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Old 02-08-2006, 06:06 PM   #1
RSEnigma
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Join Date: Jan 2003
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Location: moving back to MA soon!
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'04 S2000
Suzuka Blue

Default drivability issue with full tank of gas

ok i did some searching and came up empty handed. so i'll ask the masses. i hav a 2000 RS with a usdm wrx swap. nothing overly complicated, and for the most part it runs great! everything works and runs fine until i fill up. when i fill up and am running on a full tank of gas it starts to act up. i believe my fuel level arm is stuck up but havn't had time to open up the cap and check that yet. from driving and vibration and bumps it comes down a little bit but when i fill up it pegs to F and stays there for a while. it only comes down to about a 3/4 tank despite the fact there's less gas in the tank. now when i fill up it cranks slower at start up, and driving around i get a strange hesitation at partial throttle cruising and then big misses and bucking when i try and boost. my fuel pump also starts going on the fritz and sounds as though its cutting out and gargling. when i add electrical loads such as lights on or pull my window switches up the noises get worse and sometimes it sounds like the fuel pump isn't even running. its a walbro so normally i can hear it 2 houses down the street.

so lets re-cap. runs, starts, idles, boosts great with less than say 3/4 tank of fuel (i don't know for sure where it runs fine because the fuel level arm i believe is stuck above that). once i fill up, it hesitates, cranks slow on start up, bucks violently when attempting to boost (3/4-full throttle), fuel pump sounds as thought its cutting out, makes a gargling (almost running water) sound, and gets worse with other electrical loads applied.

any advice or similar problems and how they were solved would be greatly appreciated. thanks a lot.
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Old 02-11-2006, 06:17 PM   #2
RSEnigma
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'04 S2000
Suzuka Blue

Default

ok, so i drove from springfield to brimfield and had to pull over twice because i was getting no power or even increased engine speed when i pressed on the throttle pedal.

i talked to a friend who informed me he had seen another car with the same issues and the problem was that the pressure cut off for the fuel pumps wentbad and would let you fill the tank right to the top. the extra fuel would overflow into the charcoal canister i believe and then have nowhere to go but into the intake manifold. so you'd have the simptoms i'm having. the thing that messed me up was i was under the assumption that my fuel level signal was messed up cuz i'd drive enough to have used a lot of fuel and it would still read like i had say 3/4 tank left, but it was just due to there being so much more fuel beyond F on the gauge. this all made sense for the most part, especially when i drove to springfield and after doing the math in my head i shoulda been at 1/2 tank after about 150 miles. my needle read 1/2 tank, my odo read 150 miles, and the car was running perfect. so i figured "great, i know what's wrong". but when i went to leave springfield it started acting up again. the fuel needle read about 3/4 full and then slowly krept up to about full again. its been there since and my driveability issues have gotten more violent.

i tried turning all the other electrical components off whenever i got to a stretch of road where there was good lighting and there were no other cars. with all other electrical loads off the car went back to almost running perfect. i got to my friends' house in brimfield and turned the car off. someone asked me to start the car and move it over, i went to start it and it cranked really really slow and refused to even sound like it wanted to start. the biggest thing that bother's me with this problem now is that i just put a brand new optima red top in there.

anyone's have any ideas with this new information?
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Old 02-11-2006, 09:23 PM   #3
HndaTch627
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yeah you have either a bad fuel pump or a bad fuel pump controller(provided you are running one). Subaru's aren't known for fuel pressure regulators being faulty like older GM vehicles(which is what your friend described when they fill the intake plenum/airbox). I would look for a poor connection at the fuel pump(where it's spliced in) and also check that fuel level sender.

jeremy
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Old 02-12-2006, 04:37 PM   #4
RSEnigma
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'04 S2000
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Default

i'm almost positive that the small manilla colored box that cuts off the pump at the gas station is bad, because twice now its let me put way too much fuel in. one of the main reasons my problems were getting so much worse and worse especially as i got close to my friends' house in brimfield is that my alternator was crap. it wasn't getting the initial positive signal to then send a charge back to the battery. so i swapped in an RS alternator off of another car down there, jump started her, and let her run for a while. after that all the major problems seemed to be gone. i think what happened is that the alternator was just dying more day by day and after a while i was running on just my optima, and it just happened to have enough juice to get me to my friends' house lol. lucky huh.
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Old 02-12-2006, 04:54 PM   #5
HndaTch627
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'09 Concours 14 ABS Black

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well its actually very possible that your alternator was over-charging and forcing your ECM into a fail safe mode(i've seen a couple civics do this in the past). Most ECM's are okay up to 17-18v but over that they are forced to shut themselves down. glad you figured it out though but man that's random. BTW: i am using a WRX alternator but just not using the 3rd pin in the wrx harness, my alternator charges fien without it.

Jeremy
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Old 02-13-2006, 12:54 AM   #6
RSEnigma
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'04 S2000
Suzuka Blue

Default

nah i doubt it was over charging anything. it wasn't doing anything. if anything it should have been less output than what's in there now because the RS alternator has a higher output. the wrx alternator is what crapped out on me. and besides, it was definately not making enough power with the wrx alternator that was in there. with electrical loads the problems would get worse. when i turned everything off and only electrical need was ignition and fueling it ran alright.

i was under the impression that most alternators have a voltage cut off where once it reaches a target output it starts to limit or not send the charge, something like a thermostat controls coolant temp. i havn't done a lot of electrical work since college so i may be wrong, its just what i thought i remembered from my 1st year electrical (4 years ago).
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Old 02-13-2006, 03:08 AM   #7
HndaTch627
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'01 GC8 Dinged STM
'09 Concours 14 ABS Black

Default

Quote:
Originally Posted by RSEnigma

i was under the impression that most alternators have a voltage cut off where once it reaches a target output it starts to limit or not send the charge, something like a thermostat controls coolant temp. i havn't done a lot of electrical work since college so i may be wrong, its just what i thought i remembered from my 1st year electrical (4 years ago).
you are correct but problem is that most of them need a signal wire which tells them what the current battery voltage is. On honda's we use what's called in Electronic Load Detector(ELD) and that's installed in the fuse box. when they go bad they can cause all kinds of funky charging system problems, they are what tell the PCM current battery/alternator load and the PCM then ramps up or ramps down the alternators output.
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