oncesir

Do you experience oscillating love/hate emotions towards your LGT, and yet you still keep the car? If yes, then you're probably crazy like the rest of us.

Thats a great way to describe it. I'm extremely picky about the running condition of my cars and the stumble is like having an unresolved problem. Aside from that I love the car. Its fun, handles decently and has never left me. Its had its usual 4th gen issues but thats more just repairs based on age.

I will say that after adding the 3 ft of inlet hose to the fuel line that the stumble is still relatively minimal. It comes and goes but is definitely less than it was before. Maybe Ill add a fuel pressure gauge on the inlet side and see if that helps. Before this is all said and done Ill have 50 different fuel dampers, gauges and other BS in that 3 ft of hose just to remedy this one issue.

I posted several pages back about my fuel setup on my etuned stg2 LGT. Sti FPR, BOV reference line for FPR and slightly longer fuel hoses. Ive had the stumble for quite awhile since I last posted. None of the above took care of it completely. Im at the point where Im looking for answers and found this on one of the romraider forums. http://www.romraider.com/forum/viewtopic.php?f=15&t=4911&hilit=stumble&start=285

Recently I added more hose (3ft) to the inlet side of the fuel rail fitting and reset the ecu. It was much smoother after the reset but I can tell its relearning the stumble again after only a few miles. I know M Sprank talked about blocking out the learning capabilities of the ecu for that area of the tune. Has anyone ran a t-style fitting on the inlet hose to stop the water hammer effect? Am I understanding the cause of the stumble correctly??? TIA

One other question. Im not sure if this is just me or what but I also feel that different brand fuels cause the stumble to be more or less pronounced. Am I crazy? Lol

Installed the Sti FPR and reset the ecu about a week ago. Ive been driving around hoping that the stumble didnt return and so far so good. Sending logs to Dave @ Cryotune shortly and will report back. Overall the car feels so much smoother at the usual stumble rpm of 2500-3000. I did notice that the Sti FPR is a bit noisey on startup for some reason. It goes away once the engine is revved fwiw. Not concerned about a bit of noise for smooth driveability though.

One thing I noticed and experimented with was that after I installed the Sti FPR I didnt reset the ecu. The stumble was still noticeable. After resetting everything the car has actually gotten smoother as I have put miles on it. Granted, there is a small stumble from time to time but this is a Subaru after all... Overall I'm happy with things. A huge thanks to all those involved in this thread.

any progress?

Nope. Stumble is still there. Gonna try the Sti FPR and see how it does. Ill update shortly.

I would recommend contacting a professional tuner for assistance in that matter. But, there is free software that can be used to do it.

 

I have had some cars where the owners no longer felt any stumble with just the mechanical fixes. We got into the tuning side of the fix quite a bit after the mechanical side as it seemed to work for many customers.

The car was etuned by Cryotune last yr. I decided I'm going to put some miles on the reset Ecu and see what happens. I'll report back shortly. Thanks guys.

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.

Took your advice and ran a plenum source for the fpr. I didn't reset the Ecu and went for a drive. Immediately I noticed less of the stumble. How do you stop the Ecu from relearning the stumble? I have the sti fpr right next to me and it's tempting to install just for simplicity sake. TIA

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.

Is the supply line the too one or the bottom one going to the regulator?

Honestly I'm not sure. I extended the top hose on the manifold. I planned to experiment first to see what worked and then trim my 3ft of hose. Lol

Supply and return. Using a larger size hose can be dangerous. It tends to lead to leaks.

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.

The "fix" has been known for several years. All it really takes is elongating the fuel lines to reduce the "water hammer" effect (what is causing the stumble). Relocating the FPR can help with the really stubborn ones. Subaru even elongated the lines themselves in the 15 STi. We have performed the mod successfully more times than I can recall. That is why we keep 25ft rolls of fuel hose on the shelf, Lol. Good to see you finally got around to doing it yourself.

I'm in the process of tuning with cryotune and have this same stumble. How long do you make the new fuel lines? Do you extend both of the lines that connect to the manifold or just the supply hose? I also read that if you use a bigger size hose you won't need to use a longer hose? Any truth to that? TIA

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Willards, MD

98 Legacy GT 5spd

Black w/ 05 WRX wheels