Backfiring up front
 

When I give a little more than normal gas or at WOT it kinda starts to give up, and then backfire up front. I am pretty sure that I have an exhaust leak. I was checking the manifold last night and I could wiggle it a little as well as missing the fwd most bolt. And I have a feeling that the gasket is definitely bad. So is that a good starting point, or should I check sensors or somewhere else. Work has picked up and it is dark by 5 PM now, so thats why I am trying to take shortcuts on the trouble shooting. Thanks.

It's a 4.0 auto.

OK ya I'd start with the manifold gasket. But I'd also check you plug wires make sure all plugs are firing all the time.. Those would be your best places to start..

do you get any codes? maybe get a code reader and see if you can narrow it down that way. i know my XJ has the cylinder 3 misfire problem sometimes, as do most other 00 and 01's.

not in an 87, no.

What is a easy way to check the plugs. I was messing with the vac lines and noticed with the MAP line disconnected the idle went down to normal ranges. And I am also having a whole lot more stumbling right now. I am also leaning heavily to putting the old airbox back in. Would a bad IAT cause this as well. It was oil soaked and I cleaned it and put it back in.

A little update. I snagged some injectors from a 4.0 explorer today(red top). And after installing them i can accelerate without any backfire. But it does backfire if I really give it gas, but I can accelerate in any normal driving conditions and I got it up to 60 no problem. I am still going to do the gasket but I think I will wait now till I get a new exhaust manifold.

whats your timing set at?

Sounds like you found the problem

Probably where the factory locked it in at. Timing is most often controlled by the computer. Even in 87.

I would lean more to the manifold gasket. When air is allowed into the leading end of the exhaust system, backfiring can occur.

Might I suggest getting the manifold changed while you have it off, as they are prone to cracking. Often, welding up the crack is only a stop-gap as they almost always re-crack. Trust me, this is something you do not want to do more than ONCE. eBay is the best place to find them. The seller I bought my TWO from usually has them for $89.95 Buy It Now. That price includes shipping. They come with both the gasket for the head and the pipe.
Why TWO?? I have a '91 Laredo and a '94 Sport.

Here's a link to his eBay store (Manifold catagory)
http://stores.ebay.com/DoctorAutoPar...QQftidZ2QQtZkm

Just scroll down past the Mazdas

dam, even free shipping:head:

Like I said, I have installed 2 of these...never want to do that again.
Not a real pain...just takes time.

Even better if you are doing a "full-system"

Helpful note: When installing a manifold w/o a new system behind it...
Hang manifold loosely by the front and rear studs, do not tighten.
Makes easier to line-up the system and get the flare connection bolts started.
Once started...go to town.

2nd Helpful Note: Start nuts and washers that will be "under" intake by a few threads. These bolt the intake and exhaust to head together (Washer crosses bosses in both manifolds) When you are THERE, you will see what I mean. Then carefully slip the intake down with it tilted slightly to drivers side. There are two locator pins that stick out from head that the intake needs to sit on/over. Once the intake is nestled behind the mounting washers...tilt to passenger's side until intake sets over locators. Install rest of hardware and torque everything down.

This was my plan, just waiting to get the money for it all at once. I want to get the exhaust manifold as well. I just had to try the injectors to see if I had a fuel problem as well. The injectors I pulled off were 2 different types, so it looks like the DAPO just pieced it together.

Dontcha just love DAPOs???

Well I was still having the problems as well as stalling after driving for awhile. So I pulled out the fuel pump and the hose on the from the pump to the line was barely hanging on. And it was pretty deteriorated, so after switching that and a new strainer it started within 2 seconds. And the pressure was so high the regulator started leaking. I guess I crushed some of the o rings when I did the injectors but there never was enough pressure to leak. So the backfire is gone i think it was pulling air into the fuel rail with weak pressure and causing the problem. I hope this helps anybody else.

Always good to revive an old thread with the solution to the problem.

Bet your Xj feels and drives like a whole different Jeep now, right.