CEL flashing above 75 mph

[atikovi]

Yes.

 

[mattd]

Ordered 3 Motorcraft coils for the front cylinders before doing anything else. I can imagine the new ones in the back are causing an imbalance with the Chinese front ones and that's being interpreted as a misfire under higher engine speeds.

IMO you wasted money.

Does the engine run poorly or is it simply the CEL flashing? Ford misfire counters take ALOT to turn the CEL. A simple “imbalance” will not make the CEL flash.

 

[atikovi]

Two of the "new" Chinese coils in the back were bad. I have no problem spending the money to replace the front ones too. While they might not be totally bad, I can imagine they might be weak, especially under load at high speed. And aftermarket Chinese coils are known for a high failure rate.

 

[Hal-9000]

Ordered 3 Motorcraft coils for the front cylinders before doing anything else. I can imagine the new ones in the back are causing an imbalance with the Chinese front ones and that's being interpreted as a misfire under higher engine speeds.

This doesn’t really make sense, and throwing parts at a problem isn’t the way to diagnose and fix. You may consider bringing it to an experienced mechanic so he diagnose and fix the problem. For all you know at this point it could be a lazy valve spring and have nothing to do with ignition.

 

[atikovi]

I don't trust the Chinese coils in the front and would replace them anyway, but if replacing them doesn't make a change I'll deal with it then. A lazy valve spring would likely have noticeable effects. Love how people go on about replacing all tire pressure sensors when only one goes bad, but heaven forbid you only replace one coil in this situation.

 

[Hal-9000]

A lazy valve spring would likely have noticeable effects.

Indeed, and sometimes the effect is no misfire under light conditions with no load, but under higher load (like when you’re driving fast, uphill, etc) and more seat pressure is needed, a slightly binding valve or weak spring or combination of the two will be enough to cause a constant misfire. A cooked cat usually results in short time afterward.

 

[The Critic]

Indeed, and sometimes the effect is no misfire under light conditions with no load, but under higher load (like when you’re driving fast, uphill, etc) and more seat pressure is needed, a slightly binding valve or weak spring or combination of the two will be enough to cause a constant misfire. A cooked cat usually results in short time afterward.

Like this?

2008 Toyota Camry V6 P0303

No air at all out intake or exhaust? Interesting it’s out of the crankcase. Especially with a 10% variation in leakage. Also interesting your diagnostics tell a problem with cylinder 2 but the ECM is blaming #3. What’s the firing order? Definitely got a mechanical issue. Alldata says...

bobistheoilguy.com

 

[mattd]

FWIW I have never seen a 3.7 valve spring issue out 250 of these vehicles we have.

 

[Hal-9000]

Like this?

2008 Toyota Camry V6 P0303

No air at all out intake or exhaust? Interesting it’s out of the crankcase. Especially with a 10% variation in leakage. Also interesting your diagnostics tell a problem with cylinder 2 but the ECM is blaming #3. What’s the firing order? Definitely got a mechanical issue. Alldata says...

bobistheoilguy.com

Well, that is an extreme example; however, GM had past issues with binding valves in their Vortec engines that caused similar issues that the OP has.
A GM TSB identified the problem, and their “cure” was head removal and a full valve job.
While this may have been the “right” way to fix it, the honest answer for many who felt the expense wasn’t justified due to the lower value of their older vehicle was to simply install stronger valve springs such as LS2 beehives and using comp cam retainers

 

[wtd]

A flashing CEL usually means a misfire and you don't want to drive very long with a constant misfire or you might end up putting new cats on it too.

I would think that the Autel 906 would give you misfire data.