91 running bad some times

[dave ramsey]

My 91 explorer starts running bad after you drive it along time or up a hill. when you put it in park it idles high and a little rough if I let it idle a minute it will idle back down but rough. when put in gear will kill motor. the exhaust sounds like it is half clogged.when you let it cool down a few hours it runs ok again. i'm told it has a bad catalytic converter. how do you tell? and does anyone have any ideas? thanks for any help.

 

[Sams01XplrSprt]

welcome dave

 

[Dopler174]

Bad Cat is what I was thinking as I was reading your post.

 

[marragtop]

Have you plulled the codes? Their may codes stored even if the CEL is out. You might also try cleaning the IAC. There are many posts on that in the forum.

 

[MrShorty]

two basic tests for clogged cats:

vacuum test: put a vacuum gauge on the engine. low to no vacuum (especially with increasing engine speed) suggests the possibility of a clogged/restricted exhaust system.

temperature test: a temperature sensor downstream of the cat should read much hotter than a temperature sensor upstream of the cat.

It seems that most muffler shops will test a cat for free (if you trust them), in hopes of selling a new one.

 

[huntman58]

My 91 explorer starts running bad after you drive it along time or up a hill. when you put it in park it idles high and a little rough if I let it idle a minute it will idle back down but rough. when put in gear will kill motor. the exhaust sounds like it is half clogged.when you let it cool down a few hours it runs ok again. i'm told it has a bad catalytic converter. how do you tell? and does anyone have any ideas? thanks for any help.

My 93 is doing some what the same. No fast idle if any thing a touch low. You can hear it popping in the exhaust and going up hill it is missing but only at around 200 to 2500 rpms. Get over the rpms and runs like a top. Go under and or flat ground and runs okay also may have a slight miss but nothing you will really hear or feel. I do have codes but only for KOEO they are 172 and 176 .I know that is the O2's and I take it both of them but could that really do it that bad? Or am I to looking at a cat? My cat was replaced about 6 years ago and around 80,000 miles or there about if not less. It is a one cat high flow replacement Okayed by the Calif air board at the time. I also am just passing smog checks here all at the low speed test points and always just at the NOx gas end. I also if idling for a some what long time as in traffic or long light say two in a row will get a CEL it will go out when I have driven for about 1 to 2 miles at speeds of 45 or higher so I ask again does this sound like a cat also along with the O2's?

 

[Dean403]

Perhaps a bit simplistic, but my rough running problems were solved entirely with a new set of plugs and wires. The wires are the critical part apparently.

 

[MrShorty]

I do have codes but only for KOEO they are 172 and 176 .I know that is the O2's and I take it both of them but could that really do it that bad? Or am I to looking at a cat?

Nothing in your brief description of symptoms suggests a cat to me. The codes (technically, they are CM codes, since O2 sensors can't be tested KOEO) point to a low O2 sensor voltage. By themselves, we can't say whether the sensors are bad or something else, but, especially if this is a new development, I wouldn't expect both sensors to go bad at the same time.

At this point, I would focus on the O2 sensor code diagnosis. By the book, the first test is a fuel pressure test. I'd also do a fairly thorough look for vacuum leaks. I would also run the KOER test to see if I got equivalent codes from the KOER test.

 

[huntman58]

Mr. shorty
I did run the KOER test and came up with nothing. FPR okay. Both pressure and leak down. Flow of gas is great also. Seams to be all electric or a possible mechanical problem but I do not have any way to check the compression at this point. All vac lines seam okay but again no vac gage right now as some one needed them more them me and never returned them. I believe the O2’s are what is throwing the CEL when it dose come on as brief as it is and as I said only at idle or very slow speed. I do not know if they went out together or if one went then the other as I have been fighting a slight miss on and off for about a year now. I just got back from a 1,00 mile trip in 36 hours and the miss got a lot more noticeable mainly going up hill and under load ( low rpm's around 2,00 to 2500 and in Over drive) it would also do it some what on the flats also but almost were you would not know it . I have pulled the plug and # 5 is dead and fouled out big time as in not firing at all. Looks to have been this way for a bit also. The rest look almost normal but with a slight lean look to them if any thing as there very light tan to almost white in color. I also checked the coil pack and found the prim are all okay as in ohms all in spec but the secondary (tower to tower) is out of spec some what on the high end. Wires check out fine. We are replacing the O2's plugs and coil pack and will see what it dose then. Just find it funny one dead plug but maybe that was from the get go as the miss was there then if I remember back that far now days. Dam hates getting old LOL. Any hoot any ideas are welcomed and well maybe I should start a new thread and not hijack this one.

 

[MrShorty]

I did run the KOER test and came up with nothing.

Meaning "nothing" nothing or "111 pass" nothing? If it's the latter, it suggests that the problem might be intermittent, which could make it more difficult to diagnose.

I have pulled the plug and # 5 is dead and fouled out big time as in not firing at all.

Fouling of the #5 plug strongly suggests to me an intake gasket problem. A lot of the times it seems that an intake gasket leak seems to hit #5 worst. A leaking intake gasket can allow excess air in (this is often associated with ping/spark knock), and/or allow oil in, and/or allow coolant into the cylinder. Coolant will poison O2 sensors. So any one of these things (vacuum leak at intake gasket, poisoned O2 sensors, or misfiring cylinder due to fouled plug) could, individually or in combination, trigger the O2 sensor code. So, at this point, I would suggest you figure out why #5 is getting fouled, and see if that resolves the issues.

Often, these intake gasket issues are simply due to bolts that come loose, and they can sometimes be resolved by simply going through and tightening the bolts down. Other times, the gasket needs to be replaced.

And, of course, there are other possibilities beyond intake gasket, for these issues.

 

[huntman58]

Well I did check the intake gasket and there seams to be no leaking around it. Checked it by spraying some cleaner around it and no pick up or drop in the motor at all. The KOER codes were the 111 so you were right it was some thing. I pulled the o2's to day and both were a tan color and no black soot at all but as we all know no way to see in side of them. Changed the plugs also and this time wrote down the day and miles so I have abettor idea how long it runs between. It still has a miss some what but what I did forget to say is when I did the KOER test on the cylinders it showed 4 instead of 6. Now it is showing 6 as it should. I will have a new coil pack in a day or so as it is also out of spec so I am replacing it. The truck is running better now and a bit smothers. So far I am stumped what to look at or test any farther. I have been working on cars and trucks for almost 40 years on and off from the time I was a kid with my dad and then on my own. Learned a lot on the way but each day I still learn more. I just wish the body would still let me work on them as I want to but if it did I could work again also and afford to do what I want. it is a head removal job or a full out rebuild I am sad to say this truck will be gone for me but I have had my share of good times with it I just can not put in that kind of money at this time o well some one will get a good project!

 

[MrShorty]

So far I am stumped what to look at or test any farther.

Did you check the intake bolts to see if they were tight? If it is leaking coolant into the cylinder, it will likely poison those new O2 sensors, and you'll need to replace them again. It only takes a few minutes to put a socket on most of the bolts and see if they are loose.

 

[huntman58]

ya know I forgot to say that but after I sprayed around and nothing happened I still got the wrench out and hit them nuts just to make shore they were all nice and tight and well they were not a loose on in the bunch. I am starting to believe in my tool box sticker the more I work on this thing it say " I am mechanically inclined I can screw any thing up " Mr. shorty thanks for all the hints and help you have given my self and I am most sure many others as some times just like forgetting to write it down here we all have brain farts now and then so a good mind jog helps and in may case is welcomed so thanks for all your try’s

 

[MrShorty]

So the lower intake is tight. The gasket may still be bad, but that's kind of hard to diagnose without taking it apart.

A cylinder balance test might be interesting, while the plugs are still clean, to see if there's any reason to suspect other causes of misfires (bad valves, head gasket, injector, etc.). A compression test - especially on #5 might also be warranted to see if there are any issues that can be identified.

Is the engine using coolant or oil?