Kevin Fodge Jr.

Hey guys, I just started to tune my first motor, and I believe I had a backfire through the intake, I don't have a wideband yet, but my fuel trims were all out of whack (10-30) so I figured I needed to add lots more fuel. They're still relatively high, mostly under 10 though; I can't seem to get them to a comfortable range, they just bounce right back up next drive after even more fuel(yes, I'm resetting fuel trims). My question is, I haven't disabled my maf or power enrichment yet, could that be hindering me so much that I can't get them even close? Also, I haven't messed with the spark tables yet, but I see advance values as high as 40+ under light throttle, does this seem like it could be part of my problem? I haven't noticed any spark retard though, so I didn't feel that it was a problem. I can't attach logs with the post because I'm not on my laptop, but if anyone wants to see them I'd be glad to go fetch the laptop. Any help you can offer is greatly appreciated!

Kevin Fodge Jr.

Here are my 2 latest logs. I almost forgot, the engine is an LQ4 bored out .030" with a mild cam, I'm not exactly sure of the specs off the top of my head though. Also note, it didn't backfire in either of these logs. It's very sporadic and I haven't managed to capture it in a log yet

DFORESI

To answer your question, 40 degrees of timing at light load is normal.

What is the starting point for your tune, are you using the factory file?

It sounds like you need to take a few steps back and work on a tuning strategy. I would suggest starting by disabling the MAF and working on tuning the VE table. ChopperDoc has a good youtube video on this.

DFORESI

I missed your other question. Please be aware that you CANNOT tune performance enrichment operation with the fuel trims. You MUST have a wideband.

When you enter PE your system will go into open loop, meaning that it is not looking at the O2 readings, so it will not populate the STFT or LTFT when PE is active.

Finally, if you are going to attempt to tune light load areas of the VE table with the trims your best bet is to TURN OFF the LTFT or it'll make your life miserable.

Kevin Fodge Jr.

Thanks for the reply! I turned off my maf and pe today, and I wasn't able to accomplish anything other than making it backfire more often and realize I was pushing WAY too much fuel. Although on the plus side, I did manage to capture a backfire or two on the log. I thought the best way was to log ltft and stft together?(besides having a wideband, obviously) I was hoping to be able to tune it myself, but since anything I do seems to make the problem worse I'm going to try and get an appointment with a pro tomorrow. I feel that I have a decent grasp on the fueling aspect, but it's the spark aspect of things that has my head spinning

Kevin Fodge Jr.

Also, yes I'm using a stock 6.0 tune for a base

DFORESI

Yea I think you might need to do a little more research before trying to tackle this. Also, you really shouldn't be turning off PE. Yes, turning off PE will keep you in closed loop and allow the trims to work, but it will also help you destroy the motor a lot quicker. You need the extra fuel at high loads to keep the engine cool and to prevent it from knocking. This stuff gets complicated and replacing an engine isn't cheap. Leave PE enabled.

As far as your motor setup goes, you mentioned it was bored out, did you change the engine volume in the calibration? Changing the volume will necessitate changes to the airflow calculations.

DFORESI

As far as spark is concerned, if you're worried, you can just grab the whole high octane map (out side of the idle area) and dial spark back by 15%. I really think fueling is where you're problems are, not spark. Timing isn't going to change much with your setup, BUT you will want ALOT more timing at idle with a big cam. Stock is probably around 12-14, I would start by bumping it up to 20.

Kevin Fodge Jr.

Where do you suggest I set the PE while tuning? I usually have it set at 40%; I didn't *actually* turn it off; although I might as well have, I set it to 90%. I didn't change the engine displacement in the config only because I didn't think it actually did anything. I agree, I don't want to have to rebuild this engine anytime soon. I think I'll pull timing from most of the table(besides idle) and give VE tuning another try after I read that guide you mentioned before I bring it to a tuner. On a side note, I just checked my spark table, and my engines idle range(.08-.28 grams all the way to 800 RPM) was already set to 20. Is the general idle range actually larger than that?

ChopperDoc

To do this right, order a Wideband. It’s a small price to pay considering it’s typically half the cost of a cam. I’m all for saving money where possible but having accurate fueling data is priceless and can potentially save your engine. Don’t get cheap at the end and try and tune without one, especially in PE, since you won’t have any data and will be just guessing basically. The guides are in my sig, and for the displacement, yes that matters on gen III PCM’s. VE is a representation of % vs the ideal gas law. Volume is part of that formula, just saying.

PV = nRT.... moles x 28.97 x % VE = g/cyl.

ChopperDoc

I replied from my phone and see my sig didn't appear... Check out the guides, so you'll have a general understanding of how to tune the VE. Experience is the best teacher though. And I still say go ahead and order that WB before you have a bad experience here.

ChopperDoc

Here, I threw this together for you to play around with. VE is a theoretical table, and this is the formula for it. This should better your understanding of it. Since heat plays a vital role in calculation, some errors can be expected due to temp bias from ECT and IAT. This is a simplified version not including that bias. By the way, K (kelvin) is simply degrees C + 273.15. So if it's 20 degrees C, that would be 293.15 K. This isn't for tuning, just to be clear. Just an understanding of how it works. Use your IAT temp from the scanner in K.

Kevin Fodge Jr.

Thanks for the advice! I have a wideband, and my appointment to have the bung welded into the exhaust is Wednesday. So I'll be all set then and I'll just need to figure out how to log it in hptuners. I couldn't find the youtube channel, but I'll look at the guides in your description

ChopperDoc

I touch on how to log it in the VE guide. Not sure which MPVI you have, but I cover how to do it for the MPVI1, which has 4 analog inputs, 1-4 which makes pin 5 the ground. My understanding of the MPVI2 is it has 2 analog inputs making pin 3 the ground, I would assume. Once you have the voltage input, use the transform function in the scanner for that input based on which WB you have. Most of them are listed in the scanner.

ChopperDoc

Here’s the video...

https://www.youtube.com/watch?v=vAQh...ature=youtu.be

DFORESI

Just to clear up potential confusion. Moving PE out of the way is technically a method that you can use to tune the engine with the fuel trims. That being said, I've heard it jokingly referred to as kamikaze tuning. I think most people around here would advise against it.

Realistically you just want to leave PE where it is (or potentially move it earlier depending on where your engine makes power) and tune your engine as you intend to run it on the street without your logging equipment hooked up. When you tune with the wideband you essentially just want to look at wideband error, which you can do by defining a custom maths parameter in the scanner. The formula I use is as follows:

(1 - ( [68.238] / [36.238] ) ) * 100

68.238 is the commanded equivalence ratio
36.238 is wideband equivalence ratio

as long as you are always referencing the command you can get an accurate error term and then apply this trim to your VE table.

Does that make sense?

DFORESI

Chopperdoc,

I just watched through your whole video, its very well done, but I had some questions for you.

Do you think that with the custom parameter I mentioned in my post above you could avoid having to change the target EQ table for open loop?
I BELIEVE on gen 4 pcms when you disable to MAF you still operate using the high octane spark table. At least, this is my observation from working on the E38. I know the video is for "older GM vehicles", but I thought it would be relevant to mention that as it pertains to the OPs issues.

Kevin Fodge Jr.

Chopperdoc, I have the mpvi2 (regular, not pro, so no analog inputs) so I'm thinking I'm going to use my Arduino to read the wideband's 0-5volt output and convert that into an afr then pipe that data into hptuners. Is the scanner capable of accepting data from a serial port? Update, the backfire was indeed fuel, it still did it when I pulled 15% timing advance across the board, but I followed your video and got the fuel trims to a comfortable range using stfts (-5 to +5) and the backfire stopped! Should I tune the maf now? Or wait until I get my exhaust set up for a wideband? My idle is way smoother at 21 degrees, but it still has some tremble. How much can I advance the timing in this area?

DFORESI

You may be better off order some type of USB adapter that can take in a 0-5v signal. HPTuners can record it right through your laptop, it doesn't have to go through the MPVI.... or at least I don't think so..

Kevin Fodge Jr.

I could pretty easily set my Arduino as a 0-5v pass through, and I'm not worried about the delay being that the program needed would be very small. I just wasn't sure if hptuners would accept a 0-5volt wideband input