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Chips and shift points

8

89Blazin

1/2 ton status
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Hi all.....first post, but have been a reading admirer for some time now. I especially enjoy the quick wit, glowing intelligence, and grease under the ole fingernails of the regulars.

Question: On my 89 Blazer (350TBI/700R) I just purchased, does the chip in the ECM figure in to the shift points for the tranny? Runnin down the interstate at 70 MPH, I come to an upgrade (with the cruise on) and I loose 15 MPH before the downshift to D takes place. Can this be changed by puttin in a different chip? I've heard of this tranny frequently (too often) shifting back and forth D to O and back. Mine never wants to downshift to D, until either I tap the accelerator or let it bleed off 15 MPH and then it downshifts on it's own.

An 85 Burb and an 89 Blazer
One just for fun, one for simple pleazer
 
The chip upgrade is in your head :) No offense, but really, you have to do it manually. Drop the shifter down into 3rd. Only thing electronically controlled on these transmission is the lockup of the torque converter.

Dorian
My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
 
Thanks....lol...first truck with a puter. Didn't know what if anything the ECM did between vacumn and tranny. I looked today in the glove box....GU6,,,,3.42, according to info I read here before (been takin notes). The gearing will be good for me towing the boat (in drive) this summer. It's also my daily driver right now, and in O with 33X12.5s...leaves a little to be desired goin uphill at all. Thought maybe.....nah.

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
You need a big cooler to two a boat with 3.42's...or anything else for that matter...you'd probably be happier with 4.10s and 33's

90K5

See my truck at <A target="_blank" HREF=http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502>http://albums.photopoint.com/j/Albumindex?u=1329584&a=9886502</A>
 
Got 2 big coolers....one up front for the tranny, one in the rear for the beer.....i mean pop.

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
How do the rest of the shifts feel? The TV cable may be slightly out of adjustment.

Is the cruise control compensating for the hill? By this I mean if you lightly rest your foot on the pedal can you feel it going down when you hit a hill? Maybe somehow the cruise isn't "seeing" the hill and isn't increasing power to deal with the speed loss. Just a theory...

crazy.gif
Semper Maintenance!
 
TV cable is fine and the shifts are great. That was a genius thought about checking what the gas pedal is doing...I might be barkin up the wrong tree. I'll be sure and notice....Since I first posted this, I found out my glovebox code = 3.42 gearing. With 33X12.5s, I think that's my problem, but I will watch the pedal to see what happens.

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
My '90 does the same thing with stock tires and gears. I've been trying to figure it out for a year now, with no luck. The cruise works fine until you get to a hill, but it just won't downshift the tranny. I've replaced the control module, vacuum hoses, and turn signal lever, but none of that has helped. I thought there might have been a vacuum leak and the servo couldn't pull the throttle hard enough, but that must not be it.

BONDO WILL FIX ANYTHING!!!
 
My cruise is pullin the acc. pedal in...not very fast, or much.....but it is pullin it. Would a throttle position sensor have anything to do with this? I know there is one and it feeds the ECM. But is the criuse ass'y completely isolated from any ECM control? Does the throttle pos. sensor come into play with cruise control?

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
On an 89, the ECM doesn't control the tranny, the TV cable does. I don't think the 700R4 turned into the 4L60E (electronically controlled) until 91-92. If it won't downshift while on cruise, the cruise servo probably isn't opening the throttle enough to signal a downshift thru the TV cable. Maybe this is some programmed thing in the cruise module for an 89; I don't know. On my 87, the converter will unlock when a hill appears in the windshield when on cruise, and if I'm fighting a headwind on a hill it'll downshift to 3rd.
I don't know what else to tell ya, I've used all my smarts on this one.

crazy.gif
Semper Maintenance!
 
dyeager535,

I don't doubt what you say, but would you please elobrate on what you did say? My '90 Jimmy doesn't shift like what is being described by everyone here. I am running 3.73's with 33's. When the cruise is engaged and I come to a hill I loose very little speed before droping out of od, and will downshift after a loss of 5-7 mph(aprox). What's normal?

Derf00
http://www.derf00.coloradok5.com
"Four wheel drive allows you to get stuck in a more inaccesible place."
 
Mine won't downshift at all unless you tap the pedal. Then when you do, the truck will take right off. But when you come to the next hill, you have to tap the gas again to get it to downshift. It's definitely not in the servo. I replaced mine already and it didn't work.

BONDO WILL FIX ANYTHING!!!
 
In OD....doin 70 MPH....if I come to a steep incline, it downshifts to D real quick with minimal speed loss. If I come to a long slight incline....the speed gradually bleeds off and the downshift to D takes place around 55 MPH. My acc. pedal is very slowly being pulled in by the cruise, where on starting up a steep hill, the acc. pedal doesn't hardly move before a downshift happens....almost immediately upon encountering the steep hill I get a downshift.

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
Sounds to me like you guys are working your trannys a bit too hard :). It should just shift on a whim, otherwise it would shift all the time. Also, don't forget that the unlocking of the TCC can feel like a shift and the RPM will go up. So make sure it's a gear and not the TCC lockup...

Squash
<A target="_blank" HREF=http://www.trailrunners4x4.org/users/realsquash>http://www.trailrunners4x4.org/users/realsquash</A>
 
I'll restate my original question to anyone who will answer: '90 Jimmy, 700R4, 3.73 gears, 33" tires. What would a "normal," shift pattern be? Based on all of the above, some of us may have a problem.

Derf00
http://www.derf00.coloradok5.com
"Four wheel drive allows you to get stuck in a more inaccessible place."
 
I don't know what you want me to clairfy...it's been so long since I had my 700 equipped truck, i don't know what it did. I KNOW that with the 305, 700 and 3.08 gears, I had to get a running start on hills. Dropping the thing into 3rd BEFORE you start to lose speed is going to be easier on the tranny (and motor) than waiting for the CC to catch up.

Dorian
My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
 
OK derf00, here's my answer, which will probably differ from somebody else's:

87 Blazer, 305, 700R4, 3.73's, 33's--When I get on the highway, my shifts usually go like so: If it's already in 3rd on the ramp at 25-30mph, it'll drop to 2nd when I accelerate. Around 40-45 or so, it'll shift to 3rd. I'll hold it in 3rd until I get near 65 (my usual highway speed). By now the TC will have locked in 3rd (feels like a short shift). I'll then put it in OD and set the cruise at 67-68, and it'll stabilize at 65 on flat ground. As soon as I hit an incline, the TC will unlock with a 2-3mph loss. It'll downshift to 3rd if the hill is big enough, or if I'm fighting a headwind uphill, and lose 5-6mph.

This is what my truck does the way I drive. Others' may do things a little different due to driving styles or TV cable adjustment.

crazy.gif
Semper Maintenance!
 
I don't think my TC is unlocking...before dropping from O to D after loosing 15 MPH up a slight hill. I'll pay some special attention to it....I think it's still locked at downshift. Wish I had a tach...I'm only turnin (I would venture to guess) about 1100 RPM (at 55 MPH) with the 3.42s and 33s when down shift takes place. What RPM is right for locking/unlocking. Is the locking/unlocking controlled electrically....right? What triggers it?

85 Burb and an 89 Blazer
One just for fun, one simply for pleazer
 
Thanks deyager535, you cleared up my confusion as to what you are saying. JarheadK5, my Jimmy shifts pretty much like yours. If I get on to roads that cause the tranny to shift much I will drop in down into D and not run crusie control, but in general here in Texas I can drive in OD most of the time.

Derf00
http://www.derf00.coloradok5.com
"Four wheel drive allows you to get stuck in a more inaccessible place."
 
In a book I have it tells you how to hook up a test light to the ALDL connector (under the dash by your left knee) to indicate TC lockup-unlock. I'll try to find this tomorrow night and post it, maybe it'll help you diagnose this problem.

crazy.gif
Semper Maintenance!
 
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