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Discussion Starter #1
All of a sudden my 89 won't start. I noticed the fuel pump comes on, but stays on indefinitely with the key on engine off. It's supposed to just prime for 2 seconds and then shut off until ecm starts to detect the engine is spinning.

So I'm playing with the fuel pump relay under the driver's seat. As I understand, the tan/green wire is from the ecm and sends ground only when the pump should be on. However even with the key off, I'm getting ground.

How can I troubleshoot this other than buying a new ecm?
 

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Discussion Starter #2
Interestingly, it appears the ground goes open once the key is turned on. And yet the pump still kicks on. I'm lost
 

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Qwik Enuff
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A few possible causes:

1) the fuel pump relay is stuck on
2) the tan/green (pin 22) wire is grounded to the chassis or another ground wire,between the fuel pump relay & the fuel pump trigger terminal at the diagnostic port or between the diagnostic port and the ecm at pin 22.
3) one or more of the 3 electrolytic capacitors on the ecm board is leaking onto the trace at pin 22,grounding the wire permanently.

By the sound of it,the tan/green wire or the ecm is shorted to ground.I also list it below,but
If you disconnect the fuel pump relay and ecm harness then find the ground is still present,thats a definite indication the tan/green wire is shorted to ground.
If you dont find the ground present with those two components disconnected,reconnect the harness to the ecm and test the wire again.
If the ground is now present,that indicates its shorted to ground in the ecm.
If its not shorted in the ecm,the fuel pump relay is the only part left.
#3 above is the cause 9 out of 10 times.
When the fuel pump runs continuously,that prevents the engine from starting because it soaks the spark plugs with fuel.

To test the tan/green wire,remove the fuel pump relay and disconnect the harness from the ecm.Test between the fuel pump relay & diagnostic port then the diagnostic port to pin 22 at the ecm harness plug.The wire should measure 2.0 ohms or less.If not,the wire is grounded to the chassis between those two points.The fuel pump trigger wire is the last terminal on the right side of the diagnostic port,where it has 4 terminals.
Do the following with the ecm harness disconnected.Attach a test light clip to the pos battery terminal and probe the fuel pump trigger terminal at the diagnostic port.Is the test light on??
If yes,the tan/green wire is grounded between the points I listed above.The only time this wire should be grounded is when the ecm turns the ground on,so if its grounded (which is now verified because the test light came on) eventhough the ecm is currently disconnected,that verifies the wire is shorted to ground.

If the wire is not grounded,the fuel pump relay or ecm is the cause.You can try tapping on the relay with a screwdriver handle to see if the fuel pump stops running.If it does stop,that indicates the relay is bad.

The ecm can be checked by removing it from the kick panel then removing its front and back panels.Youll see 3 blue capacitors.Those are what you need to inspect for leaking,buldging and broken/eroded posts.You can replace them yourself if youre handy with a soldering gun.Post the results of your tests and I'll post some pictures and a link that details cap replacement,if your testing indicates the caps are bad.
 

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Discussion Starter #4
First off, thank you for the very detailed explanation. I've been looking all over for more information and was worried I wouldn't find anything, but you clearly have a very good understanding of the issue. Kudos.

What I've tried:
1. Disconnected relay and ecm harness. No ground detected, so maybe it's not a short to ground.
2. There are 2.1 ohms between test port and relay. 2.6 ohms between test port and ecm harness. Using harbor freight multi meter so it may contribute to slight inaccuracies inaccuracy.
3. No visible issues with the capacitors


Yet to try:
banging on the relay. I hear it click on and off when I turn the key on and off, so I don't think it's stuck.
Using test light on positive terminal (not sure if needed since I used the multi meter)
 

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Discussion Starter #5
Ok so good news is I figured out how to start my car. bad news, I forgot to mention that I am using a Quarterhorse chip. AAAAAnd the car wont start with the chip installed. I'll reach out to Moates and EECTuning to see whats going on.

hopefully its something like the battery died. I put the leads on the battery while installed and read 0.1V.

Anyway thanks a million for the troubleshooting steps!
 

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Qwik Enuff
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Its ironic you mentioned the QH battery being low because I read a thread about that very topic the day after posting here.It indeed stated a low QB battery will cause your symptoms.Im glad you mentioned it too,because we now have yet another possible cause for fp run-on accompanied by no start issues.
 

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