Dead On Side Of Road: Fuel Starved/Vapor Lock?

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Dead On Side Of Road: Fuel Starved/Vapor Lock?

March 22, 2018, 09:23:21 pm

Hey Ya'll,

We are dead on the side of the road outside of Guadalupe National Park in TX.

1987 Chevy P30 454 7.4L.

Can't get the coach to go forward... not sure why.

Here's what she does:
1 - Starts up
2 - Seems to idle low, if you give it a bit of gas it idles better.
3 - Let off the gas and let it idle for long enough, it'll shut off.
4 - If you put it in drive and push on the gas... the engine dies.

These sound like fuel starvation symptoms.

But, I literally just put in a brand new high performance holley blue fuel pump this afternoon.

I was having Vapor Lock issues when I'd idle in traffic or sit too long as a stop light or turn it off to get gas. The engine bay would get warmer and the pump wouldn't pump fuel (assuming cause it'd be pumping vapor). And the see through fuel filter I have under the doghouse by the carb would be dry.

So reading Chevy's service manual for that issue, they recommended upgrading the fuel pump to the Holley Electric Fuel Pump: https://www.summitracing.com/parts/hly-12-802-1

I installed that this afternoon cause the wimpy electric fuel pump that the PO installed finally gave out this afternoon. It's was an off the shelf auto-zone fuel pump. Don't think it was powerful enough for this coach anyways.

After installing the new pump, the coach started right up and we drove about 20 miles before the coach started getting warm (on a flat travel surface). It's never done that before. So we waited a while and tried again about 7 miles before we hit a grade. Made it about a mile up the grade before we started losing power (ie step on the gas and engine wouldn't rev, it would lose rpms) and it was getting warm again.

We have let it sit for a couple hours now and it'll still start. The new fuel pump is pumping fuel nicely (you can see it doing it's job in the clear fuel filter under the doghouse.

But when you start and put into drive and push on the gas, it shuts off like it's being fuel starved... and we start rolling back down the hill... which sucks.

Any ideas?

I've fixed damn near everything on this engine. It's got a brand new starter, brand new alternator, radiator has been checked and flushed, brand new fan clutch, new plugs, cap, rotor, & wires. New power steering pump. New brake master cylinder. New air filters. New Fuel filters.

I didn't adjust the carb or the new fuel pressure regulator after putting in the new fuel pump... 1, cause the holley pump instruction guide said you shouldn't have to and 2, cause I don't know how.

Could the pressure regulator be giving too much/little pressure and causing it to act like this?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #1 – March 22, 2018, 09:38:52 pm

Some questions: Are you plumbed though the original fuel pump? Does the carburetor have a brass filter behind where the fitting for the fuel line goes into it?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #2 – March 22, 2018, 09:46:35 pm

Another thought is you need to double check your timing. You may need to back off the timing (retard it some) this can help both with the heating and fuel trouble. Years ago this was a common thing we had trouble with going from the flat land up to the Colorado mountains. We would also stop along the way and change jets in the carb. but that is another thread.

Mike

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #3 – March 22, 2018, 09:58:27 pm

Vacuum leak from a hose that got disturbed during install??? Smell the exhaust. Some carbs are extremely sensitive to fuel pressure. Overheat sounds like it may be too lean of gas mixture.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #4 – March 22, 2018, 09:59:26 pm

Quote from: craneman – March 22, 2018, 09:38:52 pm

Some questions: Are you plumbed though the original fuel pump? Does the carburetor have a brass filter behind where the fitting for the fuel line goes into it?

Hey @craneman!

There is no brass filter behind where the fitting for the fuel line goes. Pic attached.

We are not plumbed through the original fuel pump. It appears to have been capped off or something and the fuel lines aren't in use.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #5 – March 22, 2018, 10:01:14 pm

These pics didn't attach on the last post.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #6 – March 22, 2018, 10:02:19 pm

Quote from: Pamela & Mike – March 22, 2018, 09:46:35 pm

Another thought is you need to double check your timing. You may need to back off the timing (retard it some) this can help both with the heating and fuel trouble. Years ago this was a common thing we had trouble with going from the flat land up to the Colorado mountains. We would also stop along the way and change jets in the carb. but that is another thread.

Mike

How would I adjust the timing? Need any specialized tools to do it?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #7 – March 22, 2018, 10:06:50 pm

Quote from: Old phart phred – March 22, 2018, 09:58:27 pm

Vacuum leak from a hose that got disturbed during install??? Smell the exhaust. Some carbs are extremely sensitive to fuel pressure. Overheat sounds like it may be too lean of gas mixture.

Hey Old Phart! Good to hear from you.

There are no vacuum hoses near the fuel pump as far as I can see. But then again, I'm not entirely sure how to tell if something is a vaccuum line. I thought those were the line running from the air box down into the engine.

I've heard that the carb could be sensitive to fuel pressure, how would I test or know if the carb is getting too much or too little pressure? I assume that it's now getting more pressure than it was before, since this pump is a much higher end pump than the one that I had in there before from the PO. I believe there is a simple screw adjustment on the holly regulator that will adjust the pressure if I need to.

And another question on that... if the pump is giving it too much fuel pressure... how would that result in too lean of a gas mixture? Seems like it'd be too rich.

Last question... smell the exhaust and look for what in the smells?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #8 – March 22, 2018, 10:16:04 pm

Quote from: AKATheAlchemist – March 22, 2018, 09:59:26 pm

Hey @craneman!

There is no brass filter behind where the fitting for the fuel line goes. Pic attached.

We are not plumbed through the original fuel pump. It appears to have been capped off or something and the fuel lines aren't in use.

The filter I am referring to would be behind the fitting in the carburetor. Some Quadrajets came with them.
Also if you have too much fuel pressure it will push the fuel past the needle and seat and you would know as it would be flooding the engine. Volume is much more an issue with a carburetor.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #9 – March 22, 2018, 10:20:52 pm

Does your coach have a catalectic convertor? A plugged one would have all the symptoms you a are having.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #10 – March 22, 2018, 10:24:36 pm

Have you driven this before? or is this the first time running? Try taking the fuel cap off and see if it will run better.. Shortage of fuel it sounds like

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #11 – March 22, 2018, 10:30:57 pm

My old P32 acted that way with a clogged fuel filter attached to the framerail.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #12 – March 22, 2018, 10:37:04 pm

Quote from: craneman – March 22, 2018, 09:38:52 pm

Some questions: Are you plumbed though the original fuel pump? Does the carburetor have a brass filter behind where the fitting for the fuel line goes into it?

Good point craneman, I forgot about those ity bitty tiny filters they used to install on the carb gas inlets. Also if you changed to a different pump make sure you did not pinch a line near the pump. It all goes back to the fire triangle fuel, oxygen, and ignition source.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #13 – March 22, 2018, 10:47:16 pm

@craneman - Attached is a pic inside the carb. The fuel comes in on the bottom right of the photo. Doesn't look like there is a filter.

And it sounds like I don't have a pressure issue.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #14 – March 22, 2018, 10:48:27 pm

Quote from: craneman – March 22, 2018, 10:20:52 pm

Does your coach have a catalectic convertor? A plugged one would have all the symptoms you a are having.

I don't even know what one of those is. Lol. What would I look for for see if I have one and if it's plugged?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #15 – March 22, 2018, 10:48:41 pm

Quote from: Travelin' Man – March 22, 2018, 10:30:57 pm

My old P32 acted that way with a clogged fuel filter attached to the framerail.

Yup, Our old P-30 with a 454 had the frame mounted tank filter.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #16 – March 22, 2018, 10:50:08 pm

Quote from: DavidS – March 22, 2018, 10:24:36 pm

Have you driven this before? or is this the first time running? Try taking the fuel cap off and see if it will run better.. Shortage of fuel it sounds like

Yeah, We've been driving it since last may. Put nearly 5K miles of her. She's a good coach. It's got an old style fuel cap, it's literally just twist on to keep fuel from spilling out on curves. No pressure or anything. It does sound like a shortage of fuel. Wondering if I have another fuel filter somewhere I don't know about.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #17 – March 22, 2018, 10:51:35 pm

Quote from: Travelin' Man – March 22, 2018, 10:30:57 pm

My old P32 acted that way with a clogged fuel filter attached to the framerail.

Quote from: saddlesore – March 22, 2018, 10:48:41 pm

Yup, Our old P-30 with a 454 had the frame mounted tank filter.

Okay... Where would I look for this sneaky bastard... should I have one? I assume it would be between the fuel tank and the fuel pump... since the only filter I have found it after the pump and before the carb. That's the clear one in the pics above.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #18 – March 22, 2018, 11:05:44 pm

I went ahead and traced the fuel line from the pump to the tank. There is no other fuel filter.

I was hoping it would be something that easy.

Fuel line goes back from the engine bay where the pump is mounted, on the passenger side. Down to the a cross beam just behind the propane tank and across to the fuel tank where it is attached to what is likely a fuel pickup?

I can access this under our couch via a cut out in the floor.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #19 – March 22, 2018, 11:06:51 pm

Also, It's late and we've got to put the kids to bed and I can't do much more in the dark anyhow, so I'll check back in in the morning. We'll probably try to drive it first thing and see if we can at least get it off of the hill.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #20 – March 22, 2018, 11:09:25 pm

Yes you do have a catalytic convertor. It looks like a muffler and they do plug up, usually can tell by no pressure coming out the tail pipe.

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #21 – March 22, 2018, 11:26:40 pm

Quote from: craneman – March 22, 2018, 11:09:25 pm

Yes you do have a catalytic convertor. It looks like a muffler and they do plug up, usually can tell by no pressure coming out the tail pipe.

Good to know. Was just doing some research on these now that you gave me that tip. I can't really check anything else tonight... but I'll report back tomorrow and see if it's clogged.

If it is, can I just remove it temporarily until I get to the next town?

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #22 – March 22, 2018, 11:49:53 pm

OK, first look down inside the carburetor and have someone pump the throttle. The two primary barrels have accelerator pump nozzles that should produce a strong stream of gasoline aimed at exactly a the crack where the throttle butterfly opens against the carb body. This should give good throttle response when you step on the gas.

If you don't get a good stream out of both pump nozzles, pull the hose/fitting where the fuel hose connects to the carb where your arrow is pointing in the first phono. Put the end into a Coke bottle and turn on the ignition. You should get a good flow of gasoline into the bottle WITHOUT the engine running. The carb only needs 5-8 psi of pressure.

That failing, check for voltage at the electric fuel pump to make sure it's working OK.

A bad or plugged Cat will usually idle OK but lose power as you add more load.

Sounds like fuel starvation to me. Usually a problem that occurs after a component has been replaced has something to do with the installation of the new component.

Do you have a second tank and a changeover switch?

Pierce

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #23 – March 22, 2018, 11:51:22 pm

I am not an auto mechanic by trade but I did a little research but research to verify. Your pressure regulator that came with the model pump in your link comes preset to 14 psi. Some hot rod forums say you should run around 7-8 psi on the carbs. Anything too high can cause all kinds of strange symptoms. To adjust your regulator you loosen the lock nut and turn the adjustment screw counterclockwise to lower the pressure. But you need some sort of inline fuel gauge to adjust the pressure. Seems to me it is something to do with the fuel pump install that changed things. Just my thoughts after reading your posts. Hope you get it figured out and get back on the road.

Mark

Re: Dead On Side Of Road: Fuel Starved/Vapor Lock?

Reply #24 – March 22, 2018, 11:55:16 pm

Hey @craneman - I went ahead and took pics of my exhaust setup. 0277 is from the engine down. 0278 is the middle of the exhaust pipe. Looks like this is where the pipes were extended to reach down the frame. 0276 is the rest of the exhaust pipe. This is mirrored on both sides of the coach. So there is two of everything and they match.

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