mrrilla

I have read many "won't start" threads on this site and I just can't get my question answered.

I am doing a 1991 5.7 TPI transplant into a street rod. I am following the GM diagonstics (Chart A-3) and I am down to suspecting the ignition module. I have ample spark at the plugs, Fuel Pressure is only 20 psi at ignition on but goes to 50psi during cranking, the noid light does not blink during cranking, both injector prongs have 12v, touching the CKT430 wire makes the noid light blink.......well sometimes. I took the ignition module down to the parts store and they said its just fine.

Can the parts stores be wrong when checking an ignition module? Would unpluging the EST help? I assume my TPS is fine because the voltage changes when I try to adjust it.

I am stuck here, please help

rjt76

does it start on starter fluid?

mrrilla

After a little cranking, it will backfire but I have to turn it over for about 10 seconds (too long in my opinion) and it will not start.....only backfire (pop).

The plugs do not look wet so that leads me to belive that fuel is not getting through my freshly cleaning injectors.

What do you think?
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I should have noted that it pops or backfires on starter fluid....not on gas.
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I should have noted that it pops or backfires on starter fluid....not on gas.
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I should have noted that it pops or backfires on starter fluid....not on gas.

Kevin91Z

iTrader: (1)

If you're using the stock programming in the 1991 computer, you'll never get it to fire. The 89 and newer computers (and some '88's) have VATS in them (Vehicle Anti-Theft System). The computer needs a signal from the VATS module signifying the key in the ignition is the right one, before it will fire the fuel injectors. Since your street rod doesnt have a VATS module, nor a "key-reader" in the key lock cylinder, the computer wont pulse the injectors. You'll need to get a custom chip burned with VATS removed before it'll work. Hopefully someone local to you can help with that.

mrrilla

Leonard Sparks of Chevythunder.com made the harness and burned a chip for my application so I believe VATS is removed. Assuming it is removed, is there something else that would not make the injector pulse during cranking other than the ignition module?

Even though the ignition module tested fine, should I try another one? All symptoms seem to point to that. Is there a way to test a fautly ECM?

Guest

You may have multiple problems. First, check the timing. Might be 180 out... or way off. Also may not be getting injector firing based on the VATS issue addressed above although it should at least fire off starting fluid.

rgarcia63

I don't think Part stores test ECMs they just replace them.

Don't dismiss spark wires as a problem especially if they're a couple of years old.
My sister's '95 burb was stalling and sometimes just cranking for a while before starting, finally it would just crank. I checked for fuel in the TBI, then checked for spark, it was intermittent, turned out to be the coil to cap wire, it was arcing at the coil terminal to the closest metal it could find from edge of the boot.

You verified that you're getting spark at the plug, assuming there's sufficient compression then adding starter fluid should have started it, but because it only pops/backfires then the spark is weak, or the timing is wrong (assuming there's enough fuel.)

Can you post how you timed it to Zero DTC on the #1 cylinder compression stroke?

A steady !2v at both injector prongs while cranking indicates (an open circuit) that the side controlled by the ECM isn't being driven to ground by the ECM injector signal.

Do not manually ground the injectors as it's not humanly possible to match the short ECM pulses and grounding it for too long can damage the injector.

If the ECM is getting the distributor reference signal which is produced by the Ignition module (ppl/wht wire) then it could be the ECM is failing to pulse the injectors, I would verify that the VATS is disabled otherwise it's a faulty ECM, or associated wiring.
To test for distrbutor reference pulse connect DVOM +lead to ppl/wht wire and -lead to engine ground select duty cycle and read the value directly while cranking.

If you're absolutely sure spark is good, that there's a distributor reference pulse, that the VATS is disabled, and there are no wiring errors then get another ECM.

mrrilla

I put a new AC Delco ignition module in it, checked all my grounds again. Checked the prongs from the harness to the ECM. Found TDC with my compression tester and verifying it by making sure both valves were closed. I then double checked my plug wires.

Initially I set timing at 8 BTDC (4 marks) and had the rotor pointing towards the #1 cylinder. With the help of a little starting fluid.......it ran. One of the above things was wrong.

I rotated the distributor counter clockwise and it ran better. I then pulled the dizzy, found 0 TDC and re-installed the dizzy. The car will only start on starter fluid, not on its own fuel. There's 50 psi at the rails and my noid light flashes like crazy when the motor is running on starter fluid.

Now what? I don't think its timing anymore since it runs on starter fluid. The diagnostic charts don't help at this point.

mrrilla

I should have noted that the injectors are Accel 26# and they are all reading 14.6 ohms, the fuel pump is brand new and is obviously running because I have 50 psi at the rail. The AFPR is a mallory and there is no gas in the vacuum line.

I am getting a pretty fast drop off in fuel pressure from the time when ignition is on, FP runs for 2 seconds, shuts off, and FP drops to zero in about 20 seconds.

Could that be my problem?

rgarcia63

Yes, pressure is only half of what you need flow is the other.
You might want to do a fuel flow test, I think it's 1/2 pint in 15sec.

Do you have an adjustable fuel pressure regulator? high flow pump curves are different than stock.

mrrilla

The pump is flowing about 2oz/sec or 56 gal/hr or 212 Liters/hr. I have an adjustable fuel pressure regualtor (Mallory) but its backed off all the way. When the ignition turns on, fuel pressure bumps to 53psi then drops to zero very quickly. When it starts with starting fluid, the pressure holds steady at 45-47 psi.

Any suggestions?

DAVECS1

iTrader: (2)

You have a fuel leak somewere. Maybe an injector or injectors are hanging open. Also what type of regulator setup ar you using is it stock? Sounds like it may be bypassing too easily. Also how is your fuel return setup? Is it at least the same size as the feed line? Does it return all the way to the tank?

It would be highly beneficial to get one of the many cables built for the P4 ecm I assume you are using. If you are not using a 7730, I would highly suggest doing so. There are a couple of sensor faults that along with a bad tune will make it almost impossible to run the car. MAP, MAT, O2, CTS are the big hitters

Also check your timing, If your timing tables are way off you will not run. What is the initial base timing burned into the chip? Your distributor needs to be set to that value, otherwise you are throwing the whole timing map of by whatever amount of timing you are off. For example if it is suppose to be 6 degrees and you have it at 8. the whole map will be off by two degrees not just the initial startup.This will screw with to much to list here.

You messed with the ignition module. I have seen many of these change out and the whole time it was the pickup coil in the dissy. 50 cent piece. Make sure that your distributor wiring is correct. The reference signal needs to make it to the ECM. If there is a good tune it may start, but its dumb luck if it cold fires without an ECM reference.

That is my first shot at this problem

rgarcia63

So the ECM is pulsing the injectors which means that the ECM is receiving the distributor reference signal.

Since it won't start without a fuel prime there's no doubt the injectors are not flowing.
There's only a couple of things that would cause that:

1. All injectors are bad
2. One or more injectors are not working and pulling excessive current this keeps the remaining injectors from getting enough current to operate resulting in no flow from any of the injectors.
3. There is solids in the system clogging up the injector nozzles.

212 Liters/hour is about 345.5 lb/hour divided by 8 injectors is 43lb/hour when it drops to 47psi the flow per injector is down to 38 lb/hour this is more fuel than it needs to start up. The high pressure isn't helping if there's a problem with the injectors more so if there's gunk in the system.

Not being able to decrease the static pressure is also a problem.

At this point I'd pull of the plenum and runners lift the rails/injectors up and put a glass jar under each pair of injectors and crank the engine with the coil to cap wire removed.
If they don't flow and you can get access to an air compressor, blow air up through the injector nozzles (removed from the rail, but connected to harness) while cranking the engine as above with the fuel pump disabled.

mrrilla

I have the ALDL connected to datamaster and there is no signs of error codes. But does that eliminate the MAP,MAT, etc? I assume that because it runs on ether that the timing is at least close.All my injectors read 14.6 ohms. My fuel ines are 3/8" Braided line from the tank to rail with an additional edelbrock filter in the supply line.

I will go through the execise of checking the injectors on the rail as outlined above and report from there. Is this pump too big for my motor?

I appreciate your advice.

mrrilla

Garcia, I took your advice and tore the motor down to the fuel rails. I have a bad leak on one injector, the rest are fine. The shrader valave also appears to be slightly leaking so I'll try to replace/repair that. Turning the motor over with the injectors in jars did not do anything but I got to thinking, if the MAP, MAT, TPS and IAC are disconnected (since the plenum is off), should the injectors still spray fuel?

Would the one leaky injector cause the no start condition? would that also explain the high pressure at ignition on? Sounds like I am getting closer but I still need to help.

rgarcia63

No, the leaky injector is not the cause of the no start.
BUt it is a clue, think of what would cause it to leak other than a worn nozzle and pintle.

The ECM supplies the injector pulse, but does no controlling until the motor reaches about 400 rpm and then it takes control so the sensors won't be used until it's running.

As long as the ECM is pulsing the injectors you should have all eight injectors spraying, I had the same problem so I have experience. Clogging was my issue but isn't the only probability so you need to verify.

Use the noid light to insure you're still getting a pulse while the injectors are in the jars and fuel pressure on the rail. Once this is verifed and the injectors still won't flow then they are either all bad, but IMO ther're clogged. The injector resistance is a bit low, but proper resistance doesn't insure that the injector will work.

The high pressure probably is a combination of the fuel pump and regulator that you have, but until you get it running I would lower the priority on that item.
You can either bite the bullet and buy new injectors, or have those cleaned and flow tested. You're on the down side of this problem and should have it running soon.

Food for thought: If the injectors are clogged you'll need to expand your thinking, because whatever clogged these injectors will surely clog them again.

Don't hesitate to ask for help.
Good luck - Raul

mrrilla

After connecting my noid light, I get no pulsing from the ECM. Jumping from the ppl/white wire to 12V, the noid light blinks. I believe that I may have blown another ignition module. I will go down tomorrow and pick up another module but if that fixs the problem why does the module keep going bad? FP is still around 50psi.

Just so I get this straight, in theory with a good ignition module and the MAP, TPS, IAC and MAT disconnected, The fuel injectors should pump gas into my containers assuming they are not plugged? and with the FP disconnected, the injectors should pulse when only hooked to the wiring harness? I thought the ECM needs to know that those critical sensors are activated before it pulses an injector.

These injectors were just cleaning by fuel injection specialties about two weeks ago. Thats not to say that they are plugged now, but they were cleaned recently.

I'll try it again after I get a new module.

rgarcia63

About thinks going bad my new walbro high flow pump has less than 100 miles on it over 3 years and it's not working any more; go figure.

No the ECM doesn't need those sensors to start the motor, the ODII just runs the tests and flags any faulty sensors, if any are critical to run the motor the ECM will fall back to limp home mode and simulates the signals required to run. You can even unplug the MAF and other sensors and the engine will still start.

mrrilla

I bought new injectors, cleaned my lines and tank, checked for spark and that my noid light was blinking during cranking and vola! it started up. I ran the motor for a few minutes then shut it down so I get my tools ready to adjust the valves.

I tried to start the motor again and it appears that I have another bad ICM (no blinking noid). Whats the deal here? I have replaced this about 3 times now. What causes these to go bad? a short? chip problem? I have a large cap HEI (86?)

1989GTATransAm

iTrader: (3)

Do you have all the power and grounds attached to the computer? Each input that requires gound or power should have one. Also you should have no more than 4 injectors tied to any of the injector outputs.

mrrilla

Each bank of injectors (RH and LH) are independent of one another and have power and ground back to the ECM. I feel confident in the wiring of the fuel injection harness.

I am debating on purchasing a new distributor but I don't think that will solve the problem since I have already placed most all the components inside it.

Are there any experts in the Dallas/Fort Worth Area willing to help me out on this project?

Guest

ICM I assume you mean ignition module?
The large cap HEI has a ground strap from one of the coil bolts to the connector on the side of the cap. If its not there... could be the problem.

robotic_junky

I had a problem like that with my 87 truck with TBI and the dizzy went bad. Funny thing was that I replace the ICM, pick up coil, rotor, cap, and ign. coil. Also there's a thing that controls spark is ESC, electric spark control. Hope this helps.