Rough Idle And Missfire

[jeff]

So my comanche started missfiring really bad all over the board and running really rich. It has no power and going through gas like no other. All the grounds are cleaned and TPS are working as they should. So far the knock sensor has been replaced, the o2 sensor and the coolant temp sensor. Looked and found no vacumm leaks. Replaced the intake manifold gasket and still the same thing. Found a connecter to the CPS that was melted and just spliced in another and the o2 sensor wiring was all jacked up. Also the check engine light never came on through all this. Starting to think there might be a problem with the computer itself.

 

Its a 1988 4.0 auto 4x4. 

[Lee21490]

So my comanche started missfiring really bad all over the board and running really rich. It has no power and going through gas like no other. All the grounds are cleaned and TPS are working as they should. So far the knock sensor has been replaced, the o2 sensor and the coolant temp sensor. Looked and found no vacumm leaks. Replaced the intake manifold gasket and still the same thing. Found a connecter to the CPS that was melted and just spliced in another and the o2 sensor wiring was all jacked up. Also the check engine light never came on through all this. Starting to think there might be a problem with the computer itself.

 

Its a 1988 4.0 auto 4x4. 

Check out your MAP sensor. Would cause it to run like $#!& / lose all power.

[jeff]

The map sensor is working and the vacumm line is fine.     :???:

[ComancheKid45]

Condition of plugs/wires? Possible EGR issue?

 

The Renix era trucks do not have a CEL. So that would explain why 1 hasnt appeared for ya.

[jeff]

Plugs and wires are relatively new and in good shape. i will have to check into the EGR.

[JeffN]

make sure you have vacuum to the fuel pressure regulator, and make sure it isn't leaking fuel through the vacuum port on the regulator (a sure sign of a bad regulator)

[cruiser54]

The map sensor is working and the vacumm line is fine.     :???:

How was it determined that the MAP is fine?

[jeff]

bypassed the egr and still nothing. also replaced the coil and control module from ones out of the junk yard but still nothing.

[jeff]

A connecter for the cps to the harness was all melted and the o2 sensor wiring was messed up. I'm curious if some wires could have crossed and shorted out the ecu?

[cruiser54]

Doubtful. Shorted CPS doesn't fry the ECU. Nor does bad O2 sensor wiring.

 

Check the sensor ground circuit with a meter. It's responsible for proper grounding of the IAT, CTS, TPS, and MAP.

 

Spray along the MAP hose, especially near the throttle body, to see if it's leaking.

 

Again, how was it determined the MAP is "fine"?

[jeff]

well thanks for the help guys! i found the problem! no compression on cylinder 6! I'm pulling the engine tonight. 

[jeff]

Well the cause to no compression was the lack of a camshaft lobe. The lifter collapsed and wore out the cam shaft and push rod. Probably gunna end up getting a mild cam and maybe springs.

[jeff]

http://m.summitracing.com/parts/cca-cl68-232-4

I'm thinking this is the cam I want. What do you guys think?

[MJ_Milam]

http://m.summitracing.com/parts/cca-cl68-232-4

I'm thinking this is the cam I want. What do you guys think?

 

numbers look good. personally I'd look for something for a little shorter duration. I like a cam with a low lobe center I.E. 106 with a short duration and high lift. makes great torque but still leaves you with good idle quality but that's just my two cents. If that's the cam you go with I would like to see a write up about it and how well you liked it :cheers:

[jeff]

i will do. i ordered it yesterday. I'm hoping it will be in before the weekend so i can get it put together before the blessing of the jeeps this weekend. summit has been quick with past orders.