Crank but no start on my 99 TJ

GregBelleville

GregBelleville

TJ Enthusiast
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Sep 19, 2022
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Southern California
I've been trying to diagnose the cause for a crank no start issue.

Posted about this about a month ago. Symptoms are that if I leave the Jeep sitting for a few days it fires right up, but will stall after maybe 10-15 minutes and won't restart after that.

I've already tried replacing crankshaft position sensor with no luck. Also have tried tracing wires around the engine bay looking for any obvious wear with no luck. Today I was poking around and noticed these two nipples on the driver side of the motor, one on the right is missing a cap or connection, the one on the left has a cracked cap that is zip tied on but doesn't seem sealed. There's suction on this nipple when the engine is running.

Can anyone explain what these are for and whether there's any chance this is related to my problem?

PXL_20221203_202739024~2.jpg
 
On my 99. the nipple on the left (IAW your picture). is capped. the right one is a very thin hard plastic hose that runs to underneath the battery. I think it goes to the evap canister but not sure. I did not crawl under to see what it connected to to. sorry.
 
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The right vacuum nipple connects to a plastic vacuum line which goes along the firewall behind the valve cover and then thru the fire wall to the A/C climate controls, also to the Cruise Control vacuum motor (if installed) and the vacuum accumulator canister beneath the battery tray.
 
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CharlesHS said:
The right vacuum nipple connects to a plastic vacuum line which goes along the firewall behind the valve cover and then thru the fire wall to the A/C climate controls, also to the Cruise Control vacuum motor (if installed) and the vacuum accumulator canister beneath the battery tray.
Click to expand...

Thank you! Do you know what the effects would be of not having this line connected?
 
It creates a vacuum leak and sucks dirt etc into the engine through the open port. Also, the HVAC controls,CC etc won't work.

Auto parts stores will have a variety of caps, elbows, etc.
 
JKP said:
It creates a vacuum leak and sucks dirt etc into the engine through the open port. Also, the HVAC controls,CC etc won't work.

Auto parts stores will have a variety of caps, elbows, etc.
Click to expand...

Hmm, that's interesting because it seems like this vacuum line hasn't been connected for some time, but my AC was working prior to this problem I'm having with the engine stalling and then not starting. Either way, at the very least I'll need to find some caps for those 2 nipples to prevent anything else getting sucked into the motor.

Still scratching my head tho on what's causing the stall and crank/no start issue. I'm thinking I may need to hit up Mark @Wranglerfix about a new PCM, which send like a possibility?
 
The vacuum controls the flapper doors that direct the air to the defrost, floor, or vent positions and the hot/cold blend door. The compressor would still run.
 
GregBelleville said:
Hmm, that's interesting because it seems like this vacuum line hasn't been connected for some time, but my AC was working prior to this problem I'm having with the engine stalling and then not starting. Either way, at the very least I'll need to find some caps for those 2 nipples to prevent anything else getting sucked into the motor.
Click to expand...

Does your A/C climate control console have slider selectors OR the rotating knobs ?
Some early 1999 TJs came with the slider controls which would explain some of why your A/C system works with the vacuum missing.
The later 1999 TJs came with the rotating vacuum selector knobs.
The uncapped nipple can create a vacuum leak that will affect engine idle RPMs, but should not cause the engine to stall unless there is another larger vacuum leak.
 
CharlesHS said:
Does your A/C climate control console have slider selectors OR the rotating knobs ?
Some early 1999 TJs came with the slider controls which would explain some of why your A/C system works with the vacuum missing.
The later 1999 TJs came with the rotating vacuum selector knobs.
The uncapped nipple can create a vacuum leak that will affect engine idle RPMs, but should not cause the engine to stall unless there is another larger vacuum leak.
Click to expand...

Mine has the rotating knobs.

BTW,I saw your reply on another similar post about someone with a similar crank but no start issue. You recommended checking the 32 pin connectors to the PCM for oxidation. Would I just need to check for this by unplugging the connection to the PCM, or is there a way to actually remove the wires from the connector to check for oxidation?
 
GregBelleville said:
Mine has the rotating knobs.

BTW,I saw your reply on another similar post about someone with a similar crank but no start issue. You recommended checking the 32 pin connectors to the PCM for oxidation. Would I just need to check for this by unplugging the connection to the PCM, or is there a way to actually remove the wires from the connector to check for oxidation?
Click to expand...

You can individually unsnap each harness connector from the ECU receptacle to check for oxidation.
 
Not that harness....
Look between the firewall and right rear corner of the valve cover for a split wire loom harness which is routed around the back of the valve cover near a threaded head stud.
 
Just diagnosed a crank/no-start issue on a 2000. Ended up being a short (which we still haven't found since we haven't had a chance to look yet) in the some portion of the harness between the PCM & somewhere behind the motor-ish. Shorts in this area seem to be common from the loom rubbing against the valve cover bolts, but I've seen 2 jeeps now with shorts further down the harness, over the bell housing/transmission area. And the shorts have been on the interior of the harness, which I can't explain.

Looking ahead, it's not very hard to pull it all up into the bay. Unplug the connections at the transmssion, transfer case, and (yes) the driver's side taillight. Then you can pull it all up into the engine bay and rip apart the loom & tape to find and fix the short. The loom is all brittle & rotten anyway, it's a great time to re-tape & re-loom everything. Highly satisfying (ymmv). I recommend it even if you don't have any trouble with your harness.
 
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yes, but my experience has been further down the back of the bell housing. You might try wiggling it while somebody else turns the key. It won't tell you if you don't have a problem, but it can possibly tell you if you do.
 
GregBelleville said:
Sorry, bear with me here. I took another photo. Is this the threaded stud and harness you're referring to?

View attachment 381787
Click to expand...

That bolt is for holding the valve cover in place.
The threaded head bolt I am referring to is on the drivers side of the valve cover in the back.
The red spark plug boot is covering the threaded head bolt.

IMG_1028.jpg
 
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