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V6 30v Runs rough, Jerky; Bad misfiring, no fault codes

12279 Views 18 Replies 9 Participants Last post by  soundguybob
My 2000 Passat idles rough, and runs rough & jerky at all driving speeds, it is worse when running on cruise control.
Spark plugs are black (replaced 2 weeks ago). My scanner shows the ignition timing at idle jumping all over the place
from under 10 deg. to about 24 deg. The idle speed jumps around between 720 & 800 RPM.
It seems to be misfiring & backfiring, it is as if the ign. timing is too far advanced and varying, it is worst when I increase acceleration.
I am not getting any error codes. How can this be? Can someone please help?

Thanks Tom
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Try disconnecting the MAF and start it. If it runs good...the MAF is the problem.
Thanks zmaninco,

I disconnected the MAF, it still runs about the same, I got DTC 16486 MAF low input.
I cleaned the MAF & refitted it and got DTC 17535 Fuel trim B1 too rich & DTC 17537 Fuel trim B2 too rich.
After clearing the codes & they didn't come back, with light acceleration it knocks (ping / Pre-ignition I think).
Shouldn't it be setting DTCs? I ran it with one plug lead off & didn't get a DTC, I thought it should show a misfire.
the 2.8 is well known for getting clogged fuel injectors as it gets on in years/mileage, and I would bet that's what is going on in your car. it causes misfires, poor acceleration, etc.

you need to run some fuel injector cleaner thru your fuel system. here in the USA, we use a product called Techron. 1 bottle in a quarter tank of gas, then another again in a half tank of gas ought to solve your problem. I'd try this first before I did anything else...
This sounds like a PCV issue which is a common problem with the 2.8 and perhaps the most common. A simple test may be to remove the oil cap while the car is running. This would simulate a broken PCV hose and would produce the rough, jerky symptoms without any code that you describe, but if there is no change then that could mean you have a leak in your PCV system.
The PCV valve & pipes, and most of the vacuum hoses were replaced a few weeks ago.

This problem is far worse than what would result from a broken PCV pipe or valve.

I don't think it could be injectors. The problem started suddenly, it usually runs not too bad for the first couple of minutes after cold start. The problem is worst at low speed, when I
accelerate, but is still quite evident at 110 KM/H (70 MPH). I removed and cleaned the FPR, that didn't help.
Could it be a dirty throttle body.

Any suggestions would be appreciated.
I'd try the injector cleaner before anything else, exactly as Jay described. You'd be VERY surprised at how the injectors can affect how these V6's run... It's cheap, and should be done as standard maintenance, anyway.
My V6 was starting to show a rough idle. After replacing the air filter and changing spark plugs; it smoothed out. You say you changed plugs and cleaned the MAF but when was the filter last changed? Beyond that, maybe try the fuel injector cleaner as mentioned or the Seafoam 'black apparatus' technique.
three veteran Passatworld V6 owners answered, and three told you to try the fuel injector cleaner... survey says? ;)

sure, the throttle body could use a cleaning, but the easiest thing to do first is to dump fuel injector cleaner in your gas tank - and we've seen this happen many, many times here. I was putting 30k miles (50,000 km) a year on my V6. I've seen this more than a few times just on my car, even buying top-shelf gas, let alone dozens of other times here. at most, this will cost you $10 USD.

btw, pulling the throttle body off the V6 is a PITA. I'll guarantee some scraped knuckles if you have even smallish hands.
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Another thing to try is go to a dark place, no lights. Start the car with the hand brake on to prevent the DRL from being on. In the dark, open the hood and look for electrical leakage in the form of sparks, typically from the coil or spark plug wires. Also try misting the coil with water to see of there are cracks in the coil or spark plug wire insulation. You may see arcing in places.
I used to dump fuel injector cleaner in about every 4th tank when I first got my Passat... cant say it fixed anything (because it wasn't running rough) but it probably prevented some damage.
Another thing to try is go to a dark place, no lights. Start the car with the hand brake on to prevent the DRL from being on. In the dark, open the hood and look for electrical leakage in the form of sparks, typically from the coil or spark plug wires. Also try misting the coil with water to see of there are cracks in the coil or spark plug wire insulation. You may see arcing in places.

this would be the next thing I'd put on the list. note, you'll have to remove the engine cover to check this out. I would definitely mist the coils and plug wires from a spray bottle filled with water.
Im going out on a limb but this could be early signs of the fuel filter clogging up
Im going out on a limb but this could be early signs of the fuel filter clogging up
that one is likely not the case. that limb...??? it's pretty small. ;)
During the last few weeks I have replaced: Alternator, Timing belt & rollers, Water pump & Thermostat, AC Belt & Tensioner, Cam seals, Cam cover gaskets, Front crankshaft seal,
Spark plugs, Air filter, Oil & filter, Coolant, PCV valve & pipes, Vacuum pump, One way valve & most of the Vacuum hoses. And corrected B2 inlet cam timing.
(The chain had been installed one tooth out, by previous owner).
I cleaned the MAF & FPR. Checked the coils & plug wires in the dark, found no problem.

PROBLEM seems to be SOLVED
As this problem occurred suddenly about a week after I finished the work on the engine, I thought it must be related and decided to try the old plugs. When I removed the plugs I noticed
that No 6 looked messy, the connector was rusty and there were burn marks down the sides of the porcelain, after cleaning & refitting with old plugs it is going fine so far.

During the original work I removed & cleaned the coils & plug leads, and left them in the shed for a few days before refitting them. It appears that a small spider or something similar
climbed into No 6 plug cap and got squashed, as its juices worked their way down the plug they caused arcing.

What I would like to know now is why didn't I get DTCs, I would have expected misfires at least.

Many thanks guys for all your suggestions, much appreciated.
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how do you know it was a spider? did you see some nicely toasted spidey legs still in there? :lol:

what brand of plugs did you use? i'm religious with ngk plugs. they seem to give the least issues. bosch would be a close 2nd. any other autoparts generic brand (champion, autolite, etc.) have not gotten consistently good reviews/results for people here.
No there was nothing recognisable in there, it had to be alive because there was no way anything else could have got in there, going by the rust on the top contact on the plug
and burnt marks down the side, it had to be moist & probably acidic.

The old plugs (Bosch Super Plus EGR7DQE) are in at the moment, I will put the new plugs (NGK BKR6EKUB) back in if the burnt one will clean up OK.
Problem solved

Just remembered this thread and thought I should give it a happy and informative ending.
For anyone who may come across it:

This problem returned a few days later, I didn't return here because I knew that it was ignition
related (Any experienced person would if they had driven the car), people here were mainly
concentrating on fuel, and were getting tired of me. :banghead: Syndrome.
I had difficulty describing the symptoms well enough.

I was running the old Bosch Super Plus EGR7DQE plugs, which had been working fine, the condition
deteriorated, under light acceleration there were loud noises (like a cross between bang & boom) from the
engine compartment (seemed to be toward RHS), with each noise the car jerked as if the brakes had
been applied sharply.

I fitted new plug leads, and new NGK BKR6EKUB plugs.
Started it and idle was smooth, took it for a run, it was like a new engine.
It is still going without any problems.

The leads had carbon tracks (Which I couldn't see), and it was arcing down the sides of the plugs.
One of the two damaged new plugs, had fine grooves that you could see and feel, burnt down the
side of the porcelain.

I had checked in the dark with & without water, and saw no sign of light.

Here's another example of this problem:

I think the noise was caused by the unburnt fuel (From a misfire) being ignited on the exhaust stroke,
and blasting into the intake manifold (The valve would be partly open), burning the fuel and blasting out
through the air-cleaner, and removing all the fuel and air from the entire intake system.

And I think the jerk was caused by all cylinders dying suddenly, due to the lack of air.
(These engines do fire on exhaust strokes).

I don't understand why this happens with this fault, but doesn't happen under other ignition misfire conditions.

And again thanks to all who tried to help. :salute:
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Thanks for posting back with your resolution! Too often, people don't bother.

We do have a method to our madness, and those of us that have had the V6 for a good while have learned that the Techron treatment often addresses the issues you originally described. We've seen several people post with similar symptoms, even after having replaced the coils, plugs, and wires, ultimately to have Techron be the resolution. My personal experience and observation has been that the fuel treatment addressed similar issues about 90% of the time, so that's why we tend to beat that drum when we see these issues.
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