Official Fuel injection questions thread

[VW_Jimbo]

[war.hog]

OK Gents, Here is a new one for you. Quick history is 1978 Beetle with supposed 16k miles. Sitting for years, turning into a squirrel home. Wiring harnesses and interior chewed to oblivion. Have spent months returning to functioning car. Have replaced ECM, FI harness, Temp sensor, all 4 injectors, Fuel filter and AFM. All were not replaced until tested and confirmed bad. Here is where I stand.............After sitting until completely cold, engine will fire up and idle reasonably well. Giving throttle will result in hesitation and bogging unless done very slowly. Once engine warms it will stall and will not restart. Seems to be running very rich. I have gone over every test for checking fuel injectors again, point gap set, timing, egr, aar, vaccum leaks, etc. Finally, hooked up fuel gauge to cold start line (for what seems the 10 thousandth time), and here is what I find. New - rebuild AFM is not running fuel pump. If you run pump with starter or jump terminals from AFM, pressure runs up to 37 and stays constant. Line stays pressurized when left to sit - so no leakage in injectors - yes. Here is the weird part - when the car is running, the fuel pressure shows between 0 - 5 psi. I believe this is just gravity pressure from tank. If when running I jump the terminals on AFM for pump to run, the pressure jumps up and car immediately dies. I can make the car start when hot, but only if someone is running the ignition and I remove the trigger from coil and slowly tap contact with wire until fuel pressure drops, then connect it and it will run.

I am wondering what could be causing the fuel injectors to seemingly be stuck open, which is the only way I think it could run this way. Except that I have a flashing signal with a test light from injector harness when cranking and none of the injectors are internally grounded. I suspected the AFM since the fuel pump contact is obviously not working, but the continuity readings jive with what is in the Bentley manual. I don't know what readings I should be getting once the flap starts to open, but closed readings are right.

Any ideas??????????? I am so close to having this done I don't want to succumb to the urge of molotov cocktails.

[busdaddy]

Welcome!
Sounds like a few different issues all adding up. 37 psi is a little on the high side, are you sure the fuel return line under the tank isn't kinked or pinched/restricted somewhere? You'll also want to check the continuity between the temp sensor wire and it's terminal in the ECU plug, and/or try grounding the sensor wire to fool the system into full lean mode for a test.
The AFM not switching the pump could be misadjusted contacts, or a large vacuum leak you haven't found yet, or a funky double relay, I'm guessing the pump doesn't respond when you poke the flap through the aircleaner while the key is on? The contacts can be adjusted, but if it's "rebuilt" and under warranty shouldn't the rebuilder be dealing with that?
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[war.hog]

[war.hog]

Have continuity from temp sensor plug to pin 13 on ecm plug.

[busdaddy]

Time for some testing then, even better if you can do it at the ECU plug: http://www.ratwell.com/technical/TempSensorII.html
If it checks out and you are confident the pin in the plug is actually contacting the board in the ECU (they sometimes push back or get bent) then fuel pressure is next on your list, you are after ~28-30 PSI running (or with vacuum applied) and ~35 static (no vacuum).

Here's something to keep you entertained regarding the AFM, you might find something helpful: https://www.thesamba.com/vw/forum/search.php?searc..._chars=200
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[war.hog]

OK I have done some testing and am starting to see the problem. Definitely an issue with Temp Signal. Here is what I have............removed top cover from ECM plug. Confirmed all pins are solid and plugging into ECM.

3115 ohms from pin 13 to temp connector w/ sensor unplugged
OL when ECM is unplugged
3050 ohms when testing sensor itself ( about 60 in garage )
1547 ohms pin 13 to ground ( ignition off everything connected )
OL when ignition is keyed to ON

This seems to tell me that the problem is from ECM to ground??????
Possible Double Relay issue????????
I did remove the relay from car and disassemble and clean.
I will retest it with the Bentley Manual tests.

I also checked and have continuity to ground from pins 5, 16 and 17; which Bentley shows as grounds from ECM.

[war.hog]

Scratch the first 2 readings.....they were to ground not to plug connector.

I am getting the same reading at pin 13 as I get with the sensor itself. Problem is when it gets plugged into ECM. I am unsure as to where this signal goes and comes out in ECM.

[war.hog]

Also, voltage is reading 6v at pin 13 when ignition is on.

[busdaddy]

There's some ECU schematics here: https://www.thesamba.com/vw/forum/viewtopic.php?t=690922

What happens if you ground that TS2 wire to the engine case? does it run any different?
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[war.hog]

Everything I check appears to be OK. There is something I am missing, or not understanding. I am wondering why powering up the ECM with ignition on is breaking the continuity through sensor. Power shouldn't change that. If I ground the sensor plug and test with ignition on, I still have continuity. Which made me believe the temp sensor was at fault. Started it cold and ran it, again pressure spins up with starter but then drops to basically 0 while running. If I engage fuel pump at all to build up pressure it stalls out immediately. When letting it idle with no pressure, there seems to be no perceptible change in running condition when grounding temp sensor.

[war.hog]

BTW, I originally suspected a bad gauge, so changed for another and am getting exact same readings.

[busdaddy]

It's possible the sensor is flawed internally, I've never measured voltage on that wire so I have no idea if it's "normal", to sense resistance it has to use some sort of voltage. Maybe it retains continuity for your OHM meter but breaks down when the ECU has a go at it? . Have you tried grounding the sensor wire and engaging the fuel pump as it idles?
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[war.hog]

Yes. I had sensor grounded when trying pump this morning. No difference in outcome.

[busdaddy]

Hmmmm...., well aside from the slightly elevated fuel pressure that "rebuilt" AFM would be my next suspect. https://www.thesamba.com/vw/forum/viewtopic.php?t=540965
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[VW_Jimbo]

[war.hog]

Of course you can interject. All input is appreciated. I have checked and rechecked all mechanicals. Had engine out, so did all adjustments while out of car. Even retorqued heads. Replaced fuel filter last week. I have started over on the problem twice now, and was just figuring a fresh mind might come across something I am missing.

The engine is running quite well. So I am most sure valves etc. are OK. I understand checking everything, but I am sure problem lies with whatever is triggering injectors to stay open. I think once that is cured the fuel pressure can be run up.

[VW_Jimbo]

[busdaddy]

[war.hog]

Single beveled screw on alternator.