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 > 80's 454 fuel supply challenges

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brycedub

SLC, UT

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Posted: 07/06/21 12:31pm Link  |  Quote  |  Print  |  Notify Moderator

Long time first time.

I have an 86 The Executive with a newish crate 454 and 95 Chev TBI on top of it. On a recent trip, we had some intermittent stalling except when I'd step on the gas at which point it would rage forward until I let off the gas. Strangely, that issue went away if we turned on the generator, and later, after refueling, we didn't have to run the generator and it was fine and we traveled another 100 miles home without incident, including a multi-hour traffic jam in the Utah mountains.

More recently, we went on a trip and made great time on the interstate, even passing some Uhaulers on hills. We refueled and as we pulled out, the ol thing stalled completely. I was able to restart and work the accelerator to keep it running but it would only just idle and maybe give me 1/16th the power if I lightly touched the gas. We turned around, spent the night, and hoped it was just a cool down issue. The engine always runs from 220 to 280 degrees.

No luck with that, so we limped over to a small town garage and started down the usual checklist. We replaced all fuel filters, checked fuel pressure and checked the timing. No luck with anything. We went to a second place that had a big block specialist and swapped out the ignition controller, idle air controller and even rebuilt the TBI (which strangely didn't have its gaskets after a previous rebuild), but no luck. We concluded it must be the fuel pump, but there were none available for days. I changed the fuel pump the next day, and still, no power.

Strangely, the plastic protective shroud around the pump wires had melted in a few places between the engine and the pump...

We cut bait and got a shuttle back home, then I drove back to it the next day after remembering I didn't hear any noises coming from the fuel tank selector when the key was turned, which I had heard during some previous repairs. I disconnected the fuel supply and return and put them in separate gas cans - one full, the other empty - to see if it would work. Sure enough, it started right up and ran pretty well, so I replaced the selector, but it still didn't work, so i just bought five bucks worth of plumbing parts and bipassed the selector, which looks like it has low pressure, high volume helper pumps. It ran great for another 120 miles in the hot Utah heat.

But! When we arrived at our destination, it stalled a little when I restarted the engine to move to a second location. When I checked in there, it sat for about 5-10 minutes. I hopped back in to restart it, and there was obviously no fuel getting to the engine. I coasted to our spot with the two pumps of brakes I had. I then replaced the fuel relay and was able to start it up and get into our spot.

The end of the next day, I fired it up and started to head out of town, thinking the fuel relay had been the culprit the whole time, which would have explained why the switcher wasn't working and pump might have been heating up wires to the point of melting the shrouds (wires were still in good shape). BUT! We got just a couple miles out of town when it started to slow down and lose power. NOT AGAIN! I almost changed the fuel pump back to the original, but thought the new relay might have been trying to send power to the tank selector, so I disconnected it, fired it up, and it seemed things were great.

UNTIL! We refueled again. I put premium in thinking it would help use maybe a bit less gas thus less strain on the pump. But, when I tried starting it again, it wouldn't start, and made some new weird noises like the starter wasn't releasing after I released the key. After a couple minutes, it would start and had power, so we were on the road again. All was well.

But it wasn't, we started losing power again, but it was like it was before, with maybe a high idle and no real power unless I floored it. We made it another 180 miles like that and got home. Strangely, it never went above 220 degrees that whole stretch, which included some steep mountains between Helper and Spanish Fork.

It stalled at a stop sign 200 yards from our house after idling downhill a couple blocks, but I restarted it and it seemed the power issue had fully reset, it didn't stall, sputter or fight back. But it was a very short distance.

My theory is the fuel relay was indeed bad, that the pump is struggling and drawing too much juice trying to feed the big engine and that power hasn't been getting back to the switcher for a while. But it's odd things work sometimes and not others.

WHAT IS HAPPENING???? HELP! Thanks

* This post was edited 07/06/21 01:50pm by brycedub *

enblethen

Moses Lake, WA

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Posted: 07/06/21 01:46pm Link  |  Quote  |  Print  |  Notify Moderator

Some of the early P-30 based MHs had an electric pump in the big tank and relied on the mechanical pump to suck out of the small tank.
The solenoid gas valve or switch assembly could be issue.
If you have the dual tanks check to see if your small front tank has an electric pump. If it does not, you need one.


Bud
USAF Retired
Pace Arrow

2003 Chev Ice Road Tracker


allbrandauto

maryland

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Posted: 07/06/21 02:08pm Link  |  Quote  |  Print  |  Notify Moderator

I would say the ecm is bad replaced a lot of them back in the day when its running tap on it see if the is rpm changes you said you checked fuel pressure what was it. throtle body injection ran at 11 psi

brycedub

SLC, UT

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Posted: 07/06/21 02:09pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks - when they put the TBI on they added the requisite electric pump and have two high volume, low pressure pumps back at the tank switcher for support. Those are not working now as they use the same power as the switcher. Can't seem to track down a fuse etc for that setup. Oh, should have mentioned it's on a P30 platform.

brycedub

SLC, UT

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Posted: 07/06/21 02:20pm Link  |  Quote  |  Print  |  Notify Moderator

PSI was at 32 after the electric pump, but that was at idle. My guess is that the switcher was open a little but not enough to allow for flow, so it released the pressure in idle, but then gasped for more fuel. I'd love to put a second pump on, but I'm not sure where the power comes from for it to reset it.

Will give the ECM a tap; when they put in the TBI the positioned the ECM under the passenger seat... Lots of extra wires in the doghouse, labeled, but just hanging out there. I'm seriously considering having a standard carb put on to simplify all of this.

When I bipassed the switcher and just had the one electric pump drawing gas, a previous backfire issue went away, which made me think the return line was also blocked by the switcher causing a bit of gas to remain and ignite.

enblethen

Moses Lake, WA

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Posted: 07/06/21 02:56pm Link  |  Quote  |  Print  |  Notify Moderator

In my old Chev pick up, the fuel transfer came off an odd circuit. I think it was off back up lights.
Some after-market transfer valves need power in each position.
Remember the solenoid only gets power when only one tank is called. There is a primary(main) and secondary(auxiliary) tank. You may want to run a new circuit to the pumps via a toggle switch on dash from a hot in run location.

TUBE PULLER

USA

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Posted: 07/06/21 03:04pm Link  |  Quote  |  Print  |  Notify Moderator

Simple Test for you.

Old rig, old wiring, lots of resistance. 12 volts to the pump has lots of termination points before it gets to the pump. Fuse, relay, low oil pressure switch, an inertia switch and lots of harness plug connections. All of these things are old and either weak or corroded.

I have seen this intermittent problem more than once. Test by running a fused, 12 gauge wire, directly from the positive battery terminal to the fuel pump positive connection. Remove the factory 12 power wire from the pump and tape it off and make sure the pump is grounded.

Try it this way for awhile, if the problem never shows it's self again you know you need new fresh wiring to the pump.

Of course, during this experiment you have to be aware of everything that is happening around you due to the fact that all the safeties have been bypassed.

Good luck

brycedub

SLC, UT

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Posted: 07/06/21 04:01pm Link  |  Quote  |  Print  |  Notify Moderator

I did run a quick test of the pump connected directly to the battery at one point before realizing the issue with the switcher, and even bought a switch for just such a scenario. Will try that again with it all hooked up.

Thanks enblethen for the new circuit tip. It still switches the gas gauges, but the power for the high flow, low pressure pump and the switcher are toast. Wonder if the relays back there are bad. Will have to put the ol' multimeter on it.

enblethen

Moses Lake, WA

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Posted: 07/06/21 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

My old rig did not have any relays. Power came directly through the switch to the solenoid. One lead went to the solenoid and another to the gauge in one switch location. The other switch location fed gauge only.
You see if this link different switch configurations.
Different switches

Different styles of valves.

TUBE PULLER

USA

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Posted: 07/06/21 05:33pm Link  |  Quote  |  Print  |  Notify Moderator

I accidentally discovered I was getting low voltage to my fuel pump on the side of the road while broken down.
It was the tenth time my RV died after trying everything under the sun just like you, I crawled underneath and put a meter on the fuel pump power supply wire right at the pump.
I was only getting 8 volts, by the way, when a motor is supplied low voltage, it draws more amperage which in turn creates more heat.
The same way people burn out their air conditioners at an RV park with low voltage during hot periods when everyone is drawing off of the system with high loads.

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