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Right after my rebuild I noticed my oil pressure was getting erratic while idling. Always at 90sec after engine start. The idle becomes lumpy as well at that time.
It seems that at closed to open loop switch something was preventing my engine from holding nominal idle. Digging through mountain of similar topics I found several comments about ECU coding plug: 928.607.421.00 causing some problems, so I removed it.
Idle drop, oil pressure drop WITH: 928.607.421.00
Cold engine start - switch from closed loop to open loop at 10 seconds mark
Seemed to solve my problem and I had not have this problem return. It is worth noting that I had brand new O2 Sensor. Even thou the coding plug makes the ECU pay attention to the O2 sensor and going by common reasoning that should make the car idle better, it wasn't the case for me.
Question: After removing the coding plug, does the ECU still uses the O2 sensor for anything?
Seems I recall that cars with no plug have a pressure sensor to do altitude correction. I wil see if I can find that info.
I wonder if anyone really knows how the dme processes the o2 sensor info. You would think that o2 info would be beneficial, especially at speeds other than idle. Is the o2 sensor narrow band or wide band?
I am certainly not an o2 tuning expert, but In fooling around with other vehicles, I have seen idle A/R ratios that like to be considerably richer than a narrow band sensor could tune to.
Maybe someone who has looked inside a dme will chime in, Steve Wong perhaps.
Seems I recall that cars with no plug have a pressure sensor to do altitude correction. I wil see if I can find that info.
The pressure sensor correction table was zero'd out (80'd) after the 1st year of production.
Originally Posted by onevoice
I wonder if anyone really knows how the dme processes the o2 sensor info.
If you were to disassemble the 8051 binary stored in the 964 DME EPROM you would discover that there is a one-to-one mapping with the descriptions given in the Bosch M-Motronic Engine Handbook.
Originally Posted by onevoice
You would think that o2 info would be beneficial, especially at speeds other than idle.
It is also used during partial throttle.
Originally Posted by onevoice
Is the o2 sensor narrow band or wide band?
narrow
Originally Posted by onevoice
I am certainly not an o2 tuning expert, but In fooling around with other vehicles, I have seen idle A/R ratios that like to be considerably richer than a narrow band sensor could tune to.
Porsche uses fuel scheduling to control cylinder head and catalytic converter temperatures in the air cooled motors. What I've noticed is that some tuners mess with the partial throttle fuel correction maps to improve throttle response instead of the acceleration enrichment fuel mapping.
What exactly do you mean by "fuel scheduling"? Is there a feedback from the temp sensor to adjust mixture?
You sound like you know a lot about the dme, I hate to sidetrack this thread, but do you know how the dme switches the ground on the fuel pump circuit of the dme relay? I have a no start issue, I have spark, and can start with the dme relay jumpered. Tried two different dme relays,(both of which test good on the bench, one is new), but I never get a ground on the fuel pump side of the relay. I know it is looking for the switch to be in start position, or looking for rpm, but how is it determining rpm?
There is an inductive sensor at the rear of the engine that counts teeth on the flywheel.
yes, the dme needs this speed input for the engine to run - correct? So, my dme has a speed input, it should be providing the switched ground to 85b, but it isn't. Should also provide the switched input when cranking, but it doesn't
09-05-2016, 09:18 PM
Oil pressure and idle issues - Solved!
