rgs944

The cruise is the last major function of my car that I want to get working but my electrical skills are limited. Can someone help me troubleshoot in dummy terms. First question is, where is the ccu? When I first got the car the cruise worked. I did the napa rear brake light socket intall and the bulb control defeat to get rid of the stop lamp warning light. When I had my pod out I just removed that bulb so now I could reverse the defeat mod and would no longer see the light. I did that and now my cruise has not worked since. One thing I may have done is not get the wires back in place correctly at the bulb control. They all came competely out at one point and it is a maze to get them all back in place. I have a much better understanding of mechanics than I do of any electronics.

John Speake

It's on the RHS (passenger side for your car) just behind the radio. Accessable with the console side cover removed. There are a series of tests to confirm is is getting all the required inputs in the WSM.

If those check out, then there may be some fractured solder joints where the connector joins the circuit board in the box.

joejoe

cruise brain is located on passenger side center consul. remove the side carpet and will see it up front. it is held with a 7mm nut. there is ample wire there to remove.

rgs944

I want to do Borlands ccu mod. Will that completely seperate the ccu from the bulb control?

rgs944

Thank you I did read about baking the unit. I really think this has something to do with what I did last, meaning screw with the bulb control. Do you think if I did Borlands mod on the ccu that would be a good first step. Also does someone have a link to the wsm troubleshoot. I do not have a hard copy and might have trouble following the schematics anyway. Maybe the best thing to do is have the ccu sent off and tested in a working cruise car.

syoo8

Do you have the workshop manual? It is section 27, pages 10-13.

The Cruise Control (aka tempostat) amplifier is inside the center console, You remove the right carpeted cover (to the left of the passenger's left knee) and I think there are two or three bolts (and I think they were an odd size, like 7mm) which will release the amplifier.


The amplifier is a silver metal box, with some taupe colored plastic at the end, mounted on top of the tunnel next to the firewall. Remove the bolt on the right side.

The workshop manuals include a check of the servo by bridging terminals 3 and 5 on the plug. "Connect a push button switch on terminals 7 and 12. Turn on ignition and press the push button switch with engine stopped. The vacuum servo should move the throttle uniformly to full load position. This requires vacuum."

Remove the multiple pin plug. Then, with a voltmeter, you can check the pins. With ignition on:

Between terminal 5 and 12: battery voltage.
Between terminal 6 and 12: battery voltage when brake is pressed
Between terminal 8 and 12. battery voltage, unless you pull cancel on the CC lever, at which point it should go to zero.
Between terminal 9 and 12: 0 volts, unless you push the lever forward on the CC level, at which point it should show voltage.
Between terminal 10 and 12: 0 volts, unless you push the lever down (reset), at which it should show voltage.

With an ohmmeter:
Between terminal 12 and ground: 0 ohms
Between terminals 3 and 7: 14 ohms
Between terminals 11 and 12: should alternate between 0 and infinite ohms when you turn rear wheel.

If you check all these and they are "spec" then your CC amplifier is no good. Both of my 928s had this problem. You can either reflow the solder in your CC amplifier (which I have tried several times with no success) or buy a used one. IIRC it is actually a 911 part, and there are quite a few of them on the used market.

John Speake

What is Borlands mod ?

rgs944

Here it is. https://rennlist.com/forums/928-foru...?highlight=ccu

rgs944

Thank you, those look like checks that I can do this week.

John Speake

Thanks for that link. However Borland's picture is of the later type 911 part number device, which is not the same as your 928 617 127 00 part.

The principle on which is works may be the same but best to check with him first.

rgs944

I have not done any electrical checks yet and I am also starting to research the vaccum part of the equation. I have vaccum out of the blue valve by the brake booster but lose vaccum at the four way going to the canister. Obviously there is no way for the cruise to work without any vaccum. I must have a major leak somewhere near the cannister.

Don Carter

I sent the brain from my 86.5 to Automotive Scientific (ASI,www.autoecu.com) for rebuilding. When it came back it didn't work, so I sent it back and when I received it the 2nd time, it still didn't work. Need to pull it and send it back again. Return shipping is adding up....

rgs944

Coming off of the 4 way the vac lines go into the fender with two lines, a white vac line and a black line that are connected to a two way splitter. I am thinking one goes to the cruise and one goes to the storage canister. Is that right? I do not need the vac that goes to the heater valve so I wonder if I could just make sure the cruise line is getting vac and see if it works for temp use. Does anyone know if the black or white line would be for cruise?

rgs944

I connected the brake booster vac line directly to the two way splitter going into the fender thus eleminating any leakage problems the havc system could be contributing. I can get the cruise to hold if I hold the accel button pressed forward. When I let up my finger pressure it does not hold on its own. Do you think an electrical problem could still do this or am I most likely looking at a vac leak yet somwhere around the egg carton cannister?

rgs944

Update with now a stronger vacuum to the controller. I believe my blue check valve was being restrictive. I put a new universal check valve in and now the cruise accel works much better. Before it would only hold its speed but now it accels rapidily when held. Still no cruise so now I am thinking it is an electrical bug somewhere, at least I made some progress stroger vacuum now. Now I need to get the side console off and go through the electrical checks.