Hesitation on WOT

[mike74]

Afternoon guys,

As title says, my 1995 ABY homefried coupe is missing on full throttle. In fact, its become more noticeable after fitting the Mark-H mod to the intercooler and going through all vacuum/boost hoses checking connections etc. (problem started a couple of months ago)
I'll try to describe the symptoms and what I've recently changed on the car. First thing in the morning when its about 11°C outside, the car will do a 4th gear pull from 2k RPM with no or at least very little issue. Doing the same thing on the way home when its about +16°C outside the car holds back, stutters and generally isn't very happy. Going up through the gears quickly also shows signs of not pulling properly, hesitating and holding back. It definitely seems to be temperature related, probably more oil temperature than anything to me and the hesitation is more pronounced when the car is at peak torque. Driving the car normally doesn't give any problems whatsoever and cold starting/running is fine too.

Things I've checked/replaced:

Fault code check brings up 00561 which has been there since I got the car.
New plugs last week (FWIW, its running TFSI coils too). The plugs that came out weren't sooted up at all. If anything maybe slightly too light coloured at the electrodes.
Fitted new lambda sensor a few days ago (removed original which had covered about 148k miles!! Again, not sooted up at all)
Buzzed out the MAF, checking voltages, resistance & continuity and are all perfect.
Checked IAT resistance, which I think is operating correctly.
Swapped FPR with original one (made no difference whatsoever).
New fuel filter fitted approx. 7k miles ago.
N75 valve clicks repeatedly when engine is revved.
All smaller vacuum pipes have been replaced with silicone ones. Other hoses have been checked out and clamp security & tightness checked.


After going through all the above, the only thing that springs to mind now is the original fuel pump. Uncle Dave will probably flame me for not replacing it but up until now there's been no issue with the running of the car so I didn't see the need.

Would changing the pump sound like a reasonable next step or is there anything else I should check first?

many thanks guys & cheers for now

mike

[Christophski]

Have you checked and cleared out the breather system? It can also leak vacuum from there too so is worth a look...

[rynaqui]

How old are the coils? I'd say they might be the issue.

Also what plugs are you running?

[Error404]

00561 is a fuel trim code, it means the ECU cannot trim to the AFR it is requesting based on the 02 sensor return. Have you done a boost leak test? Boost leak is or sure the most common cause of fuel trim problems.
Depending the detail of the code, that can tell you if it rich or lean - i.e. Exceeded or Not Reached. From memory Exceeded is a lean condition, Not Reached is rich. Lean might indicate a misfire, although I believe 00537 is more likely to be thrown for a sporadic fault. I believe you can log the fuel trim in Vagcom to determine what is going on.

PRJ posted some detail on this a few years back I will try and find it.

[Monkeymagic]

I had this,when breather was split. It wasn't easy to spot.

[mike74]

The coils are only around 8 months old so would hope they haven't expired yet. Plugs are NGK BCR8ES gapped to 0.7mm. I was hoping to get the car put onto VAGCOM this week to elaborate on the code but as I say, I would reckon the car is running lean rather than rich. Fuel economy wise I normally get about 280-290 miles to a tank with mixed styles of driving so certainly not excessive.
Admittedly, there is a couple of PCV hoses at the back to the head which I can't really get to easily. All I've managed to do so far is try to move the clips around to see if the pipes were loose or not.
I've attempted a boost leak test a couple of times (with a foot pump!). I blocked the MAF hose with a tin of spaghetti and the MAF side of the PCV return connection. Where the BPV connects to the inlet, I connected a tee and a pump. I then systematically went round the system with soapy water and watched each connection while I pumped like an idiot. Couldn't find anything remotely bubbling anywhere and according to the gauge on the pump it was hitting at least 20-25 PSI with each pump. That is excluding the couple of PCV connections round the back that I can barely see.
Can you remove of all that breather pipework easily enough and replace with a catch tank?
Alex, if you could find that post it would be very helpful indeed

cheers guys

[sjw185]

http://www.s2forum.com/forum/showthread.php?t=62598&highlight=00561

Think this is the one error is talking about.
I also had a split hard pipe going to Ecu which I only found after 1 bar.
Could it be related to a faulty throttle pot or wiring issue?

[mike74]

Ill stick some air in that pipe tonight but I'm sure I checked that some time ago...

[mike74]

Cheers for link BTW, will read later on

[Rusty]

Bost leak test, test again and test again

Worth checking if there are other issues with those plugs, just in case.

Check the exhaust manifold nuts, turbo nuts and downpipe nuts - I had a 00561 for ages and it was due to a leaking EM gasket.

[UrS4boy]

One Missing and Hesitation Diagnostic with links

One Missing and Hesitation Diagnostic with links:

http://forums.quattroworld.com/s4s6/msgs/22611.phtml

[mike74]

Right, I've just done another boost leak test with peculiar results...I can now hear a gurgling noise coming from the sump while the pressure bleeds off!? Does that mean there's a dodgy valve on the PCV system that's allowing my boost into the sump and straight back into the MAF hose? If so, which one(s) would I need?

[UrS4boy]

3B/AAN/ABY/ADU PCV System Information

Right, I've just done another boost leak test with peculiar results...I can now hear a gurgling noise coming from the sump while the pressure bleeds off!? Does that mean there's a dodgy valve on the PCV system that's allowing my boost into the sump and straight back into the MAF hose? If so, which one(s) would I need?

3B/AAN/ABY/ADU PCV System Information:

http://forums.quattroworld.com/s4s6/msgs/22506.phtml

[mike74]

Thanks Dave, very useful and informative info as always
So going by this info, I'd probably be best to replace the bleeder and pressure regulating valve?
I'll order up new valves ASAP and report back once fitted

Many thanks guys much appreciated

[newsh]

My experience is that if you don't disconnect the breather tube from the MAF hose then you'll pressurise the sump and you get air coming out the oil filler. If you disconnect the breather and plug the MAF hose outlet to it then you'll get air blown through the turbo seals, down the oil drain and you'll hear a bubbling in the sump

It's definitely worth fitting a new bleeder valve though.

Have a look at your injector plugs to make sure the pin holders are not broken. An injector that's not connected properly can cause this kind of misfire, not sure if you'd get the adaptation code though.