Lean Misfires at 2700-2800 rpm

[TurboBob]

Originally Posted by OwnGTP/WantRTTT

I also switched to 560 injectors at the same time though.

I'm guessing this is a big part of it.

I have some things I'm going to try this winter on this.

Can someone summarize the RPM, TPS, and MAP readings where this happens?

B

[OwnGTP/WantRTTT]

I'll try to grab a log of it tonight Bob.

[OwnGTP/WantRTTT]

Also Bob, I did notice that in the VE table (I’m using table #2), there is a slight shift in the table around the point where this lean spot occurs. I’ll try hooking up the logger tonight and seeing if I can tune it out using the VE table.

[DoctorDex]

Edited my last post for clarity.

[badass3000]

Originally Posted by DoctorDex

That has been my assumption as well. You're right, a miss will show up as a lean spot because O2 sensors measure oxygen, not fuel. What I find strange is the front and rear banks o2 sensors have identical waveforms during the miss, which makes it look like the miss is happening on both front & rear banks simulatenously.

I do have a WB and its located past the "Y" in the downpipe.

Edit: Post edited for clarity

I cant remember if NB and WB react the same to a miss?

[TurboBob]

Originally Posted by badass3000

I cant remember if NB and WB react the same to a miss?

they do

[OwnGTP/WantRTTT]

Bob,



Let me know what other info I can provide. I also took a log with my HHH logger so I can tell you what the ECU is reading if you'd like.

[DoctorDex]

Conducted another test today.

Here's what I did:

1) Revved the car in neutral from 1000 rpm - 5000 rpm and made some logs. The rpm would plateau everytime it'd miss @ ~ 2700 and both front and rear O2s would read lean (as well as the WB).

2) Then I made some more logs, while revving from 1000 rpm to 5000 2-3x, on 2 separate occasions, while spraying in a mix of 80:20 methanol:H20. This caused an excessively rich mixture (beyond which my wideband can measure, probably in the 8-9 range). I was afraid of hydrolocking my motor so I didn't keep the meth-h20 on for more than 4-5 seconds.

The results: While spraying meth, there was no miss and no rpm plateau @ 2700 rpm.

I'd like to repeat this test again, using 100% meth, just so I can be sure. However, I won't be able to do this until this weekend. Nevertheless, the preliminary results point to a fueling issue, which strangely enough, does not respond to just adding more fuel with the SAFC/MAFTranslator. Whats even more strange, is its occurring on both the front and rear banks simultaneously, only in a certain rpm range.

Any ideas?

Edit: Been thinking about these results for the past couple of hours and to me, these results make no sense. Before I go jumping to conclusions, I'm going to repeat the test a few more times.

Edit2.0: Maybe its time to revisit TurboBob's idea of modifying the coolant temp sensor to dump in more fuel (and then lean it out with the SAFC).

[TurboBob]

Originally Posted by OwnGTP/WantRTTT

Bob,



Let me know what other info I can provide. I also took a log with my HHH logger so I can tell you what the ECU is reading if you'd like.

PM sent

[TurboBob]

Originally Posted by DoctorDex

Conducted another test today.

Here's what I did:

1) Revved the car in neutral from 1000 rpm - 5000 rpm and made some logs. The rpm would plateau everytime it'd miss @ ~ 2700 and both front and rear O2s would read lean (as well as the WB).

2) Then I made some more logs, while revving from 1000 rpm to 5000 2-3x, on 2 separate occasions, while spraying in a mix of 80:20 methanol:H20. This caused an excessively rich mixture (beyond which my wideband can measure, probably in the 8-9 range). I was afraid of hydrolocking my motor so I didn't keep the meth-h20 on for more than 4-5 seconds.

The results: While spraying meth, there was no miss and no rpm plateau @ 2700 rpm.

I'd like to repeat this test again, using 100% meth, just so I can be sure. However, I won't be able to do this until this weekend. Nevertheless, the preliminary results point to a fueling issue, which strangely enough, does not respond to just adding more fuel with the SAFC/MAFTranslator. Whats even more strange, is its occurring on both the front and rear banks simultaneously, only in a certain rpm range.

Any ideas?

Edit: Been thinking about these results for the past couple of hours and to me, these results make no sense. Before I go jumping to conclusions, I'm going to repeat the test a few more times.

Edit2.0: Maybe its time to revisit TurboBob's idea of modifying the coolant temp sensor to dump in more fuel (and then lean it out with the SAFC).

So, its just lean then.......

My guess is that its such a narrow window, that its hard to tune out because the ECU re-learns the tune.

I have a few ideas. I need to get the AC/Alternator idlers changed before I can do much more testing, but I think I have a solution.

Bob