VehiGAZ

There is a relay that will bypass the particular sensor and keep the car from going into limp mode. Search for my threads from 2008-2009 for details...

soontobered84

What you are describing is the Ignition Monitoring System (IMS) which was not available on 928s until MY 1989, therefore is not available on the OP's 928.

bureau13

I believe no limp-home mode for S3 cars...

VehiGAZ

That is exactly the module I was thinking of. Thank you for the clarification!

AO

That's GREAT news!

Double check the spark plug wiring. It's easy to swap a couple leads by mistake. WHo knows what the PO did. The plugs may also be fouled again, so unless it's really lumpy, let it run and see if it will clear up. That car hasn't run for a long time.

If it continues to stumble, you should be able to tell by pulling the spark plugs and see which ones are clean and which are not. That should tell you. where to look next. You can also try pulling one spark plug wire at a time to see if there is a change in how it runs. Obviously if it runs worse, that plug is working, so put it back.

Bill Ball

Don't confuse "limp home mode", which is related to having a broken MAF, with the Ignition Monitoring System (not present until 89, as mentioned) "4-cylinder mode". Limp home mode is a very limited fuel map mode that is substituted when the LH is not getting a MAF signal. It provides only a couple of fueling levels based on RPM when there is no indication of air flow from the MAF. If you unplug the MAF, you will enter limp home mode. I've driven cars home 30 miles that way. Requires a lot of throttle feathering, but the car will run. The IMS 4-cylinder mode kicks in when the two exhaust temp sensors detect a difference between two cylinders after a warm-up period, each of those being served by different ignition coils, caps/rotors and final stages. It assumes any significant difference being reported by the two temp sensors is due to failure of that half of the ignition system to the colder cylinder and it then shuts off fuel injectors serving those cylinders primarily to prevent cat fires from unburnt fuel. Again, the car will run, although seriously down on power and with some stress being placed on torque tube shaft from the altered power pulse intervals. My 89 has entered that mode a few times due to a false signal from one of the sensors when, in fact, the ignition system was working properly.

Anyway, Van, I'm glad to hear it is running at least somewhat now, although you're not sure what was the remedy. I'll be over tomorrow morning to help see if we can get it running better. :-)

VehiGAZ

Oh that's right! There is a difference between the two. I put those horrible memories (of stuck in 4-cyl due to bad connection at the temp sensors) out of my head, it seems.

So is the diagnosis for limp-home mode to disconnect the MAF and note if there is any difference in how the engine runs?

SMTCapeCod

That's the diagnosis-- or an indicator-- of a bad MAF, having poor running condition that improves when MAF is unplugged.

I really like Andrew's point about firing order...occam's razor.

Also maybe a hose popped off/was loosened from IAV or the oil neck. Or maybe your fuel pressure is jacked.
Have you checked the # on the ECU to see whether it is correct, and whether it has been rebuilt/messed with?

Sorry, but once you get it firing properly on 8 cylinders, and assuming no clutch slippage, this thing will positively maul your '80.
You'll be quite pleased. Then Porken/X-pipe.
;-)
But first things first.

vanster

Bill Ball came over yesterday and we found a bad connection one of the injector connectors
My error in crimping it and using a noid light we found it and I repaired it.
Now it runs on all 7 and will not idle. Fuel pressure?

Even running on 7 it's quicker than my 80

vanster

Also there is an 8 inch black wire that comes out of the harness in front of right bank that is disconnected
It's near the belt indicator light...what is it?

AO

Sounds like you are making progress. But why only 7? Which one is not firing?

Probably the AC? The AC compressor signal come from a single wire near the belt tension wire and has a rectangular block protecting the connector.

WallyP

The black wire sounds like the AC compressor clutch power lead.

The NSX dude

Any updates? I loved watching this car on BAT and the 700 comments from fellow car nuts chiming in trying to help. It was also just voted car of year on there. Good stuff!

vanster

I'm just stunned that it won this award. Not really sure what to say but most important this award
does say a lot for the interest in 928's.
Good news is that I have at long last secured a time slot with Greg Brown for January 18th. I am almost sure
the problem is a broken valve spring along with bad injector lead. I almost tackled it myself, but logic prevailed.
As good as this car is, in my opinion it requires the hand of GB. If there is anything else amiss he will see it as I most likely would not, i.e. cam guides, maybe even do the water pump while in it etc. Once he as gotten into it and gets it to be the strong runner, I'm confident that I can manage everything else on my own. I'm looking forward to years of
ownership and many miles to come.

cobyryan

what a crazy experience--- congrats! had a very similar issue with my Euro spec S2... sold it and bought a 912