Thermotime Bad??

[Cipotifoso]

After reading through many posts trying to solve a cold starting problem on my '75 CIS, I've torn the cold start circuit apart and performed many tests. I've found out that:

CSV dribbles a couple drops at best when ignition is switched on and 12v is applied manually across the terminals. I hear the solonoid click, but not much gas. From the wiring diagrams and past posts, I understand the fuel pump has no relay as on later models - only the ignition needs to be switched on to engergize the pump, so the circuit should be pressurized. I haven't confirmed this yet with a pressure gauge, but the car runs fine after starting, so I assume that the pump is OK. To double check, I lifted the air flow sensor plate with the CSV hooked to fuel and the power plug with the wife turning the key and the CSV in a jar. The result was still only a couple of drops as I could hear the main injectors activate. From this I've deduced that the CSV is bad.

When I hook a voltmeter across the CSV contacts in the harness and energize the CSV/Thermotime circuit with 12v, I get about 1.6 seconds of power before the Thermotime cuts off the ground to the CSV on a stone-cold engine.

A check of the resistance on the cold thermotime switch shows 0 ohms on terminal W (where the CSV ground hooks to), but only 0.3 ohms on terminal G (the heater circuit). Previous posts have had values for this terminal in the range of 20-60 ohms.

Is the thermotime switch bad???

[Cipotifoso]

Bump....anyone know?

[Cipotifoso]

Well, after re-measuring the resistance on the thermotime switch this morning (with the ohmmeter set to ohm x 1000, not diode circuit check), I come up with: Terminal G to ground: 0 ohms; Terminal W to ground: 25.6 ohms; Terminal G to Terminal B: 25.6 ohms. Everything checks out.

Also, I sprayed some carb cleaner in the CSV on the bench and while activating the solenoid, blew some compressed air through the valve, achieving a good spray pattern.

On the '75 I also verified that their is no fuel pressure until they ignition is switched to start. The time it takes for the fuel pressure to come up (not yet measured), combined with the very short cycle time on the Thermotime could be why the cold-start circuit does not work(?).

I haven't been able to pinpoint anything yet to designate any part to replace. I don't want to start part swapping until I understand the problem fully.

Has anyone had similar findings?

[T77911S]

i read something that said it stays on for about 7.5 sec. at -20C. at say 60 or 70 deg F i would imagine it is much less. i may get froggy one day and go time mine.
if you had no spray that may have been your problem.
the WUR provides additional enrichment when the engine is cold.
you may want to check the cold and hot pressure.
my 77 has 1.8bar cold and 2.8bar with power applied to the WUR and the engine not running.

[Cipotifoso]

I've read that warm starts are problematic when the valve in the fuel pump doesn't keep the system pressurized. If, when cold, the fuel pump doesn't run until the start position is reached on the ignition switch, the system is unpressurized until that point. How can a cold start be quick without prior pressurization (unless the pressures come up really fast)?

I'm toying with the idea of installing a contact switch that will activate the pump before attempting a cold start. I could then hold the switch for a couple of seconds before I turn the key. Has anyone done something similar or is it a crazy idea?

[spuggy]

One of the leads on the thermo-time switch on my '78 930 motor was disconnected. Couldn't... Quite.... Reach.... It... because of the intercooler hard pipe.

Car still started fine in the UK in December with much heavier frost on the ground/car etc. than I've ever seen in the Riverside area (I've done a few dawn skydive loads at Perris).

I know it's tempting to fix it anyway (and I'm not trying to talk ya out of it), but I honestly doubt it has much bearing on your problem.

[T77911S]

if the car didnt need it to start it when it was new, why modify or jurry rig it now to cover up another problem, who knows, it may rear its ugly head down the road and you will have to fix it anyway.
thats just the way i try to look at things, besides, i find it a challenge to fix it plus i always learn something when trying to fix it.

[Cipotifoso]

Further testing the start circuit revealed the following:
- Hooked up a remote starter switch so that I didn't have to depend on the wife to test.
- No CSV attached, fuel line in a jar. Hit the starter and fuel comes out like crazy at once. So, no problem with fuel delivery.
- Test the CSV electrical circuit - lights up on start, so I have both fuel and electricity. CSV tested out on the bench, so now time to test it in the circuit.
- Hooked up CSV and put it in a jar. Disconnected terminal G on the thermotime so that it wouldn't time out. Hit the starter - nothing!
- Unplugged the CSV and put a voltmeter across the terminals - measured 8.5 - 9v. Hmmmm.
- Reconnected CSV. Disconnected double lead yellow wire from throttle switch that runs to CSV and thermotime and ran a lead to it. Hit the starter switch and touched the lead to the top fuse on the left-side fuse panel (where I had earlier measured 12.5 v). CSV sprayed nicely!!! But hooked up normally it doesn't work - obviously a voltage threshold issue (what is the specified voltage threshold for the CSV solenoid?).
- Tested voltage at single wire on thottle switch that comes from terminal 50 on the starter: 9 volts.
- Tested the continuity on this same wire, from terminal 50 under the car on the starter to the throttle valve switch: 2.5 ohms. Would that reduce the voltage from 12.5 to 9 volts?

So now I'm at a point where I'm not sure why I'm only getting 9v at the CSV circuit. I've read previous posts where the ignition switch is not sending enough current to the circuit, but I'm starting it with a remote starter switch. At this point I'm not sure where to look next. Anyone have any ideas?

[T77911S]

the book i have shows the start path from the switch going to the seatbelt relay then the starter. it may just be hard wired in and out, i dont know. for the 76 and 77 it does not go to the seatbelt rly. it may be a misprint. if not, you may be getting the voltage drop in that relay. why they would go thru it, that i dont know. bad contacts and dirty connections can cause voltage drop. 2.5 ohms on a wire?? what was the voltage at term 50 on the starter. keep going back until you find 12v. good trouble shooting!

[Cipotifoso]

Thanks for the input, T77911S. I don't see a seatbelt relay on the wiring diagrams that I have and I don't know if a '75 has one. If it does, it's been bypassed, since I don't need to fasten it before starting. Anyways, some more measurements:

Terminal .......................................Ign on...Starter on

Starter Terminal 50----------------- 12.58v 10.10v
Thottle switch wire------------------ 0v 9.2v
Top fuze in Engine Compartment-12.58v 10.10v

So, when the starter is activated, it draws the battery voltage down to 10.10 volts, but with the 2.5 ohms in the wire going from terminal 50 on the starter to the thottle switch, only 9.2v is seen here.
Testing the CSV, if it is hooked up normally, it will not fire at 9.2 v. If I jumper it to the top fuze on the Engine Compartment Fuze panel while hitting the remote start (10.1v), the CSV fires.
Unknowns: Correct trigger voltage for the CSV. Mine seems to fire at a threshold between 9.2 and 10.1 volts. I don't know if this is within specs. Also, the pull down in voltage with the starter engaged from 12.58v to 10.10v - is this normal, or does the starter have an abnormally high current draw? The battery is approximately 2 years old and is always connected to a Battery Tender when the car is parked, so I believe that can be eliminated as a variable.
My first plan is to go through the grounds and connection and make sure that I have good contact thoughout. If the voltages do not change and assuming that the two unknowns are not the problem, one solution to the problem that I am considering is a hard start relay:

<http://www.wolfsburgwest.com/wired/wired_03_01/wired_03_01.htm>

This is something that the owners of older VWs, especially the Type 2's (microbuses). In these vehicles, the current to the solenoid (up to 30 amps) has to flow from the battery in the back up to ignition switch and back to the starter. The result on older vehicles is that circuit proves to be too weak to trigger the solenoid. A Bosch WR-1 Low Voltage Relay kit is installed, across the solenoid circuit, dropping the demands on the solenoid circuit through the ignition switch down to somewhere in the region of 0.5 amp. This could be a good item for the ignition circuit in the earlier 911s as it would take a load off of the ignition switch. This seems to be the same idea of the Sucro relay kit for the headlights with respect to the headlight switch. But, if instead, I installed the WR-1 relay kit in CSV circuit, this would allow a higher voltage to reach the CSV, which would allow it to fire.

[T77911S]

good call on checking grounds, never hurts. dont forget the one from tranny to body.

10.1v at starter term50 to throttle switch 9.2v is a .9v loss.
i dont know if that is acceptable or not. check for corrosion on the wire where it crimps to the connector.

was the battery voltage measured at the battery while starting?

CSV firing voltage? maybe someone out there knows. this may be the cause of many hard/no starts. car turns over but not enough voltage to CSV

[Cipotifoso]

Well, I got under the car, dismanteled and cleaned the ground contacts. Next was the battery ground and contacts. I then measured the voltage at the battery: Off 12.7 v; Ignition on: 12.7 v; Starter engaged: 11.5v. Looks good.
I then went ahead and got the Bosch WR-1 kit that I mentioned in a previous post at a local hot-rod VW shop. Hopefully the installation of this kit and the cleaning of the ground contacts will bring the voltage seen at the CSV up to 10.1v or greater. I like the fact that it will take some load off the ignition circuit and provide some insurance for activating the starter solenoid. It wasn't designed for the extra current of the CSV and thermotime on the trigger circuit, so I'm not 100% that it'll be the right solution.
Unfortunately, I've got to leave for Europe tommorrow, so it'll be a couple of weeks before I get to find out if my fix will work.

[T77911S]

you may want to research the CSV firing voltage some more. if it is going bad you just have to replace it later anyway.
9.2 to 10v doesnt leave much for battery to start the car. if the battery is 11.5 when starting, that only allows for 1.5 to 2v drop in battery voltage before it wont start when cold.
if someone out there has one out of the car, try hooking it up to a 9v battery as see if it fires.

[Cipotifoso]

I thought that I would add an epilogue to this story to assist with someone hitting the search button (that has helped me a lot).

It appears that the CSV had a threshold somewhere above the cranking voltage seen at the top terminal on the engine fuze panel (approximately 10.1 - 10.6v), and even more so from the voltage at the terminal from the starter (9.8v). I ordered a new CSV from our host.

I compared the resistance across the terminals - existing CSV: 4ohm; new: 11.2ohm. This was an indicator that the old CSV was failing. I hooked the new one up in the circuit, hit the remote starter and it fired!

So, you may read in other threads to hook it up to 12v to test. This is not exactly correct as it won't give you a valid result. If you suspect the CSV, you have to test it in its circuit under actual cranking voltage seen at the connector.

As a side note, don't install the WR-1 kit on your starter as shown in a previous post. It may work on VWs, but isn't compatible with my car. I don't understand exactly why, but after it was installed the starter would activate if the throttle plate was lifted. Somehow breaking the circuit on the throttle activation plate rest position sensor sent a voltage to the relay circuit! I didn't study the wiring diagrams in detail to figure out why, I just removed it!

[T77911S]

thanks for the info. i am curious to now what the LOWEST voltage the new CSV will fire at. this may be good ino when trying to start a car with a LOW battery.

[Paulporsche]

Good info. Thanks for the followup.