accelerates this process.  Unplug each one, one by one, and examine the metal ends for corrosion and a tight connection.  While you have the link out, flex it... any that flex more easily than others (and may or may not have charred/burned/discolored insulation) are bad.  One link will have "ECI" on the black plastic box... that link is THE power source for the fuel system.  It's critical.  Another is labeled "IGN" which feeds the ignition key and thus everything controlled by the ignition key including the ignition system.  If you unplug the battery and then remove the thin metal plate between it and the fender (two 10mm nuts and a slip-fit joint at the bottom) you'll see another collection of links.  Notice the links have different color insulations - each color specifies a particular size.  You can safely swap the ECI link with another link of the same color (you probably have to clean the insulation with spray carb cleaner or Simple Green to see the proper color) and see if anything in the ignition and fuel system changes.

2.  Ignition system operation: inside the distributor is a pick-up coil that generates small voltages as the "+" shaped piece inside rotates past it.  The Ignitor box receives those pulses and triggers the ignition coil.  No diagnostic code is generated if that pick-up coil is bad... you just won't have any spark.  Of course, if there is an issue with the engine timing chain, the camshaft, the extension shaft on the front of the camshaft, or the distributor's gear, then the distributor won't turn with the engine and the ignition system will seem dead.  While trying to start, does the tachometer wiggle at all?  If so, that's a sign the ignition system is trying.  With the ignition key ON, look for +12 volts on the black+white (black wire with white stripe) wire at the ignition coil.  No voltage there means an issue with the ignition key, wiring, or IGN fusible link.

3: the ignitor will ground the blue+white wire (which may have a cable-TV style shielded "coax" wire going to it too) to magnetically charge the ignition coil; when this ground is removed the magnetic field collapses into the coil's secondary side to make the spark.  This terminal is also what feeds the tachometer.  The fuel computer (ECU) also sees this signal to know if the engine is running or not... if there are no ignition pulses the ECU assumes "engine is stalled" so it cuts off power to the fuel pump - don't want the pump running in case fuel lines are busted after an accident!

4. the ignition key/switch has multiple outputs (three actually) for the ON position... so just because some stuff seems to work okay with the key ON does not mean the switch can be trusted.  It can be "partly-good" in this case.  The voltage test on the black+white wire checks the side of the ignition switch that feeds the ignition system.  And to make things even more fun: the START side has 3 separate outputs too!

So, to test: verify the +12volts on the black+white wire as I already described.  Then see if the blue+white wire shows a lower voltage which probably isn't happening on your car.  Follow the wires from the base of the distributor (not the spark plug wires) looking for the round electrical connector... in theory it's in the clips at the base of the EGR valve.  (EGR valve is the flying-saucer shaped thing at the bottom/front of the throttle body).  Open that connector.  It'll have 3 pins: one on top and two side-by-side.  With an ohmmeter, measure the side-by-side terminals - you should see somewhere around 1000 ohms if the pick-up coil is not busted.  Pick-up coil breaking, fusible link issues, or the ignitor module failing are the most common ignition system problems.

Look at the clip below the EGR valve... attached to one screw should be a ground wire going towards the driver side fender area.  That's commonly busted/missing.  It's mostly to keep the entire intake manifold stuff at the same "ground potential" as the engine block since there are many gaskets separating the engine parts... but missing ground wires are a common source of problems on many cars including StarQuests.

"TPS" error code: Throttle Position Sensor.  This is just a potentiometer, like the old rotary volume controls on radios and TVs.  When old, the electrical contact that moves along a resistive strip gets flaky so the output jumps rather than smoothly varying with the position of the input shaft.  Radios and TVs would get "scratchy" volume when this happens.  (it's also common on the balance and fader controls of the StarQuest stereo unit!).  The fuel computer watches the TPS output to see if it's CHANGING or not.  If it's increasing, that means you just stomped on the throttle and want to accelerate so the ECU will dump in extra fuel - mimicking a carburetor accelerator pump.  If the TPS output is reducing, that means you are lifting off the throttle so less or even no fuel is required.  The TPS has absolutely nothing to do with the ignition system... only the "driving" characteristics of the engine.  A TPS error code means the TPS output was outside expected limits at some point.  The ECU won't clear/reset a TPS error code once the TPS is replaced either... you have to manually clear the codes by disconnecting the battery for 10 seconds or so with the ignition key OUT OF THE IGNITION!  The O2 (Oxygen Sensor) code means the oxygen sensor isn't outputting anything either... this is normal and expected on a cold engine.  O2 sensors have to be heated by the exhaust to a temperature 700+ degrees before they come to life.  So an O2 error is expected right after the engine is started... it'll be cleared by the ECU once the O2 sensor wakes up.

mike c.

#6 Preludedude

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Posted 07 April 2019 - 07:41 PM

mike c. with the essay.  

Every single post of yours just needs to be a FAQ.  

:)

#7 JMartinez

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Posted 07 April 2019 - 11:00 PM

Thanks Mike.  So much information to follow.  I canít wait to get my hands dirty.

#8 JMartinez

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Posted 08 April 2019 - 05:22 PM

Hi Mike,  you asked in item 2... While trying to start, does the tachometer wiggle at all?  

The answer to that is no.  What does that means?

#9 mikec

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Posted 09 April 2019 - 01:33 AM

The tach typically shows some motion while the engine is cranking - after all it is turning albeit at a low RPM.  Thus it should read a few dozen RPM.  So no "life" in the tach indicates no pulses are coming from the ignitor due to ignitor issues, fusible link issues, pick-up coil issues, or the distributor body not turning.

mike c.

#10 JMartinez

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Posted 09 April 2019 - 04:31 PM

Ok then.  I have to check the ignator and fuses.  The coil is in good condition and the distributor is turning.

#11 Jay40245

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Posted 11 April 2019 - 08:37 AM

View PostPreludedude, on 07 April 2019 - 07:41 PM, said:

mike c. with the essay.  

Every single post of yours just needs to be a FAQ.  

:)
I second that.




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