[T3] Ken's lean exhaust

Phil Hof phil.hof at ostronic.org
Sun May 7 13:06:21 PDT 2017


—————————————
I will echo Jim’s comments, sorry for the repetition.  I’ve had good luck using an Innovate A/F meter but I seem to be one of the lucky ones.  I’ll share what I found but I also agree that chasing fractions of A/F points with a meter is probably not the best approach unless all else is spot on.

You have a lot of “all else” to clean up before going there.  Mismatched FI components will just never work.  Your lean condition under acceleration is a good example.  AS Jim posted, your mismatched system has no way to perform full throttle enrichment.  All you have (maybe) are the extra injection pulses driven by your throttle valve switch.

So lets start with a list of the part numbers for your major components:
ECU
MPS
TVS

One final word… do NOT open your MPS up unless you are going for major surgery and have a reliable A/F meter that reacts instantly.  On the C/D/E systems, that “plug” is NOT just a plug; it’s the full load enrichment adjustment!  Idle is not affected by that plug.  One of the two inner adjustments controls idle.  Another internal controls part-throttle mixture.  Then the outer plug controls full load enrichment.  There is considerable overlap and interactions among these three, and you will spend hours of trial and error, not just with the A.F meter, but also with drivability under various conditions.

I’ve got mine pretty well dialed in, though not perfect.  I invested in an expensive meter, the expensive MPS rebuild kit (Porsche prices), and frankly have been lucky that worked out consistently.

I now see about 14:1 at idle, on the verge of a lean hunt. Midrange cruising is about 13:1.  When I floor it, it spikes to 10:1 for an instant, then levels out at about 12 as the revs increase.  Form what I’ve read, this is about ideal.

My engine is higher compression after the rebuilds and 1776, so it took a bit of experimenting, and I also removed the vacuum advance.  It knocks under load and overheats with it in place, since it drives timing at high speed to something like 40 degrees BTDC, way too much for my compression, even on premium.  Effectively, I have “009-like” timing, and get slightly worse fuel economy and throttle response at low to mid rpm.  I may experiment with different mechanical advance springs or weights, since this distributor model MUST be timed at TDC for the injection timing to be right.  Experiments for the future...

I feel you will get more improvement by eliminating all vacuum and exhaust leaks, and being VERY picky about dwell and timing.  I have found that only a few degrees makes a HUGE difference in throttle response, probably due to the dual effect on ignition and injection timing.  My point hold-down screw doesn’t seem to hold very well, and every time the car seems to buck when floored at 2000 rpm, run hot, or hesitate, I find it has slipped.  I’ll probably send a spare distributor to Jim and/or Glenn to have its various components cleaned, checked, and adjusted.

So tio summarize, let’s get the right parts on your car, check/tighten the connectors, work on leaks and timing, and ONLY then think about fiddling with the MPS.

-Phil
----------------------------



More information about the type3-vwtype3.org mailing list