The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1988 - 1998 GMT400 Chevy & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 10-03-2015, 07:26 AM   #1
speedygonzales
Registered User
 
speedygonzales's Avatar
 
Join Date: Jan 2006
Location: Smithfield, VA
Posts: 1,501
Lightbulb 5.7 Vortec misfire condition....Never before encountered

Summary: Jerky idle and poor performance due to intermittent firing of plug but PCM doesn't see it as that plug, but thinks it was another. No SES! You can skip to the dot ■ below if you don't want to read the explanation.

Wanted to throw this information out there for others searching for a weird jerky feeling to their 5.7 Vortec. Just in case they are using a search engine to help them locate some trouble shooting information.

Had a weird jerky feeling while driving average highway speed in normal flat land driving for example around town and back.

Only way to describe it is to say have you ever felt an escalator jerk under your feet. That's what this felt like. Did it for some months.

Took a couple of long trips same as usual weird feel. Then one day poor idle, real jerky while driving almost like a misfire but not quite as bad as if you removed a plug wire. NO SES light coming on.

Decided to do an injector balance test. All 8 came out the same. Put the scanner on misfire detection and saw number 4 would occasionally come up but so did others. But 4 was more than the others by probably 4 or 5 times as much as the others.

Pulled number 4 no problems put it back in and same thing.

Let the engine cool, and had the wife start it while I checked the header primaries with an IR thermometer and number 8 was staying at 175° while the other 3 on that side went well over 300°.

■ Found the number 8 plug wire had slipped quite a ways down on the plug and there was a gap between the plug and the connector. Pushed it on with a "click" and all was good again.

So 8 was misfiring but the PCM was reporting 4 more than any others.

Since the firing order is 1-8-4-3-6-5-7-2
you see 4 immediately follows 8. It seems the PCM is slow to observe the "misfire" of cylinders and could lead someone in the wrong direction.

Just wanted to get this information out so others can take advantage of it the next time they are troubleshooting a jerky idle and poor performance.
__________________
99 Z71 (98 body style)
Pride and joy
speedygonzales is offline   Reply With Quote
Reply

Bookmarks

Tags
idle, misfire, plug wires, vortec


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 05:20 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com