Problem with surging / fluctuating power

[Derick]

Hi everyone,

As some know, Al has bought my Jetta and it will once again be cruising around the great white North So I've been addressing and fixing little issues with the car so that it's in grade-A status when he takes possession. I brought my Jetta ('02 1.8T) into the dealership to have a surging problem fixed. The problem is that when I'm accelerating, it feels like the power momentarily drops for a second, and then picks up again. With steady and hard acceleration, this pattern continues through the rpm range, although it is most noticeable around 4200rpm. Basically, it feels as though I'm taking my foot on and off the gas pedal during acceleration. VW ended up giving me the car back, basically giving up since they couldn't find the cause! I'm totally stumped and was hoping someone might be able to shed some light on possible causes. FYI the diagnostics came back totally fine and nothing was showing up on the computer to indicate a problem. I thought it was the turbo itself, but they assure me that it's in perfect form. The engine is also completely stock except for a CAI.

Here are the things VW tried, but these did not fix the problem (I'm sure I'm missing a few things)...
1) ECU upgrade
2) Replaced vacuum hoses and looked for manifold leaks
3) Replaced MAF
4) Replaced diverter valve
5) Replaced battery
6) Checked transmission controller
7) Checked air intake and hoses
8) Checked turbo

They cited the CAI as a possible cause and recommended I go back to a stock air box. I have my doubts it's the intake, but would appreciate everyone's feedback.

Thanks!

[Khyron]

Re: Problem with surging / fluctuating power

n249 valve? I bypassed mine.

http://forums.vwvortex.com/zerothread?id=1333194

Might be something, but might not.

[VAG_Tech]

Re: Problem with surging / fluctuating power

Check your fuel filter. It's the most overlooked item in the fuel system.

[Kor]

Re: Problem with surging / fluctuating power

Hi everyone,

As some know, Al has bought my Jetta and it will once again be cruising around the great white North So I've been addressing and fixing little issues with the car so that it's in grade-A status when he takes possession. I brought my Jetta ('02 1.8T) into the dealership to have a surging problem fixed. The problem is that when I'm accelerating, it feels like the power momentarily drops for a second, and then picks up again. With steady and hard acceleration, this pattern continues through the rpm range, although it is most noticeable around 4200rpm. Basically, it feels as though I'm taking my foot on and off the gas pedal during acceleration. VW ended up giving me the car back, basically giving up since they couldn't find the cause! I'm totally stumped and was hoping someone might be able to shed some light on possible causes. FYI the diagnostics came back totally fine and nothing was showing up on the computer to indicate a problem. I thought it was the turbo itself, but they assure me that it's in perfect form. The engine is also completely stock except for a CAI.

Here are the things VW tried, but these did not fix the problem (I'm sure I'm missing a few things)...
1) ECU upgrade
2) Replaced vacuum hoses and looked for manifold leaks
3) Replaced MAF
4) Replaced diverter valve
5) Replaced battery
6) Checked transmission controller
7) Checked air intake and hoses
8) Checked turbo

They cited the CAI as a possible cause and recommended I go back to a stock air box. I have my doubts it's the intake, but would appreciate everyone's feedback.

Thanks!

Okay well a million things can cause this so its more of a troubleshooting game than a suggestion.

- Try running with your MAF unplugged, you will have a code, see if it goes away.

- Double check for leaks then check again, any hoses with surface cracks especially in the elbow parts is bad.

- Could be faulty or gummed up N75 but thats not a free fix

- Throttle body could be dirty and sticking, could clean it or get someone else to do it.

- Could run some injector cleaner, might not hurt? Ive never done this though

Well those are some ideas, good luck with it.

[Speed Cat]

Re: Problem with surging / fluctuating power

i feel your pain

[95rado]

Re: Problem with surging / fluctuating power

Check your fuel filter. It's the most overlooked item in the fuel system.

Bam... that solved my vr6 problem. and for about 12 dollars

[Jester B]

Re: Problem with surging / fluctuating power

Check your fuel filter. It's the most overlooked item in the fuel system.

Ah, Dave is as smart as he seems. Your problem sounds very similar to one I have with my old Corrado G60 that was ultimatley diagnosed (after a LOT of effort) to be a weak fuel pump. I'm with Dave that it's somewhere in your fuel system...

[VAG_Tech]

Re: Problem with surging / fluctuating power

I'm just wondering if he did change the fuel filter??

[Khyron]

Re: Problem with surging / fluctuating power

How often is recommended for changing it anyway?

[VAG_Tech]

Re: Problem with surging / fluctuating power

Read below. I totally agree with this article from Vincent T. Ciulla and About.com

"Quote"


I receive a lot of questions concerning power loss, hesitation and hard starting in a vehicle. Many of these complaints can be traced to a clogged fuel filter. As the fuel filter gets older. More and more dirt collects inside it, gradually restricting the flow of fuel to the engine. A partially restricted filter will usually pass enough fuel to keep the engine running at idle or low speed, but may starve the engine for fuel at higher speeds or loads. So your engine may run fine putting around town, but sputter and lack power when you try to drive at highway speeds or pass someone.

I am often asked, "How often should I change my fuel filter?" If you have a high mileage vehicle you should replace the fuel filter once a year. By the time your car is six or seven years old, there can be a lot of dirt and rust inside your fuel tank. Normal condensation and moisture inside the fuel tank can form rust and every time you put in fuel, dirt can enter the fuel tank. All of this can cause a fuel filter to plug up fairly quickly, so replacing the fuel filter annually will prevent many problems

Many newer vehicles do not specify a recommended replacement interval. And many have a so-called; "Lifetime" fuel filter they claim never needs to be replaced. But any fuel filter will clog and need to be replaced so don't fall for that "never needs changing" story.

At my station there are fuel filters in the pumps to give the fuel a final filtering before you buy it. This prevents a lot of junk from getting into your fuel tank. I replace these filters on the first of every month whether they need it or not. However, there are a lot of stations out there who do not have fuel filters on their pumps so the fuel you put in your tank may be contaminated with water from leaky underground storage tanks, improperly mixed alcohol blends, or even watered-down by an unscrupulous operator who's trying to make a fast buck.

Replacing the fuel filter once a year as a preventative maintenance item is insurance that reduces the risk of the fuel filter plugging up. Brand new cars right from the dealer are as susceptible to getting dirty fuel as any other car so even though the car is new, the fuel filter will start to clog fairly quickly.

Replacing the fuel filter once a year as a preventative maintenance item is insurance that reduces the risk of the fuel filter plugging up. Brand new cars right from the dealer are as susceptible to getting dirty fuel as any other car so even though the car is new, the fuel filter will start to clog fairly quickly.

Replacing the fuel filter once a year as a preventative maintenance item is insurance that reduces the risk of the fuel filter plugging up. Brand new cars right from the dealer are as susceptible to getting dirty fuel as any other car so even though the car is new, the fuel filter will start to clog fairly quickly.

Another question I'm often asked is; "How can I tell if my fuel filter needs to be replaced?"

Well, contrary to what a lot of fast oil change places tell you, you can't tell if a fuel filter needs replacing just by looking at it. Well, you could if you have X-Ray vision. And the only guy I know of that has X-Ray vision wears a red cape and a tight suit and I have never seen him working at a fast oil change place.

The only way to tell for sure is to remove the filter and blow through it. If there's little resistance, the filter is still okay and does not need to be replaced. But if there's more than minimal resistance, the filter is dirty and should be replaced.

"End quote"


Also on the 2002 VW maintenence schedule it doesn't have an interval for the fuel filter..

[Khyron]

Re: Problem with surging / fluctuating power

VW claims it's a lifetime part, along with the tranny oil I guess.

100K isn't a bad time to do it, I will give it a go next weekend. Walkthrus on vortex seem simple enough, just beware of the clips - breaking them means replacing fuel lines.

[VAG_Tech]

Re: Problem with surging / fluctuating power

So, I was wondering if there is any progress with the repair?

[Al]

Re: Problem with surging / fluctuating power

going to replace the n75 valve, thats what been diagnosed apparently? any thoughts?

[Al]

Re: Problem with surging / fluctuating power

so this is what my car is doing.... http://media.putfile.com/oscillation , any info would be greatly appreciated, im leaning towards putting in a n75j valve...