LLY: Need help...odd misfire at ~3,000rpm [Archive] - Duramax Diesels Forum

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duratothemax
07-13-2011, 10:05 AM
So ever since I put this engine (stock LBZ long block, LLY injectors and fueling/ECM) in my truck ~6,000 miles ago, its had a random odd misfire above 3,000rpm or so.

It only happens when its warmed up to temp. When its cold, it will rev up to the rev limiter (3,900) and smoothly hold that rpm (no misfire) with my foot on the floor. As the truck warms up, the "rev limit" (where it starts to misfire/cough and wont rev above) progressively gets lower until when its fully warmed up, it wont rev above 3,000rpm. Like when the truck is "half" warmed up, it will rev up to ~3500ish and then start to sputter/misfire.

Yes, its been doing this for 6,000 miles. No, I havent really cared to spend time diagnosing it until now because ive been too busy and I stopped beating on the truck/driving it hard two engines ago. Obviously I cant go WOT when its warmed up because the shift point is above the rpm that it starts missing/sputtering at. Ive just gotten used to lifting just enough to get it to shift at 3,000rpm right before it starts missing.

NOTHING strange/abnormal shows up in the logs, ive already logged the thing 100 times. Rail pressure is fine, main rate holds steady, pulse width stays steady, etc etc etc...

Reflashed to stock tune, still does it. Its not the tune because I ran the same exact tune on the last engine that was in it (stock LLY long block) and it never had any issues like this.

The only thing I can think of is the ECM is losing crank signal/resolution at higher RPM's for some reason. I have not tried a new CKP sensor, and I have not tried a new CPS sensor.

The only 'wild card' with this engine is its running an LBZ reluctor wheel (yes, I cut a tooth off, otherwise it wouldnt run at all. Pat did this on one engine and didnt notice any abnormal effects.

AND it has some bizarre front cover. I dont know what it is, maybe an early prototype LB7 front cover??? Schulte and I got it in the mountain of parts that we bought from Curtis (DPR) when he closed shop in wisconsin. At first glance it looks normal, but the mounting place for the CKP sensor is different. On normal production dmax's, there is a big hole in the front cover, then there is a spacer/bushing/mount thing that bolts to the front cover, and then the CKP sensor mounts to that spacer.

On this oddball front cover, there is no spacer, the mounting flange is spaced out a little differently, and the CKP sensor bolts directly to the front cover.

I suppose I could answer my own question and swap front covers, but Id rather get some input (Fingers???) on if anyone has seen a dmax do anything this, before I spend a whole afternoon swapping front covers.

The thing that baffles me is it only does it when the engine is warmed up.

I know im going to get 100 responses that say "must be in the tune, check your tune", so Ill say it again, its NOT in the tune. :)

In the video im slowly increasing revs to 2900-3000 where it just barely starts to miss, then as I press my foot down more and more (as if I wanted to increase RPM's further), the misfire/sputtering gets more violent/severe and it clearly wont go above ~3,000rpm.

0Pb1dVzO4hc

thanks
Ben

Redbowties88
07-13-2011, 10:13 AM
subscribed....

duratothemax
07-13-2011, 10:17 AM
maybe a bad FICM too? When the fuel temp heats up (and thus makes the FICM heat up) the drivers/dc-dc converters in the FICM start to operate erratically at higher duty cycles????

Redbowties88
07-13-2011, 10:20 AM
no codes right? if it was a crank or cam sensor why would it only crap out at 3k? you would think it would be more of a random issue.

can you log the voltage from them to check for consistency?

duratothemax
07-13-2011, 10:25 AM
no codes right? if it was a crank or cam sensor why would it only crap out at 3k? you would think it would be more of a random issue.

Not sure...maybe its weak/positioned slightly differently (due to the oddball front cover) and as RPM's increase and the ECM has to process the signal faster, it gets goofed???


can you log the voltage from them to check for consistency?

CKP and CPS signals are an AC sine wave, not a simple DC 5v ref voltage, afaik.

no codes obviously. I wish there was because its stoopid simple diagnosing crap when the ECM trips a DTC.

jonathancasey19
07-13-2011, 01:43 PM
This might sound kinda stupid but my truck did something very similar. Sounded horrible only in higher rpm range. Turns out my dsp2 switch was loose. It was trying to merge both tunes at once...BUTTTT I see you reflashed back to stock tune.

Chevy1925
07-13-2011, 03:37 PM
maybe a bad FICM too? When the fuel temp heats up (and thus makes the FICM heat up) the drivers/dc-dc converters in the FICM start to operate erratically at higher duty cycles????

thats kinda what i was thinkin. do you have a lift pump on there ben? maybe try bypassing it and see if would go over?

duratothemax
07-13-2011, 05:06 PM
thats kinda what i was thinkin. do you have a lift pump on there ben? maybe try bypassing it and see if would go over?

Yes, airdog-2 165gph. Its making plenty of pre-CP3 pressure.

Fuel temp (when the engine is hot) is ~145*. Which seems hot to me, but I dunno.

Like I said, when the engine is cold it will rev up to 3900 just fine.

My FICM is painted black too (I did it a long time ago, just for lolz). Its the original FICM that came with my truck from the factory, so it has 160k miles on it. Maybe the FICM is overheating? :confused:

But I had the black-painted FICM on engine #4 (stock LLY engine, only was in the truck for ~2 weeks back in october 2010) too, and it didnt have the sputtering problem.

The engine thats in the truck now, engine #5, is a stock LBZ long block (actually its the engine that came in dmaxfiremans truck from the factory) with LBZ heads, LLY injectors, LLY fuel system, LLY ECM, LBZ reluctor with one tooth cut off, unknown oddball LB7 (?) front cover, stock LLY turbo, big dipper injectors, ppe race valve, airdog 2 165gph...I think thats it. I dont remember for sure if it has an LLY or LBZ CP3 on it. I think its an LLY CP3.

Unrelated, but I think the turbo is on its way out too?? Above ~15psi it makes a whooossshhhh/whirrrrrrr/wooooooooooo noise that gets louder/higher as the boost increases. Its not a straight "WHOOSH" like a boost leak, it has a pitch/whirrr to it. Or maybe its a leaking up-pipe gasket, they've only been reused like 15 times or so ha.

The whirring at higher boost levels I dont care about, Ill deal with that later. The sputtering is kind of annoying though because for the past 6,000 miles Ive had to plan carefully when I want to accelerate on the highway, or pass someone (with a downshift) when the engine is up to temp.

ben

S Phinney
07-13-2011, 05:13 PM
It could a the CPS. I had a misfire similar to that before. It didn't through any codes until it completely went out.

Sent from my SCH-I500 using Tapatalk

Chevy1925
07-13-2011, 05:39 PM
Yes, airdog-2 165gph. Its making plenty of pre-CP3 pressure.

Fuel temp (when the engine is hot) is ~145*. Which seems hot to me, but I dunno.

Like I said, when the engine is cold it will rev up to 3900 just fine.

My FICM is painted black too (I did it a long time ago, just for lolz). Its the original FICM that came with my truck from the factory, so it has 160k miles on it. Maybe the FICM is overheating? :confused:

But I had the black-painted FICM on engine #4 (stock LLY engine, only was in the truck for ~2 weeks back in october 2010) too, and it didnt have the sputtering problem.

The engine thats in the truck now, engine #5, is a stock LBZ long block (actually its the engine that came in dmaxfiremans truck from the factory) with LBZ heads, LLY injectors, LLY fuel system, LLY ECM, LBZ reluctor with one tooth cut off, unknown oddball LB7 (?) front cover, stock LLY turbo, big dipper injectors, ppe race valve, airdog 2 165gph...I think thats it. I dont remember for sure if it has an LLY or LBZ CP3 on it. I think its an LLY CP3.

Unrelated, but I think the turbo is on its way out too?? Above ~15psi it makes a whooossshhhh/whirrrrrrr/wooooooooooo noise that gets louder/higher as the boost increases. Its not a straight "WHOOSH" like a boost leak, it has a pitch/whirrr to it. Or maybe its a leaking up-pipe gasket, they've only been reused like 15 times or so ha.

The whirring at higher boost levels I dont care about, Ill deal with that later. The sputtering is kind of annoying though because for the past 6,000 miles Ive had to plan carefully when I want to accelerate on the highway, or pass someone (with a downshift) when the engine is up to temp.

ben

i wonder if the pressure is too much though from the air dog. kinda like how if you bump it up too much on a lb7, some guys get a lope. jsut a theory though. Or could a possible ECT sensor for the ECM be going bad but hasnt quite gone out yet?

duratothemax
07-13-2011, 05:57 PM
i wonder if the pressure is too much though from the air dog. kinda like how if you bump it up too much on a lb7, some guys get a lope. jsut a theory though. Or could a possible ECT sensor for the ECM be going bad but hasnt quite gone out yet?

I logged coolant temp and its all normal.

Im going to try a new CKP sensor I think, ill see what happens.

duratothemax
07-13-2011, 05:59 PM
It could a the CPS. I had a misfire similar to that before. It didn't through any codes until it completely went out.

by CPS, do you mean crank position sensor? Or cam position?

I know im splitting hairs, but just for technicality's sake and to make sure im understanding you correctly....?

CPS = cam position sensor
CKP = crank position sensor

Fingers
07-13-2011, 06:16 PM
Not sure...maybe its weak/positioned slightly differently (due to the oddball front cover) and as RPM's increase and the ECM has to process the signal faster, it gets goofed???




CKP and CPS signals are an AC sine wave, not a simple DC 5v ref voltage, afaik.

no codes obviously. I wish there was because its stoopid simple diagnosing crap when the ECM trips a DTC.

The signals are actually square waves. The CPS has a strange cadence.

If it was me, I would be using a scope to look at several things.

One, the CKP signal. Though it is supposed to be a square wave, it is possible the prox sensor sensitivity fades as it gets hotter. Such that the gap between pulses closes up at higher speeds. Without a scope to look at, I would simply swap in another used sensor.

The FICM could be getting hot and failing. Easiest thing to do is just swap it and see if there is any improvement, but I would scope the input and output from the module.

I would also look at the signal coming from the ECM itself. It is possible the drivers in the ECM are overheating.

Lastly, IIRC, the injectors are ground switched. That is, there is always positive voltage present and the ground is connected and disconnected to cause current to flow through the injector. I would check that the voltage is stable on the + side of the injectors.

duratothemax
07-13-2011, 06:21 PM
The signals are actually square waves. The CPS has a strange cadence.

If it was me, I would be using a scope to look at several things.

One, the CKP signal. Though it is supposed to be a square wave, it is possible the prox sensor sensitivity fades as it gets hotter. Such that the gap between pulses closes up at higher speeds. Without a scope to look at, I would simply swap in another used sensor.

The FICM could be getting hot and failing. Easiest thing to do is just swap it and see if there is any improvement, but I would scope the input and output from the module.

I would also look at the signal coming from the ECM itself. It is possible the drivers in the ECM are overheating.

Lastly, IIRC, the injectors are ground switched. That is, there is always positive voltage present and the ground is connected and disconnected to cause current to flow through the injector. I would check that the voltage is stable on the + side of the injectors.

great thanks Jon!

I already tried another (known good) ECM. Ill have to borrow a known-good FICM to try that next. That and a known-good CKP sensor.

Interesting info about the waveform on the CKP/CPS sensors, thanks for correcting me.

Ben

S Phinney
07-13-2011, 06:36 PM
It was the crank position sensor Ben. Either sensor on a LB7 will interchange and work. Don't know on the other models but I would think they would too. Heat is what was causing the intermittent problem before it finally gave up.

Big Angry
07-13-2011, 06:37 PM
Ben, FWIW, you may have a Medium duty front cover. My buddy has 2 4500s, and I drove to Michigan to pick up a short block for him from Tony B and he told he that I was in luck as it already had the medium duty front cover on it. So, apparently they are different. Might be what you got from Curtis.
Sorry, I have nothing else to add to this that is useful.
Good luck.

duratothemax
07-13-2011, 06:45 PM
Ben, FWIW, you may have a Medium duty front cover. My buddy has 2 4500s, and I drove to Michigan to pick up a short block for him from Tony B and he told he that I was in luck as it already had the medium duty front cover on it. So, apparently they are different. Might be what you got from Curtis.
Sorry, I have nothing else to add to this that is useful.
Good luck.

Ah ha! You could definitely be right, thanks for that bit of tech info. :thumb:

Ive never looked at a Kodiak front cover closely, but Ill try to take a picture of it (the cover thats on my truck now) and post it up to see if its something that looks like the kodiak front covers that you have seen.

duratothemax
07-18-2011, 10:17 PM
OK I figured it out.

I feel like an idiot, but Im confident enough to where I can admit Ive made a stupid mistake/overlooked something.

I swapped FICM's, no change. Then I went down to the CKP sensor to unplug it to swap it out, and it wiggled all around. Bolt was a little loose and the CKP sensor wasnt seated all the way. I pulled the CKP sensor out, cleaned it up, put it back in, seated it tightly, tightened the 10mm bolt down, plugged it in, turned the key and.......no-start. WTF.

I thought maybe all the wiggling around for the past 6,000 miles took its toll on the CKP sensor, and when I moved it around and tapped it in to seat it, it killed it completely. Swapped out to a known-good CKP sensor, put it in carefully, tightened the bolt, plugged it in, turned the key and........no-start. WTF.

It wasnt a wiring problem, because the ECM wasnt throwing any "circuit" codes...it just simply wasnt picking up any CKP signal. So I thought meh what the hell, and pulled the sensor out a bit to the "loose-ish" position that it had been in for the past 6k miles. Turned the key and...starts/runs fine (but still has the high RPM stumble). WTF.

So then I push the sensor all the way in, but just for grins, I clocked it about 5-10* counter clockwise. (sensor seated all the way flush against the front cover mounting surface, but the bolt hole doesnt really line up) Turned the key and....starts/runs perfectly. AND revs right up smoothly to my 3,800rpm rev limiter with no hesitation or stumbling.

HUH.

To further support my diagnosis, I started the engine, and very carefully reached my hand in and slowlyrotated the sensor to the "proper" (IE, so the bolt hole in the sensor lines up with the bolt hole in the front cover) position...when I got the sensor to the point where the bolt hold ALMOST lines up, the engine shut off.

The only thing I can think of is back to the fact that this is an oddball front cover with a unique CKP sensor mounting setup/style unlike any other dmax front cover I have seen. Probably a pre-production front cover that used a different style CKP sensor that has the mounting tab clocked slightly differently. Because when I put a production LB7/LLY CKP sensor in and clock it so the bolt hole lines up properly, it wont pick up a CKP signal.

So I either have to:

A) drill/tap a new hole in the front cover so I can run the sensor clocked slightly differently

B) swap front covers to a "normal" duramax front cover (screw that, im not pulling the whole thing apart, ill run it re-clocked with no bolt holding it in before I go through that much trouble of swapping covers)

C) oval-out/cut the CKP sensor mounting tab and use a washer on the CKP sensor hold-down bolt


Probably go with option (C). Its the easiest/fastest, and I dont think ill be able to easily fit a drill and tap in the fender-well to re-drill/tap a new mounting hole for the sensor.

So I guess in summary...im not a "complete" idiot, because even though the CKP sensor was loose and the bolt not tight (whether it was me who didnt tighten it initially or it loosened itself up over time, ill never know), even with the bolt tight and the sensor in "properly", something was still wrong with the mounting on this oddball front cover.

Luckily I thought outside the box a bit (rotated the sensor to the "wrong" position/clocking) and didnt just go through the motions and take that front cover's CKP sensor location as the gospel... I doubt anyone has ever seen/come across this problem before, and I doubt anyone in the future will ever come across this problem either...but I figured Id post up in case anyone cares as to what the problem/solution was.

Ben

Fingers
07-19-2011, 05:46 AM
The sweet spot on the sensor is actually a stripe running across the face. Ideally it would be perpendicular to the reluctor wheel. I can see that clocking it would cause a problem, but never thought the holes in the cover would be so off.

Good catch.

McRat
07-19-2011, 06:40 AM
Interesting.

Did you try swapping cam/crank sensors?

I used to throw them all in a box, until one time I got a no-start. I swapped them, and it ran. Yes, after I cut off the reluctor tab, I hit 4500+ rpm at max effort.

Did you try a crank position relearn? Not even sure it's avail for our engines, but have fixed similar issue on LS1.

duratothemax
07-19-2011, 07:43 AM
Interesting.

Did you try swapping cam/crank sensors?

If the cam/crank sensors were swapped, it wouldnt even run at all. The thing is, my engine would run....it would just start to miss/sputter around 3,000rpm.

But just for grins I did put a CPS in the CKP position a few minutes ago. It would start and run, but barely...rattling/knocking etc...

Did you try a crank position relearn? .

there is no such thing on a duramax........


I ended up just cutting the sensor mount tab and using a washer on the bolt to re-clock the sensor. Yeah its ghetto and yes I would do this sort of thing to my own truck. There is no way in hell im going to go through the trouble of swapping front covers. Ill just run it like this, and if it shuts off on me while im driving sometime in the next couple days, oh well, its not like I wont know what the problem is.

Several pics. Of my unique front cover, the sensor in the "correct" position (well, 'correct' according to the cover, but in reality it wont start when its positioned this way), the sensor in the "wrong" position (but it starts/runs/revs fine with the sensor clocked here), and finally, my awesome fix.

ben

SHOTZY
07-19-2011, 08:27 AM
Just finished reading this hole thread. After my build I had one hell of a time getting it to run. Btw they will run with the sensors swapped. I know this because mine did. Not well though. Would start shut off, start shut off. Then once I did this about a hundred times it actually puked its way to life. I actually was able to drive it. Next morning same sh*t. What our conclusion was that the heat from cranking caused the waves to align enough to run. Might be wrong on terminology there but you know what I mean. Now take a known cps and a known cks compare them, the clocking IS different. Now I'm not fimiliar with this front cover issue so I cant add anything there. But try swapping sensors. Good luck with this. I hate chasing this kind of sh*t.

SHOTZY
07-19-2011, 08:32 AM
Just looked at your pics. IIRC the clocking should be straight up and down not rotated at all.

DIESELMAFIAPER.LB7
07-19-2011, 09:07 AM
lol didnt read the second page gald to see you fixed it ben i deleted my comment :D

duratothemax
07-19-2011, 09:36 AM
What our conclusion was that the heat from cranking caused the waves to align enough to run.

what heat is generated during cranking....????? :confused:

Now take a known cps and a known cks compare them, the clocking IS different.

Yes im aware of that. :)

But try swapping sensors.

I already tried that. It barely ran. If I had had the CKP and CPS sensors swapped for the past 6,000 miles there is NO WAY it would have run as well as it did. (it ran perfectly, up until ~3,000rpm where it would start to sputter/miss)

The conclusion/source of the problem here is that the front cover is apparently not a final-production piece. Its something else. Because production LB7/LLY CKP sensors do NOT have their tab/hole clocked correctly to work with the bolt hole in this particular front cover.

Im just going to run it like this until I finish getting the [second] built engine together. It runs just fine, right up smoothly to the rev limiter with my "elongated hole" and washer trick holding the CKP sensor in the front cover.....so I see no reason to mess with it.

Its going to be odd being able to floor it without sputtering and missing. Its been 6,000 miles and probably 8 months since my truck has completed a proper WOT upshift. :)

Now I just need to fix my bad front right wheel speed sensor to get rid of the ABS light thats been on for 6 months, figure out what the wailing/whooshing at high boost levels is (its not a boost leak, I think the turbo is on its way out) and OMG it will be like I have a brand new truck.

Redbowties88
07-19-2011, 09:38 AM
is it possible that a medium duty could use a different ckp?

duratothemax
07-19-2011, 09:41 AM
is it possible that a medium duty could use a different ckp?

no idea? :confused:

Someone (Johnny/gasuout??) will have to take a look at the picture of my front cover and confirm if, yes, its a medium duty cover, OR its something else.

I doubt the medium duty trucks use a different CKP sensor, but Ive definitely been wrong before.

Redbowties88
07-19-2011, 09:50 AM
just thinking aloud, if so then it would be an easy fix as long as the kind of signals it sends are identical...

JoshH
07-19-2011, 10:40 AM
If the cam/crank sensors were swapped, it wouldnt even run at all.
What is the difference between the cam and crank sensors? I thought it was just the way the tab was positioned? Maybe the cover you have is made so the same sensor could be used in both spots?

Fingers
07-19-2011, 11:49 AM
The connector should be straight up and down.

You are missing the adapter plate that sits under the CKP sensor.

duratothemax
07-19-2011, 12:06 PM
The connector should be straight up and down.

You are missing the adapter plate that sits under the CKP sensor.

ahh thats what I first thought too....but look closely... ;)

On the normal 'production' front covers, when you remove the adapter plate, there is a much bigger hole (1"?) and two bolt holes. On this production covers, the adapter plate bolts to the front cover with 2 bolts, then the CKP sensor bolts to the adapter plate with 1 bolt.

If you remove the adapter plate on a production front cover, there is no way a CKP sensor will fit in it properly (and spaced out correctly)...this 'magic' cover I have was not designed to have an adapter plate.

duratothemax
07-19-2011, 12:13 PM
see heres what a normal 'production version' LB7/LLY front cover looks like with the CKP sensor adapter plate removed.

Fingers
07-19-2011, 12:26 PM
Just looked it up in the SI manual. The sensor is different for the medium duties. Note the connector orientation.

duratothemax
07-19-2011, 01:12 PM
Just looked it up in the SI manual. The sensor is different for the medium duties. Note the connector orientation.

ah ha! Thanks for the picture. So apparently I have a medium duty cover. Who would have thought GM used a different style sensor on the medium duty trucks??? Doesnt make sense at all, from a cost-perspective...having two different sensors.

SHOTZY
07-19-2011, 02:09 PM
what heat is generated during cranking....????? :confused:



Yes im aware of that. :)



I already tried that. It barely ran. If I had had the CKP and CPS sensors swapped for the past 6,000 miles there is NO WAY it would have run as well as it did. (it ran perfectly, up until ~3,000rpm where it would start to sputter/miss)

The conclusion/source of the problem here is that the front cover is apparently not a final-production piece. Its something else. Because production LB7/LLY CKP sensors do NOT have their tab/hole clocked correctly to work with the bolt hole in this particular front cover.

Im just going to run it like this until I finish getting the [second] built engine together. It runs just fine, right up smoothly to the rev limiter with my "elongated hole" and washer trick holding the CKP sensor in the front cover.....so I see no reason to mess with it.

Its going to be odd being able to floor it without sputtering and missing. Its been 6,000 miles and probably 8 months since my truck has completed a proper WOT upshift. :)

Now I just need to fix my bad front right wheel speed sensor to get rid of the ABS light thats been on for 6 months, figure out what the wailing/whooshing at high boost levels is (its not a boost leak, I think the turbo is on its way out) and OMG it will be like I have a brand new truck.

The heat was generated when it started and shut off. 10 minutes of this and it will get hot. Sorry didn't see where you swapped them. Glad you got it figured out.

HEEPJEEP
07-19-2011, 08:14 PM
ah ha! Thanks for the picture. So apparently I have a medium duty cover. Who would have thought GM used a different style sensor on the medium duty trucks??? Doesnt make sense at all, from a cost-perspective...having two different sensors.

Fawking engineers....:D

duratothemax
07-19-2011, 08:51 PM
Fawking engineers....:D

blow up.