'79 F.I. Hard Start when Cold, stumped! FIXED!!!!

[Gregg in the 603]

Hey guys. I'm out of ideas! I'm chasing a very hard start issue, only when cold. I've checked everything. Purrs like a kitten when running, idles right away very well. Vacuum lines are good, look good and I don't see any leaks. All connected.

Fuel pressure (though not maintained on shutdown, probably need a new regulator) 40psi at the fuel rail with pump running, about 30psi when engine is running.
Thermo Time Switch gets warm to the touch after cranking over expected 8 second timeframe, seems good.
Cold Start Valve excellent spray pattern when supplied 12 volts and confirmed by Cruzin a year ago, works great
Auxiliary Air Regulator new Bus Depot Nissan model, works great and keeps revs high when cold, decreasing as it warms

It appears I can't get the CSV 12 volts when cranking. I grounded out (via jumper wire on the connector) the TTS to supply power directly to the CSV bypassing the TTS, but still can't get it to operate. I even unscrewed it from the intake air plenum and turned it around to check if it's spraying, nothing. I've run a test light on the CSV and TTS and they each only illuminate for a flash when initially cranking the starter. After that, nothing.
I was able to duplicate the test light flash by opening up the AFM cover and turning the vane so the fuel pump energizes. As soon as the fuel pump turns on, the test light flashes and that's it until I try it again.
So, it appears the CSV is not getting a sustained 12 Volts when cranking, any ideas what could be causing this?
I've been chasing this for a while, and its getting cold out!
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1979 Mexico Beige Westy auto
Dirty Dover, NH

[cmonSTART]

I had to flip through my Bently to confirm it, but it appears CSV power goes through the double relay at some point. Bently says there may be a possible fault with the double relay if you're not getting power to a test light at the CSV when it's cold out.

FWIW, my bus starts pretty easily even without the CSV in cold weather.z
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'78 Bus 2.0FI
de K1IGS

[busdaddy]

A test light on 86 at the double relay would narrow down what to suspect is breaking down while cranking, power at 86 while it's cranking says suspect the TTS, a short flash or no power says relay issues.

https://www.thesamba.com/vw/forum/viewtopic.php?t=334340
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[Gregg in the 603]

Right on guys, thanks for the input. Test light on terminal 86 of the double relay same thing, flashes for a second when cranking, but otherwise not illuminated. Is the double relay bad?
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1979 Mexico Beige Westy auto
Dirty Dover, NH

[SGKent]

be aware that there are two versions of the double relay in 1979. One for federal and one for California. I can't say what the difference would be if someone put the wrong one in. There are actually two different FI wiring diagrams for that year too. Make sure you are using the correct one.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Gregg in the 603]

Thanks Steve. It is a '79 Cali that the PO converted thankfully and I'm riding the wave of that. I redid the harness and all of the parts of the FI is '77. The double relay is not original, but has the terminal placement on it.
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1979 Mexico Beige Westy auto
Dirty Dover, NH

[SGKent]

I haven't studied the AFC manual in a while so I could be wrong on this. What it looks like to me on a 1977:

The starter motor solenoid, when it is engaged provides power to 86a of the double relay. That passes thru the relay on a straight wire bus to pin 86. Pin 86 provides 12V to the CSV and TTS. I would start by checking to see if there is 12V to pin 86a when the starter is cranked. if not then the error is likely to be between the starter and pin 86a. If there is 12V as long as the starter is cranked, then I would check for 12V at pin 86 as long as the starter is cranked. If not then something is wrong inside the relay. If there is 12V at ping 86 then I would check to be sure there is 12V at one side of the CSV. The other side gets grounded thru the TTS.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Gregg in the 603]

Okay, pin 86a shows 10.34 volts while cranking, which should be within spec? Pin 86 shows .45 volts while cranking, so basically not much at all. Faulty double relay? Based on what you said, that's what it's looking like...
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1979 Mexico Beige Westy auto
Dirty Dover, NH

[furgo]

[SGKent]

check for corrosion, pull the cover off the relay and see if either solder joint has broken. The wiring diagram shows they should be internally connected to one another. That doesn't mean that the TTS didn't go bad internally and short out, causing the wire inside the double relay to open up or melt solder.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Gregg in the 603]

Hey again. Opened up the double relay and checked the connection between 86 and 86a, shows zero Ohms, so connection looks good.

Solder looks good too.

Still not sure what's going on or what to check next? Thanks a lot so far for the help.

[airschooled]

Achtung!

If your fuel pressure regulator is allowing the pressure to zero out after a few hours of sitting, it will take your system a few seconds of cranking to build enough pressure for the system to run correctly. In that time, the TTS might cut off the CSV so the CSV won't actually spray any fuel.

Assuming electrical gremlins are sorted out, you can check this theory easily… Before the first start of the day, turn the key on, but don't start the car. Use a pencil/dowel in the air filter intake to activate the AFM flap and run the fuel pump for ten seconds, or until your attached pressure gauge shows at least 30psi. With the pressure at 30psi, start the engine, and note any performance differences.

Good luck!
Robbie
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[Gregg in the 603]

Thanks Robbie, I've tested that theory and assumed that was my problem since this first creeped up. I've pinned the AFM flap to energize the fuel pump. Fuel pressure pumps up to 40-41 psi within a second of energizing it (and drops to 0 within 3 seconds after shutdown). I've waited a good while and cranked. No noticeable difference.
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1979 Mexico Beige Westy auto
Dirty Dover, NH

[airschooled]

[busdaddy]

[airschooled]

[curtp07]

I had the same hard start issues...

Same set of symptoms...quick falloff of pressure after shutdown.

Replaced FPR. Fixed.

Curt
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Subaru

[Gregg in the 603]

[SGKent]

yes I have it.

Here is my question. if 12V is at one connector and no volts at the other, how can that be possible unless the schematic is wrong and there is a coil or something in between. I tried to see the pin numbers in the photos but could not clearly see.

You can also measure VOLTAGE (be careful not to put it on ohms or milliamps or damage may occur) across pins 86 and 86a. The differential should always be zero if they are hooked together internally.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

Colin has this schematic of the starting circuits active on the double relay. He is usually accurate.

Also - if the FPR were subject to in the box failure they would be hermetically sealed - and think how soon they would fail once installed. This one is from about 5 years ago when they started to go NLA - I bought one without realizing I already had a new spare. This is the newer of the two. The other one is in the older yellow box. Both are genuine Bosch. I am only selling one but I don't care which boxed one sells. Just getting my cost out - no profit. You can call bus depot and see if the one they are shipping is Bosch or aftermarket.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin