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Rough Running, Wont Idle
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TOPIC: Rough Running, Wont Idle

Rough Running, Wont Idle 8 years, 3 months ago #15934

  • AgRacer
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So I developed a few problems at the conclusion of my last race.

As the week end went on, I developed a high RPM stutter where it felt like the motor would loose power but then climb out of it. I have since done some reading and think it may be the sweeper arm in the AFM loosing electrical connection in a sector of the sweep. I havent taken the cover off to inspect, but this feels like the right answer.

The more pressing issue is the fact that after the 1 hour enduro, my last race of the week end, the car would no longer idle and wanted to die as I was rolling into the pits. The car will start, and run with throttle application, but will die as soon as the throttle is released.

I have troubleshot the following with no change to the problem:

New temporary vacuum lines
Swapped reference sensors (also tested resistance levels, no oscilloscope)
Swapped in an early DME/AFM as I have a newer style in the car (this actually caused the motor to not run at all which makes me think one or the other is faulty)
Tested/inspected the coil
Cap/rotor are new (cam sprocket bolt backed out at the race previous)
Spark plugs are ~3 week ends old
Replaced fuel filter
Verified that the fuel rail holds pressure, but unknown at what level

Unknown plug wire age
Unknown Fuel Pressure Regulator status

I am thinking of ordering new speed and reference sensors as well as an FPR just for peace of mind.

My thoughts are that the easiest viable fix at this point is that the FPR has failed in the closed position cause excessive fuel rail pressure and thus causing the injectors to shut down unless throttle is added.

If that isn't it, then some of my other research could suggest either a lifter or a valve spring failure or maybe even something more catastrophic in the head. I dont want to rip the camshaft assembly off if I dont have to.

Thoughts? Any easy way to look under the "valve cover"?

I was also running wide band data to my data logger that week end if anyone thinks that will help diagnose.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60

Re: Rough Running, Wont Idle 8 years, 3 months ago #15944

I would look at the AFM first.

The new (-64), and old (-28) AFM are not interchangeable, and no the car won't do anything other than (maybe) idle when they are swapped.

Master power switches can get old and cause hard to pin down misses, too. I now time them out after 3-4 years. They are cheap, and can ruin a race or even weekend when they go out.
Eric Kuhns

National Director Emeritus

2007, & 2008 National Champion
2011, 2012 2nd

Re: Rough Running, Wont Idle 8 years, 3 months ago #15945

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I swapped both the AFM and DME out togther as a pair. I do need to verify that the spare set I have are compatible with each other though because I got no spark when I swapped out the my spare AFM/DME with what I've been running on the car.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60
Last Edit: 8 years, 3 months ago by AgRacer.

Re: Rough Running, Wont Idle 8 years, 3 months ago #15948

Ah, crack open the DME that you have, and see if the wiper tracks are worn.
Eric Kuhns

National Director Emeritus

2007, & 2008 National Champion
2011, 2012 2nd

Re: Rough Running, Wont Idle 8 years, 3 months ago #15954

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Just tested both AFMs with no negative results meaning my spare DME maybe bad since it wouldnt even fire with my current issues. Need more ideas else Im going to start taking the cam assembly off.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60

Re: Rough Running, Wont Idle 8 years, 3 months ago #15958

Does it seem like an electrical miss, or just losing power/won't rev. If it's the former, I'd chase down the electric possibilities, if it's the latter, go looking at valve springs.
Eric Kuhns

National Director Emeritus

2007, & 2008 National Champion
2011, 2012 2nd
Last Edit: 8 years, 3 months ago by Sterling Doc.
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