Think I found cause of my misfire - fuel pulsation damper

I've been hunting a #3 misfire in my 05 LGT since I bought it a month and a half ago, and I finally think I found it! I haven't seen this cause discussed directly on any forum thread I've found, so I thought I'd leave it here in case anyone else goes through something similar.

 

Canned backstory is:

 

I bought the car despite the fact that I felt a misfire at idle while checking it out. About a week later, it threw P0303 twice in a row. This prompted me to buy a VAG COM cable, install RomRaider and get to diagnosis. Saw #3 missing up to 50 counts per 10 second sampling period, with #1 occasionally picking up a few roughness counts as well. Before I knew quite what else to look for in logs, I tried the following to no avail:

 

Replace plugs

Switch coils and injectors between #1 and #3 cylinders

Injector cleaner

Clean MAF sensor

Check valve clearance and compression (#3 was best of all cylinders in both regards, and all were either in spec or not very far off)

 

As I learned more about what to log and the more intricate features of the EJ255, I found the following:

 

http://legacygt.com/forums/attachment.php?attachmentid=256091&d=1506726984

 

That would be the misfire flaring during warm up idle, right as my TGVs opened. I did a boost leak check, and the car held some pressure but vented eventually. Found a couple at the boost control solenoid and BPV return line, but boost still leaked. Replaced both upper and lower TGV gaskets, and in the process found that both the turbo inlet and TB/IC hose clamps were pretty much finger tight. Put the car back together, warmed it up excitedly, and watched it misfire just like it did before. Phooey.

 

AF learning values did get better as I drove the car though, so at least it was worth the effort of finding the cause of the boost leaks.

 

Then I started thinking about fuel delivery. Read around, and came across this thread a couple of days ago:

 

http://legacygt.com/forums/showthread.php/famous-stumble-fixedi-232816.html

 

Sure, why not try it? Didn't really have a stumble or a stutter, but fuel system resonances can feasibly mess around with injector pulse volume, especially when they're driven by a cylinder that fires 180 degrees out of phase with #3. Went ahead and teed the FPR to BOV reference line instead of the manifold, and it made no difference.

 

Then I noticed the fuel pulsation damper mounted between #1 and #3 cylinder. Yeah, this thing:

 

http://legacygt.com/forums/attachment.php?attachmentid=256092&d=1506727082

 

 

That's a damped oscillator if I've ever seen one. Popped the caps off of both, and found that one of the adjuster screws had backed completely out! What's interesting is that this was on the driver side (#2 and #4):

 

Driver side:

 

http://legacygt.com/forums/attachment.php?attachmentid=256094&d=1506727150

 

Passenger side:

 

http://legacygt.com/forums/attachment.php?attachmentid=256093&d=1506727114

 

 

So, it appears that the driver side was damped at a lower frequency, since the diaphragm had max travel range, while the passenger side was damped to some degree at a presumably higher frequency. Since I don't know how these were adjusted at the factory, and I don't trust the passenger side to not have backed out some as well, I tightened both down all the way and started backing them out a little bit at a time every chance I had to do a cold start on the car and watching for changes in misfire counts. I'm currently backed out 1 turn on each, and my misfire counts now look like this, consistent across both today's before and after work warmup logs:

 

http://legacygt.com/forums/attachment.php?attachmentid=256095&d=1506727216

 

My thoughts are that given that the passenger side cylinder bank is farther away from the main FPR than the driver side likely means I'll have to adjust that side a little looser. Will have to be trial and error, since there doesn't seem to be an adjustment procedure out there, and the dampers aren't even labelled in the FSM. I have a spare pair of dampers from a set of rails/injectors I bought, and perhaps it's worth it to replace the rusty one in case moisture got inside and corrosion may be impeding the travel of the diaphragm. Either way, I hope this helps someone in the future!

 

 

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UPDATE 5/4/17

 

Just for shits and giggles, I decided to see what effect doing the rubber fuel hose extension would have on all this. In the STI FPR recommendation per the thread linked above, Cobb states that this combined with the FPR re-reference is ideal in terms of fuel system resonance. So, I cranked down both pulsation dampers again, cleared the ECU, and extended both rubber hoses to 2 feet apiece. Shazam, the misfire is back!

 

http://legacygt.com/forums/attachment.php?attachmentid=256097&d=1506727261

 

Then, I put back the short hoses, cleared the ECU, and warmed the car up again. Misfire subsiding!

 

 

http://legacygt.com/forums/attachment.php?attachmentid=256098&d=1506727418

 

So, it seems that the longer fuel hoses lower the resonant frequency of the fuel system enough to mimic (at least partly) the effect of a super loose pulsation damper. Not sure about the damper adjustment yet. Last time, I hadn't reset the ECU. This time around I did, and with the dampers cranked all the way down, the misfire appears a little bit worse. It's possible that shifting the resonant frequency down a a little bit could reduce this by shifting whatever harmonics contribute to this effect, but it's difficult to say. Time to get adjusting again. I've got this idea in my head to buy a pair of 60 psi pressure transducers and make a little pressure monitoring rig with an Arduino. That'd really substantiate what I think I'm seeing here. Let's see if the planets align and I find some free time to do it.

 

 

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UPDATE 5/6/17

 

Went for a 400 mile drive to see the folks yesterday. When I parked the car and watched it idle, my misfires were back. Counted about 30 misses in a sampling period. Uh oh, did I just shift the resonance into a different set of operating conditions? Left the car and went inside for the night.

 

Came back out this morning, and watched the car warm up. 0 misfires, until the TGVs opened. Oh balls. Just to be sure, I went to check out on my dampers. Passenger side was set just as I had it when I left on my drive (~1.5 turns). The driver side was at about 3 turns out, having only been 1.5 turns previously. I cranked both down and backed them out 1.5 turns, and misfires subsided. The log below shows the misfires. Started right before I went out to adjust the screws. When I came back in the car, the roughness counter was reading zero. It appears that the misses spiked when I wonked the side to side screw adjustment while resetting them, and then dropped to about zero once I had both back at their original setting. Even if this isn't fully conclusive since I wasn't actively watching the misfire counts while making the adjustments, I've never seen the misfire counts just drop like that during previous warm-ups. When they did reduce, they did so tapering off gradually.

 

http://legacygt.com/forums/attachment.php?attachmentid=256099&d=1506727465

 

I think there may be something to the outward appearance of the driver side damper, and the fact that it was running without the limit screw threaded and sitting on its seal for an unknown period of time. It seems possible that there's some internal corrosion that may intermittently mess with the function of the damper. So, one of two things could account for the screw being much looser after my drive:

 

1. The diaphragm stopped short of the screw limit, effectively unloading the threads and making the screw more susceptible to vibrating out of the hole while driving

 

2. The diaphragm's movement remained restricted after it bound up in its low position during the drive, and the screw actually remained more or less adjusted. Tightening the screw all the way down and backing it out again may have "reset" the damper.

 

I gotta make that rail pressure logger. Thankfully, I brought a much nicer looking damper with me from my spare rails . That's probably going on next, but I wonder if I should wait so I can log fuel pressure pulsation before and after.

 

I've noticed that the thread turns to "fully tight" depend on the fuel pressure in the rail. That is, once there's pressure the diaphragm in the damper deflects and the point where you feel the limit screw at full tightness changes correspondingly. As such, all my adjustments are done with the rail pressurized. If you go full tight with the rail unpressurized (before first start of the day, for example), I think you may effectively disable the damper. There appears to be 2-3 turn difference between the screw being fully tight with versus without fuel pressure.

 

 

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UPDATE 5/18/17

 

 

For those that may stumble upon this thread: after I got my fuel dampers replaced with spares, everything seemed hunky dory. Then, about 1000 miles into driving, my misfire steadily came back. Turns out the same driver's side damper screw had started to back out. I'm not sure why this happens anymore. Before my car got wrecked, I was experimenting with an STI FPR and some inline pulsation dampers. The thought was that the dampers on the stock LGT FPR, or the FPR itself may have been behaving strangely, and the STI parts were cheaper to source than the whole LGT FPR assembly. Car totaled the day I got my fuel pressure transducer :/

Sorry if I'm dense today - are these OEM parts, or someone installed an aftermarket attempt to solve the fuel line resonance, and basically they were adjusted really badly?

Sorry if I'm dense today - are these OEM parts, or someone installed an aftermarket attempt to solve the fuel line resonance, and basically they were adjusted really badly?

 

Yep, OEM parts. I have a pair of OEM rails I bought from a member here for the injectors, and they also have the dampers on them. Not sure if 07-09 Legacies have them since they use top feeds, and I can't seem to find a convenient picture of one of their OEM fuel rails.

Yep, OEM parts. I have a pair of OEM rails I bought from a member here for the injectors, and they also have the dampers on them. Not sure if 07-09 Legacies have them since they use top feeds, and I can't seem to find a convenient picture of one of their OEM fuel rails.

The rail dampers are only used in sidefeed applications. So, 05-06 LGTs and 04-05 STIs. The topfeed injectors use an inline damper.

Was there anything special about popping the covers off, or do they just pull right off?

 

If this fixes my problem you'll be my hero.

Was there anything special about popping the covers off, or do they just pull right off?

 

 

 

If this fixes my problem you'll be my hero.

 

 

 

They just pop right off. The one on the passenger side is kind of crappy to get to and mine was kind of stuck on, so I had to carefully pry it with a long screwdriver after loosening the turbo coolant reservoir. Good luck, would love to hear whether it works or not!

good find!

Oh shit dawg, more graphs! Original post updated.

Tightening the damper all the way (about three full turns) didn't fix my issue, but some time ago I relocated the FPR ref line using about 3 feet of hose... so maybe that's a bad thing now that my damper is tight.

Tightening the damper all the way (about three full turns) didn't fix my issue, but some time ago I relocated the FPR ref line using about 3 feet of hose... so maybe that's a bad thing now that my damper is tight.

 

Weak, would have been really cool if it worked for you just like that. Did it happen to decrease the roughness counts at all? Possible it needs finer adjustment. I wonder what effect that FPR reference line has, it's not something I had considered. Did you run yours run to the MAP sensor instead of the BPV reference line?

 

On a more selfish note - were both of your dampers ~3 turns out from fully tight?

Tightening the damper all the way (about three full turns) didn't fix my issue, but some time ago I relocated the FPR ref line using about 3 feet of hose... so maybe that's a bad thing now that my damper is tight.

 

Did you use the 3 ft for the vacuum line or the fuel line? The fix for the stumble is lengthening the fuel line.

 

You want your fpr reference line to be as short as possible.

Update. Another interesting finding.

Wanted to thank you for your post. This seems to have fixed my cylinder 2 misfire. Already threw all new injectors, fuel pump, gaskets, etc at the car..nothing fixed my misfiring at idle. So i fire up romraider logger while car is running and monitor the misfire counters while adjusting the fuel damper screw in increments.. eventually ended up with 0. Been holding steady so far. Here I was worried my exhaust valves were burnt. You rock.

Wanted to thank you for your post. This seems to have fixed my cylinder 2 misfire. Already threw all new injectors, fuel pump, gaskets, etc at the car..nothing fixed my misfiring at idle. So i fire up romraider logger while car is running and monitor the misfire counters while adjusting the fuel damper screw in increments.. eventually ended up with 0. Been holding steady so far. Here I was worried my exhaust valves were burnt. You rock.

 

Glad it helped! To those that may follow this, I have one final addition to the first post. As my LGT was totaled by a careless driver this Tuesday, I don't think I'll have a chance to look into this any farther It's been a fun two months, maybe I'll get a hold of another.

Oh no! Another 5mt GT wagon gone from the earth...

Hopefully you're ok.

 

Thanks for the effort you shared with us while your car was alive.

 

I think you should buy another one

 

*edit 9/28* OP's pics copied from poopiebucket and uploaded to this server per CR's suggestion on page 2. I'll remove these pics if a mod or the OP updates the first post.

*edit 10/3* pics removed

Update: Well, the new dampener did seem to help temporarily at the time. But, I thought I should let everyone know the ultimate culprit was the heads (two burned valves, and the lash on most were off). Got both re-worked and the misfires haven't been an issue since.

I'm going to have to try this.... besides the obvious massive vacuum leak i cant find... it's always misfired here and there....

Thank you for this post awfulwaffle! Mind doing us a solid and uploading those pictures to the forum before Photobucket takes them down? I tried to download them but PB would download blank images.

Thank you for this post awfulwaffle! Mind doing us a solid and uploading those pictures to the forum before Photobucket takes them down? I tried to download them but PB would download blank images.

 

Good suggestion. Maybe a mod can do it if the OP doesn't come back because the car is gone

 

Until then... Somehow I was able to copy the images (even though photobucket is blocked here at work?) so I added them to my post #15 at the bottom of page one.

Thanks! Yeah not being able to download the pics meant screenshoting and quality loss, so glad you could do it!

 

Hopefully OP or a mod can update the first post, since image order is important for that post.

Sorry guys, I somehow just got the notification from all your posts just now. I'll upload everything to the forum when I get home from work.

As a work-around to still use your PB photos and put your photos into their proper location in your thread, do this. I'd do this on a computer because it's much easier IMHO. It's a bit convoluted, but it gets very easy as you do it.

 

• Open your original thread, Click Edit, Go Advanced > http://legacygt.com/forums/images/editor/attach.gifPaperclip icon. The Manage Attachment window will open.
  

 

• Open your PB account to your 1st photo.
  

 

• Right click and copy that photo's image link. Make sure that there's a .jpg suffix, if not, then right click your photo and choose View Image. Then right click and copy that link.
  

 

• Paste the URL link into one of the two Upload File from URL address bars in Manage Attachment window. Do this with your 2nd photo, then > Click Upload.
  

 

• Do this as many times as necessary to get all of your PB photos loaded to the site's server. > Click Preview Post and you should see all of your PB photos loaded into the Thumbnail area at the bottom of your thread.
  

 

• Once you make sure all your photos are loaded, then > Click Submit Reply.
  

 

• Open a second copy of your thread, I just drag the thread URL into a New Tab > Once your copy thread opens, > Click Edit.
  

 

• Scroll to where your 1st picture will be and delete the PB notification that your link is broken. Put your cursor where you want your picture to load.
  

 

• > Click http://legacygt.com/forums/images/editor/insertimage.gif and leave that address bar open
  

 

• Go back to your original thread. Right click the photo that you want to have in position 1 in your thread, then right click that and copy the image link
  

 

• Go back to your copy thread, paste that image link into the http://legacygt.com/forums/images/editor/insertimage.gif address bar, and > Click OK. Your photo will load exactly where you have your mouse cursor and you'll see your picture appear in the edit window
  

 

• Repeat this process until all of your photos are loaded to your thread in the sequence that you want them, where you want them.
  

 

• > Click Preview Post and if everything is good, then > Click Submit Reply. Your thread will now have all of your PB photos reinstalled in your thread, where you want them, and you'll also have all of your photos resident for posterity in the Thumbnail area.
  

I'd volunteer to do this for you, but there's a lot of photos and I'd hate to get one of them incorrectly located.

 

You can't simply use the http://legacygt.com/forums/images/editor/insertimage.gif image load feature, because PB will break the link again.

 

LMK if you have any questions. I'll also put this process into the how-to on the Home Page.

Man, was Photobucket always such a popup minefield? All done. Hope this helps someone in the future. Maybe someone with a pressure transducer wants to get the effects of the damper adjustment nailed down?

Man, was Photobucket always such a popup minefield? All done. Hope this helps someone in the future. Maybe someone with a pressure transducer wants to get the effects of the damper adjustment nailed down?

 

Thanks! Yes it's been like that for a while, guess it's still not enough to pay the bills. There is a good chance that Photobucket will be no more in the near future, so getting everything out while we can is the notion.