Kick down mystery

[bad larry]

Alright...so.. I've read that on TBI trucks that the kick down is controlled by the ecm. My question is what information (sensors) are telling the ecm its time to innitiate the kick down? My truck seems to be downshifting a little too late for my taste, no one else would prob notice but I do.. I know I've got to open up the gas tank and replace the fuel pump sock/filter and I'll prob do the pump while I'm at it.. Do you suppose low fuel psi could affect the kick down via TPS somehow? Like since I've got to press down more than normal because of low FP than somehow its kicking down late or something like that....?

 

[boz42]

I am guessing we are talking about your crew cab, but...

What year? which transmission?

 

[bad larry]

I am guessing we are talking about your crew cab, but...

What year? which transmission?

Yeah, you got it, sorry I took that for granted... 1988 v30, TBI 454, th400, np205, D60-14bff 4.56's...

 

[boz42]

Don't worry I do that all the time.


Th 400's are not ecm controllled. They run off of vacuum & a govenor.

What size tire, & what gear in the 14 bolt?

EDIT after reading first post again:

T-400's do have an electric kickdown, but that is only for wide open throttle. I am not sure if TBI trucks ran that off the ecm or not.

 

[Greg Ducato]

There is a switch mounted above the throttle pedal in the cab with a post that intersects the throttle and activates a 12 volt signal to the trans when the throttle is fully depressed. Make sure your throttle is fully depressing the switch, sometimes you will need to wrap a short piece of rubber tubing around the switch post so it makes contact under wide open throttle. Vacuum will also affect kickdown at lower vehicle speeds, check your line to the modulator and make sure it isn't coked up with carbon at the engine side, check the nipple into the intake as well. The TCM or TPS have no control over the trans in this application.

 

[bad larry]

Th 400's are not ecm controllled. They run off of vacuum & a govenor.

What size tire, & what gear in the 14 bolt?

EDIT after reading first post again:

T-400's do have an electric kickdown, but that is only for wide open throttle. I am not sure if TBI trucks ran that off the ecm or not.

There is a switch mounted above the throttle pedal in the cab with a post that intersects the throttle and activates a 12 volt signal to the trans when the throttle is fully depressed

Thanks boys, I am aware of the WOT kick down swithch at the pedel. Im not sure if my WOT kick downs are affected(been a while since I let-er-have-it!) but I would assume they are.. I do however know that part throttle kick downs are def affected. I failed to mention that I installed a ATP adjustable vacume modulator last week to bump the shift points on upshift and again not to sure if down shift is inversly affected; no mention in the literature that came with it or from what I have read for that matter.. Greg thanks, I'll check the line a maybe flush it w some solvent. I've got a transgo pro 400 kit sitting on my table, maybe I'll install it this weekend..

 

[Greg Ducato]

The factory lines neck down at the ends and this is where the clogging usually occurs. My advice is to use a tubing cutter and cut the line just in front of the flare, leaving the flare but eliminating the necked down portion. Then give the line a good spritz internally with some carb cleaner, followed by a little air dry and blow out with some compressed air.

 

[bad larry]

My advice is to use a tubing cutter and cut the line just in front of the flare, leaving the flare but eliminating the necked down portion. Then give the line a good spritz internally with some carb cleaner, followed by a little air dry and blow out with some compressed air.

Roger! I'll take a look.. BTW how common is this symptom? If frequent, are the traits I described the usual ones..?

 

[Greg Ducato]

From what I understood of your post, your trans is not kicking down as soon as you would like it to, meaning you have to crowd the pedal further to get the trans to drop to a lower gear. Is this correct?

 

[bad larry]

From what I understood of your post, your trans is not kicking down as soon as you would like it to, meaning you have to crowd the pedal further to get the trans to drop to a lower gear. Is this correct?

Yeah, you got it Greg, you are correct..

 

[Greg Ducato]

Then , yes, this is a pretty common occurrence in a vehicle such as this and you are on the right track by checking vac lines and kickdown switch adjustment. It would still not be a bad idea to check fuel pressure as this leads to a loss of power and may be contributing to what you are trying to describe.