Misfires

[lewisweller]

Anyone have some plug reading experience to share please?

It seems without codes it very hard to help people out I know.

I see a few other ctt owners are having similar issue but they get idle problems which I don't strangely, although I'm happy I don't as idle issues tend to lead to costly major repairs.

Appreciations in advance

[Ahsai]

I think you need Durametric as there could be fault codes that can't be retrieved by other scanners. Also, how do you know your engine is running lean when you mentioned lean misfire? Have you checked fuel pressure and flow rate are up to spec? I'm not familiar with Cayennes but based on stuttering under load (not at idle), that doesn't sound like an intake air leak. Sounds more fuel and timing related.

[JFP in PA]

Anyone have some plug reading experience to share please? It seems without codes it very hard to help people out I know. I see a few other ctt owners are having similar issue but they get idle problems which I don't strangely, although I'm happy I don't as idle issues tend to lead to costly major repairs. Appreciations in advance

 

The first three look about average, the next two however look a tad on the rich side.  I would agree with Ahsai, get the fuel trims read and also look for any stored or pending misfire codes, which will point to specific cylinders.

[lewisweller]

Thanks guys for replying.

First 3 plugs are bank 1, so bank 2 is maybe the issue here. VCDS when it arrives will hopefully reveal more info on misfire and fuel trims out of wack maybe. I'm hoping not timing issue as this lead to starched chains and a whole load of money. Side note I've had this car on Durametric and PIWIS before head gasket was diagnosed and didn't reveal anything except SAI fault which is because they are both funked, but regardless in middle east they never run any way).

 

Reference vacuum leaks I think with all the bits I replaced and checking done, there may not be any leaks remaining. When pulling the dipstick you can hear now a distinct change in sound and airflow, and if removing the oil cap a bigger change and vacuum pressure sucking the cap back down with both respective O'ring sealing instantaneously when touched back into situ.

Maybe I ruled out fuel pressure/delivery too quickly as higher rpm the rev is cleaner to redline.

 

Ill post back some tangible data asap. 

 

Thanks again Guys.

[mbagge01]

So I think that I finally fixed my surging issue. After further investigating, I found that the T connector at the back of the engine where the exhaust line from the turbos to the crankcase system was cracked in half so I had a large PCV leak, which never threw a code. I initially performed a temporary fixed with some cement glue and plastic connectors which helped the driving somewhat. I then decided to perform a proper repair and given its location behind the intake, I ended up going to route of taking off the intake manifold for better access. I also was able to inspect the vacuum hoses on the back of the intake and replaced some of them with silicone hoses along with replacing the intake manifold gaskets and the throttle body gasket. I also cleaned the throttle body thoroughly. As a word of advice, be careful when removing those old vacuum hoses on the back of the intake because I ended up snapping off one of the plastic ports and the back of the intake and had the carefully glue it back of. After all of these repairs, I can't say 100% what repair actually cured the issue but I have a feeling it was the crankcase line that was wide open due to the T connector being broken, which apparently is a common issue with this car. Now with my EVOM tune, the car drives like a beast and finally I have found resolution to the problem.

[lewisweller]

Ok so I got my vcds and plug in to the ctt, works a treat on single module or auto detect use "touareq" it found every module I needed. Bad news is no fault codes in the engine or transmission. Only Dtc is 00907 for some power intervention fault, which must have sometime to do with the rear tail light warning which pops if battery voltage is down to 13.2v approx ie the AC fan is on high. Maybe the alternator is weak now as the battery is brand new. After leaving it a month it started right up in 40oC heat so can't be too bad?

The problem is the vcds doesn't have label files for the cayenne modules so I have to guess or educate myself better on the data I see and work out what I'm viewing in the measuring block groups. 

Can anyone give a list of group numbers for the cayenne for what they show, (the usual roos tech listed ones don't match the cayenne exactly I checked) main stuff is lambda, full trim, misfire count, I understand most of them but it's the fact that so many groups show the same or similar % figures and it get confusing which is actually what I want to review. 

Using on my audi was easy cos Advanced measuring blocks are available and all descriptions are there. 

 

Appreciate some technical help I got to find this misfire problem. 

 

Throwing this out there could the feel of misfire at stationary revving specific rpm and whilst driving the same rpms be engine mounting, transmission, flywheel, torque converter or anything else weird like that? Thinking outside the box here but it definitely reduced performance which is why I ruled all these things out already. 

[lewisweller]

On 18 July 2016 at 7:29 AM, mbagge01 said:

So I think that I finally fixed my surging issue. After further investigating, I found that the T connector at the back of the engine where the exhaust line from the turbos to the crankcase system was cracked in half so I had a large PCV leak, which never threw a code. I initially performed a temporary fixed with some cement glue and plastic connectors which helped the driving somewhat. I then decided to perform a proper repair and given its location behind the intake, I ended up going to route of taking off the intake manifold for better access. I also was able to inspect the vacuum hoses on the back of the intake and replaced some of them with silicone hoses along with replacing the intake manifold gaskets and the throttle body gasket. I also cleaned the throttle body thoroughly. As a word of advice, be careful when removing those old vacuum hoses on the back of the intake because I ended up snapping off one of the plastic ports and the back of the intake and had the carefully glue it back of. After all of these repairs, I can't say 100% what repair actually cured the issue but I have a feeling it was the crankcase line that was wide open due to the T connector being broken, which apparently is a common issue with this car. Now with my EVOM tune, the car drives like a beast and finally I have found resolution to the problem.

Can you post some pictures of these pipes and maybe some part numbers please. This is one area on the back I haven't searched although one pipe was found broken when they did the engine out head gaskets. Someone had also glued that tighter badly before it seems. I bought new from Porsche. 

[mbagge01]

The part number for the crankcase line that I am referring to is 94810721552. It is the T connector that splits on it which is located behind the engine.

[lewisweller]

I checked today the short  fuel trims are Ok all between +-10% I view on odb11 basic function but for some reason the long fuel trims stayed at 0.0% always even when I pulled the dip stick to introduce a vac leak not any change. The short terms did as expected and rose and then slowly came back down. 

I also looked at the ignition timing at idle was between 1.5 and 5 degrees body,  idle stabilisation cam timing was -1kw but I also had a -16.5kw  which I think is continous cam timing adjustment? With out the label file to show the description of readings I'm struggling with this. 

Pls anybody used vagcom on cayenne or even touareg maybe that can post the measuring block group numbers and descriptions? 

 

Side note the misfire vibration when revving is exactly 1200rpm 2200rpm and 3200rpm. What are the chances? This must be something sequential but I have no idea what could cause that?? 

[hahnmgh63]

You probably already tried here but check out their site if you didn't. At least the RS6 (C5) also used ME7.7.1 Motronic so the blocks might be the same.

http://www.ross-tech.com/products.php

[lewisweller]

Ok so I went back to basics after not seeing anything stand out in the data from the vcds. 

I unplugged both maf sensors and notice a change in behaviour rpm hunting around idle, idle stabilisation stumbling and revving lumpy. Ruling that out moved onto the map sensor which I clean already and made no difference, disconnected and no surprise you don't get any boost at all, but still misfires at certain rpm.  Reconnected map sensor and then disconnected the cycle valve aka N75 soleniod valve bingo misfire and stutter gone, revs freely and clean except the boost is limp mode 0.4 bar as wastgate spring is only in control and no vacuum assistance to increase to 0.8 bar to hold the boost as per the dme signal to the n75 valve. 

Ive ordered a new one after checking the pipe work is all in good condition. 

What really stumped me on this was the stutter misfire even when sat revving in Park. Anyone got some more in depth explanation about the activation of the n75 valve during off load conditions ie free revving when stationary? So weird to get a misfire at 1100 2100 3100 rpm etc from this pesky n75 solenoid valve intervention. 

 

For those who are still trying to figure out a misfire or hesitation without dtc codes then try this list:

1. Check Coils for cracks and sparks plugs for wear, correct gap and Visual condition.

2. Check for vacuum leaks, I found a total of three separate leaks, broken pipes etc 

3. Check both Diverter valves diaphragm is not split. One of mine was split I changed both anyway, bosch 710 P revision. 

4. Check Throttle body is clean, replace gasket and do alignment, look at the intake Y pipe bottom push fit vacuum pipe connector squirt a little water on it and listen for a engine flutter and also check for hissing around oil/air separator.  

5. Pull dip stick out at idle you should hear a quiet sucking noise and slight idle difference, open the oil cap and it should suck hard to pull the cap back down, if not maybe your vacuum is leaking somewhere else.

6. Smoke test your intake by removing the map sensor one screw and disconnecting the air boxes piping and blocking it off with a thick clear plastic bag and cello tape. 

7. Rinse Clean your maf and map sensors with pure alcohol do not scrub or rub them, air dry the alcohol off and repeat rinse. Don't soak the electrical ends. 

8. Compression check/ leak down test on all cylinders could be in order if you suspect an issue. 

9. Burnt or chipped exhaust valve is a possibility, not closing properly. 

10. Battery faults and DME issues can cause weird problems but not the most likely if start up cranking speed isn't an issue. 

11. O2 sensor faults will not be present during cold start running so if first few minute is good then once warm it start to misbehave then maybe o2 sensor closed loop malfunction. This can also be a sensor getting hot and malfunctioning. 

12. Fuel injector blockages and dripping. Use techron a few times to clean injector pintle, if dripping then start up is harder normally, especially hot starts. 

13. Fuel pump/ filter or regulator will normally show at higher rpm and hard to start 

 

There are loads more possibilities and a lot more knowledgeable people on this forum than me can offer their experience. But I hope this helps out someone trouble shooting in the future as without codes it can be very frustrating and costly to fix. 

 

[lewisweller]

Ok so got a new n75 valve for £20 not bad! I checked the pipework and everything looks to be spot on. Fitted the new n75 valve and guess what...... no difference! 

Unbelievable, if I disconnect it no misfire hesitation when revving in neutral and smoother acceleration but of course lower boost as the wastegate is not being helped to stay shut and build boost so it runs flat at 0.4bar only max boost. Plug the n75 valve back in new or old one and then it stutters through 2k 3k 4k and less noticeable but 5k rpm as well under boost. F***ing annoying and not a pleasurable driving experience. 

This must be a very uncommon problem as believe me I have read 1000's of forum posts, technical literature and applied my own Engineering knowledge (garages here are pants Fyi and the stealership is mega expensive). 

What I tried yesterday was to disconnect the vacuum pipe from the Diverter valves to just see what it did. As expected the DV released boost at about 0.6bar (as much as the spring can hold without the vacuum pipe which is in fact positive manifold pressurised when on Throttle, switched via the n249 change over valve) the jerky stutter and hesitation was worse even though I had less max boost which is normally +0.8bar needle off the dial slightly. So what did this teach me? 

Well either I have a weird n249 valve or associated piping issue or the wastegate one or both has some issue which I have no idea what would cause these symptoms. Sticky maybe? Not leaking as I blow down the vac pipes and no leaks through. 

In my desperation to get to the bottom of this I have ordered a new n249 valve against my better judgement of throwing parts at the problem. The Porsche parts guy here is now a good mate  so I'm able to get trade prices inline with what Auto Atlanta and Pelican can offer minus the horrendous air freight shipping cost to the uae. 

 

A side note for any one who didn't follow or could be bothered to read all the history behind this (don't blame you), this fault was present when I bought it, after some tlc servicing coil plugs filters etc it started overheating and head Gasket on bank 1 was disaginosed. After a complete engine out new head gaskets, all the trimmings, vac pipes, Seals thermostat water pump temp sensor the whole hog, no corners cut promise. They gave me it back all running and not overheating or anything.......but the hesitation and stutter was still there which I was sure was head Gasket related, wouldn't you? The indy German garage German engineer/Manager even said to me this was normal! Haha Sorry I'm not an idiot customer. 

His durametric and another indy Piwis my v-checker pro and ross tech original vcds showed NO fault codes at all ever throughout the whole saga. How frustrating! 

Following the head gasket repair I then found: 

Vacuum pipe between DV and change over soleniod valve was split (replaced that) and got full boost +0.8bar previously only got 0.6bar. Then found the DB drivers side was split diaphragm replaced both bosch 710 P revision (same as what was in there already in fact left side wasn't leaking so kept it as my emergency spare), cleaned the MAF's, MAP sensor, new n75 valve, smoke tested intake no leaks, couple of tanks of techron, always use 99 octane fuel. 

 

So come on guys Wtf am I missing here PLEASE someone read this that knows what could be the cause. 

 

Quick symptom example: Accelerate (lower gears from lower speed is worse).....boost comes in hits 0.4bar quickly rises to over 0.8bar and holds perfect....bucks hesitates and surges through 2k rpm then 3k rpm then around 4k and less noticeable around 5k then to red line it's smooth and perfect. 

Everything above is yelling coil packs or boost control requested vs actual hence the n75 valve control I suspected but seemingly not? 

[ekstroemtj]

Maybe i mention i am a lover of z cars too.  Hope thats not a problem here.

 

the older model had frequent behavoir like you describe it. Stalling. No smooth running engine when drving etc.

 

there was a guy who worked a lot to find the reason because no mechanic could help. Find his report here. 

 

Maybe its a lot but i found it helpful.

 

 

http://www.zhome.com/ZCMnL/PICS/hesitation/hesitation.html