Idles fine but starts to misfire at 1500 rpm - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 04-04-2007, 11:16 AM
70bird's Avatar
Smile if you know Jesus
 

Last journal entry: Waiting for a tranny
Last photo:
Join Date: Apr 2004
Location: Bakersfield, Ca
Age: 38
Posts: 516
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Idles fine but starts to misfire at 1500 rpm

What gives? My truck started to misbehave this morning. It ran fine yesterday. It warmed up just fine. When I started to drive away, and as soon as it hits 1500 rpm it starts to misfire (or lose a cylinder). When in park it will not misfire. I disconnected the vacuum advance and no change. Fuel pressure looks good. All the plug wires seem to be attached well.

chevy 350 carbed, 12* initial.

Any other ideas?

    Advertisement

Last edited by 70bird; 04-04-2007 at 12:03 PM.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-04-2007, 01:45 PM
Member
 
Last photo:
Join Date: Jan 2005
Location:
Posts: 3,707
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
how is the battery? a low battery will make an HEI misfire like that but it'll run fine at idle. Definately sounds like a spark thing.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-04-2007, 01:49 PM
Member
 
Last wiki edit: Wiring diagram 1953 Chevrolet
Last journal entry: Spare Tire Dent Removal
Last photo:
Join Date: Aug 2003
Location: a little S/E of Nome
Posts: 789
Wiki Edits: 647

Thanks: 6
Thanked 4 Times in 4 Posts
Place foot firmly on brake, shift into drive, push down on throttle pedal and see if it misses and what RPM. Could be fuel related or choke still on. Changed the fuel filter lately?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-04-2007, 03:30 PM
70bird's Avatar
Smile if you know Jesus
 

Last journal entry: Waiting for a tranny
Last photo:
Join Date: Apr 2004
Location: Bakersfield, Ca
Age: 38
Posts: 516
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Battery is good. 6 month old optima.

I'll try the break and accelerator test when I get home.

I checked the screen in the holley a couple months ago.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-04-2007, 03:56 PM
docvette's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Rebuild an alternator Last photo:
Join Date: Mar 2004
Location: Lafayette, california
Age: 62
Posts: 7,362
Wiki Edits: 12

Thanks: 0
Thanked 6 Times in 3 Posts
Doc here,

Have the Module Checked, It is probably going thermal (breakdown under load) and if a new one is needed, have it tested also, they have a high OBF fail rate..like 1 in 3 or 5..and after you leave the store, it's your $30 problem..

Check the primary resistance on the coil, less than an ohm, but more than 000 on a DVOM, Set to R x 1 , calibrated to "000".

Check the secondary, Set to R X 20K or higher, it should be between 6,000 and 30,000 Ohms..Either outside of ranges indicates a failing coil, replace.

Doc
__________________
Aftermarket Solutions
Electronic & Electrical
Innovations
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-04-2007, 03:59 PM
Registered User
 
Join Date: Apr 2007
Location: Canada
Posts: 4
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I goofed on my first qoute

Last edited by ranchwagon1; 04-04-2007 at 04:02 PM. Reason: goofed , wrong procedure for quotes
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-04-2007, 04:05 PM
Registered User
 
Join Date: Apr 2007
Location: Canada
Posts: 4
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
missing at 1500 rpm

Check out the counter weights on your distributor, a spring may have popped off, idle is usually good, but they can advance too much if a spring is broken or weak ..

Good luck
Ranchwagon1
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 04-04-2007, 10:29 PM
70bird's Avatar
Smile if you know Jesus
 

Last journal entry: Waiting for a tranny
Last photo:
Join Date: Apr 2004
Location: Bakersfield, Ca
Age: 38
Posts: 516
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I was hoping for the easy fix of a spring but no cigar.

Doc,
I don't have a DVOM but I do have a multi meter that will measure rx1k and rx10.

How do I check primary and secondary resistance on an HEI setup? I have touched the button on the cap and the inner center prong the the MM set at Rx1k and get a 30 K ohm reading. My guess is this is a secondary resistance.

I cannot get a reading from any of the other terminals.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 04-04-2007, 10:34 PM
docvette's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Rebuild an alternator Last photo:
Join Date: Mar 2004
Location: Lafayette, california
Age: 62
Posts: 7,362
Wiki Edits: 12

Thanks: 0
Thanked 6 Times in 3 Posts
Doc here,

Measure between the BATT and TACH terminals..R X 1 , clibrated to "000"..





Doc
__________________
Aftermarket Solutions
Electronic & Electrical
Innovations
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 04-05-2007, 12:03 AM
70bird's Avatar
Smile if you know Jesus
 

Last journal entry: Waiting for a tranny
Last photo:
Join Date: Apr 2004
Location: Bakersfield, Ca
Age: 38
Posts: 516
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The Ohm reading came out good.

Does anybody know if the MSD Super HEI modules can be tested with the same hardware as an OE style module?

I think I'll stick the Birds distributor in the truck tomorrow after work and see how that goes. I wish I had though of that earlier today.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may 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
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Exhaust Diameter Formula ChevelleSS_LS6 Engine 11 04-27-2012 09:21 PM
Turbo vs Supercharger - Write up!! FastChevyTruck Engine 107 02-16-2011 12:18 PM
351 windsor running rich ???? ve3ham Engine 19 08-08-2005 12:48 PM
Is 2 1/2 pipes big enough? Mustang_Killa66 Engine 7 02-12-2004 08:04 AM
idles fine until in gear operationgetdown Engine 1 09-07-2003 10:54 AM


All times are GMT -6. The time now is 12:21 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.