[T3] Fuel Pump relay not energizing
Jim Adney
jadney at vwtype3.org
Thu Feb 23 13:50:15 PST 2017
On 23 Feb 2017 at 20:27, Dorough, Don CIV, NPPSC N3/PSD Pensacola
wrote:
> My question is why is this signal not coming from the ECU and what
> does the ECU check for before it will energize the fuel pump relay?
> I'm thinking there is a problem somewhere else and not in the ECU.
Sounds like you have a good handle on the situation and have done
good troubleshooting so far.
A few extra things to understand:
The circuit in the brain that connects to that wire to the relay is
automatically grounded for about 1 second when you turn the key ON.
That circuit gets refreshed by the trigger points each time a trigger
point opens or closes. So yuou get another second every revolution of
the crank. This keeps the pump on while the engine is running, but
shuts the pump off after 1 second if the engine stops for any reason.
This is an important safety feature.
So, if you just turn the key on and then try to check the relay, it
will be off after 1 second.
The wire to the relay has an in-line connection in the engine
compartment. It's located against the front "fire wall" just to the
left of the intake air distributor. You can do another test by
grounding that connector with the key ON and listening for the fuel
pump relay.
None of this works if the brain isn't getting power. FI power is
provided by the FI power relay under the back seat. You should be
able to hear that relay click ON when you turn the key ON and click
OFF when you turn the key OFF. That relay gets its ground via a
ground wire to its mounting screw, so make sure that screw is tight.
I see you're in Florida. It's possible that your brain has suffered
from corrosion that has damaged the transistor that controls this
circuit. I've replaced that transistor in one other southern brain.
If you trace this problem back to being inside your brain, then you
can either look for a better 311 C brain, or I can replace that
transistor for you. I can help you with either one, the prices would
be about the same; one is all parts, the other is all labor.
If you get to the point of suspecting the brain, I can tell you what
to look for.
--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************
More information about the type3-vwtype3.org
mailing list