My car (91' Z28 5.7 TPI) quit on me a few times late this morning, once after idling for a few minutes, then while driving it randomly died a few times, once at idle and the other times driving. It didn't start back up right away a couple of times either. My first thought was the ignition control module but I decided to go ahead and test fuel pressure first. Of course while I'm testing fuel pressure priming, idling, and revving...not once did it die or quit..it ran perfect idling for 15-20 mins.

Before I started it though I hooked up my fuel pressure tester gage to the fuel rail schrader valve, turned the key to prime, heard the fuel pump prime, watched the needle on the pressure gage swing to 45 psi....but then it immediately drops to zero after the fuel pump finishes the 2-3 sec prime. I then decided to start the car to see what the fuel pressure read at the rail and it swings to 45 psi while cranking then starts and is steady at 38 psi. So the pump is completely within spec.

I don't have the OEM injectors, but my understanding is that the pressure at the rail should at least hold for 30 secs or so...right?

The gage never showed the rail holding pressure after fuel pump prime, I checked it for leaks and the bleed off valve in the pressure gage has fuel in it but no pressure. I'm thinking if my gage was leaking that I would see fuel somewhere on the face of the gage, hose, or connection. It was dry as a bone.

It cranked an started everytime this afternoon. When it failed this morning it wouldn't start back up each time, one time resulted in it being pushed in the grocery store parking lot to get it out of the way.

It would seem that the rail would keep pressure so the pump didn't have to prime each time immediately after. I don't suspect my fuel pump is bad as it primes to 45 psi and then stabilizes at 38, and increase when I stab the accelerator to 48-50 and goes back down to 38 psi.

 

It should drop no more than 5 psi or so initially, then maybe drop gradually, then should hold at least half (20 psi ish) overnight. Doesn't matter which OEM your injectors are.

If it primes and drops to 0, something is not right. FPR, pump, or leaky injectors.

 

If the pump was bad it probably wouldn't prime to 45 psi or idle at 38 psi right? Doesn't the FPR control flow back into the tank? When I get it started fuel pressure is rock solid at 38 psi at idle. It's only if I prime and shut off the key does it bleed off or does the pump have a return built into it that can fail? I was always thought if the pump was bad or weak it wouldn't prime or run at the correct fuel pressure.

If any of the above is true regarding the pump I will probably try the OEM FPR diaphragm first as it's pretty easy to get to by removing the plenum...thoughts? Thanks


I will go through the troubleshooting procedures. I've chased these issues in thirdgens and they have ranged from bad ICM, Fuel Injectors, Fuel Pumps...and the last most troubling in my Firebird was a bad ECM. The good news about that is that basically every sensor got replaced CTS, IAC, etc., plus FP, FPR, Injectors, and ICM so once the ECM was replaced it drove perfect until I sold it.

 

Not necessarily; there are several parts to the pump, some of which might work fine and some not so much.

Yes. The pump is constant volume; if its output is totally UNrestricted, pressure will be 0, and if restricted, it will go … quite high. The pressurized fuel comes into the end of one fuel rail, through it and around to the other, and the FPR allows an amount to return to the tank such that the pressure is held at the desired level.

Last I knew the FPR was like $20 - 25 but that was some time ago. Still, a pretty cheeeep and eeeeezy swapout to troubleshoot by way of. While I'm not a fan of random parts-swapping in general, there are times and particular parts that it's the best way, especially when the part in question is somewhat failure- or wear-prone and is the most likely diagnosis anyway (or close at least). The FPR qualifies.

 

I had a TPI swapped blazer at one time and it had started acting up. It had starting issues and would run but not very well. It turned out to be the rubber coupler that connects the fuel pump to the sending unit had deteriorated. In addition to a bad FPR or leaking injector this would be something to check.
When you have the pressure tester hooked up and engine running can you give it throttle blast and get an increase in fuel pressure ? If not replace FPR, if the situation stays the same with the new FPR, man I hate to say it, but drop the tank and investigate the coupler.

 

Just completed some quick trouble shooting. I pinched off the return line to and primed the rail to see if the FPR was holding. Pressure dropped immediately the same as with the return line open. I then had my wife turn the key to prime and pinched off the feed line (return was still pinched off) and the pressure fell immediately so I don't believe it has anything to do with the fuel pump. I then disconnected all of the fuel injectors, released the fuel send line, primed the rail again and pinched off the feed, the pressure fell off the same as before. All the fuel injectors are silver with black tops (look like Delphi) they are obviously bleeding off the pressure and leaking quickly. I'm not sure if this could cause it to die while driving...really part throttle and idle is where it quit...like coming to a stop or taking off from stop lightly, but it is definitely not correct.

I will pull the injectors and buy some new ones. While I'm in there I will replace the FPR and swap in a new ICM just for ease of access. Car started and idled just fine this morning too. If it does it again I suspect an intermittent ECM Fuel Injector driver problem and will go that route. After I chased this issue on my old Firebird I was both relieved and pissed that it ended up being a $100 ECM. I just happen to be checking it and noticed the ECM had dislodged from the little plastic bracket and was hanging by the connectors on my Firebird. But I know for sure I have leaking injectors with out them being hooked up so the ECM is not causing that.
Thanks

 

I wouldn't buy "new" ones, necessarily; lots of injector services can supply you what you need. Cleaned, tested, flow-matched etc. I think there's a board sponsor in that business, I've used them before with good results.

 

Hey....we have any size reman injector you need. They all come with a warranty..guaranteed to flow within 1% or less. Plus thirdgen members receive 10% discount

 

Just ordered the Bosch 22lb replacements.
Thanks

 

great...if you have any questions at all...give us a call at the shop...we are up and running.

 

The Bosch's fit perfect, no leaks, starts right up, idles great, part throttle, and WOT had no issue either. Not sure what would need to be tuned but certainly nothing noticeable by me or my wife driving.
Thanks

 

Just because it's within the ability of the ECM to adjust the BLM and INT values significantly to make it seem to run "correctly" does not mean it's operating as designed. Having the fuel trims railed gives the ECM no ability to counter other sensor drift or environmental conditions. Yes, under ideal conditions with all other sensors performing correctly it is within the ability of the ECM to compensate. But it won't be able to compensate for anything else.

GD

 

Appreciate your knowledge on the topic and not trying to disagree with you on it. As a follow up question, based on what you stated should I expect that other sensors will have an issue or be more prone to failure (including ECM) if I continue to run the Bosch injectors? If not I'm just going to keep driving the vehicle and will report back whether they are running fine or triggering SES lights. I did keep the OEM injectors and plan on sending them out to be reconditioned in the event the Bosch don't work out and plus retaining the OEMs.
Thanks

 

Funny thing is, it may seem to be "running fine" now; but who knows how much BETTER it might run if tuned properly to match the new injectors.

But no, there should be no reliability issues with the ECM or whatever, related to the different injectors. People use them often in these cars.

 

Almost got to laugh sometimes at this stuff thankfully my Thirdgen is not my only source of transportation these days..although I had one that was decades ago.

So last night I go to take a ride and the car is idling and then dies. Will not start...whereas before it would intermittently run then die. As above I replaced all of the injectors...convinced my OEMs ones are still good now anyway as they all ohm check.

So I decide to pop off the dizzy cap and check around. I observe a slightly worn cap and rotor, and a lot of rust surrounding the ICM. I take off the ICM and it doesn't look burnt or melted. I decided to buy the Napa top of the line cap and rotor, ICM, (made in USA) and a new ignition coil (made in Poland). The reason for buying the ignition coil is that imprinted on the side is "Made in China" and every time I saw it...it griped me, plus I'm thinking if I replace the ICM I might as well replace the ignition coil.

I swapped out the dizzy cap and ICM and go to start.....NO start...same issue. Then I decide to hook up the new ignition coil (not made in China...but in Poland lol) and the car fires right up. So it looks like the Chinese ignition coil was my intermittent problem all along.

I go for a drive everything is fine, I go to put the car in reverse and it stalls and dies. I'm like great...stranded again. But it turns over and starts fine. With my foot on the brake I hear a slight pop and the brake pedal depresses further down. Then the brake light comes on the display and will not go out. Every time I'm sitting for a moment and put it into drive or reverse it stalls and dies...but then starts right up and if I put it into drive it is fine.

When I got home tonight I noticed fluid coming from the driver side rear wheel well, I touched it with my finger tips and it smelled and felt like brake fluid.

So I'm assuming I'm having two new separate issues.

First Issue
Brake Light stuck on dash display (Red !), soft pedal, and brake fluid on the ground...kinda sounds like a busted brake line or leaky one. I check the brake reservoir and the cap was still on tight and there was plenty of brake fluid in it. The brake booster vacuum lines look good everything is in place running to the intake.

Second Issue
When shifting into drive or reverse after idling for a moment....car stalls and dies. Car then starts right back up again and so long as I immediately shift into drive it drives fine. I'm assuming this isn't because the voltage of the new fuel injectors is slightly different (although I did consider it after reading the above) but before the coil completely crapped out I road tested a few times and the car didn't stall at all when putting it into drive or reverse.

 

Obviously fix the brake fluid leak and do not drive it till that's safe. I would highly recommend replacing all the hoses. Braided stainless kits are available and relatively cheap. There's really no downside to such an upgrade IMO.

The stalling when shifting into drive is most likely an issue with the idle control. Try cleaning and inspecting the IAC. Also reset you minimum idle are, tps voltage, and check your ignition timing.

GD

 

I had forgotten that when I replaced the fuel injectors I disconnected the IAC valve. I did the reset on it and it seems to be working ok. I let it warm up and then selected Drive and went to Reverse, then back to Drive and the idle seems to be right about 450 rpms when in gear, in Park it looks like 900. I will know more after I drive it for a bit but I have to rebuild the rear brake drum as that is where the fluid is leaking from. I purchased C6 wheels and once the tires wear out on my OEM 16" I will put the C6 wheels on and go big brakes front and rear. Thanks!

 

It may not in fact be within the ECM's ability to compensate. Since I have changed out the injectors to the Bosch the car will die sometimes while idling in drive with my foot on the brake, like if I'm at a signal waiting for the light to turn green, the rpms will be at about 500 then drops and dies. I thought maybe the IAC valve was bad, so I purchased a new IAC valve and replaced it. Since the old IAC valve still looked good I didn't think the new one would fix anything. I went though the procedure of warm up and driving it for 40 miles too.

Where it is a real problem and fails (dies) almost every time is when I'm in drive with my foot on the brake and I shift quickly into Reverse or even after it is warm and come out of Park into Reverse...kind of a hard type drop into gear it drops below 500 rpm and dies. I'm sure it is the fuel injectors having a different fuel trim as you suggested as this problem never existed with the old injectors. The problem all along was a bad ignition coil

I will probably just re-install the OEM injectors...OR...OR lol can I adjust the minimum air screw on the throttle body to compensate...basically increase the idle manually to some extent?

 

Buying moates.net xtreme aldl cable would be a good purchase.
Your mask is $8d. You can datalog with tunerpro rt as well as watch iac steps.

 

Is it fairly self explanatory, I mean I would still have to order a new prom correct?

 

If it’s lean yes, but why wouldn’t you want to see what the iac is doing, target idle speed and blm/int .

 

where did you get them? How much & what’s the part #?

 

Check out southbay fuel injectors D3 might need tuning or the Delphi’s more of a direct replacement.

 

if you decide to purchase a set...use code tg11 for your 10% discount.
However paypal has some kind of glitch that will not allow the code to be accepted.
If you pay with a credit card you will not have a problem

 

Have the same issue that my pressure "seems" to leak far too fast, are you actually sure your tester is working correctly? (I really think the pressure release on mine is actually the issue)
If you have a severely leaking injector you would most likely see it immediately (my car was smoking like crazy )