My LT4 spins over for 10-20 seconds and tries to start. The second attempt spins for a shorter time and runs slowly for a few seconds. The third attempt, it fires up like nothing is wrong and runs fine. This only happens when cold. What am I looking for? Fuel pressure regulator? Fuel filter (new only 2000 miles ago) New plugs just installed, new Opti & water pump 1000 miles ago.

That's a good start. Need spark, fuel, and air to start!

I would check the fuel pressure at the rail, first. I actually need to do that to mine. I have a hard time starting the first couple turns, but then fires right up. I'm ASSuming at this point I have leaky injectors or a bad FPR. I just have to get to the store to get the gauges.

Keep us posted!

Matthew

Thanks--It sounds like we have similar problems. I ohm'd the injectors and they all read between 16.0 and 16.5 ohms. I need to check the fuel pressure and then check for codes. With the help of the forum here, we'll get to the bottom of these problems! It seems odd to me that after the first cold start the thing runs so strong that you would never know there is anything wrong. This car will run 13.40's all day at 106 mph!!! It's all stock, on street tires, through the mufflers, original clutch (66000 miles).

Mine runs pretty strong after it starts up, too, but I think it's lacking a little in acceleration.

I bet you could get that baby into the high 12's with little mods!

Matthew

Yes, I agree, but right now I would like to solve this problem, and then try for the 12's. These cars are so strong stock, that I think it would not take much to make them faster. I have a 1987 Buick Regal Turbo that I got in the high 11's with a few mods. That car is still scarey fast!

One of these days we'll have to meet up in the middle, cause I'd love to check out that LT4 power!

Matthew

btw - I plan on getting a FP gauge and working on the car tomorrow.

next time you start the car, turn on the key, count to 3 then try to start it.

OK Bogus--I'll try that. I also thought to turn the key on and off three times. It seems to me this problem is fuel related. Either not enough fuel or not enough pressure.

I agree with Bogus, might take a few seconds for the pressure to build. As said, you need to get a gauge on it and find out what the pressure is key on, cold without starting the motor.

How does it start up with a hot motor after it sits for like a half hour?

These motors should start on one or two revolutions. My LT1 fires every time in about a 1 second.

Pull the sender unit out and have a look at the strainer sock on the bottom of the pump.

this could also be a bad check valve on the pump.

OK fellas--this gives me something to work on. All your suggestions will be tried and either they will solve the problem, or they will narrow it down as to where to look next. Thanks for your imput, I will report back with my findings.

I bought my FP test gauge today - I'm gonna check it tomorrow and let you know my findings.

Matthew

Quote:
Ive encountered that myself recently too.

I have encountered this phenomena my self. Sometimes I turn the key and it instantly starts and other times it might spin for a few seconds. Generally less than 5 seconds but always starts.

First thing I did was to hang a fuel pressure gauge on it. When I turn the key it hits 40+ lbs of pressure instantly. When I ran it all was normal. Fuel pressure would respond to throttle/ vacuum response. Had even checked return flow at one time at tank. Played with this for a few days and found nothing. Have considered check valve in pump but since pressure is there instantly, I didn’t feel it was a factor. It does hold pressure for a good while but have never seen a spec on or what the norm is for how long it should.

Not even thinking about injectors being bad. No symptoms of any kind, and even if one was so what. 6 or 7 cylinders working should pop right off anyway. And besides the injectors of the 94 vintage are much more reliable than the earlier C4s of the 80s. And yes they all measure 12 ohms not that that really means much in regard to a leaking injector.

Ignition system seems to be in good shape and opti just a few years old. But my gut feeling is that it might be fuel related, point being injector pulse width.

After driving around with a Tech 1 for awhile I have seen things happen not as advertised in any book. I believe the code or software in the PCM in the way it works (runs) and thinks in that all information is not know about it, and I’m not talking about tuning.

If you read the FSM on starting it takes various inputs from the CHT, MAF, TPS and several others and comes up with a pulse width for a cold start on that day. Perhaps the correct pulse width is not selected and some days its just way off, other days right on. There is no cold start valve so the PCM decides how much fuel to give it.

Anyway this is just my theory as to what might me going on. Right or wrong I’m willing to go in either direction. Just something to think about since the symptom seems to come and go. Open to any questions or ideas.

I have replaced the fuel filter ---no change-- I thought I would try something simple first. The new filter was just as easy to blow through as the old one ( 4000 miles ). Today I am going to get a scanner on it, I will let you know the results tonight.

Well--- Here is the results-- Code P1171-D I think that is a lean on acceleration code. The fuel pressure, hot, is 36 lbs. All injectors ohm at 16-16.5. I have a fuel pressure gauge, and tomorrow morning I will check the pressure cold. Does this sound like fuel pump?

Yup-- that's what is was ---a fuel pump. Now she runs like it should!!!
The fuel pressure would drop as I floored the accelerator!! The pressure would go from 36 lbs. to 20 lbs! My first thought was the fuel pressure regulator, but when I disconnected the vacuum line it ran the same. So I replaced the pump and now the pressure stays at 45 lbs, even when I floor it. It starts instantly, no stall, no stumble!


Thanks Paul---