Author Topic: Intermittent power loss. I suspect the fuel pump (Read 357 times)

AliceKelly · « **on:** December 31, 2020, 07:38 PM »

Mainly bouncing ideas off yall.

I changed my cracked manifold which as it turned out was broken in half.

She has been acting stranGE for a month. When she warms up and driven a few miles she intermittently will loose power and die unless I hammer down the pedal and let the fuel catch up

This is a new fuel pump I put on just six months ago. If she gets really warm she will stop dead for an hour to cool.

I have rebuilt carb and put in two fuel filters just in case the tank was dirty. And then there's the heat issue that has been fixed. I suspect the mechanic fuel pump the accelerator pump or a fuel filter.

Open to comment... Thanks Happy new year!

Oz · « **Reply #1 on:** December 31, 2020, 10:29 PM »

Start with checking your fuel filter.

AliceKelly · « **Reply #2 on:** December 31, 2020, 11:19 PM »

Ty oz

AliceKelly · « **Reply #3 on:** January 03, 2021, 01:53 AM »

Something is fishy. Originally when I baught this winnebago /w 350 it had one of the ac Delco three line pumps like has a bigger canister on it. It was my understanding that the three lines were supposed to stop vapor lock. But I got some info here that said put in an electronic pump near the tank. And for a short time she acted better. But few hundred miles and she began doing the fuel starved trick again. I changed a two fuel filters and saw no improvement. Took out the electric pump and bam she ran like a champ for two days and bam back to acting fuel starved

So I've replaced the mechanical pump. It's less than one year old. Put in and removed an electric pump. And replaced fuel filters. And replaced any rubber hoses. For the most part the lines are steel. Except near the carb to pump.

I had thought that it was all about heat in engine compartment but I replaced the broken exhaust manifold and it's almost cool in there now. The pump shouldn't be having heat issues any more.

There is a point where the starter manifold and fuel li es are all sandwiched close together but it acts like it can't keep enough fuel in the line to feed the carb but at one point I put one of those plastic plates under the carb between intake and carb so I'm guessing the carb is cool enough.

This problem is driving me nuts. After about 20-30 miles she will just die till either I hammer her with starter fluid or let her cool. She always starts and runs perfect cool and doesn't miss.

I don't think it's vapor locked maybe sooper heated fuel or something. Wondering if I should re rout the part close to exhaust with rubber for maybe two feet to the pump to maybe keep the lines cool.?

AliceKelly · « **Reply #4 on:** January 03, 2021, 01:55 AM »

Ps my other thought is going electric only and / or changing the carb

Oz · « **Reply #5 on:** January 03, 2021, 03:12 AM »

I'm not carb problem saavy, but did have a similar issue with my original one. Assuming there is no vapor lock issue and adequate supply to the carb, you can either start troubleshooting the carb, or replace it.

I replaced mine with a edelbrock 750 cfm (for 440-3) and matching intake manifold.

AliceKelly · « **Reply #6 on:** January 03, 2021, 03:29 AM »

Will it use a stock ac Delco fuel pump?

Oz · « **Reply #7 on:** January 03, 2021, 03:38 AM »

I'm more knowledgeable with the Dodge chassis and not the Chevy, so Im afraid I'm not much help there, but I'm sure this is addressed in other topics, though need to check since most are 454 and not 350.

AliceKelly · « **Reply #8 on:** January 03, 2021, 04:02 AM »

Thanks Oz something to ponder. Originally I had the stock quadrajet but it dumped fuel so I baught a core and rebuild it. Might try a cheap re uild n swap and see how she acts before a whole intake. I have to smog every 5 years and would have to swap everything out every five years lol

Oz · « **Reply #9 on:** January 03, 2021, 04:16 AM »

Every 5 years? Yikes!
As for the fuel pump, it should be a stock replacement.

You don't have an in-tank pump, do you?

AliceKelly · « **Reply #10 on:** January 03, 2021, 08:59 AM »

No Oz. My mech pump is up on front of engine

Eyez Open · « **Reply #11 on:** January 03, 2021, 04:59 PM »

Quote from: AliceKelly on December 31, 2020, 07:38 PM

Mainly bouncing ideas off yall.

I changed my cracked manifold which as it turned out was broken in half.

She has been acting stranGE for a month. When she warms up and driven a few miles she intermittently will loose power and die unless I hammer down the pedal and let the fuel catch up

This is a new fuel pump I put on just six months ago. If she gets really warm she will stop dead for an hour to cool.

I have rebuilt carb and put in two fuel filters just in case the tank was dirty. And then there's the heat issue that has been fixed. I suspect the mechanic fuel pump the accelerator pump or a fuel filter.

Open to comment... Thanks Happy new year!

Without going into a technical malaise take the temp of your carb once warmed up, I can almost assure you it will be above 190 degrees, actually, anything above 160 is to much. Modern gasoline boils at 160 and your carb gas lines are the carb itself heating up is the problem.

A phenolic spacer will isolate the carb reducing the heat dramatically, the heat source is the emission control system. 40 yrs ago it was hi-tech..today known as junk...lol harsh I know but it is what it is. Cold carb hot intake makes for a happy engine...well warm carb..not engine temp.

https://www.amazon.com/Moroso-64941-Carburetor-Spacer/dp/B001GHYUSO/ref=asc_df_B001GHYUSO/?tag=hyprod-20&linkCode=df0&hvadid=366288796258&hvpos=&hvnetw=g&hvrand=2128759558975722627&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032828&hvtargid=pla-787937548033&psc=1&tag=&ref=&adgrpid=83058288464&hvpone=&hvptwo=&hvadid=366288796258&hvpos=&hvnetw=g&hvrand=2128759558975722627&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032828&hvtargid=pla-787937548033

Some backround here Vizard knew long ago high temp carbs were a bad thing so along came the spacer. Actually GM back in the 60's tried this hot carb approcach and came up with the spacer fix..
https://www.hotrod.com/articles/0601phr-best-carb-spacers-cheap-horsepower/

AliceKelly · « **Reply #12 on:** January 03, 2021, 10:19 PM »

Ya I have a spacer on it. Didn't help at all. Just stole. Power from the carb.

Eyez Open · « **Reply #13 on:** January 03, 2021, 11:29 PM »

A few things, is this spacer phenolic or aluminum and is it made for a Rochester. As odd as this may sound can you take a temp reading of your gas line and carb during operating tempatures. Heat build with a AIR emission system is enormous, 1600 degrees is common your cast headers have demonstrated as much. All steel gas lines only promote heat transfer..judging from the conversation ive seen this carb has been rebuilt a time or two..

You should not have lost any power with a spacer, they are not bolt on power enhancers they only isolate heat. Smiles not to glamorous but solid products.

AliceKelly · « **Reply #14 on:** January 04, 2021, 07:48 PM »

I just baught a new in box Rochester m4mc. A fuel pump new exhaust manifold air tubes. New intake filter and all gaskets all around etc. I'm going to try new carb first then change fuel pump... Last but not least I'm thinking if it still does it I'll run 30 feet of new 5/8 rubber fuel line

BTW yes its a plastic square

tmsnyder · « **Reply #15 on:** January 05, 2021, 10:52 AM »

Intermittent power loss after it heats up, and fires up after it cools down??

Sounds like the ignition module.

https://www.rockauto.com/en/catalog/chevrolet,1985,g20,5.7l+350cid+v8,1045954,ignition,ignition+control+module+(icm),7172

Pargin4 · « **Reply #16 on:** January 05, 2021, 02:35 PM »

I read through all of the posts and didn't see mention of the "sock" filter on the pickup in the tank - this could be an issue. Also any old hose that was reused when filters and things were replaced - these could go bad much like a brake hose. If you have removed emissions equipment and installed a bunch of vacuum caps, the fuel system may not be properly vented. An easy way to check that would be to take a drive with the gas cap off and observe for a change. You're looking at this issue as a function of temperature - which is perfectly understandable, but it could also be a function of time - the ideas i'm throwing at you are things that are more likely to cause problems after a few minutes, but not right away.

AliceKelly · « **Reply #17 on:** January 05, 2021, 11:30 PM »

She acts fuel starved. As if she used the fuel in her. Line and it was back filled. When she looses power and dies she has to be cranked hard to get the fuel back. I've had an electric pump pushing the mechanical pump but she acted as I'd the pump wasn't enough psi. @5 psi.

She has always needed a carb. So I baught a spanking new one and a mechanical fuel pump. I eliminated everything on the line. My next thought is to empty the tank look for rust or filters

Pargin4 · « **Reply #18 on:** January 06, 2021, 12:35 PM »

If you don't mind test driving with the engine cover removed, you can run it until it dies, then remove the air cleaner and pump the throttle. If it's truly fuel starving, then the accelerator pump in the Rochester shouldn't have anything to pump and you should not see gas squirt into the front two barrels. Since the carb is brand new, it could assume with some confidence that if the rest of the fluid path is fine, then the thing would run.

Since you have to smog check i'm guessing I'm not near you or I would check it out. I love our old Winnie and it's cool to see other people enjoying them! Just got back from Jacksonville, NC last Saturday and ready to find the next place!

AliceKelly · « **Reply #19 on:** January 06, 2021, 09:27 PM »

The carb that was on it was rebuilt today I put the brand new one on and she didn't stop or act starved at all. The new carb needs some tuning but otherwise runs great. This seems to have solved the problem. I'll keep you posted as I dink with timing and plugs