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Discussion Starter · #1 ·
Driving home Thanksgiving night the engine turned off suddenly. Didn't stall or turn off electric, acted like it has no gas. We could smell gas inside the vehicle. Turnover = not starting, but turned over fine.

Today I take a look at it, started it, it ran for ~15 seconds then shut down. Would turn over but not run. If we put the gas down while turning over it blows off the air filter cover (shock at first!).

I took the air cover & throttle body off & recorded what it's doing.

This is a new one to me, I was hoping it was a rusted fuel line or something I could fix up pretty easily.

Here's what's happening:


Any help appreciated. :D
 

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One of mine was acting like that last week when the vacuum line on the valve cover fell off.



My other WJ has been leaking gas for 6 months and it starts hard. I would think if you had a fuel leak you would see it or smell it. If it is a fuel line it won't be an easy job. That's why I have put mine off so long. Someday it will probably leave me stranded and I will have to fix it. I do plan to fix it next month if it will last one more month for me.
 

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Discussion Starter · #3 ·
I looked under the hood for a gas leak and under the vehicle, and looked in the spare tire area where I cut the hole to change the fuel pump, saw/smelled nothing. The valve cover vacuum hose was still solidly attached to the valve cover when it initially blow off the air filter housing.
 

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start checking for codes even if CEL is off.

any recent work?

Fuel pressure check with a gauge post PSI.

Remove and "read" plugs, they may help pining this down. - Fouled, wet, dry, black, damaged, wrong part.
 

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Discussion Starter · #5 ·
Went to check the codes this morning and the jeep's locked with the keys in it. :( Damn me for fixing the latch in the back.

Hood's not shut though, so I can check the plugs this morning.
 

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Discussion Starter · #6 ·
ok, got in the jeep. no codes when I do the code check via the ignition. Next I'll check the plugs. There was a check engine light a could days ago but it just came on & was running fine so I wasn't worried about it right away. When this happened light went off. The light does light up when the key is turned though, like it should.

Last work I had was a couple months ago, replaced radiator, related hoses, belt, things like that. Nothing engine related.
 

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Do you have a scanner that can access live data? If so, check what the computer thinks the engine temp is. If the engine coolant temp sensor fails, the fuel map gets all screwed up. I had one fail open on my Suburban. It caused the computer to think that the engine temp was -40 degrees. It was dumping in WAY too much fuel for the engine to start on a Texas summer day. ;)
 

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Well I do not mind making a guess and being wrong, so here is what I see. Motor does not run, backfires with a little throttle. Sounds like a timing issue to me, spark at the wrong time. Not knowing much about what controls spark timing, I suppose my first guess would be cam position sensor, perhaps hand-in-hand with crank position sensor. I think the PCM comes into play there as well.

What else could cause fire to come back up the intake? Intake valve failing to close sounds like a possibility. What could hold the valve open on a straight six 4.0? Maybe a broken valve spring. When intake valves fail, the compression stroke shoves the fuel mixture back into the intake which can cause other cylinders to misfire due to the fuel rich condition, maybe stop your motor from running at all, idk.

I would suggest more diagnostics like jtec mentioned. The easiest of which is pulling the spark plugs and inspecting. Check gap and qualify plug condition: look for chips/cracks, carbonization (black and crusty), lean fuel mixture (light brown), saturated with fuel or oil, probably others I cannot remember. While you have the spark plugs out, drop a borescope into the cylinders and look for fluid, coolant or oil. Do a compression test to check for open valves or bad pistons. A compression leak-down test may help identify failed head gaskets.

Check the fuel pressure with a gauge if you have a test port.

Those tests can help rule out several issues and give us a general idea of the motor condition.
 

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Discussion Starter · #11 ·
The plugs all looked physically good. Some carbon buildup, but not covered in oil, physically dented, scorched, etc. Gap was off. Cylinder 2 & 6 was ~0.050, the rest were ~0.040. I adjusted to 0.035.

I was having trouble with my bore camera *it's cold & dark & only got to look @ cylinder 2, but there was nothing in there that drew my attention. It just looked like a cylinder with some carbon buildup.

The plugs were last changed 3/24/[email protected] 161,503 miles. It's currently @ ~190,000 miles, so it would be time to change them.

The past couple weeks I've been driving it ~3-4 days a week and my mileage hasn't dropped off either.

My normal mechanic is shutdown due to a covid case so I've contacted a mobile mechanic to do some other tests for me.
 

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Well I do not mind making a guess and being wrong, so here is what I see. Motor does not run, backfires with a little throttle. Sounds like a timing issue to me, spark at the wrong time. Not knowing much about what controls spark timing, I suppose my first guess would be cam position sensor, perhaps hand-in-hand with crank position sensor. I think the PCM comes into play there as well.

What else could cause fire to come back up the intake? Intake valve failing to close sounds like a possibility. What could hold the valve open on a straight six 4.0? Maybe a broken valve spring. When intake valves fail, the compression stroke shoves the fuel mixture back into the intake which can cause other cylinders to misfire due to the fuel rich condition, maybe stop your motor from running at all, idk.

I would suggest more diagnostics like jtec mentioned. The easiest of which is pulling the spark plugs and inspecting. Check gap and qualify plug condition: look for chips/cracks, carbonization (black and crusty), lean fuel mixture (light brown), saturated with fuel or oil, probably others I cannot remember. While you have the spark plugs out, drop a borescope into the cylinders and look for fluid, coolant or oil. Do a compression test to check for open valves or bad pistons. A compression leak-down test may help identify failed head gaskets.

Check the fuel pressure with a gauge if you have a test port.

Those tests can help rule out several issues and give us a general idea of the motor condition.
I'm with you, it sounds like an ignition timing issue. If it ran fine for 15 seconds then shutoff, I think you're also on the right track with a cam or crank position sensor, as I'd think a mechanical metal component failure wouldn't just repair itself for 15 seconds, then fail again.
 

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Discussion Starter · #15 ·
I'm not showing any codes. The check engine light turned on a couple days before the jeep stopped working but hasn't come back on since. It does turn on when the key is turned like it should, doesn't stay on.

I'm guessing old codes are in the computer & could be read by something, just not sure how nice a scanner would be necessary.
 

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I vote to check fuel pressure as well. If your fuel pressure regulator is blown, it would dump a lot of fuel into the engine as well. Might explain the fuel smell and the harsh cranking/backfireing issue. Almost sounds like its trying to hydrolock? Were any of the spark plugs wet with fuel when you pulled them out?. If not any of these items, I wonder about a timing chain gone bad, and your hard timing is now off...
 

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Discussion Starter · #17 ·
Sparkplugs we're all dry, not wet. They smelled a bit of gas but I thought that would be because the fuel pump/injectors were putting some fuel in the cylinders.
 

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Discussion Starter · #18 ·
There's no fuel pressure check port on my fuel rail. The mechanic was pretty confused why not, but there's not. I confirmed there's not when I looked up pictures of Jeep WJ fuel rails by looking at pictures of ones online: no screw in part for the pressure gauge.

computer shows no previous codes. :(

So..... with the coils disconnected we went to turn it over & it turned over a maybe 5-10 times (not seconds) & stopped. Acted like it was flooded (remember, coils not hooked up so it's not burning fuel). I took out the spark plugs & they all were wet with fuel, so with the plugs out we turned over the engine & a TON of fuel came out of cylinder 5 (could of been 6, but it looked like 5). Barely any out of the others. The mechanic said could be a leaky injector but the regular could also be bad too.

I have a fuel filter/regulator in the basement so I can install that ASAP. Then I can try running it again. Then I can go from there.
 
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