LH Jetronic Failure with Happy Ending
08-06-2009, 03:55 PM
#1
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LH Jetronic Failure with Happy Ending
My 1989 928 recently failed an emission test. Beside running quite rich, I would say that the idle would wander a bit, but not always. The car was powerful as always and an instant starter no matter what.
After a bit of testing my tech said most likely the LH was the problem (we did a swap with a good one and that confirmed the issue) and he said he would start looking for a used one.
That is when the bulb above my head went off and I said I recall I had read on Rennlist about a guy out in AZ who does a complete repair on these things. My tech gave me a glazed over look...."some guy on the Internet is going to do the repair? Good luck with that one."
I emailed Electronik Repair Inc on Monday and received a response from Rich within hours with shipping instructions and details of the repair ($600. for my unit, plus shipping). I sent it out overnight on Tuesday, Rich repaired it the same day and got it to FedEx that evening and I had it back on Thursday.
Wow! I can't say for certain you will have the same turn-around time (24hrs is the norm from when he receives it) but the guy did an outstanding job.
The car's idle is rock solid and the throttle response is amazing with gobs of power. Since my LH did not completely fail, I emailed Rich to learn what he found out about the unit and how he did the repair.
His response:
"This generation of engine control used on the Porsche 928 (and Saab, Volvo,
etc of the mid-late 1980-890s) was built using "standard off the shelf"
components (8-bit microcontroller, A/D converter, timer/counter) and a
custom designed circuits to do functions that were not available as standard
products. The main function of the hybrid circuit (see the attached photo)
is to bridge the 12V external world of the chassis electronics to the 5V
standard semiconductor world - and in addition provide several other
specific functions. This custom circuit is called a hybrid, because it
contains several smaller functional elements combined on a single 40 pin
ceramic substrate (thin-film resistors, thin-film capacitors and two custom
integrated circuits). Bosch designed and manufactured this hybrid circuit
as well as the printed circuit board.
The hybrid circuit is failing due to age, the failure mode is most likely
oxidation (rusting) of the custom integrated circuits. Just like an old car
in the east coast can rust in many places, these circuits start failing in
different ways because different parts of the circuit "rust to failure" at
different times ... One of the failure modes is the inability to hold the
air/fuel ratio to the proper mixture (excessive rich mixture - failing
emissions testing). Your LH module was in the "failing" but not completely
failed mode - given time it most likely would have failed completely.
Electronik Repair uses a proprietary design to replace the Bosch design -
this replacement uses new semiconductors and concepts that were unavailable
in the mid 1980s, it has higher reliability, uses less power (runs cooler)
and cannot fail like the old design. In addition to replacing the hybrid,
several other components are replaced that may not have failed but are most
likely to fail in the future - hence the term "rebuild" is used rather then
just "repair" which is what most of my competition does".
Obviously I am a very happy customer and wanted to share a good experience with all of you. The interesting part to me is the LH can fail slowly and exhibit what might not be classic behavior as when the car just totally quits or the injectors start to clatter.
Thank you Rennlist and thank you Rich at Electronic Repair Inc (480-839-1937)
David
After a bit of testing my tech said most likely the LH was the problem (we did a swap with a good one and that confirmed the issue) and he said he would start looking for a used one.
That is when the bulb above my head went off and I said I recall I had read on Rennlist about a guy out in AZ who does a complete repair on these things. My tech gave me a glazed over look...."some guy on the Internet is going to do the repair? Good luck with that one."
I emailed Electronik Repair Inc on Monday and received a response from Rich within hours with shipping instructions and details of the repair ($600. for my unit, plus shipping). I sent it out overnight on Tuesday, Rich repaired it the same day and got it to FedEx that evening and I had it back on Thursday.
Wow! I can't say for certain you will have the same turn-around time (24hrs is the norm from when he receives it) but the guy did an outstanding job.
The car's idle is rock solid and the throttle response is amazing with gobs of power. Since my LH did not completely fail, I emailed Rich to learn what he found out about the unit and how he did the repair.
His response:
"This generation of engine control used on the Porsche 928 (and Saab, Volvo,
etc of the mid-late 1980-890s) was built using "standard off the shelf"
components (8-bit microcontroller, A/D converter, timer/counter) and a
custom designed circuits to do functions that were not available as standard
products. The main function of the hybrid circuit (see the attached photo)
is to bridge the 12V external world of the chassis electronics to the 5V
standard semiconductor world - and in addition provide several other
specific functions. This custom circuit is called a hybrid, because it
contains several smaller functional elements combined on a single 40 pin
ceramic substrate (thin-film resistors, thin-film capacitors and two custom
integrated circuits). Bosch designed and manufactured this hybrid circuit
as well as the printed circuit board.
The hybrid circuit is failing due to age, the failure mode is most likely
oxidation (rusting) of the custom integrated circuits. Just like an old car
in the east coast can rust in many places, these circuits start failing in
different ways because different parts of the circuit "rust to failure" at
different times ... One of the failure modes is the inability to hold the
air/fuel ratio to the proper mixture (excessive rich mixture - failing
emissions testing). Your LH module was in the "failing" but not completely
failed mode - given time it most likely would have failed completely.
Electronik Repair uses a proprietary design to replace the Bosch design -
this replacement uses new semiconductors and concepts that were unavailable
in the mid 1980s, it has higher reliability, uses less power (runs cooler)
and cannot fail like the old design. In addition to replacing the hybrid,
several other components are replaced that may not have failed but are most
likely to fail in the future - hence the term "rebuild" is used rather then
just "repair" which is what most of my competition does".
Obviously I am a very happy customer and wanted to share a good experience with all of you. The interesting part to me is the LH can fail slowly and exhibit what might not be classic behavior as when the car just totally quits or the injectors start to clatter.
Thank you Rennlist and thank you Rich at Electronic Repair Inc (480-839-1937)
David
08-06-2009, 05:40 PM
#2
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Rich is the man. I may be sending him a unit it here shortly. I think the one in my car is crapping out on me...i have used spare enroute from Gio that will probably go out for an ovehaul at some point as well.
08-06-2009, 05:47 PM
#3
Inventor
Rennlist Member
Rennlist Member
08-06-2009, 07:22 PM
#4
Race Car
Rich, is beyond great. He's extremely patient and understanding and is willing to really go out of his way help with troubleshooting. A true asset to the 928 community.
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08-08-2009, 08:30 PM
#8
Race Car
If it was me I would open the box and look what was done, but thats just me. See if it has a security sticker on it, I'm sure it would void the warranty if the sticker is damaged.
08-09-2009, 12:33 AM
#9
Nordschleife Master
JDSporsche does this as well and has a couple of centers, not sure of the TAT, but iirc it is alot cheaper than $600.
But glad the problem was solved!
But glad the problem was solved!
08-09-2009, 08:55 AM
#10
Rennlist Member
Louie Ott always has my rebuilt LH's in stock, price is $495 USD. 3 year warranty but I don't expect them ever to come back....
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