X180R17

That's the same thing I was thinking. Dave

Grey Switch 1 pump on 1900-2350psi and warning at about 1600 Grey switch 2 pump on 1800-2300psi and warning 1500-1600 (the warning cam on about 1500 but didn't go off till 1600 so it was sticking a little Grey switch 3 pump on 1800-2300 but the warning light was on full time below 1500 and on intermittently above 1500 indicting a bad warning switch. We tested with 2 Gauges and the second gage indicated about 100 psi below the above values for whatever that's worth. When all is said and done I guess I'll be sending my gauge in for calibration. So in the end it's still a really small sample. If you can get yours tested do so and report the results. I will say you should remove the switch periodically and drain that port and clean the switch. You don't get all that much fluid out but It seems to be a low point that doesn't get much fluid exchange and I drained out some ugly gunk on this car when I removed it the first time. That could be contributing to the switch failures. I'll have this car here for about another month so if anyone over here in the US wants to send me their grey switch to test, I'll test it, report the data and mail the switch back. Dave Cammack St. Paul, MN

That's the same conclusion I have been coming to for the last 2 weeks but I've been doubting myself because everyone Seems to have accepted the 2200-2700 psi values as correct, including the people making these replacement switches. I had enough doubt that I borrowed a second pressure gage and verified my readings. Someone else reported today too that his '91 manual listed the same pressures as the '95. I wish someone had a printed spec on the grey switch but until then I'll assume these are good working switches. The low pressure warning is not as simple to check when the switch is working but I will test that this week and report back. Dave Cammack

That's the same copy that I have, and I have always assumed the same thing, but finding the consistent results with these 6 switches got me wondering. I looked up the service manual for the 90 Olds Cuttlas which used the same system and came with a black switch and it lists those same pressures. Of course GM could have updated the switch and service manual for those as well but unlike Lotus I have not been able to find a service bulletin for the Olds that replaced the switch. Dave

In 1993 Lotus issues a service bulletin and changed the pressure switch to reduce the operating pressure on the system but nothing that I have specifies what the actual pressure change was. The original switches were black and the new ones are grey. All of the switches I've found in a Lotus have been grey, even on older cars so they had been updated. Does anybody know what the pump activation and warning light pressures were on the original black switch vs the new one? I have just tested a number of original switches both black and grey and found the pump pressures of these grey switches are running from 1800-2300psi and the black switches are 2200-2700. From my Lotus manuals the correct pressure should be 2200-2700 but which switch was that referring to? I would just discount these numbers as a worn out switch operating below its normal pressures except that I tested 3 of each and they were very consistent, and the older black "higher pressure" switch matched the book numbers precisely. I guess the good news in my case is that if the lower pressure is correct, I don't have to change the switch and if the high pressure is correct I have one that I can use. Does anybody have a grey switch that is pressure gage verified to be running at 2200-2700 psi? Dave Cammack

donation made.

I'll take one and Im considering a second as well. Shipping to St. Paul, Minnesota 55107. Dave

What do you mean by differential pressure switch? To me that means a switch that works off of the difference between 2 fluid pressures which isn't what were looking at here, so I'm confused. I'd love to know that a standard pump activation switch exists in the pressures desired.

Certainly nothing wrong with doing a manifold and 2 seperate switches, and the straight pressure switch for the warning is pretty simple. The difficult part is still getting the pump control part, because it needs 2 pressure points. It would almost be easier to do 3 simple pressure switches and set up a self energising relay to handle the pump cycling. Electrically its pretty simple. A low pressure switch that activates a relay below 2200 psi to run the pump. Set the relay to keep itself energised once started and then add a second pressure switch to cut power to the relay above 2700 psi, thus turning off the pump and resetting the relay. Low pressure will activate the relay and it will keep itself going until the high pressure switch shuts if off, thus keeping the pressure between the switch points. Dave

The switch is not a simple pressure switch. its actually several things in one and not simple in operation. The low pressure warning circuit is fairly simple. Its open below the low pressure warning point of I think 1800psi so in normal operation on the esprit its closed (above 1800 psi). When it opens below 1800 psi it breaks the ground to the ECU and that signals the ECU to operates the warning lights apropriatly. The pump motor switch is the more complicated part. It is on (closed) whenever the pressure drops below 2200 psi and off (open) above 2700 psi. There is a 500 psi dead zone where it does not switch over though. This is what allows it to turn the pump on at 2200 psi and then keep it on until the switch opens at 2700 psi. And then keep it off until the pressure drops back down to 2200 again. Without that the switch would activate whenever youtouched the brake and the pressure dropped even the slightest amount. Mechanically its like a little overcenter metal clicker in there. With pressure against one side and a spring against the other. But it has a certain mechanical resistance to popping overcenter that gives it the dead zone in the middle. Pressure drops far enough (2200 psi) the spring can push the clicker over to activate the pump and then when the pressure gets high enough (2700psi) it can push it back to shut off the pump. If they can reproduce that then you have a winner! Dave