TS1 roadside bypass options and resistance values?

[airschooled]

Hi folks,

I was working on some FI issues the other day, and I pondered a hypothetical issue. What if the TS1 inside the AFM went out like TS2 senders sometimes do after a while?

Since it is a NTC (negative thermo-couple) just like the TS1, the warmer the sensor is going to show a lower resistance reading, in ohms. 2800 ohms at 68°f is spec, but has anyone measured the sensor on an extra hot or cold day? Has anybody disconnected the sensor and tried running their FI bus without it, or with it grounded? What were the effects?

Please discuss, and save the banter for my engine thread…

Robbie
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[Wildthings]

The Vanagon Bentley has a chart showing the resistance at temperature for the TS1 sensor, IIRC the graph is identical to the one the Bentley shows for the TSII sensor. Ratwell.com has a graph for the TSII which shows a resistance of ~1000 ohms at 120°F. FWIWI don't think the TS1 is as critical to the operation of the vehicle as the TSII, but could be wrong.

[danfromsyr]

perhaps a clip in Potential-meter would allow a TS-II bypass.
a position for cold start and a setting for 'operating temperature'

here's a thread to read thru
https://www.thesamba.com/vw/forum/viewtopic.php?t=248511
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[SGKent]

the TS1 reads incoming air temp. Early AFM did not have it. I think it was added when preheat was removed in 1976 1/2
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[raygreenwood]

I think we kind of went through this in other threads...but OK.

I made a TS-1 some years ago that is a variable resistor. Its mounted to a circuit board and is inside of an old type 4 headlight dimmer relay box. I was using it to see if I could tune away the seasonal hot to cold idle issues in D-Jet. It worked but was interesting.

TS-1.....just going off of memory here....in L-jet...affects fuel mixture in about a 5-10% total range. By total range.....I mean a spread of 5-10% which is a +/- 2.5 to 5%.

While a 5% total change is nothing to sneeze at.....I agree with SGkent that because of the way it functions it is less significant to engine running. This would be because unless you are dropping down the side of a mountain fast...or going from air that ranges from room temp to frigid going in and out of tunnels....the intake air temp is relatively stable.

However.....5% is 5%. Each engines state of fuel tune will affect this. The affect of all enrichment devices is cumulative. If your system is already running a few percent low or high in fuel mixture....due to either variation at TS-2, fuel pressure, main load setting at the AFM or vacuum leaks...having a +/- of 2.5% to 5% can make a difference in running.

While I dont think on an otherwise perfectly tuned engine the TS-2 makes a significant difference to RUNNING....it will make a difference in idle and cold starting. If your engine as mentioned is NOT perfectly tuned and you have other cumulative +/- fuel inputs and its really cold.....having the TS-1 be off can the difference in starting or not.

Other items that can be counted in that "perfectly" tuned collection can be ignition timing issues, low compression from an engine showing its age etc. So in my opinion.....and just based on the limited TS-1....and extensive TS-2 experiments I would say depending on your cumulative state of tune....a variable, dial in TS-1 could be useful.

The thing I have always liked and disliked about the "basic" L-Jet on the buses and 412's....is that while it is far simpler to run well than D-Jet, K-jet and the others there is not much actual fuel tuning you can do. You have idle and AFM air by-pass......and a really critical tweak you can do to the cog wheel (which is always a compromise because you cannot just adjust one narrow range of flap motion)......there ia not much else you can adjust.

But getting into tweakable TS-1 and 2.....you can affect a good 15% of fuel mixture at certain temp ranges. Also....an adjustable rising rate fuel pressure regulator can make a good amount of adjustment at certain points.....but the ones that I have tried in the past like those you find at Summit and Jegs....just do not seem to be in the perfect increments for us. Ray

[furgo]

[Wildthings]

Waiting for owners of '75 Bays to weight in here and tell us what running an engine without a TS1 sensor and a non working intake air preheat is like. From what I remember hearing it is no big deal. There is probably an optimum value for a resister to replace the TS1 sensor on the later FI setups, so maybe it would be advantageous for someone to do some experimenting. Since the TS1 essentially just plugs in and the resistance of the OEM TS1 sender is shown in available charts, this should be a pretty easy experiment to do and the out of pocket cost would be just a few bucks for a bag of miscellaneous resisters.

[airschooled]

[SamboSamba22]

Continuing the conversation regarding the TS1 units, does anyone have sources or information on locating a replacement unit?
It’s also come to my attention that we don’t necessarily know the specs for resistance of these units? Mentioned they are comparable to the TS2 sensors?


Attempting to diagnose (with much help from Robbie) a cold start issue on a 77 bus. The AFM has been rebuilt by FI Corp, looks good. 7 pin, late FI unit appropriate for the 77 year model.

The cold starting valve is working, resistance is good, cleaned within an ultrasonic cleaner. TS2 was replaced. Aux Air Sensor is within spec, good working order. There seems to be no present issue with the ignition system.
Fuel pressure 31 at idle, 39 with vacuum removed. Vacuum added back to regulator, pressure balances back out at 30ish psi.

Swapping out the rebuilt AFM with a known good stock AFM, the cold starting woes are eliminated. Considering the cost of the rebuilt units, I’m wanting to know if I can make it operate and function as intended, but am coming up with a lack of source for replacement TS1 units.


When one has their AFM rebuilt, do we know if FI Corp checks the resistance of the TS1, and if so, if found out of spec, where do they source replacements?
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[Wildthings]

[airschooled]

We do know the approximate resistance of TS1 at 68* from the AFC training manual. Though I don’t recall a chart like it has for TS2, grab 2,800 ohms of resistance and stick it in line using the terminals that furgo posted. That will pretty much tell you right away if TS1 is the problem.

It should be 68* at your place this afternoon
Robbie
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[raygreenwood]

[furgo]

[Wildthings]

[raygreenwood]

Yes....it will affect it. Carbon is inductive. If anything with resistance touches the carbon....is connected to....no matter which pole....it affects its response.

I have spent the last year workong on carbon inductive sensors for an automotive safety sensor company......and learned quite a bit. How it affects it and how much? Remains to be seen.....but if its connnected....its connected....and affects it. Ray

[Wildthings]

[furgo]

[Wildthings]

Just a note on any potential oscillation in the signal from the rheostat in the AFM. I independently came up with the idea of adding a 22uf capacitor between the rheostat signal lead and ground nearly thirty years ago to control Vanagon syndrome. Not only did it take care of the Vanagon syndrome, but it smoothed out the idle, so I did the mod on any other Digifant Vanagon I picked up even if it wasn't experiencing Vanagon syndrome. I also did the mod on the Digijet Vanagon I acquired as well, there too it smoothed out the idle.

I am not presently running a bus with L-jet, but if I did I would certainly try adding the 22uf capacitor to its AFM as well. Note to anyone who might try this, the sizing of the capacitor was determined by increasing the capacitors size until it caused a lag in the response of the AFM and then going back a step in size, this gave the 22uf size for the capacitor. If you try a 22uf capacitor in an L-jet system and it causes a lag, then go to a smaller capacitor. For people that have to get their rigs passed emissions adding the capacitor might well improve the emissions both at idle and across the board, YMMV.

[SamboSamba22]

Still attempting to troubleshoot the circuit for the TS1. With the main wiring harness attached to the AFM (7-pin since we have a TS1 sensor), removing the harness from the ECU and testing for resistance on pin #27 to see what action we have taking place for this sensor.

Results are? Absolutely nothing.No resistance at the AFM connection nor pin #27 at the ECU end. Tested two different AFM units.

Issues being experienced? The bus from a cold start ONLY is taking 5/6 cranks and starts before the bus will hold an idle. With no resistance within the Pin #27 circuit, there isn’t anything going to nor from the TS1 sensor to the ECU.

This would lead one to believe that there is an issue within the wiring harness from the AFM to the ECU, though every other circuit reads resistance within spec.
_________________
The Bus Barn Ltd. Co.

Oct. ’67 Double Cab (’68 Crew Cab)
[url=http://www.vw-mplate.com/mplate-44412.png]Click to view image[/URL]
March '69 Delivery (Panel Bus)
[url=http://www.vw-mplate.com/mplate-44414.png]Click to view image[/URL]

[Wildthings]