88 Beast

Thanks for the input guys. Tried suggestions and still blew fuse. Removed ac relay and no blown fuse. replaced with a spare relay, Good to go! Thanks again. Now onto other joys, noisy wheel bearing, worn u joints, etc., etc.

After many months of sitting because of engine electrical issue frustration, finally got the old girl up and running again this week (replaced ecm). Now having problem with blower motor fuse blowing in ac or defrost position. On vent and heat, works fine. Coincidence? I know the ac is tied into defrost to dehumidify the air in defrost mode. Any ideas? Was going to remove ac relay to try and eliminate that circuit but don't know which relay of the four on passenger side fender. Also now after sitting a few minutes with engine off, heater mode control looses vacuum and goes into defrost even though the mode switch is in vent or heat until engine is started and vacuum builds then returns to set mode. Any help would be great.

Unplug dizzy while engine running? With it unplugged and engine off, I am getting correct ecm input voltage to dizzy, 7v. I repaired and soldered existing sensor ground crimps. This did fix the flucuation in the harness. Did not eliminate single wire and solder all together. By doing what you suggest, this eliminates going through C101, correct? I can do that no problem.

Nope. I did all of Cruiser's wiring updates to the grounds, C101 cleaned, coil contacts cleaned,CPS cks. out,TPS adjusted correctly. Did have serious flucuations at the two ground circuits in the harness. Runs great for 35-45 mins. then engine temp starts to rise above normal. It starts to miss, backfire and eventually die. During my t/s with Renix Diagnostic info, sync sensor signal voltage test, key on w/engine off,I get varing readings. Should be 5v. I'll get 2v one time, 4.9v another and sometimes 7v, which is the input voltage from ECM. I've checked the harness from the sync connetor to the ecm and cks. out good. Could this be my problem. Has anyone taken this reading before? If so, could you let me know what you have. Getting a bit discouraged. Maybe ICM, dist.? Coil replaced last year but you never know. Don't want to start throwing parts at it. Need help.

Well folks, thought I had fixed. Ran great for four days then back to it's old tricks. Weekend before last gave it a full tune up. Ran good for a day and then left me on the side of the road. Bucking real bad, backfiring I think through throttle body, then died. This time, smoke from under hood. Popped hood, engine not overheated or boiling over but could feel excessive heat and smell of hot metal. Felt tailpipe tip and was very hot. Plugged cat I thought? Would crank but not start. Had to sit on side of road for 45 min. before it would start. This is what usually happens. Let it sit then runs good. Got it home and this past weekend removed cat. Drove to work today and started doing it's thing about a mile from work but didn't die.Damn it! Drove home, ran good until almost home. Could O2 sensor or CPS cause this intermitent problem? Both were replaced about 3 years ago. This is really starting to get on my nerves as I've got ujoints and a unit bearing that needs replaced but I've got to figure this out first. Any ideas?

After letting it sit a week, back on it today. Started fine and had good steady fuel pressure and moved into garage. Cleaned C101 connector, was full of nasty. Ran in garage for half hour with fuel pressure gauge and VOM backprobed into fuel pump connector,all good. Then took on 60 mile, 1 hour drive. Got back to the house and let it idle for a bit. Fuel press. and voltage good. Then stumbled once but didn't die and smoothed out. I guess I'll drive it this week see what happens. Wish me luck. Also I want to run fuel pump back through resister as it is noisier without, I'm getting about 9 v. to pump with resister. Is this about right?

Replaced cap about a month ago and fuel filter replaced prior to todays test drive. Been running in garage now for awhile and everything seems okay again. This is the first real problem with with this truck since I've had it 9 years now. I checked the MAP sensor per t/s guide I got online for Renix FI some time ago. The output voltage with key on/engine off is about 1 volt below spec. @ 3.6 v., should be 4.5-5v. Guide says to replace Map sensor but with engine running, output voltage @ idle is within spec. @ 1.1 v. Spec is .5 - 1.5v. Could being that 1v below spec cause my problem? Gotta get this thing figured out.

Just got back from 35 min.test drive. Ran great. Pulled into garage, let it idle. Removed tank cap to listen to pump, put back on. Couple of seconds later, started running like crap and died. Coincidence? Put fuel press. gauge on and started back up. Fuel pressure good but running bad. Checked for loose electrical connections. All seem okay. What now?

Working on it again now as we speak. Replaced pump last weekend. Ran it in garage for about 30 minutes, seemed to have good fuel psi. Took it for a drive and it died about a mile down the road. Made it home after a dozen stall outs. Fuel just dribbling from test valve. Pissed off and let it sit until today. Bought fuel press.gauge. Pressure reads good, 32 psi with vacuum hooked to reg. and 40 psi without. Have been running engine for 45 mins. at different RPM and press. holding good. Checked pressure leakdown at regulator, psi does drop below maximum allowable psi. in 30 min. with engine off. My question is, would this cause fuel press to drop off to next to nothing while driving? I'm about to take out for test drive again.

I think my fuel pump is going out. 88 MJ, 4.0 L, Left me on the side of the road yesterday. Started back up, ran for a minute then sputtered and died. Did some prilimary checks. Getting power through resistor, can hear pump running when engine sputtering. Haven't checked pump ground or pressure yet, but did have alittle pressure in fuel rail after it dies when I press schrader valve. Will do more t/s this weekend. Question is does anyone have p/n of correct pump as I've read here of pumps being for Cherokee's and not MJ. This is my DD so I want to get the right one the first time. I usually get my parts through NAPA and they list 3 or 4 different p/n's. Any help would be great. Thanks.

Check the coil too. I fought a miss and stall at low idle longer than I'd like to admit. Mine got worse after a rain or car wash. Turned out the coil was arcing to the metal case around it.

Check you harmonic balancer. Mine did the same ticking a few years back. The rubber was coming apart and allowing the outer hub to rub on the front cover. With yours ticking in gear and not in neutral, the engine thrust bearings may be worn enough to allow enough end play of crank and allow the balancer to contact with front cover.

I had a similar problem om my 88, 4.0. After replacing cap,rotor,plugs and wires, still had problem. Turned out to be coil arcing out to outer metal ring when things got damp.

I think your on the right track with TC clutch as 200 RPM is about the difference between TC locked and unlocked. There is also a switch mounted above the brake switch that controls the signal to TCU to unlock convertor when brakes are applied. You can check the operation of the switch by cruising in OD and tapping brake pedal, RPM should rise about 200 RPM and then drop as convertor locks back up.

Thanks for the input. Now to find some t/s info on lock up clutch.