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  View original topic: No voltage at terminal #10 for ECU power supply
cybervette Sat Aug 09, 2014 4:02 pm

Ok, so I have a 1983 Vanagon 2.0 air-cooled California model. I rebuilt the motors top end. All new seals and gaskets. Almost everything is new on the engine. New parts include: fuel injectors and seals, fuel lines, fuel pump and filter, fuel pressure regulator, cold start valve, coil, double relay, voltage regulator, spark plugs, wires, cap, rotor, O2 sensor, temperature sensor, catalytic converter, muffler and egr filter, battery, all new vacume lines, S-boot and intake air distributor to runner boots, thermostat. My intent was to completely re-furbish the engine and other mechanicals to have trouble free running for years to come.

I had it running decent for about 100 miles and then it quit. It will start up pretty easily, run for about 5 seconds and then die. I can keep it running if I keep squirting in starting fluid. It has strong spark. Fuel pressure is about 35 lbs. Compression is about 125 lbs on all cylinders. I suspected a problem with either the Air Intake sensor or the ECU. I sent both to Fuel Injection Corporation to have them checked out. They said the Air Intake Sensor was fine but the ECU was faulty. I paid $300 to have it rebuilt. It didn't help and the engine still won't stay running.

Per Bentley (24.15) I checked all the electrical connections on the ECU cable. All resistances were within normal range. Voltages are another matter. #4 to ground (signal from starter) is supposed to be 12v while cranking and 0v at all other times. I get 0v volts both on cranking and other times. #10 and ground (voltage supply to computer) is supposed to be 12 volts with key on and 0v with key off. I get 0v for both. #20 and ground (Pump Circuit) is supposed to be 12v with key on and sensor flap open. I get 0v again. If I plug in the ECU cable, turn on the key and open the air flow sensor flap I can hear the fuel pump running.

I believe #10 connector goes to terminal #88a of the dual relay. I measured a resistance of less than 1 ohm on that wire. A continuity check also tested good. On the dual relay I measured 12v on terminals 88z and 88y with the key off. With the key on I measured 12v at terminals #85 and #86c as well, but no voltage at #88a. Shouldn't I see voltage there when the key is on? I re-installed my old dual relay just in case I had a faulty new one but I got the same results on both.

I'm at a complete loss here! Does someone know what is the voltage source for terminal #10, #4 and #20 of the ECU cable and how do I track down the problem? I don't understand how the engine can even run with starting fluid if the ECU isn't receiving power?

cybervette Sun Aug 10, 2014 7:04 am

Just in case it is relevant I thought I should also mention that on the harness cable pin-out to the ECU I do have 12v power, with the key in the ON position, on terminal #1 (I believe from terminal #1 of the coil) and #28 (which I believe is from terminal #85 of the dual relay).

Also, when I have the harness plugged into the ECU with the Key in the ON position I also measure 12v at terminal #88a of the Dual Relay and terminal #39 of the Intake Air Sensor, which according to the schematic in Bentley 97.19, is connected to the Dual Relay at #88a. I don't measure voltage at those points unless the harness in plugged in to the ECU. What confuses me is that, according to that schematic, #88a should be a common connection point for terminal #10 of the ECU as well, however terminal #10 should be receiving power with just the Key turned ON.

crazyvwvanman Sun Aug 10, 2014 9:09 am

The ignition system is independent of the ECU and fuel injection. I suspect it will run on starting fluid even with the ECU removed.

I don't trust the wiring diagram for that dual relay. The way it is drawn makes no sense to me so I suspect errors.

I might try to unplug the power wire to the fuel pump and hot wire the pump to constant power as test. Then see if the engine will keep running.

Mark

cybervette Sun Aug 10, 2014 11:30 am

crazyvwvanman wrote: The ignition system is independent of the ECU and fuel injection. I suspect it will run on starting fluid even with the ECU removed.

I don't trust the wiring diagram for that dual relay. The way it is drawn makes no sense to me so I suspect errors.

I might try to unplug the power wire to the fuel pump and hot wire the pump to constant power as test. Then see if the engine will keep running.

Mark

Yes, I find the schematic a bit suspect as well as my double relay has terminals #88e and #88f, which measure 12v with the key on, which aren't even shown on the schematic. I have no clue what those terminal are for. Maybe the schematic is for the federal model only and not the California?

I tried the test you suggested. I hot wired the fuel pump so that it would run continuosly and tried re-starting the engine. Still won't run without shots of starting fluid.

cybervette Sun Aug 10, 2014 11:47 am

Ok, so here's another update. I unplugged the injectors to test for signal. While they were unplugged, just for giggles, I tried starting the engine with a squirt of starting fluid and it did briefly run. So obviously I'm getting fire. I showed no voltage to the injectors with the key on and no pulse when cranking the engine. I'm really starting to think they did a poor job on the ECU rebuild but that still doesn't explain why I don't see 12v on terminal #10 with the key on.

cybervette Sun Aug 10, 2014 1:03 pm

Ok, so I take it back. I re-tested the injectors with a test light and I do get a blinking light, on cranking the engine, on all 4 injectors. Don't know why I didn't see it the first time but I am having a nice conversation with myself. Anyone else willing to jump in with suggestions?

So I know I have pulse (strong blinking light) but I don't know if it's enough voltage to fire the injectors. I guess I would need an analog multimeter to be able to see the fluctuations in voltage? Also, I thought that when the Key is ON there should be constant voltage (how much?) to the injectors and that the ECU simply gives the injector a grounding pulse breaking the circuit. Is my thinking messed up?

MarkWard Mon Aug 11, 2014 7:09 am

The injectors click when they fire. I have an automotive stethoscope that I use. You can also use a long screw driver against the injector and your ear. It is more work, but you can also remove one of the injector rails with the injectors and visually check for fuel delivery.

cybervette Sun Aug 17, 2014 11:25 am

I removed the screw from the fuel rail test point and cranked the engine with the key on. No fuel!

Next I seperated the AFM from the S-Connector tube and opened the air flap with the key on. I could hear the fuel pump running but no fuel out of the test port.

I opened the fuel line immediately after the fuel pump and jumped the fuel pump from the battery. Fuel pump ran but no fuel.

I seperated the fuel line where it exits the fuel tank. I'll be damned! No fuel. Bone dry. The fuel gauge said I had 1/4 tank. Well that's embarrassing. What added to my confusion was that when I did a fuel pressure test earlier I had 30lbs pressure. It must have been the very last of the fuel.

Added 5 gallons and it now runs excellent. Lesson learned. When all else fails go back to the basics. Fuel and Fire.

Anyway, problem solved. I'm doing a happy dance! :D



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