The famous stumble...fixed?

Anybody notice what looks like an fpr in the fuel supply line over in the grimmspeed cai thread? Id link their picture but mobile crashes when i try. Im curious what that is.

This one? If so that's a damper, my 04 FXT has it too, but on return and on feed. Legacy's have a dampers too, right behind the FPR.

http://www.grimmspeed.com/content/images/intake_gr_prototype_1.jpg

Just an update, finally got to go on a highway trip post STI FPR install. Looks like A learning went high still, other areas were pulling a ton of fuel too.

Neverless got 30.8mpg with pretty heavy (but moving) traffic. I haven't gotten over 30mpg in a long time, even with this tune with D learning enabled (setting D learning to 80 so far has been hurting the fuel economy).

Car is still stumbling, but I haven't mocked with the tune yet, so that's gonna be next, I also will lengthen the fuel lines a little more thanks to BigTDogg's connectors .

I've been doing some more research and it seems like even 2013 WRX's (which don't run the same FPR assembly as us or the STI's), use fuel dampers on both the feed and return lines.

http://legacygt.com/forums/attachment.php?attachmentid=214400&stc=1&d=1439232760

Here is the diagram from the FSM. Now even our convoluted FPR's have a damper after the FPR, but not on the feed line. My 04 FXT, that has an in bay fuel filter stock, does not have a feed damper but has post FPR damper on the return line. I've read a few posts saying that the fuel filter can work as a damper, so that might be why the 04 FXT doesn't have it.

With us retrofitting the old style FPR's, I think we might need to look into running the standalone dampers, it's possible to just use the stock one (after you unbolt it from the FPR assembly, but it has 90* nipples and will be hard to use as an inline damper.

Some of the part numbers that I found from the 08+ Forester forums, these look to be just straight dampers:

Feed damper: 42086AG080

Return damper: 42086AG150

Has anybody seen this video?

Maybe the damper will help with the stumble?

I've been doing some more research and it seems like even 2013 WRX's (which don't run the same FPR assembly as us or the STI's), use fuel dampers on both the feed and return lines.

My 08 LGT has on the on manifold FPR with the dual dampeners like pictured above. Still feel the stumble. I might try extending the feed line between the dampener and firewall.

I extended the supply line about 3 ft and the hesitation is almost completely gone. I'll add length to the return next and see what the results are. I have not changed the regulator setup. Total spent so far is less than $25.

After installing the lines and resetting the ecu the car ran much smoother. Unfortunately the stumble came back after a few months of driving. I ordered an STi FPR and will report back my results.

After installing the lines and resetting the ecu the car ran much smoother. Unfortunately the stumble came back after a few months of driving. I ordered an STi FPR and will report back my results.

It will always come back as the ECM learns. The trick is to stop the ECM learning in the specific blocks required. You need to extend the fuel lines and source a manifold reference point for the FPR (not a single runner, but the plenum). No need to replace the FPR.

It will always come back as the ECM learns. The trick is to stop the ECM learning in the specific blocks required. You need to extend the fuel lines and source a manifold reference point for the FPR (not a single runner, but the plenum). No need to replace the FPR.

But it's such a nice feeling ditching so much extra crap, plus weight reduction yo!

Going from stock to the one on the left gives you room for an engine bay filter, which also works better then 3-4ft of fuel hose and much cheaper .

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/STI-FPR_004.jpg

No problem. I understand the point and your recommendation will make a cleaner engine bay.

Cleaner engine bay for sure!

Stock FPR and Fuel Filter (can barely see it):

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/STI-FPR_001.jpg~original

STI FPR and fuel filter:

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/STI-FPR_011.jpg~original

I just noticed that my FPR was already feeding from plenum vs just cylinder 4 with stock FPR. Which means I still saw the stumble and went with STI FPR (more details are probably in this thread or my build thread ).

It will always come back as the ECM learns. The trick is to stop the ECM learning in the specific blocks required. You need to extend the fuel lines and source a manifold reference point for the FPR (not a single runner, but the plenum). No need to replace the FPR.

So do we have a place in the plenum to get the signal for the FPR from ? Or is that something we need to create ?

I assume we'd need to T into an existing vacuum line ?

The fuel line is the easy part.

I'll have to check from home where I can view more of the pictures.

Thanks, Rick.

yeah, i'll end up with equal or less fuel hose, as i'm doing the same. can't copy the OP's methods though, Subaru felt a more difficult to remove FPR location was in order, and other than having to go to some ridiculous methods to remove one of the two screws holding it on (Phillips head? come on Subaru...) I "had" to make this to adapt the new STI to my fueling:

 

http://i1191.photobucket.com/albums/z471/flinkly/Subaru/Fuel%20Pressure%20Regulator/P1020177.jpg

I need one of these, #08Problems

I seem to recall something like that fitting on top of the throttle body on the old 1992 Civic Si.

Well that did work, I just checked the Honda site we used to order parts from, it was the MAP sensor, has the same flange but its the sensor not just the fitting. I'm sure there is one out there somewhere. you just have to to google the right question.

Similar products have been available for a long time.

Rick is right about not wanting to divert too much volume of air away from the BPV/BOV. He is also correct that the BOV line works as a plenum source.

To Covert, I have never tested with a fuel filter in line. But, it is possible you are still getting the "water hammer" effect through the lines. From there it is the effect of the opening and closing intake valves that causes you to need to move to a plenum source. Then the need to turn off the learning in the effected cells so the car does not try to learn around the stumble (which makes it worse).

fwiw ive never had this stumble.

transmission related?

Rick is right about not wanting to divert too much volume of air away from the BPV/BOV. He is also correct that the BOV line works as a plenum source.

While I agree it's best to have dedicated vacuum sources, it's just not worth sweating over it when your teeing an 4" line to an object that is 100% air tight (if your FPR is leaking you have other issues).

On my turbo SR20's I don't have the luxury of having more then 2 vacuum nipples. Thus I usually tee mechanical boost gauge, 3-4 feet long, to bypass valve. During normal operation never had an issue with BPV not blowing off or fluttering.

To Covert, I have never tested with a fuel filter in line. But, it is possible you are still getting the "water hammer" effect through the lines. From there it is the effect of the opening and closing intake valves that causes you to need to move to a plenum source. Then the need to turn off the learning in the effected cells so the car does not try to learn around the stumble (which makes it worse).

What if I told you I don't have a stumble anymore and I didn't touch the tune at all? I even checked it today and nothing between 2.5k-3k rpm.

I would test without the in bay fuel filter to see if that helps, but I already bypassed the tank fuel filter, thus I can't run without an engine bay filter anymore.

fwiw ive never had this stumble.

 

transmission related?

Could be, if auto it could be shifting past the stumble before you notice it, or if auto is choppy anyway.

At first I didn't get the stumble either, it took me finding an uphill road (plenty of them here) and forcefully keeping RPM's at 2.5-3k, since I usually am at 2k rpm thus below the stumble zone.

While I agree it's best to have dedicated vacuum sources, it's just not worth sweating over it when your teeing an 4" line to an object that is 100% air tight (if your FPR is leaking you have other issues).

 

On my turbo SR20's I don't have the luxury of having more then 2 vacuum nipples. Thus I usually tee mechanical boost gauge, 3-4 feet long, to bypass valve. During normal operation never had an issue with BPV not blowing off or fluttering.

All we are saying is to keep the line diameter and length as efficient as possible. Clearly your setup adds negligible volume to the system. We want the BPV to open as quickly as possible and any unnecessary volume on the signal line works against that. Having seen many DIY jobs where extra vac hose is simply coiled up and tucked in the engine bay this is more of a PSA than a statement directed at an individual.