The Wrong LH Computer.....?
07-03-2003, 12:12 AM
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The Wrong LH Computer.....?
Good grief!
Well, I've been trying to track down a problem with a miss at high throttle settings on my '85 S2 5 speed for years. The latest attempt: new MAF sensor.
The new MAF did make the car run noticeably smoother, but now it is running somewhat rich. Before, I could "blip" the throttle and not really see any smoke. I did definitely see some black smoke under acceleration when my missing was taking place, so I started thinking the MAF was a possible suspect. With the new MAF, the car runs very smoothly and feels rather strong under part throttle, but still misses, and now I can see a small amount of black smoke when I blip the throttle.
John Speake, who supplied me the MAF and a TREMENDOUS amount of help, suggested that there might be a bad connection between one of the pins on the MAF and the LH computer, since despite turning the pot on the MAF 15 turns counterclockwise, I am still a little rich. So I retired to the garage and tested the wire for continuity. The wire is fine.
In order to figure out which prong on the MAF connector and which prong on the LH connector, I had my laptop on the ground next to me, so that I could see which exact pins on the the two connectors were necessary to establish the fact that the wire was good. Of course, my mind wandered and I found myself poring over the pages...where I found the one with part numbers.
My '85 has for its LH computer part number 928.618.123.03. Which is the LH computer for an '85 928 all right...only a US model S3! I'm driving a "Euro" or ROW model S2 which is supposed to have 928.618.123.00!
WELL. Obviously, the two computers are close enough that they will operate the car's injection. The S2 and S3 appear to have very similar injection systems, though I do know for a fact that they take different injectors. I wonder if this wrong computer is the source of my rough running problems all these years?
Does anyone know enough about the computers to tell?
Normy!
'85 S2 5 Speed
Well, I've been trying to track down a problem with a miss at high throttle settings on my '85 S2 5 speed for years. The latest attempt: new MAF sensor.
The new MAF did make the car run noticeably smoother, but now it is running somewhat rich. Before, I could "blip" the throttle and not really see any smoke. I did definitely see some black smoke under acceleration when my missing was taking place, so I started thinking the MAF was a possible suspect. With the new MAF, the car runs very smoothly and feels rather strong under part throttle, but still misses, and now I can see a small amount of black smoke when I blip the throttle.
John Speake, who supplied me the MAF and a TREMENDOUS amount of help, suggested that there might be a bad connection between one of the pins on the MAF and the LH computer, since despite turning the pot on the MAF 15 turns counterclockwise, I am still a little rich. So I retired to the garage and tested the wire for continuity. The wire is fine.
In order to figure out which prong on the MAF connector and which prong on the LH connector, I had my laptop on the ground next to me, so that I could see which exact pins on the the two connectors were necessary to establish the fact that the wire was good. Of course, my mind wandered and I found myself poring over the pages...where I found the one with part numbers.
My '85 has for its LH computer part number 928.618.123.03. Which is the LH computer for an '85 928 all right...only a US model S3! I'm driving a "Euro" or ROW model S2 which is supposed to have 928.618.123.00!
WELL. Obviously, the two computers are close enough that they will operate the car's injection. The S2 and S3 appear to have very similar injection systems, though I do know for a fact that they take different injectors. I wonder if this wrong computer is the source of my rough running problems all these years?
Does anyone know enough about the computers to tell?
Normy!
'85 S2 5 Speed
07-03-2003, 12:34 AM
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Three Wheelin'
Sorry I know nothing about the differances between the Euro and USA LH boxes (FI), but thought I would ask if you checked to see if your EZK box (timing) is a Euro or USA?
07-03-2003, 11:48 AM
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I have the same '85 Euro, but have no specific knowledge on the LH system. I did, however, do a bit of part number detective work. Not sure if this helps, but might provide an explanation. All info from PET v5.5.50:
1. 1985 Euro LH control unit shows PN 928.518.123.02 for the M28.21/22 engine. This is the control unit you "should" have in your car...my car has this one. The .00 unit was dropped in favour of the .02 unit...both for the 2 cam engine. I assume either would work for the 2 cam engine.
2. 1985 USA LH unit is PN 928.618.123.04 for the M28.43/44 4 cam engine.The .03 unit was dropped in favour of the .04 unit...both for the 4 cam engine. I assume you could use either one with the 4 cam engine.
I would assume that all the 928.618.123.xx units are the same basic computer with differing fuel mappings in firmware. The 02 and the 04 units are no doubt later revisions of the injection computer...maybe emissions updates?. Again, simply a guess, but this makes logical sense.
It would seem that you have a 4 cam LH control unit in a 2 cam car. I'm assuming that the fuel mapping in the 4 cam unit would be slightly richer than the 2 cam, mostly due to the better breathing of the 4 cam unit (more air...therefore more fuel allowed).
I would think that if you tried a .02 unit...the one speced for your Euro...it might solve your problem. There would be no downside to this unit in any case...other than the cost & hassle to get one. Any chance you could swap the one you have for a Euro unit?
Again, no experience here...just deductive reasoning...which is often flawed when talking about mechanical things!
Regards,
SteveCo in St. John's
1. 1985 Euro LH control unit shows PN 928.518.123.02 for the M28.21/22 engine. This is the control unit you "should" have in your car...my car has this one. The .00 unit was dropped in favour of the .02 unit...both for the 2 cam engine. I assume either would work for the 2 cam engine.
2. 1985 USA LH unit is PN 928.618.123.04 for the M28.43/44 4 cam engine.The .03 unit was dropped in favour of the .04 unit...both for the 4 cam engine. I assume you could use either one with the 4 cam engine.
I would assume that all the 928.618.123.xx units are the same basic computer with differing fuel mappings in firmware. The 02 and the 04 units are no doubt later revisions of the injection computer...maybe emissions updates?. Again, simply a guess, but this makes logical sense.
It would seem that you have a 4 cam LH control unit in a 2 cam car. I'm assuming that the fuel mapping in the 4 cam unit would be slightly richer than the 2 cam, mostly due to the better breathing of the 4 cam unit (more air...therefore more fuel allowed).
I would think that if you tried a .02 unit...the one speced for your Euro...it might solve your problem. There would be no downside to this unit in any case...other than the cost & hassle to get one. Any chance you could swap the one you have for a Euro unit?
Again, no experience here...just deductive reasoning...which is often flawed when talking about mechanical things!
Regards,
SteveCo in St. John's
