[T3] 71 Squareback MT/FI - Intermittent Engine Stopping

[Jim Adney]

Richard,

There's something odd about your replies. The usual method is for quoted 
text to be marked with the > sign and your replies to be normal text. In your 
case this is coming thru backwards. If this is a setting that you can change, 
please do so. I don't think I've ever seen this backwards before

On 14 Jun 2020 at 13:11, Wisconsin Spryers wrote:

> Is the ground wire that goes from the fuel pump relay to the ECU
> accessible anywhere? In my wiring diagrams I see a single cable
> connector is noted between the fuel pump relay (terminal 85) and the
> ECU (pin 19), but couldn't see anything like the area where the harness
> leads up to the ECU. 

FI wire 19 connects to the car's wiring harness in a single wire connection 
that's a the very front of the engine compartment, just to the left of the IAD. 
This can't be your problem, however, because holding the primer switch in 
the Prime position is running the fuel pump, which is the only function of wire 
19.

The fact that you're not getting 2 clicks means that either:

    1) The brain is not getting power, or
    2) The brain is not getting a ground, or
    3) Something has gone wrong in the brain (rare!)

The fact that the engine still doesn't start, even when you run the pump 
manually (with the primer switch) means that the problem is not due to a fault 
in wire 19 or the relay.

> Before reading this latest reply this morning, I started up the engine
> while holding the fuel pump relay in my hand. I felt the 2 clicks as
> expected when turning the key to the ON position. The engine ran for
> about 40 seconds then died. When trying to restart for the 1st time
> after it stopped, I did not get any clicks from the fuel pump relay -
> only heard the 1 click from the main power supply relay. I then checked
> the connections on the fuel pump relay, specifically the plastic female
> connector with the two wires that plug into the 85 terminal (grey wire) 
> & 86 terminal (blue-white wire). I then tried to re-start the engine and
> I now felt the 2 clicks and the engine started. After going thru the
> additional checks you've suggested, I've successfully started the car
> multiple times since. Last attempt I let it run for 10 minutes at idle
> without issue. 

That sounds like it should tell us something about the relay connection, so 
you might want to check to make sure the female pins in that connector are 
both secure and haven't started to back out of the connector. BUT, even if 
that connection is intermittent, it becomes irrelevant as soon as you run the 
pump manually.

I'd be looking at the FI power and ground connections very carefully. It can 
be useful to have a voltmeter or test light hooked up to various places that 
you can watch while driving. 

Since you've examined most of the power and ground wiring, this COULD be 
a bad main power relay. The 2 relays are identical. I've never seen one go 
bad in the main location, but I have seen bad ones for the fuel pump. I have 
good spares, or you could take yours apart and clean the contacts.

Also, the main power relay coil gets its ground from a brown wire that loops 
up and grounds under the screw head that mounts the relay. Make sure that 
screw is tight. This is not likely to be your problem, since you've never 
mentioned a lot of relay clattering noises, but it's still a good idea to check it.

> Hummmm! Don't ya just love these intermittent problems!! 

Yes, exactly, intermittents are a bitch!  ;-p


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