Polo 1.4TDI Cold Start Problem

I've recently bought my partner a 2004 Polo TDI (the 1.4 PD 3 cylinder).

I had it in the garage for the first few days sorting a few bits out on it before i handed it over and during this time it started fine.

Now that its being left outside overnight it sometimes starts no problem but other mornings it will fire up and then cut out immediately and take some cranking till it will start again.

The lift pump can be heard cutting in, and the starter and battery seem healthy. I will probably change the glow plugs but for some reason i doubt this is the issue as its not exactly cold and my PD starts first turn in sub zero conditions without waiting for the glowplug light at all.

Could it be an issue with the coolant temp sensor? Is this the same sensor that is used for the dashboard temperature gauge? because this appears to be working fine.

Any other suggestions would be great.

Thanks.

I wouldn't have thought it would be the glow plugs if it starts ok, it sounds more like it could be a fuel problem but it would be best if you could get it scanned for error codes first as that could point to the problem.

I would replace the fuel filter and when you have the filter off, see of the filter "IN" line will squirt fuel out as the key is turned to "ON" to indicate that the lift pump is in fact working.

--Nate

Got a fuel filter on the way. First thing i'm going to do when she gets home is scan it for faults.

I think i'm going to fill up the tank aswell as the times when its been hard to start is when the tank has been low and the fuel light has been on.

UPDATE:

Scanned for codes and found none.

Unplugged the coolant temp sensor so the glowplugs stayed on and checked the harness to make sure all of the glowplugs were getting power. Then checked each glowplug.

Everything seems to be ok with all that so i'm now gonna look at the fuel system.

Tank is full also so i shall get the Mrs to note when it next has an episode of hard starting to see if theres any connection

Not sure if relevant but try the 'cage mod' on your connectors(aka use dielectric grease to seal and prevent corrosion on all the connectors). Moisture and cold weather can be bad for connections. Also do a diesel purge to clean up the injectors tho this may not be the cause of your problem. Good luck.

Yea, good call on the connectors, it can't hurt

I've filled up the tank and put in some injector cleaner for good measure. I will change the fuel filter once the tank is empty.

It hasn't done it recently so i havn't really done much to try and fix the problem. Another thing that i think i might be is some sort of immobiliser issue. The way it fires up and cuts out. (although i'd have thought it would bring up a code)I'd like to try another key but we've only got one at the moment. Need to get a spare sorted.

Right, the problem has now returned a few times and the common denominator is that its when the fuel tank is low, probably just before the fuel light comes on.

Does anybody who has experience with lift pumps reckon it could be picking some air up when its first started? It runs fine once started its just when its left overnight and while at work.

Any advice would be great

tomtom1989 said:

Right, the problem has now returned a few times and the common denominator is that its when the fuel tank is low, probably just before the fuel light comes on.

Does anybody who has experience with lift pumps reckon it could be picking some air up when its first started? It runs fine once started its just when its left overnight and while at work.

Any advice would be great

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Replace the lift pump, its shot. The tank has more pressure when it is full of fuel so the pump doesn't have so much work to do. Running it on fumes means it is working the pump harder. Alternatively don't run the tank so low.

Good call, What your saying deffinetly makes sense and ties up with the symptoms.

Thing is i can hear the lift pump when i turn on the ignition and can hear a good squirt of fuel as it primes up although i know that doesn't prove its working and delivering a flow

Is there a way i can test it? Sit it in a bucket of diesel and power it up? is it easy to get out?

Thanks again, Tom

Well my guess is the lift pump has had it. Although it may pump fuel with no resistance and probably with a full tank of fuel. It probably wont work anywhere near as well when the tank is empty and it has to push the fluid through a filter. There are probably some flow rates quoted in the Bentley manual but I dont have access to mine at the moment. There is also I believe a secondary pump driven off the camshaft on PD engines. Its not difficult to access the lift pump it is behind the rear seats under a panel but I would try testing the flow rate with the pump in situ and with the tank relatively empty.

Yes. There is a tandem pump driven off the camshaft which is a vacuum pump and a fuel pump. Thinking about it though it will be harder for the lift pump to pump diesel when not in situ as when its in situ it has the tandem pump sucking at the same time.

I've unplugged the lift pump and the car runs and drives fine, with the car stood for a few hours though it started and then idled lumpy, plugged it back in, started pumping and all was fine - This was with a full tank.

I'll try the same test again with less fuel in the tank and see if the situation is worse - i really hope its as simple as change the lift pump, but i don't want to change it and still have the problem. I have heard of lift pumps failing as in it doesn't run anymore, but none that run and don't deliver pressure.

if i knew what kind of pressure it should deliver i could rig a pressure gauge up to it maybe

don't rush on the pump. take it out and check for build up on the pickup screen

Yea, just found a few threads on here. Gonna take the pump out and check the eductor isn't blocked on the bottom of the pump.