misfire and lean running I6

[nightrider]

I just bought an 89 Jeep Comanche 4x4 AT.It misses, spits and sputters. So far I have done a tune-up (plugs,wires,cap+rotor,o2 sensor). After I installed the o2 sensor it ran fine for a day and now its running as bad as it did before the tune-up. I pulled the plugs today and the engine is running lean. I also have some nasty milky substance oosing out of the pcv tube that goes from the valve cover to the top side of the air cleaner box. As of now I am stumped and I need help, any help would be appreciated.

[tjrubicon]

The "milky" substance is more than likely condensation. Check your oil dipstick to see if your oil is the same way, if so you have water in the oil. You might have bigger fish to fry if that is the case. Other than that, I'm not sure why it's running lean.

[rick]

Have you changed the oil? See if the oil is milky, indicating coolant in the oil. Sometimes it's hard to tell from just the dipstick. If not, the milky crud could just be condensation like tjrubicon says. Does it lose any coolant, or does it stay full? It sounds like possibly a bad head gasket. This could be allowing the coolant to get into the oil. Does it have any smoke out the pipe? If you are getting coolant into the cylinder you'll likely have white smoke. Another remote possibility is the brand new O2 sensor you bought bit the dust already. I would take it back and tell them it was bad.

[Dukes69]

Have you changed the oil? See if the oil is milky, indicating coolant in the oil. Sometimes it's hard to tell from just the dipstick. If not, the milky crud could just be condensation like tjrubicon says. Does it lose any coolant, or does it stay full? It sounds like possibly a bad head gasket. This could be allowing the coolant to get into the oil. Does it have any smoke out the pipe? If you are getting coolant into the cylinder you'll likely have white smoke. Another remote possibility is the brand new O2 sensor you bought bit the dust already. I would take it back and tell them it was bad.

This is exactly what I was thinking. Thanks for typing it for me!

[nightrider]

I changed the oil as soon as I got the truck home. The oil is not milky at all, its normal. I am not loosing any coolant and no smoke is coming out of the exhaust. I searched the web and found that there is a recall on the TPS and the PCV system on my truck. Do you guys know anything about those problems? Could a bad TPS sensor be causeing the engine to run lean? It is possible for the o2 sensor to be bad already, I will try returning it and see what happens. I am also thinking that I might have a bad fuel pump, it runs alright but maybe I am not getting enough pressure from the pump. I don't have a guage but I am gonna borrow one this weekend and see what I find.

[rick]

No problem.

Sincerely,

Dukes' secretary

On a more serious note:

The TPS would likely make it run like crud, but shouldn't result in a lean run condition because the ECM will adjust the IAC (or whatever they call it on these things) to at least attempt to control idle. If the TPS is bad and the ECM sees higher throttle opening, it should be enriching the mixture, not making it lean. Try unplugging the TPS and see what happens... On that same note, unplug the idle air controller and see what that does. If it runs worse, then you at least know they are doing something!

How about timing? Have you checked that? Is it vacuum advance or electronic? Check for vacuum leaks as well, that could be a contributor although the ECM should be able to adjust for some pretty big holes in the system at idle. How is the fuel mileage?

[Davisrats]

On my 1990 the IAC was sticking, it would idle low and die often, I took it off and cleaned it,,, it is good so far.

Ron

[nightrider]

yesterday I checked the fuel pressure and the compression and everything checked out ok. A friend thinks that it might be a vacume leak but the only way I know to test for that is to have a smoke machine and I currently don't have acces to one. I am also thinking it could be a problem with the EGR. Could it also be a worn timing chain that is causing a miss at cruising speeds?

[JeepJunkie]

yesterday I checked the fuel pressure and the compression and everything checked out ok. A friend thinks that it might be a vacume leak but the only way I know to test for that is to have a smoke machine and I currently don't have acces to one. I am also thinking it could be a problem with the EGR. Could it also be a worn timing chain that is causing a miss at cruising speeds?

how many miles on the engine?? i HIGHLY doubt the timing chain is worn/stretched enough to make it miss, im fairly sure the timing chain will last 200K+

[rick]

You can test for vacuum leaks with a can of ether, brake cleaner, carb cleaner, or WD-40. Just be sure to do it when you FIRST start the engine before it's hot... Or you could have more than a momentarily high idle to worry about... The engine will speed up when the WD gets sucked in through the vacuum leak. Spray very small amounts and try to limit the amount of "run off" that could drip down to a vacuum leak and mislead you. The lighter fluids (brake cleaner, ether) are best so you minimize this possibility. As far as the timing, I would start by checking the timing with a light. The chain will likely have little to no effect unless it is severely worn out, but you can get a rough idea of timing chain slack by bumping the throttle with the light on the indicator. The timing will jump up and down erratically if there is excessive slack. If it is vacuum advance, make sure you remove the vacuum line to the distributor and plug it. If it's electronic, I'm not sure the best way to defeat the advance mechanism - you would have to look at a wiring diagram or follow the instructions for setting initial timing in a service manual.

[nightrider]

its finally fixed

I finally broke down and took the truck to the repair shop(a very rare occurance) I used to work at and had them figure out the problem. I ran out of time and patience. I am going to school in Midland Michigan and I live in Lapeer Michigan. All my tools are in Lapeer and I needed a reliable vehicle to get me through the winter. Anyways it ended up being a problem with the distributer. There is a TSB on it and all I know at the moment is you have to pull the distributer out of the block and cut a hole in something. I'll have more info at a later date. Thanks for all the help anyways.

[chris142]

[QUOTE=nightrider] I searched the web and found that there is a recall on the TPS and the PCV system on my truck. QUOTE] The PCV system does not use a valve.

There's a small maybe 1/4 inch tube that goes from the intake manifold to the rear of the valvecover. At the valve cover it has a plastic piece that pushes into a gromet. This plastic piece has a small hole in it which regulates the PCV gasses.

It gets plugged up and won't allow the gasses to be sucked out.

I don't think this would cause your problem though.