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Non starting TDI


yeha
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Son's Arosa TDi. Car was going up a hill when it lost power and cut out. Gut feel was that something had gone wrong with the fuel feed. When the ignition is switched on, there's a relay click but no fuel pump. I pulled the 109 relay and swapped with the good one from my TDi. No effect. Put it back in mine, starts instantly. Put a 12v feed to the lift pump, it works fine. Just in case it was the relay I also tried to bridge across the relay connections. Looking at the wiring diagram, pin 87 on the relay goes to the pump. Not on this car it doesn't. Wondered if it's an immobiliser issue but I've read that it will start for a few secs. Tried both keys too. I've pulled the ECU connectors and had a look for corroded pins. They're fine. No obvious broken wires or damage to the looms in the engine bay. I need to look at the connections around the fuse box and bottom of the A pillar. One thing I did notice was that the oil level is off the dip stick. Is there a level sensor? With it failing going up a reasonable hill, I did wonder if that had any affect. Any other suggestions?

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Running out of fuel would misfire and then stop not just cut out dead I would think. Pull fuel pipes off filter and see what happens with ignition on, lift pump should chuck it out as there is no pressure. 

It sounds electrical but is it turning over normally, chuffing or slow? make sure it mechanically turns over by hand 2 revolutions.

Any fault codes?

Edited by Sausage
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The gauge shows half a tank. I didn't run the pump with the lines off though. Turns over fine. I've not checked for codes yet as I need 240v and it's not near a socket. I need to buy an inverter.

The glow plug light does come on. Can't decide if it's on for less time than the one in my TDi.

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Not on the dipstick...

Very confused by the wiring. I thought the 109 relay was the fuel pump relay, J17, but it appears to be the Terminal 30 voltage supply relay, J317, although it is in position #2 which is supposed to be J17. Elsawin says that the fuel pump relay should have 167 on it. I do have the fuel shutoff relay 405.

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Sudden cutting is 100% electrical. Ok, so a number of things it could be. Loom power off (relay fault or fuse). Crank sensor failure, but then check engine light would come on. Ignition switch fault, would kill it. Interior fan working? No fault light if that. Not an engine problem.

oil level irrelevant. Not good though!

courtesey light working? Extinguishes when you turn ign on?

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Is there a cam sensor? If check engine light doesn't come on, and there's no cam sensor, I guess the ECU has no way of knowing that you're tying to make the egine run. Although i think the crank/start wire is connected to the ecu? Interesting. Hmm.

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Checked each relay's connections in the relay board and then checked it switches by connecting the coil to the battery. Somehow it suddenly decided to start. After a short period of time, it started to misfire and then cutout again. I decided to swap out all the relays from my 2001 Arosa into the 2003 Arosa. Unfortunately the fuel pump relay is different between the cars. In the earlier car it has 8mm tabs, the later one has 6mm. It still wouldn't start and the fuel pump wasn't running although the relay 53 was clicking. I don't know if there's a problem as I didn't have enough bits of wire and hands to connect a meter across the relay whilst firing the coil.

I'm hoping I have spares of all the relays as I tend to grab them all when in a scrapyard.

For future info:

J59 = X contact relief relay = relay 100

J491 = Fuel shut-off control unit = relay 405

J17 = Fuel pump relay = relay 53 in the 2003 Arosa and relay 167 in the 2001 Arosa. The 167 has 8mm power tabs, the 53 has 6mm tabs.

J317 = Terminal 30 voltage supply relay = relay 109

J52 = Glow plugs relay = relay 103

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Could be worn ignition switch, try varying pressure and angle on key as you turn it and see if it makes a difference. My 1.4s got random on starting (but didnt cut out while running which i half expected it would) would crank and not start, then became a chore to get dash lights to come on with key, needed sweet spot with key angle and pressure to start it and that quickly became very rare to achieve. New ignition switch fixed it.

The tank pump should always push fuel up unless the pressure is already high enough. 

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That last statement is incorrect. I did check the fuel line but obviously not after it had run. It was the fuel pump relay. For info relay 53 is a normal 4 pin relay. Managed to find some. It must have sucked the fuel line dry as it took a lot of cranking to fire.

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Good to know. Glad you found it! :)

So can you reproduce the fault simply by pulling the relay out when it's running? As in, does it just die suddenly, or does it splutter then conk out?

I'm surprised that there's no pressure sensor on the fuel supply circuit- running it dry would eventually kill the gallery feed pump. There must be some kind of pressure limiting device, similar to how petrol injection galleries work (@60psi), before it gets pumped up to 18,000 psi (or some silly high pressure).

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Looking closely I think it's just cheap ebay crap. It's vaguely marked like a VW part. It was nice and clean on the outside. I don't think that moisture was the cause as most of it is still shiny. The replacement genuine part has been in the garage for many years and just worked. The only downside to carrying a spare is that you also need the TX20 to remove the fusebox and then you may as well also have a spare 109, 405, 103, 100 and 19/99 just in case.

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Just looked at the spare tdi and these seem a b@stard to get to. The fuse box and white frame bottom is was not even connected and I still cant get it out of the way to even see the 53 relay, so not much point carrying spares tbh. I'm guessing there is a knack to moving the fuses out the way?

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58 minutes ago, Rich said:

When you are stuck and you have to move things, you will find a violent way.

Thump the relay box on my SDI :) 

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