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another optispark question

2368 Views 25 Replies 5 Participants Last post by  shlads
I have a 94 z28 and it wont start, i have fuel pressure and spark but no injector pulse. I feel like ive done every test possible. I think i might have found the problem but not sure. I found on my high and low resulution test for the ICM, im supposed to have like 1v while cranking, but i have 5v on high and low resulution. Does that mean that my optispark is bad? Ive just about had enough with this car, its really pissing me off. I just dont like throwing parts on somthing.
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if you have spark; that means that opti high/low res pulses are getting to the ECM, and something else is likely going on.

do you have +12v to the pink wire at each injector when the ignition is on (car not cranking)?

if you're having a vats/security issue, it may still crank if the previous owner has bypassed the anti-theft relay thingie, but the VATS signal to the ecm that enables injector pulses may not happen. is your security light on?
Yes i have 12v on the pink wire. The security light stays on for about 10 seconds.with the vats i thought it would start but would die after 20 seconds or so if there was a problem.
Nope, that's what the VATS is there for.
the fact you have spark, and power on the pink wires, that rules out a lot of things. that means it is very likely that:

- opti signals are getting to the ecm, so your opti is at least kinda working
- ecm signals are getting to the icm, so your ecm is at least kinda working

my thoughts are you're looking at a VATS system failure. it's the only thing on your entire car that would kill injector pulse but not spark, with the exception of a (very rare) complete failure of the ecm's injector driver.

do you have access to an aldl cable to tune your car with? if so we can rule that vats thing out right quick.

otherwise you can check for a VATS signal with a voltmeter on AC @ pin 25 on the red connector at the ecm. the pcm can be unplugged entirely for this check with igniton on, not cranking. you should get a couple volts if there's a signal. (use an unfolded paper clip, fits perfect....)
i will try to test for the vats signal tomorrow
can i just disable the VATS?

if it's a key and cylinder problem, you can bypass that whole thing with a resistor that matches your key. it's on shbox somewhere, i'm sure you can find it

if it's a problem with the VATS module, you have to have it tuned out of the ECM, or get a VATS signal generator. tuned would be easy; if you buy the cable for your laptop from aldlcables, i'll hook you up
Ill keep that in mind, don't really know what i need
I have 2 v on pin 25 red connector. I also found i do have one real good injector pulse at first then they are real faint, I am just using a test light .
is it ok to use a test light to see if im getting injector pulse? or do i have to buy noid lights?
Iim getting one real good pulse then its a faint pulse. If i put gas in the intake it will fire up, so im getting spark but no fuel. Im beginning to really dislike lt1s.
mm depending on your test light, that might be normal.. we're talking about a pulse here. you could pull the rails in a few minutes and see how much fuel is actually spraying

you got fuel pressure?

it's possible something is causing incorrect cold start AFR too

can you scan it?
i got fuel pressure around 40. my scanner is a obdII and it wont communicate. what is a cold start AFR?
your car has to squirt a certain amount of fuel to start depending on temperature.

lets say a temp sensor is faulty and it thinks that it's 100 degrees out. or that your car is already warmed up

it wont deliver enough fuel to start

you need to get a scanner. that'll help a lot.
i got a scanner and i came up with codes 18 and 41. So according to that i have a bad ecm.
i doubt it's your ecm. your harness is probably screwed up somewhere along the line

and if it really did throw a code 18 and fry your ecm, there's probably a reason for it, internal dead short in an injector or something, so dont just go chucking a fresh ecm into there without checking everything over

a shoddy connection to the pink part of the harness could do this stuff. so could dirty grounding

electrical is a nightmare. people throw perfectly good cars away for the diagnostic time necessary to fix stuff like this

i had to tear down and rebuild my entire engine harness to fix my gremlins, you might have to do the same
Well that just sucks, cause i have no patience for electrical crap. Thanks steveo ill do some more checking. Thanks Steveo
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