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740 Noisy fuel pump after in-tank pump replacement

alschnertz

alschnertz

Enough already!
Joined
Oct 4, 2009
Location
CT
1986 745T 162,000 miles

I installed a new in-tank pump this afternoon as preventative maintenance.
The new pump (Delphi from FCP) was not as long as the original, but the diameter was the same and the connections too.
Upon starting the car afterwards, the main pump sounds awful. Groaning like it has a bad bearing. It didn't make the noise before replacing the in-tank pump.
There's about 3/4 tank of fuel in there.

I know there is a way to jump the fuel pump relay to get just the fuel pump to run.
Is there a way to isolate the two pumps when doing this?
In other words, I'd like to test the in-tank pump and the main pump separately.

Could it be that the new in-tank pump is groaning and the noise is making its way to the main pump? The sound I hear is near the main pump.

I'm pissed that I didn't check the new in-tank pump on the bench before installing it.
 
Many reports of aftermarket tank pumps being wired backward.

Pull the hose off the back of the pressure pump and run the in-tank pump for verification.
 
Argh. Another reason I should have bench tested.
I didn't even look for a + or - on the casting prior to install. Just lined up the outlet and replaced the wires in the same location. Dumb.

I'll first try testing, but I have a feeling I'll be pulling it out again. :-(
These damn old eyes and hands just don't work as good as they used to.

Thanks for the advice.
 
I'll be adding this thread to my subscriptions, just in case you figure something out. I put in a Delphi about one year ago in a 1993 244 and it is ridiculously loud. My sometimes mechanic told me it was o.k.. Is the in tank pump supposed to run non-stop? I don't remember it doing that before, or being 3 times as loud.
 
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Both pumps run continuously with the excess fuel returning to the tank via the return line.

It has always been my pressure pump that made all the noise and some of that was because the lift pump was or had failed.
 
I would likely say the pump wired backwards, did you replace the fuel sock? Could be clogged and pump is struggling to pump fuel causing the main pump to run dry. My main pump still groans even though I have all new lines, filters, pumps, and even tank but doesn't seem to cause any problems
 
TestPoint said:
Both pumps run continuously with the excess fuel returning to the tank via the return line.

It has always been my pressure pump that made all the noise and some of that was because the lift pump was or had failed.
Click to expand...


In my case at least, I replaced both pumps at the same time. I can also definitely tell the noise is from the in tank pump.
 
A driveway test

Without a lift:

Jump 12v to the tank fuel pump fuse and listen thru the fuel filler for fuel splashing back into the tank. Or check at the fuel return hose at the rail (maybe put a hose on the rail and direct it into a container.
 
ZVOLV said:
Without a lift:

Jump 12v to the tank fuel pump fuse and listen thru the fuel filler for fuel splashing back into the tank. Or check at the fuel return hose at the rail (maybe put a hose on the rail and direct it into a container.
Click to expand...

CFT trap used to list a photo showing his clever method of running a clear hose from the tank outlet routed to the fuel tank filler neck(to observe for correct in-tank function).



:nod:
 
RickATL said:
In my case at least, I replaced both pumps at the same time. I can also definitely tell the noise is from the in tank pump.
Click to expand...

For both of you with the Delphi pumps. The one mr brick driver bought for his 740 and I installed for him was wired backwards. I knew ahead of time there was that possibility due to 15A running into the same issue. I'm betting both of you have pumps that are blocking the flow instead of helping. If you want to know for sure before going back into the tank just disconnect the fuel line an the fuel rail, put the end in a milk jug, disconnect one of the wires going to the main pump and cycle the key on and off several times. If your ECU doesn't run for 1 second to prime the system as it should, crank the starter in order to run the pump. The lift pumps make 3-7 psi. It won't send fuel out of the line like a garden hose, however, if you don't see a stream of fuel coming out of the line, the pump is one of those that is wired backwards.
 
We'll see.
Kicking myself for not checking the pump operation before installing it. It only would have taken a few minutes but I just ran with it since the installation looked the same.

Haste makes waste.
 
alschnertz said:
We'll see.
Kicking myself for not checking the pump operation before installing it. It only would have taken a few minutes but I just ran with it since the installation looked the same.

Haste makes waste.
Click to expand...

It could happen to anyone these days. The parts are crap from most suppliers these days. The inspection process consists of stamping the part "Inspected". The garbage blower motors VDO sells nowadays are absolute junk. One had the wires 6" too short. Another had so much axial play in the shaft the impeller dragged on the driver's side of the housing. Another was wire backwards. Inspected for what? That it got painted black?
 
Got back to this today.

I found a spare main pump lurking in the cellar so I decided to install it and see if the noise would go away, change pitch or whatever. It didn't. So I'm confident that the in-tank pump is the problem - whether it's running backwards or not. Ran out of patience, so doing the in-tank pump again will wait for other weekend.

But here is something that I cannot explain and am hoping someone would have an answer. Before I swapped the main pump, I started the car. It was still making the groaning noise. So while it was running, I pulled out the fuse for the in-tank pump thinking that the noise would change or go away. There was no difference in the groaning sound or how the car ran with the in-tank pump fuse pulled out.
Wouldn't you think there'd be some change?

Regardless, that new Delphi in-tank pump will be changed to something else or even the old one will go back in. Sigh.
 
2manyturbos said:
It could happen to anyone these days. The parts are crap from most suppliers these days. The inspection process consists of stamping the part "Inspected". The garbage blower motors VDO sells nowadays are absolute junk. One had the wires 6" too short. Another had so much axial play in the shaft the impeller dragged on the driver's side of the housing. Another was wire backwards. Inspected for what? That it got painted black?
Click to expand...

Have not tried the in-tank test and need to, if anything for peace of mind.

:nod:
 
I tested the GM pump I was going to install as an in-tank pump to make certain that I had it wired correctly. I used an open 5 gallon plastic bucket containing fuel.
 
So this has turned into a lot of wasted time.

Today, I bench tested the original in-tank pump and it was working fine.

Removed the new Delphi in-tank pump, bench tested that, and it too was working correctly.

Decided to reinstall the original pump in hopes that that would quell the main pump groaning noise. Struggled getting the assembly back into the tank, but after 40 minutes it was in. Started the car and that friggin' noise is still there at the main pump. I guess that means there's a new main pump in my future, but for now, I'm done. I need a break from this car. Lighter fluid and a match sounds tempting, but I don't have that in me.

Worst has been putting things back together. Not sure why I had such a hard time reinstalling the assembly. I suspect the big doughnut gasket that seals the pump/sender assembly to the tank has swelled over the past 35 years and should be replaced.
Is that typical? It was such a pain in the nuts, that it's enough to make me not want to try again till next spring.

Rant over.
 
I did use white lithium grease on the gasket for the reinstall.
Glad this is a wagon and there's room to kneel in the cargo area. But my knees were killing me by the time I was done.
This process must be awful in a sedan.
 
tank1059.jpg


tank0904.jpg


tank1023.jpg


Not a wagon, nor a 7xx. But the O ring seal bloats with the ethanol fuels same I think.
 
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