ok so i am trying to follow the writeup on the hptuners site for tuning LTFT by unplugging the maf...

http://www.hptuners.com/forum/YaBB.p...num=1101426165

i followed the steps listed: disabled the SES light for codes p0101 p0102 p0103, copied the high octane table to the low octane, flashed the pcm with the new tune, unplugged the maf and started the car up to go do some logging. one problem though, with this setup my service vehicle light comes on (NOT the SES light), but if i plug the maf back in and upload the older tune the light goes away. will this affect my logs for tuning the VE table? i did a search but i haven't found any posts about a service vehicle light coming on after disconnecting the maf. thanks for any input.

 

Don't disable the codes... those codes (at least 1 of them) needs to be set to cause the PCM to failover into Speed Density Mode...

doesn't matter if the SES light comes on (those instructions appear to be setting it so that the code is still set... but it doesn't set a light) ... I prefer seeing the light as it gives me a visual cue that I'm running in SD

Sounds like you're actually turning the codes off/disabling them from being set .. so the PCM won't failover ... so it's trying to run off a non existent MAF signal ... since it's not failing over it doesn't know what to do so it sets the service vehicle light

 

well, i thought i just disabled the SES light, but i guess not lol. anyways, i re-enabled them and im just going to do it with the SES light on, no biggie. thanks for the help

 

also... you can set the MAF Fail Frequency value to 0 (I think it's under engine diagnostics) and this will cause a P0103 ... puts you into Speed Density w/out having to pop the hood and disconnect the MAF

 

That's a good idea horist. I guess then it figures out to go to speed density instantly?

 

yup

 

i ended up doing this, worked good. thanks again for the replies

 

Go ahead and tune out the annoying light...leave the code. You'll know it is right when it still shows a code in the scanner.

 

So you can set the maf fail frequency by itself instead of dealing with changing all the other codes? Basically taking care of alot of hassle...

 

I just tried this tonight and it seems to work fine. Connect the MAF back up and change the table mentioned above to 0. You will need to either put the car in open loop or closed loop depending on how you plan on tuning the car. (I prefer open loop). Nice thing about this is you still receive the readings from the MAF like it is connected.

 

Good stuff...I haven't been able to try this yet myself seeing as how the car is down. But, if enough of you say that it is working, then I will change the write up to reflect that, as it is an easier change.

Matt

 

Open loop speed density...sweet. So are you just clicking the ltft disable button or are you unplugging your o2 sensors or what?

 

In the scanner tool you can force the car into Open Loop

 

or change the closed loop enable temp to 254

 

Nice going. Looks like a really good find. I tried only 0'ing the MAF, today and found the following.
-With EFI I could log accurate VE's even though MAF doesn't log.
-I adjusted VE values.
-Trims will log.
-It seems we can observe trims without the MAF, determine how close
the calculated IFR's are to correct and set the IFR's. Program the MAF back
and see the affect on trims by the MAF.
-Does this make sense?
PS. SAE MAF can be logged, not GM.

 

Yep. I had a feeling there was a way to convince the PCM to allow you to read dynamic airflow and MAF frequency at the same time. I'm glad somebody out there was smart enough to figure it out!

 

YOu can also use this method to derive a good workable MAF table. I posted about it a few days ago but no one was interested. All you need to do is log dynamic air and plot that against maf frequency and you will see how far off the maf really is

The trims still update wit the maf diosconnected so you will still be able to have all the fruits of live forcing the pcm into SD mode

 

Also dynamic air is back calculated from the ve values, iat and map values....

Bes tthing would be to dial in the ve table in forced SD mode and then use the dynair/g per sec to figure out a new accurate maf table

 

Precisely.

 

I'm interested.
I think when you say disconnected it's confusing. May be the reason for no response. With no MAF you can't get VE's or MAF frequency. With the MAF zeroed you get it all.
What caught my interest was realizing IFR's could be checked for correctness. I'm not sure of the formulas and their accuracy for calculating IFR's for bigger injectors. This new idea seems very important to me. If VE's are corrected then IFR's can be set with the MAF 0'd. When the MAF is hooked up again the trims should then reflect the inaccuracy of the MAF. My hangup is IFR's since if they are right setting AFR gets easier.