Need some help!! Possible heat soak?

[WhiteKnight2]

Recently brought my xj from MD to NC where I now live and it needed some big time TLC. I have been working on it installing rock slides, new tires/wheels, aluminum radiator, new radiator shroud, and hood vents. Finally runs at correct temp! Also replaced plugs, distributor w/cap and button, and air filter. Pretty sure the plugs had never been changed.! This thing runs like never before.. Until the test drive. It was about 89 degrees out (much warmer than any day in Maryland) and the jeep rad at OT just fine but about 15-20 min into it but then it just loses power. It felt like a 2 stroke fouling a plug. I push the pedal and it seems to just hesitate, let off the pedal and it will idle but a low idle. Put in neutral and it won't rev correctly. Put in gear and it will go but just seems to have only half power. The transmission seems to shift weird also.(it's an A/T)
I'm thinking a possible heat soak issue because I have had a similar occurrence trail riding with a rough start after shutdown on a hot day. I was also thinking possible ignition coil breakdown but it runs good cold and at OT for a while but after 15-20 min at OT a loss of power.?? Any ideas? I also will mention I have no catalytic converter so no clog issues here. :bang:

[4.3LXJ]

If the plugs had never been changed, it is a cinch that the O2 sensor has not either. That will affect the mixture and power. Also, once it gets going does it shift properly?

[WhiteKnight2]

If the plugs had never been changed, it is a cinch that the O2 sensor has not either. That will affect the mixture and power. Also, once it gets going does it shift properly?

I'm definitely going to change O2 sens. and fuel filter next. Yes it shifts fine up until the loss of power. I don't think the shifting is a cause or problem, just maybe a side effect of the poor engine performance. But that's my opinion. I am honestly open to suggestions bc I just did a ton of work to this thing and now it's running like crap!

[WhiteKnight2]

Also not the original engine. I swapped out of another xj and the o2 sens was from my xj. Not to say it's not the original.

[rabies]

what year jeep? any CELS?(codes)
compression test or leak down test?
possible goofed headgasket from overheating?
as far as the trans shifting funny. the tps can do that and the tps wires run right where it gets real hot. mine were crispy when i got it and it was also goofy.

[WhiteKnight2]

what year jeep? any CELS?(codes)
compression test or leak down test?
possible goofed headgasket from overheating?
as far as the trans shifting funny. the tps can do that and the tps wires run right where it gets real hot. mine were crispy when i got it and it was also goofy.

Sorry I was not specific on jeep.
It's a 95' with 4.0 and auto. No CEL that I'm aware of. (And now that I think about it I haven't looked at the CEL when I start it for a bulb check)
I'm really hoping it's not a head gasket but I haven't had a leak down or compression test. On that topic would it make sense that it only misses or runs rough after running at OT for 15-20 min that the head gasket is bad or the possibility of a cracked head.. I just thought it would do this at low temp as well.
I will also check TPS tonight. Thanks for the info!

[XJ Wheeler]

I would definitely look into that tps. It can cause shifting issues, as well as idling/running problems.

[WhiteKnight2]

Ok guys I did a little more driving last night and I'm getting the same results. I changed the fuel filter just because it needed it. I didn't expect this to solve anything just a needed maintenance item. I left the house after a 5 or so min idle/ warm up, drove around the neighborhood at around 25-45 mph. It was a cooler evening around 70-75 degrees and the jeep ran around 195-200. Plenty of spunk and throttle response. Drove like this for about 10-15 min with normal stops and takeoffs. A couple hard accelerations and transmission downshifts. Everything was as normal as a jeep with 150K miles should be. Then I pulled out slowly accelerated to about 30 and then quickly wnt to full throttle... The jeep seemed to backfire- hesitate and loose power. It seemed like you hooked a Sherman tank to the hitch. I can hear the jeep trying to accelerate but it seems to not be getting the correct fuel/spark. I stopped and opened the good and I'm almost certain the heat soak is not the issue because the fuel rail and injectors were hot but not so hot I couldn't briefly touch them without getting burnt. The engine would rev a bit but not like it should. I reved it quickly to half and then quickly to full throttle and it backfired through the intake. Tried to back out the driveway and it was the same sluggish pull. (No matter what position the throttle was in it didn't change). Put it in gear and pulled forward, same thing. Pulled into garage let it sit a little while maybe 4-5 min, stated it and pulled out of the garage in reverse put it to the floor and it picked up just like it should put it in Drive pulled like it should then went back to sluggish. I don't know what the heck is going on! I unhooked the MAP sensor to see if the CEL is working and it is. Ran rough threw a code. So before this no CEL had been displayed.
Also when I hooked up the electric fan originally I found a random plug in the engine compartment that had a switched 12v wire and hooked this to my relay for an ignition sourced 12v supply. About the second time I took it for a test drive the fan stopped working and this wire was the cause it had no 12v. I have no idea what it was for but maybe this is a cause? It is a two wire connector with a blue rubber water seal with a green wire and a blue wire with orange stripe. It is on the passenger side somewhere around the motor mount area?? Please help me find this plug and it's original purpose.
Sorry for the long post but this is getting to be a real PITA and I just want my jeep to drive again!

[rabies]

at lunch i can go look at mine and see what plug that is.
as for now my guess for it would be fog light or ac??.
http://www.dayid.org/xj/tech/93XJ_wiring2.pdf

[4.3LXJ]

I think you have two issues going on. First, get that O2 sensor changed. Then if it still is giving those symptoms when running with the right mixture, then I think your MAP is wearing out and needs to be changed. Not sure what the wire is

[rabies]

map sensor should be
vio-white
dark green- red
black-lt blue


if that unplugged plug is for the secondary o2 sensor. just leave it. it wont do any harm at all.
but like xj wheeler said. the primary o2 if jacked up can make the jeep an invilid

[WhiteKnight2]

at lunch i can go look at mine and see what plug that is.
as for now my guess for it would be fog light or ac??.
http://www.dayid.org/xj/tech/93XJ_wiring2.pdf

Awesome schematics Rabies, will definitely be saving those!!:thumbsup: Thanks so much I think it's the A/C low pres switch. Position B18 on the schematics. I removed all of my A/C stuff except my compressor a year ago. I appreciate the info and it looks like that had nothing to do with my problem. If you still wanna look and verify it would be great.

[WhiteKnight2]

MAP sensor and O2 are on the list for the weekend. Any suggestions on the brand?

[4.3LXJ]

OEM if possible, but others will work well

[WhiteKnight2]

Changed the O2 sensor and MAP sensor last night. Let the jeep warm up and took a drive. It ran as it should with good power and shifts so I started playing around with acceleration and seemed to be running better. Did a couple rolling WOT from about 25-30 and it kicked down a gear and ran fine. Then I was rolling at about 25-30 and stomped it and it. When it tried to downshift to passing gear it backfired and lost all power. From this point on the power loss started. I was about a mile from home so I limped home. The jeep seemed to run at idle decent but with throttle it has a bogish sound and little to no power. It would try to shift down when at WOT but the rpms did not allow it to stay at a lower gear. I pulled it in the garage and left it running. It idled ok but when I gave it throttle it still sounded boggish. Tried to move it in and out of the driveway and it was still bogging. It will move and reach about 25 mph but just has no power.

Parts I've Replaced Recently:
Distributor with cap & rotor
Plugs
Air filter
Fuel Filter
MAP
O2


I'm going to do the TPS today and reset the ECU. I'm thinking of checking fuel press and compression also this weekend. Maybe a timing issue? I think this is a electrical issue and haven't ruled out the ECU. One more thing I remembered is two winters ago I was riding with my fiancé and we were stuck on a steep hill In the snow. I had slid to where if I drifted backwards I would most likely flip so I ran the shit out of my jeep and it was overheated. I finally got to where I could stop and winch the rest of the hill and at the top this same loss of power and bogging occurred and was like this for a while. I didn't drive the jeep for a while after bc I didn't live in MD so the jeep was left there at my parents. I thought maybe the transmission was hot but it just seems like an engine/ electrical problem due to the fact that it still has the bogging when in neutral.

I'm running out of options and seriously out of patience on this one. I'm about to sell the damn thing and get a boat but this is supposed to be my beach buggy so I can quit driving my jk on the beach.. Any ideas??

[rabies]

mech timing wouldnt be the issue if you didnt fiddle with it...unles its very old and you have a stretched chain.

compression would give you an all together piece of crap. but our problem is inconsisnt.
you said dizzy cap and rotor you replaced. did you check electrical timing? timing light?.
did you have these problems before you replaced plugs and dizzy parts? check your plugs. and compare them to this chart.
(this pic is in the back of most haynes manuals)
5756

[WhiteKnight2]

I didn't really run the jeep much before the distributor change. I hauled it down to NC and before I had it down here my dad ran it and didn't complain about this problem. It had an overheating issue which is now taken care of. I changed the dist, and plugs just for maintenance. It was needed..
I don't have a timing light but you really can't adjust timing on these dist. Right? Can it be a tooth off and still run? Maybe that could be it.
I have the old distributor so I may swap it back and try it. The plugs only have about 3-5 hours max on them so they probably won't tell me much. I will still look tho.
Thanks for the ideas man. Any other input / help is definitely appreciated.

[WhiteKnight2]

Another question. At OT should disconnecting the vacuum line to the Fuel press regulator change the performance of the engine? I unhooked it and it made no difference..

[Mudderoy]

Don't forget to click on this to get specifics on the posters rig.

5761

[rabies]

fuel pressure regulator does need that hose to maintain proper pressure.
your timing chain wouldnt be off unless you fiddled with ti and didnt put it back to TDC and lined it up. yes you can adjust the dizzy. lossen the whole bucket and you can twist it. majority of vehicles with dizzy are like this. old honda civics/accords are famous for it and being picky

[WhiteKnight2]

Hey just for closure on this problem. I figured it out! Apparently when I installed the new distributor I was one tooth off on the timing. Being computer controlled timing I guess the computer was able to adjust the timing enough to start and run but the power loss was when the computer wasn't able to advance the timing as far as it should due to the dist being in the wrong position. Not being able to manually adjust the timing on the dist, I couldn't easily troubleshoot this problem but that was definitely the problem. It also explains the backfiring through the intake after the WOT. Jeep is running better than ever. Thanks for all the info and help.