mrmint69

I have a problem. I had the car tuned after going from stock to 42lb injectors and removing the fmu. My datalog it showing knock retard of 4 degrees and has never happened on any of my numerious runs i have recorded. I have TTS Datamaster if anyone would like to see it and help me out.

LSWHO

Are you running lean? Have you tried richening up the mix?

mrmint69

I looked at the datalog and at the exact split second the knock showed up the Barometric pressure reading went from 96.3 to 104.4. It was always the same and never changed back. The entire datalog is 2 1/2 minutes long. How do i tell if its running lean since its in cell 15 and everthing shows 128's during wot. The blm's are usually high on one side and low on the other and sometimes they read 125 then go to 135 and back down to 125 over and over again.

Injuneer

If you're running boost, it wouldn't be unusual for the MAP sensor to max out. Or do you have a 2 bar MAP sensor conversion/tune? Has the PCM been tuned for the boost, or are you running a boost referenced fuel pressure regulator or FMU? Are you sure the BTM was working and pulling timing?

mrmint69

The map is standard and i filled out the ordersheet listing everything in the mods below. The fmu was removed when i got the tune. I have the btm turned down to zero. I haven't had time to play with it to see if turning it up will help.

Injuneer

Retard the timing and see what happens.

mrmint69

I checked the datalog and let it run for 30 seconds showing the histogram enhanced view and it showed 8 of the 9 cells that were used all being very rich with one being only rich once i got over 1600 rpm's and 30 grams of air flow. I know they make it rich so it won't damage the engine so some more tuning is necessary. I guess this is good news because i made no power increase with the tune. Some more work will help a lot at stabilizing this and getting closer to the ideal mixture.

Kaj

Yeah, I agree injuneer. Try retarding the timing, and are you running colder plugs?

Injuneer

The long term fuel correction cells are developed at part load driving (closed loop operation)... not at WOT. Under those conditions, the PCM tries to maintain the stoichiometric A/F ratio, which is 14.7:1. That's the A/F ratio the catalytic converter requires to operate most efficiently, and also give reasonable fuel economy. That is hard coded into the PCM and a tuner does not change it. It is not "programmed rich to protect the engine" in closed loop.

What DataMaster is showing you is that the PCM is being forced in part load driving to add or subtract fuel to maintain that 14.7:1. If you look at the long term fuel corrections for the various cells in DataMaster, it will tell you if the PCM is having to add or subtract fuel to maintain the required A/F ratio.

All this has very little to do with what happens when you go WOT. At that point, if the PCM was adding fuel in the high load cells, it will use the long term fuel corrections from Cell 15. If it was cutting fuel, it will use Cell 15 but lock the long term at 128, or under certain conditions use Cell 18 and lock the long terms at 128. The programmer wants to get his programming correct so the long term fuel corrections are as close to possible to 128 (0% correction). That way, when the engine goes WOT, and switches to a richer, power/torque producing target A/F ratio, it can be accurately controlled with the PE (power enrichment) tables, which are what determines whether its running too rich or too lean at WOT. That's where the factory tuning is "programmed rich".

If I recall correctly, I saw you tell someone in another post you had a leak in the exhaust or EGR or something that you needed to fix???? An exhaust leak screws up the closed loop A/F ratio and throws the closed loop operation off, causing it to run richer than 14.7:1. That can hurt at WOT, but running rich doesn't contribute to knock, it helps prevent it.

Knock is typically caused by too much timing, low octane fuel, excessive compression ratio (or boost in a forced induction setup), high coolant or intake air temps (a blower hurts two ways.... high compression and the inefficiency of the blower heats the air up), or a lean condition. A blower car needs to run a lot richer than an NA setup to prevent detonation (knock).

That's why I suggeted you crank up the BTM, to pull some timing out as boost increases. I gave you the link to the MSD 6BTM operating instuctions in another post. You shouldn't need the BTM if the tuner got the timing tables set up right, but I suspect its tricky to mail-order tune a blower car, when you are still running a 1bar MAP sensor... but I'm no expert in tuning the stock PCM or in tuning forced induction, so I don't know.

'94 Bad A Z28

Why don't you jest send your datalog to Bryan and tell him what the car is doing so that he can try to correct this? Bryan is usually pretty good with correcting his tunes.

mrmint69

I am going to fix the exhaust leak this weekend so when i send in the new datalog he can adjust it correctly. I think if i remember correctly the stock map is fine with the boost level im running

Injuneer

If the stock 1bar MAP sensor is "fine" with the boost you are running, you aren't running any boost. Yes, you can have the PCM tuned to run the engine under boost, but when you look at the MAP on a scanner, it is going to max out right after the engine goes into boost. A 1bar MAP sensor will be close to max'd out at WOT (at sea level) on a normally aspirated engine. With 6# of boost, at WOT/max RPM your MAP would be about 140kPa. A 1bar MAP sensor can't read much over 104kPa. Your data indicates you have max'd it out.

mrmint69

I drove the car over 50 miles yesterday and then ran a datalog and i did the Histrogram and of the 25 hits on the right side it showed all the long term cells running at 128 and the left were all at 138. I then realized the car was still in open loop. These should all be at 128 right? I then checked all the long term cells in closed loop and the right side was almost perfect but the left side had a bunch that were lean. The short terms cells had lean at lower rpm's and rich at higher rpm's.

Injuneer

In open loop, the stored BLM's (long terms) will be used. They can be any value, unless you just happened to reset the PCM before you started the engine. In that case they would both be 128. Only the INT's (short terms) get locked at 128. Did you read my scanner guideline? You seem to be struggling with interpreting the data, and most of this is covered in the writeup.

Did you fix the exhaust leak yet? The leak will cause elevated BLM's.

mrmint69

I fixed the leak and will get it retuned soon. Thanks for the help and putting up with my lack of knowledge in this subject.