Twins with Twins, Anyone?

[kidturbo]

This crank cam sensor pick up situation deserves its own topic. But here is the short and sweet on what's Happening. First Mark broke out an old tool that was new back when he or I were in college.

Since neither of us really wanted to sit beside an engine making 700 horsepower, violently,, we patched it in on the old video monitor. However it just couldn't capture the crank sensor fluctuations.

So we moved to a more modern version, and was able 2 see it happening and replay the data. It is harmonic's related, 100% certain.

Best we can tell, the reluctor is vibrating or oscillating at a frequency that is affecting the square wave pattern seen by the pick up. And ECM doesn't know what to do with it. So it loses count, cuts the cylinders off, problem ceases, refires cylinders, ssdd over and over again.

Why it is so prevalent on the dyno, or how to resolve it, is still up for discussion. But I believe we have a short-term work around in place for the next engine. So by the end of next week we should have a better grasp of the situation..

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[DAVe3283]

Interesting. Looks like ringing on the sensor output, but the periodic nature vs. engine position sure does make it seem to be a physical issue, not electrical.

The Duramax crank sensor actually has 3 different thickness plates to get the spacing exactly right. Or at least the LB7 does (all I own are LB7s lol). You might try shaving a couple thousandths off to get the pickup closer to the wheel.

I'm surprised the harmonics carry all the way to the cam sensor. I would've figured the gears would provide enough isolation/damping to keep that reluctor wheel running true.

If you know what frequency the noise is at, you could put a bypass cap across the sensor and try and clean it up. It looks to be sufficiently high frequency that shorting out the noise at 3600 RPM shouldn't start attenuating the real signal meaningfully before 6000+ RPM.

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[THEFERMANATOR]

I know its an apples to oranges comparison, but I ran into an almost identical issue many years back on a Ford 351 in a boat. The engine would free rev to 4500 no problem, ran great, and had no signs of an issue. Put it in gear and it would hit a brick wall right around 3500 rpm's. It acted just like it was running out of gas. I ended up putting a timing light on it and seen it was dropping spark at the plugs, but the tach stayed steady with no dropout I could find in the pickup side. Ended up being he had installed a pertronix ignitor, but it was an early version with no gap adjustment. I checked the gap and had about .060". I took a screwdriver and bent the plate over to get it back down to as close to .030" as I could, and it took off like a bat out of hell with never another hiccup. So I would definately double check the pickup gaps with all the painting that was done. Hall effect pickups tend to work perfect until they lose signal, then they just dropout entirely.

 

[kidturbo]

Thanks for the input guys. Those are the first two approaches we are thinking also. Started working towards the testing gap options, thinking it might be the easiest to validate. Just didn't have time to follow thru yet, and wanted to get some time on second engine since this one has proven solid at it's normal operating RPM. Ya made me look,, but I did mask off the sensor pads on front cover so as not to change the factory depth. Recall this being brought up somewhere before. I also like point about different rector wheel thickness, cause we are running LB7 cam gears in there.

For now I would really like to learn more about filter options, since we feel that's a major difference between OEM and the stand alone ECM's which never seem to experience this problem. Even though the sensors are never changed... Going to reach out to couple electronics guru buddies for ideas, but please feel free to elaborate more. Attached a good screenshot showing a more detailed view of the pattern glitches.

While my Saleae tool picked up cam glitches also, we didn't attempt to verify this with the higher end tools yet. We focused on the on the crank since it was most critical input at speed. However an interesting trend we noticed, the ECM first logged cyl misfires and set codes on 2 & 7 [I think] when we first started our runs 2 weeks ago. Disconnecting second dyno brake, that misfire tracking issue went away. Thought we'd solved it, but rpm cut out didn't go away with it. So when we changed driveshafts to an older one without internal damper, was surprised to see that the ECM was now tagging misfires on 1,2,3,4,5, & 8 soon as made that swap...

I've always followed the theory that lack of rotating mass on the big end plays a part in this problem. Personally never had it show up, but have helped other experiencing it in the real world. Stick a heavy flywheel or converter on there and it typically goes away. Well now we have engines with more internal rotating mass than anything else out there, plus an extra 100lbs on flywheel, problem shows up.. Would love to chat with a GM engineer about it, cause they moved that crank sensor to rear for some dang good reason..

Next week we are going to test engine 2 with a stand alone ECU to hopefully get the data needed make call on these turbos. But I wanta solve this using OEM parts if possible. It's gotten personal, LOL...

 

[turbo_bu]

Main theme here is rotating stiffness and rotation mass (or inertia). As you pointed out, sticking a heavier flywheel usually is helpful. This is because you want the flywheel to keep rotating and not oscillate back and forth. If you could show a picture of the whole driveline setup it might be helpful to see where the potential torsional resonance is coming from.

As for what GM did, I can only speculate. Typically, your torsional vibration is less at the flywheel end than say at the front of the engine. This could be a good reason why GM moved it to the back. BTW, this is why your harmonic balancer (or damper) is placed at the front of the engine. It is there to calm down the torsional vibrations of the crankshaft. There does need to be a rotational balance between the damper and flywheel though.

I would be curious as to if the standalone system can control the engine. If it is truely the reluctor wheel vibration, it shouldn't matter which ECM you are using. They will both have issues at these speeds.

 

[NC-smokinlmm]

Is this a problem on both engines?

 

[Stingpuller]

High speed miss

That high speed miss is all to familiar!!! lol Not sure if its the same thing but on the dragster I tried all different gaps on the crank sensor. I machined the covers, sensors and tried different rings with no luck. Mine would free rev just fine. Put it under load and it would miss.

 

[kidturbo]

Bolting second engine up today. Am curious to compare two identically matched setups. Have plenty of data off first one, and a good bit of brain power onboard to analyze results.

Thinking about ya Sting.. The load or hooking power seems to be a key. As Larry over here put it, that dyno has ahold of it. Not many situations where you have 100% traction, so crank torsional twist gets dampened in other directions. But when nothing else is slipping, cranks a twisting..

Did you ever try using aftermarket pickups Sting? This was suggested by a Bosch engineer friend across the pond to clean up the signal quality. Also going to wheel on front of damper is in the play book.

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[SmokeShow]

That high speed miss is all to familiar!!! lol Not sure if its the same thing but on the dragster I tried all different gaps on the crank sensor. I machined the covers, sensors and tried different rings with no luck. Mine would free rev just fine. Put it under load and it would miss.

Didn't the folks at Fleece help you solve that issue eventually?

 

[kidturbo]

Second engine bolted up and hope to have some data tomorrow.

Did a quick inspection of first one yesterday. One thing we noticed was how clean the intake runners are after a dozen holds at 32-3600. Turbo inlet horns showed a little discharge after each run, but on the pressure side not a drop.

Dirty finger for comparison...

 

[Chevy1925]

Shouldn’t it be clean? Are you expecting the turbos to sneeze a bit of oil in there?

 

[2004LB7]

Where does your crank case vent go? Catch can, intake, exhaust?

 

[kidturbo]

Yeah it should be clean, but these were really clean with zero residue. There was a good film on the inlets where they sneezed on d-cel. No one has pushed these turbos over like 24psi before. Gotta remember, they've only been used on gassers, and then gated..

No catch can built yet. Wanted to make sure the valve covers were flowing good enough, and two, our shield setup under them was working. So far so good. Nothing coming out the covers but air. So catch can will go on back of engines between the turbos and vent to atmosphere outside the boat. Then will do a small drain back with check valve into the normal turbo oil return hole top of rear cover.

 

[Chevy1925]

Yeah it should be clean, but these were really clean with zero residue. There was a good film on the inlets where they sneezed on d-cel. No one has pushed these turbos over like 24psi before. Gotta remember, they've only been used on gassers, and then gated..

No catch can built yet. Wanted to make sure the valve covers were flowing good enough, and two, our shield setup under them was working. So far so good. Nothing coming out the covers but air. So catch can will go on back of engines between the turbos and vent to atmosphere outside the boat. Then will do a small drain back with check valve into the normal turbo oil return hole top of rear cover.

ah 10-4 so you were looking more for a turbo issue than anything. i must have missed the turbo deal as i didnt know they were from the gasser world and have not been pushed hard

 

[JoshH]

What turbos are you using? I don't recall reading about that in here anywhere, and if I did, I have forgotten by now.

 

[kidturbo]

Twin 61mm mirror image from Nelson Racing. Turbonetics builds them.

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[Fingers]

You position sensor noise is because of how you are tapping into the signal. Called common mode voltage. There are many ways to get rid of it, but I would need to know more about your setup.

 

[kidturbo]

Was your ears burning? Might give ya ring later to discuss our findings.

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[kidturbo]

For sale. Two beautiful like new symmetrical 61 mm turbos. Would work great with triples. Only requires a lot of RPM or cubic inches... full dyno analysis included. Feel free to make offers...

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[kidturbo]

Was able to resolve the RPM / misfire issue with Factory harness and ECU. However when we opened up the Scrolls in the turbos here is the final results..

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