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4.6L engine miss, what should I do next?

 
  #1  
Old 04-18-2012, 03:27 PM
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4.6L engine miss, what should I do next?

Any suggestions appreciated. My 97 F-150 with a 4.6L has been acting up. Missing terrible then levels out at higher RPM's and almost completely goes away after the truck has been driven for 20 or 30 minutes. Ironically, runs pretty decently after sitting overnight, but the trip home from work is a bear. I've changed plugs, wires, fuel filter, air filter, and recently fixed the broken EGR tube. I'm still getting the famous insufficient EGR flow code that I assume is from clogged EGR ports at this point. I also get a couple of "system too lean" codes. I also used some Lucas fuel treatment in it. Each and every step has improved the miss, but it's still there. Where should I go next? I figured I'd check out and clean the MAF sensor tonight. Any tips or guidance would be appreciated.
 
  #2  
Old 04-18-2012, 08:30 PM
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Look for rotted, split, holes etc in any rubber parts connecting to the intake manifold.
This would let un metered air in and upset the Air Fuel ratio and fuel metering.
The OX sensors detect this and set the lean codes.
Good luck.
 
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Old 04-20-2012, 09:51 AM
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Thanks for the tip. I found a plastic tube had fallen off that runs from the left side valve cover to the intake. Replaced it, but the truck is still getting worse. I'm thinking that I might have fouled one of the new plugs when it was running lean? The truck actually ran MUCH better right after I replaced the plugs a couple weeks ago. Now it's running rough again and so bad that it feels like it's on 7 cylinders.
 
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Old 04-20-2012, 12:53 PM
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Better look more.
You found two issue so far.
Lean 'A/F' ratios does not foul plugs.
Repair what you know about then look for the remaing issues, otherwise your chasing to many things at the same time.
A hard cylinder miss will set a code.
Good luck..
 
  #5  
Old 04-20-2012, 02:25 PM
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Did you use motorcraft plugs?
 
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Old 04-20-2012, 02:30 PM
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Originally Posted by Alex_4.2L View Post
Did you use motorcraft plugs?
DOH!! I used Autolites. The miss was pretty close to what it is now the day I changed them out. The truck ran like a champ for a few days and then started throwing those 2 lean codes and that EGR insufficient flow code again. Eventually the miss came back and is gradually getting worse. Now it's right back to where we started and maybe a tad rough. But, make no mistake, the plugs and wires helped a ton right after I changed them about 2 weeks ago.
 
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Old 04-20-2012, 07:34 PM
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If you have 171/174 codes, there are other reasons they can set.
These codes are set when the fuel tables have been shifted to their rich limits trying to account for too much extra air as detected by the OX sensors. This is the only way the PCM has, to know that issue exists.
Other causes are both excessive and too little fuel pressure. Testing will tell this.
Leaking fuel injectors, leaking fuel through the pressure regulator into the intake, Vapor recovery system, oil dip stick not seated, leaking EVR solenoid, PCV etc..
After the obvious has been eliminated you have to look deeper.
Obviously a rough idle is either too little idle fuel or to much.
Usually too much fuel at idle causes the idle to roll (hunt) instead of being rough when the PCM cannot decide what to do with it.
Good luck..
 
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Old 04-24-2012, 09:35 PM
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Originally Posted by Bluegrass 7 View Post
If you have 171/174 codes, there are other reasons they can set.
These codes are set when the fuel tables have been shifted to their rich limits trying to account for too much extra air as detected by the OX sensors. This is the only way the PCM has, to know that issue exists.
Other causes are both excessive and too little fuel pressure. Testing will tell this.
Leaking fuel injectors, leaking fuel through the pressure regulator into the intake, Vapor recovery system, oil dip stick not seated, leaking EVR solenoid, PCV etc..
After the obvious has been eliminated you have to look deeper.
Obviously a rough idle is either too little idle fuel or to much.
Usually too much fuel at idle causes the idle to roll (hunt) instead of being rough when the PCM cannot decide what to do with it.
Good luck..
Yeah those are my 2 lean codes. I appreciate you trying to help. I know this question is like a "broken record" on this forum when dealing with those lean codes and that EGR insufficient flow code. Tonight I changed the PCV valve and cleaned the MAF sensor. Cleared the codes. Drove the truck about 5 miles before cleaning the MAF sensor. No repeat codes so far. We'll see about the miss tomorrow when I drive it to work. Fingers crossed.
 
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Old 04-25-2012, 07:58 PM
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The same basic pattern happened this morning, but things changed this afternoon. Ran pretty decent to work (about 11 miles) this morning. Miss was slightly evident, but overall okay. Then, just like always, it ran terrible on the way home (about 8 or 9 hours later). It got very rough and eventually showed a new code--P0304 (misfire on #4 cylinder). I ran it almost completely out of gas and put a full tank of 93 octane and a bottle of Seafoam in it. Reset the codes and started the long way home. Within 3 miles, it started getting better in a hurry. Not totally fixed, but much MUCH better. No lean codes at all today, and the P0304 did not come back after the new tank of gas and the seafoam. My question is could the coil pack be going bad, considering how it acts at different parts of the day, temperatures, etc., and/or would I get a specific misfire code like that with bad gas in general? The more I think about it, I think I've been getting some bad gas at a different place. Thanks for the help so far.
 
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Old 04-25-2012, 08:46 PM
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The PCM IDed the cylinder for you.
If the coil is going open or turns are shorting, a miisfire results.
How does the PCM know what cylnder it is?
The crank sensor measures revolution time for every cylinder everytime.
The time is compaired to software tables. If out of limits for a certain number of revs, a code is set for that cylinders no matter what the cause of the missfire is.
Good luck.
 
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Old 04-26-2012, 05:22 PM
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Woohoo!! The new coil pack fixed it! Thanks for the help Bluegrass!! The only thing that I can add that might help somebody in the future is the fact that the truck ran differently based on whether it was hot or cold (amazingly, mine ran much better after about a 30 minute drive than it did cold).
 
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Old 10-21-2016, 05:29 PM
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Originally Posted by Doc View Post
Any suggestions appreciated. My 97 F-150 with a 4.6L has been acting up. Missing terrible then levels out at higher RPM's and almost completely goes away after the truck has been driven for 20 or 30 minutes. Ironically, runs pretty decently after sitting overnight, but the trip home from work is a bear. I've changed plugs, wires, fuel filter, air filter, and recently fixed the broken EGR tube. I'm still getting the famous insufficient EGR flow code that I assume is from clogged EGR ports at this point. I also get a couple of "system too lean" codes. I also used some Lucas fuel treatment in it. Each and every step has improved the miss, but it's still there. Where should I go next? I figured I'd check out and clean the MAF sensor tonight. Any tips or guidance would be appreciated.
take the throttle body of. The air holes for my egr valve was completely blocked with carbon cleaned them ran good for awhile. But still got a miss round 40mph. Working on that will let you know
 
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Old 10-21-2016, 07:41 PM
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Hello Marine,
The blocked holes normally would not cause a misfire.
They would cause a diagnostic code test fault 401.
The 40 mph hint it gives you may also be a faulty coil or plug wire on your 97 4.6.
In OD the system tries to open the EGR.
This causes the fuel to be cut back, the ignition timing to advance and leans out the fuel to air mixture.
If there is an ignition fault that lowers coil high voltage to any cylinder, a misfire can result under these lean conditions.
As soon as down shift occurs, EGR closes, the air to fuel ratio richens up making voltage requirements lower for all cylinders and misfire goes away until the next time the conditions are entered.
Good luck.
 
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Old 10-23-2016, 09:59 AM
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Originally Posted by MARINECOR0811 View Post
take the throttle body of. The air holes for my egr valve was completely blocked with carbon cleaned them ran good for awhile. But still got a miss round 40mph. Working on that will let you know

Thanks for the advice. I sold the truck almost 2 years ago. The coil pack fixed it as mentioned above. It's still going strong with its new owner.

Originally Posted by Bluegrass 7 View Post
Hello Marine,
The blocked holes normally would not cause a misfire.
They would cause a diagnostic code test fault 401.
The 40 mph hint it gives you may also be a faulty coil or plug wire on your 97 4.6.
In OD the system tries to open the EGR.
This causes the fuel to be cut back, the ignition timing to advance and leans out the fuel to air mixture.
If there is an ignition fault that lowers coil high voltage to any cylinder, a misfire can result under these lean conditions.
As soon as down shift occurs, EGR closes, the air to fuel ratio richens up making voltage requirements lower for all cylinders and misfire goes away until the next time the conditions are entered.
Good luck.

Thanks again!!.....4 years later.
 
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Old 04-23-2019, 04:22 AM
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Has bad miss

WE bought the truck it had little miss when we purchased it but wasn't really bad at all. My husband decided to change the spark plugs get the miss out. He was right the plugs was old as the truck. So he bought all new spark plugs put them in. Afterwards tht miss was so bad we dont want drive it the computer said number 6 cole I bought it an he put it on an still.no luck just bad as it was before we stuck it on. Anyone have any ideas. We spend all our saves trying by us nice truck an. For this to happen its nice truck. Am has be something simple. All ideas welcomeQUOTE=Doc;16666382]Thanks for the advice. I sold the truck almost 2 years ago. The coil pack fixed it as mentioned above. It's still going strong with its new owner.




Thanks again!!.....4 years later. [/QUOTE]
 
 
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