# fuel pump needs on a 400



## redhotgto66 (Sep 11, 2021)

i have a 400 pontiac from 67, nothing crazy like a wild cam or anything, for fuel im using a holley 750 single pumper w/vacum secondaries. upon hard acceleration when it hits 3000 rpm it starts cutting out pretty hard like its running out of fuel, anyone think its this stock pump going out, or do i need a higher volume pump like a holley or edelbrock 110gph ? this is an automatic turbo 400 behind it also just for info.
thanks


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## geeteeohguy (Feb 2, 2008)

The stock pump is fine, as long as it is in good condition and the lines are clear. Over the years, I've run into two separate issues that caused the same problem you are having. FWIW, the pump has been on this engine since 1988 and the issues both happened with this pump. First time, it was a collapsed sock on the fuel pickup inside the tank. Wadded up into a ball. You could blow air into the line, and it would straighten out like a party favor, and run fine for a few miles, until it wadded up again. I cut the sock off and have been running without since 1988, close to 90,000 miles, no issues.
Second time it was a cracked rubber line from the top of the sending unit to the steel hard line. Not leaking fuel, but causing the pump to pull air and not enough fuel. Replaced the line, no issues since. Mine has the stock Q-jet with the tiny float bowl and will pull redline and beyond and runs just fine. You need to verify if its fuel supply TO the carb, or if the carb itself has an issue. Could also be ignition.


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## redhotgto66 (Sep 11, 2021)

had not thought about the sock in the tank, hmmm ill look at that, i will replace the pump with a stock one just in case, they are cheap. was gonna put a new set of wires and plugs anyways, also the carb is brand spanking new so it shouldnt be that issue.
thanks


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## geeteeohguy (Feb 2, 2008)

Wires and plugs going bad will usually result in a misfire or break-up under load. It'll keep running and pulling, but will buck and surge. 
If it just 'lays over' like it hit a wall at 3000-4000 rpm with no bucking or rough running, more likely a fuel issue. 
A weak or reversed ignition coil can also have the same symptom, but not as common as fuel. 
If it is running smooth buy 'lays over', new plugs and wires won't change anything.


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## GTO44 (Apr 11, 2016)

Had this happen on a 400 motor in a TA with a Holley. It would run fine but lay over around 3,500 rpm under full load in second and third gear. Tried a few different fixes that didn't work. It also had a brand new distributor, coil and wires so wasn't ignition related. Eventually we drove it with the hood and air cleaner off. As soon as it hit that RPM at wide open throttle and high load (2nd & 3rd gear), you could see fuel pouring up and out of the vent tubes and into the carb. This would flood the engine and cause it to lay over. Once you took your foot off the pedal the engine would recover and drive like normal. Ended up putting a return regulator coming off the fuel pump to stabilize fuel pressure. 


Try the suggestions so far abut the fuel sock and fuel lines. If nothing fixes it, i recommend trying to replicate the problem with eyes on the carb. If you don't want to pull the hood you can rig up a go pro or your phone to record in the engine bay while you drive. (Just free-revving while sitting in the garage won't replicate the problem as there won't be a load on the engine.)


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## BearGFR (Aug 25, 2008)

I had a weird problem like that in my '69. Despite all new 1/2" fuel line everywhere, big mama-jama RobbMc mechanical fuel pump, all new parts - about half way through 2nd gear when I was "in it" the car would now and then seem to just shut off for a second. Drove me batty. Know what it turned out to be? A small piece of welding slag in the tank left over from when I added a rear fuel sump. The piece of slag was "just the right size" to almost completely block off my relocated tank outlet port but too big to go through it. Most of the time, under normal driving, it would just lay there in the bottom of the tank and do nothing but under hard acceleration.... 

It bugged me for a good long time until one day I needed to pull the tank for a completely different reason, and heard something rattling inside it.

Bear


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## Khmike (Jun 21, 2021)

Reading this thread after having my car go through the dreaded Rochester "hard pull give-out" on a hot day. Got my car to my destination and back home again, but the next day it would.not.start. Not a drop of fuel from the pump so my diagnostics went as far as having to replace the pump itself. NAPA only stocked the 2 ports version (the '68 has 3 on the pump). A day later I received a new Delphi brand, installed and was on the road no time. Got lucky on that one.


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## redhotgto66 (Sep 11, 2021)

well these are all good ideas, im gonna try some of them as i figer this out. what would y'all say about switching to electronic ignition ? think it would help the spark?


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## geeteeohguy (Feb 2, 2008)

redhotgto66 said:


> well these are all good ideas, im gonna try some of them as i figer this out. what would y'all say about switching to electronic ignition ? think it would help the spark?


As a retired professional mechanic who specialized in driveability: No. Electronic ignition is great for 'no maintenance' (until it fails and leaves you stranded) and it is great for being able to use a rev limiter. But, it provides no performance hain over the stock ignition, which over the long haul, is more reliable, although requiring periodic service. (points replacement every 15,000 miles or 40 years, whichever comes first).


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> As a retired professional mechanic who specialized in driveability: No. Electronic ignition is great for 'no maintenance' (until it fails and leaves you stranded) and it is great for being able to use a rev limiter. But, it provides no performance hain over the stock ignition, which over the long haul, is more reliable, although requiring periodic service. (points replacement every 15,000 miles or 40 years, whichever comes first).


100% agree. In fact, if you have a Motortrend+ subscription there's an episode of Engine Masters where they (unintentionally) proved it. They were dyno testing various ignition systems (on a big block Ford if I remember correctly), and up until the RPM where the points ignition started having problems (way above any normal RPM for a street Pontiac), there was zero difference in with HP or torque between the stock points system and the 'fanciest' electronic system they tested. 

And like GeeTee said, failure modes where a points ignition can just "go away" with no warning and leave you stranded, while not totally impossible, are WAY less likely to happen than with any electronic system. Many people who run some sort of electronic system always carry spares and tools with them for exactly that reason.

Bear


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## redhotgto66 (Sep 11, 2021)

thx guys, i was ready to buy a electronic setup cause they sound easy, i'll forget it


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## redhotgto66 (Sep 11, 2021)

well ive replaced the fuel pump all new rubber lines and filter,checked sock on sending unit looked new no help.
also put new plugs, wires,points,cap,rotor bug,coil,even changed out the distributor, no help.
next step is a free one to try, nephew has a new HEI dist and wires, cant hurt to eliminate this also.
any more ideas?


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## redhotgto66 (Sep 11, 2021)

welp put in the new HEI dist and poof ! it runs great, all those extra parts for nuttin! o well live and learn


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## BearGFR (Aug 25, 2008)

redhotgto66 said:


> welp put in the new HEI dist and poof ! it runs great, all those extra parts for nuttin! o well live and learn


Glad you got it sorted out.


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## geeteeohguy (Feb 2, 2008)

BearGFR said:


> 100% agree. In fact, if you have a Motortrend+ subscription there's an episode of Engine Masters where they (unintentionally) proved it. They were dyno testing various ignition systems (on a big block Ford if I remember correctly), and up until the RPM where the points ignition started having problems (way above any normal RPM for a street Pontiac), there was zero difference in with HP or torque between the stock points system and the 'fanciest' electronic system they tested.
> 
> And like GeeTee said, failure modes where a points ignition can just "go away" with no warning and leave you stranded, while not totally impossible, are WAY less likely to happen than with any electronic system. Many people who run some sort of electronic system always carry spares and tools with them for exactly that reason.
> 
> Bear


Thanks, Bear. Lars Grimsrud educated me many years ago on this (actually verified what I suspected about HP) and he ran experiments and found the same results. I recently saw an Uncle Tony's Garage and he showed where dual points actually beat out HEI for high rpm use. Very interesting. I simply run points because I like an era-correct driving experience and I like the reliability and repairability. I've had 2 or 3? tow-ins in 40 years due to points, and literally hundreds of tow-ins with fried modules, pickup coils, etc.


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## redhotgto66 (Sep 11, 2021)

thats the part i'm afraid of, so i will keep a module in the road kit i keep in the car. how many rpm's can i expect out of a stock type HEI system ?


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## geeteeohguy (Feb 2, 2008)

redhotgto66 said:


> thats the part i'm afraid of, so i will keep a module in the road kit i keep in the car. *how many rpm's can i expect out of a stock type HEI system ?*


Enough to blow up a stock engine with relative ease. 
In 45+ years of driving points cars, have never even carried a spare set of points like all the HEI guys seem to. Have never needed to.


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## redhotgto66 (Sep 11, 2021)

reason i ask is i can get appx 4500 rpm out of her now, no big cam, nothing special just a stock 1970 400 with a 750 holley and a turbo 400 tranny, std rearend nothing great.


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## PontiacJim (Dec 29, 2012)

redhotgto66 said:


> reason i ask is i can get appx 4500 rpm out of her now, no big cam, nothing special just a stock 1970 400 with a 750 holley and a turbo 400 tranny, std rearend nothing great.


From what I gather, the HEI is more about higher output energy at lower RPM's and the factory module seem to give up around 5,000 RPM's. The aftermarket replacement modules are designed for higher RPM's. You may want to install one of those and put the stock module in the glove box. Make sure you get the grease that goes under the module which aids to keep it cool.

Having a module in the glove box and tools to swap it is not worse than having an extra ballast resistor in the glove box for a older Mopar product - which do give out and are known for it, no big deal in my book.


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## redhotgto66 (Sep 11, 2021)

thanks jim, good info i will find a higher output module and replace


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