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3sonfather's Avatar
 
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Location: Annapolis, MD, USA
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Question Power loss at 4800 rpm

I'm stumpted on this one. Ever since I've owned my car (2yr+) I've never been able to push my car over 4800 rpm in any gear. I put in an air/fuel ratio gage and with wide open throttle the gage shows full rich. As I climb upto around 4500 rpm the needle slowly drops to full lean and accordingly, I loose power until I let up off the throttle and return below 4500 rpm or so.
I doubt it is fuel related (new fuel filter, fuel pressure checks ok at the rail).
I've since put in another airflow meter and no change. TPS checks ok.
New coil, spark plugs, cap & rotor.
Anyone have any similar experiences or advice?
Thanks,
Scott
84' 944na
Old 05-10-2003, 01:23 PM
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check exhaust back pressure and cam timing
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Old 05-10-2003, 01:28 PM
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I though you had a Turbo lag but it's an n/a. lol! What's going on? My car kicks @ss after that rpms.
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Old 05-10-2003, 01:29 PM
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Check the injectors and cat....
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Old 05-10-2003, 03:35 PM
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How can I check exhaust backpressure? Funny it's mentioned. I have an aftermarket cat el cheapo version that got me through vehicle inspection after I purchased. With a little pursuasion, it'll be gutted - always hated cats.
FRW - I was hoping you would reply but am surprised you're onto the fuel. I just checked the fuel pressure and flow. It responds 30 psi at idle, 39 psi with vacuum removed and blows off the gage whilst pinching the return line. I'll check the strainer as the tank draws empty.
What else gives?
Thanks.

Last edited by 3sonfather; 05-10-2003 at 05:12 PM..
Old 05-10-2003, 03:41 PM
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Buy a new fuel pump. Richard
Old 05-10-2003, 05:18 PM
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make sure your TDC sensor isn't fouled with metal peices.
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Old 05-10-2003, 09:17 PM
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todwic - wouldn't a fouled speed sensor cause rough running all the time? I've thought about the reference sensor not doing it's job if it isn't advancing the timing. During my clutch overhall two winters ago I spent considerable time setting the sensors to their appropriate height and even replaced the speed sensor cause it looked damaged.
I'm going after the catalytic / back pressure thing - it's making sense. I've got great low end power from 2500 to 4000 rpm but I'm missing what should be the sweet spot in torque the higher rpm range. It just stalls out at around 4800 rpm. I'll let you all know what I find.
Thanks for the input.
Scott
Old 05-11-2003, 07:17 AM
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To check backpressure there is a gage made to screw in place of the O2 sensor and measure it there or you can hook up a vacuum gage to a central vacuum source on the manifold and slowly rev it up and see if the vacuum drops off suddenly.
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Old 05-11-2003, 10:43 AM
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I think it's fuel or Ignition that has a problem. Since your fuel checks out it's not the fuel side. Since you put in a new coil, spark plugs, cap & rotor for some reason the ignition can't keep up with the high RPMs. Or maybe it's a bad Throttle body sensor that's not reading a high set position.

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Old 05-11-2003, 10:47 AM
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Heh, thats when my power starts..
Old 05-11-2003, 03:08 PM
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Cat gutted - same effect. I am resigned to bad valves: cylinders 1 through 4 read 145, 180, 185, 140. Since this is my daily driver, I'm looking for another head to swap out.
Scott
Old 05-19-2003, 05:34 PM
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Those compression numbers point to a valve problem for sure. While you have the head off, why not send your injectors out to have them cleaned and flow tested?
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Old 05-20-2003, 07:31 AM
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