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88 k5 egr issue

  #1  
Old 05-07-2011, 04:13 PM
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Default 88 k5 egr issue

had a prob with hesitation , noticed my egr valve was opening when i would crack the throttle , thought that was only to open on the highway , i pulled the vacum line off and pluged it ,seems to run better, i also unpluged the egr selenoid to c if it would thro a code , no codes were thrown , pluged the selenoid back in , but kept the egr valve vacum line pluged, truck has a 5.7 tbi 700r4 trany , , everthing on this truck is bran new , 4,500 mls on a new 5.7 ,all sensors been replaced , still runs a bit ruff , timing set on 0 with advance unplugged , any help or ideas would be great , been wrenching on this truck way to long , egr is new from advance auto craps , would that b the problem ? should i by a gm egr ?
 
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Old 05-12-2011, 07:07 AM
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I would guess your EGR vacuum solenoid might be the culprit. You can easily test it with some spare vacuum line and a whatnot.

What you've done is s a good way to blow up your engine inadvertently.

The ECU controls EGR, but didn't get feedback capability until '94, so there won't be a code. (and the v8 trucks didn't get a feedback-style EGR until '96, even though the 7427 PCM had a pintle position input) When EGR is commanded open, the ECU pulls up to 15% fuel and advances the timing up to 10* more because a mixture with exhaust gas displacing some oxygen needs less fuel and more timing due to slower combustion rate.

Pull fuel and add spark advance during normal operation without exhaust gas flowing into the mix and you will get some potentially catastrophic detonation.

The only way to safely disable EGR is by modifying the prom in the ECU. Raise the minimum coolant temp for EGR to 300*, or the minimum speed for egr to 150mph...
 

Last edited by helo; 05-12-2011 at 07:09 AM.
  #3  
Old 05-12-2011, 07:53 AM
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My 90 has a current egr code. Engine light comes on everytime I'm on the highway. It doesn't run bad so I'm ignoring it. Also my friend has a 91 pick up with the same problem as you. I plugged his egr about a year ago and he's had no problems or no codes yet either
 
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