[T3] Temp sensor and MPS problems on new motor

[William J]

 I'll offer my 2 cents for what it's worth.

  First thing that comes to mind when bucking is the issue is voltage . I 
say this only because you  now have a generator belt that adjusts how it 
should be. Also I think on Bob notch and how voltage dropped down while 
driving causing bucking.

 Both cars have a standard trans , this is more of a direct link compaired 
to an auto trans , in an auto trans one might never feel the bucking , they 
might feel lack of power or other issues.

 The next thing that comes to mind is when i remove a screw as you did in 
the MPS , I find it's really impossible removing it to tell just at what 
point it came out unless one pulls on the screw to feel it's release. . 
Going back in you can turn the screw CCW until you feel it lift thenat that 
point thread it back in. This is all to say you can be more than one turn 
off either way and not know it.

 The ony other idea I can offer is I replaced a faulty voltage regulator 
because of a rich condition that would come and go, I removed the cover and 
it was solid rust , didn't see how it could possibly work . About 6 years 
later the car suddenly was not running proper , I forgot all about the 
voltage . Point is I bumped the timing up just to see what it would do , I 
kept stopping and bumping it up until I got a ping uphill . Point is it 
drove like it did before then I realized the voltage and replaced it and had 
to put the timing back to spec, you can fool the system and it does not take 
much.

 I found in 96 trying to pass smog we had then if anything is off from spec 
it's worse that included even a slight turn on the MPS single screw 
adjustment or adding resistance the the HTC or a bit off on dwell or timing. 
Yes the fuel was quite different then . I have read that unplugging the IAD 
temp sensor brings it rich by 5 to 10% , I've done it yet never went from 
say 28 MPG to 14  . This is not to say your's has not.

 I remember on the early 69 there was a pressure switch under the right 
intake runners that does the fuel enrichment , is it possible that could be 
the issue that made this change in 300 miles. I say this because the drop in 
MPG is quite drastic just by unplugging the IAD temp sensor.

 These are just things I would check before dealing with the MPS just to 
rule them out.
----- Original Message ----- 
From: "Jessica Chase" <jesassica at gmail.com>
To: <type3-vwtype3.org at lists.vwtype3.org>
Sent: Saturday, February 20, 2016 7:24 PM
Subject: [T3] Temp sensor and MPS problems on new motor


>I think I might have been a little unclear. We have bucking when the AFR 
>goes lean but when we drove home yesterday with bad gas mileage and rich 
>AFR’s (and TS1 unplugged) there was no bucking at all. The driving was 
>smooth but the gas mileage was really bad. Plug TS1 back in and we’re lean 
>and bucking all over again.
>
> Today, we tested our fuel pressure and went for a drive with the gauge 
> installed. The pressure was at a steady 28 psi under all conditions. We 
> also tested both temp sensors under a variety of temps and conditions and 
> they both spec out fine. We also ran tests using 3 ECU’s and 3 different 
> pressure sensors so 9 tests all told pairing each sensor with each ECU: 
> two B units (neither of which ground our fuel pump) and one A unit. Each 
> pressure sensor with each ECU did the same thing: idled lean and then 
> leaned out so much under load that we bucked and could barely accelerate. 
> The fried unit has been out of commission since late November and it’s 
> sitting in a box waiting to be sent to WI for a post mortem as soon as we 
> get our lazy butts to the post office.
>
> Finally, we ran a 10th test. We re-calibrated the pressure sensor we took 
> the epoxy out of the other day. We were so fraught being 300 miles from 
> home and needing to get back that we didn’t reset the screw to it’s 
> correct depth. Anyway, it also idled lean but we were able to adjust it 
> about a half turn counter-clockwise to get it to idle at 13.2. We took it 
> on a 15 mile drive and the AFR #’s were sane and there was no bucking or 
> hesitation. We’ll do some more extensive driving and testing tomorrow. The 
> sensor is well marked as to the original position though the adjusting 
> screw on all of our sensors (both with and without epoxy) seem to be at 
> the exact same position….on a diagonal like so   /   with the upper part 
> at 1 o’clock and the lower at 7 o’clock.
>
> We do have one of Joe’s harnesses and the injector grounds are at the 
> center of the case. We also tightened up the injector connectors before we 
> installed the new motor. We’ve had issues in the past with the connectors 
> getting loose so we periodically retighten them as a precaution. We did 
> the same to the injector grounds.
>
> Jim….we want to get a B brain from you because at the very least we want 
> to be safe and be able to ground our fuel pump and we’re happy to re-try 
> everything with a known good B unit, but out of curiosity, why don’t you 
> favor adjusting the pressure sensor?
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