since you guys are the prom guru's, I have an 89 iroc set up, car has been running great, stopped it, then went out to start it up and nothing, it cranks, has spark, and fuel pressure, checked the injectors with my injector tool they fire, and after firing a few of them and trying to start the engine it will kick off just long enough to burn off the fuel in the ingine.
All the tests in the GM service book I have point at the ECM, replaced it, still same thing, had put a noid light on the wiring harness prior to replacing the ecm, and nothing, same thing with this brand new one, so only thing is, the prom, but does this sound like a possibility of a prom failing?
It is the stock prom nothing new or ever modified in it never been read for burning other chips (havent got that far yet)
just looking for some advice or a TNT dealer haha
thanks
Jack

 

hows yr fuel pressure ???after start up ?? check yr ignition coil as well. could have an internal short.

 

Could it go bad, yes. Static electricity can mess it up. I guess it could have also messed up the limp home stuff because if the prom is bad it would run off them if the combination were somewhat stock. Do you get a code 12 with key on engine off (KOEO)? You say you have inj pulse which sounds like the ecm and prom or limp home are working. Have you tried disconnecting the 4 way connector at the dist.?

 

no, there is no pulse from the injector wiring harness, but the injectors will pulse with my injector testing tool, and Im getting plenty of spark.

 

ok if the prom is bad Im just starting to get into the burning stuff, but since I need to read the prom is it pointless to attempt to read this one that is if it is bad?

 

If it's the stock PROM, most likely you can come up w/ the bin off the diy-efi.org site anyway.

 

when you say the injectors wont pulse then then they will pulse whats that mean? is it that electrically they will but no fuel is sprayed? is a full 12 volts being supplied to one side of the injector connector? is it a power supply problem or is it that the ecm isnt grounding out the injector(s) circuit? didja spray some carb cleaner in the t-body or power brake booster nipple? will it fire off with some "fake' fuel? do ya hear the fuel pump when the key is first turned towards start? details, man, details. hope this helps aim you. prolly not the prom though unless the testing procedures zapped it.(unlikely) seeya-- check the ign coil carefully with a spark tester.

 

ok Ill try to make this as clear as I can,
With a noid light in the harness, there is no pulse coming from the ecm to fire the injectors.

I have a tool that tests injectors and using it I can fire the injectors and get fuel into the cylinders.
the pump is running I can hear it and I have a fuel pressure guage on the rail and its reading 50 something PSI.

when I pulse a few of the injectors I can get the engine to fire off enough to burn off the fuel that has been delivered,

there is plenty of spark coming out of the coil, new MSD 6AL system etc etc.

all the testing that the GM book says to do points to the ECM, I replaced that last week and still same problem no pulse coming from the ECM, so I highly doiubt a reman computer being bad (since these are "supposed" to be tested after refurbishing them)

cant find any shorts yet still looking when I have a chance.

 

While not probable it is possible that the ign module is bad. The part of the module that sends a crank (dist) reference signal to the ecm may be bad or the wire may be damaged. Purple with a white tracer if I remember right. Do you have dist reference pulses (drp) showing up on the scanner? If not the ecm doesn't know the engine is spinning over so it won't fire the injectors. It may also be part of the VATS as that cuts out inj pulse but I have seen that pulse the inj's while cranking the starter if you bypass the starter kill.

 

You still haven't responded whether you have checked for SES codes? If the prom is bad, you will usually get a code 51 and go into limp mode.

Definitely check the SES codes. If you are getting only code 12s, then you have a "mechanical/electrical" problem. Not an eprom/Memcal problem.

 

Just wondered..do you have 12V on the injector harness? If you have spark, fuel showing 50 psi, the only thing I can think of would be that you have lost 12V to the injectors. The ecm only provides ground to the injectors. Check your power feed. On a remote chance...make sure the engine has a good ground to the frame. I have seen all sorts of odd problems crop up when a ground goes bad. cheers, Bob

 

no Im not getting just a code 12, there is a maf code (took of the air cleaner assy to get to dist) a mat code its not hooked up anymore, and a VSS code, not sure how it is getting these codes off of a non running car, the computer was unhooked for a long time more than long enough to clear the codes. I dont get a 51 for the memcal only had my Auto Xray to check codes, didnt have a wire or paper clip to do the KOEO test for a code 12 I dont think the Xray will show the code 12.
Havent had a chance to check for the dist pulse, but dosent the fuel pump recieve this signal to keep the pump running as well? if so then that should be fine cause the pump primes and then while cranking it runs. or atleast you can hear the relay click off a few seconds after y ou quit cranking on it.
Yes there is 12 V on the fuse side of the harness and with all the ijnectors plugged in and just the first one off you get a 12 v on the ECM side, the book says if you get all the ijnectors off and test one there should be no voltage on the ecm side and this is also the case.
As far as grounds, that shouldnt be any problem this thing has more grounds than the eiffel tower! haha but when I get the chance I will check them again.

 

is the ign module the only thing sending a signal to the ecm for a reference to fire the injectors, and if so does the module convert it to a constant signal just a constant voltage, or does it send a pulse such as a digital square wave or an analog sine wave? so I know which to test for, if its a steady 12 v then I can try to trick the ECM by sending a constant power to the ecm at that pin, if not then Ill have to try something else, but like I said earlier dosent this trigger the fuel pump as well? or does it use a different reference for that?
Also can I tap into the injector wire with my noid light, and run the other side to hot and see if its firing at the ECM to see if there is a short somewhere else?

 

The module sends out a 5v reference (I think) with a square wave for each reference pulse and yes it is the only thing sending a DRP to the ecm. The fuel pump comes on for two seconds whenever it sees key on power. This is done to prime the fuel lines. After that it needs a DRP as there is no starter signal going to the ecm. And of course the oil pressure relay also triggers the fuel pump if you crank it long enough to make oil pressure. A noid light is the best way to check for pulse. Don't get any better than that. If you have power on both sides of the inj with just one disconnected and key on, it's safe to assume you don't have a wiring problem or power feed problem.

I would just get an ign module and try it. MAybe a friend has a spare.

 

I did finally find the problem, it was the ign module, bad thing is the GM repair manual which is what the dealers use said nothing about this, so whats to say the test and replace at the owners expense if they were to take it in? and I took the old one to the local NAPA and it tested just fine, so I took one off my friends blazer, same module and walla it fired right up@! great to know that it works now just wish I would have been able to find that out sooner, like last friday, now I have to plead the parts store to take back this ECM I dont need. I figured I was going to start programming the proms here soon so I needed the new one anyway just waiting on the programmer to show up now that my cable for the laptop is here.
its almost fixed now cause all the parts stores are already closed so Ill have to wait till tomorrow to actually get it completed.
thanks for the help guys