Cylinder 7 misfire @ 2200rpm and over and rough idle

[shadowless127]

This all started yesterday morning when out of no where the truck started to idle rough and I got the flashing CEL to indicate misfire.

The car idles fine if you have it in P or N, but as soon as you go into gear it starts to idle rough. The severity of the roughness seems to be inconsistent.

Also, the misfire only seems to occur if you linger around or above 2200rpms for more then a few seconds. If you stay under that it won't misfire.

The spark plug wires are in good shape and both the plugs/wires were changed within the last year. I haven't been able to examine the actual spark plug because 1) How the hell do I get to it? and 2) lack of daylight/time. I did put in high grade fuel last night along with a bottle of STP Injector Cleaner (because no one around here has Techron readily available) but I figure the 25miles i've driven so far won't get the entire system clean yet.

What are some possible other causes?

 

[shadowless127]

I also noticed if I'm in Neutral or Park and I rev the engine and hold the RPMs in the "misfire zone" I do not get a miss.

 

[93 x]

have you changed you oil recently because in a shop i used to work in i had this car that had a miss fire and i tried for days to fix it and finally some one told me if you put the wrong viscosity of oil it does not pump up the lifters and causes a miss fire so make sure you have the right grade of oil in.

 

[93 x]

have you changed you oil recently because in a shop i used to work in i had this car that had a miss fire and i tried for days to fix it and finally some one told me if you put the wrong viscosity of oil it does not pump up the lifters and causes a miss fire so make sure you have the right grade of oil in.

also it was a ford 5.0 in the car and that is what im assuming you have

 

[shadowless127]

It was a bad spark plug wire. I forgot to update the thread.

But I do have to change the oil regardless. Hopefully I'll have some time Saturday.

 

[BonesDT]

OK, my turn now! It feels like I'm getting a misfire now too. I'm busy at work so I don't have time for endless research, and I need to tow next weekend, so I have to order parts ASAP.

I have the SOHC.

It did just start as soon as I changed my oil, but I used the usual Mobil 1 5W-30 synthetic.

I've been noticing my engine has been feeling sluggish lately before the misfire happened. I'm leaning towards clogged injectors. My truck has 143,500 miles on it and I've never replaced or serviced the injectors. I don't think I've ever replaced the fuel filter either. I read a FI post here and the guy said he put in new Bosch FIs and the truck runs so powerful now. I'm thinking the reason for the sluggishness was all of them were slightly clogged and whichever cylinder is misfiring, finally clogged completely. Also, I've had my carb'ed motorcycle clog up real bad using the sh*t 87 gas around me, some FI cleaner & premium fuel from now on cleared it up real good.

I don't want to mess around because I need my truck for next weekend, so I'm thinking about just ordering everything. I was going to get:
1) six new injectors
2) intake manifold gasket for the FI service (is this the thing that has like 6 circles and 2 triple circles?)
3) fuel filter
4) spark plugs (what's the best? Platinum (OEM) or Iridium? Single, Double or Quad electrodes?)
5) spark plug wires (any good aftermarket ones?)

The only other thing that it could possibly be is the ignition coil, but I might skimp on that.

Do you think this will cover everything? I figure my truck needs all this stuff anyway.

I see OEM FIs are 24lbs (19lbs using Ford's lesser psi standard). I'm always looking for upgrades when replacing parts. Should I be messing around with upgrading the injectors? I've been contemplating a Apten chip, would larger injectors in combination with a chip be a good choice?

 

[dothedeww]

OK, my turn now! It feels like I'm getting a misfire now too. I'm busy at work so I don't have time for endless research, and I need to tow next weekend, so I have to order parts ASAP.

I have the SOHC.

It did just start as soon as I changed my oil, but I used the usual Mobil 1 5W-30 synthetic.

I've been noticing my engine has been feeling sluggish lately before the misfire happened. I'm leaning towards clogged injectors. My truck has 143,500 miles on it and I've never replaced or serviced the injectors. I don't think I've ever replaced the fuel filter either. I read a FI post here and the guy said he put in new Bosch FIs and the truck runs so powerful now. I'm thinking the reason for the sluggishness was all of them were slightly clogged and whichever cylinder is misfiring, finally clogged completely. Also, I've had my carb'ed motorcycle clog up real bad using the sh*t 87 gas around me, some FI cleaner & premium fuel from now on cleared it up real good.

I don't want to mess around because I need my truck for next weekend, so I'm thinking about just ordering everything. I was going to get:
1) six new injectors
2) intake manifold gasket for the FI service (is this the thing that has like 6 circles and 2 triple circles?)
3) fuel filter
4) spark plugs (what's the best? Platinum (OEM) or Iridium? Single, Double or Quad electrodes?)
5) spark plug wires (any good aftermarket ones?)

The only other thing that it could possibly be is the ignition coil, but I might skimp on that.

Do you think this will cover everything? I figure my truck needs all this stuff anyway.

I see OEM FIs are 24lbs (19lbs using Ford's lesser psi standard). I'm always looking for upgrades when replacing parts. Should I be messing around with upgrading the injectors? I've been contemplating a Apten chip, would larger injectors in combination with a chip be a good choice?

Just a thought..I had a RAM 1500 before my X..and it exhibited all of these symptoms...especially misfires only when in gear..and it was a clogged cat...

 

[BonesDT]

I don't really know what it was, but the complete misfire just went away after a few days. I dumped 1/2 a bottle of Seafoam in a low tank and the other half through the vac hoses. I swapped out the spark plugs, which looked very bad and gapped very high, and realized I hadn't changed them since I bought the truck in 99 since 145,000 miles! Change the wires too, runs pretty good, but maybe I should check out the cats?

 

[Lowtide1982]

my turn now....I have a 1998 4.0 explorer and its missfiring i think in the # 4Cyl...Dont have a code reader on hand but have good spark on all plug wires. the #4 plug was all caked up with carbon and a pain to get out..should i replace the plug and see what happens. And what is Seafoam

 

[Lowtide1982]

Anything on the post above

 

[moosejaw]

Seafoam is a really nice fuel system cleaner that goes back to full carburation days.

You should clean the plug and reuse it, if it isn't worn down. Or replace all the plugs together.

One of the posters mentioned using iridium or other high performance plugs, this is not recommended for waste spark ignitions. Use only the stock style plugs (steel, copper etc) and no fancy electrode designs such as splitfire.

Waste spark will fire 2 plugs at once, one plug in the normal current direction and the other plug in the reverse direction. So the electrode and ground sides of the plug should be the same material and similar shape.

 

[2000StreetRod]

Higher flow injectors

. . . I see OEM FIs are 24lbs (19lbs using Ford's lesser psi standard). I'm always looking for upgrades when replacing parts. Should I be messing around with upgrading the injectors? I've been contemplating a Apten chip, would larger injectors in combination with a chip be a good choice?

Switching to higher flow injectors without a custom tune will result in a rich fuel mixture and probably a CEL and DTCs P0172 and P0175. Your catalytic converters will run hot and your fuel economy as well as performance will suffer. Your stock flow injectors should be adequate unless you go to forced induction (supercharger or turbocharger).

 

[2000StreetRod]

Waste spark ignition system

. . . One of the posters mentioned using iridium or other high performance plugs, this is not recommended for waste spark ignitions. Use only the stock style plugs (steel, copper etc) and no fancy electrode designs such as splitfire.

Waste spark will fire 2 plugs at once, one plug in the normal current direction and the other plug in the reverse direction. So the electrode and ground sides of the plug should be the same material and similar shape.

I agree that a waste spark ignition system uses one coil to simultaneously fire two spark plugs. The plugs are paired according to the firing order. For the V6 the pairs are cylinders 1&5, 2&6, and 3&4 for the firing order of 1-4-2-5-3-6. When piston #1 is at the desired firing position on the compression stroke piston #5 is at the same position on the exhaust stroke. However, there is no change in the direction that current flows to the spark plug. The spark is just routed via the ignition wires to both plugs.

 

[moosejaw]

I agree that a waste spark ignition system uses one coil to simultaneously fire two spark plugs. The plugs are paired according to the firing order. For the V6 the pairs are cylinders 1&5, 2&6, and 3&4 for the firing order of 1-4-2-5-3-6. When piston #1 is at the desired firing position on the compression stroke piston #5 is at the same position on the exhaust stroke. However, there is no change in the direction that current flows to the spark plug. The spark is just routed via the ignition wires to both plugs.

Fords waste spark will fire one of the plugs in the opposite direction. This is the only way to fire 2 plugs off of one coil. They don't use parallel outputs, both plugs are in series with the coil in between.

Current flow: ground =>plug one => coil => plug two => ground

If you pull the plugs on a waste spark car that has a good deal of miles on it you can see the center electrode worn down on half of them and the other half have the ground 'trode worn down.

This is why fancy plugs are a 'no go' with waste spark, if you are trying to deposit steel plasma to an iridium center electrode some not very pretty things happen.

 

[2000StreetRod]

Waste spark explanation concession

Fords waste spark will fire one of the plugs in the opposite direction. This is the only way to fire 2 plugs off of one coil. They don't use parallel outputs, both plugs are in series with the coil in between.

Current flow: ground =>plug one => coil => plug two => ground

If you pull the plugs on a waste spark car that has a good deal of miles on it you can see the center electrode worn down on half of them and the other half have the ground 'trode worn down.

This is why fancy plugs are a 'no go' with waste spark, if you are trying to deposit steel plasma to an iridium center electrode some not very pretty things happen.

My apologies to moosejaw for challenging his waste spark comment. My comment was based on an erroneous assumption instead of first hand knowledge. After doing some research I learned that on some vehicles the Ford factory installs different spark plugs in one bank vs the other because of the reverse current flow. See the following link for additional information: Ford DIS/EDIS "Waste Spark" Ignition Systems

This could explain why some members have experienced early failure with Bosch platinum plugs. The plugs may be designed for current flow in one specific direction. In the future I'll probably buy copper electrode plugs and replace them more frequently.

 

[bluestream1]

I don't know first hand, but have heard others say that Copper core plugs only last for 12,000 miles or so in a waste spark ignition system due to the high voltages.

I changed my factory plugs at 66,000 miles; but they were fine and I should have left them in. I put in Motorcraft double platinium AGSF 22 PPMF6 (part # from invoice) which cost $8.58 from dealer in 2003