Hi all, I have a 1986 LG4 Iroc z in which I am trying to find the transducer for the cruise control. I have the service manual, but I can't locate it. I have the image for the cruise control module. I am assuming is not the same?
Any suggestion in where to find the transducer?

Thanks in advanced!

 

Good read on this thread for troubleshooting:

https://www.thirdgen.org/forums/elec...-problems.html

 

thanks!!

 

I'd think the transducer would have been phased out by 86. My 85, for example, doesn't have it.

The transducer, driver's side front, should look like the following:

JamesC

 

I see... so in other words, to troubleshoot any electric problems with cruise control, will be wiring or cruise control module?

 

I'm pretty sure they stuck with the mech cruise regulator like in JamesC's pics up to the last of the carbs in these cars, but I could be mistaken.

However all that may be, if you need one of those, they're REAL TOUGH to come by used. They all pretty much fail the same way. If you take one apart and find it full of copper dust, then that's how it failed. I've never found an effective repair. Speedo shops sometimes advertise em but I've never tried that route.

Later cars used an output from the ECM to control a diaphragm that mounted up behind the throttle lever, kinda next to the distributor. The earlier version had the diaphragm mounted out on the "frame" rail, about even with the front of the exh man, and then had a LLLLOOOOOONNNNNNNGGGGG cable that went around to the firewall and back up to the carb. If any of those parts are still there they will tell you whether you need the mech regulator or not.

 

I did not see the transducer in my car, but it does have that long cable that go into that throttle lever. Essentially, the cruise control does nothing, not even come on.The servo seems to be working. I wonder if is the cruise control module?

 

If you have the long cable, and it's attached to a diaphragm mounted up around the driver's side strut tower, then you need a regulator (module, whatever).

That setup also came with 2 speedo cables; one from the trans to the regulator, one from the reg to the dash. Check if you have those. If the reg is gone, and some sort of replacement hasn't been done, your speedo shouldn't be working either.

 

Oh...my speedo is working. I wonder if some repair has been done. I will need to check on the speedo cables. I am not sure if I have seen two.

 

IIRC, there are three types of speedo cables: a two-piece running in/out of the transducer, a two-piece without transducer, and a single cable (which, of course, runs from the trans to the speedo head). This latter is the type my 85 uses.

JamesC

 

Cruise in an 86 Camaro is fed from the optical VSS built into the speedometer. No tranducer.

 

Sorry, I am not much of a mechanic, but VSS stands for? If my speedometer working, is the problem can still be the optical VSS?

 

VSS stands for Vehicle Speed Sensor , it's the device in an electronic speedometer and or cruise control equipped car that "tells" the speedometer (and cruise control) how fast the car is going . It's (usually) mounted to the transmission's tailshaft and basically turns RPMs into electrical pulses (usually something like "4000 pulses per mile" or other some such) .

So far , in my experience with these cars I've seen ;

Totally mechanical speedometer , with remote mounted VSS for the cruise control . This is the unit under the hood with the two cables described earlier .

Totally mechanical speedometer with the VSS mounted to the back of the speedometer driven by a single cable from the transmission .

Totally electronic speedometer with the VSS mounted to the transmission itself , with no mechanical cables whatsoever running from the transmission to the speedometer (just electrical wires carrying the signal to either a separate VSS buffer in early electronic setups , or straight to the ECM* in later ones)

* ECM = Electronic Control Module , sometimes called PCM for Powertrain Control Module , , AKA "the computer" ....

 

Thanks a lot!! Very helpful...does it make a difference my car is manual?

 

No Sir , The type of transmission makes no difference as to whether or not a VSS is needed . Now , I'm fairly certain the VSS is physically different in standard shift VS automatic cars so that I'm pretty sure they're not directly interchangeable , but they both will have a VSS of some kind . Looking at the wiring schematic of even the 1982 model (the very first third gen) , a VSS is shown connected to the ECM (from the VSS buffer module , which was eliminated in later years) , so all third gens have some type or other of it . You see , even if the actual speedometer head itself is still a mechanical unit , the cruise control AND ECM both need to know how fast the car is going , in the cruise control's case to maintain speed by varying throttle opening , and in the Computer Controlled Carburator's case to tailor the air/fuel ratio for optimum based on currently sensed conditions , including road speed . As I also recall , there are 2 different types of electronic VSS employed as well , one being a reluctor wheel mounted to the transmission's output shaft with a sensing coil mounted to the tailshaft housing , and the other being a self contained unit mounted to the tailshaft housing and geared to the tailshaft by conventional looking plastic gears . If you want to see a good picture of the self contained electronic VSS , check out my sticky thread "pictures of every part of a 700R4" .

PS , if your check engine light and ECM are not butchered and functioning properly , the check engine light WILL tell you if your VSS is failed . As I mentioned above , the ECM keeps track of the VSS , and if VSS signal is lost , the check engine light will light up to indicate the malfunction . Other aspects of the cruise control , like the servo or control module , are not monitored by the ECM and can thus fail without activating the light .

 

Perfect! I will check your thread. My check engine light is not coming on. Hopefully the previous owner did not mess with it. I am afraid it might be in the criuse control module. I think is somewhere behind the dashboard. do you know how to access it bestto troubleeshoot?

 

Troubleshooting Hints:

1. If the Tap-Up and Tap-down functions are the only faults in the system, replace the Cruise Control Module.

2. If the complaint involves rough throttle action in Cruise Control check the resistance of the Servo Position Coil in the Cruise Control Servo. Replace the Servo if the coil is open.

3. Check vacuum hoses for leaks, kinks, or restrictions before starting electrical troubleshooting.

4. Check for minimum slack in cruise control servo throttle linkage.

5. Visually check the cruise control wire and ground connections.

6. Check the Gauges fuse.

For the little it's worth, every time (at least twice and perhaps three times) the cruise control stopped functioning in my car, the servo was the culprit.

BTW, at the first opportunity, purchasing a GM shop manual for your year car would be a good idea.

JamesC

 

As to your check engine light , with the key on and the engine not running , the light will be on . Start the engine and the light will go off . As long as it behaves this way , all should be good with that .

As to your cruise control module , I have only owned Firebirds and not a Camaro , but on all three I've had , the module was in the passenger's side dashboard , somewhat near the ECM . If I recall correctly it's a black plastic box somewhat larger than a pack of cigarettes . The lower plastic cover is all you should have to remove to access it . I know of no good bench test for either the module or the servo other than substitution with a known good unit ....

Edit to say , Thank You James , a picture truly IS worth a thousand words ...

 

The GM shop manual provides a system diagnosis (voltage, resistances, etc.).

JamesC

 

And in most cases those tests will identify a faulty unit . I have , however , on more than one occasion , seen a unit pass all electrical checks and still fail to function . The only 100% proof positive of proper operation is to see the unit actually function in it's intended application . I've never seen one test bad and still work , but I've seen a few test good but not function properly in the car ....

 

Thanks! Service manual is on the way!. JamesC,now that you mention the slack at the servo, it is something I overlooked. I will check.

 

Ok, so I check. Servo cable is nice and tensed. Unfortunately, when i turn the key in on position, the only light that comes is the brake. No other light. So, i think the previous owner mess with "the computer" and god knows what else. It seems however, that my gauges are working, and at least all electric stuffs in the car are working...so far

 

As a side note: The ECM acts as a ground for the VSS. Remove the ECM and the cruise control won't function until the VSS is regrounded.

https://www.thirdgen.org/forums/engi...-function.html

JamesC