85 Cherokee intermittant loss of power

[Tornillo]

85 Cherokee 2.8 L V6 (Chevy Eng) 185m Miles. 5 speed standard trans. This vehicle seems to have a mind of it's own. Starts good and runs pretty good first 6 or 8 minutes, on chilly days when temp is in 40's. I can get down the road at speeds up to about 60mph ( I do not drive fast anymore since I am retired I see no reason to be in a hurry). After 6 or 7 minutes vehicle looses power and gets slower and slower until I am going maybe 25MPH I have to keep downshifting just to keep going. When I push down on the accelerator It does not respond at all. It is as if someone cut the fuel off.
The first time this happened I pulled over to the roadside and shut off the engine. It was chilly out and I really did not want to work on the engine. did not know what caused the problem anyhow. After maybe two or three minutes I thought I might just try to get back home if it would run. It started right up and believe it or not it ran good back to the house. Since that time The solution has been to turn off the engine let it set for three or four minutes and it will start right up and go on down the road. The problem has gotten somewhat worse. Usually after the first incident in the day I do not seem to have a problem but it has progressed . Now after it begans to run OK there will be times when I have gone as far as a hundred miles and then it will do the same thing again. and it may or may not run better after it sits for a few minutes. There does not seem to be any particular set of circumstances to cause this. In warm weather when temp is up in 70's or 80's the Jeep does it's thing after about 3 or 4 minutes instead of 7 or 8. Again not every time. Last week I drove a 150 mile round trip and it ran OK. Over the last 6 months I have replace all plugs, new spark plug wires, new distrib cap and new ECM. This has helped it run somewhat better but it did not cure the problem. I am on fixed income and I do like to work on my own jeep. I took it to a small garage and the mechanic cannot find a problem, I don't think he is too up on 85 Jeeps. One other little problem is that the CELight comes on usually when I down shift to go down hill it stays on for a few minutes then gois out after I resume normal driving. The mechanic I took it too suggested I replace all the sensors. Is this spendy? How many? I do have a Motors repair manual for this model. Any suggestions would be greatly appreciated. You have a terrific site here. Thanks.

 

[XJNick]

So, it only happens when the engine is hot? If so, check the 02 sensor, coolant temp. sensor (CTS), and Mass air temp. sensor (MAT). Also might be worth checking out the crankshaft position sensor (CPS).

Also, a shop manual or subscription to AllData would be extremely helpful :mrgreen:

-Nick :!:[/url]

 

[MudderChuck]

Could be many things, I´m not real familiar with the Chev. V-6 per say. Every motor seems to have it´s classic sicknesses.
Some general mechanicl knowledge that might be helpful. Most of the sensors don´t kick in, until the motor reaches operating temp. (around 140 F.) then the computer switches to a full sensor controlled mode.
It could be a failing sensor of some type (like XJ suggested), could also be a faulty contact in a connector. A diagnostic test ,may be helpful and often not really expensive. Look in your book and see if you can retrieve the trouble codes from your computer, I´m assuming your motor is a throttle body injector; in 88 Chevs. the codes could be retrieved, don´t know for sure about the 86 Chev.
I´d unplug (carefully) every handy connector and have a look inside for moisture and/or corrosion.
I´d check the wiring real close, for rubbing and/or chaffing, paying special attention to any wire running by the exhast system. Don´t think I have ever checked mine, I didin´t find something.
Take the radiator cap off, put a pan under the Jeep just in case it overflows some, and run it up to operating temp. Look for bubbles in the cooling water, could be an intermittant leak, coolant into a cylinder or two. Chev´s are known for this. Does your motor ever overheat or have any unexplained loss of coolant?
Change the fuel filter. Run a can or two of fuel injector cleaner/gas tank drier through the fuel system. I´ve picked up a few loads of watered gas, that will cause this problem, usually a change of gas stations will cure it.
I once had a leaf in my gas tank (no locking gas cap, kids) that would occasionally float up and shut of the fuel, drove me nuts, before I finally dropped the tank and cleaned it out.
Faulty fuel pumps with usually start to act up, at high speeds or higher RPM´s and get progressively worse.

 

[Tornillo]

So, it only happens when the engine is hot? If so, check the 02 sensor, coolant temp. sensor (CTS), and Mass air temp. sensor (MAT). Also might be worth checking out the crankshaft position sensor (CPS).

Also, a shop manual or subscription to AllData would be extremely helpful :mrgreen:

-Nick :!:[/url]

Thanks Nick for input. I do have some time and I guess I will be checking some sensors. I did check out AllData Site and it really gets into some depth, guess I'll be joining that. Thanks again and I will let you know if I get the Jeep going good again.
Glen

 

[Tornillo]

Could be many things, I´m not real familiar with the Chev. V-6 per say. Every motor seems to have it´s classic sicknesses.
Some general mechanicl knowledge that might be helpful. Most of the sensors don´t kick in, until the motor reaches operating temp. (around 140 F.) then the computer switches to a full sensor controlled mode.
It could be a failing sensor of some type (like XJ suggested), could also be a faulty contact in a connector. A diagnostic test ,may be helpful and often not really expensive. Look in your book and see if you can retrieve the trouble codes from your computer, I´m assuming your motor is a throttle body injector; in 88 Chevs. the codes could be retrieved, don´t know for sure about the 86 Chev.
I´d unplug (carefully) every handy connector and have a look inside for moisture and/or corrosion.
I´d check the wiring real close, for rubbing and/or chaffing, paying special attention to any wire running by the exhast system. Don´t think I have ever checked mine, I didin´t find something.
Take the radiator cap off, put a pan under the Jeep just in case it overflows some, and run it up to operating temp. Look for bubbles in the cooling water, could be an intermittant leak, coolant into a cylinder or two. Chev´s are known for this. Does your motor ever overheat or have any unexplained loss of coolant?
Change the fuel filter. Run a can or two of fuel injector cleaner/gas tank drier through the fuel system. I´ve picked up a few loads of watered gas, that will cause this problem, usually a change of gas stations will cure it.
I once had a leaf in my gas tank (no locking gas cap, kids) that would occasionally float up and shut of the fuel, drove me nuts, before I finally dropped the tank and cleaned it out.
Faulty fuel pumps with usually start to act up, at high speeds or higher RPM´s and get progressively worse.

Thanks MudderChuck, I do appreciate your suggestions. Since I have a lot more time than money guess I'll be doing some checking and testing. I just spent the last two days cleaning out and making some room in my garage so I could put the Jeep in there and have a warmer and dry place to work. I will let you know what I found out when I find out. Thanks again
Glen

 

[MudderChuck]

Steering Stabilizer Question

I´m going through the same thing, with mine now, just about in the same boat as you (more time than money). I picked up a 88 XJ (low mileage) from the dealer, that needed more work than it´s worth.
I´m slowly, picking my way, through the electical system, plugging up the leaks in the drivetrain and replacing worn out parts.
Checking out all the connectors, gonna start on the grounds and the rest of the connectors this week.
Mine has a stumble at 2000 RPM, that seems to be getting better, but seems to always return. Really beginning to think it´s a loose ground somewhere, seems to run better in the rain or when it´s wet.

Good luck, if you run out of things to look at, XJNick or some of us on the board, can probably supply an endless line of possibilities. Heck if it was easy, it would already be fixed. I get a kick, out of finding things the dealer has given up on, mostly it just requires perserverance. To often the dealer replaces sensors (sometimes the problem) and ignores basic mechanics or wiring problems.

 

[MudderChuck]

Was looking through a book and came across, retreving the trouble codes for the 80´s V-6. Said the trouble codes could be retrieved at the check engine light, by jumping the 6 and 7 pins at the diagnostic port (15 pin connector). Looks like a standard GM code list, code 12 is normal (one blink then two) all others mean something is wrong. It said to drive the Jeep at operating temp. and on the highway at half throttle, to retrieve some codes. I have a copy of the list if you find something.

 

[Tornillo]

Thanks MudderChuck, I got a Chiltons Manual for the 85 and was reading the same thing last night, it tells me what all the codes mean. I am going to try that maybe tomorrow. Had to run mama around today and didn't get in much work time. Thanks again