SP547X Spark Plug Pre Gap

[StockishS197]

Tracking down some misfires - put a new set of MC SP547X about a year ago, but noticed they come pre gapped at .054”, whereas spec for the 4.6 is .04-.05”. Could this be causing minor misfires as low load/start up? Bolt on, cammed car.

All previous MC plugs came gapped at .045”, as does the current SP546X for 5.4 3v, so what gives with the change?

Looks like HT1s still come gapped at .035”.

 

[07 Boss]

Well the stock spec for our cars at .045 is on the wide side to begin with. Going to .054 just seems like it wouldn't be a good idea. Why did we not gap them properly before installing them?

But yes, that could definitely cause a misfire issue. I run boost and gap my plugs around .028-.030, but even when I was NA I would gap them at .035. I also never liked the stirrup/strap design and either run Brisk or Accel plugs which have a more conventional ground strap.

 

[StockishS197]

Well the stock spec for our cars at .045 is on the wide side to begin with. Going to .054 just seems like it wouldn't be a good idea. Why did we not gap them properly before installing them?

But yes, that could definitely cause a misfire issue. I run boost and gap my plugs around .028-.030, but even when I was NA I would gap them at .035. I also never liked the stirrup/strap design and either run Brisk or Accel plugs which have a more conventional ground strap.

The strap design makes it hard to gap down I suppose, and the new SP547X has a welded strap vs integrated, so would be more fearful of the strap breaking off from the fatigue.

I had put them in with the thought they were .045”, but finding out it’s .054” makes me think moving to the HT1s with a .035” pre gap is the right move.

 

[07 Boss]

You can gap those plugs with the strap. I just tap them on the corner of my workbench lightly and keep checking till you get it down to the right gap. If you go too far, a simple twist with a decent size flathead will allow you to widen it.

 

[JC SSP]

I had HT0 in my 06' and switched from Brisk to HT0 in my 05'. All gapped at .045 and still running strong.

 

[StockishS197]

I went and pulled a few plugs out and look to actually be gapped at .045” per my feeler gauges.

Curious as to why Fords page says .054”, not that it matters I suppose.

https://dealer.parts.ford.com/shop/en/us/engine/spark-plugs/spark-plug-p-sp547x?pdp=y

 

[DieHarder]

Tracking down some misfires - put a new set of MC SP547X about a year ago, but noticed they come pre gapped at .054”, whereas spec for the 4.6 is .04-.05”. Could this be causing minor misfires as low load/start up? Bolt on, cammed car.

All previous MC plugs came gapped at .045”, as does the current SP546X for 5.4 3v, so what gives with the change?

Looks like HT1s still come gapped at .035”.

In my experience misfires stem more from COP issues (and possibly wiring) vs plugs. If your car is misfiring regularly and especially bogging down or loses power under load it's likely the ends of the coils were pushed too far up into the boot (happens while changing the spark plugs) so the spark must now jump a gap. Challenge is determining which one/s. If you can do that replacing them is cheap (can get a whole set of stock COPs for ~$70 on fee bay) and easy to replace (about 2 minutes each; 5 minutes if you move like a sloth).

This is one time however I will say that a diagnostic from a dealer can be money well spent. I was about to start firing the parts cannon when my car was acting up but decided to pay for a diagnostic and learned two COPs (that were recently new) were the source of my misfires. Cost me $200 but saved me several hundred more as I was about to buy a new set of injectors after buying a set of Brisk plugs (which aren't cheap either)...

 

[StockishS197]

In my experience misfires stem more from COP issues (and possibly wiring) vs plugs. If your car is misfiring regularly and especially bogging down or loses power under load it's likely the ends of the coils were pushed too far up into the boot (happens while changing the spark plugs) so the spark must now jump a gap. Challenge is determining which one/s. If you can do that replacing them is cheap (can get a whole set of stock COPs for ~$70 on fee bay) and easy to replace (about 2 minutes each; 5 minutes if you move like a sloth).

This is one time however I will say that a diagnostic from a dealer can be money well spent. I was about to start firing the parts cannon when my car was acting up but decided to pay for a diagnostic and learned two COPs (that were recently new) were the source of my misfires. Cost me $200 but saved me several hundred more as I was about to buy a new set of injectors after buying a set of Brisk plugs (which aren't cheap either)...

So I ended up datalogging misfires and while at idle and found cyl 3 as a bad offender. Pulled the COP and found the spring to be the issue.

Also replaced the SP547Xs with HT1 and car overall seems happier with the smaller gap.

 

[DieHarder]

So I ended up datalogging misfires and while at idle and found cyl 3 as a bad offender. Pulled the COP and found the spring to be the issue.

Also replaced the SP547Xs with HT1 and car overall seems happier with the smaller gap.

What do you use to datalog?

 

[StockishS197]

What do you use to datalog?

SCT LiveLink/X4 monitoring misfire counts