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Disagree on cruise Posted by Bill Homer [Email]  (#3427) [Profile/Gallery]
(more from Bill Homer) on Thu, 17 Jul 2008 10:35:14
In Reply to: Re: Cruise has little to do with the problem, oldsaab, Wed, 16 Jul 2008 16:31:29 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Oldsaab: the reason I drew the distinction on 1994/1995 cruise is that the entire cruise setup changed in 1995, I believe that the cruise function became part of the main ECU, but I'm not sure. Steve C's car is a 1994, so is mine.
The cruise function is not dependent on the main brake light switch - that's why there is a separate, smaller switch on the brake pedal which is only there to disengage the cruise function. The 1992 - 1994 cars had notoriously bad cruise control modules: I'm on my third one (which comes out of a 1992 C900, mounting ears removed) and I had to resolder components to get it to work. Yes, it's possible that the entire brake pedal bracket is bent, but getting cruise functional is not the main issue here and will take some doing due to the serially defective control modules.
I think that it is not wise to drive around with the brake lights disconnected for any amount of time - it's illegal and an invitation to get rear-ended. You do not need to disconnect any wires to test the brake light switch, here's a simple test: step on brake pedal, see if brake lights illuminate; release foot, see if brake lights extinguish. The main brake light switch is a single contact switch, one input (always on, tied to +12V), two outputs: one goes to the brake lights, the other to the ECU. If the switch is working properly, i.e. off when it should be off, this is not the problem affecting boost. Yes, it is still possible that there is a short in the circuit to the ECU, but that would be a remote chance unless the wiring under the dash is quite messed up and the hot wire to the brake pedal is touching the wire to the ECU.
Here are other electrical/ECU issues to check:
1. Disconnect the cruise control module to get it out of the picture - remember that it is an add-on accessory in some markets, it is not tied to the basic functionality of the car.
2. Are the reverse lights working properly? “Car in Reverse” is another signal to the ECU which limits boost; I believe that the signal originates on the reverse light switch.
3. Are you in third, fourth or fifth gear? The ECU limits boost in first and second to preserve the transmission.
4. Try measuring the resistance back to the ECU between pin 1 and ground and between pin 3 and ground on the wire harness plug that connects to the BPC valve. Both reading should be similar and in the megaohm range.
5. Is the BPC solenoid plugged in - yes, this has happened to someone I know very well, ......
The fact that you can hear the BPC solenoid vibrating is a very good thing; I don't know if it will vibrate when only one side is functional, but I have never tried this. The MOSFET transistors are pretty sturdy and can take a certain amount of heat being soldered on – just not an excessive amount. I don’t know what you are using to solder, but a soldering gun is not appropriate for printed circuit board work.
Your experience with lots of boost with the "W" hose disconnected does say that the wastegate is closing. Do check the small ~ 1cm diameter brass tube/hose under the throttle body which will release a lot of pressure if it is loose – when this happened on my car, it idled poorly and was limited to something less than base boost.
posted by 63.87.52...
, Wed, 16 Jul 2008 16:02:27, Thu, 17 Jul 2008 10:35:14 <-- Viewing This Message, Fri, 18 Jul 2008 12:16:30, Thu, 17 Jul 2008 15:53:49, Thu, 17 Jul 2008 20:01:51, Thu, 17 Jul 2008 21:32:45, Fri, 18 Jul 2008 12:31:15
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