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Post by 89turbolx on Jan 23, 2009 21:45:49 GMT -5
89 mustang LX with '88 Turbo Coupe motor. The car was running fine untill my brake booster went out. Was pushing 20psi boost on T3 Turbo. After replacing booster and misc vacuum leaks, car goes lean fast under any boost. Replaced map sensor, now goes lean after 10psi boost. disconnected new booster, same effect.Here are things I've done: Put fuel pressure to 60psi( no help, now at 50psi. Also have 255lph pump), adjusted base timing to 15 deg (was at 10 deg, with MSD box and btm, boost retard at 0 and base timing at 15 deg, no spark knock! Strange, because it was always an issue) Had another LA2 PCM, no change. No codes. Car has power and doesn't miss. Only pushing 15 psi boost now, but don't go over 10 psi. Have extra O2 sensor for air/fuel meter, pinned PCM, when PCM is reading lean, my gauge is reading lean, and PCM O2 is switching fine. I havent tried another VAM, bought one, but hasn't arrived yet. Any ideas? Please!
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Post by Stinger on Jan 24, 2009 12:11:33 GMT -5
Weird. Did you scan for codes? The only thing I can come up with to check is cam timing. The fact that you can run more base timing now than you could before indicates a possible drop in compression which comes with a change in cam timing (slipped a tooth).
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Post by Matt Culpepper 2300gearjammer on Jan 24, 2009 13:23:19 GMT -5
Hold up just to clarify your method of monitoring...You're using a seperate factory narrow-band O2 and a A/F gauge? I couldn't quite tell from your post. How modded is this engine?
It might seem a little "out there" but I wonder if the damn thing was losing boost out the brake booster/ misc vac leaks and relearned that it didn't have to give itself as much fuel. Once the leaks were fixed all the air the meter is seeing is now making it to the engine. Have you tried disconnecting the battery for a little bit and driving it?
Edit: Can you explain this as well "Only pushing 15 psi boost now, but don't go over 10 psi." Are you saying its set at 10 or 15 psi right now?
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Post by 89turbolx on Jan 24, 2009 14:11:19 GMT -5
Yes I have disconnected the battery, no change. Yes I'm using another O2 sensor for my gauge. I have the boost set to 15 psi but as soon as it goes over that, the gauge drops off lean real fast. The car runs the same as it did before all this happened, just goes lean.
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Post by Matt Culpepper 2300gearjammer on Jan 24, 2009 15:28:10 GMT -5
K I'm with yuo now.
The reason I asked about the O2 is because measuring A/F with a standard style sensor is not too accurate or useful. Picking up a wideband on ebay would be a safer way to go. Does the engine "ping" as its going lean?
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Post by 89turbolx on Jan 24, 2009 15:58:07 GMT -5
Sorry, I have the boost set to 15psi, but after 10 psi it goes lean.
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Post by 89turbolx on Jan 24, 2009 16:03:45 GMT -5
Engine does not ping went lean. Since the beginning of this build the a/f gauge has been a good judge of things. I know it's not a good way to judge when tuning as a wide band.
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Post by Matt Culpepper 2300gearjammer on Jan 24, 2009 16:49:21 GMT -5
ahh very good about the pinging....or "rattlin" as the ole timers call it lol
I have a narrowband in my driver, hooked to the factory sensor. I've data logged runs that were identical on the wideband but the narrow band and gauge read differently. This was with no changes to the car at all.
What kind of vacuum do you have at idle and whats the cam/cam timing?
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Post by 89turbolx on Jan 24, 2009 18:54:43 GMT -5
I have about 21-23 inches of vaccum at idle with a/f meter in the middle. Not sure what you mean about cam/cam timimg. I dont have an adjustable cam gear. Mods on the car include: front mounted intercooler, 120 deg rotated gutted intake, 94-95 mustang gt throttle body. All where there before my problem started.
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Post by Stinger on Jan 24, 2009 19:00:31 GMT -5
So is it actually running bad when it "goes lean" or is it just showing lean on the gauge?
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Post by 89turbolx on Jan 24, 2009 19:34:12 GMT -5
No. Not now. Before i replaced the map sensor, it what buck and jerk under any boost. Now, its full power but goes lean. I pulled out #1 spark plug (using ngk Iradium) showed signs of a lean condition, white on the plug. I really dont run the car long when it does it, I back off the thottle.
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Post by Matt Culpepper 2300gearjammer on Jan 24, 2009 21:45:31 GMT -5
holy cow I've never had that much vacuum with any of them. Not saying thats bad either just saying I've never ever more than 18 in/hg with a stock cam and no vac leaks. I was just wondering is it was a just cam but you said stock cam timing which is equally important.
My plugs have also always had a white look and when spraying nitrous they are white with black speckles.
Are you able to check the fuel pressure while under boost instead of just when you're setting the pressure?
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Post by 89turbolx on Jan 25, 2009 9:31:57 GMT -5
I did run the car under boost with my fuel pressure gauge hooked up. Did not lose fuel pressure when it went lean. I also replaced the fuel filter about 2 months ago. Now I'm going by what my boost gauge reads for a vacuum reading at idle.
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Post by Stinger on Jan 26, 2009 2:38:14 GMT -5
What's funny is the MAP (actually a BAP because the vacuum line is not attached to it in turbo applications) is not read at WOT, the fact that it changed the way yours acted under boost makes me think your vacuum line may still be hooked up to it?
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Post by 89turbolx on Jan 27, 2009 12:39:52 GMT -5
I never had the vacuum line hooked to the map sensor. I did push the car at 15 psi a little longer this weekend and of course it went lean, but started to buck and jerk. Does anyone know what the extra fuel regular on the fuel rail is for? One right by where the fuel lines connect to the rail.
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