Timing problems, I have a theory.

[phoenix64]

I'm crusing on the freeway 55-60mph 3rd gear, laptop data logging. Floor the throttle. Pull to about 85-90. There is no lag, so its at full boost for the whole run.

1st pull, car pulls extremly hard, 19-20* of timing, no knock.
let off the gas coast to 55 again.
2nd pull, car pulls nearly as hard, but now showing 2-3* of knock.
let off
3rd pull, now showing 5-6* of knock.
let off
4th pull, knock is up to 10-11* car now has WAY less power.

A/F is constant over all the runs. Intake Air temp is 75-90* after intercooler.
Time between runs is time required to coast down.

This is on ethanol, with an octane rating of 106. Specific heat is close to that of methanol.

I'm wondering if this is just heat soak, made worse due to the iron construction of the engine?

Any thoughts on whats going on, or what to do? Should I pull the timing back initialy, or should I let the knock sensors pull it?

[Pathogen]

Check your O2s. This could be after the car heats up.

Have you upped your fuel at all? or advanced your timing?

Your computer will adjust as the car heats and change a whole bunch of stuff.

Running a manual fanswitch and a 160 thermo makes tuning a lot easier, as it removes another variable.

Make sure to do your tuning at the car's operating temperature.

Because you're turbo, the computer isn't going to pull "enough" timing or fuel - you will need to adjust on top of everything else by adding timing/fuel.

What tuner are you using?

[phoenix64]

Check my o2's?

Hptuners, A/F shows 12.2:1 on my wideband at full boost.

Stock timing is about 20* I think. I can run around at 12* all day long and never see more than 1-2* of knock. Its just much slower intialy.

[98Camaro3.8]

Is there a big difference in ECT or IAT between the runs?

Are the LTFTs good?

Is the KR largest when you first roll into the throttle, or through the whole run?

Any way you could upload the whole log?

[Pathogen]

Originally posted by 98Camaro3.8:

Any way you could upload the whole log?

.... You're 02s should be in the 910-920 rang under boost (towards the top of the gear) .. it's a good number to judge your fuel load by.

Any KR is bad KR. Add some fuel in the RPM band that you're seeing knock and aim for 11:1 A/F.

One more silly question - you're letting off at 55mph? - what happens if you go to redline?

[98Camaro3.8]

Originally posted by Pathogen:
You're 02s should be in the 910-920 rang under boost (towards the top of the gear) .. it's a good number to judge your fuel load by.

With a wideband hooked up, there's not much use for the O2 sensors, especially since they're not used in PE mode. The big thing to look at is the LTFTs, making sure they are about +/- 5%, and adding/removing fuel as needed.

They can be used somewhat (not as a basis for tuning, of course) without a wideband, but with the wb they're not important.

Originally posted by Pathogen:

One more silly question - you're letting off at 55mph? - what happens if you go to redline?

He's starting the run in 3rd at 55mph, running up to 90mph. I'm assuming he's got a manual, but that would be pretty close to red line.

[Pathogen]

... A4 car... 43lb injectors...

... I step down ....

[phoenix64]

The KR is the worst at full boost below 4kRPM. At high RPM the KR goes away.

LTFT don't exist. For many reasons, but they don't read right on alcohol anyway.

I'll try to post some logs, if I can figure out a host.

[Nachius]

have you tried letting the car cool down all the way before runs?

Sounds like heat to me. I would let it cool down all the way and run it again and if you don't see knock it is obviously heat.

If that is the case like mentioned above you'll need to tune at operating temps.

[98Camaro3.8]

Originally posted by phoenix64:
LTFT don't exist. For many reasons, but they don't read right on alcohol anyway.

I don't see any reason the LTFT wouldn't read right. O2 sensors sure, but not LTFT. That's just how much correcting the PCM is having to make to adjust the fuel.

BTW, I'm not exactly sure how all this ethanol stuff works, but stoich on ethanol is 9.0:1, not 14.7:1. Don't know if that has anything to do with it.

[phoenix64]

Where would the PCM get LTFT is the O2's don't work?

My wideband reads in A/F for gasoline, so on alcohol, when the actual ratio is 8.3:1 it reads 13:1 because its just looking for lambda, regardless of fuel type.

Nachius, thats what I was saying with heat soak. In a drag racing situation(cool down between runs), I can run 20*, but on the street, I'm limited to 12*.

[98Camaro3.8]

Originally posted by phoenix64:
Where would the PCM get LTFT is the O2's don't work?

When you're at WOT, the O2 sensors aren't even used, because the car is in open loop mode. It checks MAF, MAP, ECT, etc.


Also, email me if you want me to host your logs. I've got more than enough space. [img]smile.gif[/img]