[T3] Question about D jet idle issues 73 T3

[William J]

----- Original Message ----- 
From: "Jim Adney" <jadney at VWType3.org>
To: <type3 at vwtype3.org>
Sent: Wednesday, January 27, 2016 6:01 PM
Subject: Re: [T3] Question about D jet idle issues 73 T3


> Will,
>
> Re: the intake runners and the hoses that connect to the IAD.
>
> Misalignment there is common, and always the result of tightening the
> IAD into position before installing the intake runners. Here's what
> should be done.
>
> Mount the IAD and both intake runners loosely and then move each of
> them to get the best possible fit to each other. Do this with the
> connecting hoses backed off, onto the runners. Tighten these 3 parts
> into this best possible place. Grab any misaligned intake runner and
> bend it until it aligns perfectly. Slide the connecting hoses into
> place.
>
> Personally, I hate to see hose clamps on those hoses, because they
> actually need to be able to slip a bit as the engine expands and
> contracts as it warms and cools. If you really feel that your hoses
> are so distorted that they need help, snug up some nylon cable ties
> around them.
>
> I also have new hoses if yours are too badly distorted, but in most
> cases, if you get everything lined up nicely and then use the cable
> ties for a year or so, the hoses will straighten out and the cable
> ties can be removed.

 Jim , I had everything lined up before I secured the IAD or runners . My 
hoses are just old and I need new ones that's why the clamps .
>
> Re: Air leaks and richness/leanness
>
> Since the D-jet system uses the pressure (MAP) sensor to determine
> the need for gas, leaks into the IAD are always compensated for.
> Think about it this way: The throttle valve, idle adjustment, and AAR
> all amount to nothing  more than "leaks", yet the pressure sensor
> adjusts for all of these. Any other leaks into the IAD are
> indistinguishable from those "legitimate" leaks, so the brain has no
> reason and no need to compensate for them differently. All such
> "leaks" are treated the same.
>
> This is different from most later FI systems, where leaks which occur
> after the air measuring device will lean out the mixture.
>
> So, the leaky vac adv can is not a problem. The lack of that advance
> will mean that you get 1-2 mi/gal less fuel economy, but only
> cruising at highway speeds, where it is active. The port for that vac
> adv is only active at partial throttle.
>
> Re: Missing at idle
>
> If the engine runs just fine in traffic and going uphill, the fuel
> pressure must be okay. It sounds like your only concern is the
> missing at idle and popping when you take your foot off the throttle.
>
> You're probably right about the popping being due to exhaust leaks,
> but missing will contribute unburned gas to the exhaust stream. That
> only makes sense, however, if you also have missing under load.
>
> Is the engine missing while you're driving?

 Jim , no it does not miss under load or ever while driving even with the 
IAD temp sensor plugged in.
>
> For the missing at idle, I'd look very closely at the ignition
> components. Use an inductive timing light on each cylinder in turn,
> to see if one of them fails to flash occasionally. That might point
> you in the right direction.
>
> If it's not one particular cylinder, consider trying a different
> rotor, especially if the one you have in there is not Bosch. Check
> the resistance of the rotor; correct ones measure ~5000 Ohms, but
> some aftermarket ones are zero, which usually works just fine. I've
> had Asian rotors fail by puncturing thru the Bakelite in such a way
> that the spark could ground occasionally to the dist shaft. Such
> punctures are invisible and you'll only figure them out by
> substitution.
>
> Clean the inside and outside of the cap and the nose of the coil. OG
> Bosch parts are your best choice here, so be wary of aftermarket
> parts, including Bosch Blue coils.
>
    Jim: the cap ,rotor and wires are all new Bosch parts not some off brand 
rubbish and the coil is a black Bosch coil and I have a spare. I checked the 
rotor and plug resistance all are well within spec you posted. I check even 
new Bosch parts .

 William.

> Finally, reread what you post. I often have trouble following what
> you write, as it tends to wander and run several topics together.
> Stream of consciousness is not what we're after here.  ;-)
>
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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