My GMC Savanah van's 5.7 L engine stalls with no warning when operating. Techs can't find problem. Help ?

Question

The problem does not happen every time I drive the van, never know when it will act up. If I let it sit for awhile, it starts up again.
This has happened at the service center but they are still unable to find anything with diagnostics.

Answer 1

Sounds like the "techs" aren't trying very hard, or else they're clueless. An intermittent problem like yours is admittedly much harder than usual to solve, but still needs to be approached in a logical step by step manner. If all they're doing is looking for codes, then I sure hope you didn't give them any money. If you see anyone at that place with a MODIS or Vantage Pro, go and talk to them right away. Just using the Tech II isn't gonna get it done. Use the low amp probe on the fuel pump relay, that's AMP not volts, display that trace (channel 1) with the fuel pressure (channel 2) and go for a test drive. Look for jagged commutator spikes consistent with pressure fluctuations. This will give you an idea of pump condition, and on the off chance the failure occurs on the test drive, the evidence will be right in front of you. Also, note that the check engine light (MIL) doesn't come on. Use channel 3 with the KV probe and graph the coil output. It could take some time, but waiting for the computer to figure it out instead of using any intelligence or training is just a crime. I never understand how these clowns call themselves "technicians" yet consistently fail to check the basics. Oh, and the quick and dirty way to monitor fuel press is just hook it to the rail, run the hose out of the hood, and zip tie the gauge to the wiper. Not pretty, but will show if you do have a major fuel issue. As for the ignition, use a see-thru tester that lights up. Can get them for 5 bucks, stick 2 of them on adjacent cylinders, then if the engine quits, have someone crank it while you look for the lights. Easy. Lemme know what happens.

Answer 2

Wow this could be a tough one to diag out, but i will give you some good general idea's where to start at. Most of the time if this is stalling out, does it do it after it has ran for awhile or just anytime. it it is doing it after it has ran for awhile i would suspect something in the ignitions system getting warm, fuel pump getting warm or the ecm internals over heating. if it is something that happens just any ole time i would look for grounds that are loose or wire connections that are not fully connected. a few other things i would also look for since this is a van would be adequate air flow to the engine bay during operation. If it is not getting enough air flow into the engine bay to help the cooling process of all the neat little parts that are assemble on the engine and firewalls, it could cause a problem with overheating of these parts, which in turn could cause stalling, rough run conditions and so forth. Other possibilities could be relays that become overheated. like the fuel pump relay.... hope this helps you out just a little and good luck.

Answer 3

One of the sensors have intermittent failure. Most likely - EGR (Exhaust Gas Recirculation) valve.