Lazy cruise control - S-10 Forum
 
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post #1 of 7 Old 04-19-2017, 08:35 PM Thread Starter
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Lazy cruise control

My cruise control has trouble maintaining speed. If I set it to 70 on flat ground, it will hold at 68 then drop to 65 going up a hill. If I don't help the gas pedal down with my foot, the cruise control doesn't have enough pull to get the pedal down far enough and my speed will just drop forever until I notice and give it help. I'm sure the components are just worn down from years of use. Could it be a vacuum leak somewhere? Should I replace the diaphragm that pulls on the throttle cable or is something else busted?


1992 GMC Sonoma SLE: 4.3L CPI Vin W, Auto, G80 locking rear dif. with 3.42's, 4x4, Off-road package, 100% STOCK
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post #2 of 7 Old 04-20-2017, 12:19 AM
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Re: Lazy cruise control

Yours has a diaphragm? I thought they stopped making them 25 years ago. LOL
Who was the genius that came up with that design? The more the throttle is opened the less vacuum you have and the farther the throttle cable needs to be pulled, at the same time.
Seriously, I'd check for a vacuum leak first. If that's OK you probably do need a new diaphragm. Usually they are like the 4wd diaphragm in that they work or don't, but I guess since the cruise has to make more subtle moves, it could just be getting tired. Rockauto has them for $28.
I swapped a digital one from a 92 Caprice into my 94 S10. IIRC it was a pretty straight forward conversion. I think the original column switch and wiring pretty much worked. Had to do a couple re-pins at the module, but IIRC the colors were even right.
That setup didn't give a hoot about saving fuel and stayed locked on to whatever speed you set it at. It would down shift the trans if it had to.
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post #3 of 7 Old 04-20-2017, 07:06 AM
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Re: Lazy cruise control

My 89 was having the same issue. I replaced the vacuum actuator (from Rock Auto) and now the cruise control works perfectly.
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post #4 of 7 Old 04-20-2017, 07:58 AM
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Re: Lazy cruise control

Quote:
Originally Posted by oldeerslayer View Post
Yours has a diaphragm? I thought they stopped making them 25 years ago. LOL
25 years ago is 1992. First Gen = 1982-1993.

Just sayin'
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post #5 of 7 Old 04-20-2017, 01:01 PM Thread Starter
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Re: Lazy cruise control

Quote:
Originally Posted by oldeerslayer View Post
Yours has a diaphragm? I thought they stopped making them 25 years ago. LOL
Who was the genius that came up with that design? The more the throttle is opened the less vacuum you have and the farther the throttle cable needs to be pulled, at the same time.
Seriously, I'd check for a vacuum leak first. If that's OK you probably do need a new diaphragm. Usually they are like the 4wd diaphragm in that they work or don't, but I guess since the cruise has to make more subtle moves, it could just be getting tired. Rockauto has them for $28.
I swapped a digital one from a 92 Caprice into my 94 S10. IIRC it was a pretty straight forward conversion. I think the original column switch and wiring pretty much worked. Had to do a couple re-pins at the module, but IIRC the colors were even right.
That setup didn't give a hoot about saving fuel and stayed locked on to whatever speed you set it at. It would down shift the trans if it had to.

Thanks guys. I would love to convert to an electronic servo instead of vacuum. Rock Auto didn't seem to have the Caprice part, do you know where I can find it?

1992 GMC Sonoma SLE: 4.3L CPI Vin W, Auto, G80 locking rear dif. with 3.42's, 4x4, Off-road package, 100% STOCK
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post #6 of 7 Old 04-20-2017, 02:00 PM
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Re: Lazy cruise control

almost every aftermarket cruise is electronic now, not vacuum. when I put these in in the early 90s I remember doing some S10s with non working cruise controls and the kits were even then made to work with the speed sensor in the trans and the factory stalk.

I would guess you have a vacuum leak too. check the line to the vacuum ball and the vacuum ball itself, they rot, and there is a check valve to keep the rotten line from impacting the engine or heater controls.

any aftermarket cruise will have dip switches to set number of gears and ppm. but be careful of which factory module you use, the early electronic trans will have half the pulse per mile on the VSS wire, and it does not get "smoothed" by the PCM like on later applications. this can impact the activation speed and turn the cruise on and off unexpectedly. I am not sure the exact year change to the higher PPM, deerslayers 94 was kind of a unicorn because it was the new body but the old steering column and some systems, but I think it still used the old VSS setup.

my 41 chevy S10 swap 4.3 auto Fenixhttp://www.s10forum.com/forum/f30/19...on-s10-789361/
my embarrassing 2.2l 5 spd 1965 fullsize S10w Ride http://www.s10forum.com/forum/f30/frankendime-458726/
my 49 chevy s10 swap 4.3 auto http://www.s10forum.com/forum/f30/49.../#post10592042
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post #7 of 7 Old 04-20-2017, 09:48 PM
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Re: Lazy cruise control

I use my cruise frequently, and have put a cumulative 600K miles on a bunch of 1st gens. I have found the symptoms described by the OP can be caused by any of the following: The check valve.
Vacuum lines.
The servo itself has two solenoids and rubber-ball valves. These valves seem to leak after 20+ years in service. So the servo itself.
The brake switch vacuum valve.


It doesn't take much of a leak to cause the cruise to "slow down", and the A/C mode doors flop around too, affecting the
Air Conditioning. (I once cracked a windshield in my Syclone because the A/C kept blowing cold air out the defrost vents onto the windshield during a Summer Arizona trip). I've often thought about adding a 12 volt vacuum pump to the system that is on when cruise stalk is on to augment the engine's vacuum. They're about $45 from rockauto, and a lot simpler to install than an all-electronic upgrade. Never gotten around to it, and I now drive a Super Duty Powerstroke for most of my long trips so I probably never will. The 2nd best feature of that truck is the Cruise. Maintains set speed within 1MPH on the Gps.
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