95 Yukon Back fireing again.

[retorq]

Got it back from shop yesterday. 5 days and they have no idea what is wrong with it either. Advanced the timing today 12 deg. It is not back firing. Will give it a couple of days and updated.

That's your problem right there.

 

[youngjs1974]

I advanced the timing 12 deg above 0. And 0 is were it is supposed to be at. Also that is not including the advance the computer does after plugging the ICM back in. Still running not back firing. Stumbles at idle every now and then.I think maybe I need to back the timming down a little.

 

[retorq]

I advanced the timing 12 deg above 0. And 0 is were it is supposed to be at. Also that is not including the advance the computer does after plugging the ICM back in. Still running not back firing. Stumbles at idle every now and then.I think maybe I need to back the timming down a little.

I'll post this since Sunlit failed to copy/paste it into any of his incorrect responses:

First, stumbling and intake backfires are two totally different things, you do not troubleshoot them the same. If after all this your intake backfiring has not returned but you still have a stumble troubleshoot that.

Backfiring thru the intake/carb/throttle body is a timing issue. It's not the fuel pressure as was suggested (although if someone tested yours properly and you have 8 PSI you have a fuel pressure issue somewhere). It's not an O2 sensor as was said. It's not a coolant temp sensor as was said. It's not low compression as was said. It's timing. The ONLY way to pop or backfire thru the intake is there is a spark event happening when that cylinders intake valve is open. It's been that way since the beginning of the internal combustion engine. That's all these TBI and Vortec engines are, internal combustion engines, they were nuts and bolts in the 1800s, they still use nuts and bolts and the same 4 principals, SUCK-SQUEEZE-BANG-BLOW! That leaves us with either a physical timing issue (ie. the gears and chain/belt behind the timing cover aren't installed correctly (please someone chime in and tell us all how a timing chain can jump a tooth I need a good laugh)), your distributor timing is off (ie. "I advanced the timing 12 degrees" (also someone tell me how a distributor only goes in two ways, the right way and 180 degrees off I still need a laugh)), you have a plug wire crossed or they are arcing thru each other firing the wrong cylinder (I'm sure someone here will have their cousin's baby daddy's brother having this EXACT issue). That last one while possible, is the least likely as spark flows like water and air, the path of least resistance. How likely is it that a given plug and wire have so much resistance that the spark jumps to the one adjacent one because it is the path of least resistance?? More then likely all the plugs and wires are junk.

Backfiring or popping thru the exhaust isn't as hard, there are a few ways to accomplish that including but not limited too a timing issue, raw fuel being dumped into the exhaust, spark plug wiring, etc.

If I were you I would reset the timing. 100% verify each and every wire is running to the correct cylinder, verify the #1 cylinder is at TDC per the mark on the balancer and verify by checking for end of the compression stroke. Make sure you use the correct size wiring separators, mark the number 1 tower from the cap on the base of the distributor and set the distributor back in and make 100% sure the rotor tip is lined up dead on with your mark. Then you can disconnect that timing wire and reset it to 0 with your light. If you need help with that let me know, I have an awesome write up on another forum with pictures and everything.

 

[ezdaar]

chain can jump teeth all are broken off half way. yess its possible.

did I win the prize?

 

[Tylerz281500]

are you unplugging the esc wire when your doing timng?. no way in hell you should be at 12 degrees

and check all our grounds both, engine, frame, computer etc.

 

[youngjs1974]

Ok i will check it out this weekend and let you know.

 

[99Vortec]

So why is the problem manifesting primarily below 30°F?

 

[rockmax77]

!pJ