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Re: [T3] Slight bucking/jerking heat related??


On 9 Jul 2002, at 18:21, Wuzmop@aol.com wrote:

> 73 EFI...Dwell, timing, fuel pressure, voltage, vital stats all good. It has 
> a sometimes slight bucking/jerking in 3rd gear at 35 and 4th at 65-70. I have 
> been observing it for over a month and found that it does not do it in the 
> morning, when temps are below 80 or so. It always does it at least once in 
> the afternoons in 90-95 degree weather. It seems to happen primarily on 
> deceleration or when I just try to maintain a speed.

Here's a test to try: Just unplug the connector to the throttle valve switch. 
With this switch disconnected you will find that the car doesn't accel nearly 
as well, but it should cruise at constant speed just fine. Ignore the 
doggyness and just pay attention to the constant speed times. Are the 
misses gone? If so, you probably need to clean or replace your throttle valve 
switch. Leave this disconnected for several days just to make sure of your 
observations, then put it back on and see if the missing has returned.

There is a pairt of contacts in there that alternately connect to a common 
contact, these spray extra fuel when you push the throttle down. If the 
moving contact wears flat enough it will span the alternating contacts and 
this will stop the FI. This wear is most common in the area where the throttle 
has spent most of its life. You can test for this problem by measuring the 
resistance between the 2 alternating contacts over the whole throttle valve 
range. You should measure infinity everywhere, but it is fairly common on 72-
3 cars for this to wear thru and cause a problem at cruising throttle values.  

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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