2001 Chevy Silverado The one no one can Figure out

Tiny
KIDBLUE
  • MEMBER
  • 2001 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 94,000 MILES
This problem only happens at speeds past 65mph. Got the Code p300 Random misfire. Replaced plugs and wires no help. Then replaced fuel filter no help. Then had the injectors cleaned no help. Replaced all 4 o2 sensors no help. Scoped eng. Found #1 #5 #6 and #8 cyls. Misfiring the other 4 cyl. Are good. Swapped #1 coil pack with #3 to see if misfiring would follow it stayed on #1 all Vacuum lines look good. No other codes show up.
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Tuesday, October 13th, 2009 AT 10:53 AM

16 Replies

Tiny
RHALL77
  • MECHANIC
  • 3,361 POSTS
If you have the plastic style upper intake, most likely is it a bad gasket. This causes a vaccum leak and causes a misfire. Check and see if your fuel trims are low like -17%. If so thats your problem. Let me know what you find
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Tuesday, October 13th, 2009 AT 5:24 PM
Tiny
KNNHON
  • MEMBER
  • 2 POSTS
I had 'misfire' that wasn't a 'misfire'. It was BAD GAS! Here in florida, i've had more than one tank that was CRAPOLA! I now use Shell[believe me, I have no connection with them, or any of oil company CROOKS!]; And I have had no issue with the 'misfire'.
And, like the other chap said, look for VACUUM leaks EVERYWHERE![Mine had canister line[plastic] that was cracked
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Tuesday, October 13th, 2009 AT 5:56 PM
Tiny
RHALL77
  • MECHANIC
  • 3,361 POSTS
So is your problem fixed?
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Tuesday, October 13th, 2009 AT 6:17 PM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Not yet been trying to look for a vacuum leak none yet
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Friday, October 16th, 2009 AT 7:04 PM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Will check the manifold this week
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Friday, October 16th, 2009 AT 7:13 PM
Tiny
QUAGMIRE86
  • MECHANIC
  • 98 POSTS
Check the rubber "elbow" that connects the vacuum line at your fuel pressure regulator. My elbow looked fine, but when I pulled it off and inspected closely (by bending back and forth)there were hairline cracks all over.
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Saturday, October 17th, 2009 AT 1:47 AM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Will do that today. Have to wait until Tues to check to fuel trim that's when I can get my hands on a tester.
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Saturday, October 17th, 2009 AT 11:51 AM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Ok pulled the boot off and there is a crack in it ill change it out today and see if that fixes it. Watch this post and ill let you know.
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Saturday, October 17th, 2009 AT 11:58 AM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Nope no help.
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Saturday, October 17th, 2009 AT 1:51 PM
Tiny
QUAGMIRE86
  • MECHANIC
  • 98 POSTS
That is frustrating since there is no code that is present to give you and idea where to look. Does the problem present itself whether the engine is cold, hot or both? It would be great to determine if it is fuel or spark (could be fpr, tps, ect or csps).
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Saturday, October 17th, 2009 AT 9:39 PM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Cold hot it doesnt mater and only 4 cyl's I'm switching #1 with #3 fuel injectors to see if it follows. I wont have access to a tester until Tues. But I'm thinking the 1st guy might be unto something but I figure I might as well do something until then.
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Saturday, October 17th, 2009 AT 9:46 PM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
OK I tested it out last night and the misfiring stayed on #1 so the switching of the injectors was no help. Now my short term fuel trim bank #1 is about -3.9 to +3 % bank #2 about the same. Long term stays about 8.6 to 9.4% on bank#1 and 5% on bank #2. As I'm going down the road my misses clime at the same time and then drop to low values at the same time then climb again then drop again all at the same time. Could that be a crank sensor?
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Wednesday, October 21st, 2009 AT 8:51 AM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
OK I changed the Crank Sensor and that fixed the problem.
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Thursday, October 22nd, 2009 AT 4:43 PM
Tiny
QUAGMIRE86
  • MECHANIC
  • 98 POSTS
Excellent. I'm glad you found it. Too bad you had to go through all the other stuff first to find it.
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Friday, October 23rd, 2009 AT 1:57 AM
Tiny
KIDBLUE
  • MEMBER
  • 15 POSTS
Thanks I'm an aircraft mechanic and that is usually how it goes isn't it
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Friday, October 23rd, 2009 AT 2:22 PM
Tiny
BILLBUNDY
  • MEMBER
  • 3 POSTS
Check your cad. On your exhaust had a 2001 pontiac was doing same thing at50 mph found cad. Was pluged
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Thursday, December 10th, 2009 AT 7:10 AM

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