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Discussion Starter #1
Hey guys,

It's been a good while since I've posted but I've come into an issue I just can't solve. It looks like my cruise control is different from any images,parts,junk yard units I've been able to find. Searching for old after market kits really hasn't yielded any results nor going through the uploaded/Haynes manual wiring diagrams.

The wiring harness in the truck isn't hacked like an aftermarket system and looks factory.

Key being, it doesn't work and I don't know the pinout in order to test the unit let alone find replacements.

Has anyone seen this type? Does anyone have a wiring diagram so I can test the unit? Does anyone know where replacement parts could be found?

Thank you!

348949
348950
 

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93 GMC Sonoma SLE 2.8 v6
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8 Posts
Hey guys,

It's been a good while since I've posted but I've come into an issue I just can't solve. It looks like my cruise control is different from any images,parts,junk yard units I've been able to find. Searching for old after market kits really hasn't yielded any results nor going through the uploaded/Haynes manual wiring diagrams.

The wiring harness in the truck isn't hacked like an aftermarket system and looks factory.

Key being, it doesn't work and I don't know the pinout in order to test the unit let alone find replacements.

Has anyone seen this type? Does anyone have a wiring diagram so I can test the unit? Does anyone know where replacement parts could be found?

Thank you!

View attachment 348949 View attachment 348950
those wires you have pictured are to your tur n signal swith its caped at the bottom along with the signal wires
 

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time to get cereal
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4,970 Posts
My '95 had the same unit. I chucked it in the trash though.
 

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Discussion Starter #4
those wires you have pictured are to your tur n signal swith its caped at the bottom along with the signal wires
I don't understand what you mean. Also, does this unit act as the cruise control module as well as servo? I thought part of the RWAL system module in front of the master cylinder acted as the cruise module as well. The main reason I want my cruise to work is so that when the air conditioning is turned on, it bumps the engine RPM like it's supposed to.


My '95 had the same unit. I chucked it in the trash though.
Hmmm, I just checked rockauto and it looks like they're offering this unit? Also only on the Blazer. Google images is also only showing that unit.

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Discussion Starter #6
That thing won't bump your idle. The IAC is responsible for that.
I thought I remember reading that that's what did it. I think what reinforced that thinking is that the wiring schematic in the Haynes on the cruise control diagram says AC input. But Thinking harder I think that's Alternating Current input, not Air Conditioning input.

But if it's IAC controlled, I wonder why the ECM wouldn't send signal to open the IAC more... It idles great when A/C is off. But is full struggle bus when A/C is on. I don't see any troubleshooting for that in the books I have.

Ideas?
 

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10+ 1st Gen 4.3's
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277 Posts
Your cruise control is an aftermarket "Rostra". The aluminum box are the electronics, the black thing with the cable is the servo.
The servo from Rock Auto is an OEM servo.

The idle bump with compressor engagement is a function of the ECM receiving the 'AC request signal' from the cycling switch and engaging the compressor and bumping the IAC counts. The 2.8 and 4.3 TBI function this way, the 4.3 CPI still bumps the idle, but does not control the compressor.
 

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Discussion Starter #8
Your cruise control is an aftermarket "Rostra". The aluminum box are the electronics, the black thing with the cable is the servo.
The servo from Rock Auto is an OEM servo.

The idle bump with compressor engagement is a function of the ECM receiving the 'AC request signal' from the cycling switch and engaging the compressor and bumping the IAC counts. The 2.8 and 4.3 TBI function this way, the 4.3 CPI still bumps the idle, but does not control the compressor.
Wow, That's impressive you knew that! I found the old installation instructions from Google so that should help with troubleshooting it. We'll see if I can get that part working again.

Any ideas on how to troubleshoot why the IAC counts aren't bumping? I'm assuming it's the same wires to control the IAC, just a different signal from the ECM. If the IAC was stuck, I'm assuming it wouldn't idle normally so it's unlikely it's that. I wouldn't imagine it could run out of stroke now that the engine's got some miles on it... Otherwise I guess I'd need to use an oscilloscope in order to see if the ECM is sending out an increase in pulses to the IAC to tell if it's the IAC or the ECM potentially acting up...

Thoughts?
 

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Been there Done it
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Engine computers rarely fail. Not impossible but rare. More apt to be faulty wiring between the A/C and the ECM pin B8
Haynes manuals have absolutely the worst wiring diagrams on earth.
This is what you need;
 
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