Re: More cool O2 sensor stuff (archive)

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No injector. You make an excellent point, that would probably explain it perfectly, that the map on the chip is programmed for an injector. The other guy who has a very similar problem also has a JimC chip . BUT - I have the stock chip also and swapped it a while back, seemed to do the same thing but I will try it again to confirm. If you are right I owe you some beer....

Decided to use O2 sensor to see what is going on when my cold driveability problems act up. Problem is of course that the sensor normally takes about 60-120 secs to start working, so by the time it kicks in the car would already have warmed up. So I rigged the sensor heater inputs directly to the accessory block next to the fuse box. The red wire here is always on 12V. So I got everything ready (had O2 sensor disconnected from DME), and gave the sensor heater 12V for 2 mins before starting the car. On startup, got immediate readings on mixture with engine totally cold. Looked pretty rich until I started going. AS I approached 3-4000 rpms where I typically loose power, the needle went to ZERO. or extremely lean. The car started it's usual surging behavior, which coincided with the needle jumping up to rich and back to lean. After the ususal 2 mins or so of driving, it suddenly evened out, needle swung to rich and car drove great.

So what is going on? The normal cold enrichment process seems to be falling short somehow. Yet when it switches out of this mode (which is determined by coolant temperature, and which coincides exactly with the end of the blue zone for me) it gets plenty of fuel.

So does this point to the DME? Injectors? carbon deposits? At least now I know what the negine is experiencing, even if I don't know why...

Todd,
Does your M5 have an cold enrichement injector?
It would be mounted at the 3-4 throttle body.
Also, Have you matched the DME and chip to ensure you have a match. The S38 without the enrichement injector uses a wider injector pulse-width to enrich during warm-up. There are a couple of chip versions and some aftermarket chip makers neglect the Motronic variation between S38B35 with and without the enrichement injector.
Also if the DME has been replaced...

Dinan Engineering lists:
M5,M6-US (E28,E24)87-88
DME 0-261-200-079 <1>(with 1 267 355 210 stock chip)
Dinan p/n: D900-3421

M5,M6-US (E28,E24) 87-88
DME 0-261-200-079 <1>(with 1 267 355 786 stock chip
Dinan p/n: D900-3422
<1>(with 1 267 355 786 stock chip

OK!
Now...
My 88, M6 is without a cold start injector and has the DME 0-261-200-079 with 1 267 355 469 stock chip.
I am running the Dinan D900-3421.
I took my stock chip to Dinan's and they said the D900-3421 performance chip was the match.

As I commented, I still have a slight to moderate sluggishness before the warm-up ends. When the DME switches over, I have to let off to keep from running everyone over. Definitely a noticeable jump in engine performance!! I do not experience and bucking or other bad engine performance characteristics.

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