Jason
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« on: February 18, 2011, 07:28:01 PM »
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First, am I right in assuming that knock control is active even at idle? I am having a difficult time tracking down the source of a miss exclusive to cylinder 6. Plugs look good, great compression, swapped coils 5 and 6, and swapped ignition drivers with no change. The car is running amazingly well everywhere, so I don't believe I have an injector issue, since they are new, but I plan on switching 5 and 6 when the car cools. I don't believe it's anything to do with injector latency, as the car was idling perfect the last few weeks and I haven't touched the tune at all.
The miss only occurs at idle, on cylinder 6 (sometimes I see a few events on 3) with the gearbox in neutral and clutch engaged, which is only noticeable because it causes the gearbox/clutch to hiccup (rattle). I have an unsprung, Clutchmasters FX850 twin plate clutch on its matching aluminum flywheel, which makes a LOT of noise. The whole combo is less than half the weight of the stock setup with LFWF. There could be inherent issues with the lack of mass here, but let's overlook that for a moment.
My thought is that at idle, enough noise is being transmitted BACK to the engine, and the knock sensors are picking this up, and then retarding the timing on cylinder 6, which then causes the misfire.
You see, if I pull on the shifter into any gear, which puts a light load on the gearbox and quiets it, the miss completely stops.
My thought is, if knock control is active even at idle, should it in theory be safe to zero out the first 3 cells of KRFKLN to result in 0 retard under 1600rpm?
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zillarob
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« Reply #1 on: February 19, 2011, 01:38:09 AM »
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I would lean toward injector (hope not wiring or connector) since you have pretty much ruled everything else out.
I think it uses the crank angle sensor more than knock sensors to detect misfires.
Misfires go away when playing with shifter prob because you have the clutch in. More load is being requested. Last one I looked at was about 22% no clutch and 28% or so with
clutch in at idle.
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coreyj03
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« Reply #2 on: February 19, 2011, 01:40:01 AM »
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i had a similar problem... turned out to be bad camshafts and broken lifters. car ran fine but 2 valves were not even opening which caused a missfire at idle.
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Jason
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« Reply #3 on: February 19, 2011, 04:32:28 AM »
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When I pull on the shifter, I am not touching the clutch, just using the drag from the blocker ring to keep the gear backlash from oscillating. I didn't see the load increasing, but I was just using the vag-com which has a poor sample rate.
The reason I suspect it could be knock intervention is that if I intentionally pull timing at idle, I start misfiring on all cylinders, and adding timing seems to reduce the frequency of misfires on 6, but that change in idle torque reserve is excessive and not optimal.
I think I need to fire up ECUx tomorrow to try to capture the misfire along with correction factors at idle. About a year ago I do recall seeing higher than normal knock voltages at low engine speeds and low loads associated with the clutch, but I can't find those logs.
I am kind of worried about your mention of valvetrain troubles - I just passed 161,000 miles. Did the DAMB just bleed down or what?
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Jason
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« Reply #4 on: February 19, 2011, 10:24:43 AM »
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Ugh. Of course it's not missing now now matter what I do.
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Rick
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« Reply #5 on: February 19, 2011, 10:52:52 AM »
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Before you change anything, why not look at the knock retard block on that cylinder? It's a slow sample rate, but you will catch it retarding as when it pulls timing, it doesn't instantly putit back in. Slight leak of obscure spray pattern from the injector will be more evident at idle.
Rick
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Jason
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« Reply #6 on: February 19, 2011, 11:03:25 AM »
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That's what I was trying to do this morning but then the problem "fixed" itself... Last night I only had my Win7 laptop with me and figured the sampling rate would be too low to catch it, so I looked at it this morning with the XP laptop with ECUx on it but didn't see anything. I will have to get the gearbox hot again in hopes it reproduces the problem.
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Tony@NefMoto
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« Reply #7 on: February 21, 2011, 12:15:59 PM »
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There are different idle maps for min RPM and min load when the clutch is depressed, and when the climate control is running.
Misfire detection is done using the crank shaft engine speed sensor. If the engine speed does not increase after a combustion event, the ECU assumes it misfired.
What injectors are you running?
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Jason
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« Reply #8 on: February 21, 2011, 12:47:10 PM »
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Brand new balanced/tested Siemens 60's. Just so we're all on the same page, this was occurring when the engine was idling, gearbox in neutral, and clutch engaged...
I haven't been able to replicate it since it happened on Friday.
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Tony@NefMoto
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« Reply #9 on: February 21, 2011, 02:01:34 PM »
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Have you tuned any of the idle maps? Is it possible that the idle maps for when the clutch is disengaged have been tuned, but that the idle maps for when the clutch is engaged haven't been tuned?
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Jason
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« Reply #10 on: February 22, 2011, 06:59:23 PM »
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No... basically all I did was correct the latencies, and everything was groovy. However, there is trouble in paradise - the clutch let go on a flat shift today, so I probably won't be doing anything with the car until I get a rebuild kit on order.
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Tony@NefMoto
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« Reply #11 on: February 22, 2011, 07:19:25 PM »
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No... basically all I did was correct the latencies, and everything was groovy. However, there is trouble in paradise - the clutch let go on a flat shift today, so I probably won't be doing anything with the car until I get a rebuild kit on order.
Well lets hope a new clutch solves all of your problems.  |
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