Hope that title got your attention. It's a 4wd '99 XJ SE with 210k on the clock. It's driven to from SF to Tahoe a couple times no problem under my ownership. All those were prior to the manifold replacement.

I replaced a cracked exhaust manifold a while back and decided I should take a celebratory drive into the headlands. I drove around for a couple of hours, everything felt fine, no warning signs but I could hear what sounded like a high pitched but quiet squeak. After about 2 hours I stopped for 45 minutes for a small hike then drove another 30 minutes into town to grab lunch. After maybe 30 minutes I decided to drive back home. About 20 minutes into driving the jeep lurched and died. It was a nice flat straightaway so just cruising along at 45mph. Upon inspection I noticed I had not connected my CCV hose to the airbox. I'm not too worried about that because at worst it was just pulling in some unfiltered air and I wasn't wheeling. Well I let the jeep sit for maybe 15 minutes and it started right up. Full power, nothing suspicious. Driving back to the city there is one BIG hill just before the GGB. Towards the top of the hill the engine lurched again and lost power but didn't fully die and I did notice my vacuum plunged to almost zero. I had not noticed vacuum on the previous stall. I pulled off to the side of the road but kept the engine on. Sat for maybe 10 minutes then took off at full power. The unfortunate thing is there's not really an option for me at this point, I had to cross the bridge. I got about 1/3 across when it lurched and died. Engine totally quit. While still rolling I hollered at my GF to grab the wheel while I got out back and pushed. I pushed that damn ****box across almost the entire Golden Gate Bridge. I was not going to wait for the pusher truck. I was lucky enough to have a nice guy in a BMW behind me directing cars to go around but all I wanted was to see some beat up truck with a redneck behind the wheel ready to push me to safety. No such luck.

We rolled into the parking lot, I laid on the concrete trying not to have a heart attack. After 30 minutes I started it up and drove the 7 miles home. After that but before I did the repairs listed below I would only move it for street cleaning. It would start right up and seem to drive fine with full power but I just couldn't trust it.

I listed my driving time in case that sounds like heat soak/vapor lock. I have since replaced the CPS and o2 sensors. I thought I might have a vacuum leak but with a smoke test I only found a small vacuum leak at the throttle body shaft at the return spring. I fixed that, cleaned the TB and the IAC. I also chased a small sputtering sound and think I've fixed that, pretty sure it was a small leak at the exhaust donut gasket. Fixed that with by disconnecting and prepping the mating surfaces with copper silicone. I haven't noticed the squeak sound again but I'm also not pushing it too hard. Oh and I discovered the previous owner removed the vacuum canister reserve canister and plugged the end. I think I'd like to replace that if it will allow me to not drop vacuum when under high load. I live in a fairly hilly area and could use the reassurance.

Anyone have any clues? I'm kinda throwing everything I have at it because where I live I can't really go for a test drive that could test it the point of failure without ending up on a mile long bridge again. Or on a windy highway or 1 lane road with no shoulder. Everything screams vacuum leak to me but I can't find one other than that tiny one at an arguably trivial place on the throttle body. Any help at all will be appreciated. And if you come across pictures of a guy pushing a blue XJ across the golden gate bridge, be a friend and send them my way.

 

Anybody have any clue? Does it sound like I'm on the right track? Wrong track?

 

Great story-telling!

But I have no clue. The vacuum dropping to zero is really weird. How are you seeing that? You have a vacuum gauge?


Maybe a heat induced vacuum leak at the intake manifold?

 

I have a bluetooth OBDII sensor and I run Torque Pro on a double din android auto stereo I installed.

 

Ah.

I'd be looking hard at that intake manifold. Do you know the trick with spraying propane to find a vacuum leak?

Oh, and stay off the Golden Gate Bridge!

 

Man, that's a really tricky one to diagnose, but even the slightest sensor change can make these guys loopy. I installed a homebrew 62.5mm throttle body on mine, and then my trans (a MONTH LATER, mind you) decided it didn't want to shift correctly anymore. Turns out the angle of the throttle plate and the TPS were out of whack and the TCM was getting all loopy. My point is, make sure the CPS and anything else you replaced are PRECISELY the same as your OEM that you replaced.

That being said, I feel you might have some mystery leak somewhere, or maybe a fuel delivery issue? Have you dabbled at all with the fuel delivery? Injector upgrades, any fuel filter changes, etc.

I coincidentally also own a 99. I can't say I've ever had that, except when it was relearning the throttle going back to the factory one - my idle was **** and it died 1 or 2 times, before sorting itself out.

 

I'm about to go try to propane test. Hoping it's not a manifold leak but it probably is.

The CPS is mopar stock replacement, O2 sensors are Bosch stock replacement.
Fuel system is stock and I haven't touched it. The only fuel system parts I've touched are those associated with the intake manifold when I did the exhaust manifold replacement. Had to of course detach the hard line from the fuel rail.

 

Welp, just went to work on it and someone tried to steal it. Ignition cylinder is totally ****ed, can't get the key in to start it.

 

Wow,
you can't make this stuff up.

 

It's 2020.

 

Just went and pulled my stereo, cb radio, fuses for the fuel pump and starter, and disconnected my coil pack. If they try to steal it again tonight they'd need a rollback.

 

OKAY! Got a new ignition cylinder and have it moved. Back to vacuum testing.

I grabbed some propane and some vinyl hose. I went all around the engine checking for vac leaks but I couldn't get a single spot to hit with a rev. I guess next step is to drive the hell out of it and while it's ripping hot try the propane trick again.

 

Just idle it for 20 minutes or so. Should get hot enough.

 

Well I can't find a vacuum leak to save my life. BUT I remembered a detail that I realized I didn't include in the original post. When the jeep died (both times) the engine quit but all the electrical stayed on and when trying to start it up it wouldn't even crank. So does that point more in the direction of CPS or something else?

 

CPS stops spark, not the starter.
Could be some weird fuel cut off but then it would sputter.