M. Requin

No tach? How about the crankshaft position sensor?

Mrmerlin

usually its the old Eprom that gives up the ghost.
With the info from the OP two hints
The tach doesnt move when cranking
The injectors are firing with the key in the run position
Both of these are signs of a failing LH

GeorgeM

Plugged in a "test" ECU from an S4 and it started. It didn't run very well, but at least it started and stayed running as long as my foot was on the gas a bit.

dr bob

George, you'll likely need to drive it a bit to clear out all that extra fuel dumped in by the failing brain. Those injector clicks and fuel pump buzz noises mean the injectors were spraying fuel in even with the engine not running. You may also want to give the oil a sniff test to see if a lot of fuel got in there. A change of oil is certainly advised regardless of sniff results.

Check with DR and see if he has a rebuilt he can overnight to you. Makes it easy to return the core if nothing else. Rich Andrade at Elektronikrepair in Phoenix has doen several for me and some other locals. Roger carries John Speake rebuilts IIRC. 928 International has rebuilts and has great shipping and overnight service available.

Last but not least, count your blessings and say an extra prayer that the failure was at home and not halfway to NC. It could have been a lot less convenient!

Mrmerlin

you will have to let the new ECU learn the cars parameters , disconnect the battery first to do this, then reconnect it after swapping the ECU.
The GT has a different chipset than the S4.
Its usually better to put your ECU in a good running car, so you dont damage the test unit.
That said if this was the only way to find out then thats what you have to do to find out your ECU is ready to have some surgery, If you hustle you may have the new set in time for Departure, Goodluck

GeorgeM

Thanks for all the help, guys. All great stuff and made my troubleshooting very expeditious.

Looking for a quick solution now. If I can find one, should be able to get it for the weekend.

Cheers,
G

Rich9928p

Hello George,

I have a loaner LH fuel injection unit being returned but it is already promised to another client. I'm checking to see if it can be diverted to you.

You mentioned that you tried another good LH and your 928 didn't run quite properly. If it was flooded it should clear up after a minute or so, try starting with a little open throttle. If it doesn't run well with a known good LH your problem probably lies elsewhere.

Heat may accelerate the normal failure of electronics, however, the Bosch LH 2.2 and 2.3 Jetronic fuel injection modules mainly fail due to the hybrid circuit that is oxidizing with age. I see many more 1987 - 1995 LHs fail then the older 25 pin LHs used in 1984 (Euro) - 1986 generation of 928s.

Good luck, hope you make the trip. I hear it is a great group of people.

Mrmerlin

928 618 123 26 for the GT/5speed 91 LH

Rich9928p

Any 1987 - 1995 LH will work in a bind for GTs. The GT LH likely has a higher idle speed then the LH's with code for non-GTs. If the idle is too low, just leave a little pressure on the go-pedal when stopped to kick up the low RPM a bit.

Jadz928

George,
Please keep us posted about finding a LH brain. If you need help, I could try to help you source one more locally. I could probably get you one from a 89 S4, 5 speed.

Mrmerlin

Just making sure the OP knows that there are different LH chip sets for the different cars

Bill51sdr

Rich, see your email...

George, change your plugs too. Helped a fellow lister with the same problem. His ran with my LH, but very rough. We had to swap out his brand new plugs in order to get it to run properly.

Have fun at SITM.

Rich9928p

George,

Good news, the loaner LH is available and can be shipped in time for you to make the event. I've sent a note with the specifics! If you haven't seen my note, check your email.

GeorgeM

Thanks again for all the assistance.

Rich, you're the man. I believe I've found a rebuilt one on the shelf ready to go. Many thanks for working it on your end anyway.

If FedEx comes through, I should be golden for the drive on Friday... knock on wood.

GeorgeM

Back in business. FedEx came through. Many thanks again for all the assistance, and to Louie for the LH.

See ya tomorrow.