Unknown Bucking???

[hquick]

I decided to post this here instead of continuing with my trany thread because I no longer think they're related.
I've been slowly tuning for the past few weeks and cannot find the cause of this bucking I'm getting at low RPM high Kpa.
The situation is, as I pull up to an intersection and then go to turn and accelerate...not particularly hard, the vehicle bucks alot.

It seems this vehicle is a one off...there is nothing to compare it to.
Please have a look at my log and tune and see if anything stands out?
Is there something else I should try logging?

[Redline Motorsports]

Can you give some more info about the engine? What plugs are you use and what gap are the set at?

[hquick]

Sorry...I knew I was leaving something out.
98 4x4 Suburban
5.7L Vortec
Mercruiser Marine Intake
Whipple SC
2 bar MAP
NGK...hmmm...TR6 or something (standard type plugs...not irridiums etc)...rings a bell. Sorry, been a while since I changed them. Gapped at .030 I believe...as recommended by many people.
42lb Bosch green top injectors.
4L80E transmission
Running 98 octane fuel

Thanks for taking a look

[hquick]

Frame 4631 - 4646 is where a marker is placed that the bucking was occuring at one stage of the log.

[TAQuickness]

Any chance you have a '98 RR?

I had a very similar experience with my 383 and it turned out to be a combo of the throttle cracker, spark, and commanded AFR. Looking at my logs, nothing seemed out of the ordinary, but by focusing on each of the three above with the RR, I was able to, by trial and error, find a happy medium that eliminated the bucking.

[hquick]

Do you mean a 98 Road runner?
No...I'm running a 99+ 0411 PCM.
I think I may be able to convince Jez to let me hook up his RR again. :master:

Thanks

[TAQuickness]

I'd throw the RR at it. The low load bucking can drive you nuts fast with the log/tune methods.

[hquick]

Last time...we thought we'd sorted it with the RR. It doesn't happen every time.
Is there something else I should be logging?
Misfires?

[Doc]

I take it you are trying to do a OLSD tune here? I do believe that P0101, P0102 and P0103 -the MAF performance enablers need to be set to "A: 1 Trip Enabled" in order for the MAF to fail and truly enter SD. Until then I think you are just in some quazi no man's land where the pcm is really confused...Not truly being in SD or MAF operation.

I do see you have the P0102 failure on you DTC page- I normally see P0103.

Maybe somebody more informed can elaborate on this...

However, in the frames you referenced in this post you are somewhat rich during the bucking event. I did notice a couple of really lean spots (tho with low counts) Specifically at the 1200rpms 65-70 MAP.

Overall, your commanded fuel values in B3647 seem kind of strange. Are you viewing your commanded fueling in EQ ratio or AFR? In the tune tool under properties, Display Commanded Fueling should be set to EQ Ratio.
The only reason I say this is because when I "flipped" that feature to AFR(you have to close the tool and re open it) then the commanded fuel values looked more in line with what one would expect to see for a setup like yours.

I have found bucking usually come from an unintended error in commanded fuel, air or spark. Spark seems to be fairly steady in the highlighted area

I didn't see any WOT during this latest posted log. Did you ever do so? In this log that is??

Finally are you using a V1 or V2?

[hquick]

Thanks for looking Doc.
I'll check into the things you mentioned.
Yes I'm attempting an OLSD tune.
I'm viewing commanded fuel in AFR. I was viewing in EQ but it was recommended I change to AFR.
I haven't tried any WOT (basically I'm scared). Lol!
I'm concerned about detonation and the amount of KR I'm seeing and am worried I'll do some damage. I'd really love to be able to plant my foot...even just once. Lol!
Oh..and I'm using V1 running cos3.

Thanks

[Doc]

Have you calibrated the voltage/ground offset in for the V1?

Read Appendix B of the Tuning manual about displayed commanded fuel values for a more refined definition but here goes my caveman version.

The pcm can't do the math. It needs to "think" in simplistic EQ Ratio in order to get the final commanded fueling from the base commanded value (in your case w/ the COS, B3647) and all the adder/subtractor modifier tables. If you or the pcm trys to add/subtract AFR numbers together you/the pcm will not end up with what you think you are getting- once again see Appendix B for a clearer example.

[hquick]

I Just read the appendix Doc but I don't see how I go about calibrating the voltage/ground offset.

Thanks

[5.7ute]

Howard, are the outputs from the plx adjustable like the lm1 ?

[hquick]

Hmmmm...I don't think so. I don't see any adjustment. They're supposed to need no calibration. Jez also said the guage was perfectly matching the data on his RR.
He said he screwed his up trying to cal it...so don't do it????

[5.7ute]

Shouldnt be a problem then. I think what doc was referring to was your actual AFR may have been different from what your wideband was reporting. Is your VE table coming into line better with the correct IFR table?

[hquick]

Here's a log and tune from this arvo.
I made some minor changes before driving home.

Frame 5189 is where I placed a marker as it was bucking.

[Doc]

I Just read the appendix Doc but I don't see how I go about calibrating the voltage/ground offset.

Thanks

Invariably, you are going to have some sort of ground offset on your analog output line going into the V1's analog input line. Since we are only talking about millivolts here, the offset can make a difference. Basic WB operation takes the readings from the sensor digitally and then converts the signal to an anlog output and a digital output. FlashScan V1 and V2 currently use the analog information. You can get the digital information straight from the controller via the USB o/p and read it with the sensors' proprietary software. Uncalibrated, you will observe a noticeable difference in readings btw the digital and analog (USB vs. Analog in on your V1). Calibrating or accounting for the offset will narrow the split btw the two for more reliable WB02 readings overall.

For the V1 you will have to modify the sae_generic.txt file for the PLX once you have done the cal.

I am not intimately familiar with the PLX but there has to be some sort of control in the setup software where you can define what the analog output voltage is accross the fuel spread. Set the PLX to command 1 volt thru 4.5 volts in .5 increments (ex. 1 @ 10afr and 1 @ 20afr)(so no matter what AFR is actually present you will have a flat dc voltage o/p) read the actual values the scantool is reading on the data page. Take the average of the readings difference and edit the sae_generic.txt file accordingly.

The nice thing about the V2 is you can do the cal via the scantool page.

This ground offset thingy is why you read about people clamouring for the digital direct capability that the V2 will offer in the near future with V8.

Did the info in Appendix B make sense? YOU MUST GET THIS PART!

[hquick]

Thanks again Doc,
yes the info did make sense.
I'll look into the cal process.
Jez took a look at my tune and pointed out that the low and high actane tables were quite different.
He then altered them a little and I tried this tune and achieved the resultant log.
Some detonation where the 1's mark the log (ie...push the 1 buttonand it takes you to that section of log..push it again and oit moves to the next marker etc).
I didn't notice any bucking this time.
Tomorrow morning will tell!

[jfpilla]

I've never seen a desired airflow table(B4307) with values that low. Are those stock for your car? If not, suggest you try a stock table for starters and see what happens.

[hquick]

Had a good run this morning.
No noticable bucking...but the run home will really be the proover!
A little KR but managed to get my foot to the floor this time.

[hquick]

Thanks jfpilla.
Those figures were derived using the RAFIG/RAFPN process.
Could they still be wrong?

[jfpilla]

It's worth trying. Desired airflow is important. Often when it's very correct other tables stay stock.
I prefer logging IACDES_B (IAC AIRFLOW) and using MAP B4307 A/C off RAFPN.
Start with the stock table and make the same additions or subtractions to both columns. Log from startup and idle to at least 92*C. I've never not had to finish by SOP.

[hquick]

Hmmm...still bucking!
Still looking.
How am I ending up with numbers as low as 10 or less AFR?

[hquick]

I logged IACDES_B and when using MAP B4307 A/C off RAFPN, these are the numbers I get.
-0.378317
-0.833999
-0.651416
-0.757419
-0.829980
-0.830892
I'm still getting the same bucking.
Here I marked it right as it was bucking at frames 7565 and 7571 ???? I don't see anything.

[hquick]

And here's another log...I changed the PE delay from 1 to 0 as per one dc_Justin's suggestion in another thread in order to get rid of the lean spike as I touch the accelerator whilst cruising.
I got some bucking at frame 7131....there's 3 markers next to eachother. I was hitting '1' as it was bucking.

[hquick]

Hi All,
thought I ought to post an update.
Found the cause of bucking...or so it seems.
I had a heater hose running against the ign module/coil.
Moved the heater hose away and no difference.
Swapped coils and it seems to be fixed.
No bucking in 3 days....and I tried to force the Burb to do so.

[stroker97k1500]

YEAAAA!
Congratz!
:cheers:

[joecar]

Howard, good job... :cheers: :cheers:

[hquick]

Thanks guys....I'm pretty happy I found it. VERY happy it's not the trany.
Now...back to tuning.

[dc_justin]

Congrats on finding the problem howard! :cheers:

[hquick]

Thanks Justin....and to all who offered advice.
I was just discussing with a friend...I might put he old coil in and setup a camera under the hood at night. It'd be pretty interesting to see if there's any arcing going on.

[JezzaB]

YESSSS!!! Top work Howard.

Jez

[SSbaby]

hquick

Great that you fixed your bucking issue.

On a side note, is there any good reason why the Lo-octane spark table has higher values than the Hi-Octane table?

[hquick]

I've been playing with the timing to try and reduce/eliminate KR and at present all timing is coming from the high octane table so the differences don't matter. Thanks for looking though.