Author Topic: Blown FET, other issues - why??  (Read 6412 times)

Offline lugnuts

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Blown FET, other issues - why??
« on: December 04, 2008, 06:48:35 am »
Hi guys,
I'm having a resh of problems with a "mostly webshop assembled #1973" board.

The wiki link is below, I'll keep it short here.

Initial Problems:
1) Fuel pump relay output primes OK, but won't pull the relay when the engine cranks
2) Tachometer goes nuts, randomly jumps to 4000+ rpm at idle
3) LCD starts up fine then turns to scrambled jibberish after 30 sec - 5 minutes

4) Most important, after driving several hours, the FET for "Injector A" output failed.
Then, when I fixed the ecu (changed wiring to "INJ F"), the ecu now cuts-out at medium-high boost (220+ kpa absolute) and the car stumbles badly.


- I'm wondering, could any of these symptoms be related, and/or point to a cause??

- I did have to take the ecu apart like 5 times in one day to fix things, maybe static? But why all the issues in the first place?

- Flyback and Grounds check out fine before and after ecu problem, visual check and resistance .1 to .3 Ohm.

Wiki Page:
http://www.vems.hu/wiki/index.php?page=MembersPage%2FKevinBlack%2FAudiAEB


Any input is very much appreciated as always.

Offline lugnuts

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Re: Blown FET, other issues - why??
« Reply #1 on: December 09, 2008, 10:43:32 pm »
Does anyone here know what is going on over at the Wiki? I posted there 5 days ago, and two other people posted above me, and there have been no responses.

I'm a couple days away from testing this ECU in my own car and building another one from scratch to see if it fixes all of the problems.

Offline rob@vems.co.uk

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Re: Blown FET, other issues - why??
« Reply #2 on: December 10, 2008, 09:04:53 am »
Sounds very much like a crank trigger problem in all honesty.  Could the sensor or its wires be damaged, or the sensor gummed up with swarf?

Offline lugnuts

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Re: Blown FET, other issues - why??
« Reply #3 on: December 10, 2008, 10:51:17 pm »
Thanks for the reply.  Crank trigger seems very unlikely for several reasons. Fresh built motor (clean), also the car runs perfect. With the fuel pump relay problem, I simply jumped the relay socket and the car ran every time. And the logs show a perfectly stable RPM signal, right up to the point where the engine cuts out. Then the logs only show "lost time" , just like you reached up and killed the ignition? 

Also I dont see it affecting the LCD and the INJ FET blowing???
 
fun fun stuff.