I bought an FP50-TOW processor a while back to fit to my AU.
Reasons were I had a customer that was having issues towing a boat with his AU ute on gas with an FP32 processor. During long periods of acceleration the processor would 'think' the car was at cruise and would try to bring the LPG mixture back to lambda 1 instead of the richer mixture that was needed.
This was happening due to the processor only using throttle position to determine if the engine was under load. Unfortunately after a short period of constant throttle position it 'thinks' you are now at cruise.

After talking with a supplier about it, he told me about the FP50-tow. But here is the next problem, No one had been buying them so he could give me any feed back.
But I wouldn't fit it to a customers car before knowing how well it works, So I bought one and fitted it to my car first. I like to have first hand experience of the stuff I sell and fit.

The installation and tuning instructions can be found in the first post in this thread: ford-lpg-hydrogen-hho-cng-conversions-f44/lpg-wiring-and-processor-setup-and-tuning-docs-t99750.html
The 'TOW' supplement is a few posts down in the same thread.


Effectively what the TOW option does is give closed loop lean cruise operation. (Lambda 1.05)
Closed loop 'just rich' operation at medium throttle openings. (Lambda 0.95)
and open loop 'full rich' at high throttle openings. (set by installer using peak flow adjustment)

The FP32 that we are comparing here has closed loop stoich cruise. (lambda 1.00)
and 'rull rich' medium and high throttle openings. (peak flow adjuster and sensitivity)

The benefit of the TOW is that cruising at medium throttle the processor is in closed loop but slightly rich, this prevents lean back fire that can occur with stoich mixtures and heavy loads.



The upgrade is pretty simple for anyone already using an FP32. The stepper valve is a plug-in job.
the main harness pin-out are the same, depending on the change over switch you have some re wiring may be needed. The diagram for the FP32 can be found in the above mentioned thread.
Extra wires are needed. The FP50 needs a pulsed input and it also has an output to control the gas valves.
The pulsed in put in this case is taken from the crank angle sensor. At the plug at the rear of the intake manifold you will find a grey wire and a brown wire that have been twisted together. Cut back the insulation on the either wire and solder in a wire to run to the FP50.
obviously the gas valve out put is run to all three gas valves (one at the tank, one just before the converter and the one IN the converter)

I took the time to replace the O2 sensor while I was in there as mine was 150 000km old and past it useful live.

Set up is covered in the instructions the unit I used was and FP50-SS with the TOW option. So no petrol start (I hate that anyway) and give the option of open loop idle. This is good for cars that stutter just off idle or sometimes back fire just off idle. Open loop idle forces the stepper valve full open at idle. It fixes the problem of the stepper not opening fast enough when you floor it from idle and improves response ALOT.


I Just followed the setup procedure outline in the instructions and drove the car home.
I can notice the difference in the way the car drives compared to the FP32, Smoother acceleration from idle and more part throttle power. This is partly due to a retune of the converter. I used to have the sensitivity spring quite tight to force a lean cruise, but this meant medium and high throttle acceleration was too lean and lacked power.
The TOW having a closed loop lean cruise lets me richen up the acceleration mixtures, which is what gave me the smoothness and the power.

Tomorrow night i'm going to hook up my wide band meter and check mixtures and fine tune things a bit.

Anyway, I'm rambling on a bit now. so I'll leave it at that.

Checked the tune and operation with the wide band meter to night on the way home.
It does lean cruise VERY WELL and the open loop idle has cured the hesitation it used to have with the FP32. Still it would be great to see these things with a built MAP sensor too.

Only problem I've got is at high rpm and full throttle it goes lean, I got off the throttle when it got past 16.5:1 on LPG scale. I've had this before, but I found a slight kink in the vapour line right at the converter and the vapour fitting had been screwed to far into the mixer body.

Thats for another day, it works perfectly every where els, so when my wife gets back from Brissy she can have her car back and put some KMs on it. That should show up any economy benefits as she gets pretty consistent mileage every week

I'm interested to see the economy if it drops or gets better....

When u in Sydney next? Come and tune my impco LPG setup...

When the FP32 was working it average 300km to about 50L of LPG (on our standard weekly to and from work trips)
When it died I put a manual power adjuster in it untill the FP50 got put in.
With manual adjuster it was getting 320km to 50L With a slight change in tune biased towards lean.

If it can match the 320km But still let me run properly rich under power I'll be happy.


The more I drive it this week the more I like it though. To have the lean cruise and no hesitation off idle. and how smooth it drives under power. You can kinda guess that hesitation used to s**t me big time.

Seems to be a good thing. we are doing 320-330km to 50L. But with improved drivability and better over taking power.

As always though I can't leave well enough alone.
I've found a mixer with a 43mm venturi that will fit snugly inside a stainless 3inch pipe.

Is it still going well? I'm thinking about an FP-50 as a possible replacement for my AEB 295 should it be diagnosed as u/s.

Yeah I haven't touched it since that last post. (still not got the new mixer on)
and the economy is still good and the drive-ability is still good.
I still have it open loop idle as my car never seemed to like closed loop idle, always had a stutter off idle. I can also start the car cold in the mornings on LPG and not have any hunting.
Did a few long trips 400km each way stuff, and the economy was really good.

I'm really happy with it.

Great news. I wonder how it'll cope with force-fed induction?

Only one way top find out I suppose...

they are cheap enough, just do it.