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Old 06-05-2014, 06:25 PM   #1
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Vortec 8.1 engine stalling

After climbing a good grade, on the downhill side of the mountain, my Vortec 8.1 has stalled out twice (felt like a vapor lock). After stopping and restarting after just a few minutes, it seems to run again. After loosening the gas cap, there seemed to be a vacuum as I could hear air being sucked in. I'm thinking it is either a fuel pump problem or vacuum being created in the fuel tank restricting fuel flow to the engine. Am I on the right track?
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Old 06-05-2014, 07:08 PM   #2
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What was the ambient temperature? Were you running the dash AC? I experienced high "underhood" temps when I had an 8.1 Vortec last summer. At high altitude, high ambient temps it boiled the fuel in the rail and stalled (vapor lock).

Vacuum in the fuel tank doesn't make sense to me. Stopping for a few minutes and restarting wouldn't change the state of the fuel tank. It may be enough to stop the fuel from boiling in the fuel rail though.

I posted about my experience in my blog here.
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Old 06-05-2014, 09:21 PM   #3
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Clogged fuel filter, ignition module would be a couple of quick guesses.
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Old 06-05-2014, 10:55 PM   #4
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Most ALL EFI systems have one thing in common. it is what they do under complete deceleration. When you let off the pedal completely going down hill.
Most are like this.
Vehicle must b going over 20 MPH
Engine must be above 1000RPM
Throttle must be closed (at idle)
when all three conditions are met it does NOT go back to idle fuel delivery.
They go 0% fuel delivery. They completely shut off fuel. some even go a step further and open the throttle to reduce engine braking. Easy to program this with the throttle by wire.

The little valve that controls idle air could be sticking some causing the problem,
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Old 06-06-2014, 12:54 PM   #5
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I'm with Koop on this one.

Jim
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Old 06-06-2014, 01:59 PM   #6
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Some very good suggestions given above. I'd start by plugging it in and reading any stored codes. This just might give a good starting point and help weed out potential causes.
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Old 06-06-2014, 05:35 PM   #7
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Ambient temp was about 70 degrees at about 7000 ft altitude. If vapor lock is the issue, is there a fix?
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Old 06-06-2014, 05:44 PM   #8
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Mekanic,

All three conditions you described were met. Is there a fix that a amateur garage mechanic can find and fix easily?
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Old 06-06-2014, 09:34 PM   #9
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Quote:
Originally Posted by Ronzolv View Post
Ambient temp was about 70 degrees at about 7000 ft altitude. If vapor lock is the issue, is there a fix?
It could be the fuel pump is getting weak, fuel will naturally boil easier at lower pressures.

A Fuel filter is NOT going to clog, then unclog and vehicle runs fine minutes later.

Quote:
Originally Posted by Ronzolv View Post
Mekanic,

All three conditions you described were met. Is there a fix that a amateur garage mechanic can find and fix easily?
You probably spent several mins at zero throttle opening and to either fix or diagnose this you can spray some WD-40 down around though the idle air control valve.
I'd recommend removing it cleaning it with throttle body cleaner, lube it up with the WD-40 and see how it runs.
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Old 09-16-2014, 10:24 AM   #10
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Another stalling 8.1

I've had the exact same stalling problem with the 8.1 on a hot day, including the re-starts after a short cool-down period. I'm thinking about solutions now. It appears that hot fuel gets returned to the gas tank and dumped into the fuel pump canister where it gets picked up and sent back to the engine. The heating of the gas by the engine combined with a hot day boils the gas and produces a vapor lock. You can use the search function on this site to find other reports where owners have experienced the exact same thing. The fix seems to be to lower the gas tank, remove the fuel pump canister and drill four 1/2 inch holes in the bottom of the canister. Or, you can re-route the return line to dump the return fuel into the tank at a different location.
Right now, I'm trying to figure out what to do with the 75 gallons of gas in the tank so I can lower the tank and work on the problem.
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Old 09-16-2014, 10:28 AM   #11
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I also heard a giant sucking sound when I removed the gas cap. Loosening the cap did nothing to stop the stalling every 16-20 miles. Neither did replacing the fuel filter with a new one. So, your experience is exactly verified by my own experience.
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Old 09-16-2014, 02:05 PM   #12
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vacuum in the tank is ok this is part of the emissions system and pulls at all times 1 to 2 psi of vacuum when stop for gassing up this system is set to pull more so the gas vapor is not lost

you did not say what year your system is so i can help you on fuel psi

but if you are under 2004 you have trun type and over 2004 returnless
and this moves your fuel pressure regulator into the fuel filter and is why most of the time a new fuel filter can fix alot

you are going to find that ... this happens most on hills and sucks up trash in are over sized tanks and we swop out alot of fuel filter
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Old 09-16-2014, 02:31 PM   #13
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Right now, I'm trying to figure out what to do with the 75 gallons of gas in the tank so I can lower the tank and work on the problem.

If you have access to a chassis lift, you can avoid having to empty the tank. Put blocking/cribbage between tank and floor. Take off tank straps and any thing else connecting fuel tank to coach. Raise coach with chassis lift.
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Old 09-16-2014, 07:08 PM   #14
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Quote:
Originally Posted by terry735001 View Post
vacuum in the tank is ok this is part of the emissions system and pulls at all times 1 to 2 psi of vacuum when stop for gassing up this system is set to pull more so the gas vapor is not lost

you did not say what year your system is so i can help you on fuel psi

but if you are under 2004 you have trun type and over 2004 returnless
and this moves your fuel pressure regulator into the fuel filter and is why most of the time a new fuel filter can fix alot

you are going to find that ... this happens most on hills and sucks up trash in are over sized tanks and we swop out alot of fuel filter
Thanks for the reply! My Workhorse was built in May, 2002, but it was built as a 2004 MH. I think it has a fuel return line. Put in a new filter, but it didn't fix the problem.
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