00 Bravada Intermittent Stalling at Speed, Then Won't Start

Here's a tricky one.

My 2000 Bravada occasionally stalls at speed, and sometimes at idle. Then it won't restart (turns over but won't start).

This only happens during road trips (i.e., far from help and home), sometimes on the highway, sometimes after stopping for a pit stop. Hot weather and cold.

Stranger still however is that when it does restart, it will idle fine but stall once moving (either immediately after pulling out or as soon as it's given gas in gear).

It happened in August and a dealer could find nothing wrong (of course, he couldn't replicate the problem). It happened again yesterday and the car wouldn't restart until I let it sit for 5 mins with the hood open (a theory to get the temperature downThen it ran fine for another 200 miles.

Vehicle is not overheating (based on gauge). Fuel pump is about 1 year old. Plugs, wires, and distributor are new. Back in August a service station checked the spark and fuel pressure while it was refusing to start and both were fine. No trouble codes at all.

Any suggestions? Thanks.

Edited to add: Replaced the crankshaft position sensor before this trip (as in that morning). No dice.

If like you say its getting proper fuel pressure and spark to all cylinders, and of course a good supply of air, then the engine will run. You say when it was checked there was spark and fuel pressure. My questions are is there good strong spark to all cylinders and also, was the fuel pressure to proper specs? If fuel pressure is under spec, even by a few pounds, you can have a hard/no start condition.

You mention that when you give it gas, thats usually the time it will stall. You need to see what running fuel pressure is. Also I would get a good scanner on there and watch things like the MAF sensor readings, oxygen sensor readings and make sure everthing is within specs. You need to do some troublshooting to narrow it down and go from there.

Sure.

The giving it gas thing is that after stalling, when it finally does start, it will idle fine but will stall if driven.

The fuel pressure issue would be a real bitch, since the current pump is only a year old (OEM, installed by me).

I still have a strong suspicion that it's related to engine temperature. Any chance of this making sense?

Thanks.

You should be able to hear the fuel pump run for a few seconds after first turning the keyswitch on if you listen close next to the drivers side rear tire. Remember that sound then the next time the motor stalls, turn the keyswitch on and listen for that same sound.
I'm kind of surprised there's no Check Engine light. What about pending codes?

Here's where you check the fuel pressure.

http://i131.photobucket.com/albums/p288/Clunk_/Image026.jpg

I agree with Chris on the fuel pressure! What you are experiencing is a common symptom of a weak fuel pump. You would still hear the pump run, and it would sound normal and supply enough fuel to start and idle the engine, but stall when accelerating. Always keep in mind that just because a part is new, is no guarantee that it's good. Check the fuel pressure: Turn the ignition to run, don't start the engine, while the pump is running, pressure must be 60 to 66psi. After 2 to 3 seconds the pump will shut off, pressure must remain above 55psi for 3 to 5 minutes. Post your results.

Bought the gauge, test results yield no clues.

With ignition at run the pressure goes to 60-62, and stays for 3 min+. After starting the pressure drops to ~54 while idling. While driving, the pressure jumps to 60 while coasting, and drops to 51-52 during acceleration (up to 4500+ rpm).

According to my manual, my CSEFI system runs at 55-61, less 3-10 while running at idle.

So, any suggestions? Any chance this is the fuel pressure regulator failing (though, as stated above, it'd only fail after a few hours of driving and hundreds of miles away from home on long road trips - never near home no matter how much driving I do)? Thanks.

In the GM dealer issue shop manual, fuel pressure specs are 60 to 66psi, pump running, engine off. They publish no specs while the engine is running. Pressure must be checked while the engine is cold so heat radiating from the engine does not affect the pressure reading during the leakdown test. Fuel pressure should not drop below 55psi for 3 to 5 minutes after the fuel pump shuts off. Intermittent problems are difficult to diagnose, you will need to have test equipment hooked up when it fails. It's very doubtful the fuel pressure regulator is the problem. Basically it involves a plunger, a diaphragm, and a spring. There are two things that can fail, either the spring will break or the diaphragm will leak. In either case, the failure is constant, not intermittent.

Well, I'm there for 60-65 (at 62), and leakdown isn't a problem (it holds for longer than 5 min), so any other thoughts?

Ignition and fuel problems both can cause stalling and no start conditions. Neither one is directly monitored by the OBDII system which means no SES light and no DTC's will be set. It also means that the OBDII system will not help you with diagnostics other than the fact that the problem is not anything that the OBDII system DOES monitor. Other than chasing a ghost, you can wait until it acts up, then figure out if it's a lack of fuel or spark.

Well, I'm driving back south early in the new year, so I'll likely get to see the problem with the gauge on. Too bad I'll have the wife and kid (and probably mother) in the car at the time...

Here's another possible clue: While driving this evening the fuel pressure test gauge needle was bouncing around in the 52-56 range. Earlier in the day it was solid. Any hints there?

Thanks.

There are too many variables when the engine is running to know what fuel pressure should be. Elevation above sea level, engine load, engine RPM, percent of throttle opening, engine vacuum, engine condition, coolant temperature, etc etc etc and the list goes on... all have an effect on engine demand and fuel pressure. That's why GM doesn't publish any specification for fuel pressure while the engine is running.

No, I mean bouncing in a fluttering way; the needle never stopping in one place but just fluttering in the operating range.

It's normal for the fuel pressure to fluctuate while driving. The ECM adjusts the injector pulse width several times per second depending on engine demand. If it drops below approximately 50psi, that might indicate a problem with the fuel pumps ability to supply an adequate amount of fuel to the injectors. In which case the pump may be weak, the strainer restricted, a fuel pressure line restricted, the fuel filter may be restricted, or there might be insufficient electrical current at the fuel pump.

Bing, bang, boom... busted?

This morning, in the freezing cold, I went out to check it again. With the key in the on position the pressure pops to 62psi for an instant, then settles on... 56. And at 56 it sits.

It started fine, but after a start and stop it still settles at 56.

Now, my Haynes manual insists that at "Approximately 55 to 61 psi" it is in spec, despite old_master's factory manual calling for 60-66 (for CSEFI, right?).

So, do I really need to spend the $250 and two hours in my freezing cold garage to fix this? Obviously I'm desperate to find some other reason for the stalling...

Settling at 56psi is not a problem, provided it doesn't drop below that. I can guarantee you that if fuel pressure primes at 55psi, or less, the engine will not start. Haynes and Chilton have been known to publish incorrect information, this is a perfect example of that. According to GM, the company that engineered and designed the system, the 4.3L CSFI and CMFI engines must have a MINIMUM of 60psi to run properly, anything less WILL cause driveability issues, guaranteed.

Well, I've just finished 500 miles and 7 hours (with just one stop for fuel) and it didn't stall, so a bad fuel pump seems less likely now. What a bitch.

Glad you made the trip OK.

Thanks, but that puts me all the way back to square 1 on diagnosing this problem. And after I spent $50 on a fuel pressure gauge.

I guess I should leave it hooked up... good karma...

Thanks, but that puts me all the way back to square 1 on diagnosing this problem. And after I spent $50 on a fuel pressure gauge.

I guess I should leave it hooked up... good karma...


PM me with your email address, I have some information that might help you.