I am trying to tune my car at idle using datamaster/tunercat. I am having a lot of trouble getting it to idle smooth when the BLMs are close to 128. If it is rich it will smooth out. It just surges from 400 to 1200 as it seems to be overcorrecting for the O2 feedback (goes lean then rich, back and forth) and not finding a good idle. I am running a 383 with 8.5 to one compression, with a p1sc at 8psi. Cam is a 218@.05in. 224@.05ex. on 114*. I have rescaled the maf and now I'm sitting at 128 and it won't idle.
Any help would be appreciated,
Botch

 

Idle rpm? Closed TPS timing advance?
Better yet, got a datalog we could see?

 

Do you still have the air pump? If you do thats why 02s are going high and low (supposed to). The problem is its dropping to 400 then right before it stalls it shoots back up. A couple of things will cause this. Have you checked the tps (throttle position sensor), it should read about .6 volts. If it does not you'll have to slot it so you can adjust it till it does. The blue wire is the one to read I believe. Next, maybe it is just having a hard time idling with all that. Adjust it to idle around 1000 in software instead (I think stock is 700).

Hal

 

Cool,
Thanks for the responses guys! I have the idle adjusted up to 950rpm and I have the timing bumped up to 32* w/TPS closed. I think I had my injector constant set too high and that was causing it to surge when it compensated for the O2 readings. How much adjustment is normal for recalibrating the MAF tables? I had to adjust them around 20% to get the BLMs around 128. Is that much adjustment normal? This is my first MAF tuning experience. (SD is what I've been using prior to this)
Thanks a million,
Botch

 

Are your BLMs split at all?

With bigger cams, you should tinker with the individual cylinder fuel trim tables, as different valve timing can affect fuel needs for each cylinder.

I even cleaned up my stock engine a lot tuning these tables!

I'd advise putting them all at 1.0 and go from there.

 

 

How are you determining which cylinders to add/subtract fuel from? Without an exhaust temp sensor on each cylinder it just seems like a crap shoot to me.

 

Yeah, it's not an exact science without an EGT sensor or IR thermo on each cylinder, but you can definitely improve things.

I do it by seeing how the engine feels after the tune, comparing MPG before/after, and checking BLMs. And starting by getting very high/low values closer to 1.0 (recently saw a tune with #7 cylinder at .91!).

Changing my values brought my split BLMs into line and the engine just feels much smoother/healthier.

If you only have split BLMs at idle, then only modify your "at idle" trim table. If you have any large trims (1.03+), take those down first on the side that is running rich. I bet this will help your problem.

 

Oh, I forgot to add: one great way to verify your results with the trim modification is to read the plugs. This could work at idle or after a WOT run.

 

if you can borrow a temp gun you can read it off each cyl header

 

Thanks for the info on the individual cylinder fuel trim. I'll work on that too, but I am really running pretty even from side to side on my BLMs.

It was suggested by a professional tuner to adjust the Low pulse width injector offset table to see if that helps.

I am running 42# SVOs @60psi
fuel pressure.

Does anyone have any info on this table? I don't want to hurt anything, and I really don't know how it works. I have adjusted the Injector offset vs voltage table, but not the Low pulsewidth injector offset table.

The problem came back with the higher boost pulley.

 

At what is your injector constant set? With your 60# of FP, it should be at EDIT: 52.09. If it's not, set it to that, put your MAF calib. back to stock, and see what you get.

 

That's where I started....... LOL..... I went from running that constant, which is extremely lean, off idle, to running a lower constant (49.61) which makes me wonder why the hell it won’t idle………..

I have read so much conflicting info on SVO injectors that I really do not know what is right. Some people say the test pressure is 39 psi and to adjust and other people say they flow 42#s at 43psi so I dunno.

Thanks again for the help,
Botch

 

How sure are you of your fuel pressure? Is the 60# at full vaccum (i.e. WOT) or at idle? If it's less at idle, then yes, you'd need to reduce the constant somewhat.

When you say you ran extremely lean with the 52.09 constant, what were your BLMs at idle and off-idle? If they were good at idle, then it sounds like you need to work on your MAF scaling for off-idle, and/or the off-idle ind. cyl. fuel trims.

And how sure are you that you actually have 42# SVO injectors?

All the SVOs I've read about are tested at 39psi. GMs are rated at 43.5.

 

Well I still couldn't get this thing to idle, so I had a theory I wanted to test. I thought that the recycled air from my BOV might be giving me incorrect MAF readings, since it exits into the intake tube after the MAF. I put the MAF on the pressure side, set me MAF table back to stock and it purrs like a kitten, no more surge.