No Idle and Back firingProblems Solved !

[RCielec]

Ahoy !

Reference my posts in Fuel System "Diagnosing Stepper Motor" and, in The Engine "Advice on Tightenting Manifold Gaskets"

Yes, the backfire/no low idle problem seems to be solved.  The cause was leaking manifold gaskets. The manifold gaskets leaked because the intake and exhaust manifold gaskets loosened, most to merely finger tight and the others just about. On some bolts, I was able to spin the thrust washer by hand. I have no idea how the manifold bolts became loose. Who wudda thunk? Is loosening manifold bolts a common problem on the 4.2L?
Replaced the gaskets this afternoon and Voila !, the engine holds low idle and there is no backfiring. So, the car is now back on the road and returned to service as the daily driver.
Thanks for all the advice and suggestions.

Richard Cielec
Chicago, Illinois; U.S.A.

[Whuntmore]

Great to hear you got it fixed!

[85AmCfreak]

The bolts tend to loosen due to the different metals expanding and contracting (the intake is aluminum the exhaust is cast iron) Also vibration could be a culprit. It is a common problem. I just tend to check the bolts periodically.

[Smitch]

I just tend to check the bolts periodically.

I do too, although there's one I have real trouble getting at. It's a bottom one between the carb and the firewall. Anyone else have this problem and how do you solve it?

[Jurjen]

Yes, they get loose.
Retighten them after a 1000mls and check them yearly, same for the (aluminum) valve cover.

[RCielec]

I just followed the advice given by other Eaglers: a universal, a shallow socket, fiddling to get right length of extension, enhanced vocabulary and plenty of patience.
Good luck, and may the Eagle be with you. Hahahaha.

Richard Cielec
Chicago, Illinois; U.S.A.

I just tend to check the bolts periodically.

I do too, although there's one I have real trouble getting at. It's a bottom one between the carb and the firewall. Anyone else have this problem and how do you solve it?

[85AmCfreak]

LOL yup thats a hard one to get ya gotta fight the wiring harness the brake booster and all the other crap in the way  cutting up my forearm and hand is always fun

[AMCKen]

Pull the engine and it is much easier. 

[n9xvt]

so i think mine need checked,, is there a torq spec? and or a sequence to these?

[BenM]

18-28 ft-lbs and alternate from the inside out. Beware shifting in the intake gasket.

The factory didn't use an exhaust gasket and often omitted the bottom rear stud.

Don't ape the bolts, you don't want to crack the aluminum intake. If it doesn't seal you need a gasket.

[AMCKen]

The factory didn't use an exhaust gasket and often omitted the bottom rear stud.

More likely the bottom rear stud has already fallen out. It seem to be one of the most loosening prone. (?)

[BenM]

The factory didn't use an exhaust gasket and often omitted the bottom rear stud.

More likely the bottom rear stud has already fallen out. It seem to be one of the most loosening prone. (?)

I've never seen one on the engines I've worked on, at least those I'm sure were original. Even when all the other bolts were tight. I recall some discussion somewhere about it where many others had the same story; I'd have to search here and a few other places to find it.

Not to say that some falling out didn't contribute to the observation, I'd bet they did. It just seemed to be more then just coincidence and loose studs.

[85AmCfreak]

Good job resurrecting a dead thread LoL we need to do this more often