94 Z28 wont start: please kill me NOW - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
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post #1 of 9 (permalink) Old 03-01-2019, 07:16 AM Thread Starter
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94 Z28 wont start: please kill me NOW

Bought my 94 Z as a non-running project. Car has 93k miles
VATS bypassed with aftermarket module, fuel pump primes and starter spins motor.

Battery was dead, replaced with new. No OBD codes. Still no start
No spark at plugs.
Since it supposedly had a new opti, replaced the coil and ICM (which tested weak) - still no start
Replaced opti (aligned w/notch, slid on by hand) -- still no start
Pulled DSide spark plugs = nice even browns, reinstalled them. all plug wires verified to correct plug
Checked spark @ plug boot with spark light module - blinks while cranking - still no start
checked fuel pressure at Shrader = 42psi. Replaced varnished injectors with new (26lb) Accell set - still no start.
-- Injectors have 12V with key on, and noid light blinks while cranking

all fuses look good, cleaned all engine bay grounds - still no start

IS IT THE CPU? It is sending signal to the injectors, opti/ignition system etc.
COULD THE PRESS REGULATOR CAUSE THIS?

Last edited by Caraddict; 03-01-2019 at 08:03 AM.
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post #2 of 9 (permalink) Old 03-01-2019, 04:07 PM
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VATs?

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post #3 of 9 (permalink) Old 03-01-2019, 05:02 PM
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Quote:
Originally Posted by Stormyweather View Post
VATs?

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Sorry didnt see the bypass. Maybe its bad does it still read right ohms?
Hook up a light to check injector pulse
Or just a sprits of go juice in the TB to see if it will light.
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Last edited by Stormyweather; 03-01-2019 at 05:05 PM.
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post #4 of 9 (permalink) Old 03-04-2019, 09:07 AM Thread Starter
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After re-reading my original post i see i've left out one key fact that may impact your answers

We haven't refilled the cooling syetem after the Opti/WPump install. Would that cause a no-start? As i've outlined already, plugs are getting spark and injectors are getting pulse signal from CPU.
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post #5 of 9 (permalink) Old 03-04-2019, 02:02 PM
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Nope it should run. Coolant level has nothing to do with it. Are you getting fuel to spray out of injectors? Try spraying a little starting fluid . just cause the plugs look good doesn't mean they work. try some fresh plugs. You've done everything else. Filter could be clogged. Do you see fuel do you see spark? Yes you've said everything has been checked.




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post #6 of 9 (permalink) Old 03-05-2019, 07:18 AM
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Try spraying some starting fluid into the throttle body while assistant cranks engine. See if engine will even try to start. If it does, you have a fuel delivery problem.

If it doesn't try to start, you have an ignition problem. Probably weak spark. Don't assume that just because opti is new that installed opti is any good. Many people install cheap China made optis that either fail right out of the box, or very soon after installation.

All lt1 owners should have an oscilloscope so they can actually see if low & high resolution signals coming from opti are the proper square wave. You can buy a pc based scope for around $70 on ebay, amazon, etc. The scope will also check for proper square wave of 50 hertz fuel enable signal that theft deterrent module (TDM) sens to PCM.

Since your vats bypass is most likely just bypassing the resistor pellot of the key, use a scope to see if TDM is sending the correct 50 hertz square wave to the PCM. Otherwise PCM will open fuel injectors while engine cranks. But as soon as engine runs, fuel supply will be cut off.
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Last edited by cocobolo95; 03-05-2019 at 07:22 AM.
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post #7 of 9 (permalink) Old 03-19-2019, 05:19 PM
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You have fuel pressure and injector pulse, you should probably verify good spark with a HEI spark tester. Maybe carbon tracking in the distributor cap or wires arcing. If good spark with HEI tester, check compression.

Could just be flooded.

Last edited by dkimbocz; 03-19-2019 at 05:32 PM. Reason: Delete
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post #8 of 9 (permalink) Old 04-02-2019, 01:22 PM Thread Starter
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UPDATE: After draining the gas tank (via the handy AUX FPump lead) and a new fuel filter, she grumpily fired and up and settled into a smooth idle.............................................. ......and then we noticed the massive gas leak coming from somewhere on top of the tank !!!!!!!!!

So now onto either dropping the tank or cutting the access panel into the trunk to find out which fuel line is leaking..............................
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post #9 of 9 (permalink) Old 04-08-2019, 05:16 PM
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Cool glad you found it

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