Thermo switch resistance value?

[Ameer Antar]

About the Bentley, mine says 0 and infinity, no 20 ohms. Are you sure the 20 ohms is for the sensor on page 25.7? Otherwise there must be some discrepancy in the Bentley, but not a huge difference... In any case, this sensor seems to only affect the idle speed control. Well, sounds like you've replaced lots of parts. CIS can be difficult to diagnose. But I think most of the difficulty is b/c of the special tools needed. If you're really set on straightening this out, I highly recommend getting or borrowing a CIS fuel pressure gauge. The cheapest is the one from JC Whitney for < $60. That's where I got mine, and it worked great. It's just a regular fuel gauge w/ metric fittings on it and a special valve to do different tests on the system. If you have access to lot's of special fittings, o-rings, and a 3-port valve, you might be able to make your own by studying a picture of it. I think there's a good pic at Blaufergnugen and probably other German auto sites. This gauge is esssential to diagnosing difficult CIS problems. It can test the fuel accum., the check valve, pressure regulator, warm-up regulator, distributor, and a few other things w/o having to move the gauge to each part. All the tests are in the Bentley. I would also test the cold-start valve connector for voltage when cold-cranking. The full procedure is in the Bentley too.

-Ameer

---Original Message---
From: George Tur <getur at optonline.net>
Date: 9/11/03 4:23:09 PM
Subject: Re: Thermo switch resistance value?

On Thursday 11 September 2003 01:23, you wrote:
> The only switch that has 2 prongs and is near the upper coolant hose seems
> to be the one in section 25.7 of the Bentley. The spec there is 0 ohms
> below 68 deg. F and infinity above 104 deg. F. The temps in between must be
> a gray area between 0 and infinite resistance. I think the only way to
> really be sure about this is to take the sensor out and place the base in
> ice water and hot water. That way you can be sure if the parts bad. I don't
> know where you live, but even up here in New England it's not that cold and
> cars tend to retain warmth even overnight.

The info you have agrees with the specs that my son found. The test procedure
in the Bentley states that the switch should show a 20 ohm resistance, but it
doesn't specify the temperature you do the measurement at. We measured it in
the late morning when the temperature was around the high 60s and the car had
been sitting over night. The block temperature was no where near 104 deg.
fahr. The block was quite cool to the touch. I would say that the switch in
the block and the switch that was sent as a replacement are both bad.
>
> Starting problems could be caused by lot's of different things. Sensors are
> a possibility, but not the most likely. The most common problem w/ these
> CIS cars is vacuum leaks. They're very sensitive to this b/c it affects the
> air-fuel ratio, and since there are so many hoses, people very rarely check
> all these hoses, especially on the undersides and in dirty areas where
> these leaks are common. Another issue could be the cold-start injector
> system. The injector itself is pretty durable, but there are several
> related components to check, such as the thermo-time switch. You can tell
> if the col-start injector system is working by pulling the injector and
> watching for fuel spray while cranking, but make sure to follow the Bentley
> procedure when doing this. The injector only fires at certain temps and
> fires for a specific amount of time depending on temp. The Bentley has a
> diagram for this in the CIS section. Also if the injectors are old, they
> may be leaking, making it hard for the mixture to ignite. But I would start
> out w/ the simple stuff first and then move on if the problem doesn't go
> away. Check all your hoses and sensors and hopefully it will be something
> simple like that. Good luck.
>
Have replaced the cold start valve, fuel filter, fuel accumulator over the
past few weeks. The fuel pump, isv, and injectors were replaced about 2 years
ago. Have sprayed a couple of cans of propane, wd40, crab cleaner trying to
track down any air leaks. No luck so far. Next items to address are the
thermo switches, warm up regulator, and the fuel/air distributor. Keeping my
fingers crossed.

Thanks for the info on the switches.

George