E30 external fuel pump connections

[lateracer]

Scrowner, are you testing for pressure at the injector rail?

My high pressure pump was crapping out on me at my last track event after replacing my in tank pump and I'm debating whether or not to just switch out to a later model tank like you're doing.

[jlevie]

Here is a picture of the item I purchased as an E30 accumulator. However, it did not solve our problem with fuel starvation in this 1986 E30. We are currently in the process of switching the fuel tank to a '91 tank, changing the fuel delivery to a single in tank pump. A number of E30 guys have indicated that the older E30s, older than 1988, dual fuel pump systems, are a problem. Yep, both our pumps worked just fine and we get the fuel starvation after things warm up in the car. So, initial few laps have no starvation then we get starvation from that point on. We tried extending the intank pumps suck-in point with a fuel line deeper into the tank but had no luck.

The dual pump system isn't a problem in a track car provided that both pumps are good, the cross over tube isn't plugged, and that the tank doesn't have loose rust in it. I have a whole season of racing 3 hour enduros in an 87 where we ran the tank do to almost nothing twice in each race as proof of that.

When I first got the car I experienced exactly what you describe, even though I'd replaced both pumps with new OE units. I cured the problem by dropping the tank, acid cleaning it, and sealing it.

[scrowner]

Hmmmm....our 1986 E30 fuel tank looks clean looking in with a mirror and flash light into the passenger side of the tank. Now, we have never looked at the pipe connecting the two halves together. There was no evidence of loose or even flaking rust in our tank, yes even inside top of the tank. We did check pressure at the fuel rail with all our new parts in place - with flow rate measured by volume into a jug and it showed 40+PSI. We did swap the pressure regulator at the rail with a new one. Our starvation occurs about 15 minutes into a 2 hour stint, tank topped off, only exiting a turn. Mind you, the corner can be left or right! Our new walbro pump seemed very warm checked between stints. Our intank pump was functioning. (all post diagnosis to the race)

Our system: 1986 E30, dual pump system, removed BMW accumulator, removed BMW pulse dampener, new OE fuel filter, new pressure regulator, Ireland fuel accumulator, external fuel pump replaced with a Walbro, internal pump is OE stock with extended fuel intake line. Only get starvation at corners and after about 15 minutes of heat up.

I like reading that someone was able to get rid of fuel starvation in a dual pump system. It is interesting you have no fuel starvation since "cleaning" the the pre 88 tank. I would like to know if you made any other mods to the fuel supply system. But simply cleaning the tank? If it is rust flakes entering the system - why do they only clog the system during a turn exit? I would expect that problem to be more random.

A number of BMW guys at the track were telling us that the dual pump system is flawed and to change out our tank and move to single pump system. 88+ tanks are bigger 63L instead of 55L, another bonus for endurance racing. But I sure would love to read it is possible to get a dual pump system to not fuel starve.

[jlevie]

That makes little sense. I can't see the car burning off enough fuel in 15 minutes for the level in the tank to drop enough for movement of fuel in the tank to matter. Well maybe if you had a large displacement V8 or V10 under the hood... And even in that case the problem should only show up in right hand turns until the tank gets really low, say to less than 4 gallons remaining. There has to be something else going on here.

My previous Spec E30 with the early tank and twin pump set up had a completely stock fuel system with the exception of the cleaned and sealed tank and used OE pumps. My new Spec E30 has the later tank (also cleaned and sealed) with the OE pump. But I've modified the system and added a transfer pump in the left side that lifts fuel into the right side of the tank. I've run that tank down to two-three gallons before experiencing any signs of fuel starvation.

[scrowner]

I agree this seems odd. But it sure feels and sounds like fuel starvation. Our last race we were pointing our fingers at the external high pressure pump as getting too hot and potentially dropping pressure - but why would that only happen exiting turns? We burn about 3.3 gallons of fuel per hour. Our races are long - 14 or more hours, sometimes spread over 2 days, sometimes continuous 24 hours. Before we swapped the external pump with the Walbro, the fuel starvation was always on right hand turns and about 1.5 hours into the race. We then switched the pump and then it seemed to happen quicker into the tank - about 15 or so minutes into racing - still upon exiting hard turns - but we had it occur on hard left turns. We had two races with the new external pump. Different tracks, different turns showed the "starvation" (always the same turns at each track) but both tracks showed the problem occurring about 15 minutes after driver change.

We are kind of committed to a single pump system and the larger tank. I have a couple of questions on the fuel system conversion:

1. What if anything is done with the charcoal can and air connections?

2. When fitting the larger tank in to the older E30s, must we add a second pump to move the driver side fuel into the passenger side? I understand the newer tank return spot is on the driver side, but how does the system move fuel from the driver side to the passenger side in a standard configuration E30?

3. The newer E30s have an expansion tank. Older E30s I see no evidence of this. So this begs the question what is done with the air line going into the driver side of the tank and the charcoal can air line?

[jlevie]

Knowing the history I think I understand what is going on. In the original configuration starvation in right hand turns when you'd burned off about 5 gallons of gas is early. That shouldn't happen until the tank is around the 5 gallon mark. After the change to the Walbro you started seeing it earlier and in both directions. That says to me that the transfer pump in the tank isn't working correctly and/or the cross over tube may be plugged. I suspect that the Walbro pump has essentially a zero lift capability and that would explain why it got worse. The OE high pressure pump will work until the tank drops below 3/4 full, even if the treansfer pump isn't working at all.

That said, since the car is run in enduros you should change to the later larger tank. Before installing the tank I suggest that you "puff it out" with compressed air as that gave me another gallon of capacity. When doing that you only pressurize the tank enough to hear it "bong". Then acid clean and seal the tank unless you are using a brand new tank. Even thn I'd seal the tank to prevent rusting since a race car sits a lot.

Fuel is equalized in the later tank by a siphon operated by fuel returning from the engine bay. That works fine in a street car, but not so well in a race car. When the tank gets low, say less than a half tank, a right hand turn can pack fuel in the left side and starve the pump. Since the pump is starved, the volume returning from the engine bay is reduced and thus the siphon's effectivness is reduced. The lower the tank gets the worse the problem becomes. The solution to that is to actively draw fuel from both sides of the tank.

I used an OE transfer pump to lift fuel to the right side since a surge tank might not be legal in Spec E30. If rules weren't an issue I'd have installed a transfer pump in both sides of the tank feeding a four port 1qt surge tank that fed the high pressure pump.

A problem that you run into when you have a pump on both sides of the tank is reading the fuel level. In the stock configuration the sensors are wired in series. But when you use a transfer pump in the left side that won't work because of the internal construction of the left side sensor used with the transfer pump (it isn't isolated from ground). One solution is to just use the right side sensor. Another, if you have an electronic dash that supports summing level inputs is to do it in the dash. There's no good way of making it work properly with a stock cluster.

As to the charcoal cannister and venting. All E30's (to the best of my knowledge) have an expansion tank in the right rear fender well. You need that to avoid dumping fuel when the tank is full in left hand turns. You can leave the charcoal filter in place or eliminate it. But the tank has to be free to breath. So if you eliminate the cannister, replace it with a small filter.

While dealing with the tank, use a hole saw to punch out the unleaded fuel restrictor in the filler neck. That lets you use a larger hose on the fuel jugs and thus reduce refuelling time.

[scrowner]

Sweet information. Most of our races we pump fuel using on-site fuel pump stations. I never noticed that the fuel fill spot on the car was restricted. I will improve as you suggested.

We spend as little money as possible on the car. The rules prevent too much money being spent - if any - and some team members are expense sensitive.

That being said a second in tank fuel pump ($200) and an external swirl ($400) and an added third high pressure pump ($150) is getting expensive. I guess my question is how do I eliminate most of my fuel starvation issues with the new 88+ tank replacing my older 86 fuel tank? Can I remove starvation in my 86 325e with this system:

88+ fuel tank (puffed, cleaned, sealed)
to 88+ OE high pressure pump in tank
to fuel filter
to "VW" fuel accumulator
to fuel rail
to OE pressure regulator
to "VW" fuel accumulator
to fuel tank. (siphon issues at less than half a tank - 2hr stints - refuel each stint?)

Fuel level - I was simply going to short the second sensor out that is in the drivers side of the tank to use only the passenger side level sensor in the system. (read this some place on the net)

The charcoal canister has one side connected to the air manifold and the other side connected - I assume - the fuel expansion tank. If I remove the canister and replace with a small air filter going to the expansion tank, what should I do with the air manifold connection? Plug?

[jlevie]

There is no cheap solution when using the 88+ tank. With that tank it is essential that the flow through the fuel system never drops so that the siphon is always working at full capacity. Or that you eliminate the dependence on the siphon by placing a transfer pump in the left side of the tank. If you tried to do it with an accumulator I suspect the accumulator would need to have a capacity of close to a gallon. Sort like a large Accusump rated for fuel use.

The minimal cost solution is to use the early tank, feed the output of the transfer pump to a four port surge tank of at least a quart capacity and feed the high pressure pump from the surge tank. Fuel returning from the engine bay goes into the surge tank and the overflow from the surge tank back to the gas tank.

There's no need to do anything with the driver's side level sensor when upgrading to the later tank. The car's harness only has connections for the right hand sensor. But be aware that as the tank runs down the fuel gage won't give you accurate information. It will vary from being wildly optimistic to indicating you are out of fuel.

If you eliminate the charcoal cannister. simply plug the hose from the intake manifold. Place a filter on the hose from the rear of the car.

[scrowner]

Ok. You indicate that the 88+ tank to work best needs a "transfer" pump. The driver side of the tank does have an access hole that is currently filled with the second level sensor of the fuel system. It looks, and I have not done this yet, that I can remove this sensor and put in a low pressure in-tank pump that is used in the pre-88 tanks. Sound like it might work? So, if this old low pressure pump mechanicals fit, this will give me a fuel out of the driver side of the tank. I just need to get this transfer pump fuel line into the passenger side tank. How did you do this? T into the expansion tank connection?

[jlevie]

That is exactly what I did, as described above.

You have to do a little filling on the one of the ears where the level sensor mounts for the transfer pump to fit. Do that before you clean and seal the tank. The picture shows how I routed the fuel from the transfer pump to the right side of the tank. What is not shown is what is below the brass elbow. The side inside the tank has a piece of 3/8" tubing soldered into the fitting that is bent to mimic what the siphon outlet does. It goes down into the fuel cup and bends to follow the curve of the cup. The steel plate is 3/8" thick and was tapped 1/4NPT to accept the elbow and pop riveted to the tank. I used JBweld under the plate and as a thread sealant for the elbow. The tubing across the top of the tank is 3/8" copper with a hose barb fitting drilled out and soldered to the end to adapt it to the hose on the outlet of the transfer pump.

[scrowner]

Jim, thanks for the help. I think our team may be able to accelerate out of all turns this Feb.! Looks like I can do this slight modification to the tank. One more detail question.

I assume since the pre-88 tanks are a dual pump system, the new transfer pump (Driver side) got the electrical for the original in tank pump. And the electrical for the original external pump is now routed to the new 88+ in tank pump of the passenger side?

[jlevie]

There is only one hot wire in the harness from the front of the car for the early fuel pumps. The ground is on the left side rear bulkhead. You'll have to splice in the connector for left side pump. Either by modding the wiring to the transfer pump or by extending the wires for the high pressure pump.

[scrowner]

Any issues with the transfer pump running, car idle or light use, and the tank is full? Should I consider a dash switch for the transfer pump and switch the thing on when we are racing but turn it off for driving the car around town?

[jlevie]

Run the transfer pump when the main pump is running. There is no reason to put it on a separate switch.

[scrowner]

Ok, I will run them as before and not worry.

Another point, You modified your gas tank with a copper connection popped through the 88+ tank for the pump in the drivers side to move fuel to the passenger side. I have a BUNCH of older tank mechanicals. As you know, the older tanks have a return line at the top of the in-tank pump. I was wondering if I could bypass the tank modification and simply connect the transfer pump's fuel to this input connection? I will be modify the main in tank pump with the TRE pump and I think the same modification to the top of the tank flange that is done for the drivers side pump will allow the old pump mechanicals to fit. This is all hard for me to describe so here is my steps for modifying an 88+ E30 tank to fit in an older 84-87 E30:

1. Modify the top flange in the driver side of tank to allow acceptance of a pre-88 in-tank pump. Then install pump and mechanicals in driver side.
2. Insert a "dummy" sensor to cover whole in top of pump in driver side. This will not be electrically connected.
3. Plug up old return fuel of mechanicals of driver's side pump. Not sure best way to do this. Ideas?
4. Pull passenger side in-tank pump and sender. Discard.
5. Use pre 88 in-tank mechanicals by slightly modifying the top flange.
6. Replace old pre 88 in-tank pump with TRE pump as found on this site instructions.
7. Insert into tank. Insert pre 88 sensor in the top.
8. Connect driver side pump fuel out to passenger side fuel in. (I think this is sweet if it will work.)
9. Set tank up near the car and connect up fill rubber, connect up expansion tank, connect up fuel delivery and fuel return to the tank.
10. Connect old external pump electrical to new driver's side pump. Use same passenger side electrical on new passenger side pump.
11. Bolt to the chassis. May need some fudging here with bolts and clips.


Let me know if there is a block to using the pre 88 fuel pump mechanicals in the passenger side to allow me to not drill and modify the tank. I happen to have a bunch of mechanicals in the process of trying to fix our starvation issue.

I am hopping to get this done this weekend.