Turbo Z fuel pump control?

Greetings all! Its been awhile since I've been around these parts, but I am getting back to working on my 86 Daytona Turbo Z, TI sock setup. I am having several issues with it:
Sometimes, it will idle very high, then calm down after a few blocks or so of driving. I have replaced the IAC, but whatever controls it sometimes sends the wrong signal. There are no vacuum leaks.

Next, whichever computer tells the fuel pump to prime, sometimes it won't work. So, it will turn over, but wont start. I know when this happens I can't hear the fuel pump prime. When I swap logic modules it normally starts up, but seems to happen on both LMs

Any help with either issue would be great. Wasn't there something that some of you have done to ensure a better connection at the LM?

THanks,
Lee

I'm not sure about the idle issue. Even mine does that sometimes, but only when it's raining.

As for the fuel pump, it's powered by the same circuit that powers the ignition coil via a switch in the Power Module which receives its signal from the HEP in the distributor and from the Logic Module. I would start with the HEP; that seems to be the usual culprit on my cars. Look for damaged wires or swap it out with a known good one and see if the problem persists. Also check for a Code 54, although it doesn't always show up.

You could try resetting base idle and cleaning the Idle motor pintle and passages to help alleviate your first problem

Quote:

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Originally Posted by turismolover22

You could try resetting base idle and cleaning the Idle motor pintle and passages to help alleviate your first problem

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I did clean that all up, and reset the base idle. I can't remember if I had this issue with another HEP. I know I've swapped them before, but that was just for a quick check of something. I should try to swap in a different one.

I have a underhood wiring harness waiting to go in that is in much better shape, not all chopped up like this one. Hopefully that also solves some of my problems?

Ok, so I drove the car last week. I have two logic modules I'm using. One came from an 86 Turbo Z, but it had an automatic trans, and mine is manual. This LM had the car doing some crazy things, irratic idle, and while it sort of ran half decent, I got it on a busy stretch of road, and leaving from a light, it kept falling on its face. So in other words, I'd give it gas, and it would shut down, as if the fuel pump was stopping and starting. I pulled over, and swapped over to my other Logic module that came with the car- A Mopar Performance one. This one works great most of the time, until some random point when the fuel pump won't prime. Today I drove it around quite a bit and it ran great.

Should I look into a new LM? Where is the best place to get a stock LM these days? I know the parts store ones are crap, and I don't know if Mopar units are still available?
-Lee

If it's doing it with both LMs I don't think that the LM is your issue.

To me the fuel pump not priming is a key sign of something wrong in the PM given that it happens with multiple LMs. The ASD relay is in the PM so you can't test the relay itself very easily. However, when the car won't prime you can check that the J2 wire is feeding the PM power (I know that's the wire on the latter stuff and I think that's where it goes on the early stuff too, but it has been a while). If it is feeding it power you should be good there. Once that proves out I would go about jumping the coil from the positive battery terminal to the positive side of the coil. If that fires the FP up right away then I would very highly suspect a faulty ASD relay in the PM. If not, then I would start tracking down a wiring problem to the pump.

Quote:

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Originally Posted by Lee'sdaytona

Ok, so I drove the car last week. I have two logic modules I'm using. One came from an 86 Turbo Z, but it had an automatic trans, and mine is manual. This LM had the car doing some crazy things, irratic idle, and while it sort of ran half decent, I got it on a busy stretch of road, and leaving from a light, it kept falling on its face. So in other words, I'd give it gas, and it would shut down, as if the fuel pump was stopping and starting. I pulled over, and swapped over to my other Logic module that came with the car- A Mopar Performance one. This one works great most of the time, until some random point when the fuel pump won't prime. Today I drove it around quite a bit and it ran great.

Should I look into a new LM? Where is the best place to get a stock LM these days? I know the parts store ones are crap, and I don't know if Mopar units are still available?
-Lee

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The auto trans module has different target idle tables based on the P/N switch.
Without this, the idle will be erratic.

Since the ASD circuit and corresponding relay controls fuel pump operation in both applications and the issue is exhibited with both modules (yet under different conditions), focus on the LM/power-module connectors and signal ground connections as mentioned by 'Cordes'.

ETA: I would check the ground at the pump too. Those have been known to cause serious problems on the older cars after all these years. It doesn't take much corrosion on that long wire to be an issue.

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Originally Posted by cordes

ETA: I would check the ground at the pump too. Those have been known to cause serious problems on the older cars after all these years. It doesn't take much corrosion on that long wire to be an issue.

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Definitely !

Ok, so there should be a ground screwed to the frame of the car near the fuel pump? I'll clean that up, and while I'm at it, I will keep an extra Power module with me, since I do have several of them in the rat hole. Next time the thing doesn't fire up, I'll try to swap the power module and see if that helps.

Cordes: Thanks for the details on how to trace the circuit. Naturally each time this happens, I am usually stuck at a restaurant or elsewhere without a meter. But good to know, hopefully I can get it squared away. Soon enough I'd like to get the hole in the floor pan by the e-brake patched up, so I can install fresh carpet, my black leather interior, and basically put the car back together.
Take care!
-Lee

I don't believe the FP actually grounds under the car back there. I think it goes through the grommet and into the car.

Lee - few details for you. the fuel pump ground actually runs up behind the trim panels in the hatch, driver's side quarter panel. I doubt that's it though, before you go tearing in to it. that ground is common to your taillights, so it would be pretty obvious if that were it.

there should be an 8-pin rectangular terminal behind the battery. your J2 circuit from the PM runs through there. disconnect terminals, clean out THOROUGHLY, apply dielectric grease generously. try that first.

I went thru this on my first gen after upgrading to T2 LM, back when; thought I was crazy, took the DMM and went through every circuit on the LM/PM system before I figured it out. I would get random no starts that had NO apparent cause. experienced the same with the random cutout as well. after regreasing, worked good as new. J2 and Z1 are likely the culprits in this situation. good luck with it, PM if you need help!

Oh, you know, I did clean that ground. The back interior panels are all removed, and have been for a few years. In chasing the various electrical gremlins, I cleaned every ground I could see, including that one.
I know the 8 pin connector you speak of, and I'll clean that. I'm thinking some electronic contact cleaner first, then maybe a toothbrush, followed by dielectric grease. Thanks again for everyone's help!
-Lee

If you jump the coil you should be able to check the voltage at the FP connector. You may as well do that while you're down there too. I bet you've got quite a drop between the battery and the pump.