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Kish,
Each fuel sender is 0-60 ohm, or 0-120 ohm is series. You cant take an ohm based input into your dash and need to use a voltage divider. We have a solution we were testing last month. You have to be VERY careful when using a voltage divider with fuel. 
I’ll ping you in a few days with our results
kishg,
You can fit a surge tank. To do so you’ll need to replace the high pressure pump in the tank now with the transfer pump from an early (up to 8/87) 325. The output of that pump goes to a four port surge tank that feeds an external high pressure pump. The ports on the surge tank are set up as follows:
The overflow port from the top of the surge tank goes back to the return fitting on the in-tank pump.
One inlet of the surge tank goes to the outlet of in-tank pump.
The other inlet of the surge tank goes to the return line from the engine bay.
The outlet of the surge tank goes to the inlet of the high pressure pump.
There is no good place underneath the car to mount a surge tank and if you mount it in the trunk you need to install a solid bulkhead between the cabin and the trunk. So what looks simple becomes a lot of work.
An alternative solution is to replace the tank in the car now with the 63l tank. You mount the high pressure pump from the tank you have in the right side and use a low pressure transfer pump in the left side. Plug the return fitting on the transfer pump and route it’s output to the return fitting on the high pressure pump. Fuel return from the engine will go to the fitting on the left side of the 63l tank.
The only difficulty with this is that the level sensor that mounts in the transfer pump has one side grounded, so you can’t simply connect the sensors in series. My solution was to isolate that sensor from the pump housing so I could series the sensors.
I don’t know anything about the AIM, but to get data from the sensor you need a stabilized voltage source and a current limiting resistor. My IQ3 provides regulated 5vdc for reference. I use a resistor of 50 ohms which limits the current flow through the level sensor to 100ma, which should be safe. The voltage swing from empty to full would be 2.7v. For two sensors in series the voltage swing 3.5v.
This seems like a stretch, but I’ve never tried to run that long. I think you should plan to burn ~5 gallons / 30 minutes.
Back up!
I have a '89 car that I would imagine should have a single pump. Definitely had sputtering issues at the 27-28 minute race mark in hard right hand corners. Car indicates it is just at about a 1/2 tank or just above.
[quote=“jlevie” post=57315]
The only difficulty with this is that the level sensor that mounts in the transfer pump has one side grounded, so you can’t simply connect the sensors in series. My solution was to isolate that sensor from the pump housing so I could series the sensors.[/quote]
What did you do to isolate the sensor? I want to do this similar setup to my 63l tank and have my old in tank pump from the 55l and a new intank pump for the later model setup and the external pump so I should have all of the pumps I need correct? (I am currently only running the late model setup with one pump) I also have a new fuel gauge that I want to use with both senders, the gauge will work with anything under 300ohm. So how should I connect the senders and should I use a resistor or do anything special to the sending units to make this work?
Thanks for the help!
[quote=“jlevie” post=57315]kishg,
You can fit a surge tank. To do so you’ll need to replace the high pressure pump in the tank now with the transfer pump from an early (up to 8/87) 325. The output of that pump goes to a four port surge tank that feeds an external high pressure pump. The ports on the surge tank are set up as follows:
The overflow port from the top of the surge tank goes back to the return fitting on the in-tank pump.
One inlet of the surge tank goes to the outlet of in-tank pump.
The other inlet of the surge tank goes to the return line from the engine bay.
The outlet of the surge tank goes to the inlet of the high pressure pump.
There is no good place underneath the car to mount a surge tank and if you mount it in the trunk you need to install a solid bulkhead between the cabin and the trunk. So what looks simple becomes a lot of work.
An alternative solution is to replace the tank in the car now with the 63l tank. You mount the high pressure pump from the tank you have in the right side and use a low pressure transfer pump in the left side. Plug the return fitting on the transfer pump and route it’s output to the return fitting on the high pressure pump. Fuel return from the engine will go to the fitting on the left side of the 63l tank.
The only difficulty with this is that the level sensor that mounts in the transfer pump has one side grounded, so you can’t simply connect the sensors in series. My solution was to isolate that sensor from the pump housing so I could series the sensors.[/quote]
Jim, are you still around? We mounted a new-model 63l non-oem tank in my '89, and now are experiencing the dreaded right-hander fuel cut after about an hour (It’s a dual-purpose Chump/SE30). I think we have the surge tank plumbed right. As far as I can tell, the new-model right-side pump has only an outlet to the engine (supply), and no inlet. How do you direct the output from the transfer pump to it?
Thanks,
Barry
[quote=“jlevie” post=57315]
You can fit a surge tank. [/quote]
I don’t see anything in the rules that clearly allows a surge tank. What provision are you using to install a surge tank? Are you considering a surge tank to be a baffle?
[quote=“BS1” post=72397]As far as I can tell, the new-model right-side pump has only an outlet to the engine (supply), and no inlet. How do you direct the output from the transfer pump to it?
Thanks,
Barry[/quote]
A late-model 318is pump has a return fitting.
on the note of gas tanks, has anyone had a problem of when you fill the tank all the way to the top of the fill tube, gas starts leaking out of the top of the tank somewhere?
Yes I have have this problem. I think it is coming from the drivers side fuel level sender.
In my case the leak when full was coming from the large (14mm ID) hose from the filler neck to the top of the tank. Not the actual filler hose, but the one with the cloth woven covering that runs under the metal cover behind the shock. It was cracked and torn where it attached to the tank. Part 5 in the diagram:
http://www.realoem.com/bmw/showparts.do?model=1413&mospid=47322&btnr=16_0107&hg=16&fg=10
During my build I replaced ALL of the rubber fuel filler, vent, supply, and return lines. I saw it as cheap insurance before racing a car of this vintage. I didn’t notice any other cracked hoses, but all were hard and many loose at the factory pinch clamps.
thanks for the replies. when the problem happened i first took off the access cover that would be under the rear seat on the passenger side, and did not notice any fuel. then i got under the car and could see where it was wet, but could not find a source. it was not coming from the filler tube, but somewhere on top. I’ll have to drop the tank and do some more inspections. my paddock space was on an incline (downhill was the passenger side) at the time, and it only happened when i filled the tank to the top of the filler tube for the long race.
what is the expansion tank for and where is it in the car?
The expansion tank gives gas vapor a place to go in the hot sun. It’s under the RR wheelwell.
Just back from the Chump BIR race. We tried using a transfer pump from an early-model ('87) 325 on the left side, and a 318is dual-nipple high-pressure pump on the right side. To make it work, we had to make our own 1/2" to 5/16" hose adapter, and wire a connector to the transfer pump, using the solid green wire from the harness for a power tap. To make the transfer pump outlet point toward the right side, we cut off a tab on the pump housing assembly to make it fit in the tank.
On Saturday just before the race, we filled up with gas and noticed a big leak. The tab-cut we made apparently didn’t seat the rubber o-ring against the tank, and/or the new level sensor we fit in the transfer pump housing had a leaky seal too. With no time to spare, I removed the transfer pump housing and replaced it with the stock '89/63l sensor. As our first driver left the pit he complained of barely being able to keep the engine running above idle. He pitted next time around, and we fitted the old stock '89/63l high-pressure housing, and sent him back out OK (meaning with the fuel-cut issue). After testing the pumps, we found that neither worked…so it was a complete failure. The lesson here is to test anything fuel-related before racing it.
Has this setup worked successfully for anyone? Our main mechanic/crew chief will not cut the tab on the tank to make the transfer housing fit. Maybe put it in with the outlet pointing in the wrong direction, and curve the hose around 180 degrees to the right-side pump? I’m thinking this should be fine, provided we have pumps that actually pump.
Well I am starting to get fuel starvation issues. Never had any serious issues till last few races. I haven’t changed fuel filter in a while so could that be the sudden cause? Fuel pump was new about 6 years ago. Could that be it? This is happening with a little over half a tank. The gauge is reading full till back in paddock and it used to be more accurate on track.
Could some vent somewhere be clogged?
Any thoughts welcome.
Starvation at 1/2 tank is common enough. Might be something easier to live with than fix. I’ve tried and failed several times to fix fuel starvation problems. Might be worth confirming what’s happening. Having a fuel pressure gauge on your dash can be darn handy when your engine starts acting up. Or as a temporary measure you could channel my ghetto fuel pressure HUD from a couple yrs back.
That’s funny and probably costs 5 mph in drag. I prefer in car gauges…[/quote]Pic is from VIR in 2009 I think. Was a darn handy idea at the time. Fought engine management problems all year. Problem was diabolical. Turned out to be the AFM causing my mixture to go lean. Didn’t figure it out until I installed a F/A meter on my dash and then…6months later, learned to trust it.
I’ve had 2 SpecE30s and an e30 Lemons/Chump car. Each had fuel starvation issues. I replaced a lot of stuff, but never fixed the problem. You’ll find threads here by guys that did fix starvation, but you’ll find that the solutions differ. To me that indicates that there’s multiple possible causes, each with it’s own solution. If it was me, I’d let it go. It’s been me 3x now. And I let it go.