What would cause richer A/F ratio at high speed cruise?

[David Claflin]

I encountered this when I had the EEC tuner in my car and was able to alleviate this by changing the exhaust pulse delay. Now that I have the moates chip and tuner pro I tried changing the delay and it didn't seem to affect it. I've leaned the MAF curve by 4% with no change either. At cruise the wideband shows 14.4-14.9 where it generally stays. At cruise of say 80 MPH the wideband shows 14.2-14.5. Should it do that??

Thanks!!

[dex]

May be you are going into open loop mode at 80mph.

[David Claflin]

You're thinking it gets to the WOT fuel multiplier with that extra load?

[dex]

No, just that you are moving off the closed loop control (i.e. targeting an A/F ratio of 14.64:1) and running off the 'Fuel Base Table' (aka FN1307).

This is the snag with not having datalogging, you cannot find the simplest of things out about what the ecu is doing

[David Claflin]

Yes, I was sort of getting the hang of reading datalogs but EA helped me a bunch. So is there a way to make any adjustments to counteract what is happening?

[dex]

The first thing would be to establish if it is indeed swapping over to open loop. If you have a F3 chip you could put very rich values into all the cells of the base fuel table and burn this tune onto the alternate memory of the chip. Then when cruising flip the F3 over to this tune and see if your wideband shows the sudden richness. If you are going into open loop you can then tune the base fuel table to get the A/F ratio you are wanting.

[David Claflin]

I can watch the wideband and see it go leaner when it has been idling for a couple minutes.
I looked at some old datalogs and saw that at high speed cruise, where the RPMs were about 2800-3000 RPMs the load was in the high 30's low 40's.

[David Claflin]

I increased the ehaust pulse delay, higher then I ever have and it seemed to help it some. I'm going to drive it for a few days and see how it acts.
I used the spreadsheet from EEC tuning for the numbers.