[T3] [Non-DoD Source] Re: Fuel Pump relay not energizing

Dorough, Don CIV, NPPSC N3/PSD Pensacola don.dorough at navy.mil
Fri Feb 24 05:56:40 PST 2017

Thanks for the detailed explanation!  This is exactly what I was hoping for.  I hope it's just a bad connection at the in-line connector in the engine compartment. I'll check that next.   Do you happen to know what color that wire is in the engine compartment (coming off pin 19 in the ECU). Mine is blue with a white dot tracer at the fuel pump relay - pin 85. But as you know, wires "magically" change colors sometimes when they go through connectors.

The power relay under the back seat clicks when the key is turned on, and I figured the ECU was getting power because the car does run if I manually energize the fuel pump relay.  

If I suspect the transistor in the ECU I will ask for more info later.  I was an ET in the Navy with micro-miniature soldering training so I would be able to replace it.

Thanks for explaining how the trigger points keep the fuel pump energized, makes perfect sense!!   None of that is explained in the Bently or the Clymer's.  Is there a detailed guide somewhere?

Have a Great Type III Day!


-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim Adney
Sent: Thursday, February 23, 2017 3:50 PM
To: type3 at vwtype3.org
Subject: [Non-DoD Source] Re: [T3] Fuel Pump relay not energizing

When replying, please consider trimming your message. Thanks! :)

On 23 Feb 2017 at 20:27, Dorough, Don CIV, NPPSC N3/PSD Pensacola

> 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

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