TheSamba.com :: View topic - manifold pressure sensor interchange question

Thu Sep 10, 2015 11:42 am

Good afternoon, Guys/Gals;

Quick question; I have a '71 FB resto, and I'm getting around now to the engine, which is a non-number-matching '71 fuel injected engine from another '71 FB. I have a "D" ECU, but do not have a 311 906 051 D MPS. I DO have two MPS's; one is a 311 906 051 B, and the other is an 022 906 051.

The 022 unit has the larger screw on the back end, whereas the "B" unit has the smaller screw; both still have the epoxy covering the screw.

The engine is out of the car, and has not been bench tested. Both units hold vacuum. Assuming they are both functional, is either of these units interchangeable with the D unit, and useable with my "D" ECU?

If not, any ideas where I can obtain a reasonably priced "D" unit?

Thanks in advance!

TTMOE

Thu Sep 10, 2015 12:37 pm

The ECU, MAP, and TPS must all match.

Thu Sep 10, 2015 1:29 pm

rosevillain wrote: The ECU, MAP, and TPS must all match.

HOWEVER:

VW eliminated the "D" MAP as a replacement since the C performed the same task just fine. 71 cars came with D MAPs as OE but the official sub was C. Since C/D MAPs are the most prone to failure, D MAPs are really tough to find.

Thu Sep 10, 2015 1:43 pm

OK. Thanks. Guess I'll just go with whichever of the two I have works best.

Thu Sep 10, 2015 3:37 pm

TTMOE wrote: OK. Thanks. Guess I'll just go with whichever of the two I have works best.

Problem is that you have a Bosch number and not a VW number on the one that's the correct style and that means it was likely a 914 part, but it will work for your application until you can find the correct 311 906 051 C part number.

You want the one with the big screw head, because only the C/D systems had the full load enrichment built into the MAP. the big screw head is actually the full load stop adjustment, and this is why A/B/E MAPS don't have it. A/B had a separate pressure switch under the passenger side manifold for full enrichment, and the E system had it built into the 5th prong on the throttle switch.

While the B sensor will "work", you'll be running lean under load and your engine will die quickly from this.

Thu Sep 10, 2015 6:37 pm

ok; thanks tram. i'll use the large screw one. appreciate the input.