Today, I set out to get a boost of heat. The heater booster had never worked since I've owned the car and with it snowing today, I thought it would be nice to try it out.
I replaced the glow plug with a new one as the old one had open circuit per the test method at type4.org. With new glow plug installed, I pulled both heater levers full up, turned the dash knob full clockwise and turned the ignition on. No heat, just blower fan. No fuel pump ticks either.
Checked the fuel pump windings and found 0 ohms across the terminals, so that was good as a blown pump would be hard to replace.
Used the wiring diagram at type4.org to find the power source for the fuel pump. Power comes from the Dual Relay (19) terminal F through the Overheating Fuse (16). This circuit is the single green wire coming from the Dual Relay and going through a fuse holder with two green wires coming out (one wire goes to fuel pump and the other wire goes to the Overheating Switch (9)). With key on, power was going to the fuse, but not out of it. The fuse was removed and found intact. Continuity from fuse holder to fuel pump was not verified until the fuse holder was cleaned of oxide.
Put wiring back together, key on, fan ran, fuel pump ticked as it cycled for a few minutes while the outlet line primed, then womf - the rumble of fire within was heard. I let it run for several minutes before turing down the temp lever to verify the heater would turn off. Then after a couple minutes, the fan shut off indicating the Temperature Sensor (5) worked.
The fuel line from the pump to the heater still needs replacing as it is obviously older than the other fuel lines (new), so I'll use the heater sparingly until then.
This has been a very interesting weekend - first time troubleshooting D-Jet fuel injection and Eberspächer BA4 gas-electric heater. It's rewarding to have resurrected some '70's technology for daily transportation using basic tools and readily available information. VW Type4Ever!
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