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Old 04-21-2002, 11:43 PM   #1
Rick G
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Have a Nice Day? So....what's the solution to the rich/lean problem?

Made you look! No flames please!
I have a 2000 RS with lots of soot on the pipe lil' flat spot at 3500rpm.woot .
YES I'VE SEARCHED and searched,read and read for a year now and every time I think its been solved someone argues the point.
So ....is it:
S-AFC?
Chip?
89 octane in winter,93 summer?
maybe even hotter plugs?
parallel fuel rails?

For the hesitation:the ground mod?

Anyone with a MY00 or 01 RS fixed this yet? What worked for you?
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Last edited by Rick G; 04-22-2002 at 11:09 PM.
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Old 04-22-2002, 12:36 AM   #2
STiTuner
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just another reason to was my car more

Brad
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Old 04-22-2002, 03:00 AM   #3
Tim Sanderson
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I guess i don't understand the question. I have soot on my tailpipe too but theres no driveability problems(54000 miles). How do you know that you are running rich/lean?
And you did'nt mention any mods so i'll assume it's stock.
Higher octane is for high compression or turbo of which you are neither so that's just a waste of money. Not to mention that it does'nt burn as completely as lower octane fuel in our cars.
I would suggest upgrading your ignition to an aftermarket brand that has multiple spark ability and higher output.
Jacobs/accel/msd.....etc.
good luck
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Old 04-22-2002, 05:12 AM   #4
CosmoTheCat
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As of right now I have no flat spot anymore.

I installed new plug wires and plugs a little bit ago. Seems the flat spot goes away with new plugs every time. And running the NGK V-powers it's not too expensive to swap them out every 6k/oil change.
This time I gapped them to .060 or whatever it is. Next oil change I'm going to pull them out and see what they look like. Clean them up if they're not fouled, recheck the gap, and throw them back in.

I've been running 91 octane (super out here, 91? 92? whatever) since new because otherwise the sufur content kills me.
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Old 04-22-2002, 09:42 AM   #5
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When I changed my plugs, my hesitation went away .But about 200 miles later, it was back.
Then I did the single ground point mod, and 600 miles later, no dead spot.
As to running rich, I'm still looking, but I know the fix isn't going to be cheap.
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Old 04-22-2002, 05:41 PM   #6
CosmoTheCat
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Quote:
Originally posted by tcs007
When I changed my plugs, my hesitation went away .But about 200 miles later, it was back.
Then I did the single ground point mod, and 600 miles later, no dead spot.
As to running rich, I'm still looking, but I know the fix isn't going to be cheap.
Oh yes I forgot. I also ran a couple of extra ground spots, and I've put over 1200 miles in it since then.

Anybody try the parallel fuel rail mod? Here's what I think. And not being an engineer, I could be totally wrong.
Ok so it's well documented that the far side cylinders (1 and 3?) get a fair amount less fuel pressure than the driver's side ones do. That leads me to believe that all things being equal, those would run a bit on the lean side. Running lean would cause trouble in the form of knock, wouldn't it? So to compensate for that the ECU richens up the mix a little, making the 1 and 3 run more stoich, but causing 2 and 4 to run rich. So by equalizing the fuel pressure between all 4 cylinders, it would allow for more equal a/f ratios to be produced.

How does that sound?

Feedback please.
(and the mod was pretty cheap from the one review of it I read... some fuel line, some t connectors, and some other fittings, that's it)
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Old 04-22-2002, 05:55 PM   #7
2Point5RS
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Sounds good to me.. but shouldn't the ECU just send extra fuel to the 1 and 3 cylinders? Or is it not THAT smart? What's the reason for the lean misture in 1 and 3?
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Old 04-22-2002, 06:01 PM   #8
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>Ok so it's well documented that the far side cylinders (1 and 3?)
>get a fair amount less fuel pressure than the driver's side ones
>do.

Where is this documented? I would like to read about this one.

/David
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Old 04-22-2002, 06:55 PM   #9
jhonas
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Disclaimer: I may be talking out of my arse...

The stock fuel system is set up in series. So say the #2 and #4 cylinders get more fuel pressure than the #1 and #3 cylinders. Changing the fuel system to a parallel set up would even out the fuel flow to each cylinder eliminating the lean problem in #1 and #3 cylinders (or rich in #2 and #4 cylinders depending on how the ecu compensates).

That's my diagnosis, whether it's right or wrong I'll leave that up to the masses to figure out. Search i-club for "fuel rail" and you should find some helpful information.
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Old 04-22-2002, 07:19 PM   #10
proecm
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According to all fluid dynamic rules, there is nothing that says that there should be any difference in the fuel pressure from beginning to end of the fuel rail (gasoline is incompressible fluid). As long as the stock fuel rail is not flow restrictive, which I higly doubt it is since there is an engineer at Subaru that has spent alot of time developing it. I am not saying it can't be improved, I'm just saying that for a close to stock engine, the stock fuel rails should not be an issue for lean/rich running conditions. I have seen a lot of talk about paralell fuel rail mods. So far I have not seen anyone hook up two pressure gauges to compare the pressure in the beginning of the fuel rail with the pressure in the end of the fuel rail. My opinion is that this mod is only for cars with extremely increased demand for fuel (turbocharged), where the stock fuel rail becomes to be too restrictive (flow wise). Otherwise I don't see any proof or reason to do it on a stock/near stock engine. Please proove me wrong.

/David
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Old 04-22-2002, 08:05 PM   #11
Rick G
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See....told ya it's becoming one of those posts! ( back and forth )
Very interesting,keep it coming guys!
I'll try the ground mod for the hesitation,I thought it was the point when it went from lean to rich at wot that caused it.

My first mod was NGK plugs and yes it did go away for a while but the hesitation came back.

I have a 2"( or 2 1/4 brospeed ) midpipe,SS Stromung muffler and a modified air box.( back botton of box cut open with K&N filter and open hod scoop )
I had a mod friendly subaru mechanic validate this ( mod )

Last edited by Rick G; 04-22-2002 at 11:14 PM.
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Old 04-23-2002, 04:36 AM   #12
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Quote:
Originally posted by proecm
According to all fluid dynamic rules, there is nothing that says that there should be any difference in the fuel pressure from beginning to end of the fuel rail (gasoline is incompressible fluid). As long as the stock fuel rail is not flow restrictive, which I higly doubt it is since there is an engineer at Subaru that has spent alot of time developing it. I am not saying it can't be improved, I'm just saying that for a close to stock engine, the stock fuel rails should not be an issue for lean/rich running conditions. I have seen a lot of talk about paralell fuel rail mods. So far I have not seen anyone hook up two pressure gauges to compare the pressure in the beginning of the fuel rail with the pressure in the end of the fuel rail. My opinion is that this mod is only for cars with extremely increased demand for fuel (turbocharged), where the stock fuel rail becomes to be too restrictive (flow wise). Otherwise I don't see any proof or reason to do it on a stock/near stock engine. Please proove me wrong.

/David
Being a layperson, I'm just guessing.

OK, here goes. With sprinkler systems at indoor garden centers there is a really large pipe at one end, which has little nozzles on it dropping into each pot. But every X distance, the diameter of the main pipe is decreased, I assume to increase the pressure the farther from the pump it gets and the more loss there is.

Granted it's a totally different situation, but wouldn't it make sense that at WOT the injectors closest to the fuel pump would get the most pressure, and those farther away would each get a little less? I don't know enough about how the whole system works to be able to tell anybody one way or the other. I can just think up reasons for the problem and let others who actually know more about the system tell me right or wrong.

It would make sense that if the fuel pump was putting a great deal of pressure on the entire fuel rail that if you poke 4 tine holes in it that each one would eject fuel with the same pressure. But if the injectors and fuel pump are maximized for a bone stock system, and you modify it to run more air through, is it not possible for the injectors to attempt to run more fuel than the pump can supply pressure for? This would actually be more of a problem with the stock fuel pump than the design of the rails. But maybe by having a Y in the rail with 2 injectors off each leg it would somehow make things mo' bettah.

I hate it when I talk out of my bum, but it sounds possible to me.
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Old 04-23-2002, 05:10 AM   #13
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Quote:
Originally posted by horatio102


Being a layperson, I'm just guessing.

OK, here goes. With sprinkler systems at indoor garden centers there is a really large pipe at one end, which has little nozzles on it dropping into each pot. But every X distance, the diameter of the main pipe is decreased, I assume to increase the pressure the farther from the pump it gets and the more loss there is.

Granted it's a totally different situation, but wouldn't it make sense that at WOT the injectors closest to the fuel pump would get the most pressure, and those farther away would each get a little less? I don't know enough about how the whole system works to be able to tell anybody one way or the other. I can just think up reasons for the problem and let others who actually know more about the system tell me right or wrong.

It would make sense that if the fuel pump was putting a great deal of pressure on the entire fuel rail that if you poke 4 tine holes in it that each one would eject fuel with the same pressure. But if the injectors and fuel pump are maximized for a bone stock system, and you modify it to run more air through, is it not possible for the injectors to attempt to run more fuel than the pump can supply pressure for? This would actually be more of a problem with the stock fuel pump than the design of the rails. But maybe by having a Y in the rail with 2 injectors off each leg it would somehow make things mo' bettah.

I hate it when I talk out of my bum, but it sounds possible to me.
you sir are 100% correct.

Jeremy
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Old 04-23-2002, 10:59 AM   #14
MY99 2.5GT
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Wouldn't a Fuel Pressure Regulator be sufficient for a "not highly modified" NA application such as ours? I mean the stock fuel pump should be sufficient unless you are severely taxing the fuel system with Forced Induction/much higher compression/Port-Polished Heads with Cams/or a higher flowing intake manifold.
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Old 04-23-2002, 12:14 PM   #15
proecm
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We are still talking theories here, not actual real life numbers, since no one seems to have done any extensive testing. While we are talking about theories, your analogy with the sprinkler system doesn't work in this case at all. The sprinkler system is not a system designed to keep the same pressure everywhere in the line, hence no pressure regulator. You have one feeding line and several "drains", no pressure regulator with a return line. A fuel injection system, from the fuel pump to the return line is designed to keep the same pressure for all four "sprinklers". This is accomplished by using a fuel pressure regulator and a fuel pressure dampener. The fuel pressure regulator will keep the same pressure in front of it all the time, that is what it is designed to do. The fuel pressure dampener makes sure to compensate for quick drops and spikes in the fuel pressure( fuel injector opens and closes). If you want to discuss harmonics or pressure pulses in the fuel rail, we can do that to. But I am completely confident in the stock fuel rail. Still we are only talking theory, and as long as we are talking theory we should use the right one, noncompressible fluid dynamics.
/David
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Old 04-23-2002, 01:14 PM   #16
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Wish I could remember where I read it, but the RS's fuel system runs about 3psi less at the far end than the start. As far as measuring the fuel ratios of each cylinder, its well know that #3 runs hot with a EGT probe. We can assume that its running leaner, most likely because its at the end of the fuel rail.
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Old 04-23-2002, 02:24 PM   #17
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>Wish I could remember where I read it,
So do I.

>As far as measuring the fuel ratios of each cylinder, its well >know that #3 runs hot with a EGT probe.
Has anyone put four EGT probes in there to see that no. 3 is the hottest, or is this done by historical purposes? By historical purposes I mean someone in the beginning decided to put the probe on the cyl 3 because he was used do do that on a different engine.

>We can assume that its running leaner, most likely because its
>at the end of the fuel rail.
I don't think we can assume that, considering that the pistons that have been braking is mostly piston i cyl 4, which is in the beginning of the fuel rail. The A/F ratio of each cyl will differ, sure it can be because of uneven distribution of fuel. But it can just as well be from uneven volumetric efficiency due to the fact that the exhaust is far from symmetrical.

I am not trying to be an ass her I am just trying to figure out what the real reason for the paralell fuel rail mod is. I can understand the reason to do it if you go forced induction, but other than that I have a really hard time to justify it.

/David
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Old 04-23-2002, 03:42 PM   #18
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David,
You're right. You're unlikely to need it unless you do turbo. But like I said what Ive heard from the turbo guys cylinder 3 is the hotest (and people were trying different cylinders in the early days of the i-club)

Probably a feel good mod more than anything. OTOH doing it wont do harm as long as you do it right and a paralell system is better even if not needed IMHO.
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Old 04-23-2002, 04:30 PM   #19
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Default Running rich w/ mods

Do a search and yew will find this to be a common complaint on the newgen Imp's w/ CAI and High flow exhaust. I'm trying to get a solution to the very same problem on my lightly modded 2002 2.5 (CAI and 2.5 exhaust,high flow cat) I saw a post a couple of months ago that explained the richness issue in technical-eze. Made perfect sense to me then but escapes me now.
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Old 04-24-2002, 06:01 AM   #20
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David - ok, I know this doesn't constitute any sort of reputable proof, but here's a link to the rs25.com thread about the fuel rail thingy. Claimed 8psi less to #3. Maybe you could add some insight over there?

http://www.rs25.com/forums/showthrea...&threadid=2126
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