Is this a TUNE based PROBLEM ??????

[dustiebutt]

I have an L76 crate motor, engine management components replaced and mild cam installed. Harness and electronic components from late '07 GM including E38 ecm.

Nelson Performance was hired (via email) to do the tune almost 2 YEARS AGO. It took close to a year to get the basics of the tune down but almost from the get go a slight vibration is felt from1000 rpm to 1250 rpm and 1700 rpm to 2600 rpm. Although the engine smooths right out above 2600 rpm , the scan shows hundreds of misfires in #5 & #8 cyl. The rest of the cylinders show normal minimal random misfires.

Coils and injectors were swapped, plugs replaced twice, plug wires replaced with new, compression tested perfect, fuel pressure a constant 60 lbs., valve springs checked, flywheel/clutch checked, replaced harmonic damper, crank sensor replaced, all wiring traced and inspected, connectors checked and thee different ecms were tried with same results (all with the same tune).

Everything mechanical looks fine. The only thing strange or coincidental I have noticed was #5 and #8 cylinders are pinned next to each other on the ecm. I have tried more than a dozen times to do the relearn hoping that would eliminate one more possibility but cannot get it to work, even when dtc's were taken care of and misfire pids removed.

I have gone over this a hundred times with Nelson and they insist it is not tune related. I am hoping someone can clarify whether it is or isn't by looking at the tune and scan which I have attached.

I don't want to drive this thing until the vibration issue is dealt with for fear of hurting the engine.

Would appreciate some expert input! Thanks

NEW NELSON ECM 6-6-2015.hpt
NEW NELSON ECM 6-6-2015.hpt with misfire log.hpl

[BigDaddyCool]

I have an L76 crate motor, engine management components replaced and mild cam installed. Harness and electronic components from late '07 GM including E38 ecm.

Nelson Performance was hired (via email) to do the tune almost 2 YEARS AGO. It took close to a year to get the basics of the tune down but almost from the get go a slight vibration is felt from 1700 rpm to 2600 rpm. Although the engine smooths right out above 2600 rpm , the scan shows hundreds of misfires in #5 & #8 cyl. The rest of the cylinders show normal minimal random misfires.

Coils and injectors were swapped, plugs replaced twice, plug wires replaced with new, compression tested perfect, fuel pressure a constant 60 lbs., valve springs checked, flywheel/clutch checked, replaced harmonic damper, crank sensor replaced, all wiring traced and inspected, connectors checked and thee different ecms were tried with same results (all with the same tune).

Everything mechanical looks fine. The only thing strange or coincidental I have noticed was #5 and #8 cylinders are pinned next to each other on the ecm. I have tried more than a dozen times to do the relearn hoping that would eliminate one more possibility but cannot get it to work, even when dtc's were taken care of and misfire pids removed.

I have gone over this a hundred times with Nelson and they insist it is not tune related. I am hoping someone can clarify whether it is or isn't by looking at the tune and scan which I have attached.

I don't want to drive this thing until the vibration issue is dealt with for fear of hurting the engine.

Would appreciate some expert input! ThanksNEW NELSON ECM 6-6-2015.hptNEW NELSON ECM 6-6-2015.hpt with misfire log.hpl

You could probably start with fixing some of the lower down fueling....... It pulls too much sometimes, adds too much on other times......... enough to probably cause a misfire but honestly could be mechanical inside? .... If its vibrating as you say.....

If your wondering about the tune........ start by turning off Dynamic (100/5) and run maf....... touch the maf table up........ and see if its any better. Perhaps you need more or less timing in those areas where its misfiring. According to your O2's mv's it may be running rich at those spots where its misfiring and to me that seems like an injector stuck open?.... drowning the engine causing a misfire? Ive had a bad injector or two in my time randomly play up.... they commonly cause misfires by drowning the engine. Either that or the fueling being out is dragging over causing the effect.

Couple of ideas for you.....

PS. As a temporary test you could restrict how much the LTFTs will compensate to within 1% to see if the car runs better......... if it does and the misfires go away you will know you just need to tidy up the low down fueling. But this is only a temporary test measure..... given your low down ltft cells are running 12%+

[dustiebutt]

Internal imbalance was a big thought on my part but it is a GM crate motor to start and knowing there is always the possibility of factory screw ups, everyone questioned thinks the possibility is quite low.

The vibration felt is not one you would feel if say the flywheel or damper was out of balance or mismatched to the engine. That type usually is constant throughout the rpm range and is much more severe than this. Its just weird that it inhabits this particular rpm range.

The Comp cam that was installed was also on my mind, thinking maybe the grind was off on these two cylinders. LSA is 111* which may contribute somewhat but I would think it would be more random over all cylinders an

Injectors and coils were the first things I swapped around to see if it affected the misfire locations.

[Earwax]

Does the motor sound like its popping out the exhaust when this occurs? Does the exhaust get extremely hot? Can you feel the miss? Does it surge when it misses? I had a similar problem a while back. I did not have HP Tuners then,but did use a GM Tech 2 scanner on it to help find the problem.Sorry for all the ?`s.Just trying to help.

[dustiebutt]

No popping or weird noises, have not checked exhaust temps but does not feel excessively hot. When trying to accelerate rpms quickly there is a hesitation or stumble around 1000 rpm to 1250 rpm where there is a slight vibration also. Not a smooth rev when you step into it quickly.

[Earwax]

The reason for all the ?`s is that I have a LY6 crate motor (removed VVT,changed reluctor,Comp Cam,AFR headers,cai,etc) that I had 3 or 4 PCMs tuned by Nelson and they all did the same things.I`m not bashing Nelsons tunes by any means.
Are the plugs snow white in color? I know you only had it idling.
I would to the relearn,either with a Tech2 or a Snap on scanner. GM requires it done if the PCM or Crank Sensor are changed.It can cause random misfires if not done.
Check your intake for vacuum leaks.I think you will find that it wants more fuel.Mine runs great when it is rich,not at stoich.(I think this is caused by the LS3 type heads).I loose quite a lot of power/response if I set it to run at stoich.It also likes alot of timing.
I returned the PCM to Nelson and bought one from another tuner.It was like night and day.All the problems I listed were gone.But, like I said it runs rich. I recently started tuning with help from a few experts on here.They have been very helpful. I am by no means an expert,but I m learning. Hope this points you in the right direction.

[Earwax]

You may want to check the general items in your tune, it is currently listed as a 4.8??

[dustiebutt]

The reason for all the ?`s is that I have a LY6 crate motor (removed VVT,changed reluctor,Comp Cam,AFR headers,cai,etc) that I had 3 or 4 PCMs tuned by Nelson and they all did the same things.I`m not bashing Nelsons tunes by any means.
Are the plugs snow white in color? I know you only had it idling.
I would to the relearn,either with a Tech2 or a Snap on scanner. GM requires it done if the PCM or Crank Sensor are changed.It can cause random misfires if not done.
Check your intake for vacuum leaks.I think you will find that it wants more fuel.Mine runs great when it is rich,not at stoich.(I think this is caused by the LS3 type heads).I loose quite a lot of power/response if I set it to run at stoich.It also likes alot of timing.
I returned the PCM to Nelson and bought one from another tuner.It was like night and day.All the problems I listed were gone.But, like I said it runs rich. I recently started tuning with help from a few experts on here.They have been very helpful. I am by no means an expert,but I m learning. Hope this points you in the right direction.

This is the second (New) ecm from from Nelson I have used to try and determine if there was something screwy going on with my original, which was from a late '07 Silverado with a 4.8L. This tune is identical to my original except for minor settings as engine size, speedo settings, etc.

The main reason for trying this ecm was to see if my original had become defunct in some way, causing the misfires/vibration. This trial has confirmed my ecm is OK and the only possibilities left for the vibe problem is tune (which both ecms have the identical tune) , relearn not being done, or an internal mechanical problem. I really need to do the relearn but haven't been able to complete it after dozens of variations and settings.

As many times as I have had the truck apart, replaced parts and put everything back together again, I want to make sure it is not the tune before I pull the engine and tear it down. My instincts tell me a crate motor has an extremely low chance of having internal problems (never heard of anyone with an LS motor having vibe problems unless it was a damper or flywheel ) . And as you experienced with Nelson, the right tuner can make all the difference. Nelson has been tinkering with this for almost two years and my patience are thin . I am not an experienced tuner either and I dont like to burden anyone with my problems but as you also know, just researching this forum and others takes hundreds of hours just to get the basic tuning experience and questions answered ( if anyone responds at all) . Just trying to get some sensible input before I try another "expert" tuner.

I can attach my original ecm tune to show any differences between the two but as I said, same vibe in the same rpm ranges for both ecms.

Thanks

[Earwax]

Looking at your log, it appears that it maybe entering PE? Which I don`t know if thats possible at idle? Here is a link to my rich problem.Maybe one of these experts could help you.I learned alot from schpenxel.

[Earwax]

Link:http://www.hptuners.com/forum/showth...ghlight=earwax