Country Boy

iTrader: (24)

Here the deal.... My car is a built forged motor H/C car with a HUGE cam... say about the size of the TRex, and when I drive around <3000 RPMs the thing just bucks, backfires, sputters like its losing track of itself (if that makes sence). If I give it some gas, it quits... I was outside watching somethings via Autotap and I got it to do it some while holding the throttle steady ~2400 RPMS and the only thing I noticed was the timing went from 40*s to ~28*s for the split second that it happened. Ive also been throwing the P0101 and a P0121. I logged the MAF flow rate and its constant and the TPS voltage stays steady also.... The only thing I can find is the timing comes way down for some reason. Any ideas as to why? Maybe a crank/ cam sensor going bad? I thought maybe the MAF was going bad, but it reads steady and doesnt jusp drastically....

Bink

what are your ltfts showing?? have you had it tuned since the cam install??
Big cams need more tuning...especially for under 3000 RPM

Country Boy

iTrader: (24)

Its been dyno tuned but Im not too sure about the VE tables.... Would the VE tables clean up the problem? I know timing and fuel have been tuned and the AF under WOT is all good.

Bink

Apparently above 4000 RPM fueling is directly through the MAF and PE tables- Dyno tune for WOT. Below 4000 RPM there are various calibrations to compensate for the inaccuracies of the MAF - these involve the VE table. So if your VE table is drastically inaccurate, due to Mods, then your Fueling will be off. Do you have a Wideband O2?
With a Wideband you can get a better look at what's occuring.
joel

Country Boy

iTrader: (24)

Nah, I dont have a wideband It would be nice, but $$$. My tuner said that the computer only uses the VE table for cranking since it says "Cranking VE" I believe. I thought about getting the HP Tuners tuner and going at it myself.... Its just all those formulas for VE are intimidating

So... If the VE is way off (and Im sure it is) it can cause the problems I have?

Bink

Yes, the PCM does use the Cranking VE table for cranking. It uses the Main VE table for fueling. You can pretty much "cookbook" a new VE table using a scanner and ChrisB's LogFile Analyzer. Can you beg or borrow a Wideband??

Yes, with a big cam it will cause the problems you have.

Country Boy

iTrader: (24)

I may be able to get use of a wideband. Itll be a couple weeks though Where can one get ChrisBs Logfile Analyzer? Thanks for the help Bink

GrannySShifting

iTrader: (10)

What is a rough amount of fuel youd generally needs to add to the low mid rpm tables? talking 5%, 15% or 25%?

HumpinSS

iTrader: (1)

Log as much data in Atap or Efilive as you can export the log file to csv format. Remove decel cell 21 and 23(if using atap) and import into ChrisB's program. Should be straight forward from there


http://automation.slowcar.net/

Bink

Can't speak in generalities when adding fuel above idle RPM. Sorry.

Bink

You're welcome. Yes, to what HumpinSS says.


joel

ataylors

iTrader: (2)

Has the car ever run right? Or has it been doing this since the cam, etc install??
If you think it might be the cam/crank sensor you can usually watch the rpm and when it starts doing it the rpms will be erattic too. Also watch for false KR