Fuel Issues maybe...

**tahoe freak** · 10-08-2008, 05:41 PM

I have a 99 tahoe 4x4 350. 2 door. It's a shame they don't make em' any more I love the 2 door look. However I'm ready to take the 45 cal. to it. About a month ago, she started giving me problems. Spitting and sputtering, kicking back through the TBI. I assumed it was backpressure from the converters. It was fine for about a week, and I back to square one again. i have trouble after letting sit for a day or two. It just doesn't want to start. On a moderate temp morning it's ok. On a warm to hot day it's even better. But this morning I get up a cold front has come in and it won't start. I have changed the entire firing sys. I have changed the Intake Air Temp sensor. The only thing I can think of, is the FUEL PUMP. I thought fuel pumps just went out. No indications or signs of pressure loss. Any suggestions will be greatly appreciated. I'd hate to waste the bullet....

**MrShorty** · 10-08-2008, 06:10 PM

First thing I would do if I suspected a fuel problem would be to put a fuel pressure gauge on it.

**GaryL** · 10-09-2008, 10:29 AM

When my fuel pump started going out this last time, the truck became hard to start, but eventually would. It also started feeling real sluggish and wouldn't pull past about 4300 rpm's. The fuel pressure was showing around 55 psi, but it needs a minimum of 60 to run correctly.

As Mr. Shorty suggested, check the fuel pressure and let us know what you find out.

**tahoe freak** · 10-10-2008, 12:31 PM

ok, did the pressure check. I turned the key on and it jump beyond 60+. Two secs. later it drops. It's suppose to do that. The manual says to cycle the key back and forth to obtain maximum [COLOR=blue! important][COLOR=blue! important]fuel [COLOR=blue! important]pressure[/COLOR][/COLOR][/COLOR]. Each time the pressure rose above 60+, and dropped back down. How do I check the FPR?

By the way, After cycling the key. It did it again, acted like it wouldn't start. Turned over and over and finally picked up and started. It hiccupped and coughed but it's runs. I waited a few munites and went back out to check the pressure and it's down to about 30 psi. Is that normal? Oh, and thanks for all of the help!!!!!!!!

**GaryL** · 10-10-2008, 01:23 PM

I merged these two threads so all the information is in one spot.

Have you tried holding the throttle to the floor when you try to start it? It may be leaking gas past the FPR and causing a flooding condition. If you hold the throttle all the way down until it starts, it may make it start a little easier.

**MrShorty** · 10-10-2008, 02:48 PM

How do I check the FPR?

Just like you did: by testing fuel pressure. It appears that the regulator is correctly regulating the pressure. However, the fuel system should hold pressure for a time after the pump is shut off. The FPR could cause this if the diaphragm has ruptured, causing it to leak gas into the intake (and possibly flooding the engine making it hard to start). I haven't seen it myself, but reportedly you can check for this condition by looking down the throttle body past the throttle plate. If you see "clean" trails or liquid gasoline in there, then you likely have a bad FPR.

Another reason for rapid loss of pressure like that is a bad check valve, which is part of the pump. Any leak in the fuel system, including a stuck open injector) could also cause the pressure to drop.

I waited a few munites and went back out to check the pressure and it's down to about 30 psi. Is that normal?

Clarification: it dropped to 30 psi while the engine was "running" or after you had shut the engine off? If the fuel pressure is dropping off like that while it is running, then something is definitely wrong. clarify this point and we'll see what, if anything, it adds.