95 YJ crank, no start

M

Mike187

New Member
Joined
Jan 22, 2024
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11
Location
Massachusetts
Hi folks,
I have a 1995 Wrangler w a 2.5 liter Automatic. I've owned it for a couple years, did a few things when I bought it, but generally a great running car.
Recently had an issue, was driving and it died, cranks but won't start. Brought it into the shop, checked a few things.... wasn't getting fuel. checked the harness at the fuel pump, had voltage, still wouldn't start. Banged on the bottom of the tank, and it started. I figured great, needs a fuel pump.

Drove it for a few miles as the tank was full, figured I'd use some fuel and make the job easier. died again about a week later. no amount of banging got it running again. trailered it to the house, rolled into the shop, no love. checked a few things, and then it starts randomly.

I swap out the fuel pump, it starts and runs fine.

Next day, i leave the house and run some errands, it dies again. When it dies, there's no sputtering, it's literally like I shut the key off. It's now in my shop, still not starting. I've checked all fuses. I've swapped out the fuel pump relay with a known good one. It has spark. No fuel.

Does this sound like ECM? That's the way I'm leaning. Don't think it's crank sensor or a timing issue because it runs fine when it's not dead. Just consistently losing power to fuel pump.

I'm all ears for suggestions. Even charged the battery, as I had read that if battery was below 10 volts when cranking, ECM wouldn't work.... Nothing.

Next issue is, where is my best resource for an ECM? Any brand name that is more reliable than others? Is there a relatively easy way to test my ECM to confirm that it's the issue? Any way to bypass? I'm assuming that there's no way its as simple as me putting 12 volts to the fuel pump when I'm running it....

Thanks in advance for any suggestions..... can't stand intermittent issues... would be easier if the damn thing would just break for real, whatever it is.
 
Have you changed the fuel filter? What is your fuel pressure reading? I had my stock Ecm rebuilt by SIA electronics on eBay. Great results.
 
redbullet said:
Have you changed the fuel filter? What is your fuel pressure reading? I had my stock Ecm rebuilt by SIA electronics on eBay. Great results.
Click to expand...
I haven't changed the fuel filter, but I've disconnected the fuel line from the tank side and turned key on, should run the fuel pump for a couple seconds to pressurize the system, got nothing. Turned key to start and got nothing also.... so fuel pressure is zero.

Do you recall what it cost for the rebuild? Online search shows that they're readily available, but the two sources I can usually order parts from say no go...
 
Holy mackerel!

That's a ton of info. Thanks for the instructions Dorf! ... I'm going to do my best to decipher all of that and do some diagnostic work I guess. I'm glad I didn't go on the hunt for a new ECM or send mine out yet. I have a friend that's quite a bit better than me at all things electrical, so I'll recruit him to help this weekend. I did already swap out the Fuel pump relay, but I haven't checked the ASD relay, so I'll check that today, along with wiring to injectors and wiring from pump to the source. Wiring actually all LOOKS good, but I guess there could be an issue somewhere there. Praying I get lucky and its the other relay. I read that there is a fuse in the block that's labeled as a dome light or courtesy light that also goes to engine control, but not sure if that applies to my year YJ.

Thx for some ideas of where to look!
 
fuel is last not first .
if the PCm detects spark fail or any kind of A142 bus overload it cuts fuel and spark both. (VIA ASD RELAY)
spark is first,, got spark? (on all 4 )
or have spark for 3 seconds only cranked.?
the flow chart covers that. ,
 
Dorf said:
fuel is last not first .
if the PCm detects spark fail or any kind of A142 bus overload it cuts fuel and spark both. (VIA ASD RELAY)
spark is first,, got spark? (on all 4 )
or have spark for 3 seconds only cranked.?
the flow chart covers that. ,
Click to expand...
What happened to the posts that were here with all the suggestions??
 
Dorf said:
fuel is last not first .
if the PCm detects spark fail or any kind of A142 bus overload it cuts fuel and spark both. (VIA ASD RELAY)
spark is first,, got spark? (on all 4 )
or have spark for 3 seconds only cranked.?
the flow chart covers that. ,
Click to expand...
I checked ASD relay yesterday, relay is good. If I go by the flow chart, i end up dead ending at vapor lock, fuel pump, or blockage... but fuel pump isn't getting power. If I go one lower, (fuel injection) I dead end at "single point, check throttle body, electronic multi point separate diagnostic" Not really understanding.
 
I did the 3 cycle key trick, all I get from the OBD is 12 and 33... battery disconnect and A/C issue, both of which I'm reading are non-issues...
 
ytradio said:
Redbullet, it is amazing what you can do with less than 20 pages.
Click to expand...
Am I missing something? Dorf posted quite a few suggestions as to what to check, all this does is tell me how to pull the codes, which I certainly appreciate, but which didn't answer my question... And now all the posts from Dorf are gone.... Did he take them down, or did a mod delete them or something??

I'm even more confused now.
 
on all cars that fail dead, we check all fuses first. (for sure F1) on new cars the PCM even tells me what fuse blew (of vast) not just F1
33 means A/C is missing (the factory only option, not aftermarket A/C) <<< ignore this
12 is a bingo? (maybe)
Fuse 1 is blown, or battery was removed, or battery was weak now or while cranking. (fusebox PDC, F1 blown)
PDC fuse 1 is it, not cab block Fuse 1 and fuse 5
okay?
I deleted all that so I can get you to focus on spark first. (and duration of the test)

the 3rd flow chart, decision is got spark. y/n so it has spark on all 4 cylinders??, we do test fuel next.
The spark must last longer than 3 seconds cranking if not ASD dropped off line (on purpose !)
it will run on test fuel every time tired, does it? < watch him do it !
if spark did work then what?, and tests fuel too then what? well swap horn relay and fuel pump relay.
test for spark for say 5 full seconds cranking to get past the 3 second PCM/ASD rule.<< it's a jeep not a Chevy.

the terse words it the flow chart means MPI means EFI /MPI , check for injection multipoint and fuel pressure at spec cranking.
mpi = multipoint injection system (EFI)
fuse 1 PDC blows and ASD and fuel pump are dead
Fuse 1 blown means the PCM can not store codes. A14 power feed all things on it are dead.

if any device in the engine shorts out A142 feed, F1 blows. injector shorted, or o2 shorted and all things in the FSM , A14 and A142 must not be shorted.
and sure can;/
if F1 blows spark too is dead. as will be A142 power feed. A142 drives power to the spark coil (induction) and if the primary shorts F1 blows
or ASD +PCM shuts down ASD fast so fast F1 will not blow, toss a coin as overloads come in 2 forms, a hard 0 ohm dead short or is near 20 amps but not there yet.

the spark test is best done for 10 full seconds, ok? so we will see if the ASD stays energized for more than 3 seconds.
did you know the TPS stuck at 5v the PCm cuts fuel 100% dead . (if the ground wire is bad to the TPS bingo stuck in magic secret unflood mode.
the spark test is key to diagosing all cars.
most cars the rule is the crank shaft must spin a full 10 turns. to see all DTCs related to spark failing. CKP and CMP are 2 top contenders.

fuse 1 PDC makes must not be blown..

the fuel pump test must be doNe correctly
most cars made the pump only runs for 3 seconds at each key on, this is to prevent fires after a crash and by DOT laws.<<< SAFETY FIRST and all that.

the test is 2 man test, not just one person, hearing the pump spin is not a full test. one can use a voltmeter extended from the tank pump wires
to the cab and crank with 1man test.
knowing all this make the test valid, and not put the tech on an endless wild goose chase.
you now have new pump and pump relay.
but do you have 41psi pressure cranking, for 3 seconds or more. 10 is max so not to overheat the starter.
rule #1 after all fuses checked is keep the battery charged fully or as the battery gets weak at below 10vdc the PCM goes off line, making all test
totally useless. to fix cars we must own a battery charger, or use jumper cables to other car.
The pump can fail if either wire to it is rust (connections) the hot wire or the rear ground there.
G104 at the rear of car is the ground to the fuel pump. it too must not be bad as is so common on all cars. MPI.

The ASD must stay engerized all the time cranking this is a key test on all JEEPS (USA made, dodge ,etc)
or spark and fuel goes dead.
spark tests with test spark plug is best gapped correctly.

when the engine stall fast, just like turning the ign key off that is spark died, not fuel , fuel pressure falls slowly, for sure at idle (dies)
if it goes dead instantly and the TACH meter drops dead like hammer hit it, that is spark lost and is ASD drop out

a key set of evidence that,
and you do know all these related EFI parts can fail intermittently.
Even a car battery with 1 intermittent cell , goes shorted and not 10vdc is there, alternators does not like this short so it goes offline in a flash
and now the PCM is really angry, it now goes off line as its internal voltage reg goes dead at 10v or less. FSM warns if this, !
newer cars my go to 8v and die but this car is not a new car. with LDO regs inside the PCM,sorry this car is old with old regs there.
take away the battery must be good and fully charged for all tests and when driving the dash voltmeter as on 14 not 10.

we even see things like this.(fuse)
I am not saying at all I know what is wrong or bad and can be 1 rusty wire(conn).
or this.
Any fuse can do micro cracks or even rust(means corroded) in the salt belt? is it? BC is not I think but IDK.
even the alternator can short the A142 wire , random. o2 shorts and injectors shorts ASD drops like a hammer.(fast)

as seen in the rust belt
this.

IF code 12 fails after a DTC reset , the DTC 12 is relevant.

fuse-is-first.JPG



take away 2 to 3

spark will last for 10 full seconds cranked, I can not see you do the test or how long done. using tests spark plug and all 4 spark full time>?
test fuel works, every time.?
fuel pressure 41 psi cranking of it will fail.
if pressure was say 20psi the FPR is dead.
pressure matters and the PCM on this car does not have any fuel pressure sensor like all new cars have.
To tests pump voltage at the tank takes 2 persons and I did not see how you did this, or if using the wrong ground to do so.
Ive seen cars with 6vdc going to the pump test correctly for 3+seconds (not less) and bingo bad wiring or relay(its new now)
the relay (FP) is closed full time cranking, it does not drop out, cranked ever. on any car. (unless battery is weak)

The PCM cuts spark when the ASD drops (PCM decision)
the PCM cuts fuel for many reasons. for sure ASD drops and the PCM DOES the drop. for A142 overloads of ANY KIND
The PCM cuts fuel of TPS goes to 5vdc (output TSP pin) cranking
The PCM cuts spark if CMP fails or CKP


As you can see what the ASD does is SUPERKEY FACTOR in finding any kinds of stalls or no starts but cranks fast and robustly./
the PCM pin a142 the PCM has magic thing inside called a ADC, analog to digital converter. that is in EFFECT just a VOLTMETER.
this magic voltmeter measure voltage on the A142 bus. and if below spec voltage the PCm drop ASK like a hammer blow.
to prevent CRASH and BUN as seen on TV.
the PCM sees any kind of spark loss the PCM cuts the ASD dead (fuel ends) to save LIVES.
that is how it all works.
do the spark test and tell how it was done. do so for 10 full seconds. to be sure spark holds UP full time.
do the pump voltgage test and tell how it was down. do so CRANKING, WHEN CRANKING 11 VOLTS (PAR) MAKES IT TO THE PUMP FULL TIME CRANKED
AND IS A 2 MAN TEST , LACKING 12FOOT METER TEST LEADS ,LIKE i HAVE.
 
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most cars this old the FPR is bad. and if stuck open as they love to do old (the piston inside it moves at ever touch of pedal throttle) or had bad fuel.
fuel pressure is way too low.
a fuel test meter is the clue here, all shops have one or MPI tests are not possible.
 
my posts are , keep an open mind, do the tests.
let the chips fall where they may.
just one loose wire can do it (or rusty)
here's hoping that it fails hard and now 10x more easy to find. for sure.
I have scan tool for mine and can scan and drive at the same time. and see DTC errors on the fly and even record them to my log file.
I have data logging DMM too (USB) that allows me to find other voltage problems on any wire in the car.(on the fly too)
hope yours is and easy fix. !
 
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