Hesitation, miss, stumble, boost leak, fuel filter, pump thread.

[DR1665]

464/1000 has been running like ass lately. I don't know if it's got anything to do with the accident last week, but she caught a Jetta with the rear clip and I'm not ruling out the impact might have knocked something loose/off. Looking for a little input regarding my theories if you wouldn't mind. I've done some searching, but still not entirely sure.

Symptoms:
Part throttle hesitation under acceleration. Typically around 2500-3500rpm. Tach climbs, boost gauge climbs (steady, no twitching), speed climbs, and pulls like a raped ape on Opposite Day. Noticeable loss of power under loads at part throttle.

Usual suspects:
Boost leak - I don't have a tester. I've never needed one. Did a thorough once-over of the plumbing last night. Stock IC and "piping" is secure. One of the two lines to the EGR had come off, but replacing it didn't mitigate symptoms. The only other questionable vac location I could find is the little BCS-looking solenoid on the front of the airbox. This was a California car until I opened up the ECU last summer. No CEL at this time. If I recall, I'm pulling down closer to 20in vac at idle.

Dirty MAF - Before the trip to SoCal this past weekend, I swapped out the dirty K&N for a clean one. I am generally very light with the oil, but the MAF got a good cleaning anyway.

Running rich - On the way to SoCal Friday night, I added a can of Seafoam to the tank, as it has probably been a while. Added to low tank, filled up on top.

Fuel filter - I wonder if getting rear-ended at 50 might have knocked some shiz loose inside the gas tank, which is now trying to make its way through the system. Don't know how long the current filter has been installed, but I dunno...

Fuel pump - Sometimes they overheat. Sometimes they just get old. Sometimes they suck up so much loose shiz in the gas tank that the pre-filter gets clogged and they can't flow enough. It's barely getting into the low 90s here in Phoenix and this pump did just fine last summer at 120* with the AC on in traffic. I doubt it's suddenly started bitching about its job. Although, shiz in the tank...?

EDIT:
Also, replaced the plugs prior to the trip. NGK BPR6ES looked good, despite being installed in January 2008, 17k+ on them. Nobody local had the right plugs, so I tried NGK BPR6EYs, which are their V-Power jobbers. I lost 4mpg on the way to SoCal. Sourced the right plugs while I was there, but saw no improvement in mileage on the return trip. Gapped to just under 35.

EDIT2:
Does seem like temperature might be a factor, as the car ran decently this morning while it was cool outside, but is running worse at the noon hour. It was so bad on the way home last night that I decided I didn't want to wait until the weekend to dick with it. Have not double checked the temp sensor connections.

Once car gets past the hesitation, it continues to pull decently, so I'd think that rules out a restriction in the fuel system, since those seem to lock you down at lower engine speeds since there's no fuel to keep up.

I don't have a logger, but I'll be looking for one here today. Just curious what you guys thought. Posted in Newbie because I found dozens of threads on this issue by other FNGs over time. Kinda hoping a little more pre-post troubleshooting might appeal to the kind mercies of the veterans. /ubbthreads/images/graemlins/worthy.gif


Thank you.

 

[Hertz]

You've always needed a boost leak tester.

Get that figured out.

 

[boostedinaz]

Yup. A boost leak tester is ALWAYS needed. Over the years I have found many slices or long cracks in hoses that, unless under pressure, looked fine.

If you are close to Moose he still has my Palm and I think my logger cable. If you can get it from him fire it up with MMcd and see what is going on. You could also try sapping out MAFs to see if that is the issue same for the ECU.

 

[DR1665]

Quoting Hertz:
You've always needed a boost leak tester.

Get that figured out.



Even when I had a 2GNT DSM? Aww...

 

[Hertz]

Oh, there's your problem right there, turbo is missing...

 

[boostedinaz]

I grabbed a logger cable from Mike last night. I'll bring it with me on Sunday and we'll try to get it all sorted out.

 

Sounds a lot like my car. I'm very interested to hear how your logging goes. My car was having significant knock issues, and when I pulled the engine I found the knock sensor had completely emptied itself of "resonance goo" all over the block. I think that combined with some noisy old lifters was maxing out the knock signal. I also found a large crack that went all the way through the original 140k turbine housing, so I had a major exhaust leak upstream of the 02 sensor that wasn't helping things. If you still have original turbo components I'd check them for cracks or leaks. Also replace the fuel filter if you're unsure of its age; they're cheap and easy, and if you have ethanol in the gas where you live it excels at loosening up crud in the gas tank that can then clog fuel systems.

 

[bmxkid415]

From what your describing it sounds like the knock sensor might be acting up. I had a similar issue, The car would build boot and RPMs would climb but it felt like you lost all power. Once you let off the gas and reapply it it sometimes went away. I grabbed my Data logger and I was seeing 45 or so counts of knock randomly. Replacing it did a world of wonders.

Keep us updated.
Cory

 

[Hertz]

Wow, Fitch and Driggs, being re-newbie on us.

Kid: I'd expect you to only have 43 counts, that's the maximum.

 

[bmxkid415]

Hertz: Was awhile ago, I knew it was in the 40's. Knock sensor had seen much better days. I'm still a noob /ubbthreads/images/graemlins/smile.gif

 

[DR1665]

Quoting Hertz:
Wow, Fitch and Driggs, being re-newbie on us.



Well, sir, I might offer that, when it comes to performance modifications on the 4G63T, I am still very much the newbie. If you recall, my time with a GVR4 has been spent as follows:

40% dealing with "the other guy's insurance"
40% tedious chassis repairs
15% daily driving
3% off road shenanigans
2% dealing with maintenance issues

On that note, I borrowed a logger. f*** a boost leak test. Both cars will be speed density by the end of the year.

O2 checked out
CLT checked out
IAT checked out
Injector DC checked out
KS reported a max of 19 counts @6500rpm, top of 3rd WOT, 4 counts @3200rpm, second/third part throttle.

99% sure it was bad gas. I stopped at a random hole in the wall joint in Blythe, California that had no other customers. They were charging $3.59/gallon for 91 octane. (It was $3.09 everywhere else.) Maybe the gas was good. Maybe they just had all their tanks filled with 87 and only charged more. Whatever. A fresh tank of Quick Trip guaranteed gasoline back home and it was running better. By the second tank, I couldn't tell any difference.

Okay. I've got a valve stem. I'll make a boost leak tester and give it a shot one of these days. After all, if it's worth doing, it's worth doing right...