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  #1  
Old 08-16-2015, 06:50 PM
65Sprint 65Sprint is offline
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Default 2003, 2.3L Misfire Under Certain Conditions

I have a 2003 XLT, 2.3L with 5sp that has a miss or stumble between 1500 and 2000 rpm under light throttle application and light engine load. The engine is fine under medium or heavy load and at any throttle opening larger than a fast idle. There is no CEL nor any pending codes. It is quite noticeable in 4th gear between 35 and 40 mph. I have done the following which have resulted in very little to no improvement.

-searched for vacuum leaks; replaced two hoses from IMRC solenoid to manifold and actuator
-removed intake manifold, checked for cracks or signs of leaks around manifold seals at head, none found.
-cleaned MAF, IAC and MAP sensors and throttle body.
-checked the intake manifold runner (flaps) for freedom of movement and cleaned them
-replaced plugs with Autolite double platinum
-replaced plug wires
-replaced coil pack as a shot in the dark
-replaced TPS as the original lost its spring tension although resistance values look fine with no dead spots in the POT

It looks like this issue has been discussed in previous threads but I have not been able to find much of a conclusion. In a few cases a replacement coil pack was the solution but not for everyone and not in this case. Can any one provide additional guidance? TIA
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  #2  
Old 08-16-2015, 08:46 PM
riscorpian riscorpian is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

I don't know about the rest of the people who had an issue like that, but I ultimately fixed it by ignoring the engine and checking everything else. I don't know what it is about this motor, but it just seems to absorb the symptoms from other parts going wonky, so to say. That is, it might seem like the engine is misfiring, but it's really just the transmission slipping or something. In my case, it was a screwy valve body in the transmission that wasn't actuating gears correctly. The way it went bad had me absolutely convinced that it was an engine issue though. It's strange.

With that much work invested into it, I'd say it's time to put on the blinders toward the engine and start looking elsewhere. Check the rest of the powertrain for clues. U-joints on the driveshaft are known for going out over time. When was the last time the differential was serviced? How about the transmission?
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  #3  
Old 08-17-2015, 05:27 AM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

Thanks for the reply and advice. I will take a look at the drive shaft and see if the u-joints might be worn and the roughness is in the driveline rather than the engine. At 123,000 miles, just about anything is possible. I changed gearbox oil a year ago and the differential is quiet and smooth. Besides what sounds and feels like an obvious miss with the throttle cracked and under light loads, gas mileage has decreased slightly from 26.5 mpg to 25 mpg. Not much, but enough to suggest something is not quite right up front. I have owned the truck since new so have a good baseline for fuel consumption.

I still think there might be a vacuum leak that I have not been able to find and is not severe enough to trigger a CEL (is that possible?). A poster in another thread advised that if the IAC is unplugged and the idle remains higher than about 500 rpm, a vacuum leak is indicated. I tried this and the idle decreased to > 500 rpm. Is this a valid test for vacuum leaks?
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Old 08-17-2015, 12:41 PM
riscorpian riscorpian is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

Quote:
Originally Posted by 65Sprint View Post
I still think there might be a vacuum leak that I have not been able to find and is not severe enough to trigger a CEL (is that possible?). A poster in another thread advised that if the IAC is unplugged and the idle remains higher than about 500 rpm, a vacuum leak is indicated. I tried this and the idle decreased to > 500 rpm. Is this a valid test for vacuum leaks?
Yes and no. Vacuum leaks are really weird. That particular test is more of a good way to check to see if the IAC itself is working fine. If the idle drops significantly once it's unplugged, then it's OK. If it seems to drop a lot, but not as much as it's supposed to, that could indicate a potentially bad seal within the IAC itself as well as a vacuum leak elsewhere. The best way to find vacuum leaks is with a smoke test. The second best is to spray carb cleaner around suspect areas and listen for idle surges.
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  #5  
Old 08-17-2015, 04:28 PM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

You confirmed my suspicion. I'll go look at u-joints.
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  #6  
Old 08-17-2015, 09:35 PM
GSF1200S GSF1200S is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

Its been my experience on trucks that speed dependent "bucking" is usually either a failing coil pack or bad ujoints. Given that you changed the coil pack I would bet its ujoints.

Thing is, they dont have to have slop to do this- they can also be binding and they will "load up" and "release" while cold (or hot depending) giving the impression you have engine stumble. The ujoints can be tight and still have issues.

I had this bucking myself only when cold- it was fixed the moment I changed the coil pack.
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  #7  
Old 08-17-2015, 11:33 PM
Tyler46 Tyler46 is offline
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Quote:
Originally Posted by GSF1200S View Post
I had this bucking myself only when cold- it was fixed the moment I changed the coil pack.
EXACT same thing happened to me. Jolting under heavy engine load, but my u-joints are pretty tight. Turns out I had a crack in my coil pack.
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People like him make me believe that birth control needs to be put in the public water supply
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  #8  
Old 08-18-2015, 07:20 AM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

Thanks for the replies. I replaced an Autozone coil pack under warranty a month ago with no change in symptoms and then recently bought a NAPA coil pack for a backup, again with no improvement. Previous coil pack failures were most evident with the engine under load and it sounds like this is typical. With this problem occurring only with the throttle just cracked open, at low rpm, and under very light engine loads, an undetected vacuum leak remains a suspect.

Weather prevented looking at u-joints last night but plan to get the truck in the garage tonight. I drove it 30 miles to work this morning and can confirm the roughness is not dependent on vehicle speed (drive shaft speed) but completely on engine speed, engine load, and throttle opening. Misfire in the thread title is probably the wrong term as the symptom is significant engine roughness, or appears to be.
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  #9  
Old 08-19-2015, 07:06 AM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

I don't see any issues with the drive train. U-joints are neither loose nor tight. I am further convinced this symptom is definitely engine roughness that occurs within the parameters described above. However, I am at a loss as to what the cause is and appreciate any "out of the box" suggestions.

One thought is that this is fuel mixture related. That is, when the throttle is barely open, either a vacuum leak or a fuel delivery problem is resulting in a lean mixture and the roughness at a particular engine speed. Perhaps I should note the problem does not occur throughout the 1500-2000 rpm range but rather at particular engine speeds within this range depending on what gear (engine load??) is selected. In fourth gear, the problem is most noticeable at about 35 mph and 1600 rpm. In fifth gear, the problem occurs at about 1900 rpm. I don't know what this is telling me but might be a useful detail to someone who has done more diagnostic work on these engines than I have.
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  #10  
Old 08-19-2015, 07:31 AM
Tyler46 Tyler46 is offline
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Did any of those replacement coil packs happen to be Motorcraft brand? If not, I think I found your problem.
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Originally Posted by guell View Post
People like him make me believe that birth control needs to be put in the public water supply
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  #11  
Old 08-20-2015, 09:20 AM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

No. I replaced the original coil pack, five years ago. The replacement was the Duralast line from Autozone. That coil pack failed two years ago and was replaced with the same under warranty. As part of the trouble shooting process, I got a third replacement Duralast under warranty and then bought one from NAPA as a backup. Are you suggesting there is something unique about the Motorcraft coil packs? Please elaborate. Thanks.
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  #12  
Old 08-20-2015, 11:26 AM
Tyler46 Tyler46 is offline
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Yup. When it comes to vital engine components, only go Motorcraft.

I've heard of someone having ongoing issues with replacing their IAC valve and couldn't figure out what was wrong, then after putting a Motorcraft valve in it was a brand new truck.
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Quote:
Originally Posted by guell View Post
People like him make me believe that birth control needs to be put in the public water supply
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  #13  
Old 08-22-2015, 05:15 PM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

Thanks Tyler. I would give a Motorcraft coil pack a try but previous failures have been fixed completely with coil packs from other suppliers. At the same time, the engine roughness remains so certainly will keep your suggestion on the table.
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  #14  
Old 08-26-2015, 07:02 AM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

I rechecked for vacuum leaks over the weekend by disconnecting the IAC, which brings the idle down to 500 rpm, and squirting water from a garden hose at various spots on the intake manifold side of the engine. There was absolutely no change in idle speed so I think vacuum leaks are not a likely problem. I am again looking at the intake manifold runner mechanism as a potential problem. BTW, there is another post describing problems related to the IMRC solenoid and a description of how the intake runners work. From my observations, the flaps open at or just above 2000 rpm, not 3000 rpm as described in the earlier post. Can anyone confirm this, one way or the other?
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  #15  
Old 08-30-2015, 05:39 PM
65Sprint 65Sprint is offline
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Default Re: 2003, 2.3L Misfire Under Certain Conditions

I continue to suspect this issue may be intake manifold related. This thread suggests that intake manifolds on the early Duratec engines (2001-2003) should be considered a maintenance item as the implementation of the intake runner system is not robust and failure of components is fairly common. Ford/Mazda must have recognized a weakness in this early manifold since it was redesigned, without runners, from 2004 onward. From some additional research, it appears that trouble with the intake runners often begins with the "button" on the fore end of the manifold, right behind the power steering pump, falling off. Mine fell off in early April creating a big vacuum leak that I fixed with JB Stick epoxy. While the vacuum leak remains fixed and the solenoid and actuator seem to be working, something had to cause that button or plug to fall/break off. Maybe it was just aged plastic or maybe it is indicative of worn bushings or some other larger problem. I am thinking about removing the butterfly valves completely or perhaps just replacing the manifold.
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