1.8t - Car randomly stutters under light load

[Sirocco20348]

Ok I just used vagcom to read engine codes... none were there. No CEL's.

I did a throttle body adaptation and took the car for a drive... it felt better but the car had a throaty noise to ?

It stuttered less... no where near as bad as before?

Just going back on the ignition control module... are symptoms of this failing usually of a more intense nature?

[h100vw]

Ok I just used vagcom to read engine codes... none were there. No CEL's.

I did a throttle body adaptation and took the car for a drive... it felt better but the car had a throaty noise to ?

It stuttered less... no where near as bad as before?

Just going back on the ignition control module... are symptoms of this failing usually of a more intense nature?

ICMs just quit usually. Plug gaps all the same and not too big. Compression test, dodgy valve/burnt seat?

Gavin

[Sirocco20348]

ICMs just quit usually. Plug gaps all the same and not too big. Compression test, dodgy valve/burnt seat?

Gavin

Hey Gav, Thanks for the reply.

I installed new plugs (gapped to 0.28mm) before the track day last month, and I didn't have any problems.

Actually maybe I should elaborate more on my boost leak test situation.

I fixed the hole in the inter cooler and replaced the hose that goes from the plenum to the pcv valve?

When I went to use my bike pump again to compress, The hissing noises were gone from the intercooler and pipe.... but I could not for the life of me build pressure.... should I be able to build up even the smallest amount of pressure with a two handed floor mounted bike pump?

With the oil cap off, I could hear a hissing noise coming from within the block? But I dismissed that as in the video link I posted, they said that some air will go through the block. Is this a concern?

[h100vw]

Hey Gav, Thanks for the reply.

I installed new plugs (gapped to 0.28mm) before the track day last month, and I didn't have any problems.

Actually maybe I should elaborate more on my boost leak test situation.

I fixed the hole in the inter cooler and replaced the hose that goes from the plenum to the pcv valve?

When I went to use my bike pump again to compress, The hissing noises were gone from the intercooler and pipe.... but I could not for the life of me build pressure.... should I be able to build up even the smallest amount of pressure with a two handed floor mounted bike pump?

With the oil cap off, I could hear a hissing noise coming from within the block? But I dismissed that as in the video link I posted, they said that some air will go through the block. Is this a concern?

If you don't block it at the throttle body, there'll always be air escaping through one of the cylinders. The smoke machine is good as you can see it and chose whether it should be there or not.

I would cap smaller sections and when you are happy join them together again.

Gavin

[Sirocco20348]

I just thought I would keep this updated...

Since I have the piratebay vagcom... I thought I would verify my results by taking the car to Gareth at Northside Euros in Mitchell and have him run the official vagcom.

He had the same results. No engine fault codes, and from the ecu point of the view, the car is in good condition.

Maf. 02 sensors, throttle body adaptation are all good.

I decided to swap out the fuel filter this afternoon. The stuttering/misfiring has become less frequent, but is still there and very annoying.

Some hills while on cruise control, would cause misfiring, while others did not. It is really sporadic.

No stuttering under full boost at all.

I will follow up with further boost leak testing.

I still have half a tank of fuel left.. I am wondering if the fuel is crap... highly unlikely but still plays on my mind.

[Sirocco20348]

Thinking aloud again...I'm trying to work out why under full boost I have no problems.

A partially blocked injector... would that have an affect only at light to medium engine load?

Under full boost conditions, would the injector be subjected to higher fuel pressure and just overcome the partial block?

Has anyone run a total system cleaner... like caltex techron 5000? Any opinions?

[Lito]

Could be a blocked fuel filter? Maybe dud o2 sensor? As the agu is narrow band it doesn't reference the o2 sensor at wot, so that could explain why it's okay at full throttle?

Edit: just saw you changed the fuel filter. Did you try a brand new Bosch O2 sensor?

[Sirocco20348]

Hey Lito,

I actually hack-sawed open the old fuel filter that had done 35,000km... and it looked pretty clean! I couldn't see any particles or build up of muck. I should have taken a photo..ahwell.

I haven't tried a new 02 sensor just yet, as returned values in vagcom were in the acceptable range.

I am holding off buying anymore parts just yet, as I could easily dump my wallet replacing perfectly good parts.

As the agu is narrow band it doesn't reference the o2 sensor at wot, so that could explain why it's okay at full throttle

This is interesting to know!

Update: I am 90% sure the problem is petrol related. The car is always filled up with 98 octane at the Belconnen Shell.

I am half way through my tank, and drove my usual 15km to work today (which is normally a misfire festival)... and I did not experience a single misfire or stutter. Cruise control worked perfectly.

I am not a chemical engineer, so making assumptions everywhere, but possibly some unwanted heavier liquid settled on the bottom of the fuel tank and its been sucked through now?... no idea..

The more I drive the car, the problem seems to be going away on its own. The true test is going home thou, as its more of an uphill journey.

Ill keep the thread updated just in-case anyone else has the same problem.

[theOctopus]

Wow just been reading over your thread.

I think we may be having a very similar problem, I know there is something wrong I just cant find it.

I have a miss fire sometimes at idle but not under power, but ive lost a lot on low to mid range boost its all up top but I want it back to how it was and ive been banging my head for the last 6 months as I really dont want to keep throwing money at it so ive been taking it slow.

Ive run vagcom with no codes.
Ive done boost leak tests.
Ive checked and reset the wastegate to 6psi.
Ive done a new o2 sensor.
Ive tested the icm pins with a multimeter.
Tb clean and vagcom adaption.
Cleaned the maf and tested it disconnected runs way better with it on so it should be good.
Ive replaced all vac lines.
Diverted the pcv to a catch can and blocked the input to the tip and blocked the intake manifold connection.
Cleaned the intercooler and pancake pipeing.
New silicone turbo pipes
New n75 valve.
New div.
New fuel filter
New plugs bkr7e .028 step.
Ran fuel doctor through the system to clean the injectors lines and tank (get it from supercheap check the website its also used to clean fuel systems in mines where servicing cant be done)

Ive been running logs but I really need to learn more about what to look for.

In the last few months ive been thinking fuel pump on the way out as well, but again its another cost I dont want to possibly not fix the problem.

Im thinking ill need to get it on a dyno to find it, but again not sure.

Ill keep checking this thread and if I find whats causing my problems ill let you know it could be the same thing.

I hope you find the problem soon, I know how it can drive you mad hunting for it.

Jake


Sent from my GT-N7105 using Tapatalk

[Sirocco20348]

Damn that sucks.

What do you mean your car has no low-mid power? Under WOT conditions? From looking at ecu maps for the Me3.8.3, I think its only has 2 maps... partial load and full load. If your foot is not planted is not going to be reading from that map.

Looking at your mods, your car should be quite quick! Maybe you remember the times when you first got your vehicle and thought,, wow my car is quick and now your used to it

I find that my car doesn't really have any power until around the 3000-3200rpm mark when full boost kicks in. But that is what I would expect from this engine/weight of vehicle.

I have driven my car all weekend and I have had zero misfires!... It is really frustrating that I cannot say definitely what the problem was.

I am going to say the fuel... but I am not 100% sure.

[theOctopus]

Im glad your car may have worked its self out, ill look at the fuel filter again on mine soon I think.

Ok what your saying makes sense so only two maps got me thinking and back to the logs.

What I meant to say in the first post was at wot my tb is opening to 83 degrees and the boost kicks in around the same rpm as yours but now it just takes forever to hit peak, ill hit the rpm limiter before I hit peak boost in all gears now, when before it hit peak boost so fast I was able to see the boost drop before the rpms went to high.

So about this 2 maps situation went over some logs, and noticed something strange.

At wot and high revs the boost rises slowly to 16psi and at low revs not wot the boost rises fast and higher 20psi so I tested it yesterday it runs better boost when im not at wot.

Could the tb be going out I did another adaption and at idle its 1.5 degrees when it was better it was between 3.6 to 4 degrees.

On another note how did you get vagcom into test mode for blocks 31-36 etc ive read posts about brake in then rpms over 3000 but can never get it happening all the instructions I found were for mk4 vr6s in the UK and they wernt sure about the agu.

It really is driving me crazy, your right it was very quick before this started and that was before the downpipe and flywheel etc so it should be even faster than it was.

Thanks for the help

Sent from my GT-N7105 using Tapatalk

[Sirocco20348]

What I meant to say in the first post was at wot my tb is opening to 83 degrees

I am pretty sure 83 degrees is the maximum it will open.

On another note how did you get vagcom into test mode for blocks 31-36 etc ive read posts about brake in then rpms over 3000 but can never get it happening all the instructions I found were for mk4 vr6s in the UK and they wernt sure about the agu.

The AGU does not use block 31-36. Here is a listing of the blocks the AGU uses in Vagcom, and since we are DBC we do not have as many options.
http://sdrv.ms/JAkJXy

I could be wrong but from what I have read on the internetz..

Block 7 for lambda values
- The value in Field 1 represents the pre-cat oxygen sensor control. The value should fluctuate at least 2% in the -10 to +10% range.
- The value in Field 2 represents probe volts. Value should be between 0.75-0.9v, if you're reading a value of .9V or higher, you're running rich, and if you're reading a value of .7 volts or less, you're running lean. This is at idle, partial and WOT.

Does anyone know which vagcom block and value is required to do the Aging of Pre-Cat Oxygen Sensor. I should ring Gareth as he did this test. He manually pressed the accelerator up-to 2000rpm.

[theOctopus]

Thanks Mate

Ill run some logs for the lambda tonight and check the values, I just replaced the O2 sensor a month or so back so I hope its ok.

[theOctopus]

I am pretty sure 83 degrees is the maximum it will open.

Block 7 for lambda values
- The value in Field 1 represents the pre-cat oxygen sensor control. The value should fluctuate at least 2% in the -10 to +10% range.
- The value in Field 2 represents probe volts. Value should be between 0.75-0.9v, if you're reading a value of .9V or higher, you're running rich, and if you're reading a value of .7 volts or less, you're running lean. This is at idle, partial and WOT.

Logged some data on the way home about 25km.

At idle the probe volts are sitting at .7 then dropping quickly to .1 then up again but a stable BTDC of 12

At partial the probe volts same as above but when ever it drops lower than .7 my BTDC jumps to 20-32 thats not good

At WOT its stable at .8 and my BTDC is 6-15.

The pre-cat seems fine at WOT its 0 at idle and partial its between -4 and 6.

What were you seeing with the bad fuel.

Im a bit worried about what is causing the big timing pull.

[Sirocco20348]

I have this problem back again.

About 800km of driving after track day, I was half way back to Brisbane, and the cruise control dropped out...

By the time I got home, the car was jumping all over the place. But only when i was feathering the very start of the accelerator pedal. This is where the cruise spends most the time on a flat road, light acceleration to maintain speed.

Under partial acceleration (1/2 or 3/4 pedal push) or wot I have no problems. So to get home I was driving up to 120kmh and letting the car slow down to 110. Sigh.

On the plus side I am getting great fuel economy on highway... Approx 750km per tank til empty. I was easily getting 700km without empty light displaying.

No idea...now I am in Brisbane I might take the opportunity to go see Jmac at Alba European.....

Sent from my Nexus 7 using Tapatalk