95 Yukon Back fireing again.

[youngjs1974]

Checked pressure and it was at 8psi. So sent it to repair shop to have a pump put in it. Hope it fixes it.

 

[youngjs1974]

Shop called today and it is not fuel issue. Think it is a spark issue.

 

[SunlitComet]

what kind of spark issue?

 

[99Vortec]

Interesting, the Injector unit checked out?

I was searching through some older posts, Sunlit. And found where you mentioned that when you got your SUV, the injector unit was dumping too much fuel in and causing a backfire into the intake system.

The Lean code just doesn't figure in though. Unless the fuel injection system is going haywire in response to temperature?

 

[SunlitComet]

That needs some further clarity. Two cylinders were getting washed down with fuel and some of the others were clogged. IIRC #5 and 7 were rich and reading my spark plugs and a balance test showed 3 other were leaning. At least one of them known at the time has cracks near the valve seats. I would look up old data records from the vehicle but I deleted some early ones by accident I think. I don't see them on any of my computers yet but am always sifting thru the 10's of thousands of files I have on different devices. An good test of the injectors is to bench test them with the proper equipment. you would think that if the valving was working correctly that the manifold would be sealed off from the chambers when sparked unless the spark timing is randomly jumping the cap and sparking a cylinder while its intake is open. The story continues. lets see what young's shop finds.

---------- Post added at 12:37 AM ---------- Previous post was at 12:35 AM ----------

oh and remember he has two injectors that feed eight cylinders and I have eight. kind of a slight difference no?

 

[youngjs1974]

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.

 

[SunlitComet]

wish you were near me I want to diagnose it in person. It should be easy to spot when in person.

 

[99Vortec]

That needs some further clarity. Two cylinders were getting washed down with fuel and some of the others were clogged. IIRC #5 and 7 were rich and reading my spark plugs and a balance test showed 3 other were leaning. At least one of them known at the time has cracks near the valve seats. I would look up old data records from the vehicle but I deleted some early ones by accident I think. I don't see them on any of my computers yet but am always sifting thru the 10's of thousands of files I have on different devices. An good test of the injectors is to bench test them with the proper equipment. you would think that if the valving was working correctly that the manifold would be sealed off from the chambers when sparked unless the spark timing is randomly jumping the cap and sparking a cylinder while its intake is open. The story continues. lets see what young's shop finds.

---------- Post added at 12:37 AM ---------- Previous post was at 12:35 AM ----------

oh and remember he has two injectors that feed eight cylinders and I have eight. kind of a slight difference no?

Yes indeed.

So at this point it has to be a timing issue?

I once had a problem on my 3.8l 231 V6 powered Caballero. It had a pretty massive acceleration problem. The plugs, wires, cap, rotor, etc. all checked out. And the fuel system checked out.

It ended up being a severely worn distributor. (Just plain shot.) It wasn't backfiring though.

Last time I had a backfire through the intake system was on a '68 4 speed Camaro. That also turned out to be distributor related.

(Scary one too as the carb briefly caught fire.)

It's the cold variable that is confusing. Something/some metal piece is contracting and yielding excessive clearance?

 

[SunlitComet]

If you want make sure it is really cold outside and take you dizzy cap and record or video or something the rotational play of the rotor. But unless there is absolutely no other thing found or you see a real problem in the dizzy I would not pull it to check it unless the engine mechanical is the only thing left. While the gear teeth can become worn it is very rare that these things skip teeth or jump timing gears. Higher probability that something electronic is wrong tho you would have a better chance at even hearing piston slapping in the cold. Other then someones oil pump having issues at start up in really cold weather or outright major bearing fail that is the most I have seen or heard this engines go thru. When they do fail mechanically there is more then a few clues at the same time. Electronically and mechanically.

 

[youngjs1974]

I have been driving it around for a couple of days now. No more back fire, Stumbles a little bit here and there. Not sure why it needed some much timing but it seems to have solved some of the problems for now. Thanks for all yalls help and advice.