XJGirl

Having a hard ime trying to figure this one out. My Cherokee started idling rough. Seems to run fine going down the road. After searching for hours this seems to be a common problem that people for the most part people just live with. I'd like to figure out what my problem is and fix it.

It's a steady rough idle, doesn't stall or hesitate on acceleration. It's very evident at the tail pipe, it chugs vs being smooth like it was.

Here is what I've found/done so far:

Pulling #1 fuel injector plug off while running makes no difference. Pulling any other FI plug makes the motor idle worse.

Pulled and cleaned up cap and rotor, looked pretty good, just a little rust on the rotor, cap had regular dirt/dust in it.

I checked for spark at the plug wires, all check good.

I swapped #1 & #2 injectors to see if the problem followed....It didn't.

Checked the signal to the injector with a noid light, it checked good.

Also swapped out 1 & 2 spark plugs with the same results.

Did a once over on all the vac lines, didn't see any problems.

I still need to get it scanned for codes since the check engine light doesn't work. I'll do this today and post what I find.

JeepingDan

Hows compression?

XJGirl

Haven't checked compression yet. But I did just scan for codes.

Came back with P0201 / P0204 Which says Injector Circuit Open on Cylinder 1 & 4. Not sure where to go with this since I checked with the noid light.

tiwvr1

I would check very closely for broken wires to injectors. And check compression. I am assuming that it acts the same weather the motor is hot or cold?

Bigsnook91

nice xj

JeepingDan

X2 something is going on there. Maybe a rodent chewed up a wiring harness. Pretty common.

Nice answer

XJGirl

Yes it acts the same all the time. I can wiggle anywhere on the wire harness with no effect. I understand the broken wire theory, but it checks good using the noid light. Which tells me the signal is being sent. I did swap the injectors which didn't help. But still.....Pulling the injector plug loose from #1 has no effect on idle.

I plan to check compression, just need to find a gauge. Just a side note, the engine oil looks fine along with the coolant.

Thanks, it's even nicer when it runs smooth.

XJGirl

Ok fellas,

Did a quick compression test. The results are grim.

#1 has zero pressure, I was on very limited time so all I could do was check #2 real quick to make sure the gauge was working. #2 showed about 90 psi and held it for about a minute before I removed it.

So I definately have a compression problem. I'm going back again when I have more time to check all the cylinders. That way I'll know exactly what to expect when pulling the valve cover and/or head off.

So with zero pressure what can I expect? The gauge didn't even move at all while cranking-like it wasn't hooked up. I'm thinking a stuck valve or maybe a bad spring. The tests i've seen with bad head gaskets showed pressure while cranking then it would drop....But still, i'm not rulling out a bad head gasket.

What do you guys think before we pull the valve cover off?

JeepingDan

Set it at compression stroke both valves closed and do a leak down test if you have access to air.
You should be able pin point were the compression is going either intake or exhaust valve. If it's going into the crank case it maybe a burnt piston or rings.
Was there any massive amount of oil on the plug?

XJGirl

No oil on the plug, no tail pipe smoke. I'm leaning more to the intake valve.

The test kit you have looks like the one they have at harbor freight.

JeepingDan

Yea then it most likely a bad valve seat then.

XJGirl

Well, did the leak down test and all the air is coming out of the throttle body. So intake valve it is.

I also did a compression test on the rest of the cylinders, they came in between 88-90 psi.

With all the clylinders low on compression it sounds like maybe a build up problem, maybe sludge/gunk/carbon.

So, the question is... Shall I take this thing apart and fix it or shall I try some kind of engine cleaner like seafoam or something first?

sycoglitch

Follow the link on my signature and seafoam the he'll outta her and also clean throttle body too. Why you're at it clean your iAC sensor

Mycherokee96

X2 what glitch said.....You might want to try pulling the plug out and pouring some seafoam into the cylinder. Let it sit overnight. Before you try to start it, spin it without starting it, with the plug out.....to get rid of what you put in there. It may free up your rings if thats part of the problem.

P.S.- I was a marine mechanic for a number of years on 2 stroke outboards. They make stuff specifically for this problem in the outboards. Its called POWERTUNE. Use that, it's exactly what it's for. I wont go into why it came about, I'ld need 2 pages to explain it. Use it, I do, in my cars, motorcycles, everything. It wont harm ANYTHING....

XJGirl

Thanks for the advice,

I picked up some seafoam today. My next day off is Saturday, hopefully I can get to it then. Thankfully it's not my daily driver. I'll post how it goes.