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HELP! engine runs rough after warm up
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TOPIC: HELP! engine runs rough after warm up

HELP! engine runs rough after warm up 11 years, 8 months ago #10798

  • jeffb
  • OFFLINE
  • Drivers Ed
  • Posts: 9
I'm trying to run down a problem...the engine runs great for about 15 minutes while driving hard. Then it begins to run very rough. It doesn't die but hardly responds to throttle input and acts very bogged down. I recently put in new injectors, removed the cat and replaced the engine temp sensor.

I'm thinking about air fuel mixture and/or sensors, any thoughts?

Re: HELP! engine runs rough after warm up 11 years, 8 months ago #10803

  • Big Dog
  • OFFLINE
  • Banned
  • Posts: 700
Keep swapping parts out until you find the problem. I found an issue with a computer box that would stumble at times. Others can add to a list of parts to think about swapping out. Here is a start:

DME
Injectors
Cap and rotor (this one was a problem for me several times)
Plugs
Plug wires
Coil
MAF
Throttle body
Flywheel sensors

Good luck.

Big Dog
Jim Foxx

Re: HELP! engine runs rough after warm up 11 years, 8 months ago #10804

Does the tank outgas a lot after it's been run, and you open the filler? Sometimes the tank venting can go bad, causing the tank to pressurize, and the motor to run rich.
after a while.
Eric Kuhns

National Director Emeritus

2007, & 2008 National Champion
2011, 2012 2nd
Last Edit: 11 years, 8 months ago by Sterling Doc.

Re: HELP! engine runs rough after warm up 11 years, 8 months ago #10807

jeffb wrote:
I'm trying to run down a problem...the engine runs great for about 15 minutes while driving hard. Then it begins to run very rough. It doesn't die but hardly responds to throttle input and acts very bogged down. I recently put in new injectors, removed the cat and replaced the engine temp sensor.

I'm thinking about air fuel mixture and/or sensors, any thoughts?


Might be good to swap an AFM with another. Make you match late to late or early to early. Last 3 digits on early are 028 and late are 064.

Could be as the AFM get hot it having issues. Remember the throttle position switch does not measure throttle position other than 3 distcint spots. Closed, part open and full throttle. Open can be cracked open or 90% open. The AFM however is designed to track with air flow into the motor so will meter fuel to match air being sucked in. I have had cases where the wiper tracks gets worn down and start affecting the signals to the computer.
Joe Paluch
944 Spec #94 Gina Marie Paper Designs
Arizona Regional 944 Spec Director, National Rules Coordinator
2006 Az Champion - 944 Spec Racer Since 2002

Re: HELP! engine runs rough after warm up 11 years, 8 months ago #10813

  • jeffb
  • OFFLINE
  • Drivers Ed
  • Posts: 9
Thanks, I'll check it out.

Re: HELP! engine runs rough after warm up 11 years, 8 months ago #10814

  • rd7839
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  • Endurance Racer
  • Posts: 625
Don't forget the basics, change the fuel filter. It's an easy job and will eliminate one more problem area. Many years ago I had a similar problem(on my Toyota), changed everything until it finally quit running. Pulled out the fuel filter, cut a ball point pen in half and used it to replace the filter until I got home. New filter, no more problems.
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