syphram

I have a 97 Bravada that is shutting down when driving, when it idles or when it is put into gear. Sometime it shuts down and kicks back on when driving. On occasion it will take a handfull of seconds to turn over. I notice the problem most often when the car sits for a bit and then is turned on. I did a tune-up and put gasoline additive in and it did not affect the problem. the check engine light is not on and teh computer does not reveal any codes. Does anyone have any clue what this could be. Cramshaft sensor, ground wire, demons?

Thanks

MT-2500

Welcome on your first post on AF.
Did you check fuel filter?
Does it quit and stay quit for a while?
One of the first things to check would be fuel pressure.
And if it stays quit for a while check for lose of spark or fuel or injector pulse.
Hook a fuel pressure gauge up and tape it to windshield or outside mirror and drive and watch fuel pressure when it acts up.

Here is the fuel pressure guide lines.
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

syphram

MT - Thanks for the post.

I replaced the fuel filter last week and the fuel pressure seems to be ok (I will post the readings when I re-do them). The car only completely shuts down on occassion and when it does it starts right back up and if the car cranks without turning over, i can re-turn the key and it will start with no problem. Sometimes the car will kick on and off while driving and i can continue down the road as if nothing happened. Sometimes i can not tell if the car mechanically kicked off or whether my dash lights turned on and off and the doors locked and unlocked for no reason, because it happens so quick. I am starting to think it might be an ignition wiring harness, since these cars are known to have wiring problems. Does this change your diagnosis? Thanks MT and everyone else who may respond.

MT-2500

If the door locks are kicking on and off you need to run a voltage check on ign switch and power feeds and grounds.
I would hook up a volt meter to ign and PCM feed out of ign switch and drive it until it acts up and watch the volt meter.
And wiggle that switch and see if power comes and goes.
97 WAS A BAD YEAR FOR IGN SWITCHES.
Run a search on here on ign switches.

__________________
Remember proper testing gives us the answer to many problems.
MT

syphram

The problem ended up being either a crankshaft sensor or an ignition coil.