Engine Rough Idle Has Me Stumped, TY In Advance For Any Advice, Suggestions, etc.
grateful1
Jeeper
Greetings, I hope all is well! Truly thankful in advance for y'alls time...
1985 CJ7 AMC 258 i6 / 4.2l T-6, PS, PB. 131,000. New to us, bought last March. She runs strong with plenty of power through the gears but I cannot figure out this rough idle, blurbing, sputtering, etc. for the life of me. All sensors, computer, etc. are removed. Idle speed will not adjust below a certain rpm, I'm guessing about 900 (no tach). Most all T/S'ing done with air filter removed, but it's clean anyway. I’ve done the following so far, all with no improvement (not necessarily in order):
• Replaced spark plugs with correct type (forget brand & number), gap slightly increased for HEI
• Inspected/cleaned rotor and under dist cap, nothing really to clean. HEI and plug wires are essentially new. Ohm'd all HV ignition wires with trusty Fluke DMM anyway, all good
• Installed a relay to feed HEI full voltage directly from solenoid. Installed resistor pigtail on alternator to correct the run-on condition that developed after HEI rewire
• Checked for vacuum leaks. The only vacuum hose connections are to HEI and PB booster, hoses seem new and good shape, but I admit I have not replaced them.
- Replaced carb-to-adapter-to-manifold gaskets, ensured all properly fitted & secure.
- Sprayed carb cleaner around intake manifold and carb/manifold mount checking for leaks, seemed to get indication @ intake manifold. Not sure, could be my imagination engine RPM changed, hard to tell with rough idle
• Adjusted idle mixture screws with vacuum gauge to best possible with poor idle, exhaust smell not quote as strong after.
• Adjusted timing with old school method of advancing until hard start, then backing off. Timing was retarded prior to that, ran a little stronger and cooler after adjusting.
• Disassembled and thoroughly cleaned the Motorcraft 2150 carb which was already pretty clean but both emulsion tubes are cracked longitudinally. Poked out all passages with wire and carb cleaner
• Replaced 2150 with Amazon carb and set idle mixture
• Removed all vacuum hoses and plugged holes at the carb to eliminate leaks from the dist vac advance and PB booster (the only 2 vacuum hoses). Disclaimer-I'm pretty sure I actually did this, it's possible I may have only thought about doing it while I was at work or something and forgot, lol.
• Fuel pressure is 6-7lbs, checked with gauge. Mechanical fuel pump, single outlet fuel filter (no recirc back to tank). I thought perhaps pressure too high with no recirc line and so flooding. Removed fuel supply from pump to run/check just on what gas was in the bowl, no change. Ran great for 15 seconds through all RPM's except idle...
My next attempt MIGHT BE to replace intake manifold gasket, but hoped to make sure I’m not missing anything prior to that, as that seems like a huge PITB that I will regret.
I'm out of ideas and I am very grateful for any ideas y'all may have for anything I may have missed. Best wishes - Rob
1985 CJ7 AMC 258 i6 / 4.2l T-6, PS, PB. 131,000. New to us, bought last March. She runs strong with plenty of power through the gears but I cannot figure out this rough idle, blurbing, sputtering, etc. for the life of me. All sensors, computer, etc. are removed. Idle speed will not adjust below a certain rpm, I'm guessing about 900 (no tach). Most all T/S'ing done with air filter removed, but it's clean anyway. I’ve done the following so far, all with no improvement (not necessarily in order):
• Replaced spark plugs with correct type (forget brand & number), gap slightly increased for HEI
• Inspected/cleaned rotor and under dist cap, nothing really to clean. HEI and plug wires are essentially new. Ohm'd all HV ignition wires with trusty Fluke DMM anyway, all good
• Installed a relay to feed HEI full voltage directly from solenoid. Installed resistor pigtail on alternator to correct the run-on condition that developed after HEI rewire
• Checked for vacuum leaks. The only vacuum hose connections are to HEI and PB booster, hoses seem new and good shape, but I admit I have not replaced them.
- Replaced carb-to-adapter-to-manifold gaskets, ensured all properly fitted & secure.
- Sprayed carb cleaner around intake manifold and carb/manifold mount checking for leaks, seemed to get indication @ intake manifold. Not sure, could be my imagination engine RPM changed, hard to tell with rough idle
• Adjusted idle mixture screws with vacuum gauge to best possible with poor idle, exhaust smell not quote as strong after.
• Adjusted timing with old school method of advancing until hard start, then backing off. Timing was retarded prior to that, ran a little stronger and cooler after adjusting.
• Disassembled and thoroughly cleaned the Motorcraft 2150 carb which was already pretty clean but both emulsion tubes are cracked longitudinally. Poked out all passages with wire and carb cleaner
• Replaced 2150 with Amazon carb and set idle mixture
• Removed all vacuum hoses and plugged holes at the carb to eliminate leaks from the dist vac advance and PB booster (the only 2 vacuum hoses). Disclaimer-I'm pretty sure I actually did this, it's possible I may have only thought about doing it while I was at work or something and forgot, lol.
• Fuel pressure is 6-7lbs, checked with gauge. Mechanical fuel pump, single outlet fuel filter (no recirc back to tank). I thought perhaps pressure too high with no recirc line and so flooding. Removed fuel supply from pump to run/check just on what gas was in the bowl, no change. Ran great for 15 seconds through all RPM's except idle...
My next attempt MIGHT BE to replace intake manifold gasket, but hoped to make sure I’m not missing anything prior to that, as that seems like a huge PITB that I will regret.
I'm out of ideas and I am very grateful for any ideas y'all may have for anything I may have missed. Best wishes - Rob
