Engine stumbles

Tiny
MUMPHRIES
  • MEMBER
  • 1997 CHEVROLET BLAZER
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 170,000 MILES
Hello, I have a 1997 chevrolet blazer with a 4.3 v6 starts fine and runs good at idle but when you push on the gas pedal it acts like it is misfiring but has no fault code and the stft at idle is at -1.7 to 0
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Monday, June 27th, 2011 AT 5:57 PM

8 Replies

Tiny
JDL
  • EXPERT
How long since a tune-up? What is the ltft? What is the 02 sensor showing, when problem occurs?
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Monday, June 27th, 2011 AT 6:08 PM
Tiny
MUMPHRIES
  • MEMBER
Tune up was done about 6,000 miles ago. The b1 % ltft is -3.1 to -3.9 and the stft b2 % is -2.3 to 0 and the ltft b2 % is -9.3.
The o2 sensor b1 s1 % is -2.3 to 0, b1 s2 % is N/A and b1 s3 % IS N/A.
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Monday, June 27th, 2011 AT 7:20 PM
Tiny
JDL
  • EXPERT
Why is bank 2 so different ltft? Both are within reason, but, I like to see it closer. Do a cylinder balance test, when problem is ongoing, anything show up?
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Monday, June 27th, 2011 AT 7:32 PM
Tiny
JDL
  • EXPERT
Look at misfire counter spec, see if one cylinder has more misfire counts than the others. Start at that cylinder.
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Monday, June 27th, 2011 AT 7:47 PM
Tiny
JDL
  • EXPERT
As far as misfire, I can list the possibilities if you want, the list is probably as long as your arm. If you want it, I'll be glad to post list.
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Monday, June 27th, 2011 AT 8:00 PM
Tiny
MUMPHRIES
  • MEMBER
I dont have a way to perform the cylinder balance test
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Monday, June 27th, 2011 AT 9:06 PM
Tiny
JDL
  • EXPERT
This is for misfire isolation. I don't usually unplug any sensor with engine running. This info is from our database. Start engine. Disconnect iac motor. Using insulated pliers, remove one spark plug wire from a spark plug, and ground it against engine. Note engine rpm as wire is grounded, reconnect spark plug wire. Repeat procedure for all cylinders. Stop engine and reconnect iac motor. If engine speed drops equally, within 50 rpms on all cylinders, refer to " rough, unstable or incorrect idle" symptom. If there is no engine rpm drop or no excessive variation on one or more cylinders, check spark or compression on respective cylinder/s.
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+1
Monday, June 27th, 2011 AT 9:25 PM
Tiny
JDL
  • EXPERT
Some possible causes. Check for restricted exhaust. Bent push rods--broken valve springs--worn cam lobes. Problem with ignition wires. CCheck distributor cap for dust--cracks-- moisture. Check ignition system for faulty grounds. Check spark plug tips for wetness-- heavy deposits, anything that doesn't look right. Check poor fuel quality and fuel pressure. Check egr valve. Check ecm for proper grounds. Check tps. I'm sure I probably left something out.
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Monday, June 27th, 2011 AT 9:56 PM

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