P-30 454 CID fuel feed problems.

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MAKE: Pace Arrow
MODEL: P-30 Chevy Motorhome Chassis
DESCRIBE ISSUE.... Exhaust manifold for this old model has O2 sensors for each cylinder, one plug fell out, what a noise, threads are goo in the manifold, searched for these plugs, without luck, anybody know the thread size. Suppose I could measure it, didn't even know they were using 8 separate O2 sensors in any engine.

Second problem is lack of fuel, 80 gallon tank in the rear, 30 gallon tank in the front. On a 700 mile trip a couple of weeks ago, front tank quit working, fuel filter was plugged, think I got bad gas, but replaced that and all is okay again, got home fine on the rear tank.

This last weekend, front tank worked fine for a hundred miles, than quit, fuel filter still good drove fine on the rear tank again, but coming back rear tank was starving for fuel. Was fine for the first hundred miles, then engine died. Has a six port fuel valve Two tank inputs, return pipes for to each tank to prevent vapor lock, than two inputs to the fuel pump. Have a new Carter, gee on 17 bucks for these.

What I had to do was to pull over, leave the ignition on, this valve feed an electric fuel pump and let that run for about five minutes. Engine started instantly, was good for another 10-15 miles or so, then died again. Bit frustrating, but did get us home. Both fuel filters are new and clean, quite the mystery.

Suppose I can take everything out and check it, but did anyone ever have a problem like this before? Maybe I have water in both tank, this would be a pain to check.
Screwed this up, engine fuel pump has fuel inlet and return, either switched to the front or rear tank accounting for the six ports. Have the electric fuel pump attached to the valve fuel pump outlet. Need that to fill the carburetor bowl because not a daily driver, saves grinding the starter for 30 seconds for the engine driven pump. Also needs a booster for that long fuel line running to the rear tank. Rear tank is the default, switch on the dash energizes this valve for the front tank. Also switches the fuel senders.
8 o2 sensors AND its a carburetor? is it the fun filled M4ME elec qudra'jet ?

could it be a tank vent issue? I remember another post someone had that issue - hoses were installe d wrong....

What if any emissions testing on a 80;s model do you have to deal with ? Anyway I see some modifications in your future plans....
Whatever those holes are for, a 1/4" NPT tap fit, cleaned out the threads, and used a galvanized plumbing plug, let the manifold get hot so good and tight, no more leaks.

Gas problems will have to wait until next spring, 80*F last Sunday, today freezing.


Staff member
Yes, 1/4" pipe is *sorta* close, I used to make thermo-couple fittings to go in there from 1/4" MPT fittings; I would re-chase the male thread with a 1/2"-20 die. The 1/4" NPT is bigger, though, so if you have run a tap in, the manifold threads are rather ruined for their original purpose.

If I just want to plug those ports, I use... a short 1/2"20 screw.
Can't post a photo, can't get a camera in their, but the screw was of the allan hex type, hole is recess or counterbored about an eighth of an inch, so anything with a head on it wouldn't seal very well.

The three front holes from what I can find on the net use 1/2" hex head bolts, but this one at the rear, both sides use this larger hole. front 3 are called AIR, rear is for the O2 sensor. 454 has been around for a long time, didn't find these plugged holes back then, but claim new exhaust manifolds will fit the older ones with plugged holes. Exhaust manifolds were always a problem with the 454, but these are in a 27 footer, use the same engine and drive train in a 43 footer, these are the ones that have the most problems.

You don't want to put your hand in front of that open hole with the engine running, will blow it off. Replaced all the fuel lines about ten years ago, ha, I am finding myself ten years older. Been a lot of water in gas problems up here, lots of rain, also can't use ethanol in this thing, pump says ethanol free, hope they are not lying.

Everything works fine in this thing, generator, both AC systems, cruise, dual refrigerator, all this started about two weeks ago, but maybe time to get rid of it. Lost four of my old military buddies in the last two years, only two of us left. Think about this also.
Could finger start that 1/4" NPT a couple of turns, then had to use a wrench, started off easy enough, but near the end got awfully stiff. Used a mirror to see deep cut threads. Plug when in tight with only about two threads showing, ha was tempted to weld it, because have no use for that hole.

One of the rear left side is practically flush with the manifold, does have a Allan type hole in it, looks badly rusted, would have a heck of a time removing that one. So hope it will stay there.

Also had problems with the exhaust manifold bolts working loose, had to tighten them a couple of times. Thought about the number of times I would break the heads off these bolts, and had to heat them with an acetylene torch to get them out without wrecking the heads. Remains a mystery.


Wrench. I help when I can
Also had problems with the exhaust manifold bolts working loose, had to tighten them a couple of times. Thought about the number of times I would break the heads off these bolts, and had to heat them with an acetylene torch to get them out without wrecking the heads. Remains a mystery.

From experience, "and yes I know you have more than me", those manifold gaskets are useless on these RV's and pretty much any 454. better to go metal on metal. Cast iron block, cast iron headers. since this is a HIGH application for the 454, it has to tow a large capacity, especially with all the gear and family, gas, water, waste water, etc.

Metal to metal will not snap exhaust bolts. They both have same expansion rate and the gaskets interfere with this. I just chuck them in the waste bin when redoing a motorhome with a 454, and most of this era ran those. The worst things alot of guys do is install those 454's with the gaskets cuz they come with the kit. Better without them. Throw them out and the header's do fine.


Wrench. I help when I can
I encountered this when I was younger and I left this guy ride home in his winnibago from quebec and his final destination was alberta. I got a call from himin manitoba, headers were loose. He said my motor home sounds like a harley.

I had installed the header gaskets, lesson learned cuz I got chewed out by the guy that redid the crank on this 454 in quebec cuz I installed those gaskets, and since then, I have never redone a 454 with header gaskets, and they all stand up with no loose header bolts.

Ususally they are slotted so if you get them loose, but not all the way, just slip the gaskets out and rebolt to a reasonable torque (elbow torque) and you should do many miles without that nuisance.

BTW, that particular RV split a cylinder wall, so whole engine had to be removed and redone. What a job!!!!!!!! I still enjoy christmas cards from that guy. He wasn`t mad at me. But the older guy from the engine shop was pissed. But hey, I installed what came with the kit and didn`t know better. He sure did. I will never ever install header gaskets again on a 454 again, whatever application.


Wrench. I help when I can
Disclaimer, without gaskets, they do sound for a bit, but once eng is up to temp, can go for miles without a hitch, so just have to suffer initial warm up sound.

I know they sell plug kits for the dual bed cat system. can`t seem to find a link but I am sure down where you live you can find that. Alot of 454`s are still alive down there.

Try this link. I don`t know. I just know they sell a plug kit to get rid of those pre age cat systems. http://www.summitracing.com/int/search/section/exhaust-systems-kits/make/gmc/engine-size/7-4l-454

Just do away with the dual all together and go with a racing header.


Wrench. I help when I can
I used a few hooker systems and sadly as it sounds, I still have the stickers on my tool chest. I don`t know, I liked the look of the sticker.

But they make a serious header.