ecm commanding no advace?


flexsource
12-12-2011, 12:22 PM
2000 jimmy. 4.3. Static set to 0. Why would scanner show "no data" and 0 degrees of advance when key turned on ? Same while cranked. No connectors unplugged.Any help appreciated.
Thanks

maxwedge
12-12-2011, 12:26 PM
Hmm, maybe the base programmed timing is 0, what do you have running?

flexsource
12-12-2011, 02:15 PM
Bone stock gmc 4.3 jimmy. Cavalier on driveway next to it shows advance immediately with key on and no crank.
However the tahoe right by them showd same no data and 0 advance with key on. After start, tahoe shows advance.
Chasing the ever popular 4.3 random hard/no start, missing intermitently,wont start at all in cold weather blah blah blah. Strong spark. All new stuff. 61 psi fuel press. No bleed down. Thought i might have pinned something down on the advance issue but tahoe seems to prove gm random application differences are still alive and well. Raw gas down the intake - no go. Compression fine. Raw gas under jimmy and a lit match would at least warm it up a little.... Intake gaskets lower and upper replaced after standard water leaks confirmed. Torque retested. Water in gas? I dont even want to think about it at this time of year. All other sensors indicate in bounds. Known good egr swapped in. No start. Just buck and fart a little. All vac sources plugged/tested okay. Im convinced its going to be something stupid simple now.....

maxwedge
12-12-2011, 08:03 PM
If you have good spark it should " pop" with some starting fluid. It s possible the dist is out of synch when the manifold was done or the dist. gear is stripped.

flexsource
12-13-2011, 10:52 AM
Thanks for replies maxwedge. Possible - yes. Its been driven quite a few times though since the gasket work so maybe stripped. I know it will start if it is warm outside. Also I can get it to start if I hold my hand over the entire throttle body opening but it wont stay running unless i hold it there (OUTSMARTING THE IAC) and nurse it into running until it warms up. HOT it will restart fine. Cooled off a little, then it will grudingly restart. If its cold - its a no start

IAC is responsive. COOLANT TEMP and IAT are AOKAY (new)

I believe our gasket repair was flawless. Don't expect a vac leak there but acts like a cold vac leak or spark timing way off.

maxwedge
12-13-2011, 07:53 PM
I would get a scanner on it and look at the intake air temp sensor and coolant temp sensor inputs, also you neeed about 65 psi for reliable cold starts. If the gear was damaged, temp would have no effect.

flexsource
12-14-2011, 09:00 AM
Thanks again. Scanner is on it. IAT and Coolant temps well within expected ranges. 61-62 PSI fuel. I'm going to do a RE_START of all the checks again to see if I missed something. Distributor will be pulled to check gear. I'll report what I find but I have to do it hit and miss. Pesky work keeps getting in the way...

flexsource
12-17-2011, 05:33 PM
Typical. 55 degrees out today. Went out and cranked on it about 4 seconds and it stumbled to a start and run. Starts every time now. Just to comfirm - 3 O2 sensors on this 2000 Jimmy 4.3 - correct?

And any clues as to typical O2 volt readings? The bank 1 and bank 2 sensors go back and forth like I kind of expect but the bank 1 sensor 3 ( POST CAT I ASSUME) climbs to .9 and persistently sits there.

This thing definately has a temperature related problem. And it shows up as an intermittent miss at really random intervals when its warm too.

maxwedge
12-18-2011, 09:49 AM
Once warmed up post cat should be pretty steady at 400-600MV, that just tests cat efficiency.

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