97 Jeep Cherokee: Rough Idle/Misfire

[fonty493]

Hello, this is my first post here but Ive seen some very helpful responses on these forums and thought I'd ask for some help.
I bought my Jeep with a blown radiator, replaced that to find a very rough idle which goes away at 2000 rpm cold and 1500 rpm warm in neutral and it goes away almost instantly when driving. The check engine light came on as well so I put the code scanner on it and got cylinder #1 misfire and cylinder #2 misfire (I believe the codes were P301 and P302). So far I have replaced the dist. cap and rotor, plugs and wires, the IAC, and the #1 and #2 injectors. I have also run seafoam and fuel system cleaner through it, and checked for vacuum leaks. The Jeep also had a weak alternator and bad battery which I have also replaced. When the Jeep is at idle I can pull the connectors off of both the #1 and 2 injectors and idle does not change at all, but at higher rpm's pulling even one off of course makes it run like [censored]. Pulling any of the other 4 connectors at idle makes a very noticeable difference. When using a long screwdriver to listen to the injectors I can hear the #2-6 injectors firing happily away, but the #1 sounds much quieter even though it is new. Nothing I have done so far has helped even a little bit. The oil is clean and no sign of the milky goo under the valve cover so i don't suspect the head gasket, although that is what many people have been suggesting.
I haven't been driving the vehicle other than a few test drives and other than idle it runs and drives great, no overheating, no smoke, no antifreeze smell from the exhaust.
Im at my wits end with this thing, any suggestions on where to go from here??? Tomorrows plan is to swap the #1 and 4 injectors and see if the misfire follows and maybe try a TPS.

 

[Zaedock]

Do a compression check of all the cylinders before you start swapping injectors. If you bought it with a bad radiator, who knows how long it ran without coolant. The head gasket could be compromised between cylinders 1 & 2 or with an oil passage.

 

[Gary Allan]

Hmm..if this is an ignition issue, I think you're into the crank position sensor. The flywheel/flexplate triggers the spark with indentations that the probe reads.

Pull the injector wires and plug wires for #1 & #2 (to keep raw fuel out of the cat) see what the spark looks like. If it's healthy, then you're getting a good trigger. If it's weak ..then there may be some (

) virtual dwell time issue.

 

[mechtech2]

Do a quick swap of the bad injector with one that is OK.
This will identify if it is an injector or injector signal problem. This will eliminate 1/2 of the equation, or fix it.

You ignition coil for those cyls may be bad.
A vacuum leak that affects only those cyls is possible - a line or manifold leak.
Low compression [from a variety of reasons] is another thing to check. A simple cranking compression check is a good idea. [throttle open, no fuel or spark]

 

[fonty493]

Thanks for the replies guys, heres an update:
I tested the crank position sensor which turned out good.
I pulled the fuel rail and made sure it was clean and swapped around the injectors, still no change.
In my frustration I swapped the #1 and 2 injector harnesses just to see what would happen and oddly there was still no change. (so i put them back before i broke something)
I also changed the TPS which did make a noticeable improvement but the problem is still there.
I am going to do a compression check today and if that checks out ok I'm thinking maybe camshaft position sensor?
On a side note, my headlights seem awful dim for having a fresh battery and alternator, which is externally regulated. Could a bad voltage regulator maybe be causing all this?

 

[Gary Allan]

The cam position sensor controls the injectors. I think that they use a batch fire method ..that is 3 triggers for 2 injectors at a time. It won't explain the 1&2 deal since they're a good bit apart in terms of stroke.

You may indeed have a couple of coked ring packs on those two cylinders. They may be dipping their paddle.

Yes, the alternator should be regulated by the PCM. You should also have a battery temp sensor in the battery tray that will limit the enabling of the field windings by the PCM.

 

[Greaser]

Did you try cleaning the Idle air control valve?That controls the idle air intake and can make the engine run like po@p if dirty or spent.

 

[fonty493]

Actually the battery temp sensor looks quite terrible, is there a way to test it? And yes, the i replaced the idle air controller, that was actually the first thing i tried.

 

[eljefino]

What's your battery voltage not running, idling, and 2000+ RPM? I suspect you should be able to spark and fuel with as little as 8-9 volts though as it needs to happen during cranking.

The computer has a fail safe for a totally shot battery temp sensor... but of course it could just be halfway gone. I expect anything that increases resistance would make it think the world was colder and overcharge the battery. If you can get at a connector an ohmmeter should give a reading which you can compare to various charts online.

If it makes you feel better or worse I got a cherokee from my work that had a leak in its original rad, would get driven until the overheat light came on (no gauge) by idiots with no vested interest in the darn thing. A new rad, and a wicked lot of rust flushed out, and it survived the ordeal.

Also check your fuel level, below 1/4 tank the pickup can get air depending on how it's tilted. Can you get the fuel rail off easily and blow compressed air through it like a flute?

 

[fonty493]

12 volts with key to on, 14 at idle and a little over 14 at 2000.
It also starts ok, but the starter seems kinda slow, suspicious for a brand new battery. Now im looking for bad grounds. This Jeeps gonna drive me to an early grave.

 

[fonty493]

Well, I shoulda just done it in the first place...
Compression test revealed 40 PSI in #1 and 2 cylinders (they wouldn't even hold it for a second either) and 140-150 in the rest.
I'm still perplexed by the fact that there is no overheating, no coolant loss and no trace of coolant in the combustion chambers.
Any last minute ideas before it goes in for a new head gasket/valve job?

 

[mechtech2]

Clean BOTH ends of all cables. And where they seat - nice and shiny.

But a leakdown or compression test is next.
I am not 100% sure it is not ignition - not yet.
And check for vacuum lines/leaks on runners near the offending cylinders. Plus manifold leaks there.

 

[Gary Allan]

Originally Posted By: fonty493

I'm still perplexed by the fact that there is no overheating, no coolant loss and no trace of coolant in the combustion chambers.
Any last minute ideas before it goes in for a new head gasket/valve job?


Pull the plugs for those two cylinders. Put compressed air in one of them (loosen the rockers to close the valves). See if air comes out the other plug hole. That will tell you if the gasket is sound between cylinders.

Otherwise, you're not seeing any evidence of a head gasket failure.

That would lead me to conclude that those two cylinders have no ring seal.

Did you do a "wet" test on those cylinders? Gently squirt some oil into them and see if compression improves. If so, then you may try several of the piston soaks that are offered somewhere in BITOG history.

If the thing was more drivable, I'd definitely recommend a double dose Auto-Rx treatment.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1083082#Post1083082

 

[fonty493]

Its drivable, just idles terribly. Is there anywhere I can purchase Auto-Rx locally (Im in York, PA) or will I have to order it?

 

[fonty493]

No, I didn't wet test those cylinders, I will be checking that in the morning. Given the condition of the oil that was in that motor when i bought it a good engine cleaning is definitely in order. As far as the rings being hung up, im not sure. With the compression that low i would think i'd have an oil consumption issue. Ive only driven the thing a total of maybe 300 miles, but there has been no loss of oil or any oily residue on the back of the vehicle.

 

[Gary Allan]

Quote:
With the compression that low i would think i'd have an oil consumption issue. Ive only driven the thing a total of maybe 300 miles, but there has been no loss of oil or any oily residue on the back of the vehicle.


That's why I suggested the compressed air test to rule out the gasket between the cylinders (not "knowing" if there's a non-water outlet in there). If you hit compressed air to either of them with the valve cover off (remember, valves have to be loosened) and the drain holes start erupting ..that will tell you for sure that it's rings.

That may be more work then you are prepared for (although you've done a good bit here). google auto-rx.

 

[fonty493]

Well, its dark outside and rather than sitting here twitching, wishing i could do some more troubleshooting on the Jeep I decided to go give the evil empire 8 bucks for another can of Seafoam.
This time it did make a difference, and a rather significant one at that. Slightly better idle and drastically better acceleration. Its still not fixed, but much better. That gave me enough hope that I went ahead and ordered 3 bottles of Auto-Rx, 2 for a double dose and another for after the rinse cycle (being from Colorado I'm all for natural remedies). I'm going to let the Seafoam work its magic overnight and try the wet compression check in the morning. If that doesn't prove to be the problem I'll bug my neighbors till I find one with an air compressor and pull the valve cover again. Thanks for all your help guys, I appreciate all the responses.

 

[Gary Allan]

Please update us on how this shakes out.

Best of luck!

 

[mechtech2]

You put the Seafoam in the crankcase?

 

[fonty493]

Yes, I put most of the Seafoam in the crankcase and sprayed some in the throttle body, here are the results:
without adding oil to the cylinders, #1 stayed the same at 40psi and #2 went up to 60psi, neither would hold pressure however.
Added a few squirts of oil to those cylinders and #1 came up to 60 and #2 came up to 70 psi and both held pressure.
So it is rings after all, I'm sure glad I found this forum, I was about to go blow an obscene amount of money on a head gasket job i didn't need. Come on UPS guy, hurry up with my Auto-Rx!!! Thanks again for all the help, I'll let you know how the ARX treatment goes.