We have 20 bad ecu's (3.2 engine computers) in the shop. I sent a couple to Steve Wong / 911 Chips for repair. He asked if they were from a 914-6 conversion car since they had a particular defective part. They weren't but most of our cars are 3.2's into early 911's so sort of the same idea. Steve said the reason we were blowing ecu's is because we were mixing the ecu's with a non 3.2 tach. It's very common for a 914 conversion to either modify their 4 tach with an electronic unit or modify an early tach to work with the 3.2. Steve said it may work for a short time, sometimes longer but failure often happens at high rpm. Go to the track, ralley or just some spirited driving and the higher rpm's kill the ecu's. I have to believe him since we have a pile of them to prove it. We had one burn out after 1.5 miles. Even hooking up the shift light wire on the 3.2 tach incorrectly will burn up the ecu's. Not right away but over time. A rebuilt ecu runs $900 and the burnt core is worthless. It's a known problem so it isn't accepted by most, if not all of the ecu rebuilders. You also must use a coil for a 3.2. No substitutes. All of this was unknown to me and the guys at my shop until today but you can be sure they will be more careful about this in the future. 1 more thing and it's something we did already know and practice, always remove the battery terminal from the battery when connecting your ecu.

VERY good info, thanks for sharing!

Another example of the awesomeness of 914 World members.
Thanks for sharing. I'm sure you've saved a few folks just south of $1K!

We're lucky to have you here.

Wow, this isn't something I would have thought of at all. Do you think that it would apply to other conversion engines as well? Would it be safer and perhaps easier to just use a different tach on any conversion?

Maybe the same for 3.6. That's the only other engine that has a similar ecu.

The short version that I heard from Steve was - 3.2 needs a stock 3.2 tach that's wired properly from the start. That's the only way to protect the stock motronic ecu.

Very interesting; any 3.2 914 owners experience this ??

I also wonder if it would be a similar issue with a V8 or Subaru engine or if its purely a Porsche engine issue.

It's a tach - 3.2 ecu issue. Has nothing to do with a V8 or Suby since they are not using a Bosch motronic ecu to control the EFI. Steve told me this is a common issue in the ecu's that he gets back from 914-6 conversion cars, thus the reason for my post.

Interesting. Stock tach (or modified stock, etc.) likely doesn't have enough impedance for the motronic output channel and then the board burns when too much current starts flowing (or just too much current over time).

No. nor do I intend to!

Interesting..... luckily I bought a 3.2 tach by accident when I installed my 2.7 back in 86. So when I upgraded to a 3.2, it worked like a charm. All my gauges are 3.2 gauges.

Can't open it up and see what component let the smoke out?

I am with Mike on this one: Opening up the component and see what smoked; the internal circuitry may give further indication on what has/caused the problem.

Another question relates to the shift light whether to use connected or not, connections, etc.

The only problems other that "thieves stealing parts" relate to a tach going south but the engine and its parts have 145,000 miles on them. Tach, fuel pump, wiring harness, coil, etc. came with the engine. Tach was replaced with 3.2 tach.

Do know the costs of DME replacement IF YOU CAN FIND THEM! They are getting extremely hard to find in serviceable condition. Protect them.

We do need to find out more since these items are becoming rare and expensive.

Steve

Steve told me which part buns out but not knowing electronics, it means nothing to me. According to him, the part is not available, leaving the unit junked. Most of the 20 non working ecu's at our shop, probably have the same issue.

First, thanks for the info with these 3.2 conversion.
I have a few questions in my mind: I have friends that have converted from 2.7 to 3.2 then to 3.6. They have been driving these conversions for 10 + years. I know some drive them as intended- on the track and have not experience any concerns.

The other question I have is, if one sends an early tach to say, North Hollywood Speedo for a conversion to work with an electronic pick-up ( 3.2) if they aware of these problems and will they simply ignore this and perform conversion? I had one converted - they changed the whole electronic module and gave me back the old one- in case I wanted to convert back... they have been around for 40+ years . Steve is local to me, I guess its time to call and get some education

- time to go back to the Brazilian F1

Steve is a great resource and really know his stuff. NHSS does too bit Hartmut tetired and I am not sure all of his knowledge was passed down. I have spoken with Steve many times and he is always generous with his time and knowledge.
Yes call them and ask.

Steve is one of the guru's on this kind of stuff. I'm probably just a poor translator of some of his knowledge. I would contact him if you have any questions or concerns.

As I am getting closer to installation of the 3.0, does anyone have a particular recommendation on the appropriate gauge set for my Weber festooned SC motor? / Or will the stock SC gauge for oil temp /press etc. be fine? And is the tach special to the SC motor verses my original 71 tach??

Thanks for the sage advice.....

I just ran this by Brian Farmer at Einmalig in Huntington Beach; he was unfamiliar with what might blow in the ECU, and commented that they send them out on occasion for rebuilding....?

And, he carries the 3.2 Tachs in inventory if anyone needs another source.

Interesting... wow.

I had a weird tach issue that was the opposite of this problem. My 3.2 tach would only "kind of" work with my 3.6 engine, the tach needle was slow and lazy, would lag behind the engine by about one second... fricken drove me nuts.

Blowing up ECU's, thats bad.

So the question I have is what are people I swing to convert the stock 4cyl tachs to 6cyl pre 3.2s?

My understanding is with a 3.6, sometimes a 3.2 will work. Best is to source a 3.6 tach and or take it to North Hollywood Speedo for a conversion.. That's what I did...with a OEM RSR tach to convert to accommodate the new electronic. I'm sure there's other options like simply plug in a 3.6 tach- but it will not look vintage. To each its own.

Isn't one tach electronic (3.2) and all the older ones electric ?
SC 3.0 tachs are an exception as they are low voltage output and the early are high voltage output,but they operate in a similar way.
Surely an Ashlocktech tach-adapt would sort this issue,I have been working with Bob directly and find him super helpful,he has basically given all the specs for a great ignition set-up.
Mark I would be happy to contact him and run it past him,his unit is very versatile and has a great rep for reliability unlike the MSD unit.

That was my understanding also, and to be fair the tach did work, but very slow to react. However my 3.6 has a light flywheel and revs up very quick. The tach pictured was built for me by NHSpeedo and required a 964 movement.... an expensive proposition. This conversion took significant time and energy as NHSpeedo had to do what they call the "Singer" modification.

Mark
Thanks for the heads up. Just drug out my dash and checked the part # on the tach i bought for my conversion. Turns out, I got lucky and bought a 3.2 tach. one less worry.
Dave

WOW - thanks!

curiously - Steve never raised the issue when i b'ot the chip a couple months ago - and he knew it was going in a 914-6

has anyone yet checked to see if NHS or PAS can put new 3.2 guts in our older tachs? - at what price?

last nite i b'ot the only used 3.2 tach on ebay from msroadrace -
expensive but half the price of replacing my 28-pin 082 DME with Wong chip in it - - call it insurance


fwiw - currently running oem 911/914-6 tach that is orig'l to car; it's been fine with the 3.2 for 3 yrs, but not many miles, nor sustained high rpm like we'd do on track-

i have 2 good spare 3.2 DME's as well - looks i can let one go now!

, (and dump the spare SC tach as well - sounds like it is useless with the 3.2 DME)


wiring diagram for 3.2 tach here
http://forums.pelicanparts.com/porsche-911...tml#post3972081


p.s. - here is a good link from one of our colleagues http://forums.pelicanparts.com/porsche-911...lity-chart.html

to wit:

"5. 1978-1983 Tachs. These are driven from the "TD" tachometer drive output from the six-pin CDI box because the points were eliminated in favor of a magnetic reluctor. According to the following thread, the SC tach signal is the same as the later Motronic:SC Thread

6. 1984-1989 Tachs. These are driven from the Motronic box. Chris Bennett posted the Motronic signal here: Motronic Thread"