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Old 04-06-2010, 08:30 PM   #1
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Default Aack! Car won't go past 5psi / Rich AFR

WTF ..... I haven't done anything to my setup lately .... was driving along enjoying the spring weather .... suddenly my car won't go above 5psi and the wideband is showing super-rich AFR at that level. Vacuum leak? Bad injector seal? (I listened with a long screwdriver and they all sound fine.) No symptoms when not in boost, although my father says he smelled fuel when I started the car.

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Old 04-06-2010, 10:33 PM   #2
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raw fuel means: no spark, no combustion, less air

what did you touch?
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Old 04-06-2010, 10:46 PM   #3
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Originally Posted by Braineack View Post
raw fuel means: no spark, no combustion, less air

what did you touch?
Nothing! All I've done in the past few months is install Clearwater door speakers. Oddly, that ptoject worked perfectly the first time ... I should have known it was a bad omen.

(Okay, I did one other thing. Last week I brought the plu gap down from .030 to .025, in order to eliminate misfires, in order to pass OBD-II inspection. But I had no problem getting full boost after that, so I don't think it is related.)
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Old 04-06-2010, 11:24 PM   #4
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Fuel pressure regulator leaking into the vacuum system?
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Old 04-06-2010, 11:27 PM   #5
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Fuel pressure regulator leaking into the vacuum system?
Can you elaborate? I don't know anything about the fuel system. Where is this regulator gadget and where does it involve the vacuum system? Do all Miatas have one, or only certain years? (Mine's a 2004.)
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Old 04-07-2010, 12:15 AM   #6
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I'll admit I am from the GM world where this was common on some models and am still learning about Miatas. If your car has a fuel pressure regulator that references the manifold pressure (which most do) then there is a possibility that the diaphram can leak fuel into the vacuum system. Look for a cap with a vacuum line attached to it on the injector rail or on the return line. Pull it off with the car running and see if fuel is coming out. The engine speed will go up or if it is a MAF based system you may throw a code, stall ect.
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Old 04-07-2010, 12:28 AM   #7
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I'll take boost leak for 500, Alex.
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Old 04-07-2010, 12:59 AM   #8
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I guess if it is a MAF system I can see the going rich thing with only 5 PSI. Might have a winner.
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Old 04-07-2010, 10:19 AM   #9
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Like if the hose to the throttle body came off, or whatnot. MAF would read a shitload of air coming in that's being leaked. Car gets xxx fuel for that amount of air. Pig rich, low boost. Try it evan.
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Old 04-07-2010, 11:38 AM   #10
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I don't know guys...my bet is on the ACLU bumper sticker, -65whp (it was distributed amongst those unfortunate enough to not have a turbo).
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Old 04-07-2010, 11:44 AM   #11
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I loled.
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Old 04-07-2010, 12:05 PM   #12
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I know when mine runs a bit funny...I re-load me old map and everything runs nice again

But it does sound like a boost leak.
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Old 04-07-2010, 01:15 PM   #13
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Oh wait, he has the megasquirt controlling fuel and spark. I doubt the MAF has any control at all over the fuel. In that case, a blown off I/C hose won't cause the rich condition. Hmmm.
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Old 04-07-2010, 01:25 PM   #14
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He took MS off to go to inspection. Keep up with it, Tim!
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Old 04-07-2010, 01:53 PM   #15
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Oh. I figured he put it back on cause he was boosting around. I dunno. Maybe he should put it back on.
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Old 04-07-2010, 02:35 PM   #16
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Oh. I figured he put it back on cause he was boosting around. I dunno. Maybe he should put it back on.
That's the plan. But first I will send it back to DIY to look for any glitches, and/or maybe I'll upgrade to MS-II. Right now I'm extremely busy with work and family stuff (my mom has cancer, so I'm going to NYC several times a week to visit her at the hospital .... luckily the bus stop is 100 feet from my house!)
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Old 04-18-2010, 05:06 PM   #17
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Fixed!

Finally had time to dig into the problem today. Noticed that vacuum was less than usual at idle, so I figured. "Damn it, must be ANOTHER bad injector seal!!!" .... PITA to work on those in an MSM so instead I poked around the engine bay for a while .... and eventually noticed the throttle body elbow wasn't very tight where it meets the intake manifold.

D'oh!

Tightened. Test drove. Boost is back.
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Old 04-18-2010, 05:20 PM   #18
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Quote:
Originally Posted by chicksdigmiatas View Post
I'll take boost leak for 500, Alex.
Quote:
Originally Posted by TurboTim View Post
Like if the hose to the throttle body came off, or whatnot. MAF would read a shitload of air coming in that's being leaked. Car gets xxx fuel for that amount of air. Pig rich, low boost. Try it evan.
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I know when mine runs a bit funny...I re-load me old map and everything runs nice again

But it does sound like a boost leak.
hmm!
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Old 04-18-2010, 05:26 PM   #19
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I know, I know. I never doubted ya'll. But sometimes, for a mechanical moron like me, it helps to "discover" these things for myself.
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Old 04-18-2010, 10:54 PM   #20
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Quote:
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I'll take boost leak for 500, Alex.
I'll take "the rapists" for 500, Alex.
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