Herman A

My 928S4 1990 is equipped with an LH Jetronic 2.3 fuel injection controller from Bosch. The fuel pump relay driver inside the unit which is connected via pin 20 in the 35-pin connector, to the relay coil, have finished working. This means that it does not pull one side of the relay coil to ground anymore. This seems to be a not uncommon problem with this controller. The IC (Integrated Circuit) is a 20 pin standard 0.300" DIL (Dual In Line) package. The ID on the PCB (Printed Circuit Board) is BS203 and the IC itself is marked with the Bosch logo and 30047 2489. This is a Bosch marking but the IC is likely some standard octal (8 inputs and 8 outputs) driver, maybe with OC (Open Collector) outputs. I have tried to localize it trough databooks and IC manufacturers homepages but without sucess up to now. Is this a commercial type of IC and if so; what is the part number of a replacement IC? Does anyone know if there exists electrical schematics, PCB components placement diagrams and list of components for the LH 2.3? They are for shure not available trough the manufacturer, but I am just wondering if anyone have made some "reverse engineering" of the unit.

drnick

you could check with john speake at JDS porsche. he repairs broken ECUs.

martin D

http://www.jdsporsche.com/

John is on this forum, so will chip in at some time

John Speake

Hello Herman,
This was a special custom made IC for Bosch by a minor IC provider, long since defunct.

As you say, quite a few cars have this part of the IC blown up - this is often because someone has "jumped" the fuel pump relay incorrectly, and this blows up the IC.

I make up a discrete component replacement to cure this problem.

Regards

Lorenfb

More than likely your LH control unit has other problems besides the lack of the
fuel pump relay driver. Typically, most think that a non-functioning fuel pump is
the extent of their LH problems. Just ground pin 20 of the LH unit and FULLY
evaluate the engine's running before concluding that it's just the fuel pump
driver circuit.

Glenn M

I've got the same problem. Fuel relay was jumpered when I got the car. Saving my pennies until I can send it to John. Runs fine and I don't leave the key on accessary.

Rich9928p

I've seen several LH modules where someone thought they could "wire around" the fuel pump "turn on" problem - one of the several LH failure modes. The main failure cause is the hybrid circuit, and unless that circuit is replaced the module cannot be properly repaired. More often than not, attempted repairs by someone who doesn't know the Bosch LH module will greatly complicate the problems (and make repairs much more difficult).

Repair should be done only by a qualified LH rebuilder.

John Speake

Herman,
Unless you are very sure what you are doing, I would not recommend trying to fix the LH yourself.

Even if your diagnosis is correct, and only the fuel pump driver stage is faulty, if the hybrid is not replaced, it will fail some time in the future.

Trying to repair the LH yourself could result in it being unrepairable.

Regards

Garth S

As 'jumpering' the pump relay is perhaps a too common trouble shooting step, what is the correct way? - or what is the hamfisted step to avoid?

Steve Cattaneo

As 'jumpering' the pump relay is perhaps a too common trouble shooting step, what is the correct way? - or what is the hamfisted step to avoid?







With a diode and fuse wired in series with the wire. There are automotive power probes that allow the user to safely diagnose the electronics of a car.

John Speake

Hi Garth,
The correct pins on the relay to jump are 30 to 87. 30 is a direct to battery +12v connection.
87 goes via the fuel pump relay fuse to the pumps. These contacts are opposite each other, and are at right angles to each other.

85 and 86 are the relay energising coil. There are orientated in the the same plane opposite each other.

One end of the relay coil is fed from ignition switched +12v. The other end of the relay coil is grounded by the LH on pin 20. The output stage in the LH which enrgises the coil of the relay has a limit on the current it will deliver (a few 100mA) . It is not overload protected. It can easily be blown up.

If someone by mistake "jumps" pins 85 to 86 instead of the correct pins 30 to 87, then ignition switched +12v is applied with no current restriction to the LH pin 20. The output stage then self destructs.

The safest way to jump might be to adapt an old relay base with a wired in jumper. Then it would be correctly polarized.

Regards

John Speake

Steve,
The fuse wouldn't help here - the output stage blows at a few 100mA, the fuel pumps take many amps. The diode won't help either, in this case.

Regards

TAREK

If jumpering the fuel pump relay sockets can damage the LH. Could that in turn damage the fuel pump? My 86.5 car is mysteriously and quickly killing fuel pumps. I did use jumpers as part of the initial diagnosis.

Garth S

Thanks John, Steve for the clarification. I wasn't sure what you meant initially John: I've always done the load side for diagnostics, +12v @ #30 to #87 which you agree is correct.
Absolutely avoid the trigger/switching side of the relay (85-86) - so worth making a point of this for anyone with jumper in hand ....

Herman A

Hi John an all,
Thank's for the information about the obsolete driver IC and for all hints. I was not aware of that a missing pulse train from the EZK can also have this effect on the pump relay and therefore I need to verify the output and input signals from/to the EZK, before trying to figure out whether the driver or the hybrid is gone. I have done the jumping correctly and I agree that jumping without knowing exactly what to do and how to do it is very dangerous for the electronics. As in all repair work of ECU's, and even if you are experienced in electronics, the lack of schematics and components is the big problem.