98 xj misfire ive tried everything

I have a 98 xj 4.0 ive been stuck with a misfire on the number 1 cyl. I have replaced plugs with copper (gapped to spec), wires, distributor (with a new cam sensor cap and rotor), injectors, fuel pump, 02 sensors, catalytic converter, checked manifold bolts, installed new valve springs, IAC, and a crank position sensor. Compression is low between 120 and 100 on all cyl. When i replaced valve spring (i used air to hold valves up) the exhaust valve on number six leaked a little. i could hear it at the tail pipe. So my question Is would a bad exhaust valve on number six effect number 1 and cause it to misfire also when air conditioning is on the misfire clears up. at least until the compressor cycles off and then when it cycles back on it clears up again. I only notice the misfire at idle. I no longer want to keep blasting parts at this thing can someone help me.

Im in the same boat buddy.
I feel your pain.
Cps.
Tps.
grounds.
I would start there.

exhaust/intake gasket leak

Is the misfire bad enough to cause stalling, or is it only annoying ? At 270,000 or so miles my 1998 started to have misfire issues. The problem comes and goes and seems to be mostly related to buying cheap gas. I have tried all the usual routine maintenance steps and a few different fuel additives, and nothing seems to cure it. (I don't see any relationship between the CPS or TPS and the misfires.) I attribute the problem to old age and advanced miles on the odometer. I recently put half a tank of 89 octane fuel in it and for two days now no misfires at idle. I ordered a genuine Jeep coil and will install that when I get chance.

Tim_MN said:

Is the misfire bad enough to cause stalling, or is it only annoying ? At 270,000 or so miles my 1998 started to have misfire issues. The problem comes and goes and seems to be mostly related to buying cheap gas. I have tried all the usual routine maintenance steps and a few different fuel additives, and nothing seems to cure it. (I don't see any relationship between the CPS or TPS and the misfires.) I attribute the problem to old age and advanced miles on the odometer. I recently put half a tank of 89 octane fuel in it and for two days now no misfires at idle. I ordered a genuine Jeep coil and will install that when I get chance.

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I also found my fuel lines were gummed up.
Pull It at the rail
remove the filter. and blow down the line.
you will know.
this is a hard one to find because it will pull correct pressure

Is it throwng a code (P0301)?
Is it a steady miss, or is it just ocasionally stuttering.

Do you have access to a scan tool? If so, what are the fuel trim numbers in the live data reading at?

Check to be sure that the fuel injector wire harness is not chaffed or rubbing against the
rear tip of the fuel rail and shorting out a fuel injector(s). This one got me a few years
back. The fuel injector wire harness exits the long black plastic wire harness protector,
then runs across the firewall behind the brake master cylinder, and goes to the ECM
(Electronic Control Module) near the air filter box.

Sometimes the wire harness will slump down and rub against the rear-most tip end
of the fuel rail. After a while the tip of the fuel rail will wear through the wire harness
and cause a short. The break will be very tiny and almost invisible. I had to open up
the corrugated wire cover and unravel the loom tape to find the break in wire
insulation. Fix any broken wire insulation and zip-tie the wire harness to the firewall.

^I've also had a customer's truck do this.

Been busy with work lately yes its a p0301 code its a inconsistent misfire meaning its always there but its not a steady miss you can tap your foot to. Also fuel trim numbers are usually 0 for stft and ltft is usuelly no more then +2 or +3

Ill check wiring as well

Alopanec said:

I have a 98 xj 4.0 ive been stuck with a misfire on the number 1 cyl. I have replaced plugs with copper (gapped to spec), wires, distributor (with a new cam sensor cap and rotor), injectors, fuel pump, 02 sensors, catalytic converter, checked manifold bolts, installed new valve springs, IAC, and a crank position sensor. Compression is low between 120 and 100 on all cyl. When i replaced valve spring (i used air to hold valves up) the exhaust valve on number six leaked a little. i could hear it at the tail pipe. So my question Is would a bad exhaust valve on number six effect number 1 and cause it to misfire also when air conditioning is on the misfire clears up. at least until the compressor cycles off and then when it cycles back on it clears up again. I only notice the misfire at idle. I no longer want to keep blasting parts at this thing can someone help me.

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No. Assuming everything is in working order, a bad valve on #6 would affect #6 and #6 only.

We know that compression is low on all cylinders. (It should be 120 to 150 PSI with a max variance of 30 PSI between all cylinders.) The next variable we need to factor into compression testing is your altitude. Higher altitude= less air= less pressure= lower compression readings. Long story short, I shamelessly snagged these numbers from another site-

Alt. Correction factor
1000 .9711
2000 .9428
3000 .9151
4000 .8881
5000 .8617
6000 .8359
7000 .8106
8000 .7860

For example, when I bought my XJ and first compression tested it, 130 PSI seemed a bit on the low side at 4,500 ft, but was really good since 150X0.87=130.5 PSI.

If your compression readings are in fact low for your altitude, the next thing to do is find out why. The easiest way of doing this is by squirting a bit of engine oil into each cylinder through the spark plug hole and re-performing your compression test. If the numbers come up quite a bit, you've got worn rings or cylinder walls.

If not, you've got a problem elsewhere- worn cam or timing chain, broken or stuck valves, I've even heard or bent connecting rods causing low compression numbers. The next step then would be to perform a cylinder leak-down test.

I have seen vehicles that have had the injector wires swapped. Not a lot of experience on HO but on the Renix, it is really easy to get them switched. Look up the color codes for the wires and make sure they are correct. Swapping will cause a bad timing of the fuel going into the intake and cause a ton of problems, especially at low rpm's.

Swap injector plugs 1 and 2. Drive around tell us what happens.

Since the misfire is only on cylinder #1, why would one suspect mixed up injector wires, especially if the trouble code occurs intermittently and randomly ?

My experiment with mid-grade 89 octane gas did not turn out as successfully as I anticipated. The first tankful went well, and the second tankful allowed a random misfire to occur during several times on one day. My second experiment is adding a few ounces of ATF to the gas tank. ATF has high concentrations of detergents and may help clean up any injector issues or carbon deposits. I still somewhat suspect that the misfires are due to timing chain stretch and is likely aggravated by buying cheap gas.

Tim_MN said:

Since the misfire is only on cylinder #1, why would one suspect mixed up injector wires, especially if the trouble code occurs intermittently and randomly ?

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It may help to get a better understanding of what is going on. It is cheap, easy, free and won't cause damage. The next request would be to return the wires to the original location and swap injector 1 and 2. Again cheap, easy, free and won't cause damage.

You should list your compression figures, dry and wet.