302 missfire under light load
Thread Starter
|
New User
Joined: Feb 2013
Posts: 13
Likes: 0
302 missfire under light load
Hey, I have done a lot of searching on this forum and most of the solutions for this problem have been on the 80s and 90s models and I wasn't sure if I could apply the same fixes since I don't have all of the electronics systems. The engine has always had a bad miss when it starts out cold, this is because we attempted to rip out the old EGR system a long time ago and I can't find the vacuum line that operates the choke. However, once the engine warmed up it ran fine. Recently it started missing at high and low RPM ranges. I found a loose vacuum line that was pulling in air and plugged it off and that solved my high load miss, however it is still missfiring under a light load (when my foot is just barely on the pedal it misses really bad running around 35-40 MPH. But when I put a little more gas to it running around 50-60 MPH it runs fine. I can't really tell what idle is like.) Any ideas? I want to blame the motor craft Carb because I have had issues with ever since I started driving it.
Cargo Master
Joined: Apr 2009
Posts: 3,038
Likes: 4
From: South west Idaho
Yeah, blame the carb, one of the best 2bl. carbs made. You already said " we attempted to rip out the EGR system". So you messed things up and just blame the carb. easy out.
Okay, no more lecture , go back and check for any vac. leak and fix ,no matter how small. Check your timing, make sure it's right on. Reset the idle screws . If still not right ,rebuild carb. they are a simple carb to put a kit in.
Okay, no more lecture , go back and check for any vac. leak and fix ,no matter how small. Check your timing, make sure it's right on. Reset the idle screws . If still not right ,rebuild carb. they are a simple carb to put a kit in.
Thread Starter
|
New User
Joined: Feb 2013
Posts: 13
Likes: 0
I wasn't downing the Carb, just saying that I've had a lot of issues out of it. The engine that I have now has over 350k on it, but the original engine had to be replaced around 12k. But I will try to check the remaining vacuum lines. I already checked the timing and separated the plug wires.
Cargo Master
Joined: Apr 2009
Posts: 3,038
Likes: 4
From: South west Idaho
It may be the carb then but they are pretty easy to rebuild. Main thing is clean it good , i clean the parts with a carb cleaner if they are pretty bad, but some times i just use lacquer cleaner. I like to dry it all with an air nozzle . You may not need this information if you have rebuilt carbs before.
Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
Hey, I have done a lot of searching on this forum and most of the solutions for this problem have been on the 80s and 90s models and I wasn't sure if I could apply the same fixes since I don't have all of the electronics systems. The engine has always had a bad miss when it starts out cold, this is because we attempted to rip out the old EGR system a long time ago and I can't find the vacuum line that operates the choke. However, once the engine warmed up it ran fine. Recently it started missing at high and low RPM ranges. I found a loose vacuum line that was pulling in air and plugged it off and that solved my high load miss, however it is still missfiring under a light load (when my foot is just barely on the pedal it misses really bad running around 35-40 MPH. But when I put a little more gas to it running around 50-60 MPH it runs fine. I can't really tell what idle is like.) Any ideas? I want to blame the motor craft Carb because I have had issues with ever since I started driving it.
What were these "issues" you had with the carb?
Thread Starter
|
New User
Joined: Feb 2013
Posts: 13
Likes: 0
I couldn't find anymore vacuum leaks. The miss fire didn't start until about 2 weeks ago. As far as the Carb goes, it been rebuilt twice and I think we have put 3 or 4 flush pumps on it since I've been driving it. If I can get some left over cash then I will try replacing the plug wires, those seemed to be a common issue with the 90s 302s.
Senior User
Joined: Mar 2004
Posts: 280
Likes: 2
From: Alabama
Sounds like you have the infamous "off idle stumble"... If you have the engine running and manual open the throttle a little and it stumble, misses, etc... unplug a vacumn line from the carb and plug the port and see if it changes (goes away). Do each port and hopefully it is a simple vacumn leak. I had a similar issue with a Holley and it ended up just being the PCV valve connected to the wrong port. If you smoke or have a buddy that smokes, stuff a rag in the carb, disconnect the vacumn line from the brake booster and start blowing smoke into it and see if it comes out anywhere...
Thread
Thread Starter
Forum
Replies
Last Post
john smith jr
1948 - 1956 F1, F100 & Larger F-Series Trucks
7
Nov 22, 2008 01:12 PM
Adam79
Ford Inline Six, 200, 250, 4.9L / 300
6
Jul 31, 2005 11:21 PM
packrat56
1948 - 1956 F1, F100 & Larger F-Series Trucks
5
May 29, 2004 12:34 AM
