Stumble & Bogging down while accelerating...I can't figure it out!

Hi guys!

OK, i'm starting to get extremely frustrated with my XJ

I've been trying for about a month now to track down this problem I am having. It is proving to be a hard one to track down. This is an 89 XJ w/ Renix 4.0l non-HO engine and AW4. Initially I thought it was my tranny slipping when the problem first surfaced at highway speeds in 4th (OD) gear. While accelerating slightly I would get a sudden lurch or jolt in the driveline. This was intermittent, but was definately happening when I was on the accelerator and never while coasting. Lately the problem has gotten a little worse, and on top of this jolting in 4th gear, I am also having problems going up steep hills and accelerating on level ground. The problem is not happening under normal city driving conditions, but when I need to get on the gas heavily (all the way to and INCLUDING WOT) I am getting an intermittent stumble and bogging down. While trying to accelerate heavily, the engine seems to waver back and forth between full power and very little power.

So here is what i've done up until this point.

- spent countless hours searching this forum for the magical solution!
- replaced TPS (adjusted it properly to 83%)
- replaced O2
- checked the CTS and MAT with voltemeter
- checked the CPS (reading ~265 ohms)
- checked all over for a vacuum leak
- cleaned the contacts for the balast resistor
- hit the cat to see if it's making noise (which is isn't)

I think that this problem is timing related. There is an intermittent pinging happening when i'm accelerating heavily. If the engine is suffering from pre-ignition, does this rule out a back fuel pump and a clogged up cat? I have a hard time believing that it is fuel related simply because under low-normal acceleration there is a lot of power and torque. I can also not understand how the XJ starts up and runs smooth (idle between 500-900rpm with maybe a 50rpm lope here and there, which I would say is normal for a 17yr old Jeep). It does not show any signs of this issue if you rev is while in neutral either.

Any help or ideas at all would be definately appreciated! Sorry about the long post!

I have a new CPS that I will be putting in this weekend, but I was always under the assumption that this sensor either works or doesn't...so i'm assuming that it won't fix the problem. I really thought the TPS and O2 sensor would fix it...now I don't know!

Koenig

1989 Jeep Cherokee Laredo
~140,000km 4.0L AW4 NP231

Just an FYI. I had the very similar sypmtoms and checked all of the above.

After all the trouble shooting and new parts, I finally rechecked my injector wires and "click", one of them was not quite all the way engaged. They all looked and felt fine. But one was just backed off enough to cause intermittent fuel loss in the 5th cylinder. I had installed new Ford injectors about 3 weeks before my problem started.

I pulled them all, cleaned the plugs, added a little dialectric grease and made SURE they were all the way on and the little clips were securely fastened.

Might be worth checking again if you haven't already.

Have you checked or changed the fuel filter?

The jolt you feel my be the torque converter clutch engaging. If you are coasting in 4th, stepping on the brake releases the tcc, and when you step on the gas, it engages. If you are heavy on the gas, the rpm's will rise then drop with the jolt as the tcc engages.

Well I found it!!

The #2 spark plug was fouled up really bad...and replacing it has cured all of the symptoms...so far

Here are a couple pics...






Of course, now I will have to be concerned with what is wrong with the #2 cylinder! Looks like oil is seeping in there...

Thanks for suggestions. This is one of those rare cases when throwing a cap/rotor/wires/plugs at a problem actually fixes it!