New fuel pump spits air, what next?

My 90 ran pretty well with a noisy pump. I planned on replacing it and fuel filter anyway because the car had been sitting.

While waiting for those parts to arrive, the car decided to run like crap with no power, so I parked it. I replaced with new bosch pump and filter and still had the same run condition. I chased other branches of the decision tree (it needs a head gasket job for sure), before discovering that while I have initial pressure of 36 at the rail, that doesn’t hold for long and when I jump the relay, I have a “spitting” condition of intermittent fuel delivery.
I worked my way back, first discovering it at the rail, disconnecting the line at the outlet of the filter, same low spitting condition. Disconnected pre-filter and have the same spitting direct from the pump with lots of air, not a steady stream - though the pump seems to be running quietly.
Ran out of daylight and time.
I know my next step is to disconnect on the feed side of the pump to check if the pump is getting unobstructed fuel direct from the tank, but I’m just thinking through why a brand new pump would behave this way. I REALLY do not want to take the tank out.
Please somebody hold my hand and tell me we don’t have to take the tank out.

Maybe the fuel pump strainer is clogged? The pump sits in a plastic canister that supposed to be filled with gas. If the pump is spitting air out then the canister doesn’t have enough gas in it.
In this case the tank has to come out.

Question: Does fuel put in through the tank filler cap descend into the internal canister or just into the tank itself? Has anyone cut open a discarded tank to see the internal configuration? If so, a photo posted would be useful.

I have the 1990 year, which has the external pump. It would make sense that there is some kind of internal pre-pump screen/filter, but to answer @John_Quilter , I’ve never seen a good exploded view of a tank. (I shouldn’t use “exploded” around gas tanks, should I?)


John, the gasoline goes in the tank. The pump strainer is attached to the bottom of the canister. The feed and the return fuel lines are attached to the top of the canister.


But he has an external pump so I don’t know what’s in the tank in that setup.

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Yes, I know the plumbing and pump are different between the intank pumps and external pumps. I’m wondering about the internal configuration with the Bosch external pumps which my 1990 car has. But having said that, I do not know why the return line feeds into the top of the canister as shown in the above photo. It seems this would put fuel heated by the fuel rail, . engine compartment and proximity to underfloor exhaust components right back into the area fuel is sucked out and sent to the engine. Seems that putting the fuel into the tank would dilute the heated fuel over the full tank capacity.

The question is… what is inside a fuel tank - of external pump models? Is there a screen or other fitting where the lines enter/exit. Or is just two holes in the bottom that will get clogged. (and to John’s point, pickup and return fuel in essentially the same location, so hot fuel is dumped where cool fuel is picked up).

Then it seems to me the hot fuel would be closest to the pickup and likely get hotter and hotter as it cycles back and forth to the engine bay. I think this is what caused Jaguar to issue a bulletin on fuel pump cavitation and stalling in continuous running in very hot ambient temperatures. I engineered a work around for this issue that affected my car from time to time.

When the fuel level is above the canister, the returned fuel mixes with the cooler fuel in the tank because of the small holes on top of the canister. When the level is below the canister then I guess the cooler fuel still cools the returned fuel somewhat through the plastic wall of the canister.

You could be right but it would still be interesting to know how tall the canister is. I think Jaguar calls this a swirl chamber. Would be very interesting if anyone has risked cutting one of these pre internal fuel pump tanks apart and taken a photo of what’s inside.

I think I figured out why I have a fuel delivery issue… :thinking:
This car has spent most of its life sitting… The contents of the jar are just a fraction of what is still in there and I’m sure lurking behind the swirl barrier.
needless to say this tank is going to be extracted and treated. And the lines blown out too.
“mystery” solved, I suppose.

Jitneybead …

I once drank some moonshine when I was visiting friends in North Carolina that look about like that. And although I took a swig I definitely wouldn’t put it in my car (thank God I’m not blind :sunglasses:)

EVERYTHING in your fuel system needs to be flushed and cleaned or replaced, not only the tank, fuel filter and fuel pressure regulator, also the injectors.