Running rough, Please Help

[neilbarrett]

Hi James,
nope, it just happens randomly and when I put my foot down I get no revs but when I pump the accelerator I can keep the revs up. as soon as I take my foot off it splutters and eventually stalls. I start it back up again and it runs fine for a while and then out of the blue it starts again. super frustrating!!

[jamesdavid]

You said in your previous post that you saw black smoke coming from the exhaust correct? Black smoke is usually, not always, but usually a sign of over fueling resulting in incomplete combustion, this falls in line with air/fuel ratio codes which keep being thrown.

There is a few possibilities, but please don't assume i am right or i would make a living out of it haha. We need to know how the ecu calculates fuel injection quantity. From memory it will use the air mass meter, the coolant temp sensor probably the air intake sensor and charge pressure sensor in the case of a forced induction engine, there will be others i.e fuel temp, etc etc but leave that for now.

I know that faulty coolant temp sensors dont always throw a code as the engine cannot see that its not functioning correctly, but a faulty coolant temp sensor will produce rich mixtures and i know for a fact stalling. Usually though if it stalls though it wont fire straight away until the engine is cooler.

From memory the ARX,AGU,ARZ etc 1.8l turbo engines air mass meters were not an uncommon fault on them. I saw a previous post that said disconnect the air mass meter and run it, it will most likely run better as it will run on a base mapping stored in the ecu. If thats the case i d hazard a guess at a faulty air mass meter.

Work with what you have, for combustion we need air,spark,fuel. thats never changed. If you keep getting air/fuel ratio codes focus on air and fuel. My ideal suggestion would be to see to see if you can get a airbox with the air mass meter attached from a working car, If i was diagnosing it that would be the first thing i would attempt as its quick,cheap providing you can get someone willing to help and will help narrow the problem.

[neilbarrett]

The mechanic is going to give it a good going over on monday. He said he will also put in a test MAF. The only problem is it can run fine for hours then suddenly it will start playing up. Anyway, if they dont sort it this time then its 3rd strike your out!!! I will unplug the maf tomorrow and see what happens. Thanks heaps for the detailed message.

[neilbarrett]

unplugged the maf today and she started running really bad, pretty much un drivable. does this rule out the maf?

[neilbarrett]

Been in the mechanics for 5 days!!!! they told me their was something wrong with the fuel pressure. they changed the fuel regulator on the end of the fuel rails, test drove it a couple of times tested it and said it's running fine. I picked it up and after 10mins it starts running rough again!!! took it back, took one of the mechanics out for a drive and showed him the problem. They are Stumped!!! Could be this, could be that,could be a number of things!!! Im up to $1200 still no fix. Is this normal ? Should I find a new mechanic?

[jamesdavid]

If they think that their is a problem with the fuel pressure i would be looking into the high pressure pump, I have seen a few cases where the delivery volume is insufficient and as a result the car doesn't get enough fuel, which if its running rough and eventually stalling unless you blip the throttle sounds plausible.

I m not sure on your engine but i think the high pressure pump should be on the top of the engine towards the back, it should be a single piston pump with a big brass colored nut on the top of it. They are fairly quick to replace, if they could get a pump off of a working car and swap them over (will not take long at all) it would narrow things down even further. Judging by the fact that they replaced a regulator i assume they have identified low fuel pressure.

I m in 2 minds about that though, as they are saying its fuel pressure related, but you have previously said that you have seen black smoke coming out the exhaust which has been known to be over fueling. I know in audi in the 1.8l turbo engines there was commonish problem with leaking injectors, they would internally leak into the cylinders and the car would be running rich as the ideal air/fuel ratio would have already been calculated but due to the injectors internally leaking it would throw out that ratio. I would be at least removing the spark plugs and checking for wetting in the cylinders and on top of the pistons, at least it wont cost anything in parts.

James

[h100vw]

This is a 1.8T so there's only 1 pump and it's in the tank.

gavin

If they think that their is a problem with the fuel pressure i would be looking into the high pressure pump, I have seen a few cases where the delivery volume is insufficient and as a result the car doesn't get enough fuel, which if its running rough and eventually stalling unless you blip the throttle sounds plausible.

I m not sure on your engine but i think the high pressure pump should be on the top of the engine towards the back, it should be a single piston pump with a big brass colored nut on the top of it. They are fairly quick to replace, if they could get a pump off of a working car and swap them over (will not take long at all) it would narrow things down even further. Judging by the fact that they replaced a regulator i assume they have identified low fuel pressure.

I m in 2 minds about that though, as they are saying its fuel pressure related, but you have previously said that you have seen black smoke coming out the exhaust which has been known to be over fueling. I know in audi in the 1.8l turbo engines there was commonish problem with leaking injectors, they would internally leak into the cylinders and the car would be running rich as the ideal air/fuel ratio would have already been calculated but due to the injectors internally leaking it would throw out that ratio. I would be at least removing the spark plugs and checking for wetting in the cylinders and on top of the pistons, at least it wont cost anything in parts.

James

[guile]

I have only read the last part of this thread so completely throwing this out there to try and help, don't flame me if i've missed something early on!

my friend had a simialr problem and it turned out to be the crank sensor (i'm sure there is a more technical term but i think thats what its called). I guess this fault should throw a code but i'm pretty sure it didn't and he had similar diagnostic issues.

good luck with it mate, i feel your pain.

[jamesdavid]

I m not too good with my year models volkswagens lol apart from mk2 as i own one. Can i assume we are talking about the 1.8l turbo 5v engine? Could still be a pump delivering a less than desirable flow rate, wouldn't be the first time, especially as a fuel pressure problem has been identified. But its a tough one, it is not really desirable for one to replace a fuel pump only to find out that it hasn't changed anything.

[guile]

I have a standard fuel pump you can try if you like although I'm not sure of the age or condition. i removed it to upgrade the flow rate as the a3 is tuned but if yours is standard it could be worth a shot

[neilbarrett]

Fuel pump, crank sensor, coolant sensor, leaking injectors. thanks for all your help. I'll get on to it and keep you informed on the progress or on any new developments.

[craig_the_german]

This may sound odd but i had a similar situation with my 1.6. Turned out to be the alternator. Replaced and ran like a dream. Check the alternator output.

[Jmac]

If im ever asked to make a diagnostic check sheet, at the top would be battery static and cranking voltage then charging voltage. This should be checked at the d positive wire at the back of the alt, not the main B positive one. Its surprising how often battery and charging gets missed with a running fault. Lots of systems are very voltage sensitive, easy check and at least you can then tick the boxes and move on. See it all of the time
Good luck with it
Jmac

[neilbarrett]

Sounds like a good Idea I will add it to the list

[Stan]

jmac is right, a damaged or faulty battery can cause all sorts of weird grief, and not just on vws