Fuel solenoid issue(n109). possibly related to my fuel quantity?

Ok, I have had this problem since I got the car. car was had at auction with a bad motor from a blown timing belt. I rebuilt the motor, and the first problem was a code. n109 fuel shut off solenoid. open or short to ground. to start the car I just put a wire to the fuel shut off. started up. just to mention, 109 relay has been replaced. I know there isn't any relation but it is always suggested.

after posting this on here, lots of guys came and suggested things. I went and ohmed out the wires and found the wire from the fuel solenoid was 0.3ohms. it was fine to the 3 pin connector, to the 24 pin connector, to the 62 pin connector, and all the way threw. the thought was the ecu is toast. I picked up a known good ecu today, same part number and everything. the fuel is the same. same fuel curve to it. I have .216 nozzles in the thing. you would think the thing would smoke like crazy without a tune. I can only get it to smoke right when I put the foot to the floor. after that nothing.

so after breaking in the motor, I was able to bring the motor up past 3k rpms and noticed the lack of fuel. after looking at the vag com, I found the injection quantity at idle was 1.8mg/str. it should be 3-9mg/str. I didn't think too much about that until I did a log. my log looks like this for fuel.


I am at a turning place. knee jerk reaction says my quantity adjustor in my pump is toast and I should get another pump or have it rebuilt. however, my brain tells me(some other people that I respect in the tdi world too) that I need to find what the real problem with the n109 wiring is. I am not even close to being electrically saavy. I can read a bently ok, it pains me sometimes. I need some suggestion of where to go from here.

so the questions are:

What tells the ecu to operate this n109 fuel solenoid?

Is the n109 anywhere connected in the ecu circuitry to the fuel quantity?

Where is the grounding point for the ecu? does it get its ground from the chassis by bolting it down or does it have its own ground? I have cleaned all the engine bay grounds

Please dont' suggest the "replace the rubber line in the ecu" statement.

hammer mod time?

the n109 fuel cut-off solenoid? The ignition switch tells it what to do...

I don't believe there is any correlation between the fuel-cutoff solenoid and injection quantity. In fact, 1.8 mg/st at idle when warm isn't all that unusual for a mk3.

I'm not sure I see a problem with the injected quantity graph either...

If you hammer mod the car back into the 3+ mg/st range, it will actually REDUCE fueling at higher RPMs, and thus reduce smoke. This is a trick a lot of us who have larger nozzles and a chip use to reduce smoke. Increase the injected quantity @ idle number and it actually reduces the amount of fuel injected at higher RPMs, which lowers the amount of smoke.

If it's only smoking a little when you hit wide open throttle, that's all you want. My A3 was the same way with only nozzles. It didn't smoke significantly until I put a chip in it. And even with hammer modding it, it still smokes a decent amount (A3 cars usually do that when modded...)

With stock programming, the software is designed to dial back the fueling just enough to keep smoke/emissions down (thereby prolonging catalytic converter life among other things).

My A3 was at the exact same injected quantity @ idle as yours after I installed my nozzles. It didn't smoke except a little haze at WOT. Until I put the chip in.... Then it smoked REAL good! I've since hammer-modded it to 5 mg/st at idle.

I don't see any problem with your QA. You just need to get the shut-off solenoid fixed so you don't have to use some extra switch to activate it

A3s smoke like crazy WITH a tune. Without it it's minimal.

So, at this point you aren't getting any command from the ECU to pull in the N109 solenoid? This is problem 1 as I see it.

Is this correct? You don't have 12V at the solenoid when cranking?

Problem 2: Is the car low on power? I'm unclear on this or is the only issue we have here the fact that you have to manually jump the fuel solenoid to start and run the car.

ok. I am still trying to track down the n109. is there any way to test if the key is putting out the right voltage to turn on the n109?

side note, 38mpg driving conservative. I know that isn't right.

hammer mod: pull head off pump and tap the quantity adjuster?

A: we are low on power

B: fuel solenoid issue. correctly stated by you jolly green, ecu doesn't command the pull on the n109
also in fault codes it says n109 fuel shut off solenoid

I had one last week that was low power and intermittent but steadily occurring 100% of the time. The car would start and run fine just low power and a N109 mechanical malfunction code, no boost codes whatsoever but clear lack of outright boost and major delay as well. I went through the boost system with the finest of combs. With wastegate pressure line disconnected, the car should have overboosted as the system can't open the wastegate but alas, the car still performed poorly. All ECM inputs checked out fine.

I was thinking that either the wastegate wasn't returning to it's seat and allowing exhuast energy past the turbine and thus low boost or the engine wasn't getting the fuel it needed. I replaced the N109 solenoid with a practically new spare I had and the problem vanished. Even though the culprit solenoid worked fine and pulled all the way up on the bench, my feeling was that somehow with it installed, it wasn't pulling all the way up and restricting the fuel into the HP potion of the pump ( an orifice/restriction if you will ). Car has been returned and in action for a few days now and "is running better than ever". This seemed odd to me and I really was surprised at what I found to be the root cause but it did seem to fix the problem on that car. I am still not 100% sure that was the problem but it was the switch that seemed to resolve all the issues the car had.

As far as the wiring issue goes, it's a really simple circuit. Your tests show it should work but it doesn't. If it were me and I was confident in the test results, I would find the backside of the ECU pin for N109 signal and backprobe it with a paperclip, to measure the voltage at that pin immediately from the ECU with the engine running.

Heck, you can even try disconnecting the 24 pin connector and feeding battery voltage to the correct pin assignment to ensure the solenoid clicks and pulls down through that portion of the circuit, I think it's safe to say that you have an open that you need to pin down.

This is a stupid question but, you did measure voltage at the disconnected feed wire to the N109, correct? One meter lead to it and the other to ground?

BTW: On that same car, the two wires going to the advance solenoid ( shares the same 3pin connector with the N109 ) were chaffed through very badly right at the corrugated collar where the bare wires exit to their respective paths. I repaired the wires and could see quite easily how the N109 wire could open at this point with prolonged chaffing damage, goes against your tests I know.

ok I fixed the problem. I believe I fixed the power issue. now I have lots of black smoke and it goes to redline very fast as before it didn't. I havn't done a log yet but I am assuming its fixed.

this is what I did. I pinned them for a proceedure I found on another post. that to make sure the ignition switch was fine. I did that and checked the fuel solenoid and it was fine. I had a jumper wire for 3 months to the fuel solenoid and it was running right, but not giving me enough fuel. it seems to be fixed now, however, I am leaving the toggle with jumper wire incase this is intermittent. I guess I can suspect the ecu fixed the problem but I am unsure. when I put the know good in there, there was no voltage. now there is.

thanks for all the help.