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Fuel pump intermittent failure dilemma - why?

Old 04-14-2019, 09:58 PM
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Fuel pump intermittent failure dilemma - why?

I have a problem going on with my fuel pump it seems. Car is a LT1 swapped third gen with a 78 mm turbo, all DIY etc..

I used a Quantum Fuel system 340 LPH pump in the tank, which seems to be up to the task of feeding the engine just fine. However, I have a intermittent problem that I'm chasing.

This is the second pump from them. When the first one quit, I pulled it out of the tank (after verifying voltage was getting back there) and applied 12v on the bench it ran just fine. Hmm. Pump isn't fun to change to decided to just buy another one instead. So put that in a couple weeks ago. Everything was fine, no issues whatsoever, until Friday night it just would not work. Relay working but no fuel pump. (had been running and stopped / started several times already that day.). At least it quit in the garage. Nice.

Let it sit for a couple days, worked on some other stuff, then decided to try it just for fun before I dug into what was going on. WOuldn't you know it, pump is now working. WTH? However, now I'm skeptical, and find if I cycle the key on / off a 2 - 3 times every couple seconds, the pump will fail to start on the 3rd or so try. Not sure what's up with that. If I then wait 30 seconds, the pump will fire up fine. Cycle key on/off again, and pump decides to quit again. Again can still hear the fuel pump relay, but the pump isn't running.

So I'm at the point now where I can't hardly trust the pump to behave. Don't really want to get stranded somewhere for hours or whatever.

I still have stock wiring on the car, etc., which I know isn't necessarily ideal. Could that be causing the issue somehow? Seems unlikely but??? Also seems unlikely I got two bad pumps.

Do I just need to bite the bullet and get the Aeromotive version of the 340lph pump ?

Just getting into nice weather and hate that I can't trust it to drive it very far.


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Old 04-14-2019, 10:46 PM
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Re: Fuel pump intermittent failure dilemma - why?

Are these crappy pumps? What you are describing is when a factory pump begins to fail. It stops on dead spots and then needs a tap to get it to go once it has been shut off. The dead spots grow in time as the pump is shut off and lands on dead spots more and more often. This usually happens only with older, high mileage pumps.
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Old 04-15-2019, 01:29 AM
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Re: Fuel pump intermittent failure dilemma - why?

Grab the wiring harness where it enters the yellow bulkhead connector and enters the sending unit. Move the wires around slowly and watch for the continuity to break. Not saying that's what it is, but I've seen that happen with GM cars in the past.
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Old 04-15-2019, 07:28 AM
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Re: Fuel pump intermittent failure dilemma - why?

Sounds like a bad pump. Especially if its all factory wiring. No offense but I wouldn't be trusting a $79 fuel pump for as far as I could throw it, especially if you have all the work done to the engine in your signature. At a minimum i would be putting a Walbro or Aeromotive pump in it.
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Old 04-15-2019, 09:28 AM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by Tootie Pang View Post
Are these crappy pumps? What you are describing is when a factory pump begins to fail. It stops on dead spots and then needs a tap to get it to go once it has been shut off. The dead spots grow in time as the pump is shut off and lands on dead spots more and more often. This usually happens only with older, high mileage pumps.
im definetly questioning the Quantum brand. Agreed it seems like a failing pump but shouldnít be since itís so new.
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Old 04-15-2019, 09:30 AM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by Drew View Post
Grab the wiring harness where it enters the yellow bulkhead connector and enters the sending unit. Move the wires around slowly and watch for the continuity to break. Not saying that's what it is, but I've seen that happen with GM cars in the past.
Ill give this a shot tonight and see if that does anything. Will say though that the pump wonít stop ever (so far) with the car running and driving which I would think would jiggle the wiring somewhat and show the problem as well. But who knows. Worth a shot
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Old 04-15-2019, 09:33 AM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by 86CamaroDan View Post
Sounds like a bad pump. Especially if its all factory wiring. No offense but I wouldn't be trusting a $79 fuel pump for as far as I could throw it, especially if you have all the work done to the engine in your signature. At a minimum i would be putting a Walbro or Aeromotive pump in it.
Haha yeah maybe I was asking for it. Guess Iíll return the second new one to amazon and order an Aeromotive and hope for the best.
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Old 04-15-2019, 11:07 AM
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Re: Fuel pump intermittent failure dilemma - why?

Some things are just worth the extra money. I always ask my self what happens if this fails and is it worth the trouble when it does. Just my
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Old 04-15-2019, 11:16 AM
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Re: Fuel pump intermittent failure dilemma - why?

did you try eliminating the wiring and relay and computer?

How do you know it isn't the computers output to the fuel pump relay. Or the relay itself. Did you try putting power directly to the pump?
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Old 04-15-2019, 12:47 PM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by 86CamaroDan View Post
Some things are just worth the extra money. I always ask my self what happens if this fails and is it worth the trouble when it does. Just my
yeah for sure. I read several reviews on the aeromotive pump on the summit website that were saying the life was short etc on them. So didnít seem like a slam dunk there either. Couldnít find info about Quantum.

Im sure thereís lots more cars riding around with aeromotive though and of course itís the negatives that make headlines. Much like the optispark.
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Old 04-15-2019, 01:03 PM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by Kingtal0n View Post
did you try eliminating the wiring and relay and computer?

How do you know it isn't the computers output to the fuel pump relay. Or the relay itself. Did you try putting power directly to the pump?
Good questions

i swapped the relay out and get the same results. Also tried using the fuel pump bypass wire which sends voltage straight to the pump and get the same results again.

When the pump doesn’t start running I can still hear the pump relay clicking (hood up) but I haven’t verified power at that time with a meter.

EDIT!! -- A little later, I had a helper and we did determine that the computer is in fact shutting the pump off when I cycle the key on/off. Doh!. The sound I heard clicking is in fact something else - not sure what it is. Right as the pump would "stall" after the key on / off routine, my helper hit the fuel pump bypass wire with 12V and the pump would run. So, it wasn't actually stalled under those conditions. Makes a little more sense. EDIT

Ive verified voltage at the connector behind the rear seat but that’s as far as you can really go and that’s with no load.

I think ill turn the pump on manually and then get under the car and wiggle the wiring and connectors in different spots to make sure I don’t have something loose somehow.

It’s weird that it works well even under load and the failure is just failure to start.

Last edited by hotrodf1; 04-16-2019 at 07:19 PM.
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Old 04-15-2019, 04:45 PM
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Re: Fuel pump intermittent failure dilemma - why?

I would put the pump in a bucket and test bench it. Run it the way it runs in the car.

If you hear the relay click but the pump stays off and did all that other stuff. It sounds like it must be either the wiring somehow at or around the pump (as opposed to ecu/relay related) or the pump itself.

Just use a quality pump from now on... Never had an issue like this with aeromotive
Their 'small' stealth pump supports like 550rwhp on gasoline through a 5/16" line (-5an) so its more than most people without FI will ever need
In daily driver and reliable apps, its usually worth the extra $$ with fuel pumps, injectors, turbos, internals, etc...

If the base engine/vehicle is already 'cheap' enough (lots of extra stock engine/trans/diff on the shelf and easy to swap) and the car doesn't need to be reliable (a trailer race car) the cheap parts are viable, people have built at least 9, 8, who knows how fast second cars for around 3k using $380 turbochargers and E85 with almost any engine
you just have to decide first what kind of car you are building or changing into. reliable not necessarily economical daily or engine diaper, t-brake scattershield trailer car thats not necessarily reliable.
It doesn't make any sense to mix the two categories. For example you wouldnt want a $2 turbo with a $8000 engine, the turbo could take out the engine as they share oil supply. You wouldn't put $2 injectors in an 8k engine either, I hope. Or a 3k transmission with a $2 converter. The mismatches possible seem endless

Last edited by Kingtal0n; 04-15-2019 at 04:55 PM.
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Old 04-16-2019, 07:42 PM
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Re: Fuel pump intermittent failure dilemma - why?

Originally Posted by Kingtal0n View Post
I would put the pump in a bucket and test bench it. Run it the way it runs in the car.

If you hear the relay click but the pump stays off and did all that other stuff. It sounds like it must be either the wiring somehow at or around the pump (as opposed to ecu/relay related) or the pump itself.
As I said above, I was wrong about that fact - the pump wasn't being commanded to run by the ECM under those conditions.

What remains though is that the pump did in fact not work for 2 days, and then came back to life with no movement, etc happening.

Just use a quality pump from now on... Never had an issue like this with aeromotive
Their 'small' stealth pump supports like 550rwhp on gasoline through a 5/16" line (-5an) so its more than most people without FI will ever need
In daily driver and reliable apps, its usually worth the extra $$ with fuel pumps, injectors, turbos, internals, etc...
Yeah I feel pretty stupid for taking a chance on a fairly unknown brand for a fuel pump that was probably a bad idea. Gonna throw the Aeromotive stealth 340 in there and should be plenty good. I hope hope hope this fixes it for at least a year or two. LOL

On another note, it's sometimes hard to know who is actually selling a better part, and not just a rebranded unit like others are selling. I know it happens a lot more than we think. Sometimes the folks selling the stuff should really do a better job differentiating themselves from their competition - it's a marketing thing. If Aeromotive said that they have an exclusive design, and here's why it's better, blah, blah, I would have gladly paid the extra bucks for the stealth at the beginning. I just didn't see that kind of info out there. Holley / Accel does the same thing - pump are slightly different color but look basically the same. ???? The QFS pump I bought has / had a 5 year warranty, each one tested with a individual flow chart with it, which seemed like would stand behind it. Obviously changing out pump after pump for "free" isn't really where anyone wants to be, but I kinda figured they had done enough R&D to feel good about offering a 5 year warranty. Also, sometimes following in the footsteps of "everyone" doesn't necessarily guarantee a better part / outcome. THen again perhaps everyone goes a certain way because they know better. Could be . . .Anyway . . .. .

If the base engine/vehicle is already 'cheap' enough (lots of extra stock engine/trans/diff on the shelf and easy to swap) and the car doesn't need to be reliable (a trailer race car) the cheap parts are viable, people have built at least 9, 8, who knows how fast second cars for around 3k using $380 turbochargers and E85 with almost any engine
you just have to decide first what kind of car you are building or changing into. reliable not necessarily economical daily or engine diaper, t-brake scattershield trailer car thats not necessarily reliable.
It doesn't make any sense to mix the two categories. For example you wouldnt want a $2 turbo with a $8000 engine, the turbo could take out the engine as they share oil supply. You wouldn't put $2 injectors in an 8k engine either, I hope. Or a 3k transmission with a $2 converter. The mismatches possible seem endless
I agree with you. For example, the whole deal behind my current build was to use "stockish" parts, and cheap eBay / amazon other stuff for the turbo. Did do VS racing for the turbo, but it's no BW or Turbonetics of course. The flip side of the coin is the road race car - I can't tolerate failure on that car for a number of reasons. Safety being first and foremost, but secondly I have lost a few 1st place finishes due to mechanical gremlins of one type of another, and that's actually double costly, due to not taking home the contingency money for the race and then having to repair the car as well. So, it doesn't take long to figure out that the best brake fluid you can buy is all of sudden worth reducing the risk of fluid boil, etc. etc..

If I blow up my stock lower end LT1, I can source used stuff pretty cheap and not be out much other than a roll back home. I'd rather not spend a crazy amount of time building motors, so I do tread cautiously with the tune. I kinda hate redoing stuff for some reason. But if it does happen, I'm at least not out a boat load of money.

So I have tried to mix cheap with cheap for the most part, tune it myself, fab it all myself, painted the car myself, etc. etc. cause that's how I roll.

Just so darn frustrating to have one freakin part ruin your day, several times on different occasions. Part of it I guess.

At the very least, I can not at this time recommend the Quantum Fuel System 340 pumps. Perhaps after I run the Aeromotive unit for a while, I can do a follow up.
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