4.6L "light load" misfire

I have a "light load" misfire ranging from about 20-50MPH. It happens in 3rd and OD gears when the RPMs and load are low. It is not torque converter shudder. I checked and rechecked. It does not present itself when idle or at heavy loads. When I get on the gas hard, the engine makes plenty of power and doesn't miss a beat. But when maintaining speed on a flat road, this is extremely annoying.

I changed the spark plugs in March which did not help any. I cleaned the COP boots and springs and applied generous amounts of dielectric grease which did not change anything. I checked for vacuum leaks, it's at 20" Hg when idle and steady as a rock.

When I disconnect the EGR vacuum solenoid it DOES go away. However, this leaves the engine running lean, EGTs hot, and stores a code for the EGR solenoid circuit which illuminates the CEL.

I removed the DPFE multiple times and tapped the moisture out of it. The hoses are connected correctly and the electrical connection on firmly.

When I apply vacuum to the EGR valve, it opens, I can hear exhaust gas flowing through it, and the engine nearly dies and then re-trims itself to a near-normal idle.

It has been around for over a year and I want to get rid of it once and for all. It seems to be getting worse in the warmer weather.

This is on a MY2000 4.6L in a Grand Marquis, by the way.

Hey Blue. Have a scan tool that can read mode $06 data and see which cylinder has the misfire. A lot of times the coil boots will arc through the center to the heads. If there are small cracks on the boot bottom they can misfire also.

I used my laptop to read $06 misfire data and gave me nothing. I also forgot to mention that about a year ago when this problem first started, I bought all new boots and springs for the COPs and this did not change anything.

In your opinion, would a problematic COP be responsible for this? It just seems weird that it happens during light load and not at idle or high loads.

For what it's worth, I've been digging more around the internet. It seems alot of people who have this error do infact have some sort of weak coil/COP or an MAF issue.

I checked my MAF readings in drive and neutral idles and the values seemed higher than what they should have. However since this is a Motorcraft 80mm MAF used on trucks and Mustangs, I can't say for sure that this is the problem. The readings I was TOLD I should get is around 0.65v in drive idle. I am getting 0.915v in drive idle.

I asked my tuner to see if this is expected and taken account for in his tune.

In addition, I also opted to get a set of 8 Accel COPs from Amazon. I know they don't increase power or efficiency as some people claim., but they were a good deal and I am uncertain that my old, tired COPs are the problem or not and want to eliminate more possibilities.

We have run into many COP that will cause an intermittent misfire under light load. If you have a friend that has a Ford IDS or a scope that can look at the ignition firing you can pinpoint it. The IDS has a power balance feature that compares each cylinder. A weak coil shows up very clearly.

Unfortunately I don't have a friend with the IDS. My software could probably do it but I'd have to know the actual HEX command to send via the console as there is no "click and do" option to perform it. That's how I got the Mode $06 data.

It may be a mute point anyway. Amazon is being amazing as the new COPs are estimated to arrive at my house tomorrow (ordered only this morning)!

I will update once I get them installed and do some test driving.

I have the new Accel SuperCoils COPs installed. After an initial test drive, everything seems so far so good. I was trying varying throttle positions and loads and no miss! I did not drive it long enough to fully relearn the fuel trims and whatnot yet (I reset the ECU KAM by disconnecting the battery), so it is not yet a sure thing.

But here are some pictures.

Before
http://a3.sphotos.ak.fbcdn.net/hphotos-ak-snc6/253998_10150203814996107_605211106_7237928_2850866 _n.jpg

The new versus the old
http://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/249255_10150203696241107_605211106_7236983_6373142 _n.jpg

After
http://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/250165_10150203815396107_605211106_7237931_939038_ n.jpg

For anyone else interested in aftermarket COPs, these are Accel 140032 Super Coils and work with most (if not all) 2 valve Ford 4.6L and 5.4L engines that use Coils-On-Plugs. Kit of 8 + shipping for under $200 vs. Motorcraft costs close to $500 on average. I have nothing against the Motorcraft coils, but this was the best cost effective solution for me.

Unfortunately, this did not fix the issue.

I also replaced my HO2 sensors with Motorcraft OEM ones I had laying around to see if that helped. They also did not change anything.