Cruise Control

[whisky_mac]

My 1998 P38 has a cruise control fault. The mechanic says the mechanical side of thinks check out. The auto electrician adjusted the brake switch and then went looking. He had it working once when he moved the vacuum pump and then could not get it to do it again.

I know that it was getting a bit intermittent before it died totally which makes me think it is electrical.

Any suggestion.

Jim

[Junosi]

Could be the cruise control ECU. If both your vac hoses and brake switch check out then that's where I'd be looking. I'm not sure on a '98 but early P38 models (and discovery) used AMR 1173 which failed often enough - I had to replace my AMR 1173 in both my old disco and my current '95 P38 to correct weird/erratic faults. Mine works faultlessly now - got mine used from eBay for about $20.

[Scouse]

1995 - 1998 RRs used the D1 ECU.

I have the diagnosis procedure if you want to pass it on to your mechanic but it does seem like an ECU issue.
PM me an email address if you want a copy.

[whisky_mac]

Hi Scott & Junos

I have sent a PM to Scott re the diagnostic. I think you are both right on the ECU. I will be asking the leco to ID the ECU which he tells me is under the right hand side under the dash. Once I have the part number I can begin to source it.

As a mate mentioned, electrics are a mystey, everyone thinks a strange element called voltage makes it all work but my mate points out that every time he has had a problem smoke comes out of the wiring which makes him think it is smoke that makes it work. He only has trouble when the smoke starts leaking out of the wires. He may be right!

Cheers
Jim

[jbell110]

try checking the vacume lines, as a small crack or split will
stop it working

Jeff

[whisky_mac]

try checking the vacume lines, as a small crack or split will
stop it working

Jeff

Thanks Jeff, as I said, all the mechanical side of it checks out OK including the vacumm lines. The problem seems to be a vacuum pump that only works when it wants to but we are having trouble finding out why. The suggestion of the cruise control ecu seems the most likely so we just have to test that or get a part number and chase on up. My knowledge about all things electrical is limited so the auto electrician will have to do it.

Jim

[whisky_mac]

I hope this helps others with a problem with the cruise control.

The problem has been found. A very simple one but easy to overlook. The clip holding the brake switch in was broken on one side. Could not see it until a vent pipe was removed.

Jim

[whisky_mac]

The clip on the brake switch unit was broken but it turned out to not totally fix the problem. It worked and then did not, you could not pick when it would or not to the extent that it would drop out for no reason.

Replaced the Cruise ECU with an exchange one from Ritters ($220) and it seems to have fixed it.

The unit was not working properly when I brought the car and it has been a long road to find it with several problems not just one to fix. Thanks for everyone's help.

[PaulP38a]

thanks for following up on this Whiskey_Mac. It is always good to see these issues closed off for the rest of us to learn from.
Cheers, Paul.