S4 fuel pump questions
02-11-2010, 04:54 PM
#1
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S4 fuel pump questions
I'm trying to flush the fuel system on my 87 S4, prior to restarting the partially rebuilt engine. I thought I could power the fuel pump and flush the gas in the tank and line to the engine, by putting in a freshly charged battery and turning the key to the on position (or cranking the engine). I seem to remember the fuel pump powering up when the key was turned. I loosened the feed line on the passenger side fender well from the hose going to the fuel rail loop, and connected a hose to it.
I assumed I could just run the fuel into a bucket, until I was sure it was clean and flowing well. Try as I might, the fuel doesn't flow. I've jumped the relay (XX) and still get no power to the fuel pump. I removed the pump and jumped the terminals straight from the battery. Still no action, so I assumed the pump was bad and replaced it with another off my other S4.
BTW, it sure is great to have a second car to "borrow a part for testing" or compare locations etc..
But I digress - the second fuel pump "torqued" when jumped, but did not push much fuel past the check valve. Assuming this one was good, I removed the check valve, and jumped the terminals. Now there was a flow.
I tossed the check valves (one from the original pump and the one from the second pump into the same parts dish and although they are identical, they "test" differently.
#1 allows me to blow back through it, while #2 does not. I'm guessing #2 is the one functioning correctly.
Here are my questions:
Am I right about the check valve?
Why don't the wires going to the pump show current, with the key "on" and the fuel pump relay (XX) jumped ?
Why doesn't the "jumped" pump push fuel past the check valve?
As always, all advice is appreciated.
I assumed I could just run the fuel into a bucket, until I was sure it was clean and flowing well. Try as I might, the fuel doesn't flow. I've jumped the relay (XX) and still get no power to the fuel pump. I removed the pump and jumped the terminals straight from the battery. Still no action, so I assumed the pump was bad and replaced it with another off my other S4.
BTW, it sure is great to have a second car to "borrow a part for testing" or compare locations etc..
But I digress - the second fuel pump "torqued" when jumped, but did not push much fuel past the check valve. Assuming this one was good, I removed the check valve, and jumped the terminals. Now there was a flow.
I tossed the check valves (one from the original pump and the one from the second pump into the same parts dish and although they are identical, they "test" differently.
#1 allows me to blow back through it, while #2 does not. I'm guessing #2 is the one functioning correctly.
Here are my questions:
Am I right about the check valve?
Why don't the wires going to the pump show current, with the key "on" and the fuel pump relay (XX) jumped ?
Why doesn't the "jumped" pump push fuel past the check valve?
As always, all advice is appreciated.
02-11-2010, 05:04 PM
#3
Team Owner
check the fuel pump fuse its quite possible with a frozen pump the fuse blew.
the check valve should only flow one way, if you have any doubts replace both of them, also use new sealing washers on every fitting at the pump or overtightening will deform the hard line and cause a leak
the check valve should only flow one way, if you have any doubts replace both of them, also use new sealing washers on every fitting at the pump or overtightening will deform the hard line and cause a leak
02-11-2010, 05:24 PM
#4
Rennlist Member
Relay only energizes when cranking, OR there is signal from ignition the engine is turning over - safety feature so pump stops when engine is stopped for whatever reason.
A piece of debris in the pump can jam it and produce a jump (torque) when powered - BTDT. Try reversing polarity on pump - this cleared a jam for me once. If there is debris in pump, it means the tank interior is suspect, and/or the in tank filter, or prepump is suspect. If you have wires going into the tank fitting where the supply hose to the external pump comes out, you have an in-tank pump. These VERY commonly break the short hose connecting them to the outlet, and the pieces jam the external pump. Do a search for some of the many threads on this topic. My car has no internal pump, and it survived in 120F temps,so I favour replacing the in tank pump with the pick up filter (much cheaper), VERY lightly tightened (just enough to not leak, with a new washer/gasket) with lube on the threads.
jp 83 Euro S AT 52k
A piece of debris in the pump can jam it and produce a jump (torque) when powered - BTDT. Try reversing polarity on pump - this cleared a jam for me once. If there is debris in pump, it means the tank interior is suspect, and/or the in tank filter, or prepump is suspect. If you have wires going into the tank fitting where the supply hose to the external pump comes out, you have an in-tank pump. These VERY commonly break the short hose connecting them to the outlet, and the pieces jam the external pump. Do a search for some of the many threads on this topic. My car has no internal pump, and it survived in 120F temps,so I favour replacing the in tank pump with the pick up filter (much cheaper), VERY lightly tightened (just enough to not leak, with a new washer/gasket) with lube on the threads.
jp 83 Euro S AT 52k
02-11-2010, 06:37 PM
#5
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Okay, I took out the in-tank filter (87 S4).
Whadda ya think? Should I replace it or clean it up and re-use ?
Just kidding.
BTW, I think MY 89+ had in-tank pumps. Thanks for the info regarding the tendency of the connecting hose on the in-tank pumps to break up, with the pieces landing in the exterior pump, causing it to fail. Ask me how I know. Now I know to replace that hose before installing the pump.
Whadda ya think? Should I replace it or clean it up and re-use ?
Just kidding.
BTW, I think MY 89+ had in-tank pumps. Thanks for the info regarding the tendency of the connecting hose on the in-tank pumps to break up, with the pieces landing in the exterior pump, causing it to fail. Ask me how I know. Now I know to replace that hose before installing the pump.
