Greetings all, got a question.
I have a 92 XJ. It will fire right up first thing in the AM, no sputters, smooth as can be. but after running just a few minutes, it will be super hard to start, and takes opening the throttle wide open to get it to start at all. After starting this way, it runs rough and sputters badly for about 10-20 seconds. This is what I have done: replaced fuel filter, cleaned tbody and IAC (iac was NASTY) The jeep has a fairly fresh set of plugs (champion copper, about 3 months old) I have also applied thermal shield tape around the injectors and rail. I am thinking that the IAC may be bad, but after starting, it idles perfectly. Also; starter, alternator, o2, fuel pressure regulator, distributer, and PCM have been replaced in the past year. New intake gasket and exhaust manifold as well.

So, I am thinking IAC replacement needed, I just wanted to double check here because of the awesome experts that lurk here!
Thanks for your time

Garon

 

The symptoms have the hallmarks of a failing/failed upstream O2 sensor. Cold start will be fine because the sensor is not used by the computer to adjust air/fuel mixture until it is warmed up. Subsequent starts will use the O2 sensor much quicker (after just a few seconds).

Another possibility is that your battery is marginal, and your 2nd start is suffering from a low voltage condition and corrects itself after the alternator has been turning for a while and gets things back to a sustainable level.

I suspect #1 is the more likely possibility.

 

Thanks Jordan,

I did put the new O2 in this morning, probably will need a few drive cycles to sort out.

 

Ok, folks,
Minor update:
I installed the new o2 sensor, reset the PCM. Jeep is no longer running super rich, but, it is still super hard to start after warm up. AND now, will sputter and occasionally die until the engine is warm.
I guess I will start checking over the vacuum lines and such? Oh, by the way, the only way she will start is by opening the throttle wide open after warm up. don't know if that has anything to do with it.

 

Hello All, this morning fired her up to check tranny fluid, and my other half asked "what's that whistling noise?" she helped me trace it down to the MAP sensor. (I am hearing impaired) so at some point today I will replace it, and try and catch all the vacuum hoses, as the do seem to be in rough shape. Just continuing to post results until the problem is solved, for other users.

 

Consider leaking fuel injectors.

They did have fuel injectors way back in 1992, didn't they?

 

Please test once that's done, before you do anything else, and let us know the results.



Here's a tip for finding vacuum leaks: ether. With the engine running, spray short bursts of starting fluid where you suspect a leak. Not a long blast, just a quick shot. If the ether is sucked into a vacuum leak it will cause the engine to rev a bit. Do this OUTDOORS ONLY!!! I have also heard that WD-40 will work, but I have not tried that.


Liquid electrical tape is a good temporary fix for cracked vacuum hoses.


Thank you!

 

A leak in the hose to the MAP sensor surely causes issues. Get that fixed.

jhc7399 here on the forum supplies nice rebuilt injectors at a reasonable price also

 

Good morning, Folks.

Ok, here's what I have done so far: I ordered a set of upgrade injectors, installed them, and found out that 2 of them were DOA. reinstalled old injectors. Map sensor had a small crack in the housing, next to the vacuum inlet, replaced with BWD brand sensor, liquid electrical taped all of my visible vacuum hoses, found the plug on the vacuum line to the heater control valve had fallen off, replaced that. Relocated the crank sensor wire out of the way, and ran heat shield tape over the wire. Still having the same issue with warm starts. I do have a new carquest brand fuel pump assembly. I was poking around and saw that the fuel pump ring, wire, and hoses were really old looking, it was a beast getting the fuel filter off and back on. I will keep y'all updated.

 

what does this mean?

liquid electrical taped all of my visible vacuum hoses,

 

Oh, I am getting frustrated, is all, I am starting to throw parts at it, as it is beyond my diag skills. I coated the tubes just to make sure I didn't miss a silly leak I cant hear.

 

Use a liquid like carb cleaner. Then you dont have to listen for vacuum leaks.

 

Allrighty then.
Using Ether, checked all of the vacuum hoses, Tbody, manifold, not a vacuum leak.

 

Heh, Just 4 years newer, and I could plug in and look at the pids…….

 

Afternoon, fellas

So, I have my xj on a lift, and low, and behold, I see about 4 inches from where I shielded my crank sensor, a melted spot. I guess I just didn't see it when I was monkeying around with it this weekend. how it got melty where it is, no idea... the wire is intact.. but the insulation is melted and charred. My guess is it gets hot and there goes the clean crank signal. Just a guess.
Thanks