Comanchejess Posted July 25, 2019 Share Posted July 25, 2019 Hey there everybody. My 1987 Comanche, (some 1988 parts from the factory) won't stay running. It starts fine every time, but it will not stay started. It's misfiring, and if I can keep it going long enough to get somewhere it bogs down when I am accelerating after braking or coming out of a turn. This is my daily driver, and currently the only vehicle I have that I can drive legally in my state, so any advice here would help. I've ruled out fuel delivery as an issue, as it is getting fuel. Link to comment Share on other sites More sharing options...
13 Legion Posted July 25, 2019 Share Posted July 25, 2019 A little more info...2.5, 4.0? Last time it’s had a tuneup? Link to comment Share on other sites More sharing options...
Comanchejess Posted July 25, 2019 Author Share Posted July 25, 2019 4.0, *I've* never completed a tune-up, so at least 2 years since I've owned it. I just replaced the timing chain/timing chain cover/harmonic balancer two weeks ago. could I need to adjust timing at the distributor? I wouldn't think so since it was running fine before two days ago. Link to comment Share on other sites More sharing options...
87MJTIM Posted July 25, 2019 Share Posted July 25, 2019 Does it start and run if you give it gas? if so, could be the IAC. Link to comment Share on other sites More sharing options...
Comanchejess Posted July 25, 2019 Author Share Posted July 25, 2019 6 minutes ago, 87MJTIM said: Does it start and run if you give it gas? if so, could be the IAC. It will start without giving it gas, however, once it starts going, it'll go, I can't keep it running. Link to comment Share on other sites More sharing options...
DirtyComanche Posted July 26, 2019 Share Posted July 26, 2019 Did this start when you replaced the timing chain? Link to comment Share on other sites More sharing options...
Pete M Posted July 26, 2019 Share Posted July 26, 2019 there are sensor testing procedures in the link in my sig. timing is controlled by the computer. Link to comment Share on other sites More sharing options...
Comanchejess Posted July 26, 2019 Author Share Posted July 26, 2019 2 hours ago, DirtyComanche said: Did this start when you replaced the timing chain? No, it was fine up until Tuesday. Link to comment Share on other sites More sharing options...
Comanchejess Posted July 26, 2019 Author Share Posted July 26, 2019 54 minutes ago, Pete M said: there are sensor testing procedures in the link in my sig. timing is controlled by the computer. Thanks Pete. Link to comment Share on other sites More sharing options...
Pete M Posted July 26, 2019 Share Posted July 26, 2019 just to expand on the second bit, technically the timing can be "off" (for example if the distributor or timing belt is off a tooth) but you cannot tweak it a degree or two like older engines as the computer will always try to put it where it wants it. Link to comment Share on other sites More sharing options...
Comanchejess Posted July 26, 2019 Author Share Posted July 26, 2019 37 minutes ago, Pete M said: just to expand on the second bit, technically the timing can be "off" (for example if the distributor or timing belt is off a tooth) but you cannot tweak it a degree or two like older engines as the computer will always try to put it where it wants it. so if I replace the distributor, and time that correctly id still have to change a computer setting? or is there no way to fix timing at all? Link to comment Share on other sites More sharing options...
Pete M Posted July 26, 2019 Share Posted July 26, 2019 there is no way to control the timing (except for the CPS mod that ticks the computer and gives it a tiny bit of advance). like any modern FI system, the computer controls the timing for you and tweaks in in real-time for the best results. but computer failures are rare. more common is a simple sensor gone bad, fuel pumps, vacuum leaks, or wiring issues (grounds are a real problem). For example, the fuel pump grounds behind the taillight and corrosion there can cause all sorts of wonky things to happen. If you haven't yet, see the link in my signature and find Cruiser's MJ tips. most are wiring related. Link to comment Share on other sites More sharing options...
Comanchejess Posted July 26, 2019 Author Share Posted July 26, 2019 29 minutes ago, Pete M said: there is no way to control the timing (except for the CPS mod that ticks the computer and gives it a tiny bit of advance). like any modern FI system, the computer controls the timing for you and tweaks in in real-time for the best results. but computer failures are rare. more common is a simple sensor gone bad, fuel pumps, vacuum leaks, or wiring issues (grounds are a real problem). For example, the fuel pump grounds behind the taillight and corrosion there can cause all sorts of wonky things to happen. If you haven't yet, see the link in my signature and find Cruiser's MJ tips. most are wiring related. I was reading through some of your links... there's lots of interesting troubleshooting (or just plain interesting) stuff there. I have a lot of stuff to check out in the morning ;0.. hopefully *something works before I have to start spending money.. Link to comment Share on other sites More sharing options...
Pete M Posted July 26, 2019 Share Posted July 26, 2019 every single applicable fix (not all years have the same issues) from Cruiser needs to be done to every MJ so after you find the problem at hand, don't stop. Link to comment Share on other sites More sharing options...
DirtyComanche Posted July 26, 2019 Share Posted July 26, 2019 Pull the distributor cap and check the contacts and rotor, clean with contact cleaner or similar and buff any corrosion off. Check the spark plug wires for cracks, damage or corrosion. Pull the plugs and check them for gap and condition. Fire it up and use brake cleaner (non-chlorinated pure heptane is best) to check for vacuum leaks. Then check sensors, grounds, fuel pressure, etc. Link to comment Share on other sites More sharing options...
Manche757 Posted July 26, 2019 Share Posted July 26, 2019 15 hours ago, Comanchejess said: I wouldn't think so since it was running fine before two days ago. By chance did you fill up your tank with some bad gas just before it started? Link to comment Share on other sites More sharing options...
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