Gas tank pressuer

[Infidel Edition]

So my talk is having pressure issues
Ta k of gas drive 200+/-mi
And tbere was so much pressure I'm surprised it didn't blow a seam
It was positive pressure blowing out
So I drove a bit more with cap off... started blowing gas out?

Help

[4.3LXJ]

Tank should be vented at the top in two places to the charcoal canister in the front. Sounds like it is plugged. How is the fuel pressure at the rail?

[Infidel Edition]

Haven't installed that pressure gauge yet - left on my desk 345 mi. North
The vent lines have been disconnected for at least a year.
Had to get to drill and parked it for the weekend
Won't see it again till the a.m.
I think I have a vacuum pump ( like to blead brakes)
I'll check what I can pull on the lines at the point of disconnection.

[Infidel Edition]

Heading home
Decided to risk it.
Zero pressure issues on the tank...
And awesome MPG.
Dazed and baffled?
Gonna install the fuel pressure gauge tomorrow.
Also gonna swap the CPS as it had some mis-fire stalling issues the other day.
I'll try to sumerize better when not using phone connection

[Infidel Edition]

OK... my jeep is haunted!
but I think I'm a little closer to that issue I've been hunting for 6 months now!

summary of events:
for months now I've had this random high idle. when I first start it = 650 / 700 and at temp can run at 650 OR AS HIGH AS 1200 RPMs.
* assumed vacuum leak....

back in Sept, I had that issue where it made it almost a 1000 mi. and then just petered and died
* assumed CP's or TPS related issue
** had already swapped CP's as potential solution to the random high idle, but not the fix.
*** followed the advice and checked / adjusted TPS.
= ran fine all the way home.

in Dec, while driving to K-Falls (drill 300 miles away), it had a repeat of the above sputter and died, but this time at 45'ish MPH.
* assumed bad gas?
= added gas dryer and after drill it ran fine most of the way home.
** had minor repeat! + when I popped the clutch to keep it going (was cold and miles from?????) it fired back up but had many backfire issues!

no issues around town driving...
Friday I drove to drill, 1st time ever when the gas guy (we can't pump our own gas??!!) called me over.
turning the cap was releasing LOTS OF PRESSURE! Like minutes of pressure.
so I thought I'd drive the last 75 mi without a cap = no bueno! gas spewing out the side as I went down the road + that same sputter and died!
I put the cap back on and sat for a few = ran OK for a bit and repeat sputter.
stopped for gas and before pulling in loosened the cap so the attendant wouldn't ....
let pressure out for mi Ute's again. she I tried to restart = as if out of gas.
panic!!!
15 minutes later it started and ran fine!
* assumed = no f'ing clue!

after it sat for 2 1/2 days, I decided I'd drive home and stop every 60 - 70 mi and release pressure.
BUT ZERO PRESSURE AT 75 MI AND AGAIN AT 158 MI!
and I drove (in 4 wheel drive 1/2 way over snowy pass) and got 23 MPG!
...she was trying to make nice :beer:

so I drove the rest of the way home like all was fine....
2 blocks from home = high idle (like 1200) and I thought I heard a strange groan??
got home and decided to turn the cap = over 5 minutes of pressure release before I had to pee and tightened it and went in!

the difference between 1st half and second half of the trip
1st half rpm's I kept below 2000 because I thought maybe cps issues at higher ROMs (O'Reilly so I'll replace for free).
* at temp idled at 700'ish when I stopped for a break...
2nd half I drove normal and didn't stop for a 130 mile stretch and did 70+ most of the way... so rpm's over 2000.
* at stop sign in neutral I noticed it was idling high again....

is the higher speed higher rpms causing a fuel pressure build?
...or a higher pressure fuel causing higher idle???

I'll install the fuel pressure (perm. to fuel rail) and drive it around and when I notice high idle = I'll check the fuel pressure


ideas?
thoughts?
exorcism?

:headbag:

[bigjim350]

I wonder if maybe your fuel pressure regulator is messing up. From what I remember the jeep fuel pump makes way more pressure than the jeep needs if unregulated. Perhaps sometimes its letting way too much pressure into the fuel rail, causing high idle, and sending the rest of the pressurized fuel back to the tank in the return line. Causing pressure build up in the tank. Just a guess though, cause I've never seen it happen before.

Sent from my SPH-L300 using Tapatalk 2

[Infidel Edition]

Crawled under with a mechanical type friend to look...
:rolleye0012:
He said to start it up...

:mad0090:

Problem solved (most likely!).

a BIG whole had rusted through the tail pipe just in front of the rear axle so that it was more of a straight pipe than anything.
So when it's running, it's like a 200* heater blowing directly on the gas tank! :flameon:

And the 1st half of the drive was a little slower / lower RPM's AND in the snow! So the heat out the pipe was lower and the snow reduced the rest...
The 2nd half was faster, engine up to temp, no snow = heater blowing on tank!

Thank God I didn't blow myself up with that one...

But that puts me back on the WTF is up with the random idle!
Still gonna swap the CPS since it's covered. And going to clean the connections on the ECU and such... :crazy:

[Infidel Edition]

Update to above...
The engine running temp at the sensor is 200* F
I was reading online that the temp at the header can hit in excess of 1200* F
And it can heat up at the Cat. as well depending on octane levels...

Potentially, the heat blowing on my gas tank could have been well in excess of 300* to 400* or more. I didn’t find at what point gas a gas tank would explode… But I’m betting I was pushing that limit!

No Bueno! :flameon:

[Brasscatz]

Wow, glad you found that before something went kerplooey. Gas caps are also supposed to allow some pressure to escape if too much pressure builds. Might need to look into getting that cap tested - unrelated to your issues, just a side note.

I cannot recall if I had told you about that thread I found on the PCM screws causing a short in the computer or not... if not I'll try to hunt it down for ya. Seems more common in Grand Cherokee's, but common in Jeeps in general.

[Infidel Edition]

Wow, glad you found that before something went kerplooey. Gas caps are also supposed to allow some pressure to escape if too much pressure builds. Might need to look into getting that cap tested - unrelated to your issues, just a side note.

I cannot recall if I had told you about that thread I found on the PCM screws causing a short in the computer or not... if not I'll try to hunt it down for ya. Seems more common in Grand Cherokee's, but common in Jeeps in general.

I think you did.
But it's a RENIX ~ and the short is usually caused by the ground wire above the hood release from what I understand.
I'm going to pull the ECU and coil and clean all connections there. Swap out the CPS (just cause it's covered and free to do with O'Reilly) and run that ground jumper.
... and get an angle piece on the end of my tailpipe so the heater points at something less volital than gas :flameon: