chris92pfb

Hope someone here can help me with an issue I been having, If I'm posting this is the wrong place, please refer to me where I should go.

The problem is quite simple, my injectors will not activate.

To expand a bit, this is a 92 firebird 305 TBI, I have done quite a bit of poking around for a while now since this problem started an found that everything seems to be working fine other than the injectors simply will not deliver fuel.

I replaced the ECM at the advice of some people an that did not correct the problem, my fuel pump runs fine an I broke lose the fuel lines on the backside of the carb to make sure of pressure..

If I dump fuel in the carb it will Immediately start an run till that fuel dries up.. 3-7 seconds, depending on amount.

I have ripped my entire dash apart looking for hidden secrets that may be the culprit of this problem an cannot find anything that is blown or missing.


If anyone has any clue what I might have overlooked or some steps I can take to solve this problem I would greatly appreciate any an all help you can give me.

If I've failed to provide any info, please ask an I will get whatever you might need. 3am here for me an my eyes are breaking after an extensive search on the web tonite.

Sorry for the drawn out post.
Thanks
Chris

dynocar

Just because you have fuel coming out of the fuel lines to the throttle body does not mean that you have adequate fuel pressure for engine to run. Checking fuel pres on such systems is tricky, need special adaptor for such applications avail from auto parts store. Check the Inj 1 and inj 2 fuses. Next you will need a volt meter or 12V test light, unplug the electrical plug on each injector and check the pin with the pink with black stripe wires for +12V, should have it if fuses checked OK or you have a wiring problem. I've got to run now and if you get this far you should have found the problem, I think it's fuel pressure though.

chris92pfb

Hey Dynocar

Thanks for the reply

Here's where I'm at so far;
I got +12v on the injector plug ( red an white )
there is no continuity on the dark green or dark blue (no ground, no volts, no pulses of any type)
I don't have a noid light.. do I 'HAVE' to have one to check this accurately or is it just a ground pulse being sent to complete this circuit?

I have double checked all my fuses (with meter an test lamp) an they all seem to be just fine. I can't understand why there is no pulse for these injectors.

I still need some help, so if you read this an have time or any more ideas, I really do appreciate it.

Thanks
Chris

dynocar

"I don't have a noid light.. do I 'HAVE' to have one to check this accurately or is it just a ground pulse being sent to complete this circuit?"


You do not have to have one, your voltmeter would work, you should see your voltage change up and down while cranking, do not use your test lite because it is too low of resistance and could damage your PCM. Yes, it is a ground pulse coming from your PCM to complete the circuit. I

DeltaT

iTrader: (5)

Make sure the engine has a thick ground strap attaching it to the body. Often times the engine is not enough of a ground and you do not complete the circuit. I like to ground the block and BOTH heads via braided straps to the body. Use star washers that cut through the paint and dirt.

Jim

chris92pfb

Thanks again Dynocar

I tried what you said.. Cranking an checking the contacts on the injector connections, an got no voltage at all.. the ground simply isn't there.. I've got a constant +12v if I ground to chassis, but the ground signal never comes.

Where do you think I should go from here, I dont know enough about ECMs to do any troubleshooting with it (nor should I have too, its brand new), but I really am begginning to doubt that my trouble is with the ECM anyhow.

Please give me some direction here.

Thanks again for your patience an help

Chris

Syxx613

iTrader: (8)

whoa whoa whoa.. lets take a few steps back here. lets clarify something. This is one single injector TBI setup? If so, u may not have an injector problem at all. Ur PCM might not be receiving a Ref signal, thus it will not fire the injector. ur injector may be perfectly fine, but if its not getting that ref signal, u wont get **** period. Check ur distributor pickup coil. this is what provides the ref pulse. if the PCM fails to receive this signal, it will shut the fuel injection system down. check that, i bet ull find ur answer!

chris92pfb

Hey Syxx..

Not sure if it's what you call single, there is actually 2 seperate injectors in the Throttle Body, Niether of which will produce a ground on the connections upon cranking.

Can you explain to me (I'm not an expert by no means) what I'm looking for on this reference, I wouldnt know where to look or what I'm looking for.

Thanks.

Syxx613

iTrader: (8)

well pretty much, u are lucky cuz u have one of the simplest ignition systems from GM ha ha. ok here is what i can help u with.. There will be a voltage pulse coming from the distributor pickup coil whenever u are cranking or ever running the engine. the pickup coil is inside the distributor underneath the cap/rotor. im not sure which color wires are the output to the PCM for this signal, so i cant tell you which ones to test. There should be a few wires coming off of the side of the distributor near the bottom of it close to the back of the intake. its a connector. if i knew which ones to tell you to test, you would probably find that you are not seeing any voltage going to the PCM. I guess you could hook up ur multimeter and put a T pin into the back of the weatherpacking and see if you are getting voltage as you try to crank. if you are willing to wait until tomorrow, i could look up which wires to probe for u on my schools computer. but you wont hurt anything by trying to see if there is voltage coming from that connector. if there is nothing, ur pickup coil is bad.

chris92pfb

Thank you very much Syxx

This actually sounds very promising.

If you wouldn't mind identifying the colors an such for me tomorrow that might be really valuable info to me, I won't be doing anything else with this tonite since it's so late.

Is this pickup coil a integrated part of the distributor? or something that can be replaced without taking the distributor out of the engine?

I may poke around with this again early afternoon if I have time, otherwise it will be later in the evening.



Thanks again everyone for the help.. seems like we're actually about to narrow down where this problem lies.



Thanks
Chris

dynocar

chris02pfb states, "If I dump fuel in the carb it will Immediately start an run till that fuel dries up.. 3-7 seconds, depending on amount."

From that statement I assume that the distributor/ignition system is functioning and that the PCM is getting the signal necessary to trigger the two injectors because he is getting spark, thus I excluded the distributor as a possibility, but you know what "assume" means, at least as it refers just to me. We have to make absolutely sure that we know if the injectors are or are not getting the ground pulse from the PCM while cranking, hard to see with a voltmeter. If the voltmeter has an AC scale, try that in this voltage range or lower measured across the two pins of each injector.

Syxx613

iTrader: (8)

i dont think u understand. unless the pcm sees the refrence pulse from the distributor it will NOT FIRE the injectors. so it doesnt rule out the possibility of the pickup coil. ive given him information on what wires to back probe for voltage and if he sees no voltage and has no spark, he is looking at a bad crank sensor. however, he has spark so it is most likely this pick up coil. hope i explained that well enough for ya.

dynocar

Well here is what I think I understand, if there is no reference pulse from the distr to the PCM, it will not send the EST signal back to the distr that controls ign timing and initiates spark. So all of this must be working if he can pour fuel in the TB and it runs. This working will also create injector pulses from the PCM to the two injectors, if the PCM and wiring is OK. A '92' TBI system did not use a crank sensor, HEI distr with inductive pickup only. Obviously I'm not unstanding something or he would be running by now. Good luck, hope he gets it running.