Rpm drop when stopping.

[NickTransmissions]

I have a TECH2 and Snap On Verus so between them we should be able to gather some useful information...let me know..

 

[Hodgeee]

Holy poopies, im in the stone age compared to you. Ill send you a message.

 

[Hodgeee]

Interestingly, i have a friend mechanic that works at the local Chevy dealer. Turns out that he is pretty good friends of the main mechanic that does all the Police Tahoes under contract. He took the truck first thing this morning, went over everything he could related to the braking issue, testing all sensors and main electric components. He found nothing wrong, BUT, he found that the fuel pressure would drop at the last few moments to 43psi from the steady 48psi, when braking. He said 43 to 48 is right in the range of where Flex Tahoes are supposed to be, but said there is no reason the fuel should drop. After stopping, the fuel pressure would immediately go back up to the 48psi. BG1988 stated that it was the DFCO, the mechanic stated the same, and stated it may need to be reprogrammed, but unsure, he believed that only the Hybrids had it. He asked if anyone I knew used HP Tuners and could turn it off, or reprogram it. I dont know anyone who does, but the local shops told me $580 to program it. He then also told me that in nuetral and manual gear selection it is deactivated but only on hybrids again. He said if it is on mine, there are no specific alternate settings, just turns on at about 1200 to1600 rpms, and turns off the same. This would explain why mine does it in nuetral or manual gear select. He stated on 2013 and up models, they added Hill assist braking, that auto down shifts your tranny so you dont go over the listed speed of the cruise control.

I don't suppose anyone in Vegas in the Forums has HP Tune?

 

[Dustin Jackson]

Interesting

 

[Hodgeee]

Just wondering if anyone else has vapor lock issues, not the topic of this post. We had a break from the normal 105 degrees today, it was rainy and overcast and was only 78 degrees outside this monring. While running errands, no idle issues, and the rpm drop at braking, seemed noticable less. Still there, but not the vehicle shuddering at every stop like usual.

 

[Dustin Jackson]

@Hodgeee Back when I had Cherokee XJ's vapor lock was a common problem with the 4.0 straight 6 motors, amazing things by the way. I have never heard of vapor lock being a problem with these motors and I've been a member of several Chevy forums for the last 4 years and haven't heard a peep about vapor lock until you mentioned it. I am open minded and haven't jumped to discount your concern but this is my experience of the subject.

 

[Dustin Jackson]

To add to the vapor lock subject, It was a problem when turning off a hot motor and attempting to restart the motor again after the gasoline had a change to "cook" above the hot motor. People would have difficulty starting their vehicles after shutting them off when it was really hot outside.

 

[Foggy]

The DFCO settings aren't doing it... The DFCO kicks in rarely and usually only above
about 1600 rpm. I actually set my DFCO to be MORE reactive to try and help out
my fuel mileage when i cammed it and got rid of the DOD crap

 

[Hodgeee]

It aint bad, once again, the weather was cool today, only 90 out, and the problem was much less noticeable. Plus raising the idle rpm to 600 made it drive better, and less affected by the rpm drop. Im kind of accepting that its normal maybe. Just waiting on the new AcDelco TB. mine is Dorman, and the one i tested out was a Dorman also.

My chevy mechanic friend told me that the reset procedure doesnt work on non Gm throttle bodies. He said when he tried the reset on the throttle body, the scan tool stated incompatability error. He is wondering if the TB is off a little and not allowing the computer to adjust it properly. I forgot to add that in my previous post. Ive also read the aftermarket TB dont work the same as oem on other forums, and Youtube.

 

[swathdiver]

He stated on 2013 and up models, they added Hill assist braking, that auto down shifts your tranny so you dont go over the listed speed of the cruise control.

GM calls it Cruise Grade Braking - Normal Mode. Older GMT900s have it in Tow/Haul Mode as well.

These trucks run at 43.5 psi with little fluctuation on a good pump.