Hi All...

Hope someone can give me some guidance. It's a 91 305 TPI Firebird with Auto trans. I had a no start issue which I traced to a bad fuel pump. No fuel at the rail etc. After doing the right thing ...IMO, and dropping the tank etc. put it all back now I get 45 ish pressure at the rail but no start condition still. I checked for codes, just keeps flashing 12. checked the injectors with a noid light... flashing. spray with starting fluid and she runs until it evaporates. started checking ECM... Getting power and ground so far. Tried changing out the ECM just for kicks cause I have another good one lying around, no difference. Getting Spark... Obviously since she runs. Now is the time to talk about VATS... I believe that would throw a code if it were bad wouldn't it? The other question is fuel pressure drops like a stone with the key off, but maintains pressure while cranking. I don't think this is an issue since I replaced the injectors years ago and noticed after replacing the fuel regulator that pressure dropped more quickly than it did with the original. It still ran fine for years this way. In any case I'm going to troubleshoot the ecm more but was wondering if anyone had a magic bullet to put me out of my misery.

Appreciate any and all help my friends

 

VATS won't necessarily throw a code if it's bad. Has your starter interrupt relay been bypassed already? VATS does two things when it gets the right resistance from the key; it activates that relay allowing the starter to spin, and it sends a square wave to the ecm to fire the injectors. Thus, dead VATS usually presents itself as "I turn the key and nothing happens.", unless the relay was bypassed, then it's endless cranking with no fire. If you want to eliminate VATS as a suspect, bypass that relay and install one of these:

https://www.ebay.com/itm/28270041228...EAAOSwXQpeq1fC

 

Thanks for the reply Komet... Let me ask this though, if it sends the two signals one being the starter and the other the injectors. The starter does crank so I assume that means it's sending that signal, and the injectors according to the noid light are being sent firing signals. Could there be something else that the vats is not sending? or is the noid light not conclusive that the signals are being sent to fire the injectors? It just seems that according to the tests I've done so far that those requirements seem to have been met, the injectors firing and the starter engaging.

 

Better to check than make assumptions. That's all VATS does, if the relay hasn't been bypassed and the car is turning over, that is a sign that VATS is at least half functional. Is the security light coming on and off like it's supposed to? If so, that's another sign that VATS isn't your problem.

Are the plugs wet after cranking?

 

Was this just running and the pump failed, or has it been sitting? Did you do any other work what so ever besides the pump? Out of curiosity, do you have an AFR or just the standard? Check for sure that you connected all the vent/fuel lines to the tank in correct order. I did this mistake and it gave me high pressure that I could not regulate during prime, but would drop instantly. Swapped lines back to the correct order and was perfect.

 

Better to check than make assumptions. That's all VATS does, if the relay hasn't been bypassed and the car is turning over, that is a sign that VATS is at least half functional. Is the security light coming on and off like it's supposed to? If so, that's another sign that VATS isn't your problem.
Are the plugs wet after cranking?
Komet: Yes I agree. the relay hasn't been bypassed and I haven't checked if the security light is coming on or not yet. I'll do that tomorrow along with checking the plugs.
Was this just running and the pump failed, or has it been sitting? Did you do any other work what so ever besides the pump? Out of curiosity, do you have an AFR or just the standard? Check for sure that you connected all the vent/fuel lines to the tank in correct order. I did this mistake and it gave me high pressure that I could not regulate during prime, but would drop instantly. Swapped lines back to the correct order and was perfect.
3rdgenzroc: The car has been sitting in my garage most of the time and occasionally I would move it around for other cars to be worked on. When you say AFR I assume you mean the fuel pressure regulator? I have the standard regulator. I've been thinking maybe I swapped one of the 4 fuel lines at the tank, but I'm getting about 45 psi at the rail. I know the vent line is correct and the feed line from the pump can't really be swapped. The only 2 would be the return and I guess the other is for the evap canister? I would think the evap canister would fill with fuel if it were swapped no? anyway, I'm going to see if I can recheck those lines as it is the only thing I did besides pull the rear end down and change out the driveshaft seals.

Thanks again for your responses, I'll check tomorrow and reply with results at some point.

 

Today I did some checking. Re checked the fuel lines according to some of the info and pics on here to see if I messed up there. Not 100% certain but it think it's right. I think the only lines I could have messed up is the return and the vapor canister line. I'm assuming the larger is the return but I need to trace it further. Checked the security light... It comes on and goes off after a couple seconds. SES light stays on with key on and cranking but still not throwing any codes. just flashing 12 all the time. Checked VATS at the ECM & its getting 2.5 volts there which is correct according to the service manual. getting good ground at the ECM and power. The only thing concerning me is how quickly the fuel pressure drops after turning the key on. drops from about 45 to 0 in about 10 seconds, but when you try to crank it comes back up to 45 and stays there the whole time your cranking. I've given up for today ...frustrating.

 

Progress is good. I'd say your issue isn't likely to be VATS, the security light is doing what it should, and you can crank the car. IMO, fuel pressure dropping in 10 seconds is no good, my system will lose like 10% pressure in an hour and then stay at some lower level for weeks. Does the fuel still drop if you pinch the return line? Try pinching both return and supply separately, then both and see under what conditions the pressure still drops.

 

Thanks Komet... I pinched the return line today and fuel pressure held... unfortunately too high at about 70! until i released it and then it dropped as usual. Hopefully I didn't blow anything out. So I suppose it's the regulator. Although, when I crank it still holds at around 45 psi which i think would be enough to at least try and start the car. You'd think it would stumble a little when cranking. I think next I'm going to pull plugs and see if there's any indication of anything. I sprayed the ecm contacts & some other connectors with contact cleaner just in case a solid connection was not being made there. Thanks again for your help. Not sure how much I'll get done this weekend with troubleshooting, but if I come up with anything, I'll post it of course.

 

It sounds like your injectors are not actually firing. Just because they are being triggered does not mean they actually work. This is very common in cars that sit for years.

 

Thanks @jkris53406,
that was actually on my mind. I want tro take the plenum apart because I believe my pressure issue is the regulator anyway and needs to be replaced. while I'm at it, that's exactly what I'll check. haven't been able to do anything since Saturday. Probably won't get back to confirm anything until the weekend. thanks again for everyone's input. I'll post back with results next weekend.

 

I agree with this after reading the thread. Its a PITA job but if you are replacing the regulator diaphram you might as well do the injectors while you are in there.

 

The only thing is I replaced the injectors about 5 years ago when one of them was shorted. So I put in Bosch injectors. It was after that I had the replaced the fuel pressure regulator and it started not holding pressure for long, although it seems worse now. I'd wish I'd rebuilt or replaced the original injectors because those Bosch injectors are really noisy! sounds like multiple valve taps all the time. I guess it could be possible that one of those bosch injectors had been leaking from day one? and the regulator was not the problem. I didn't pinch the supply line to find out, but that's probably something I should do. I just assumed the injectors were fine since they're not that old. thanks @ughmas

 

I ended up putting new bosch D3's in from southbay when I did mine the most recent time last year (I've replaced them on a couple different cars), they were indeed a little noisy/clicky but it didn't bother me personally, they flowed great. I could not hear them with the hood closed. Just be careful about installation if you go with Bosch again, if you don't seat them as instructed the o-rings can leak fuel.

 

I forget what bosch model I installed but there may lie one of my issues, the o rings, maybe I didn't install them correctly the first time which wouldn't surprise me.

 

Have you ohmed out your injectors? This is a batch fire system, so, if one of the injectors is internally shorted, only one in that batch will attempt to fire.

 

Thanks ploegi... I have not ohmed the injectors yet... This week I've been getting in so late I haven't had a chance to diagnose the car at all. I'll probably get around to it on the weekend though. I ordered a fuel pressure regulator and plan on installing that because of the pressure drop. I did take a noid light to all the injectors and they did light. I think the last time when I had a bad injector, (shorted), it prevented the ecm from sending a pulse to fire any of the injectors if I'm not mistaken. but I will ohm them anyway just to make sure. I'll report back with any results next week. Thanks again for everyone's help on this.

 

Just an update... I didn't really get a chance to do too much this week, but I did change the fuel regulator and now it holds pressure... most of the time... which is odd after cycling the key and trying to start her a few times it holds pressure well, although it takes a few tries before it will actually hold. So I have fuel pressure, spark, injector pulses... checked for various reference voltages at ecm... giving up for now... too many things to do around the house. Going to diagnose according to the service manual again in case I overlooked something. I'll keep anyone posted who is interested. thanks for all the previous responses!

 

After a long hiatus on the Firebird... I have a Fiero I'm disassembling now as well... Fuel Pump tank whole car is crap... don't know why I keep at it, but anyway. I went out to do some more checking and I thought my fuel lines might have been reversed or something since thats why it died in the first place and after tracing my lines, I don't believe I mixed them up. The feed line can't be swapped with anything else in any case since it's the only line with a fitting to the fuel filter. Checked I'm getting fuel at the rail , that's ok. I got a new programmed chip from someone on Facebook which took forever to get. I keep getting code 12 constantly which according to the manual, if your getting 12 and the ses light is on it's either a bad chip or ecm. I have 2 ecm's known to work previously and they didn't start the car. It starts with starting fluid. noid light pulses ok, ohmed injectors, ok spark ok. The next thing I have read about is to check the reference pulse from the distributor to the ecm. Just giving my status so far. I wonder if anyone knows if you could bring just the ecm somewhere to get checked out? anyway. that's all for now folks!

 

I'm suspicious of the injectors. Are the plugs wet after cranking?

 

I checked that today Komet... after cranking they're dry... with a bit of carbon for sure but as far as I could tell no fuel to the cylinder I checked. Although I put a noid light to it and that pulsed. I also checked that I have 12v with the key on to both injector wires. I keep wondering about my swapping lines after changing out the fuel pump. I retraced them today. It seems the feed line can't be swapped because of the fitting. I also have fuel pressure around 40+ at the schrader valve. Would swapping the return and the vapor canister line cause a no start condition? I also did a squeeze of the return line at the engine bay and fuel pressure went higher. still runs when I spray starting fluid but stops when it runs out. According to the service manual... if it keeps flashing 12 that points to either a bad ECM or Prom. Well I tried a new prom and I have 2 ECM's I've known to be good previously and no change. Very frustrating.
So now I have Spark, Fuel Pressure at the rail, Noid light pulses at Injectors, ohmed injectors... all around 14 ish, but dry plugs... runs with starting fluid. Injectors are Bosch replaced about 5 years ago. I wouldn't assume they would all clog up at once, would they? stumped

 

Code 12 is the self diagnostic code. This is not a bad ECM. You said yourself, you have injector pulse, you have spark, you have fuel pressure. It runs on ether for a few seconds then dies when it runs out so you have somewhat close timing at the least. YOU HAVE SEIZED INJECTORS. Nothing in the ECM or PROM can change a mechanically defective part. Take the intake apart, prime the fuel system and trigger each injector to see if it fires. Just because they were new 5 years ago means nothing. Everything you have done up to now, points to seized injectors from sitting.

 

Yes, I believe your correct @jkris53406 taking the intake apart but I thought that would be my next step as well. I had it partially apart about a month ago when I replaced The Fuel Pressure regulator. I should have taken it further down then. I'm going to take it apart this weekend. I actually miss my original injectors... I still have them and only 1 is bad. The originals were so much quieter. Always sounds like a valve tap when it's running with the bosch.