landlubber Posted January 3, 2015 Share Posted January 3, 2015 I have a 1991 comanche 4.0l that I have been driving around with no drivability issues since I got it, but the last few days it has developed some sort of misfire.It feels like someone is turning the key on and off, or like a revlimiter or a lope tune even. It will do it at idle, revved up, driving around. Seems to be mostly random but if you rev it up a little and snap off the gas it seems to initiate it.I am lost at this point. I replaced the fuel filter and it has very new cap/rotor/wires. fuel pressure is 30ish/idle and 40ish/vac line off regulator. Any ideas or input is appreciated. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 3, 2015 Share Posted January 3, 2015 Distributor sync sensor and/or CPS. And there's no reliable way you can test either except by replacement. Did you check for codes yet? Link to comment Share on other sites More sharing options...
landlubber Posted January 3, 2015 Author Share Posted January 3, 2015 I should mention that it does not backfire when it cuts in and out. Also it always starts fine and runs fine more often than not.I checked for codes but I think I created some of them, I will go and check it again. edit: The only codes it pulled were ones caused by me testing things. 12 - battery disconnected (just got a new one) 13 - map sensor 33 - a/c removed 55 I have a few spare cps' kicking around. Worth it to swap one in just to see if it helps? Link to comment Share on other sites More sharing options...
landlubber Posted January 4, 2015 Author Share Posted January 4, 2015 It was acting up significantly more than normal when I drove it up to the barn - and it did backfire if you layed into the gas pedal when it was sputtering/missing. all the cps I have are renix era, I pulled it out anyways and cleaned it. I also pulled apart the distributor and blew it out with compressed air, cleaned a fair amount of corrosion off the "pulse ring" and double checked timing. it seems to work now, It may just be toying with me, drove home fine though. The distributor seemed to have a lot more play in it than I am used to, maybe 10 degrees of slop at the tip of the rotor - is that normal? Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 4, 2015 Share Posted January 4, 2015 I'd clear the codes by disconnecting the battery for a few minutes then reconnect, start it up for a minute, shut-off, then check the codes again. Make sure the #13 MAP code is gone. The HO distributors all have some play, so I don't think that's the problem. 10* may be a bit excessive though. But drive it for awhile, maybe you found the problem cause. If not, in order to change the pulse ring (sync sensor) on the 91 distributor you have to pull the distributor, drive out the drive gear roll pin and tear down the distributor to replace it. When mine went out, I replaced the whole distributor with one from a 94-97 4.0. It's better because if the sync sensor goes out again you don't have to pull out the distributor to change it; it's all done from the top. Then rebuilt the 91 dizzy at your leisure for a spare. Also make sure the contacts on the round CPS 3-pin connector hanging from the fuel rail are clean and shiny before replacing the CPS. On the CPS I would not use anything other than a genuine Mopar OEM sensor; been burned a couple of times with the aftermarket junk. 4.0 distributor info: http://www.xjtalk.com/showthread.php?t=9111 Link to comment Share on other sites More sharing options...
landlubber Posted January 4, 2015 Author Share Posted January 4, 2015 Thanks for the info. seems to be working for now. I cleared the codes and back down to 12, 33, 55. Link to comment Share on other sites More sharing options...
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