MBMB

I need to test my FI brain in someone else's car. An S4 will do. I'll come to you. Anyone?

Thanks,
Mark.

Steven Ko

I'm more than willing to let you use my FI Brain but mine is an 86.5. I don't know if this will do you any good. I'm imagining the large difference between the older 32 valve engines without knock sensors and yours may be too much but the offer is there if it will help you out.

Rich9928p

The '85 - '86 LH controller will not work with an S4 or newer 928s. The early LH is a 25 pin device, the S4 and newer LHs are 35-pin devices. Same issue with the spark controllers.

Any '87 - '95 LH will work for trouble shooting (to determine if the car will start). There are year/model specific calibrations so injection and spark modules aren't interchangable (if you want to keep it to original spec).

MBMB

My car will start with my LH brain; the problem is a gradual enrichment of the mix until it's undriveable. For example, I'll start it, drive it about 25 miles until it's too rich, then stop and let it cool for 5-10 minutes (dry?), and it'll start up again and it'll be good for another 20-25 miles.

Rich9928p

The fuel mixture being too rich is is one of the many failure symptoms of the LH-Jetronic module used in the 928.

Just last week a friend of mine EMAILed that after being out of town for two weeks his '89 928 wouldn't start. He spent the afternoon running through the diagnostics and was able to get his fuel pump to run with a jumper wire, but the car just sputtered. He is local, so I drove over to his home with a rebuilt module and plugged it in. His 928 started immediately.

Common symptoms of a failing LH injection module are :

- Fuel injection valves click when the ignition turned is on and engine is not running

- Engine will not run at idle

- Air-fuel mixture is too rich (this can damage catalytic converters)

- No fuel pump operation, but the fuel pump operates when its relay is jumpered

- The engine will not rev higher than 3000 RPM

- A/T cars: no idle speed regulation when switching between drive gears and neutral or park

- Engine will not start, spark plugs are dry and the ignition system produces spark.

Rich9928p

Another possible problem could be with the Mass Air Flow Sensor (MAF). A quick test would be when your 928 is running at its worst, unplug the MAF. If it starts and idles well, the MAF could be the bad guy.

The MAF is located under the plastic air box. Be careful when unplugging the connector, there is a wire clip to hold it in place and it is easy to loose it when removing it.

If there is no change, plug the MAF back in. The next step is unplug the Temp II sensor (in the front of the engine) near the oil filler. If the engine is cold, it may take a bit of pressure on the gas to get it started. If the engine is warm, it should start OK. In one of my previous posts, I outlined the ohm tests and that the temp sensor has an effect on the fuel mixture ... If the LH "thinks" that the engine is cold, it applys the enrichened "start-up" fuel mixture.

If there is no change after all this diagnostisc, your LH module is most likely bad.

MBMB

Rich -- I just saw this. Thanks. Will do when I get the car back together and on the ground (it's in the air right now, waiting for brake bleeding and other things).