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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4508
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Chevrolet P30 Series: my 1983 P30 chassis RV, 454 engine starts

Customer Question

my 1983 P30 chassis RV, 454 engine starts normally, but when it gets warmed up the engine dies and will not restart.
Submitted: 2 years ago.
Category: Chevy
Expert:  Jerry Newton replied 2 years ago.
What do you have to do to get it to restart, just let it cool off? When it's cooled off, does it fire right up, or does it require a good bit of cranking before it starts?
Customer: replied 2 years ago.
It has to cool off and then it will start right up. If it has not cooled off, then it will turn over and it sounds like it trying to start but will not catch. Local Peterbilt/GM dealer suggests new distributor cap and coil.
Expert:  Jerry Newton replied 2 years ago.
I'd want to know for myself what's actually going away: it's either losing spark, or fuel. Being that it's carbureted, you can simply remove the air cleaner lid, look down into the throttle, and pump the gas pedal. If it squirts gas down the throttle body, then you have fuel. Likewise, you can remove a spark plug wire boot at a spark plug and test for spark. If spark is going away, I would probably lean more toward replacing the distributor, complete with module and pickup coil. Heat affects these things and they will shut right off on you. If you have spark, but no fuel, then you are vapor locking, and you'll have to figure out what's going on with the fuel system. Since it starts right up when it cools, I'd say you're losing spark, because if your carb ran out of fuel, it would take 10 seconds or so of cranking to get the fuel going into the carb again.
Customer: replied 2 years ago.
I replaced the distributor cap, coil and rotor. So far it is still running, so I am pretty certain it was electrical.
Customer: replied 2 years ago.
OK It was idling just fine. Then I tried to rev it up some and it quit. Then same as before, I can crank it and no go.
Customer: replied 2 years ago.
I took off the air cleaner cover and don't see any gas when I turn over the engine. There is a good spark.
Expert:  Jerry Newton replied 2 years ago.
OK, it sounds like you definitely have a fuel supply issue. Vapor locking was common on these big block P chassis RV's, you have to make sure the fuel lines are well away from any extraordinary heat source, such as the exhaust manifold or exhaust pipe. Look upstream, towards the fuel tank, to make sure the lines are not near exhaust and consider insulating with reflective tape. There are myriad measures people would take to prevent this. Clothespins on the fuel line used to be one old timer trick. Seemed to work, the idea was that the fuel line had a heat sink, so the fuel wouldn't boil in the lines. Google "vapor lock" and you can find all sorts of home remedies, but avoiding the heat source in the first place is key. That can be a tall order in an RV, but anything you can do reduce the heat on the fuel lines will also reduce your vapor locking problem.
Customer: replied 2 years ago.
I took it out on the road yesterday. It ran fairly decently, but everytime I got it up to 35 mph, it would lose power. It finally quit climbing an overpass. It would only start again when the outside air temp cooled down. Today I checked the fuel line. All connections seem tight and good. Could it be a problem at the gas tank? I can't get to that area unless I drop it down.
Customer: replied 2 years ago.
This is a frustrating problem for me because when I first bought this RV 3 years ago, I drove it over 4,000 miles with no problems.
Expert:  Jerry Newton replied 2 years ago.
Have you replaced the fuel filter yet?
Customer: replied 2 years ago.
Yes. Also the filter cap has a good seal and is tight
Customer: replied 2 years ago.
Could a damaged oxygen sensor or EGR valve shut down fuel to carburetor?
Expert:  Jerry Newton replied 2 years ago.
No, neither of those things would shut down the fuel. Fuel system is completely mechanical, the computer has no ability to stop fuel delivery. Even if you unplug all of the computerized stuff, the fuel system would still work, although not ideally. This coach is running out of fuel, and there are only a few reasons for this: sucking air due to a cracked sending unit or cracked rubber lines, a faulty fuel pump, or a vapor locking situation. I asked about the fuel filter because that would be another culprit. You replaced the one in the carburetor, yes? I don't know if there is an inline filter or not, but there should be one in the carburetor inlet as well, that's often overlooked.
Customer: replied 2 years ago.
I have replaced both inline and carb fuel filters. Where is the sending unit so I can check it for cracks?
Expert:  Jerry Newton replied 2 years ago.
It is in the tank, which of course means removing the tank. But check/replace the rubber fuel lines first, that's easier and less expensive.
Customer: replied 2 years ago.
I have replaced all the old fuel lines. So it must be vapor lock somewhere. I baffled so I am taking it to a mechanic. Thanks
Expert:  Jerry Newton replied 2 years ago.
You're welcome, good luck with it.