Fuel sense (or lack of!)
Discussion
Right, am currently installing my Stack pod and have decided to stick with the fuel tank/sender switch that's on the original loom (on advice from the factory). However, I'd like to use the fuel guage in the Stack as opposed to the analogue guage supplied by the factory. It seems a shame not to use is now that I've paid for it.
So, each tank has it's own pump/sender and can be switched from the dash to provide a main tank and reserve so you run from one or the other (the alternative is to 'T' the tanks together and use one pump to supply a swirl tank and another to supply the carb).
Question is, I know that a calibration procedure is required for the Stack 8130 fuel level to work. I've checked the resistivity of both senders and they're identical, so can the Stack cope with switching between the two (don't see why not)?.
Secondly, I have the option of running the main Stack loom back into the engine bay or using the existing loom and just splicing into it at the dash end. Short of problems with cable length resistivity I see no reason why I shouldn't do this (after all, all the necessary cables are in place in the main loom) and I can connect everything up and still have access to the connections through the right hand side (offside) access hatch in the cockpit shell.
Thanks for any info you can give as it's holding up the build somewhat whilst I procrastinate.
So, each tank has it's own pump/sender and can be switched from the dash to provide a main tank and reserve so you run from one or the other (the alternative is to 'T' the tanks together and use one pump to supply a swirl tank and another to supply the carb).
Question is, I know that a calibration procedure is required for the Stack 8130 fuel level to work. I've checked the resistivity of both senders and they're identical, so can the Stack cope with switching between the two (don't see why not)?.
Secondly, I have the option of running the main Stack loom back into the engine bay or using the existing loom and just splicing into it at the dash end. Short of problems with cable length resistivity I see no reason why I shouldn't do this (after all, all the necessary cables are in place in the main loom) and I can connect everything up and still have access to the connections through the right hand side (offside) access hatch in the cockpit shell.
Thanks for any info you can give as it's holding up the build somewhat whilst I procrastinate.
Question is, I know that a calibration procedure is required for the Stack 8130 fuel level to work. I've checked the resistivity of both senders and they're identical, so can the Stack cope with switching between the two (don't see why not)?.
The answer is yes. This is the way I did it and it works very well. One of my senders was slightly more resistive than the other which means that my offside fuel tank has a built in error of approx 5 litres. I can live with this.
As for using the factory loom aft of the dash, again, the answer is yes. Stack advised me to run separate earth connections back to the negative terminal of the battery rather than to earth individual components to the chassis as I was proposing to do. According to Stack, the chassis has an small inherent resistance which can affect the accuracy of the readings. I would double check this with Stack as I think that the man I spoke to was being rather pernickety.
Funny. I was told this wasn't possible! Then again I didn't have a forum like this to get advice from.
Why do people want two fuel tanks, why not join them and let them act as one?
Also why would you need swirl pots for the fuel, you would only need this if you think your going to pick up air and if you join the tanks together effectivelly (ie not with anything smaller than -12) then that will never happen unless you run them dry. You will also have to fill each independantly!
Reason I ask is because with forced induction any fuel starvation will be punished severly. I expect by running one pump per tank means only one will run at a time, so were's the benefit of having two?
STIG in my view, with your engine you really have to go for overkill with the fuel and oil, if you have air-con you have no chioce but to go for an electric fuel pump, just make sure it'll pump like a tap!
Why do people want two fuel tanks, why not join them and let them act as one?
Also why would you need swirl pots for the fuel, you would only need this if you think your going to pick up air and if you join the tanks together effectivelly (ie not with anything smaller than -12) then that will never happen unless you run them dry. You will also have to fill each independantly!
Reason I ask is because with forced induction any fuel starvation will be punished severly. I expect by running one pump per tank means only one will run at a time, so were's the benefit of having two?
STIG in my view, with your engine you really have to go for overkill with the fuel and oil, if you have air-con you have no chioce but to go for an electric fuel pump, just make sure it'll pump like a tap!
Ok Stig here is some professional advice 
To correct the statement from Stack (probably Angus) the resistance of the chassis is far less than the cable run for an insulated negative return. So using the chassis for a ground is perfectly acceptable, anything else is pure paranoia from Stack, i dont need to go into calculations but considering the steel thickness and distance to and from the tank / battery / fuse box / Instruments and Chassis its more than likely to be well less than 0.1 of an Ohm.
But i can measure it on my chassis if you need proof.
The only reason i can think of, is the different metals corrosion that could occur between the earth eyelet and the chassis which might happen later in the vehicles life due to moisture ingress. The use of prohibitive material such as Petrolium Jelly or CopperSlip at the joint should make it last for the lifespan of the car
The addition of a corrective resistor is a good idea and should present no technical difficulty once you know the resistive values of the senders in both tanks. Just make sure the resistance differential is the same at the lowest, mid and full sensor positions, plot the difference on a graph and calculate the mean average of difference and then select the correct resistor for the tank sensor with the HIGHEST reading as the addition of a resistor to ground drops the value.
I have not got as far as requesting tanks from the factory as yet so i dont know the type of sensor they use, if someone cares to post the type and model numbers i can get on to the manufacturer and get the tech specs and work it all out for you. Another easy route is to use a variable pot resistor and fine tune it that way to match
If both taks are fed using the same wire sizes (im sure Teds supplier aint that stupid to make such a fundamental mistake) and both tanks are grounded at the same point to chassis with adequate size and type cable of approximately the same length 10 to 30% difference will introduce less than a 2% deviation in resistive value to the sensor.....my advice is to fit a braided earth strap from each tank to the chassis and thus eliminate any errors and stop corrosion of the tank to chassis due to static and differential materials....every little helps
Ont the interconnection from your Stak to main loom, i dont see why you cant use the original loom from the vehicle...like you say, everything is there. I would opt for an interconnect, something like a AMPmutilock style connector to make the stack and vehicle looms mate.
How far into this are you ? If you are in the UK i can come along and help you out with the connectors (i have hundreds of different automotive and racing types of connectors in my workshop)
Contact me on a.huggett@btclick.com and i can get back to ya very soon
Regards
Andy
I hope that all made sense
>> Edited by UltimaAnimal on Saturday 21st December 13:49
>> Edited by UltimaAnimal on Saturday 21st December 13:55
To correct the statement from Stack (probably Angus) the resistance of the chassis is far less than the cable run for an insulated negative return. So using the chassis for a ground is perfectly acceptable, anything else is pure paranoia from Stack, i dont need to go into calculations but considering the steel thickness and distance to and from the tank / battery / fuse box / Instruments and Chassis its more than likely to be well less than 0.1 of an Ohm.
But i can measure it on my chassis if you need proof.
The only reason i can think of, is the different metals corrosion that could occur between the earth eyelet and the chassis which might happen later in the vehicles life due to moisture ingress. The use of prohibitive material such as Petrolium Jelly or CopperSlip at the joint should make it last for the lifespan of the car
The addition of a corrective resistor is a good idea and should present no technical difficulty once you know the resistive values of the senders in both tanks. Just make sure the resistance differential is the same at the lowest, mid and full sensor positions, plot the difference on a graph and calculate the mean average of difference and then select the correct resistor for the tank sensor with the HIGHEST reading as the addition of a resistor to ground drops the value.
I have not got as far as requesting tanks from the factory as yet so i dont know the type of sensor they use, if someone cares to post the type and model numbers i can get on to the manufacturer and get the tech specs and work it all out for you. Another easy route is to use a variable pot resistor and fine tune it that way to match
If both taks are fed using the same wire sizes (im sure Teds supplier aint that stupid to make such a fundamental mistake) and both tanks are grounded at the same point to chassis with adequate size and type cable of approximately the same length 10 to 30% difference will introduce less than a 2% deviation in resistive value to the sensor.....my advice is to fit a braided earth strap from each tank to the chassis and thus eliminate any errors and stop corrosion of the tank to chassis due to static and differential materials....every little helps
Ont the interconnection from your Stak to main loom, i dont see why you cant use the original loom from the vehicle...like you say, everything is there. I would opt for an interconnect, something like a AMPmutilock style connector to make the stack and vehicle looms mate.
How far into this are you ? If you are in the UK i can come along and help you out with the connectors (i have hundreds of different automotive and racing types of connectors in my workshop)
Contact me on a.huggett@btclick.com and i can get back to ya very soon
Regards
Andy
I hope that all made sense
>> Edited by UltimaAnimal on Saturday 21st December 13:49
>> Edited by UltimaAnimal on Saturday 21st December 13:55
You might also remind the general audience about the importance of grinding off the powder coat at each of the negative grounds to the chassis. I did this on all my earth connections, but you'll definitely need to apply an anti corrosion product to the joint. With our high humidity, 6 mos. is all it took to corrode my battery earth connection which caused some rather erratic behaviors.
Just out of curiosity, but on a similar subject, have any of you had problems with the voltage reading on the stack under full load (with aircon and lights running)? Mine drops down below 11 volts under full load at idle, as displayed on the stack, but when I check the voltage at the battery its over 13. I was a little worried that the battery was not being recharged. Its recharging. Increasing the revs to 2500+rpm does not help. I'm not quite sure why I'm getting inconsistent readings. I've run a very large battery earth, and have checked all my grounds. Any thoughts?
Cheers!
-Mack
Just out of curiosity, but on a similar subject, have any of you had problems with the voltage reading on the stack under full load (with aircon and lights running)? Mine drops down below 11 volts under full load at idle, as displayed on the stack, but when I check the voltage at the battery its over 13. I was a little worried that the battery was not being recharged. Its recharging. Increasing the revs to 2500+rpm does not help. I'm not quite sure why I'm getting inconsistent readings. I've run a very large battery earth, and have checked all my grounds. Any thoughts?
Cheers!
-Mack
Steve_D said: Alan
I'm not an electronics person but I believe you should be able to put an appropriate size resistor in one of the sender wires to correct your missmatch.
Steve
Steve, you're right and I did consider doing this but as the error in my offside tank is only just over a gallon, I didn't think it was worth the hassle. I never run my tanks down too low anyway. Alan.
Thanks again all for excellent advice.
Let me put a few points straight:
1. I considered T'ing both tanks together, using a swirl pot etc. but decided against it as it's unecessary and can promote fuel cavitation.
2. Balancing the tanks is OK, but, I only have -6 take-off's so it would take a while to balance the tanks anyway. The senders are matched resistance wise (will test at 1/4, 1/2 and full tank) and I never tun them anywhere near empty anyway. Incidently, on a full tank, my 460SE can read anywhere from 1/2 to full on a right hand bend so go figure!!!
3. I went for the main/reserve setup as that's that the factory recommends and it saves hacking away at yet more of the loom (which I've already done enough of for the start button and FIA kill switch).
4. Fuel supply should not be a problem. The Carter pumps that the factory supply are way above the anticipated fuelling anyway. I have fuel pressure montitoring so will detect the problem early enough to rectify IF it becomes apparent.
Finally, I've discussed this issue with Ted and Gail and am fully confident that the setup works. After all, we only get the chance to test it with one car, the factory have done it with hundreds!
Thanks again for all your welcome advice
Let me put a few points straight:
1. I considered T'ing both tanks together, using a swirl pot etc. but decided against it as it's unecessary and can promote fuel cavitation.
2. Balancing the tanks is OK, but, I only have -6 take-off's so it would take a while to balance the tanks anyway. The senders are matched resistance wise (will test at 1/4, 1/2 and full tank) and I never tun them anywhere near empty anyway. Incidently, on a full tank, my 460SE can read anywhere from 1/2 to full on a right hand bend so go figure!!!
3. I went for the main/reserve setup as that's that the factory recommends and it saves hacking away at yet more of the loom (which I've already done enough of for the start button and FIA kill switch).
4. Fuel supply should not be a problem. The Carter pumps that the factory supply are way above the anticipated fuelling anyway. I have fuel pressure montitoring so will detect the problem early enough to rectify IF it becomes apparent.
Finally, I've discussed this issue with Ted and Gail and am fully confident that the setup works. After all, we only get the chance to test it with one car, the factory have done it with hundreds!
Thanks again for all your welcome advice
Re joining the Stack and Factory looms. I soldered the connections together as I couldn't envisage any circumstance where I would want to separate the two halves of the loom in the future. If you do solder the connections, make sure that you stagger them, otherwise, by the time you've fitted the heat shrink tubing to each of the connections and then re-wrapped the loom, you'll have something that resembles a snake that's just swallowed an ostrich egg.
I believe that my car was one of the first to have a Stack instrument so I expect that Stack has improved things in the intervening 4 or 5 years (gulp) but I did have some problems. Anyway, for what it's worth, I initially began to calibrate the fuel tank using fuel increments that were too small. Because the lower section of the fuel tank is long and deep, putting in 5 litres of fuel barely moved the sender float and so the resistance reading did not change between 2 of the calibration points. This completely bamboozled the instrument. I contacted Stack when the fuel read out simply wouldn't work and they ran a simulation on one of their test rigs using all of my data. They had exactly the same symptoms as I was getting (the read out drifted up and down aimlessly). Hopefully, this has long been sorted but I thought I'd mention it. Also, in my Stack manual, it recommends that you drive to your local garage to do the calibration at one of the pumps. You need to be on particularly good terms with the proprietor as you could be there for some time. Fuel calibration was (and for all I know, still is) a very precise business involving pressing buttons in a very definite sequence. If you make a mistake, you'll have to start again, which means pumping the tanks dry: a real pain.
As I said, it's been a long time since I fitted my Stack and it's probably much easier now but as the old saying goes, forewarned is forearmed.
I believe that my car was one of the first to have a Stack instrument so I expect that Stack has improved things in the intervening 4 or 5 years (gulp) but I did have some problems. Anyway, for what it's worth, I initially began to calibrate the fuel tank using fuel increments that were too small. Because the lower section of the fuel tank is long and deep, putting in 5 litres of fuel barely moved the sender float and so the resistance reading did not change between 2 of the calibration points. This completely bamboozled the instrument. I contacted Stack when the fuel read out simply wouldn't work and they ran a simulation on one of their test rigs using all of my data. They had exactly the same symptoms as I was getting (the read out drifted up and down aimlessly). Hopefully, this has long been sorted but I thought I'd mention it. Also, in my Stack manual, it recommends that you drive to your local garage to do the calibration at one of the pumps. You need to be on particularly good terms with the proprietor as you could be there for some time. Fuel calibration was (and for all I know, still is) a very precise business involving pressing buttons in a very definite sequence. If you make a mistake, you'll have to start again, which means pumping the tanks dry: a real pain.
As I said, it's been a long time since I fitted my Stack and it's probably much easier now but as the old saying goes, forewarned is forearmed.
I run two tanks and a link pipe between the two tanks, and just one pump. I works fine and is a lot easier when filling the car - you dont need to worry if you can only fill one side because it will level out. Only down side is if the pump goes bang, but also noticed if you park the car on a slope, one tank will "overfill" Never been a problem though.
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