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1996 Pontiac Firebird Stalling at high RPM

Tiny
SOL3ARCANE
  • MEMBER
  • 1996 PONTIAC FIREBIRD
  • V8
  • 2WD
  • MANUAL
  • 144,000 MILES
I have a 1996 Firebird Formula 5.7litre w/ 6spd manual tranny. Six months ago I replaced all of the ignition components -- the optispark, the coil, everything. This was primarily a preventative measure because I was preparing to drive the vehicle cross-country. The PCV valve is also new. Cold air intake system. Full custom exhaust system, but the cats are probably 4 years old. I do all the work myself -- I'm not a mechanic, but I know this particular vehicle like the back of my hand.

About a month ago, I was merging onto the freeway, and when I hit about 3800RPM, the car stalled. I pulled over to the side of the freeway, tried starting it again, and it would turn over great but wouldn't fire. I quickly checked all the fuses, and finally gave up and called a tow truck. Five minutes later, I turn the key, and the car fired up immediately, like nothing was wrong. I went to pull out into traffic -- babied it through first, then got into second and mashed it. Again, the car hit about 3800RPM and stalled. So I pulled over, and it wouldn't start. Gave it a few minutes, tried again, and it started great.

When the vehicle is idling in neutral and I mash it, the engine will nail the 5800RPM rev limiter and everything is fine. But any time there's resistance on the drivetrain (i.E. In gear, on pavement) the car stalls around 3800RPM. The other day, I went to the Dr's office, and when I came out, the car would turn over but would not start. So I opened the schrader valve and released the fuel pressure. Turned the key, and the car fired right up as though nothing were wrong.

I'm going nuts here! I'm thinking it's something in the fuel system, or possibly in the ECU, or maybe even a relay? What can cause this? I have emission testing coming up soon, and they will reject the car if it stalls on them in the middle of their tests! Please help!
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Thursday, March 12th, 2009 AT 5:45 PM

11 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Hook up a fuel pressure gauge to rule out a failing fuel pump/ regulator and filter and report back with the pressure readings we start here.

Also check the injector/s -have helper crank engine over and you listen to it if its clicking in a uniformity manner or use a noid lite
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Thursday, March 12th, 2009 AT 6:26 PM
Tiny
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I need to get a new pressure gauge, mine is broken. It will be a couple of days until I can get one, and I will reply back with the pressure reading.
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Thursday, March 12th, 2009 AT 6:38 PM
Tiny
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Roger-I'll be waiting
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Thursday, March 12th, 2009 AT 6:43 PM
Tiny
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Okay, I have not had a chance to listen to fuel injectors yet. However, I purchased a fuel gauge and used it on the Schrader valve behind the fuel rail, that is hooked into the fuel line coming from the tank.

The car was sitting in the driveway for 3 days. I hooked up the gauge, and had 0 pressure. I turned the key to "run" and heard the fuel pump prime, I went and looked and pressure was at 38 PSI. I started the car, and it rose to 39 PSI. I then played with the throttle control under the hood while I watched the gauge. A very slow rev up to about 4000RPM showed no change. Then I let the RPM come back down to idle and threw down on the throttle cable as quick as I could -- went from idle to 5800 in like 1.5 seconds or whatever, like normal -- when I first mashed the throttle, the fuel pressure dropped to 34PSI for a very split second and then jumped back up to 39PSI. Then I pushed down on the throttle cable really fast but only for a split sec, to rev it up to about 2500RPM from idle. Same thing, right at the beginning, it dropped to 34PSI then immediately returned to 39 PSI.

I have HEARD that correct fuel pressure for an LT1 engine is 44 PSI. But you would know better. I have quite a few mods running on it, probably producing about 80 more HP at the flyweel than stock.

Have a feeling it's not the injectors, but gotta wait til my wife gets home so she can crank the engine over for me.

Also, I was looking through my maintenance receipts, it hasn't had a new fuel filter in 4 years / 38,000 miles (yikes, I think)
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Monday, March 16th, 2009 AT 4:42 PM
Tiny
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Well, I donated $10 the first time, just to be told to hook up a fuel pressure gauge and listen to the injectors. Apparently I must donate again to hear the results of my test, so sorry, but this time I'm not donating much. Let's get me some results and then I'll start donating more money.
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Tuesday, March 17th, 2009 AT 12:28 PM
Tiny
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Oh, and the injectors are clicking uniformly.
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Tuesday, March 17th, 2009 AT 12:32 PM
Tiny
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Have you checked the fuel pressure again? The fuel pressure should be 41-47psi yours is on the low side

Fuel injector solenoid resistance is 11.8-12.6 ohms
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Tuesday, March 17th, 2009 AT 2:18 PM
Tiny
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Thanks for the specifications. Injector solenoid resistances are within tolerances, but the fuel pressure is not. So therefore I am going to assume that it is the fuel pressure regulator, the fuel filter, or the fuel pump.

I have one more series of questions to ask. And then I'll make a final donation and be done with this thread.

I ordered a new fuel pressure regulator (adjustable from 35 to 60 PSI) and a new fuel filter. The fuel tank in my car is above the axle and exhaust, so in order to replace a fuel pump, I would have to either remove the axle, exhaust, etc or use a dremel tool to cut an access panel in the trunk. So, I'm thinking of bypassing ALL that mess and going with an in-line fuel pump. I've researched a lot of this on Google, but who knows how reliable that information really is, right? That's why I need to ask you these questions. To make sure I do this right the first time! So, here are the final questions that I have:

1) If I do install an in-line pump, can I leave the in-tank pump where it is, or do I have to remove it in order for fuel to flow properly?

2) Is a 172lph in-line fuel pump potent enough to deliver up to 47PSI of pressure?

3) Other than the obvious precautions of relieving the fuel pressure, not electrocuting myself, and not causing a gasoline explosion, are there any other precautions I should take, or other things you feel I should know, before attempting to replace/install any of these parts?

After these questions are answered, I will make a final donation!

Thank you.
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Tuesday, March 17th, 2009 AT 2:58 PM
Tiny
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1) If I do install an in-line pump, can I leave the in-tank pump where it is, or do I have to remove it in order for fuel to flow properly?

Xx Install the new fuel pump and read the pressure if it comes to specs by adjusting the fuel pressure your good if not you gonna have to go in the tank and investigate is how to make it flow without any type of obstruction.

2) Is a 172lph in-line fuel pump potent enough to deliver up to 47PSI of pressure?

Xx This one I'm not sure-The fuel pump has to deliver the correct fuel pressure as specified in order for the fuel system to function properly.

3) Other than the obvious precautions of relieving the fuel pressure, not electrocuting myself, and not causing a gasoline explosion, are there any other precautions I should take, or other things you feel I should know, before attempting to replace/install any of these parts?

Xx If you have to use additional fuel hoses make sure its designed for your fuel system
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Tuesday, March 17th, 2009 AT 3:27 PM
Tiny
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Thank you for the information and letting me bounce this stuff off someone that is an actual mechanic :) I will come back again and start another thread if I have any questions.
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Tuesday, March 17th, 2009 AT 3:44 PM
Tiny
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Sir-do not start a new thread stay here and post it
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Tuesday, March 17th, 2009 AT 4:01 PM

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