factory spark plugs, now horrid mpg - Page 2 - Ranger-Forums - The Ultimate Ford Ranger Resource

4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

LinkBack Thread Tools Search this Thread
Old 01-04-2011
Blhde's Avatar
Join Date: Oct 2005
Location: Northern IL
Posts: 2,804
Originally Posted by 02FX4U View Post
yes, i reset the ecu for a good 5 min. i imagine i can check the o2 but why would it go out suddenly right when i change the plugs? should i go back to the .054 since there was no jolting before that?
O2's just lose sensitivity over time they are part of the tune up of an efi engine.

I would expect a mileage drop for a tank or two after resetting the computer as it relearns the engine. The 4.0 doesn't get good mileage and your mood effects as much as 30 percent of your mileage.
Reply With Quote
Old 01-04-2011
IN2 FX4's Avatar
Join Date: Feb 2005
Location: Costa Mesa, CA
Posts: 855
When I changed my spark plugs at around 70K miles, I used the Autolite Double Platinums. I, as you, did found the original plugs with a huge gap. The truck was running fine but decided to check one plug to see how it was doing. That told me to change the plugs right away.

I accidentally gapped the new plugs tighter than spec. I think it was around 0.059. I was concerned after I figured out it was not to spec but I was too lazy to go back and re-gap them. The truck ran great with no issues and I don't recall any change in gas mileage. The mileage is near 120K now and the truck is still running great. The plugs are probably worn enough to be in spec now but I will be pulling one of the plugs soon to see what it looks like.

I changed the spark plug wires at around 100K miles. When I took it out for a test drive it suddenly started misfiring under hard acceleration. When I got it back home to check out things I found one of the spark plug wires was not seated all the way on the plug. Apparently I did not get it all the way seated and it vibrated loose. That solved the problem and all is well. You should consider changing the spark plug wires. They can cause misfire issues if they are not in good shape.

I think the 4.0 SOHC engine is a great engine and plan to use it for at least 300K miles. It has plenty of power for my needs, which includes towing my race car all over the country.
Reply With Quote
Old 01-04-2011
Thread Starter
Join Date: Apr 2010
Location: orange county, ca
Posts: 136
ok guys good news. i regapped the plugs to .056 and made sure all plug wires and stuff are set. everything is back to normal, no jolting were it was before, idle perfect, engine sounds just as beefy as it was before, i did a number of hills, steep and not, plug flat road and i didnt feel any jolting. my only conclusion is to stay within the .052-.058 range thats in the FACTORY MANUAL, NOT THE RADIATOR EMISSION STICKER! found that out the hard way. .062 gap is WAY too big.

ill let u guys know after a couple tanks of gas what the mileage situation is. i will also look into the o2 sensors as i will prolly have to do those soon anyway. but throughout this whole thing, not one CEL light. hope this helps someone.
Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Spark Plugs Wires & Spark Plugs vancouverisland 4.0L OHV & SOHC V6 Tech 8 07-26-2017 12:28 AM
mpg and plugs foxrider1987 4.0L OHV & SOHC V6 Tech 17 04-11-2009 09:48 AM
New Spark Plugs - Better MPG - Halo Plugs SnowWhite 4.0L OHV & SOHC V6 Tech 3 05-29-2007 06:06 AM
PDQ!! Seafoam question......new plugs before, or new plugs after??? Fx4wannabe01 General Technical & Electrical 9 05-22-2007 11:55 AM
98 3.0 MPG Log (shows how mods affected MPG) Marcaronio 2.9L & 3.0L V6 Tech 23 05-11-2007 09:11 PM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -6. The time now is 09:58 PM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.