Why am I hitting DFCO (or something like DFCO)?

[mck1117]

Hi all, I have a gen3 5.3 flex swapped in to my Volvo 240. 862 heads, Sloppy Stage 2 cam, 4.8 pistons, gen4 5.3 rods, gen3 computer with 1bar SD OS.

After bumping up the idle speed and idle airflow, it starts and idles pretty well.

The problem is that it seems like DFCO is activating too aggressively. I know it's something DFCO-like, because I can hear the injectors stop firing at 1600 RPM, and start firing again after the RPM drops. Looking at all of the DFCO settings in "Fuel -> Cutoff, DFCO", everything looks reasonable.

• MAP is above the MAP threshold (38kpa actual vs. 27kpa entry MAP)
• TPS is above the TPS threshold (4% actual vs. 1.25% enable TPS)
• VSS is below the threshold as I don't have the VSS hooked up (and the car is on jack stands in neutral anyway)

The only conditions met are that I'm above the entry RPM, and the ECT is high enough, but DFCO is supposed to meet all conditions to engage.

What's going on?

[mck1117]

Oops, and here's the tune and a log of it happening. Starting at 48 seconds, I hold the throttle at ~4%, and the engine gains rpm, cuts, and repeats.

[Lakegoat]

If you are speed density tuned, no maf---Go to DTC's and make P0101,102,103 Mil on first error and uncheck the ses boxes so you don't get a light. Make MAF freq fail high to 0. Dynamic airflow high rpm disable to 8000. Turn off dfco by Enable ECT to 284 degrees. Don't log any maf functions in channels. I don't see a wideband. How are you tuning this in open loop?

[mck1117]

If you are speed density tuned, no maf---Go to DTC's and make P0101,102,103 Mil on first error and uncheck the ses boxes so you don't get a light. Make MAF freq fail high to 0. Dynamic airflow high rpm disable to 8000.

I thought the SD OS killed the MAF completely, but I guess not. Thanks for the reminder! MAF is no more.

Turn off dfco by Enable ECT to 284 degrees.

Tried that, same behavior.

I don't see a wideband. How are you tuning this in open loop?

I have an external wideband (gauge) that I haven't bothered wiring in to anything yet. I'm well between the limits of cylinder washdown or lean misfire, so I'm not even worrying about fiddling with the VE yet.

Other useful data: if I unplug the TPS, it's happy to rev past 1600. Here's a log of that (the car stumbles after revving because the idle adapt gets confused with the TPS unplugged, so don't worry about that): working_tps_unplugged.hpl

And here's the current tune, with DFCO enable temp set really high, and MAF stuff disabled: 04 fix dfco.hpt

[5FDP]

Your abuse mode is set to 1,600.

Remove that, set it to 8,000, lower the MPH to 0mph.

Swap vehicles have this issue all the time.

[mck1117]

Your abuse mode is set to 1,600.

Remove that, set it to 8,000, lower the MPH to 0mph.

Swap vehicles have this issue all the time.

Ah ha, I bet that's it! I'll give it a try later tonight.

Is there anything else I should change like that given that I have a swap in to an older car?

It would be great if there was a guide for "here's all the settings you should change if you have an old, dumb car"

[Lakegoat]

5FDP owns the book