Gas Tanks, Fuel Pumps and Fuel Starvation ?s

#1

Last year, I rented Jim Pantas’ SE30 Pink Panther at Sebring. I do not recall what year the car was. I would fill the tank to the top, and about halfway through a 30 minute session, the car would sputter for just a second after I made a hard turn. I think it was right-hand turns that it didn’t like. As the time got later in the session, the sputter got worse and longer. I believe Pantas said the problem was it had some kind of dual fuel pump system from the factory that didn’t work well, or maybe it needed the dual pump system and it only had the single pump system, I don’t really recall. What I do recall is that he said the car needed a tank change.

Am I going to have issues with the tank and pump system in my 87 325is? Can you run a 1987 325is hard for an hour without fuel starvation issues?

Thanks in advance.

-Scott

#2

You’re just going to have to give it a go and see what happens. Some cars have the problem, others not. Seems to be a number of causes for similar symptoms, so those that fixed it often did it in different ways. Each track has a different hiccup point for my '87. Roebling is the worst for me where I start hiccuping at ~1/2 tank, which is a bit shy of an hour. The PO replaced everything but the tank and vent lines.

#3

I can run my '87 down to almost empty now. I replaced the tank, both pumps, the filter, damper, and crossover. No starvation issues at Watkins Glen, which I was getting before coming out of the esses.

#4

Got 3 '87 cars. One runs good, the other two cut out at half tank.

Set the car up, weight wise, to where you fill up to the brim to race. The fuel weight is where you want to have weight, right?

Problem solved.

RP

#5

Patton wrote:

[quote]The fuel weight is where you want to have weight, right?
[/quote]
It is the ideal location, but it sloshes around more than I like my ballast to… :laugh: :wink:

#6

A weak link in the early 55L tank is the cross over tube between the tank saddles. If there is rust in the tank (highly likely for an original tank) it can settle out in the cross over tube and restrict flow. I’ve seen them so plugged up that you can’t clear the tube with a blow gun until you rod out the tube with a spring wire. Fuel will seep through the clog and eventually equalize the fuel levels, but you need fast response on the track.

The other problem that rust causes as the tank runs down, which affects the early and late tanks, is that sediment on the bottom of the tank gets stirred up and clogs the pump inlet screen. The sediment will fall off once the pump isn’t running and everything is fine until the situation reoccurs. The less fuel there is in the tank the more sloshing and stirring occurs. Rust is also highly abrasive and will wear the pump(s) and reduce their effectiveness.

A weak or failed transfer pump in an early tank will also cause problems as the tank gets to half full or less.

The weak link in a late model 63L tank is the internal siphon that lifts fuel over the saddle. It works fine as long as there is plenty of fuel returning from the engine bay. But if the pump isn’t delivering full volume, the filter is restricting flow, or the return line is obstructed the engine can suffer starvation in right hand turns with a low tank.

The fix for any/all of this is to make sure that you don’t have a rusty tank, that the pump(s) are operating within spec (see the Bentley for the test suite), that the fuel filter is clean, and that the return on a late take isn’t obstructed.

#7

jlevie wrote:

[quote]A weak link in the early 55L tank is the cross over tube between the tank saddles. If there is rust in the tank (highly likely for an original tank) it can settle out in the cross over tube and restrict flow. I’ve seen them so plugged up that you can’t clear the tube with a blow gun until you rod out the tube with a spring wire. Fuel will seep through the clog and eventually equalize the fuel levels, but you need fast response on the track.

The other problem that rust causes as the tank runs down, which affects the early and late tanks, is that sediment on the bottom of the tank gets stirred up and clogs the pump inlet screen. The sediment will fall off once the pump isn’t running and everything is fine until the situation reoccurs. The less fuel there is in the tank the more sloshing and stirring occurs. Rust is also highly abrasive and will wear the pump(s) and reduce their effectiveness.

A weak or failed transfer pump in an early tank will also cause problems as the tank gets to half full or less.

The weak link in a late model 63L tank is the internal siphon that lifts fuel over the saddle. It works fine as long as there is plenty of fuel returning from the engine bay. But if the pump isn’t delivering full volume, the filter is restricting flow, or the return line is obstructed the engine can suffer starvation in right hand turns with a low tank.

The fix for any/all of this is to make sure that you don’t have a rusty tank, that the pump(s) are operating within spec (see the Bentley for the test suite), that the fuel filter is clean, and that the return on a late take isn’t obstructed.[/quote]

Just encountered fuel starvation issues for the first time today at Summit Point on the Shenandoah Circuit. Can anyone tell me which cars had the early 55L tank and which ones have the late 63L tank? Also, how do you check to see if the the return is obstructed? Thanks.

#8

I think the only ambiguity is the '88. Otherwise it’s early model and late model. RealOEM can probably get it down more specific.

To see if return or crossover is obstructed, remove them and blow air thru.

#9

Cars built from 9/87 on have the 63L tank.

#10

jlevie wrote:

My 8/87 has the big tank (I think). No crossover at the bottom and one in tank fuel pump.

Michael

#11

ilateapex wrote:

[quote]jlevie wrote:

My 8/87 has the big tank (I think). No crossover at the bottom and one in tank fuel pump.

Michael[/quote]
Odd. My 4/87 has the small tank, crossover and 2 pumps.

#12

Now that I’m thining about tank size, was wondering about my 91 318is that we just swapped over to a 2.5. Anyone know the size of the OEM tank? Is it the same on a 318 vs 325?

Thanks,

#13

Steve Ferrario wrote:

It should be the 55L tank with a cross over tube.

#14

I had bad starvation problems on my '87 at my last event at VIR with about a half tank of gas. I had never had a problem before.

I made a jumper wire with switch, borrowed a nice new fuel pressure test kit from AutoZone and did the fuel pressure and flow rate tests described in the Bentley manual. The pressure and flow rate at the fuel rail were good. The pressure spec coming out of the in-tank pump is pretty low (4 psi?), so I couldn’t get a real good pressure reading on that pump with the gauge in the kit, although it did pump fuel when the jumper was switched on.

Anybody know of another way to test that pump? I pulled it this week and checked the inlet screen. I cleaned some black residue off it, but didn’t really see any rust.

While I had the pump out, I stuck a flexible magnet in the tank and moved it around to see if it would pick up any rust particles and got almost nothing. I looked in the tank with a flashlight and it looked relatively clean from what I could see.

I’m going to pull the crossover tube this weekend and see what it looks like.

Any other suggestions to diagnose/cure the starvation? I guess the next step is to try a new in-tank pump, but I hate to spend the $$$ if not necessary.

#15

There’s long threads both here and at BF.c on this. Different folks solved it in different ways. A lot of us just live with it.

There are different kinds of rust. “Black” rust is magnetic. Others not.

#16

Randy87is wrote:

[quote]I had bad starvation problems on my '87 at my last event at VIR with about a half tank of gas. I had never had a problem before.

I made a jumper wire with switch, borrowed a nice new fuel pressure test kit from AutoZone and did the fuel pressure and flow rate tests described in the Bentley manual. The pressure and flow rate at the fuel rail were good. The pressure spec coming out of the in-tank pump is pretty low (4 psi?), so I couldn’t get a real good pressure reading on that pump with the gauge in the kit, although it did pump fuel when the jumper was switched on.

Anybody know of another way to test that pump? I pulled it this week and checked the inlet screen. I cleaned some black residue off it, but didn’t really see any rust.

While I had the pump out, I stuck a flexible magnet in the tank and moved it around to see if it would pick up any rust particles and got almost nothing. I looked in the tank with a flashlight and it looked relatively clean from what I could see.

I’m going to pull the crossover tube this weekend and see what it looks like.

Any other suggestions to diagnose/cure the starvation? I guess the next step is to try a new in-tank pump, but I hate to spend the $$$ if not necessary.[/quote]
As I recall there is a spec in the Bentley for the volume of the transfer pump. If you are getting that rate, the pump is okay.

Use a stick to str the bottom of the tank. If there is a layer of rust you’ll see it. A magnet won’t pick up red rust.

#17

I figured I would update this thread. My winter project was replacing the gas tank, both fuel pumps, and fuel filter for my older style fuel setup. I had ZERO fuel starvation issues this weekend at Road Atlanta and was finally able to take the car under half a tank with no worry of starving for fuel coming out of T7.

#18

King Tut

Where did you get all your parts???

I have an 87 and the same issues.

I want to simply replace EVERYTHING as you did and move on.

THanks for your advice.

Shoe

#19

Haha, I didn’t see this thread till I replied in the other one. I got the two pumps from Pelican Parts as they always have parts in stock and free shipping. I got new rubber fuel lines from Pelican Parts as well. You won’t find any local parts stores that will have the larger diameter fuel injection hose that goes over the top of the fuel tank. I got to warn you the pumps are each quite expensive as in more expensive than the fuel tank that I got from The Radiator Connection was.

#20

bringing this thread back. i had some fuel starvation issues at Mid Oh this past weekend (partly due to my lack of a fuel level gauge which i am rectifying asap). I have a 91 318is chassis so I guess that’s the 55L tank but I only have the one in-tank pump. What’s the recommended solution to be able to go below 1/2 tank? I’ve heard of folks using fuel accumulators, any rulebook issues i should be concerned about? Also, anyone know the resistance range of the stock fuel level sender? I have an AIM dash and I’d like to be able to wire the stock sender wiring to it as an analog input.