Info for Bosch LH and EZK for the 928

This page is under construction !!!!! - 2/04/04 - Added some Fuel MAPs

There seems to be a lot of black magic surrounding the brains for the 928, this has only been compounded by astronomical repair prices and with this comes less than reputable repair shops. What I am hoping to achieve here is the sharing of knowledge which should benefit all 928 owners plus some additional developments which I aim to do, if someone gets there before me fine as this is really a hobby for me.


Here are some links for background reading on the Bosch LH, no need to repeat what others have already published on the web.

Saab LH Overview   ,there has been a lot of activity in the Volvo/Saab community much of which is relevant to the 928

Theo's LH Page

Additional Info

blah blah blah ...... (more info to add here )

87 and later units have all the same hardware, only the code is different, if you want your brain to be able to store fault codes you just need the 88 and later code. If you want the Bosch Hammer Diagnostic ability then use the 89 and later code, you will then need to wire in the connector but how hard could it be ? :-)

Schematics and .bin files

Over the past couple of months I have been working on and off on the schematic for the LH unit, this is by no means finished but I shall be updating it as I get time. Its in PDF format so the majority of you can see it.

I also want to build up a complete table of all the standard EPROM programs for the LH and EZK units, a number of owners have aftermarket chips in their cars and this is a good way to get the standard programs back in the car for troubleshooting as some aftermarket chips are less than spectacular.

12/1/04 LH_schematic - if anyone has any corrections be glad to hear about them !

87 928 618 123 10 
88 928 618 123 11
88 CS 928 618 123 12
89/90 928 618 123 13
89/90 CS/GTS 928 618 123 14
91 S4 928 618 123 25
91 GT 928 618 123 26
GTS 928 618 123 30

Seems like they had 3 updates for the EZK in 88, hmmm wonder what the problems were .....

87 928 618 124 11
88 928 618 124 12 &14
88 and up 928 618 123 15
88 CS 928 618 124 13
89 928 618 124 15
89 CS 928 618 124 16
89 GT 928 618 124 22
90 + 5 speed 928 618 124 22
90 + Auto 928 618 124 15
GTS 928 618 124 30


Fuel Maps

OK, so I performed some experiments, there are two fuel maps within the LH, one is used for normal running, lets call it a cruise map for want of a better term and then there is a WOT map. I zeroed out the WOT map and it changed the the cruise a little so there is some interaction between the two but not much. I can only assume that the LH does some calculations and takes a value from cruise and WOT then the the two values must be given a weighting depending on conditions

Also found the LH cannot read a MAF voltage greater than 5.85V, the SuperCharger and Stroker guys have found this to be a problem which explains why the piggy back computer has little effect on these engine configurations. With a few modifications to the LH and the fuel MAP I think you could rectify this but without a car to experiment on its a little difficult ...

Interesting to note that the fuel maps for all MY are the same except the GTS WOT which is different.

This is the WOT map which is the same for all models except GTS.
Here is the GTS WOT MAP
Here is what I call the cruise MAP, its the same for all model years.


John Speake has been given good feedback, bought the price of repair down to more reasonable levels. 

Never ever send or buy a unit from Partwerks <- You have been warned.


So what do I have in mind ?? Well the first thing is to identify the fuel maps in the code, actually working on deciphering all the code but first things first, I do after all have a day job and a young family !!

Anyway when I have worked out the WOT 2D fuel map I intend to head of to the dyno and reprogram the settings in a similar what some of the aftermarket piggyback brains do. This will enable me to map my cars MAF and get the mixture spot on. If you look at my dyno-graphs you can see the mixture is waaay off at the top end, as are most S4's. When I have been through the whole procedure i'll publish it so if any of you want to , you can do the same.

One of the outputs on the LH brain which the 928 does not utilize is the 'Engine Light', the code for displaying engine faults on the light is there. Easy enough to add an LED and then pull the codes for yourself.

Beyond this there are a whole host of things that could be done, but one thing is for sure the days of wallet emptying costs for these units is coming to an end, a couple of new repair shops (see the 928 Forum magazine article) are already out there.