# Thermotime switch issue



## jhelmuth (Oct 10, 2011)

So I've been having the typical CIS hot start problems with my 85 Golf with cis 8v. After a long day of testing the fuel system with the CIS fuel pressure kit and replacing a lot of tune up parts we've come to this -

-Fuel system (Pump/Accumulator/WUR) all good
-No vacuum leaks
-Did a full tune up with plugs/cap/rotor/coil
-Reset the fuel pressure sensor plate torque to factory spec
-Reset the fuel/air ratio back to factory spec (45-50 on dwell meter)

-Is the 5th Injector suppose to spray once at startup when the motor is hot or only cold? 

We experimented with an extra thermotime switch I had lying around but putting it in the car while the motor was hot to see if the hotstart problem would go away. Note that we put the spare (cold) thermotime switch in the HOT motor . The motor perfectly started up with the 5th injector spraying at startup on a hot motor. After driving the car around the block and getting the motor AND the new thermotime switch hot the car still barely started up at a restart after 15 minutes and idles terrible until it clears out. I'm thinkin that the extra thermotime switch I had is also junk, but that would only be a bad switch if the 5th injector IS suppose to spray at startup on a hot motor. Tomorrow I'm going to make sure that the 5th injector is not spraying at startup on a hot motor with the spare thermotime switch in the car. I'm only expecting the 5th injector to NOT be spraying because the car doesn't like to hot start.


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## ziddey (Apr 16, 2006)

The CSV is not supposed to spray unless the TTS is below 40*F or something like that, and it'd only spray while cranking. Power goes from the starter to the TTS to the CSV.

If you need the additional fuel to start when hot, it sounds like you may have a residual fuel pressure issue or your baseline mixture is tuned too lean still. You can bypass the TTS and shunt the plug with a paper clip to make it always spray while cranking, but if you say it runs poorly when first hot started, it won't fix that. What do you see on your dwell meter when you first hot start it and it's running poorly?

Have you tried flooring it while hot starting?

Not sure what to say in terms of vapor lock / residual pressure. Maybe Waterwheels or someone else will be able to chime in on that one. I believe there is a check valve at the main fuel pump.

I'm assuming you have the idle boost valve(s) and not the newer idle stabilizer valve? Verify that you are able to idle with that disconnected electrically. Again, that wouldn't help poor initial running upon hot start (which points to a metering / delivery issue)


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## WaterWheels (Aug 14, 2005)

Can’t make any calls right now but only field some questions and things to look into maybe. 85 with CIS Lambda should have a hot start pulse relay to aid in hot starting, I see no talk about checking that function. Typical statement about fuel system being good, pump, accumulator and WUR but no mention of how they were tested and the results. Forgive me but that leads to questioning the fact. If they really were checked or just assumed they are OK because it ran before or they look OK or whatever, often the case. Fuel dripping/leaking into the engine from a bad cold start injector or one or more fuel injectors, an accumulator being bad or bad pump check valve can all cause hot start issues. Doing a residual pressure check whould show if one of them may be giving you a problem. So informing people of how the tests were done and the results really helps much more than just stating everything is fine, it's not harassment.

This one I think requires some explaining "Reset the fuel pressure sensor plate torque to factory spec”. 

"Is the 5th Injector suppose to spray once at startup when the motor is hot or only cold” A lot depends on if the car does or does not have a working hot start pulse relay. Cold, engine temperature below about 35°C, it should spray continuously for as long as the starter is turning until the thermotime switch heats up (depends on air temperature but say 3 to 8 seconds). After the thermotime switch has heated, either via engine temperature or from the heating element inside, it should not spray unless it has a pulse relay in the circiut which then controls its actions.

If hot starts are the issue and it starts fine when cold then I would be looking into residual pressure or the hot start relay operation. Heat soak never seemed to be a problem with A2 models. Do you have any problems with cold starting?


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## jhelmuth (Oct 10, 2011)

OK well I had a friend come over with his CIS fuel pressure testing kit to test the fuel system and I'm just going to post his response on the test results on the car which was in another one of my threads...

"Ok, as mentioned, I went over and hooked up a CIS test gauge to John's car. Without the gauge we'd only be hypothesizing on bad components and throwing parts, money and time at the car hoping to fix it. Been there, done that and I'm done with that method. John's fix was technically free.

- System pressure checked out fine @75 lbs, ruling the fuel pump out.
- Had to start the car to witness the hard hot start so with a 24 lb "cold" and 55lb "warm" control pressures, the CPR checked out fine.
- Rock steady 42 lb residual pressure after 15 minutes told me there were no system leaks. Suspect areas if pressure were inadequate would have been fuel pump check valve, unions/hoses, injectors, or accumulator.
- Sensor plate height looked fine, so we pulled the injectors and I rotated the mixture screw a full 1.5 turns before I saw fuel start spraying. Way too lean, so that was a culprit.

Being a Rabbit guy, we have hot start pulse relays. Didn't see any mention of it in the A2 Bentley, but I'm used to errors and omissions in Bentleys. It works off the thermo time switch, so that was tested. John's engine was hot so it couldn't be tested as the Bentley described. 

Testing for continuity, his read open and so did the JY part. One was obviously bad. I couldn't remember if these are normally open or normally closed, so we did a comparison test. We pulled the 5th injector out and cranked the starter. Next we disconnected the thermo time switch and did the same. We got the same "no spray" both times.

JY thermo time switch gets installed and we repeat the test. Im not 100% sure, but I believe the 5th injector sprayed when we had the thermo time switch disconnected. Seeing life when we previously had none made us leave the JY part in.

Button everything up, start the car and I attempt to set the duty cycle. The car is pig rich with a dwell reading of 10. Stochimetric will be bouncing between 45-55. I don't hear the frequency valve buzzing so I blame the O2 sensor. Not hugely critical, but it should be fixed.

Take the car on the road to get it to running temperature, then shut it off. We waited 15 minutes and it started rough. Being that it never wanted to hot start at all is an accomplishment. I blame the rough start on the bad O2 sensor. 

All in all, I'd blame the hot start issue on both the thermo time switch and the lean setting on the fuel injectors. Luckily he had the JY part. I've never owned or worked on a A2 before Sunday, but if I had to guess, I'd imagine that there's a hot start pulse relay in the car somewhere. 

Its been years since I've needed to work on CIS, so it took a bit longer than it should have. I forgot the methodical steps that should have taken so we had to backtrack a couple times. I was told that it ran that way since he got it 3 months ago, and if I hadn't forgotten a fuel fitting, it'd have been less than a 3 hour diagnosis. 

Thanks to John and his dad for doing most of the dirty work. 

-Todd"

So I read deep into my Bentley find that my cars 5th injector should NOT spray at start up on a hot motor. I need to check tomorrow night to see if it still sprays at a hot start up, but I don't think it is because the original thermotime switch that was in the car did NOT spray when we tested it at a hot startup, so why the car is loaded up at a hot start still boggles my mind. I need to locate where the hot start pulse relay is in order to test it if I even have one.


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## ziddey (Apr 16, 2006)

The CSV should not be spraying when hot.

I'm not familiar with cis-l at all, but if it's going pig rich on a hot start before the o2 sensor comes online, I believe the system uses a warm up regulator (WUR) to control "cold" enrichment? If that's the case, I don't know if there's any adjustment/repair that can be done to that. Have a spare to try?


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## 92_MK_2 (Oct 11, 2010)

Watch


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