2000 GMC starting problem

Thanks Bob in Mass.

Check your fuel pressure regulator. H

If you have to crack the throttle to get it started when it's warm, the problem isn't not enough gas, it's TOO much gas, and cracking the throttle plate leans it out enough to get it to fire.

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

I'm assuming this is the same as a '98 5.7. ie Vortech/Multiport with fuel pressure regulator inside the intake minifold.

Drive it until temperature comes up to normal. Shut engine off. Remove ducting at intake to access throttle body. If you can see or smell fuel inside the intake manifold (through the throttle body) your fuel pressure regulator is leaking.

Cold starts don't mind a little extra fuel. Warm starts need a little more air if it is getting too much fuel. Once running, the computer control will compensate and decrease the fuel delivered by the injectors.

Good Luck.

Bob

Drive it until temperature comes up to normal. Shut engine off. Remove ducting at intake to access throttle body. If you can see or smell fuel inside the intake manifold (through the throttle body) your fuel pressure regulator is leaking.

Cold starts don't mind a little extra fuel. Warm starts need a little more air if it is getting too much fuel. Once running, the computer control will compensate and decrease the fuel delivered by the injectors.

On the newer engines, the FPR is on the fuel rail on the drivers side of the engine. You simply warm the engine up, shut it off, wait a half an hour or so and pull the vacuum hose and check for the presence of fuel. H

Doc, Hmmm.....too much gas? I'm having the same type of starting problem after my engine is warm too. What can cause too much gas? Can a leaking fuel injector(s) cause this? I'm thinking that I might have a leaking injector or two. I measured the fuel pressure after turning the ignition on (but without trying to start the engine) and I read 56 psi for 2 seconds. Then after the 2 seconds, the fuel pump stops and the pressure starts dropping slowly but continuously to about 20 psi after about 15 minutes. So then, to see if the check valve in the fuel pump was leaking and causing the continuous drop in fuel pressure, I tried again except I pinched-off the fuel line after the fuel filter underneath the driver's side and the pressure still continues to drop. Therefore, I'm thinking something after the pinched fuel line is leaking. Thanks for any thoughts, help or ideas that you could suggest that might help us resolve our problem.

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

Jabs,

On most EFI vehicles, the computer ignores the TPS signal while cranking, so having to mash the pedal to get it started just lets more air in, no extra gas.

I need to know the year, model, engine and milage.

Also, when warm, is it having trouble cranking or having problems turning over?

Doc

Jabs

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

Jabs,

On most EFI vehicles, the computer ignores the TPS signal while cranking, so having to mash the pedal to get it started just lets more air in, no extra gas.

I need to know the year, model, engine and milage.

Also, when warm, is it having trouble cranking or having problems turning over?

Doc

Jabs

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

Jabs,

On most EFI vehicles, the computer ignores the TPS signal while cranking, so having to mash the pedal to get it started just lets more air in, no extra gas.

I need to know the year, model, engine and milage.

Also, when warm, is it having trouble cranking or having problems turning over?

Doc

Jabs

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

5 seconds before it actually starts-up. Then once it does start, it stumbles for about two or three seconds. Then after that, it runs fine with no complaints. So far the only thing I can come up with is; I'm thinking about taking it into a carburetor/fuel injection shop to have a "Fuel Injection Service".

Jabs

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1. When's the last time you tuned her up? Checked the condition of the plugs lately?
2. After it's been sitting and is harder to start, does cracking the throttle get it started more quickly?
3. When it does finally turn over, and raw fuel smell or black smoke from the exhaust pipe?
4. Gas mileage been any worse lately (not that you'd really notice with a

454, he he he.)

In the meantime, dump three or four bottles of Chevron Techron fuel injector cleaner with a tank of 93 octane to clean her up. One bottle treats 12 gallons so you'll likely need 3 bottles .

Doc

On most EFI vehicles, the computer ignores the TPS signal while cranking, so having to mash the pedal to get it started just lets more air in, no extra gas.

I need to know the year, model, engine and milage.

Also, when warm, is it having trouble cranking or having problems turning over?

Doc

Jabs

You need to get it to Autozone or Advance Auto and have the PCM scanned for error codes.

Doc

Thanks Bob in Mass.

Doc, I haven't looked at the plugs lately but I did change them at 100,000 miles along with a new cap and rotor. The spark plug wires are still the originals. Yes, if I crack the throttle a little it seems like it will start sooner (after about two seconds instead of three seconds). Yes, I have a raw fuel smell but no black smoke. And for gas mileage, about the same as it always been; about 10 MPG.

As far as Chevron Techron fuel injector cleaner with a tank of 91 octane, I have done that several times in the past, because I had a rough idle about

50,000 miles ago and a couple of bottles of Chevron fuel injector cleaner and a full tank of the best Chevron gas I can get in Southern California (91 octane) straightened that stumbling problem out. However, that trick didn't work this time.

Jabs

From what you've stated it sounds like one of a few things; these are just educated guesses so take them for what they're worth!

1. Leaking fuel injector (s).
2. PCM not getting an accurrate air or coolant temperature reading on warm start. It's seeing the incoming airflow as being too cold, the coolant temperature as being too low, or maybe a little of both.
3. Bad FPR which is allowing too much fuel to the injectors during warm start. You don't notice during cold start as she likes lots of gas in that situation.

AFAIK, the MPFI systems do not have the "autobleed" function that the TBI systems have and should maintain fuel pressure when the engine is off for more than 15-20 minutes.

If you get her up to temp, shut her off and let it sit for 10-15 minutes then re-start, how does it act then?

Doc