[T3] stumbles on acceleration

[Jim Adney]

On 16 Feb 2013 at 4:32, Chris Sheridan wrote:

> it stumbles on acceleration from a stop. it doesn't stall but the idle
> is not completely smooth but fumbling a bit. I'm going to get out the
> timing gun and confirm I'm at 0 degrees. I'm looking for a fuel
> delivery or ignition problem, correct?

Yes, confirm the timing first. Don't do anything else until you're 
sure the timing is right.

I would also check the dwell with a dwell meter. It should be between 
45 and 55 degrees, and should be relatively stable. If it's bouncing 
around more than 4 degrees, there is probably a distributor problem.

Then, see if the idle settles down if you push gently sideways on any 
of the injector electrical connectors. (Have you already gone thru 
those connections and tightened them up? If so, skip this step.)

If the idle is fine, but the car just doesn't like to accelerate, I 
suggest you buy a pressure gauge and some hose so you can check the 
fuel pressure and watch it WHILE you're accelerating. If this is a 
squareback, you can do this with a short hose and an passenger. If 
it's a fastback, you'll need a long hose so you (or a passenger) can 
watch the gauge while driving. 

If you do this, you MAY find that the pressure drops while 
accelerating. This means that the fuel pump can deliver enough fuel 
for idle but isn't able to deliver enough fuel for acceleration. This 
is usually caused by a clogged fuel filter and/or filter screen.

Another way to check this would be to remove the inlet gas hose to 
the fuel pump and see how much fuel come out. If everything is 
normal, you should get a scary amount of gas out. If it just dribbles 
out, you have a clog somewhere. Do this OUTSIDE; no smoking.

Finally, there are several possible problems in the distributor: a 
worn breaker plate, sticky advance mechanism, or worn FI trigger 
points. If you can't find the actual source of your problem, I 
suggest you send me your distributor to be cleaned up and rebuilt. 
This will often fix problems that are hard to find otherwise, and 
they can be too subtle to find on your own. I can't promise that this 
will fix your problem, but it's a good thing to do as a bit of normal 
maintenance, and it eliminates one group of possible suspects.

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