Engine Trouble

I got a 90 xj that I am trying to keep running. Had some problems with it idling so finally got that taken care of with a new throttle position sensor. But lately it has developed a new ailment. It hesitates a bit out of a stop and then slowly accelerates. Seems like its always after its warmed up, and sometimes I get like a clunk from the front end as it kicks in and starts accelerating.

It seems to run a little hot too, Everytime I check it there is a fair amount of pressure built up and the coolant steams. Just replaced the Thermostat. I tested the old one and it didn't open up till about 205 degrees. So I thought that might be it, but doesn't seem to be making a difference.

Hallo. How is the status of maintenance? Filters, sparkplugs, cap/rotor,O2 sensor.
If ok, I would check the CTS (Coolant temp sensor) with a DMM (Ohms) for a start.

As wim mentioned, always a good time to review tuneup hardware when symptomatic. Replace as necessary.

What temp is your engine running at? Most run in the 200-210 bracket. The 4.0 is designed to run hot. If yours is running approx. this temperature, you're okay. However, the coolant shouldn't STEAM. Exactly where is the steam coming from? The devil is in the details here.....

The O2 sensor was just replaced. Don't know about the spark plugs, I was just thinking that they might be part of it. It runs a little rough. And especially at low speed it really almost stalls when I hit the gas. And if I contine to hold gas down I start getting some clunking banging noises?

The steam comes off the overflow bottle when I open it up, and there is a good amount of pressure built up. Don't have a temp gauge so can't give temperatures.

Air filter is brand new, I need to check the distributor make sure that is good. So I might change spark plugs and see if that helps. BTW where is my coolant sensor. Can't seem to find it. There is a sensor with two wires going to it on top of the engine on the drivers side, is that it?

Thanks alot for your help. I really appreciate it, I am still learing alot here.

Do you still have the closed sys in it? If steam only comes out when you open it then the cap is fine..It will build pressure in it.. Did you burp the air out of it?

Rough idle could be plugs or..... depending on how many miles, it may need new injectors. I replaced mine somewhere around 180K with a set from fiveo motorsports. Huge improvement.

The other thing to do is replace the cap and rotor. Get brass if you can find it.

Again, depending on the milage, consider new plug wires.

Check the EGR system for proper operation.

Clean the TB.

Check for vacumm leaks. Inspect all those plastic vac connecitons on the front of the intake manifold.

Clean the valve cover and the associated breather parts.

I hoped you replaced the Tstat with a 190 and not a 160, though I get by with a 185. Go with a high flow one from NAPA. I checked a bunch of different ones for open area and it is the biggest. Drilling a 1/8 holde in the top of the Tstat prior to installation helps bleed the air out. Do a search on this topic.

Coolant sensor is on the output tank, drivers side, of the radiator about half way down. Big sucker with two wires coming out of it.

Double check the TPS settings. Could be it needs adjustment. Lots of threads on here with instructions. Search is your friend.

Thanks for the replies. Just replaced spark plugs, and now it runs smoother but still no difference as far as the stumbling with acceleration.

I put a 195 degree thermostat, same as what was in there. The overheating problem may just be some air in there, I haven't burped it thoroughly, also I have been taking care of some leaks and such so that may just be a fluid level thing. And yes I still do have the closed system.

But this acceleration problem is what I'm worried about. Is it possible the fuel pump is acting up? I could try swapping out the fuel injectors from the 93 XJ sitting in my driveway, see if that helps. Although it does have more miles on it than my jeep so may not be worth it.

I am pretty sure the TPS is adjusted correctly. I adjusted it to the 0.8 volts its supposed to have with key on. Also the stuttering problems were the same before I replaced that.

Gotta finish that tuneup before moving onto other more complex things. If you don't, you can be chasing your tail. Can't stress that enough. Replace the distributor cap and rotor and plug wires. Simple job and not too expensive. Cleaning your idle air control and throttle body is never a bad idea as a matter of course and I consider that part of an XJ tuneup.

Other ideas....try a bottle of "Techron" fuel injector cleaner in a half a tank of gas for concentration. Or swap in the new injectors and see if that helps. Checking fuel pressure at the schrader valve on the fuel rail only takes a few minutes; compare your numbers to factory spec.

after you complete the tune-up, test fuel pressure to confirm that its not a fuel issue.

then i would test/inspect the egr system(solenoid, transducer, valve, vacumn lines) for proper operation.

If you floor the gas and accelerate through the gears, your greatest gas demand is at higher RPM's. If it only hesitates at low speeds, it's not the fuel pump. Is '90 the last of the RENIX or the first of the OBDI?

89xj said:

after you complete the tune-up, test fuel pressure to confirm that its not a fuel issue.

then i would test/inspect the egr system(solenoid, transducer, valve, vacumn lines) for proper operation.

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EGR is a good idea as that should be closed at idle. If it's stuck open, it's like a vacuum leak.

winterbeater said:

If you floor the gas and accelerate through the gears, your greatest gas demand is at higher RPM's. If it only hesitates at low speeds, it's not the fuel pump. Is '90 the last of the RENIX or the first of the OBDI?

Click to expand...

Last of the Renix.

93 has different injectors, might make a differnece anyway.
http://www.jeep4.0performance.4mg.com/tech_specs.html

Complete the suggested activites, especially the cap and rotor. Even if you take them out and clean them up by removing all the oxidation, it may improve.

You said you just replaced the O2 sensor. Was it running better before you replaced it? Sounds like it's running too lean, maybe a bad sensor?

If you aren't sure about the spark plugs, it's time to find out. My kid was just complaining about his Escort barely running and not taking any gas. I reminded him that it still had the original plugs like it did when I sold it to him over a year ago. He pulled the plugs. Gap should be .050, but looked like .150" (from 120k miles of sparking). New plugs, runs like a top again for $8.