LS6 Misfire

[pormgb]

I have a LS6 in a Porsche 944 but I have been experiencing a vibration between 2000 and 3000 rpm, after 3000 rpm there is no sigh of the vibration. I have changed plugs, coils and wires, the motor also has a set of fresh 243 heads.

Initially, I thought I had a balancing problem but I think the vibration is a misfire, its more pronounced when decelerating and the vibration is in sync with a muffled sound from the exhaust. I have been doing some logging and have found positive fuel trims and misfires around that rpm range so I ran a CALC VET and the vibration significantly reduced. The vibration is still there so I am trying to determine if I am missing something in my tune, I have attached some log files with my current tune, looking for any advice.

Specs,

- LS6 Motor
- 226, 229 - 575,585 116 LSA Cam
- 30lb SVO Injectors
- Professional Products 85mm TB

[joecar]

I put you on my queue of things to look at...;

make sure all the ground connections are intact (including the ground point at the rear of the LHS cylinder head);

make sure there are no aireaks between MAF and heads, and between heads and O2 sensors.

[pormgb]

Thanks,

I do have all the correct ground straps, I will check intake manifold for leaks

[Highlander]

Clutch vibration....

[pormgb]

Clutch vibration....

It may be but the vibration is very light when cold the gets heavier as the car warms up, as I tune the car the vibration gets less and I am seeing misfires.

[joecar]

VE table is incorrect.

PE table is lean... go Edit->Properties and set Fueling units to EQR, restart tunetool and redo B3618 PE table (set it to 1.175 EQR).

[joecar]

Start with those, and then there's a few other things to fix.

[Highlander]

if the missfire is off PE there is nothing he can do to PE that fixes it... If its not a balance issue (it has happened to me like that before) then he should start checking out spark plugs and wires.

LEAN or Rich will not cause missfire and vibration. Loss of spark on one cylinder will.

[joecar]

Agreed, he should first test for spark at each cylinder.

His tune is setup lean, so it needs work anyway.

[joecar]

pormgb,

Take the stock LS6 VE table and add 8% from 3200 rpm to 5400 rpm, and start tuning from there.

Post pic of MAF plumbing.

I'm still looking thru rest of tune.

[pormgb]

VE table is incorrect.

PE table is lean... go Edit->Properties and set Fueling units to EQR, restart tunetool and redo B3618 PE table (set it to 1.175 EQR).

After changing the above, do I then do another CALC VET?

[pormgb]

Will make those changes.


17738

[pormgb]

if the missfire is off PE there is nothing he can do to PE that fixes it... If its not a balance issue (it has happened to me like that before) then he should start checking out spark plugs and wires.

LEAN or Rich will not cause missfire and vibration. Loss of spark on one cylinder will.

Ok, I have a brand new set of NGK V-Power TR-55, I will get them installed. Wires and coils are all new, I have tried many sets of coils.

[pormgb]

Another note, my motor will not return to idle properly when warm if B0120 is set to 4000, I have had to leave it at 400.

[Highlander]

The tuning process can't be all at the same time... you have to start from idle and up.... first deal with idle and that the car returns back to idle then deal with the rest....

for the idle... select all the missfire pids, and verify which cylinders are missfiring and that will get you a base idea on what you are up against.

[Highlander]

B0120 is the switchover for SD/Maf hybrid calculation. If you set it to 4000 and it doesn't want to idle it means you have to work out your idle section. For that you will need to disable the MAF and fix the VE Table... I recommend that you use the hybrid mode to about 2000rpms then use pure maf mode for the rest.

[pormgb]

Restored the VE table to a stock LS6 and added 8%, the car ran very well and pulled much better at higher rpm, I also done some more misfire logging and attached the file. With the stock LS6 VE table I still have the problem when changing B0120 to 2000, I will take a closer look at idle tuning.

[joecar]

Take the stock LS6 VE table and add 8% from 3200 rpm to 5400 rpm, and start tuning from there.


After changing the above, do I then do another CALC VET?

Yes, you will have to start over.

[joecar]

Another note, my motor will not return to idle properly when warm if B0120 is set to 4000, I have had to leave it at 400.This indicates that MAF table is reasonably good, and VE tables is not correct.

[joecar]

Good idea about logging the cylinder misfire pids as Highlander said.

Usually Calc.VET can get the VE table pretty close on a cam like that... but if it fails to work, then as Highlander suggested, disable MAF and CL/trims and use a wideband to correct the VE table (i.e. AutoVE procedure... or a modified Calc.MAFT procedure).

[joecar]

What injectors do you have...?

Is your FPR manifold referenced or unreferenced...?
What is measured rail pressure (with reference hose removed during mesurement)...?

[joecar]

Misfire:
- are you seeing the MIL flash...?
- are you seeing any misfire DTC's (P0300-P0308)...?
- were you able to do a CASE relearn...?
- so you're able to feel/hear a miss...?
- what ignition coils do you have...?
- did you check for spark at each cylinder using this: ST-125 HEI Spark Tester

(http://ecx.images-amazon.com/images/I/615UI5-xWwL._SL1319_.jpg)

[pormgb]

Thanks for the advice, I am going to try going back to a Stock LS6 tune with the necessary deletes, I will then adjust the VE as suggested then run a RAFIG. I think my tune has had too many changes and I think the a stock ZO6 tune should be really close. Finally I will run a CALC VET to correct the table as per the cam.

[pormgb]

What injectors do you have...?

Is your FPR manifold referenced or unreferenced...?
What is measured rail pressure (with reference hose removed during mesurement)...?

I have Ford SVO 30lb injectors fed by a stock LS1 FPR, IFR has been modified to match injectors.

[pormgb]

Misfire:
- are you seeing the MIL flash...?
- are you seeing any misfire DTC's (P0300-P0308)...?
- were you able to do a CASE relearn...?
- so you're able to feel/hear a miss...?
- what ignition coils do you have...?
- did you check for spark at each cylinder using this: ST-125 HEI Spark Tester

(http://ecx.images-amazon.com/images/I/615UI5-xWwL._SL1319_.jpg)

- Yes, I am seeing P0300 with a check engine light
- Done a CASE relearn yesterday
- I am sure I can hear and feel the misfire, especially on deceleration, I can hear it in the exhaust tone.
- I have stock coils, I did have MSD but replaced them with brand new coils to pass the referee inspection
- I do have a ST-125 but haven't tested spark, I will do that over the weekend


I have also attached the latest misfire log, as you will see, every cylinder has misfires but cylinder 1has the highest count.

[joecar]

I have Ford SVO 30lb injectors fed by a stock LS1 FPR, IFR has been modified to match injectors.FPR set to 58 psi, ok.

[pormgb]

FPR set to 58 psi, ok.

Yes, I have a gauge on the fuel rail that shows 58psi.

[joecar]

Thanks for the advice, I am going to try going back to a Stock LS6 tune with the necessary deletes, I will then adjust the VE as suggested then run a RAFIG. I think my tune has had too many changes and I think the a stock ZO6 tune should be really close. Finally I will run a CALC VET to correct the table as per the cam.Good idea, start from stock and only make necessary edits.

[joecar]

Misfires:
- false misfires: the misfire detection mechanism in the PCM must have correct information;
- real misfires: something is wrong, either spark, fuel, or air (in the sense that the airflow/airmass model is incorrect).

[joecar]

- Yes, I am seeing P0300 with a check engine light

...

I have also attached the latest misfire log, as you will see, every cylinder has misfires but cylinder 1has the highest count.That log shows very low misfire counts... almost acceptable...

but, if you get any of the P030x DTC then there has to be a reason (faulty misfire data, or physical problem, or incorrect airmass model).

[pormgb]

That log shows very low misfire counts... almost acceptable...

but, if you get any of the P030x DTC then there has to be a reason (faulty misfire data, or physical problem, or incorrect airmass model).
What do you mean by incorrect airmass model? I am running a non stock 85mm TB, I have not done any tuning for that TB:

For my cam (226, 229 575, 585) would I have to alter misfire tables?

[joecar]

MAF plumbing is ok.

Can air filter be blocked off from radiator heat...?

[pormgb]

MAF plumbing is ok.

Can air filter be blocked off from radiator heat...?

Yes, I can build an aluminum shield between the back of the filter an radiator.

[joecar]

"Stock LS1 FPR"... stock truck or stock car...? Where is it located...?

[pormgb]

"Stock LS1 FPR"... stock truck or stock car...? Where is it located...?

Its a stock car FPR, when I bought it I think it was for a Corvette. The FPR is located on the RH side of the engine bay, you can see it in the attached photo.

http://www.ebay.com/itm/LS1-LS2-LSX-Conversion-fuel-filter-w-regulator-6-AN-/161500268299?pt=Motors_Car_Truck_Parts_Accessories&hash=item259a2a870b&vxp=mtr

17745

[joecar]

So the FPR has a return line, and it has no intake manifold reference line, ok understood.

[statesman]

Does the engine have its original flywheel?

[joecar]

What do you mean by incorrect airmass model? I am running a non stock 85mm TB, I have not done any tuning for that TB:

For my cam (226, 229 575, 585) would I have to alter misfire tables?VE and/or MAF are incorrect... but they would have to be alot incorrect in order to get a lean misfire.

[pormgb]

Does the engine have its original flywheel?

No, I built the motor from a short block; flywheel, PP and clutch were not bought together.

[pormgb]

VE and/or MAF are incorrect... but they would have to be alot incorrect in order to get a lean misfire.

I also took a closer look at my tune, I must have copied a base tune from a 2002 Camaro and modified it, my current tune is very different from a ZO6 LS6 tune.

I wasn't able to use a LS6 tune, the motor would not run, just started and would not rev then died. What worked was taking all the parameters from an LS6 tune and copying them to the Camaro tune, many items like spark were very different in the LS6 tune.

So far, I have the LS6 VE (added 8% 3200 to redline) and MAF tables and all other LS6 parameters, the car starts and runs, I now have do a CALC VET on the VE MAF and figure out the return to idle issues.

What odd about the vibration is that it varies with the tuned state and with the LS6 VE table the vibration felt worst. I can also clearly hear the motor moaning in sync with the vibration when decelerating, the vibration is the worst when decelerating.

[statesman]

No, I built the motor from a short block; flywheel, PP and clutch were not bought together.

I suspect that your vibration is being caused by one of those three components.