Domaas

Hello all,brand new here and to jeep as well. But not new to offroad..lol I have seached countless forums and still cannot find an answer..so please bear with me an shed some light on the subject.

Engine will not start without being primed first..IE..pouring fuel into the TB.

Once started...the engine continues to run, but at high idle, and really fat. backfires when shut off.

Has great spark while cranking

Fuel pressure is 30 psi after prime(key on) primes for approx 3 sec, holds pressure for hours..so i dont think its the check valve on the pump. 39psi while cranking, seems like a good reg.

Replaced the ckp(cps)

changed the collant temp sensor thinking this might lean out the engine and help with the fat condition.

air temp sensor checks out(2500ohms at 80'

Jumped new grounds to the body and block.

New grounds to the common injector splice.

Map sensor 5v signal

Tested and adjusted tps for idle..(.8 volts connected)

I just purchased this jeep, and plan to cage and build it, but wanna get it running right and smogged before i begin the build.It would seem that a have two distinct problems..no start...run rich condition

new parts,cps(ckp) coolant temp sensor(on the block, not the one for the guage) cap plugs wires. coil is good, good spark.

does anyone have a vac diagram for a 88 4.0 auto california jeep

Please help.

also looking for a stock air box

Quezzy

Do a sweep test on the Tps to see if there any dead spots.

Domaas

ran a full sweep using a fluke 88...sweeps normal. its a auto trans so it has a dual tps?Cant find any info on that second built in tps?i believe it may be exclusive to the trans.

Domaas

checked and cleaned the c1? connecter at the fire wall. Contact cleaner and dielectric greased..no change. Gonna test wiring back to the ecm. But looking for a pin chart for the ecm.

Domaas

just got back from a trip to ecology...found a complete stock airbox..20 bucks...sweet.

Domaas

update...after a afternoon pulling my hair out and trying several foroums..got nothing

But..I found a massive voltage drop through the ground side while craking, and after the engine is running(primed through throttle body).


5V from battery pos, to ground on tps.
Cranking .7 volts
Also drops voltage when ever the fuel pump turn on to prime.
stays at .7 while running.

checked the wiring diag. looks like the ground comes from the ecu.

I aslo have the same voltage drop at the common ground to the injectors,which also come from the ecu.

So heres the question..can a bad ecu be the root of all my causes?

Domaas

update even though no one reads this thread..lol!!

It was the ground path insde the ecu, i removed the ecu,and the cover, found a bad ground path on the circuit board.Input at D3(ecu) had a bad pin connection to the board.

Slick761

Very nice diagnoses and fix. This could be a very. Helpful thread to someone later on.... I read it! I like cruising the threads to help and get new ideas like this.... not the most obvious problem..... knew you weren't getting fuel but the pump checked out. I usually go to the Computer last unless its obvious. Only cause I don't like to deal with it. Anyways nice job

SirLasVegas

im facing a similar problem, however the initial cause of mine now not starting was a coolant hose blew. After the hose popped the jeep shut off and wont start now. Ive taken the distributor cap off, cleaned the contacts on the rotor, check the plugs and wires (getting spark just not sure how strong as the plugs are soaked) plenty of fuel pressure, replaces CPS, fuses look good, oils clean, headgaskets fine...
Only difference is I CANT get mine to start on a prime. Im thinking when the hose popped, it got something wet that wasnt supposed to, or something got so hot it shorted. It really seems like something on the ignition end, just not sure where to go.

Domaas

i would start by drying everything off first, if you have a air compressor you can use a blow gun and some electical cleaner to clean some off the contacts on the weather pack connectors,especially if any of them have bad "o" rings.

Just remember that the gycol in the anti fress will appear dry...but still leave a "film" on the parts.

My two cents...as i am new to jeeps.