mx5cartalk.com

A problem many may have come across adding an after market ECU to an NA6:

I found this one on an automatic VL commodore at the wreckers. Its particularly interesting as not only does it provide a variable TPS output, it has the same switch functions as the origional B6 TPS, with the same connector with the same pinout:



Firstly lets take the origional TPS out. Ah you have got to be kidding me!



I was planning to weld the VL TPS into the metal base plate of an origional TPS so the bolt holes would line up. But I was amazed to find under the origional TPS was two holes almost perfectly the right distance apart for the VL TPS.



The finished assembly. Unfortunatly the switch CAM's in the two TPS's are not that same. The WOT switch is almost spot on, but with all the adjustment i could get out of it, the IDLE switch in the VL TPS hangs on for about 25% of throttle travel. The origional is off at 5%, just a fraction of a throttle opening.



I'm curious to do some driving with the OEM ECU to see what affect this might have, maybe it will make no difference, maybe it will do bad things driving around with low throttle openings. (ie cruising at the 60 / 80 / 100kph speed limit in a high gear).

I followed the guide on MT.net and used a BMW E30 VTPS that is a direct drop-in except for some wiring work

BMW E30 VTPS

I couldn't find any (only older versions that were switch only). Australia is swimming in wrecked VL commodores which is handy.

True, it is always convenient/handy to use something that is readily available

Tks for sharing Davo!

how is that going for you? looking to do this some time soon and may be keen on a VL one:D

vespa wrote:how is that going for you? looking to do this some time soon and may be keen on a VL one:D

Actually very bad. The IDLE switch position on the MX5 turns off at about 5% throttle opening, the VL IDLE switch turns off at about 25 - 30% throttle opening - and there is not enough mechanical adjustment to make them match.

The end result is your driving down the road (on the standard ECU) and when throttle travel gets to 10 / 15 / 20% where the origional NA6 ECU expects the idle switch to be off, but its still on the car almost completely cuts out. (ie its trying to maintain an IDLE scenario when your trying to accelerate the car at 1500rpm+)

If your ditching the OEM ECU completely it wouldn't matter, if you dont use the switches the VL TPS is a cheap easy to find option.

But for me im retaining the OEM ECU to control the idle solenoid and as a backup / limp home option if the Megasquirt dies, so at any time i want to be able to run the car off the OEM ECU and the switches need to work.

Its abit of a shame that for everything else that fits so neatly with little modification, the most important aspect is not compatible

To get me by i made a little comparitor circuit which switches the IDLE switch at the correct position based on the analoge TPS signal - but its a messy solution.

A friend has a small hobby CNC, long term i might have a crack at designing a new switch CAM so it can be the perfect plug in replacement TPS.

Thanks for the feed back.

Just got a MS PNP and trying to work out what the best nex step is. I have been told the E30 was the best one to go for but as you mentioned have had some trouble finding one and VL commos are a dime a dozen.

Gives me somthing to think about i guess:D

AVO ended up making an adapter plate to fit a TPS from a 1.8l, I told them about the BMW part but only the non variable BMW TPS, it has a slightly different part number to the one listed in other threads, I don't actually know what the difference is but I wasn't willing to make a $220 gamble, is availible from repco now.

Didn't solve the problem on my car, still has issues returning to idle.

davo5 wrote:But for me im retaining the OEM ECU to control the idle solenoid and as a backup / limp home option if the Megasquirt dies, so at any time i want to be able to run the car off the OEM ECU and the switches need to work.

Umm that's not quite right.
The standard ecu will still idle your car easily without the switchpoint tps, when using the megasquirt. Just don't cut the CMP/CKP (Cas wiring) to the stock ecu, share it with the megassquirt and it will be fine.

The only issue you will get is a tiny idle dip on start up, but that can be tuned out in the MS via the fuel + timing tables easily enough.

My TPS has been on Stefan's car for close to 6 months and I just have the bare spindle showing, no issues other than I lost my boost control (was tuned on TPS values).

But props to you for finding the VL one, for reference the Nissan skyline/pintara 6cyl ones should work, I've just been too lazy to take a multimeter to verify their operation at the pull apart wreckers.

Another TPS that works if off the Audi/VW v6 engines and it is a direct bolt in (has about 6 pins, variable and switch on/off) but they're herder to find cheap than the bmw ones, i got lucky and grabbed it for $5.

Hey dave, i found an ad for this stand alone computer in a u.k mag. http://www.civinco.com/index_eng.html
It is for na6 b6 motors. part number SA500G3

The standard ecu will still idle your car easily without the switchpoint tps.

Yeah I found this out the other day, was doing some tinkering and forgot to reconnect the comparator circuit, didn't even notice the difference driving around. If I had have known that before I started I wouldn't have bothered replicating the switch inputs at all.

davo5 wrote:

The standard ecu will still idle your car easily without the switchpoint tps.

Yeah I found this out the other day, was doing some tinkering and forgot to reconnect the comparator circuit, didn't even notice the difference driving around. If I had have known that before I started I wouldn't have bothered replicating the switch inputs at all.

davo5 wrote:If your ditching the OEM ECU completely it wouldn't matter, if you dont use the switches the VL TPS is a cheap easy to find option.

so are you saying that the VL TPS will work as a variable TPS with a MS?

madboy wrote:

davo5 wrote:

The standard ecu will still idle your car easily without the switchpoint tps.

Yeah I found this out the other day, was doing some tinkering and forgot to reconnect the comparator circuit, didn't even notice the difference driving around. If I had have known that before I started I wouldn't have bothered replicating the switch inputs at all.

davo5 wrote:If your ditching the OEM ECU completely it wouldn't matter, if you dont use the switches the VL TPS is a cheap easy to find option.

so are you saying that the VL TPS will work as a variable TPS with a MS?

Yep works well:



You just wire in the pot and leave the switches not connected to anything.

I know this is an old thread, but nice find!