1999 jeep cherokee, retired sheriff's dept vehicle with 'police package'.

4.0l high output motor.

It sat in a field in texas for... 3-4 years before I got it. I dropped a battery in it, and drove it home. It ran smooth as glass all the way home. It continued to run smoothly until...

I put fresh gasoline in it. Texas is a mandatory ethanol state, this may be a factor.

All of a sudden, it ran like ****. stumble, stutter, shake. I looked it over, and noticed all the plug wires looked like rat-chewed crap, because, well, they were rat-chewed crap.

So I replaced cap, rotor, wires, and plugs, correctly gapped to factory spec.

problem persisted. Fed it some injector cleaner, problem mellowed, but still persisted.

I now have a parts jeep, and I am considering replacing the injectors, as the injectors in the parts jeep are not even a year old.

Am I on the right track?

 

Fuel filter?

What plugs did you put in it? Copper core?

 

I have not replaced the fuel filter yet.

as far as plugs, I replaced them with what was in the jeep when I aquired it.

I'd have to go look to see.

My reasoning for replacing the #4 injector is...

1. it ran smoothly when first resurrected.

2. I'm not getting misfire codes on any -other- cylinder.

3. the engine shows plenty of power, so compression is not a likely issue, if it had bad compression, it would have run like crap from the beginning.

4. As I have the parts, it's a 'no cost solution'. I figure swapping the injectors for newer ones isn't going to hurt anything. If the misfire persists, I know it's something else.

 

If you decide to swap injectors, I would swap all of them, and not just one.
Btw, your fuel filter is in the fuelpump assembly, it's not a separate one like in pre-updates.

What year is your parts jeep?

 

I would think that 4 year old gas would gunk up a filter..

 

THe parts jeep is a 1999 sport, with exactly the same injectors. it was a running car that got hit by a dump truck.

I did swap all of them, and cleared the code log, and I'm going to be taking it for a check ride later tonight. It starts and runs, and -seems- smoother so far, but the real test is the check ride.

 

As far as gunked filters go, it ran smooth when I first got it, and only got weird after I started adding more fuel. the other reason is, if it was a clogged filter, I wouldn't get #304, and number #304 -only-. I'd get random misfires. I've cleared the code log twice, and the only code that shows up is #4 cylinder.

So, all 6 get replaced. If some of the 'new' ones fail, I'll mark em bad, and remove them. They're all chrysler OEM injectors with the same part number, so mixing and matching can be done, -if I have to-.

I sure hope I dont.

 

1. Yup, replace all injectors.

2. If misfire continues, you must run a compression test. The only way to know internal condition is through testing. Don't assume anything. The compression spec. for the 4.0 is 120-150, with no more than a 30 psi variation between cylinders. Compression testing will take very little time and even if it doesn't reveal anything, it is a good "snapshot in time" for a new-to-you vehicle.

Good luck and keep us updated!

 

If the #4 cylinder continues to misfire, yes, compression test. If all of a sudden I get a misfire on the #1 cylinder instead, I'm going to (rightly, I think) assume one of the salvaged injectors is crap, and swap it. I marked the one 'bad' injector when I pulled it, and kept it seperate.

don't get me wrong, if I had money to burn, I'd totally go out and buy all new squirters. but as poor people... you run what you can get.

 

Roger that. You have a plan. Let us know how it turns out. Single cylinder misfires are not normally that hard to figure out.

 

Well, this is annoying.

#4 cylinder is still acting up, and much worse than before. While I'm going to do a compression check as soon as is feasible, I'm strongly suspecting perhaps a dirty contact, or a loose wire somewhere.

it's only number 4.

replacing cap, rotor, plugs and wires did not fix the problem.

it's intermittant.

it smooths out at higher rpms.

it's not burning oil, or making mud pies in the cooling system.

it's getting roughly 20mpg, highway, at 85mph, with -zero- problems blasting down I-130 at 85-95mph...

I doubt I'm going to be having compression problems, I suspect what I've got here is an electrical problem of some sort. I'm going to try some things over the weekend.

 

which is not to say I wouldn't like some help.

 

you should find out if you have copper core plugs. I threw misfires after new plugs in my 00 because they weren't copper cores. cheap stuff first.

 

ok, for the sake of argument, let's assume it's non copper core plugs. if so, wouldn't there be misfires on -all- the cylinders? I've got this thing hooked up to a laptop, and the only bore that misfires is #4.

I think there might be a bad wire in the harness. tomorrow, I do things with multimeters.

bed for now.

 

That's what I thought too. And I thought it was crazy, I thought I was crazy. But I never saw the cel again.