[T3] Mysteries and FI Parts

[Jim Adney]

Whoa, Jeremy, take a breath.  ;-)

Make some paragraphs (leave a blank line.) That will make your stuff 
lots easier to follow. 

Read on below.

On 9 Aug 2011 at 16:18, Jeremy Menzies wrote:

> I've been chasing a mystery engine problem for a few months now on my
> '71 Squareback (MT, FI, rebuilt stock 1600 w/a '69 case) 

> In short, I've gone through everything that I and the guy I've started
> working with can think of: set all the basic settings (timing, points,
> valves, etc); replaced all the vacuum (even the charcoal canister) and
> 99% of fuel hoses (not the ring main yet, it's not too old); good
> rebuilt fuel pump and filter; removed, cleaned and replaced gaskets on
> the intake manifolds and intake air distributor;

Do you have the special Type 3 FI bakelite insulator gaskets between 
the intake air runners and the heads?

> replaced head temp sensor (it was iffy); checked ohm and volt values on
> air temp, TVS, MPS, Injectors, Trigger points (all within spec from
> what I can tell and what the Bentley says).  I tested then pulled the
> trigger points and cleaned and bench tested them (ohms are 0 on one
> side and maybe .5-.6 on the other, openign and closing properly in
> car); 

You can do basic trigger point tests with an ohmmeter, but the 
rubbing block wears (slowly!) changing the dwell. This can lead to 
eventual running problems. I reset them when I rebuild a distributor 
($50) or I can just do the trigger points ($10.) This is not 
something you can check yourself unless you have the Bosch D-Jet 
tester; you'll have to send them to me.

> pulled the plug to the brain and checked continuity to all end points
> (either 0 or at most .2); pulled all sensor plugs and cleaned and
> tightened up all internal contacts; made separate grounds from batt to
> case ground and both FI and fuel pump relays; 

Did you tighten up the connector pins that connect to each injector? 
These sometimes get loose and make intermittent contact.

> pulled a vacuum on MPS
> (holds at +15"hg); compression good (140 on 1&2, 145 on 3&4); fuel
> pressure set and holds at 28.5psi when engine is running; hooked a
> smoke machine up to the intake (small leak around TVS but none others
> spotted); pulled, cleaned, lubed and checked Aux. air regulator
> (closes around 150F out of car but seems to stay open in car after 1-2
> miles of city driving); new spark plugs; new plug wires; tried both
> good coil and condenser (from well running cars); checked charging
> voltage at generator (haven't yet from regulator), 12.6-13.6 at idle,
> 14-15 at 2200; isolated generator from coil, no change in problem. 

This all sounds fine. The AAR is probably fine, it's just confusing 
you because you feel vacuum when you put your thumb over the hose. 
The test is to see if the idle changes when you close the hose with 
your thumb. It never makes a perfect seal, it's just good enough to 
make no change in the idle.

> Trans mount looks original but no cracks, tears, not loose, feels
> solid; pulled, cleaned and lubed rubbing block in the TVS then
> adjusted as per Bentley 'click' test (haven't rechecked with ohm
> meter). 

The TVS check is a continuing problem. The click test is only valid 
on 68-9 cars. You need to use an ohmmeter or the Bosch tester to set 
the later TVS's. I have a writeup on this if you want it. It calls 
out all the versions of the TVS, of which there were more than 5.

If you think the TVS might be the problem, just unplug it as a test. 
Your car might be a tiny bit more sluggish, but if your same old 
problems are still there, the TVS is not the cause.  

> Checked ignition oddities by pulling plug wires at idle to note
> changes, no one cyl. acts vastly different from the next; tried a
> different set of plugs, no change.  Pulled injectors to test spray,
> cleaned and bench tested, checked ohms (spray looks pretty fine and
> conical, sparkling clean, tips snap in and out on bench, ran some
> alcohol through to get any grime out, ohms are within Bentley specs). 

All sounds fine.

> So, the mystery is: 

> Pt. 1- Runs OK at idle set to 850 (way too high with aux. air reg. left
> open, like 1600 so I plug it) but something sounds amiss.  It's kinda
> like a misfire but it's very subtle and doesn't isolate to one cylinder
> through ignition wire pulling.

What happens if you leave the AAR connected and let the engine warm 
up. Does the idle come down? If not, maybe it really is stuck. Yours 
can be taken apart carefully and freed up. If yours is broken, I have 
good ones.

> Pt. 2- When driving, no matter the speed of the car, the gear, or RPMs,
> the whole car lurches and bucks, especially at lower RPMs (like in the
> bottom of gears or under load).  It's as if you had a switch on it and
> were flicking it off and on, comes in and out of power, off and on with
> smooth RPMs.  It doesn't seem to do it in a pattern either, kind of
> when ever, randomly coming off and on while going.  It's hard to
> describe.

Are you setting the timing to TDC at about 900 rpm? With the timing 
light, can you see the timing advance as you open the throttle and 
let the rpms climb up?

> Pt 3- This happened once the other day and I haven't duplicated it yet.
>  I took it out for a test spin, trying to get it more warmed up to see
> if the AAR closed and see what generally happens when it's warmer.  I
> got maybe 1.5-2 miles from home (in rush hour city traffic, so it warms
> up quickly) and all of the sudden the idle just dropped out and it
> would putter at idle, kinda stumbling and low but not stalling (sounded
> like those low revving race engines, sputtering and grumbling). 
> Shortly thereafter, I pulled in to get gas (only had about 1/2 gal) and
> the gas pedal would not respond at all for 10-20 seconds, not with
> pumping or holding or gentle persuasion, nada.  And then boom, on all
> of a sudden, high revs and going.  Got gas, checked AAR (still wasn't
> closed) and exhaust was very sooty black, bumped up idle screw with no
> difference.  The gas pedal remained unresponsive every time I let off
> and came into a stop then tried to go again, so I wound up laying it on
> thicker and made it home.  Like I said, I haven't duplicated the
> non-existent gas pedal symptom, but I haven't driven it much at all 
> aside from around the block on test runs.

Possible reasons for running rich: system voltage too low. Connect a 
voltmeter to the fuse box and watch the voltage while you're driving. 
Check it when the engine starts to falter. Does the voltage still 
come up around 14 V or so if the rpms are above 2000?

> Pt. 4- It smells like it's way too rich (gas smell but no leaks), the
> plugs get coal black instantly, and the exhaust looks black but
> according to an emissions tester, it shows up lean. 

Get in the driver's seat and turn the key ON. You should hear a relay 
click and then a second click about 1 second later. Do you hear both 
clicks?

> Conclusions thus far: I'm pretty stumped!  Everything tests within
> specs and technically is functioning properly and or good but it still
> won't drive right (it used to!).  Next step: Start trying to swap out
> other components and see what happens, if anything.  

While anything's possible, my bet is that it's not a problem with a 
defective FI part. The brains are almost always okay. The 70-1 
pressure sensors fail occasionally, but you did the right test and 
yours passed.

> These would be things I'd like to try first:1. ECU- 311 906 021D (I
> have black sticker, not sure if it matters)  side note: I saw a
> rebuilt unit with 021DX as the end in the part #, anyone know if this
> would work? (I imagine the X indicates remanufactured) anyone have
> luck with remans?2. Aux. Air Regulator- not sure on the # but it's not
> the electric version (mine seems to not close properly when it's in
> the car, so...)3. Wiring Harness or master plug to ECU & end plugs for
> Mar. '71 production (I want to rebuild mine but don't want to pull it
> all apart to do so. I'd rather get one with as many of the connectors
> as possible and redo the wiring and boots then install it)4. Manifold
> Pressure Sensor- 311 906 051C5. Throttle Valve Switch- 311 906 111C 

It's almost certainly none of those parts. I have all of them if you 
really wanted them, but it would just be a waste of your time and 
money.

Let us know what you find when you do the extra tests above. Consider 
sending me your distributor or just the trigger points.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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