TFGgarage

1986 2.5TBI AX4 with 4wd I haven't wrenched on my Comanche for a while because I still can't figure out why it randomly dies on me. It will idle until its out of gas but if you start driving it'll randomly die on me, could die before i get out of the driveway or 5 miles down the road and when i cycle the key it will run for another minute or two before shutting off again. I have spark and fuel until the engine stops turning. Had a fancy diag guy come out with an oscilloscope and he also checked all the sensors but that got me no where. Ive also replaced/cleaned all of the grounds and electrical connections that Cruiser recommends but still no improvement. Fuel Pressure is steady 15psi at the TBI. I keep running into dead ends on the electrical system and I want to yank it all out and make it carbureted like god intended. I was thinking about pulling out the AMC 2.5 and throwing in a GM 2.5 so i can get a vacuum advance distributor and an intake manifold for a carb. I wanted to see if anyone has any better ideas or if anyone has done something similar. I am newish to posting on forums so if yall have any links for old threads on this topic please send them my way! Thank yall for all the help so far, can't wait to get this MJ back on the road!

No test drive yet, but for the first time in a few weeks she finally idled long enough to get up to temp! Test drive coming soon

Thank you so much cruiser! I keep seeing your stuff pop up all over and it’s a tremendous help.

Just wanted to know if anyone has posted a list or could help direct me to a list of grounds on the 2.5L, 4 speed manual Comanche. Ran some diag on my MJ today trying to figure out why it keeps dying. All the sensors and the TBI are acting mostly normal. The computer wizard came in and said for whatever reason the injector isn’t opening. It’s totally random and we’ve swapped the injector and everything only to have the same issues. Computer wizard says he believes we are having trouble with my ECU or possibly a bad ground. I want to make 100% sure it isn’t a ground fault causing my engine to act up before I go and pay for a new computer. Still newish to forums and having trouble navigating so any help is more than appreciated!

New fuel pump, sending unit, sock, filter, fresh gas and some injector cleaner for gits and shiggles. I used a tractor oil pressure gauge that reads up to 30lbs and had the right thread to fit the testing port on the TBI, was reading 11 lbs. Should have included that in the original post! Currently trying to figure out the cause of that but even when idling it’s running at 11 lbs so the gauge could be off

My first ever forum post, advice is more than appreciated! Gotta provide a tiny bit of history. This Comanche had been sitting about 12 years till I got around to it due to needing new floor boards and running extremely rich. I cleaned the ground on the firewall, replaced MAF and 02 sensors, oil was flushed then changed, flushed all other fluids, and it ran like a dream for a couple weeks till I did some more work on it. I replaced cap and rotor, ignition control module, coil, plugs, wires, some broken vacuum lines, power steering and alternator/generator belts, newish (2 year old and unused) recharged battery, PCV valve, coolant bypass hose and finally the fitting on intake manifold. When I went to flush and bleed the coolant after all that, it started up and idled absolutely perfect like nothing happened. After about 5 minutes it shut off but it started right back up. Finished bleeding the coolant and went to back it out of my shop and it died as soon as it was out the door and would start but die immediately after. I ordered and installed a new fuel pump and sending unit from “justgastanks.com”. Once I did that itll run for a couple minutes and then die and won’t idle again unless I leave it be for a while but will start and instantly die like before. I then replaced the CPS, fuel pump relay and 02 sensor heater relay with “URO parts” brand from autozone and I cleaned the multi plugs associated with the relays. Now I can reliably start it by priming the fuel pump three times using the ignition, and it’ll start up for a couple minutes then dies but usually starts up after priming the fuel pump a couple times again. Currently cleaning the ground behind drivers tail lamp and removing the trailer harness that some one botched (what are you towing with an anaemic 2.5 anyway). TLDR MJ randomly dies after lots of work.