Puzzling engine symptoms on '91 4.0 manual YJ

[baldjohnny]

YJ starts up and idles fine, at least to my "untrained" ears. It's had the "tap" sound that I have heard others describe, that mostly goes away as it warms up. What it's doing now:

1. 1st gear acceleration- great.
2. 2nd gear acceleration- good, but I can feel the beginnings of a miss. Around 2000-2200 starts the miss.
3. 3rd gear & 4th gear- Seems to be a miss that is more exaggerated now, but I can "minimize" the miss by keeping on the gas.

It threw some codes I caught by reading the check engine light: 1-2, 3-3, and 5-5. I checked the fault codes and the 1st one makes sense (disconected the negative battery cable), but the other two... don't have A/C for # 2 and the PCM reference is puzzling on # 3.

Worse case scenario I'll run it down to the dealer and have them hook it up, but it baffles me why it will accelerate just fine in first and most of 2nd, then shudder in 3rd and 4th. I put in the clutch, it goes away as I am rolling down the road. Replaced coil, cap and rotor, wires are fairly new.

Does this ring a bell with anyone? Like I said, it may be dealer-bound because I'm getting tired of playing with it and really don't want to take what may be a minor problem and turn it into a costly "what the hell have I done now" problem, but I sure like the idea of trying to figure it out myself first! And hell, if I can't ask you all, who can I ask?

Thanks for any suggestions.

John

 

[AlwayswrenchN]

Possible vacuum leak, as your excelerating through 1-2 you are in a low vacuum state. Then as you get up around cruise your engine starts to build vacuum. By staying on the gas you are maintaining a low vacuum state thus minimizing the miss. So I would look for a vacuum leak, specifically around the distributor and intake manifold.

Other areas of possible problems are plug wires even thou they are new they can bleed voltage. Easy way to find those issues is to go outside at night and look under the hood while its running. If you see a light show then you'll know you have problems. Try and make sure the wires don't touch each other.

Hope you find your problem. Good luck

 

[SteelHeadz]

Also check your ECU/PCM connectors for corrosion or poor connections. The sensors associated with the ECU/PCM reference also would effect the performance of the engine, both at idle and at WOT(wide open throttle).

 

[carnuck]

CPS or possibly the speed sensor. '91 YJ is a single year with pass through cable and VSS combined. I'd also try the fuel filter.

 

[baldjohnny]

Update- appreciate the replies, it's very comfortable being able to ask a question and have people that have gone through similar experiences answer!

Took it to the dealer... yeah I know, succumbed to the "damn the costs, fix it" theory! After some research they said it was the double cardigan joint with issues, and were very fair in the cost for the time they spent checking other things out (clean bill of health). I don't like taking things to dealer's generally because they can be more expensive than independents, but I'll give credit where credit is due. Thank you Petersen Stampede in Nampa; you were fair, I left there feeling it was worth it and that's all I can ask.

I pulled it off and sent it back to Tom Woods after talking with Troy; they made it for me several years ago along with selling me a SYE kit, they'll repair/ rebalance it for me and have it back next week. He did point out that it is a good idea to watch as you're greasing the u-joints as sometimes a cap might not be taking grease when the other three are. Makes sense to me and will be part of my routine from now on. Learned another thing, I'm a sponge...

Just a little bummed I missed the diagnosis since I did put hands on it, but since my errors were pointed out I have since traced a squeak back to a rear U-joint on my Dodge Ram! It's fun to work on things that they haven't engineered out of a DIY'ers hands, so I take missing the joint problem on the Jeep as a learning experience.

So anyway, wanted to give you feedback. Thanks again!