I have had this persistent issue with my truck since i bought it and I cant figure it out. It seems to drop a lot of timing for a second and the truck feels like it ran into a big gust of wind and slows down for a second. I notice it more on the highway.

I scanned it the other day and I cant seem to see anything out of the usual. If you look at the scan, there is no definitive action that causes the timing to drop sharply and resume. I also noted a 4.5 KR hit that was caused at constant speed/tp. this hung and slowly trickled off. I can't reproduce it on command and seems to come and go as it pleases.


Anyone see anything that i am missing? I dont want to start throwing parts at the truck and I am not getting any reports on the DIC. Anyone have a clue where to start looking? I have yet to start messing with things, but my first place will be to go through the spark plugs and wires and then take a look at the TPS which seems (to me) to be a little irradic. (prob not the cause)

Take a look at frame 3700 and beyond for the timing drops (where i am feeling the "gust of wind") and 2500 for my giant KR hit. this is a cruise to the highway and a little short constant speed run. basic driving with a little jump on the throttle in the middle.

truck is an 01 EX 4.8l with corvette servo... AKA stock.


appreciate it in advance.

 

I'll bet your AC was on, wasnt it?

The knock could be false knock....notice how it linearly decreases. If it was real knock, it would look like stair steps.

The computer pulls timing slightly when the AC clutch engages, you can change that if you want.

 

Are you telling me that the AC is engauging and disengauging every 20-50 seconds? Does it really pull nearly 20* of timing each time that it does it? If you look at frames 3700 and beyond on the scan the timing is a serious drop over and over. Im not cycling the AC on and off, so what could cause this?


I wonder what would cause the false knock. To me, 4.5* is quite a bit for false knock. Are you thinking thats its electrical and not a mechanical cause for the false knock (like exhaust banging or loose bolt on accesory). Right now, I'm not concerned with chasing it down, but I brought it up to see if it could be linked to the timing drop.


Thanks

 

The AC compressor cycles on and off, yes. Your not manual turning it on and off on the controls, the computer cycles it so it doesnt over pressurize, this is normal. Post up your tune file.

 

Interesting. Ill have to grab the file and post it up in a few.

Hope I still have enough credits...

 

Got it.

BTW, I have had some issues from my AC... It stopped working for two days straight, then came back to life. I also turned it off today and is still stayed cold and "kicked".

What is the AC controlled by? Is it the bcm or something else?

 

Alright went in and did the usual... speed limiter and bumped the idle up as a temp fix for a little dip im getting.

Went in under the timing table and disabled the ac bump tq spark. Ill try that...



BTW... Holy hell there are a bunch more tables for me to play with than what
i am use to with the 3.8l V6's. You can actually adjust how the computer calculates the data from the fuel sender...

 

haha, yea there are a lot of tables to play with. ac bump torque spark under engine > spark control > spark advance is what you want

 

done and tested... Worked like a charm...

I also bumped the a/c disengage down and the TPS disable down under the system section for a/c.

Appreciate you help.

 

No prob

about those AC settings....there is a big debate on the hpt forums about if they even do anything at all, and their labeling isnt exactly self-explanitory.