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Old 12-27-2005, 06:15 PM   #1
TyranosaurusWRX
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Default Symptoms of a bad fuel pump?

I've been chasing down a high rmp stutter for a dogs age and there isn't much left to replace. I was considering the fuel pump, but I have logged runs and it doesn't seem to lean out under boost when it stutters (monitored via WB02). Oddly though, if I sit still and rev it above 5k, it seems to hit the target AFRs, then leans out slowly. Is there still a possibility that the pump could be bad and not lean out under load? Unless there is just inconsistent pressure, I would think that you would see a lean condition. I have a fuel pressure guage but it's kinda cheap and I can't watch it under wot conditions.
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Old 12-28-2005, 03:48 AM   #2
sixpack subaru
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List your mods, if any? If you have a std uppipe with pre-cat they are known for collapsing and restricting gas flow. I had one that did it like clockwork at 5000rpm.
Also made a bit of 'wastegate' type noise while it was doing it.
Is the fuel gauge no good because the needle 'jumps' too much to read?
You've obviously changed your plugs(sorry).
What's the boost doing during all this?
Cheers
Sixpack
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Old 12-28-2005, 06:13 AM   #3
TyranosaurusWRX
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Quote:
Originally Posted by sixpack subaru
List your mods, if any? If you have a std uppipe with pre-cat they are known for collapsing and restricting gas flow. I had one that did it like clockwork at 5000rpm.
Also made a bit of 'wastegate' type noise while it was doing it.
Is the fuel gauge no good because the needle 'jumps' too much to read?
You've obviously changed your plugs(sorry).
What's the boost doing during all this?
Cheers
Sixpack
Well, I am kind of just focusing on the fuel pump at the moment. I gutted the uppipe many moons ago, so that shouldn't be a factor. The stutter usually picks up after 6k rpms...and yes, the fuel gauge shows an average 46-ish psi at idle, but the needle jumps all over as you stated...yeah plugs have been changed, coil packs swapped out, swapped out injectors (modded stock), used a different ECU, checked relentlessly for vacuum leaks, adjusted valves (re-shimmed) for more accurate clearances, compression tested ok, changed out knock sensor, changed fpr, checked injector harnesses, etc. Boost actually holds. When the car stutters out, you feel the power just drop. I'll try and find a log....

Last edited by TyranosaurusWRX; 12-28-2005 at 06:22 AM.
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Old 12-28-2005, 06:19 AM   #4
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I took this from an older thread that I posted a couple months ago. I still want to find a newer one. If you follow the rpms on the left-hand side, you can see it bounce up and down. Boost only fluctuates a small bit with the stutter. On the far right, AFRs seem relatively constant
Code:
5192 +13.9 4.6 100  90    00   W/B  +22.9   56.0  -0.8  -9.5 320.00 3.4  11.42 
 5482 +20.2 4.6 100  90    00   W/B  +21.9   53.3 +15.6  -9.5 320.00 3.5  11.20 
 5274 +23.7 4.6 100 100    00   W/B  +22.6   62.0 +15.5  -7.2 320.00 3.5  11.01 
 5411 +24.1 4.6  99 100    00   W/B  +21.2   64.7 +15.5  -7.1 320.00 3.5  10.76 
 5482 +23.5 4.6  99  90    00   W/B  +23.3   58.1 +16.0  -9.2 320.00 3.5  10.52 
 5574 +23.5 4.7 100  90    00   W/B  +22.6   61.4 +16.2  -9.3 320.00 3.5  10.65 
 5592 +22.5 4.7  99  90    00   W/B  +22.7   60.4 +16.4  -9.2 320.00 3.5  11.11 
 5747 +22.1 4.7 100  90    00   W/B  +23.1   63.0 +16.5  -9.2 320.00 3.5  11.20 
 5797 +22.1 4.7 100  90    00   W/B  +23.4   60.5 +16.5  -9.1 320.00 3.5  11.14 
 5837 +21.9 4.7  99  90    00   W/B  +23.4   61.2 +16.5  -9.1 320.00 3.5  11.12 
 5858 +22.1 4.7 100  90    00   W/B  +23.9   61.6 +16.5  -9.1 320.00 3.5  11.06 
 5910 +21.7 4.7 100  90    00   W/B  +24.4   62.1 +16.5  -9.1 320.00 3.6  11.06 
 5973 +22.5 4.7 100  90    00   W/B  +25.4   62.9 +16.5  -9.1 320.00 3.5  11.02 
 6049 +22.1 4.7  99  90    00   W/B  +25.6   61.5 +16.5  -9.0 320.00 3.6  11.05 
 5995 +22.7 4.7  99  90    00   W/B  +25.7   64.0 +16.5  -9.1 320.00 3.6  11.01 
 6207 +22.7 4.7  99  90    00   W/B  +26.6   61.3 +16.5  -9.2 320.00 3.5  10.93 
 6313 +21.7 4.7  99  80    00   W/B  +32.6   61.6 +16.9  -9.5 320.00 3.6  11.01 
 6253 +21.7 4.7  99  80    00   W/B  +35.0   61.3 +17.3  -9.5 320.00 3.6  11.08 
 6349 +21.5 4.7  99  90    00   W/B  +35.4   63.5 +17.2  -9.2 320.00 3.6  11.14 
 6447 +21.2 4.7  98  90    00   W/B  +36.1   61.8 +17.6  -9.2 320.00 3.6  11.08 
 6397 +21.5 4.7  98  80    00   W/B  +36.5   63.1 +17.8  -9.5 320.00 3.5  11.02 
 6435 +21.2 4.7  99  80    00   W/B  +36.7   63.2 +17.6  -9.5 320.00 3.5  11.06 
 6587 +20.8 4.7  98  80    00   W/B  +36.7   62.7 +17.6  -9.5 320.00 3.6  11.11 
 6747 +21.2 4.7  98  90    00   W/B  +36.4   65.2 +17.6  -9.2 320.00 3.6  11.08 
 6693 +21.0 4.7  99  80    00   W/B  +36.4   63.4 +18.2  -9.5 320.00 3.6  10.95 
 6535 +21.5 4.7  98  90    00   W/B  +37.1   64.4 +18.0  -9.2 320.00 3.6  10.93 
 6830 +21.2 4.7  99  90    00   W/B  +36.6   61.6 +18.2  -9.1 320.00 3.6  11.06 
 6747 +21.5 4.7  99  90    00   W/B  +37.2   64.4 +18.5  -9.2 320.00 3.6  11.12 
 6872 +22.1 4.7  99  90    00   W/B  +37.4   62.3 +18.5  -9.0 320.00 3.6  11.14 
 6761 +22.5 4.7 100  90    00   W/B  +37.0   63.2 +18.5  -9.2 320.00 3.5  11.24 
 6872 +19.4 2.9   0  70    11   W/B  +10.4    8.5 ECU.  -10.2 ECU.   1.5  11.43
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Old 12-28-2005, 08:29 AM   #5
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did you do any maintenance/troubleshooting to the maf sensor?
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Old 12-28-2005, 11:56 AM   #6
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Well, I sprayed it down (carb cleaner) last summer just in case, but I haven't had the maf sensor a year. Is there anything else I can do (to maf sensor)?

Last edited by TyranosaurusWRX; 12-28-2005 at 07:25 PM.
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Old 12-28-2005, 12:17 PM   #7
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Fuel filter?
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Old 12-28-2005, 07:24 PM   #8
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It's relatively new. I replaced it last year, haven't had the car on the road long enough to put a whole lot of miles on it.
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Old 12-28-2005, 07:41 PM   #9
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im having the same issues also, i think my walboro 255 may have crapped the bed, only has 3k miles on it. I have the same stutter and the car always has a fuel smell to it
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Old 12-28-2005, 09:18 PM   #10
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Interesting. I am going to put the stocker back in and turn down the boost and see if there is a change....
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Old 03-20-2006, 12:15 PM   #11
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any updates on this? I am experiencing high load/extended periods of high load fuel lean out (by about half a point).
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Old 03-20-2006, 01:14 PM   #12
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Quote:
Originally Posted by MRF582
any updates on this? I am experiencing high load/extended periods of high load fuel lean out (by about half a point).
FPR or fuel pump not doing its job anymore? This is assuming that it at one point you were not leaning out by half a point.
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Old 03-20-2006, 01:25 PM   #13
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i don't know if i feel comfortable making that assumption since i've kind of had this problem for a while. It has gotten worse as I've tuned the car for more boost and power.

What i did notice however is this.



notice the factory supply line has no fuel dampner (i'm assuming that's what it's called). my 04 however has a fuel dampner in line right where the white arrow is. Now is that really a fuel dampener or a restrictor? So I have one right before the fuel filter and then one right after the fuel pump. Do i need to get rid of the one right after the fuel pump?

I believe my problem stems from that. the build date on my car is May 03 if that helps.

thanks for your help.

EDIT - Another thought, are the power and return wires generally considered to be of a heavy enough gauge on our USDM wrxs?

Last edited by MRF582; 03-20-2006 at 01:46 PM.
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Old 03-20-2006, 01:51 PM   #14
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My situation ended up being unrelated. Still haven't confirmed the problem. I know I didn't have a damper in that spot on my 02, that's for sure.
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Old 03-20-2006, 03:51 PM   #15
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Subaru Stars

Quote:
Originally Posted by MRF582
i don't know if i feel comfortable making that assumption since i've kind of had this problem for a while. It has gotten worse as I've tuned the car for more boost and power.

What i did notice however is this.



notice the factory supply line has no fuel dampner (i'm assuming that's what it's called). my 04 however has a fuel dampner in line right where the white arrow is. Now is that really a fuel dampener or a restrictor? So I have one right before the fuel filter and then one right after the fuel pump. Do i need to get rid of the one right after the fuel pump?

I believe my problem stems from that. the build date on my car is May 03 if that helps.

thanks for your help.

EDIT - Another thought, are the power and return wires generally considered to be of a heavy enough gauge on our USDM wrxs?
If you do dump the dampners, which you probably need to.., (how many HP?).
You will need to insulate the fuel lines from the inner chassis rails and each other as they will 'slap around' as the fuel pressure fluctuates in the lines.
The dampners were introduced to eliminate 'rail knock', (well, that's what we used to call it! ). On anything with o/size injectors will generally do it

Dump the dampners and see what happens

Cheers

Sixpack
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