4.6 Misfire Diag Help

[Mymeatb18]

Hey guys,

Need some help brainstorming this.

So I've developed a misfire in cylinder 2 according to mode 6 test in Forscan and many misfires counted on each drive cycle 300+. Weird thing is when running the mode 6 test it says cant verify something about egr duty cycle and something about catalyst but egr pid shows cycling and downstream o2s are fine. Only while normal driving at about 35-50 will it miss and feels like something tugging at it. If I give it about 30-40% throttle feels fine and flooring it feels fine.

Things done directly to Diag
Moved coil
Swapped injector
New spark plug
Finally new injector

I guess the next step would be compression test but it doesn't run as if there is something wrong with valves. I also have no loud ticking noises or anything. Really kind of stumped on this one. I kind of want to replace the rest of the injectors cu it's had a rough idle ever since I bought it. I feel like the one injector I put made it idle slightly better. The reman oem injectors I bought about a year or 2 ago may not be good. I think the one I swapped out for new was truly bad but I was also putting in a bunch of my original injectors I kept and didnt change a thing.

Any thoughts are greatly appreciated

Things I've done in the 3 years owning it (40k miles)
Spark plugs
OEM coils
2 egr valve (first one crappy last one OEM)
TPS
Upstream o2s
Maf
Fuel pump
Reman oem fuel injectors
Intake manifold gasket (inspected IM for cracks)
73mm BBK plenum/throttle body
K&n drop in with 73mm intake pipe

 

[Mymeatb18]

In case anyone is interested, not over yet but improvements made.

So ended up taking it to a mechanic. Not sure what they were looking at or what scanner they have but they changed the spark plugs and said it was running good but blamed on maybe a transmission. Using the number of misfires pid in for scan proves otherwise.

So before driving home today decided to disconnect and cap off the vacuum hose to the EGR valve. This made a huge difference. I went from 300+ misfires to 91. I did notice some spikes on the highway while decelerating but like pressure on the throttle. So I think they may be some inaccuracies in the reading and the stuttering was almost non existent, I probably felt it only about a handful of times.

Interesting thing is no check engine light was set as opposed to blocking it off. I might do this to see how many misfires I see with that. I have already changed this 2 times in the 3-4 years I've owned it. First one was car quest brand. Last one was motorcraft after car quest lasted only one year before failing. This one is probably 6-8 months Old. I guess I should smoke test to see if it's leaking.

 

[Turdle]

Compression check.

 

[mountaineer2004]

Henry Ford said success is mostly perspiration rather than inspiration, keep plugging and you'll find the answer. I hate intermittent problems! Anytime I had problems like yours, changing injectors/coils/plugs always led me to solving the problem. Good luck and keep us posted.

Does anyone more knowledgeable than me have any hints to help this guy?

 

[Mymeatb18]

Compression check.

The mechanic said they did that and everything is good. They are relatively reliable, Ive used them onece before I don't suspect an issue in that regard because when its not missing it drives and runs beautifully. What led me to check the EGR is the fact that it was only missing while cruising, which is when the EGR valve is open.

I may start to isolate other vac lines to the solenoids and purge valve to see if it improves more.

 

[Mymeatb18]

So it seems I figured it out finally.

I blocked off the vacuum line going to the evap purge valve solenoid. Found the hose that blocked off for the EGR valve comes direct from EGR solenoid on bank 1 side.

Drove the same one hour drive to work and had a total of 14 misfires. Thats a win to me. I tested by replugging the EGR valve and misses spike to 28 in 5 mins.

So the final diag is both my EGR solenoid and purge valve are done, they had a good 20yr run. Going to smoke test for leaks in my EGR valve, if it's good I'll change the solenoids. If that thing is leaking again, I'm ripping out EGR stuff, cuz I'm not changing that pos again.

 

[Mymeatb18]

Changed a questionable hose that goes to the first charcoal canister from the purge valve. Replaced the EGR solenoid. All is good.

I'm going to change all the vacuum lines. Bought a vacuum manifold block and going to kind of hide them a bit and with all black lines.