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Discussion Starter · #1 ·
.... cranks but wont turn over unless i turn key on and off several times. Any clues what would possibly be the cause ? cps ?
Bought this a few weeks ago and have founds lots of things wrong. HAd random shut downs/stalls, replaced the PCM and the distributor. Pcm rusted out and corroded and the distributor shaft had a lot of play in it and a knocking noise + there was no O gasket on it. The random stalls seemed to have gone away and she runs a lot better. I had also removed the throttle body and gave it a good cleaning and the IAC valve careful not to move the pentyl .Since doing that it now it doesnt want to start after its been sitting for a couple hours or more unless i do the key on off deal, but starts right back up n o problem. Also when it does start i get like a 2000 rpm high idle so perhaps i did mess up the iac valve ? WHen the high rpms happen i unplug the tps and it returns to normal rpm's . Got a new iac and tps to put in tomorrow. Also i did clean all the grounds and put in a couple 2 ga. ground cables, one from batt to body and on from batt to engine block .
 

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Key cycles to get it to start screams of a failed check valve in the fuel pump. It allows the line to drain back into the tank requiring the multiple key cycles to prime the system and refill the line. A fuel pressure test can show you if this is the case before you spend the $$ on a new pump.

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Nope, security system lets it start and then kills it.

That's as close to textbook fuel pump module as it gets.
 

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Discussion Starter · #5 ·
Ok, tested the fuel pressure with the key on and a big fat 0 for pressure. Swapped out the relay and bam 44psi ! It was a wonder it ran at all before. But, i still got it not wanting to start, just cranking. Fooled around with the shifter in and out of gear and retry key and started right up. So most likely "hopefully" its the neutral safety switch. Pulled the shifter bezel didnt see it there . Perhaps its on the side of transmission ? Still doesnt explain why it starts back up after getting it started no problem time after time, but 2 hours later no start.
 

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Neutral safety switch will cause a no crank, no start situation. You need to connect the fuel pressure gauge, cycle the key until it starts, then shut the engine off and let it sit with the gauge on it. Check it every half hour, or so, and see if the fuel pressure drops.. The fuel rail is supposed to hold pressure, and the check valve back at the pump is what makes that happen. When it fails it allows the fuel to drain back into the tank causing the pressure drop you see on the gauge at the rail. It takes a few key cycles of the pump running to refill the fuel line and rail back up to the pressure it needs to run.

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Discussion Starter · #8 ·
Had some time to work on it today. Sooo, the fuel pressure jeep running is about 45 psi, shut motor off and after about 30 minutes it drops to 15 psi. Also, when i turn on the key the fuel gauge isnt working and the out of fuel light comes on even though i have 3/4 tank of gas in it.
I changed out the crank sensor and the neutral safety switch today too but it didnt make any difference.
I dont understand why it just cranks and doesnt want to start and repeated tries id does start and and sometimes stays running but most times when it starts it shuts right back off after about 10 seconds. I had thought it to be a security system issue, i grounded out the purple n yellow wire from the drivers door to disable the security system which it does but doing that still made no difference on the start issue. To note, i had a couple weeks ago grounded out that wire and i didnt know at the time but the interior lights stayed on and drained the battery dead overnight. Upon jumping the jeep that morning i didnt have anymore start issues for several days and then it returned. Today the same thing when i grounded out that wire, all the interior lights stayed on and would not go out so i re hooked that wire back up.
Could this a combo fuel pump and security issue ? At this point im at me wits end on this jeep. I have had to put a lot of $ into this and its getting deep now ! :(
 

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Discussion Starter · #10 ·
Still sounds like fuel pump/pressure issue

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Messed around with it some more today, hooked up scan tool and tried to go into and check the ecm and i get "communication error with ecu" message. This is with the new ecm installed. CAnt find a fuse or relay for it to check that. Previously before i got this crank no start issue a health report scan showed no issue with the ecm.
 

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So back to basics this far down...what year and engine?

For whatever reason Chrysler called it the Auto Shut Down, or ASD relay. That relay provides power to the injectors and ignition system.

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Discussion Starter · #13 ·
So back to basics this far down...what year and engine?

For whatever reason Chrysler called it the Auto Shut Down, or ASD relay. That relay provides power to the injectors and ignition system.

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Ahh the asd, got it. Its a 98 with 4.0
 

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Discussion Starter · #14 ·
Welp, throwin in the towel ! I put in another new pcm and changed out the cps today from the standard motor products one i put in to a napa one. Still no com connection to the pcm. Shes dead now i guess. Low fuel light comes on and the gas gauge is zero'd out even though i have an almost full tank with the key on position. It cranks though but no start. All fuses are good, put in a new relay for the asd and fuel pump. Dont hear the pump prime at all, dont suppose it would if the pcm isnt working. Towing it for a shop appointment next monday, probably gonna be booKoo bux to get this sucker going again :( Might as well have em do the rear main seal while theyre at it. There goes all the xmas $$$.
 

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Discussion Starter · #15 ·
A couple of questions:
When i ground out the purple/yellow wire to disable security system the interior lights stay on and will not go out unless you turn the ignition key on. adjusting the interior lighting slider next to headlight switch does nothing to turn off the lights. What else do i need to look at to get the interior lights to turn off with sec system disabled ?

Also, in wiring diagrams say a wire goes into a S100 "juncture" is that a fusible link ?
 

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Correct, on a second gen you can't permanently disable the security system.

The second gen also deletes the interior lights off from the dimmer thing that a lot of mopar had pre 96.

S100 is just a splice in the harness.
 

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Discussion Starter · #17 ·
Ok thanks :)
I will need to test for 5v to tps and map sensors later to see if those are getting power from the pcm, also need to check the fused B+ from the black c1 connector. Would that have a fusible link in it from battery ? Trying to track down as to why no comm from scantool to pcm .
 

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Discussion Starter · #18 ·
OK tests results, seem to have 5v issue, what is the source for the 5v power ? Bcm ?
UNplugged pcm connectors and test voltages from the connector pins. Is that corrector or should connectors be plugged in and key on to test voltages with a tap into each connector pin wire ?

Ignition Key on, pcm connectors unplugged :

Pcm connector c1 black:
Grounds pins 31,32 good
pin A22 fused b+ = 11.78v
A2 fused ignition switch = 11.78
A17 5v supply = 0.92v

C2 wht connector:
pin 31 5v = 0 v reading

C3 grey connector:
pin C3 ASD = 11.73v
C30 ccd bus+ = 2.34v

Pcm connectors plugged back in:

Map sensor blk/wht wire = 0.29v
Tps sensor blk/wht = 0.29v
Crank sensor blk/wht = 0.30v
 

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Discussion Starter · #20 ·
Ahh, so need to test the voltages with pcm connectors connected to pcm with key on and tap into each 5v wire ?
Would that A17 pin in the C1 blk connector 5v supply be input supply or output ?
 
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