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Air flow meter sensor
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Mrbazza
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PostPosted: Sat Aug 01, 2020 3:34 am    Post subject: Air flow meter sensor Reply with quote

Hi guys.
Does anyone know if the sensor/thermistor on the Bosch l jet AFM is replaceable and if so what size?

This is the only info I can find
Thanks
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Abscate Premium Member
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PostPosted: Sat Aug 01, 2020 4:17 am    Post subject: Re: Air flow meter sensor Reply with quote

I looked for pictures of this but couldnít find any. Itís down in the air flow corridor of course, not on the circuit Board.

A thermistor meeting these specs isnít too hard to find at a place like DigiKey

You want An NTC thermistor like this one, and match up the resistance specs

Letís see, if itís a 2000 ohm at 20c. And 200 ohm at 50c. You want the TCR parameter to be 3%/c

So that 30C reduces the resistance by 90%

https://www.digikey.com/product-detail/en/vishay-bc-components/NTCS0603E3222FMT/BC2478DKR-ND/2505766

You can take the 99 from the minimum order and make nice earrings out of them ...😅
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SGKent Premium Member
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PostPosted: Sat Aug 01, 2020 8:07 am    Post subject: Re: Air flow meter sensor Reply with quote

if you are refering to the TS1, a plastic dome in the AFM, I don't know. You could call Fuel Injection Corp in Livermore https://fuelinjectioncorp.com/ and see if they have any. I have never heard of anyone replacing one of those. Not all AFMs have those. Some early ones did not.

here is a thread on it https://www.thesamba.com/vw/forum/viewtopic.php?t=690337&highlight=ts1
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PostPosted: Sat Aug 01, 2020 1:54 pm    Post subject: Re: Air flow meter sensor Reply with quote

Ah, this damn bastard part. Robbie and I were battling cold start issues on one of my customer's bus for a couple weeks while I trouble shot about everything. The bus was a 77, so used the 7-pin AFM. As SGKENT mentioned, the earlier versions didn't use a TS1 sensor within the AFM, so the AFM units only had 6 pins.


I ended up opening the 7 pin AFM and detaching the TS1 wires (just simple spade connectors attached to the sender for the TS1). Doing so, I eliminated my cold crank issues on this customer's bus. Please note that the resistance within the bus' wiring (FI) harness had excessive resistance, meaning the harness was worn out from age and hot/cold cycles. So in my case, was a combination of the TS1 and the wiring harness.

From what Robbie and I gathered, no one including the shop in CA replaces these units as they're not out there.


Good luck,

Sam
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Mrbazza
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PostPosted: Sat Aug 01, 2020 5:31 pm    Post subject: Re: Air flow meter sensor Reply with quote

Thanks for the info guys.
This is the only sensor left to try to eliminate poor running once up to running temp. I even tried swapping out the internals of the 7 pin afm into a bigger 5 pin afm from a volvo 340. It runs nice and smooth (after a rough start) up until it gets to temp. Then the hesitation and erratic idle start
I have been told to put it on a rolling road for proper diagnosis. It's looking that way now...
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Wildthings
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PostPosted: Sat Aug 01, 2020 5:36 pm    Post subject: Re: Air flow meter sensor Reply with quote

You can short out the TSI sensor or use a variable resister in its place to try and see what resistance gives the best performance.

Has this rig ever run correctly for you?


Last edited by Wildthings on Sat Aug 01, 2020 5:36 pm; edited 1 time in total
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PostPosted: Sat Aug 01, 2020 5:36 pm    Post subject: Re: Air flow meter sensor Reply with quote

Is there an issue with too much enrichment of fuel? Once warm, too much fuel from a bad/leaking injector or cold start valve could cause fuss.

And also as I mentioned above, the resistance within the fuel injection has needs to be right. Any issues with the throttle body? Excessive wear or slop?


Sam
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Mrbazza
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PostPosted: Sun Aug 02, 2020 11:27 am    Post subject: Re: Air flow meter sensor Reply with quote

Wildthings wrote:
You can short out the TSI sensor or use a variable resister in its place to try and see what resistance gives the best performance.

Has this rig ever run corretctly for you?


I tried shorting out and also connecting 1k potentiometer to vary resistance but only made things worse or wouldn't run at all.
No it has never run properly since I fitted it Sad
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PostPosted: Sun Aug 02, 2020 11:49 am    Post subject: Re: Air flow meter sensor Reply with quote

This isnít the TsX sensor(s) , itís a thermistor inside the AFM in the air flow area.
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Mrbazza
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PostPosted: Sun Aug 02, 2020 1:10 pm    Post subject: Re: Air flow meter sensor Reply with quote

I noticed the throttle body spindle wasn't opening fully and p/o had cut the arm under the pedal so I lengthened it and now have wot which makes it much more drivable.
Good on a long run but when in traffic and the head temp rises it starts running erratically again.
So it does seem temperature related. I will try and get a suitable thermistor to replace the one in afm.... Not sure what size is required. The charts I've seen, if lower temp matches ohms needed then higher temp is no where near. Confused
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SGKent Premium Member
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PostPosted: Sun Aug 02, 2020 1:46 pm    Post subject: Re: Air flow meter sensor Reply with quote

Mrbazza wrote:
I noticed the throttle body spindle wasn't opening fully and p/o had cut the arm under the pedal so I lengthened it and now have wot which makes it much more drivable.
Good on a long run but when in traffic and the head temp rises it starts running erratically again.
So it does seem temperature related. I will try and get a suitable thermistor to replace the one in afm.... Not sure what size is required. The charts I've seen, if lower temp matches ohms needed then higher temp is no where near. Confused


I had an AFM that did that, nothing could tune it when it got hot from idling too long. Bought a NOS one. Problem solved immediately. You should also check the TS2 if you haven't.
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