For the life of me I can't figure this out. I can't go any further with this project until I fix this rough idle. If it's going to require something major I may just sell the heep as it sits. I'm frustrated beyond belief. Been two years going with problems at every turn.

The jeep has a slight miss. Sounds good, but, has a rough idle or slight miss that you can feel shake the jeep. Not exactly a steady shake. Flooring it from a dead stop is weak. Now, this has 31s, but, still feels like it's lacking power in 2wd.

See below for what I've tried:

Spark
-New Bosch plugs (year ago but less than 3 miles since then)
-New plug wires 3 times.
-Changed out caps 3-4 times. All working units.
-Verified spark. Blue/white. Ignition coil can jump about 3/4".
-Reset timing twice this week
-unplug spark plugs one at a time and all worsen idle

Fuel
-32 psi at idle. 39 when vacuum line removed.
-Holds pressure well now.
-Put in a new to me fuel pump today. Changed dirty clogged strainer. Pressure now bounces between 30-32 psi. Steady when vacuum line removed. Will likely put old pump back in.
- removed connector from all fuel injectors and all worsen idle
- changed FPR with a few others. No change.
- new Bosch fuel filter
- pulled fuel rail with injectors. Sat on towel and primed ignition. No leaks.

Misc
- checked TPS. 0.7 volts at idle and 3.6 volts at WOT. Put a different one in for good measure...no change.
- disconnect O2 sensor and it idles worse after a 10 seconds or so
- checked map sensor vacuum line. Good.
- new temp sensor in head and thermostat housing
- bent a pushrod the other day (ticking). Cleaned and checked all pushrods. Replaced bent rods. All is well and no ticking.

I don't think it's spark, timing, or fuel. But, I'm looking for guidance and I'll test anything. Really don't want to throw parts at it until it's fixed. My pockets aren't that deep.

I'll update the info here as I think of things I've done. I'm sure missed a good bit.

 

time to take it into a shop that has a proper scanner to diagnose this, they may need to put a lab scope on it.

 

Can you do that with an OBD1? It's rolling, but, not really driveable at the moment. I could tow it I guess.

 

Do you have a Catalytic converter? Could be clogged.

Mine is a 95 and it is OBD1, you probably can get some info from from your 94.

 

Yes. It had a cat. Cat seems okay when I bang on it (not shredded). Feels like plenty of air leaving the exhaust.

 

I'm thinking next step is to re-do the compression test I did a year ago. This time with the motor being at operating temp. After that I can do a homemade leak down if the local parts store doesn't have a leakdown gauge.

Hopefully this will allow me to confirm or rule out bottom end issues. Outside of changing to champion plugs and replacing the 02, I'm stumped.

 

Okay, so, I did a vacuum test and came up with this. Still haven't done a compression test. Thoughts?

At idle

While playing with throttle

Also I noticed this. I've been having hard starting lately when it's sat for a while. Thought fuel pump might fix but no dice. The past few I've had a high idle as well. See example. Doesn't happen every time. Yet

 

I'm not sure it matters, but, here is a picture of how I hooked up the vacuum guage.

 

Throttle body work ? Good cleaning and new gasket. IAC cleaned up too while your there. Intake/ exhaust bolts re torquing. When my idle goes south, these 2 are always suspect.

 

I've checked all that except the intake/exhaust manifold bolts. I put them on and torqued down to specs when the engine was out. I checked a few of the top ones. Don't hear anything hissing, but, I'll recheck tomorrow to be sure.

 

That's quite the list, has to be frustrating. Only other input I have is try a stock type spark plug if you have the platinums. NGK or Champion stock is all my jeep likes, I dont know why platinums give mine a crappy idle but they do.

 

I actually just put champion coppers in as well. Tonight. No dice.

 

For tune up-I would buy a new cap and rotor. Really cheap. I see you wrote that you changed them out but I assume that meant they weren't new.


I had a problem with '87 (not sure if it applies to you) where it would start fine and then every thirty seconds or so it would stumble, then it would be ok for around thirty seconds or so etc.

It was a "slow" O2 sensor. It read voltage according to my scan tool but once warmed up, I guess the ECU was trying to adjust the fuel, timing etc based on it's weird readings. Once I changed it out, it was like a new Jeep (lots of power). The stumbling would almost always happen when I was on the on-ramp for the highway and I would floor it to get it going and that would cause a backfire.


By the way, my XJ runs rougher than yours. I'm thinking mine is valve related however.


Good luck.

 

As much as I hated to since I have 3 or 4 lying around, I bought a new cap and rotor with brass plugs. No change. Thankfully autozone let me damage them out so I didn't eat the cost.

The one thing I've disregarded is the O2 sensor. I don't have an analog meter to read it. Guess it's worth a swap? I just hate throwing parts at this thing. I've already doubled my budget to build this thing and I haven't gotten to the fun stuff like brakes, new tires, and linex on the body.

I'm too afraid to do anything until this thing gets fixed right. I don't want to keep throwing money at it until I know I have a good motor.

At least I know I'll have a bunch of parts to sell once I have this thing fixed. I have an xj salvage yard at my place. Every bolt on part you could need for the motor...I have two of them at least. Plus an extra short block. Lol

 

Anyone have anymore ideas? Or should I go back to square 1?