92 Fleetwood Flair with 454 no power issue and getting worse

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C

Clubhouse

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Joined
Nov 8, 2023
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6
Location
Canada
I've been working on this unit since November, when I got it, it had been sitting for a year or so. It actually ran fine even with old fuel. In preperation for putting it into service I dropped the fuel tank, replaced the sending unit and fuel pump, the fuel filter, put in fresh gas and took it for a trial run.
It didn't seem to pull as hard under load as I thought it should and it is progressively getting worse. I replaced the fuel filter again to make sure it didn't somehow get plugged with some remnants out of the gas tank. I replaced the plugs with AC Delco even though it had a complete tuneup before it was taken off the road previously. I also took the distributer cap off and cleaned all the contact points. At first I thought it was an ignition problem but the more I work on it the more I'm leaning to some type of fuel problem. I'm thinking my next step is a TBI rebuild, in particular the fuel regulator. I'm not sure what type of symptoms a bad regulator could cause but I think if the regulator was bad it could allow the fuel to cycle from the tank to the TBI and back to the tank without building the pressure required. Is this a possibility? It starts no problem at all and idles really well but within 5 minutes of driving it really starts to act up. Any suggestions would be greatly appreciated, I'm very mechanically inclined and am trying to work through this is a logical flow checking the results after each change.
Thanks
Randy
 
It sounds like this started right after the the fuel pump was replaced. It could be defective or you may have a clogged line or injector nozzle. Some auto parts stores will loan fuel pressure test kits. Test the pressure as well as the flow rate.

But distributor caps wear out from the constant arcing and can get cracks. I noticed you cleaned it instead of replacing it. My son once sold a car to an uncle because it slowly got to where it wouldn't go over 40 mph. The uncle was honest enough to return the car after he found the distributor cap was all that was wrong. Don't forget other things like dragging brakes can also cause performance issues.

You can tell a lot from a vacuum gauge, see here
 
A plugged exhaust can cause low power. Suspect since it sat a while. A vacuum gauge can indicate air/exhaust flow problems.

Mark B.
Albuquerque, NM
 
Ok, so todays update, much progress more information to go on. I removed the Catalytic converter to eliminate that as a possible problem and as I was putting on the air cleaner and it dawned on my that I never watched to see where the end of the intake snorkel went up front when I had put it on previously.
I discovered that it was not going into the opening it needed to so I made sure it was in the right place.
Took it out and all the power I would expect was there, not sure if it was the removal of the Cat or that the air intake was blocked.
Regardless, great power..... For about 10 minutes, then it started to lag, buck and serge, not as bad as before but very noticeable.
I wondered if it was a tank venting problem so I shut it off went and removed the fuel cap, there was a fair amount of air escaping when I removed it, but the cap even says right on it that it would so remove slowly.
Fired it back up and instant power again..... For about 5-10 minutes then it started acting up again.
Shut it off, counted to 60, fired it up, ran like a champ again....then acted up again. Shut if off counted to 30 and instant power again.
Did this cycle for a count of 15 and then ultimately just shut it off and back on again.
Each time, it appears that shutting off the ignition and then starting it back up again seemed to reset whatever is causing this problem. The fact that I don't have to wait tells me that it is some type of electrical/ignition issue and not a pressure release/buildup issue.
What in the system would cause it to start to run rough and lose power after a few minutes and shutting it off and restarting it would solve the problem?
 
had an 81 Chevy that ran fine for about 20 minutes then would backfire sometimes and would lose power only at highway speeds. Turned out to be the electronic ignition module inside the distributor.
 
I think I eliminated that when I removed the gas cap, I left it off for the rest of test run and was still having the same recurring issue so there should have been no pressure or vacuum buildup.
 
Fuel pressure needs testing. For the 92 it is 9-13psi preferably closer to 13psi. When it comes to TBI that is the first item one should check. You'll need the following: Our fuel psi guage to fuel line adapter mounts inline directly to your GM tbi throttle body!!!

You'll also need a fuel schrader valve 1-8 mnpt

The following is mine after rebuild...

454 TBI rebuild

Going to rebuild the TBI on my 1994 GM P-30 chassis motorhome one thing I noticed with the TBI Delco rebuild kit. The base gasket is not shaped the same as the OE one. Does it matter? Also the bakelite spacer/gasket that sits under the regulator housing on the OE one is thicker than the kits...
www.gmt400.com www.gmt400.com

Mine is a 94 and uses different injectors and higher fuel pressure 26-32psi. Both the 94-95 years were same fuel pressure and injectors.
 
Richard, you win the prize, see below for my full description of what finally transpired and steps to resolve.

One of the biggest issues I've ever had with forums is you can read an entire thread and then it stops, no indication if the problem was ever solved and if so how and what was the cause. I promised myself I would not be that person so here goes, This Problem is Solved.
I was able to get a loaner fuel pressure tester from the jobber store. Tried to hook it up at the throttle body but the steel fuel line was not flexible enough to allow for the additional space required for the adapter. I was able to find a connector from the steel line to a flexible line back to the steel line just under the passenger side frame rail which allowed the movement of the engine separately from the chassis. Inserting the adapter there allowed the gauge line to be passed up through the dog house opening so it could be monitored while driving.
At start up it pressured up to 13 psi and held that steady under full throttle and long loads. After about 8 to 10 minutes it started to drop and the engine performance issues started to appear.
When it was at it worst conditions the fuel pressure was down to 8 or 9 PSI.
Shut it off and back on it was instantly back to 13 to 14 psi. Started to run it again and it was fine for about 3 or 4 minutes then the pressure started to drop and performance again fell apart.
So it was definately a fuel issue. Having already replaced the pump I was reluctant to accept that I could be so unlucky as to have gotten a bad fuel pump.
Pulled the tank again and removed the fuel sender/pump assembly to see if there was anything obvious and there was.
The fuel sock that attaches to the bottom of the pump looked like it was 50 years old. Removed it and you couldn't see any light getting through it so it was pretty obvious crap in the tank was the route cause. I think when I pulled the tank the first time I had drained the fuel to make it a bit easier to manage. The tank was empty for 4 or 5 days and I think that was just enough for the 30 years of scale etc to dry up. When I put it back in I cleaned it up best I could and then put fuel in it. I think that washed out the crap and the first time I fired it up after fueling it the sock probably loaded itself up with all that crap and probably reduced its capacity right away.
I think as it ran subsequently, the more the pump tried to draw the more crap started to plug up the few spots still available to draw fuel until it was restricted enough that it would loose pressure. As soon as it was shut off, no longer creating a suction enough of the crap would drop off that it would momentarily work as expected.
I replaced the sock, cleaned things up again and ran it with the pressure tester again. This time 13 to 14 psi, never dropped a bit, even on a very long steep hill starting from a dead stop.
I'm not overly optimistic that I'm in the clear of the crap in the tank, if I can get through a full tank of driving without issue then perhaps. I did buy a spare sock and at least I know I can get the tank out in about 30 minutes.
On the plus side, I think I've got a pretty bullet proof runner now that its had a full tuneup, new Ignition Control Module, Temperature Control Sender and the Catalytic Converter removed.
Thanks to all who had responded and offered up suggestions, hopefully somebody else will find this helpful.
Randy
 
Before it happens again I'd drop the tank and thoroughly clean it. The old time method of dropping a chain in the tank and sliding the tank back and forth around works to physically knock scale off. Then flush the tank and run a chemical cleaner through it to get any residue.
 
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