Hey Guys.. I've been fighting this issue for a while now..

What would make my truck intermittently forget where the timing is? I just had to replace the computer for a Trans fault (0758) that fixed that problem but an old one has come back to haunt me. The truck sometimes wont start. Cranks fast, strong spark, plenty of fuel, battery ok. It seems like the timing is way off.. coughs back up through the intake. I’ve looked at almost everything I can think of.. No amount of cranking will make it start. All I need to do to get it to start is to walk away. Come back tomorrow… turn the key and it starts right up and runs like a clock.. if it starts in the morning it will usually run fine all day.. then come back the next day and it’s a crap shoot.. same symptoms. A day later it will start fine… Needless to say I’m about to torch the f-in thing.. Temp, humidity, battery charge.. don’t seem to matter.. some days it starts and some days I’m walking… Going through wires and connections, grounds… now…

Does anyone have any suggestions? I’m running out of places to look… Wife wants me to get rid of it..

97 Tahoe… 79k, 2Dr, 4wd..

Thanks for anyone’s input…
Dave

The first thing to check on a Vortec engine exhibiting those symptoms is the distributor gear. When it goes bad, it does what your truck is doing. See this thread for a discussion on the fix.

Speeder, I thought about that.. but when it starts it runs perfect.. I 'll take a closer look...

Check the fuel pressure. Fuel will only burn f in vapor form... Liquid fuel WILL NOT BURN.

Hey, new computer. Do those trucks come with Passlock or Passlock 2? If so, next time it acts up try turning the key to on without starting, then leave it on for at least 10 minutes. After 10 minutes, turn the key off, then within 20 seconds try starting. If it starts right up, then you may not have any further problems. That stupid Passlock system causes all sorts of weird problems that happen one day then disappear like it was never there and make you want to pull your hair out.

Another problem with the Vortecs is the positive battery cable. If you haven't cut the red connector off and replaced the lead washer with a brass one, try that. The lead washer will crush and distort, then you can't get the cable quite tight enough. Replace the washer, don't just discard, because without the washer the bolt is long enough to crack the battery on the inside.

I've had both of these problems with various vehicles. Two times I replaced fuel pumps without needing to.

Thanks again Speeder.. I have tried the "10 minute re-learn" 3x last time it didnt start. I replaced the battery connector a while ago.. I was looking at changing the ICM but it started right up this morning.. It's harder to fix when its not broke ! After that I'll look at the Crank or Cam position sensors..

Prices seem a little high... Rock auto has a few options.. Delphi, 2 - standard, and OEM brand..

Stay tuned I'll post my results..

Good point with the passlock but I dont think that came till 98. Passlock will disable the injectors tho so youd still have puel pressure and spark

OK the ICM did not fix the problem...

On the + side Rock auto is pretty good... I ordered the ICM on Monday around 3 in the afternoon.. It was at my house when I got home on Tuesday.. less the 24hrs.. amazing..

Next --- Crank Pos Sensor.. ???

Of you got spark its not going to be a crank sensor or anything ignition related. You said it has lots of fuel are you checking it with a gauge? these trucks NEED at least 58 psi to run give em 55 and they wont, while 55 looks like alot of fuel when pushing the shrader valve it isnt enough

Thanks I'll be sure to check the fuel pressure..

The one symptom it has is it coughs up through the intake and pop’s out the exhaust. Thus the reason I’m thinking about the timing… And all I have to do is walk away and come back a day (or 2) later and just touch the key and it fires right up and settles into a smooth idle.. Its killing me..

Maybe the pressure is just under what's needed at 11v when starting but is enough at 14v when running....

ok.. Fuel pressure up around 60... But I did find a burnt pin on a connector just below the Dist.. Not sure what it is.. 3 pin connector, attached to a sensor that has an elbow and goes down into to block right next to the dist shaft.. can anyone help me identify it?

Davevv wrote:

ok.. Fuel pressure up around 60... But I did find a burnt pin on a connector just below the Dist.. Not sure what it is.. 3 pin connector, attached to a sensor that has an elbow and goes down into to block right next to the dist shaft.. can anyone help me identify it?

Seems like it was an oil pressure sender on the rear of the L31 in that area

Its the fuel pump oil pressure switch.. and although burnt it still must be working... My dealer installed alarm/remote starter fried... thats what took out my ECM, looks like I still have an electrical issue somewhere.. Mother F-er...

Going to check more connectors...

Thanks Stroker...

Cam Position sensor next?? Connector looks ok... After this I give up...

I have some time to work on the truck today... and... it starts right up !

But at least I was able to take it to NJMV inspection and it passed !.. Its a good thing they didnt shut it off !

It started on Saturday... but not on Sunday.. I replaced the Cam POS sensor.. still wont start..

I have to figure out what to check next...

Stay tuned...

Davevv wrote:

Its the fuel pump oil pressure switch.. and although burnt it still must be working... My dealer installed alarm/remote starter fried... thats what took out my ECM, looks like I still have an electrical issue somewhere.. Mother F-er...

Going to check more connectors...

Have you removed the fried alarm? Installing an alarm usually requires that certain wires be cut to splice the alarm system into the wire. Since the alarm is fried, I would remove it completely, ensuring that all wires it is spliced into are respliced correctly, then see where you are. Since it's hosed, and one of the functions of the alarm is to prevent the vehicle from being started, this may be the source of the problem.