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seeking help debugging 3.6 Motronic in early car
Hi,
I have a 1991 3.6 in my 914 and it's ran great for the past 5 years, but now I've had two problems in one month. Maybe they are unrelated, maybe not... ? The engine is mostly stock with the exception of 993 rs cam profile, 996 air flow sensor, 996 speed sensor, headers, etc. The chip re-programming was done by Protomotive (when they were still here in California) and it has worked amazingly well and trouble free for 5+ years. I had the first problem about a month ago that just turned out to be a dead "ignition module". I was able to diagnose using the scientific method because that was the one component in the system the didn't work (the car can run on one coil/ignition module). I replaced the module, and everything worked perfect again for about 2 weeks. I parked it for about a week (still running fine), and when I went start it again it's running very rough. It's not the same coil/ignition module problem. Both coils are firing and the car can run on either set (although rougher with just one). It's hard to start and sort of "gasps" when I touch the throttle. It barely idles, and after revving the engine it won't come back to a smooth idle and needs to be restarted. My *hunch* is that it's the air flow meter (recall, it's a 996 unit and my 964 chip has been reprogrammed to work with this), but don't have any ideas on how to really test this other than to just start replacing fairly expensive parts. If I unplug the air flow meter the car will still barely start and it still runs horribly, and maybe even a little worse - so perhaps it is doing *something*. Any ideas? Any tips on how to debug this? Thanks, Steve   
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06-27-2010, 12:58 PM
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Join Date: Dec 1999
Location: Novato, CA
Posts: 4,740
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Your best bet might just be to take it to a mechanic who has a good running 91 so he could swap parts from it to yours to isolate the problem without having to buy all new parts.
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06-27-2010, 02:23 PM
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You should be able to hook up a PST2 or Bosch Hammer to see fault codes. And then there is the flashing out fault codes via the CEL. If this is hooked up to the DME harness it will tell you what the DME is "unhappy" about.
Ingo
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1974 Targa 3.6, 2001 C4 (sold), 2019 GT3RS, 2000 ML430 I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs Porsche "Hammer" or Porsche PST2, PIWIS III - I can help!! How about a NoBadDays DualChip for 964 or '95 993 |
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06-27-2010, 08:12 PM
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> You should be able to hook up a PST2 or Bosch Hammer to see fault codes.
*Should* be able to, if I had added the plug during my conversion. Doh. I think I'll do that... (and I've started a new thread): how to add OBD plug to 3.6 transplant -Steve |
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06-28-2010, 03:39 PM
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1974 Porsche 911 Targa 3.6
