Stutter/miss under load

[Green96]

I am having trouble. I have a stutter/miss under load. I have new plugs that will go in tomorrow with dielectric grease on the coil boots. What else should I be looking for. I have been suspicious that my EGR or DPFE have not been working correctly, but no CEL. Here is the the sequence of events.

1 - I noticed that the car was not shifting down when I try to accelerate at highway speeds. If I press harder, but not quite WOT it would finally kick down.

2 - Early one morning I accidentally put 87 octane in the tank. I was cruising at highway speed for about 90 miles. I finally realized what I had done when I hear it pinging that evening under load. I blended in some 105 octane E85. Don't ask be how I know, but I know that late model Fords can handle up to 35% ethanol. I ran down the tank without any further issues. I hope this mishap is unrelated to my troubles, but it was worth mentioning.

3 - Some time has gone by and I have picked up a stutter or miss under heavy load. At first it was just at part throttle and would go away if I went WOT. Now 2 tanks since I noticed it, it is present at WOT too.

Other info - I have 74,000 miles on it. I am running a Zack tune. I have had copper plug in it since about 40,000. Trans was last flushed at about 30,000. No check engine light with Zack tune or stock tune. Let me know what other info could help diagnose this issue.

PS. I really feel that it is not sensing load correctly. I have not checked my vacuum levels.

[martyo]

What is the history of your coil packs?

Have you scanned for DTCs?

[Green96]

Coil packs are original. I scanned for codes about a week ago with nothing but it has gotten worse since then.

[Green96]

I have heard that any kind of backfire can cause carbon tracing. I hear that once that happens the miss just keeps getting worse.

I was planing pluges and dielectric grease on the coil boots.

[Pat]

+2 on the coil packs. I suffered through this for a long time, Dealer couldn't find it, no CEL, took it to a back yard mechanic and he bought a cheap coil pack and "walked" it through five cylinders, three were bad, before he told me to change them all. No problems since. I kept the cheap one for troubleshooting purposes. Stay with OEM, no Chinese.

[lifespeed]

The OEM coil packs are a common problem on these cars. Don't assume the DTC codes (or lack thereof) will be able to identify the problem with 100% accuracy.

The funny thing is, the Ford replacements appear to be highly reliable and are a different part number so they seem to have corrected the issue. Definitely replace them all, attempting to just change the "bad" ones is a waste of effort. They are all the same flawed design. They seem to burn through the plastic case and arc at the output.

[BLACKMARAUDER04]

It is suggested that you change the Transmission fluid every 30,000 miles.
Your trans might start slipping if you don't.
That happened to me early on in my Marauder's life.
Now I change every 30.

[Green96]

Update: I changed the plugs tonight. No sign of carbon tracing on the outer insulation. They were worn to .062 gap from the original .054. They were tr55 plugs from NGK.

New plugs are in. They are tr6 plugs gapped to .035. I put anti seize on the threads and dielectric grease in the coil boots.

Problem gone!

The next question is do I go ahead and put in the new coils that I have on the way or return them?

[camelgrundle]

If you have original now throw them in if your not real tight on the budget.

[martyo]

New plugs are in. They are tr6 plugs gapped to .035.

On an NA motor?

[Green96]

On an NA motor?


Yeah. You don't think I should have changed heat range?

[martyo]

Yeah. You don't think I should have changed heat range?

That plug is perfect, but I am not so sure why you are running such a tight gap?

[Green96]

No good reason to back up that decision. It looked like a lot of 4v cobra guys (old NA cars) are running tight gaps including a friend at work running .035 on his NA cobra.

Based on only getting 30k out of the old ones I think .054 was too wide. I would have expected them to last at least 50k.

[RF Overlord]

Based on only getting 30k out of the old ones I think .054 was too wide. I would have expected them to last at least 50k.Copper plugs are generally only good for ~30k...

[martyo]

No good reason to back up that decision. It looked like a lot of 4v cobra guys (old NA cars) are running tight gaps including a friend at work running .035 on his NA cobra.

Based on only getting 30k out of the old ones I think .054 was too wide. I would have expected them to last at least 50k.

I would recommend a .045, but that's just me.

[Green96]

I would recommend a .045, but that's just me.


I am going to give this about a week and then I might pull them and adjust.

Thanks everyone for all of the advice.

[lifespeed]

You made the load on the coils less by gapping the plugs too tight. If the coils were a problem (and they are a known problem) you threw a monkey wrench into your diagnosis attempt. You may not get a sign from God like a check engine light, DTC code identifying the cylinder, or a burn mark on the coil. Just lots and lots of Marauder owners who have cured a misfire with new coils.

Gap the plugs correctly and drive it for a while. If/when the misfire returns replace all the coils.

[HotRaud90]

While merging on to the highway last night, I went WOT and experienced periodic hesitation from 40 up until about 85-90 mph. It wasn't really a stutter as much as it was like a hesitation.

If it makes any sense, it was like it accelerated smoothly, then it would plateau and hesitate for just a half second, accelerate again, then plateau and hesitate again, so on and so forth. It only hesitated about 3 times. I'm at 81k right now. Does this sound like what you were experiencing (or anyone else for that matter)? No codes thrown for me either. Original plugs and coil packs as far as I know.

[Green96]

Mine was a distinct shudder. Your issue sounds different.

[HotRaud90]

Mine was a distinct shudder. Your issue sounds different.

Gotcha. Well, they sound at least similar. I read somewhere else that the shuddering can also be found when under very light load as well. Seems to happen under heavy and/or light load. I have experienced this as well. Usually right after start up as I'm pulling down my long drive slowly. Acceleration isn't smooth and seamless, has some stutters and pauses in it.

[lifespeed]

Gotcha. Well, they sound at least similar. I read somewhere else that the shuddering can also be found when under very light load as well. Seems to happen under heavy and/or light load. I have experienced this as well. Usually right after start up as I'm pulling down my long drive slowly. Acceleration isn't smooth and seamless, has some stutters and pauses in it.

Sounds like a misfire to me.