Engine stalls at 1/3 throttle only when using main fuel tank

zaa · June 21, 2015, 11:18 AM

I have some ideas on this one, but I thought I'd run it by you folks, maybe you'd have some other ideas.

*ONLY on the main tank* The 454 runs great, except after accelerating from a stop, anything beyond about 1/3 throttle, it stalls for a few seconds, but eventually recovers. If I run from the auxiliary tank, it doesn't exhibit this behavior. I have plenty of fuel in both tanks.

I need to say, this doesn't happen if you're moving say, 35mph, and accelerate in the same way, it seems to have to do with taking off from a dead stop.

Do these tanks have lift pumps in them? I can't hear anything in the tanks, and I can only see one wire headed up towards the sending unit, though I can't say for sure.

Thanks for reading,
Z

GONMAD · June 21, 2015, 11:20 AM

You might have a small pin holed fuel line. I had this rust problem with BOTH of my fuel lines & being under a slight vacuum won't leak just sitting there. It allows air pockets to draw into the line causing the stumble. It drove me nuts until I pressure tested all lines & it looked like a garden sprinkler under there! The solution was to replace all the lines & install lift pumps at the tank to stop the deficiency in the stock system.

The tanks will not have pumps unless it's injected. I've posted pictures of the mods to the fuel system in my pics section. I just have the pumps on relays for better power distribution. Hope this helped!

C YA! GONMAD

zaa · June 21, 2015, 11:22 AM

Ahh yes, a pressure test would be a good idea.

I have a fuel filter and line ready to install. Unfortunately, they've got the tank switch and filter wedged between the frame and the right front storage compartment. I took the lower supports off the compartment (breaking one hanger in the process), along with getting the recliner seat and seat belt bolts out, and drilling out the rivets, only to find out that due to its shape, the storage compartment can't be removed, at least not without somehow removing part of the fiberglass body panel. Some of the hose clamps were apparently installed before the body was assembled, so you can't get at them. They also have a plate with bolts holding the switch valve in place that appears to have been welded to the frame after the bolts were put in, meaning they can't be removed now. After having already done brakes that day, I wasn't up to the battle, so I left it for another day. I'll need to cut off the old clamps with a tin snips, and be careful not to break the plastic on the switch valve.

I'm also not sure my fuel gauges are working properly, I have tested the instrument cluster, and that appears to be working, but I'm expecting rust on the sending units. I can't *wait* to drop the tanks

Anyway, thanks for the idea!
Z

Rickf1985 · June 21, 2015, 11:23 AM

Gonmad, these tanks DO have pumps in them with carburetors. They also have a regulator, most of which are in impossible to get to places and they do leak. I think they started putting pumps in the tanks in the mid eighties to overcome vapor lock problems. My 89 Chieftain had a single 80 gallon tank. I think I would rather have the two smaller tanks!

gpw9552 · June 21, 2015, 11:24 AM

What Rick said.

My 1987 has a electric pump in the main only. Some time later they put a electric in the aux tank.

Look at your fuel selector switch. If it has a little flush mounted light next to it you have a electric in the main only. When you switch to aux the power to the electric fuel pump is switched to the lamp .
The above description is based on the drawings Winnebago sent me.

GONMAD · June 21, 2015, 11:24 AM

You are correct sir! I now remember one around the corner with a regulator INSIDE the frame. My neighbor had to cut the straps to drop the tank to gain access to the leaking Holley regulator. A four hour fix for a ten minute problem. Re assembly was worse than everything else involved. I guess patience is a prerequisite for a job of this sort. Good luck. GONMAD

MotorPro · June 21, 2015, 12:10 PM

Main tank does have an electric pump. The aux does not.

cncsparky · June 21, 2015, 12:43 PM

If you do have a fuel pump in the tank, most likely you will need to drop the tank and repair the rubber hose that goes bad. Many of us have had this same issue.

gpw9552 · June 21, 2015, 01:02 PM

REALLY, REALLY GOOD POINT.
I had a intermittent problem with the main tank.
1. Split hose. Ran good until the fuel level fell to the split. Mechanical pump would pull fuel until then.
2. Bad select valve relay under the dash. It was NOT the dreaded safety relay.

BTW the sock strainer on the bottom of the fuel pump is NOT listed at NAPA for the 454 but is the same one listed for the 350.

zaa · June 21, 2015, 06:35 PM

I just wanted to stop back in and say, I've fixed the stumbling problem, it was indeed failing fuel lines. I replaced the frame fuel filter, the one in the carburetor, and all the rubber hoses along the frame. I also managed to get the front AC converted and recharged, and the thermostat switched out.

I still don't know for sure whether there are pumps in the tanks. The title for this unit says 1985, but the VIN says it's a 1986. I do not have the light by the tank switch, and I only have a mechanical pump on the engine, unless there's an electric one hiding somewhere, but I don't hear anything.

Rickf1985 · June 21, 2015, 08:53 PM

usually due to idle being to high.

zaa · June 21, 2015, 09:01 PM

Okay, thanks for the info. I'll definitely check those items.

Thanks,
Z

MotorPro · June 22, 2015, 09:29 AM

The electric pump is in the main tank

cook elandan · June 22, 2015, 11:22 AM

It depends on the year if it has an electric pump in the tank. My 85 does not have an electric pump at all. So he is saying his is 1985 so he may not have the pump. I have dropped the tank and it only has a hole big enough for the float and fuel tubes to go through and fuel lines running all the way to the switching valve so there are no other pumps or filters from the rear to the switching valve.

legomybago · June 22, 2015, 01:05 PM

From just about every fuel related issue I've read on this forum about the P30 chassi's, The 1985 chassi has only a mechanical fuel pump. 1986 is when they first installed a factory electric/and mechanical pump on the chassi. I haven a titled 1986 Komfort class A, but it is mounted on a 1985 P30 chassi. U can guess what set up mine came with stock, so yes I added a Holley red pump back near the fuel tank to stop my vapor locking issues, and it works beautifully. Im also having a dieseling/clunking problem at start up and at shutdown half of the time...it's driving me nuts. Subject for another day.

Rickf1985 · June 22, 2015, 06:38 PM

Start and shut down is timing to far advanced.

Rickf1985 · June 22, 2015, 06:44 PM

Zaa, what you are describing does not sound like a starvation issue since you say that at higher speeds you have no problem accelerating. Are you running fresh, I mean less than two month old gas in that main tank? Do you have a clear filter in the line anywhere you could check to see if you are getting water out of that tank? What you are describing sounds almost like the beginning stages of phase separation of the gas due to moisture in the gasoline with alcohol in it. Do NOT put any gas dryer in there! That is just more alcohol.

DaveVA78Chieftain · June 22, 2015, 08:03 PM

In the Members Free Manuals area, under the Chevy/GM P-30 Chassis section, there is the free '79-'94 Chevy/GMC P-30 Chassis Service and Maintenance Manual. Under the VAPOR LOCK CAUSE AND CURE section (Appendix 7-7, pdf page 135) is a complete description of what GM did, or recommended you can do, regarding the 80's era P-30 chassis fuel system. Takes all the guess work out of what actually was done. There are also many posts on the site describing the replacement/repair of the regulator that was used with the in tank electric pump on the carburetor models (85 1/2 - 89).

Dave