97 TJ 2.5L 140k miles
The other night while playing in the snow, I suddenly lost a smooth idle. It feels like a tractor at idle and then seems to smooth up after idle. Today I took a timing light and proceeded to check all 4 plug wires to see if I wasnt getting spark to a cylinder. All 4 have spark at the plug wire. The exhaust doesnt smell rich either, so I believe this rules out a problem with spark. I then moved on to fuel and removed each injector clip to see if one of them didnt make a difference. Pulling the injector clip on the #4 cylinder made no perceivable difference. Well, I checked voltage across the wires running to the injector and got 2.3 some odd volts across each injector wiring while the jeep was running.

I believe I have narrowed it down to a bad injector, but does anyone else have experience with this problem?

I do plan to check compression tommorrow, but it is 0 degrees right now and I ran out of propane in the heater, so working on the Heep isnt really pleasent to say the least.

Possible injector, but I would also check for a vacuum leak at the intake manifold first. The rear stud that hold the intake/exhaust manifolds break off all the time. It causes the manifold to warp and after a while it will suck the intake gasket in and then you have a major vacuum leak..

does the tj still use a cps(crankshaft position sensor)or is the distributor adjustable?/my 90 had some really bad running probs when my cps went bad//but i think it was at all speeds//backfireing & crap//not just idle//
def check 4 vac leak like gary said

replaced the injector, now the rail itself leaks cause it is rusty and shitty, but, no real change that I could tell, hell, these OBD 2 Jeeps that I cant change timing or idle or anything on are a pain in the arse

When was the last time you changed your fuel filter? Mine did the very same thing and that solved it right away.

I am working on that on my next move I believe before I pull the valve cover to check for a bent pushrod or valve. I bought the Jeep not long ago, so I havent even done routine maintenance.

replaced the injector, now the rail itself leaks cause it is rusty and shitty, but, no real change that I could tell, hell, these OBD 2 Jeeps that I cant change timing or idle or anything on are a pain in the arse

Just curious... according to your own statements you do not know how to pull money out of your ass..... soo.... why are you changing parts without finding the real problem first... If you have that kind of money, send me some.

Have you checked the compression?
Did you check for a vacuum leak?
Have you checked for codes?
Have you checked for any bad vacuum hoses going to the intake?
have you checked the vacuum booster for leaks? etc.etc. All of this should be done before replacing one single part..

sounds like it would be cheaper for you to take it to a shop and get it checked right..

Gary TJ, I checked the injector the best way that I knew how and spent 5 dollars on a junkyard injector in hopes that it would be working correctly. I am not about to go replacing parts that I have no reason to replace. I had reason to believe that the injector was faulty so I spent 5 dollars to go ahead and replace it. I did feal for a vacumm leak around all vacumm hoses that I could find. I plan to replace the fuel filter because I have no idea how long its been since it was last replaced. I am pulling plugs soon to check for improper gap and while they are out will check the compression. It is not throwing a check engine light or I would immediately get the codes checked. If I am unable to find the problem soon, I certainly do not plan on pouring money into it until it gets fixed, instead I will take it to a shop w/ experience and equipment to analyze the situation better than I may be able to. However, I will exhaust my resources before I bring it to someone else.

I am curious as to what parts I have replaced that were not faulty?

Have you swapped the plugs and wires to see if the missfiring cylinder changes? There should be 12 volts at the injector on one side, and the computer controls the ground on the other side. To properly test an injector takes a labscope and a low amp probe, although sometimes you can find a bad ohms reading, just compare injectors.

FWIW if you touch an injector rail you must replace ALL the seals. I have seen cars burn to the ground from trying to cheat.

I swapped plugs with no real change, although the old plugs were close to double the gap of what they should be. It still idles way too low and seems to miss + sounds like a tractor. The roughness diminished once I replaced the number 4 injector.

Yeah, from what I can tell the fuel rail is leaking above the injector at the connection between the injector bung and the rail itself, it is rusty enough where it should be replaced anyway. The whole burning to the ground thing makes me worried so I havent driven it lately, makes it difficult to work on w/ out a garage and the temps weve been seeing around here.