05 Ford F150 Misfire

Hey guy I am working on a 05 f150 5.4 engine with a random misfire only at idle but cyl 6 has the most. Customer replaced all ignition coils and plugs, and also cleared the codes along with the freaking data
FT are normal O2's are normal
I scoped the coils secondary and have hi fire lines with short burn times "50ms" which I believe indicates lean condition among a few other things, so I checked fuel pressure 39 psi at idle.
Maf voltage @ idle .79V
snap throttle max 2.8V
Baro 155
The engine was quick to rev up not lazy and no hesitation so I don't think it has a plugged cat but I could only get the 2.8V on the Maf so I told him to get a new one, but now I am second guessing myself on that call.
I remember a few months ago watching a video with a bad intake rocker arm on a ford causing problems but I think that was noisy problem and this engine is quiet.
Whats everyones thoughts?
I don't want to blow my first job at a new customer
Thanks for the help!

Hi..

I think you are looking at mode 6 and looking at the misfires, I also think you see only cylinder 6 as the problem. You stated that you changed all the coils but you never said anything about the plugs.

If I change coils I always change the plugs as well. Now lets not go nuts and start over thinking, we have a problem with #6 so focus on #6. You changed the coil and did you retest for spark ? If you have spark you need to look at injector for #6.
I would if you can scope the # 6 injector and see what you get. If you don’t have a scope you can move the injector to another cylinder and see if the misfire fallows. if it does you proved that the injector is bad. Remember to use oem parts…

Good Luck
Doc n2mx

johnphufnagel wrote: The engine was quick to rev up not lazy and no hesitation so I don't think it has a plugged cat but I could only get the 2.8V on the Maf so I told him to get a new one, but now I am second guessing myself on that call.

Hey John! Was this while revving it in the bay, or on a test drive? Just wanted to clarify.

I remember a few months ago watching a video with a bad intake rocker arm on a ford causing problems but I think that was noisy problem and this engine is quiet.

Definitely a possibility... That'd be tough to detect, maybe you could catch it on an in-cylinder waveform? Or, perhaps running compression.

I'm thinking you meant a 5ms burn time, right? Instead of 50ms? Not sure if the built-in injector balance test is available on this '05, but it might be worth running if available.

I was looking at cylinder contribution test and they were all negative -1-2 except for number 6 it was -4 to-5
The customer replaced all coils and plugs
I checked secondary and primary ignition and all coils are contibuting so are injectors
Scoped the injectors also have great looking waveform.
Thanks

Damn this is the second time I replied to your question and it didn't post
I reved it in the bay
I will have to go and recheck the burn time again because now that I think about that, 50ms is way to high and so is 5ms
It has a Relative injector flow test, I never heard of this and not sure what to make of the data.
#1 Flow 113ms
#3 115ms
#7 115ms
#2 112ms
#6 117ms
#5 118ms
#4 119ms
#8 112ms
I am guessing that they are timing the injector til it drops to a certain pressure. Let me know if I am correct and what are acceptable times.
Thanks

Burn time burn time should be between 1 - 1.5 ms, I believe.
Can you do an injector balance test?

POLE71 Yes you are correct burn time should be 1 to 1.5ms. My question was since ford uses a multi strike ignition what burn time do you go by, the first, middle or last, they are substantially different.
And can I do a injector balance test, Yes and no. Yes I have a timer tool but no the verus don't have injector balance test. It has a relative injector flow test.
I am currently unable to do a in cylinder pressure test because ford sucks and don't use a normal spark plug so I need to order the correct adapter to use my pressure transducer.
I narrowed the misfire down to bank 2 so I did a pressure test before the cat and at 2k it is + 3.6 psi and -1.9psi. He had some old good cats from the same year and model of truck so he is going to change them.
I haven't got a lot of experience with back pressure waveforms but the +3-2psi has me concerned that he may have a exhaust valve sealing problem

Come on Guys I know yinz are busy, please give me some direction. I ordered the hose I need to do a in cylinder pressure wave, but it wont be here for a few days. Am I looking in the right direction or am I just not seeing something obvious?
I have seen posts with relatively simple problems get more responses. :dry:

Hey john, I like the results of you relative injector flow test. I'm not terribly experienced with it, but I believe that a problem would result in a greater spread between low and high. Plus, the #6 injector was in the middle of the range, so I think you can put injectors aside for now. I had another thread going on that test here .

About the exhaust backpressure measurement, was that a steady 2-3 PSI at 2000 RPM? Or, was it bouncing down to -1.9 PSI at times? If it was bouncing badly, then you might be on the right track with a valvetrain problem. How about a vacuum gauge on the intake during the idle misfire? A bouncing needle there would definitely be a red flag.

Thinking along the same lines, you could also be chasing a broken valve spring? Though, I figure that'd get worse off idle and under load. :huh: I don't see that you're missing anything plainly obvious!

You stated it has random misfires. Are these misfires obvious? Or, are you, merely, relying on Ford's Cylinder Contribution test? You stated Data and Codes were cleared. Have you gone on a sufficient test drive to restore Data and Codes? If so, did any codes return?

Do some reading on Mode $06 TID $53.

I like to see exhaust backpressure at 1.5 psi or less. 2-3 is OK, but I don't really like it. 3 and over is a concern.

Thanks for replying. I put a vacuum gauge on it and its a steady 19-20 inches, Wow I just thought of this, I connected my vacuum gauge to the booster hose, I wonder if there is a check valve and that's the reason for a steady gauge.Back pressure reading on my pico was going positive 3.6psi and neg 1.9psi. I didn't put a sync on it to match it with a cylinder because with 3.6psi back pressure I am pretty confident the cat is going bad. But with a partly plugged cat and very little if any back pressure at idle, I have a hard time believing that it would cause misfires only at idle

pole71
Yes the misfires are definitely noticeable I only used the cylinder contribution test as a guide. I have not taken the truck for a drive, I cant drive customers vehicles for a year. Its a long story that happened almost 20 years ago.
Customer said he put about a 100 miles since codes were cleared and has the following codes that I think are irrelevant to the problem.
P1000
p0579 Cruise multi function A circuit range
P2100 Tac motor circuit/open
P2107 Tac module processor
P2110 Tac system forced limited RPM
Lol I literally just seen this code! I am going to kick myself in the ass.
P2006 intake runner control stuck closed bank 1
Well I was thinking maybe that was my problem but my misfires are on bank 2 not bank1 although thats a problem dont think its the cause for the misfire.

Am i reading your back pressure results right, is the exhaust actually going into vacuum @ 2k RPMs? Is that normal for this engine? (I'm thinking about some engines that use valve overlap instead of an EGR valve)
There should be a check valve in the booster hose, I think you may want to revisit the intake vacuum test. I'm sharing your initial suspicion of an exhaust valve issue. Maybe a cylinder leakdown test in in order...

Also, it may be late now, but Fords only use the Multistrike strategy at idle. If you bring the rpms up, you'll get a single spark event for each cylinder.

Hope you get it sorted out.

Still paying for 20 year old mistakes? No need to elaborate, trust me, I'm not going to :oops:
Sounds like the Commonwealth of Massachusetts...

Thanks Noah
Yes it is going into a vacuum like I said before this is the first backpressure test I did with my pico. So I am not sure if that is normal. I wanted to check bank 1 but the O2 is in a difficult position and I didn't have time. I am supposed to get my adapter for my WPS500 today. I plan on going back to the shop tomorrow and do a in cylinder running compression test on both banks along with backpressure on the cat for bank 1. I know there is a check valve in the booster itself I will check the hose to see if it has a valve also.
Thanks to everyone that has replied I really appreciate the help.
Ya my mistake happened 20 years ago and I was just to thick headed and play by the commonwealth of PA rules and after 20 years I finally realized that they are always going to win

I could maybe see that IMRC thing being an issue, but then why aren't the fuel trims skewed from bank to bank. :huh:

I hadn't realized the exhaust backpressure measurement was done with your Pico - that's totally cool, just made me realized that I've never done a backpressure test with a transducer. :lol: Always used the vacuum gauge or one of the specific backpressure testers. Anyway, I'm wondering if those kind of highs and lows are normal, and just get smoothed out when a gauge is in use? I'll have to try this.

Can't wait to hear what the in-cylinder test shows!

Hey guys I just wanted to thank yinz for helping me out and sorry it took so long to get back and let you know what happened. After the customer replaced the cats and there was no improvement he took it to the auction and sold it after I repeatedly asked him to wait 1 week, I really want to know what was wrong with it. He is not mad at me he was just tired of putting money into it. He already put over 500 into it before calling me. I assured him that the cats were bad and needed replaced but unfortunately that wasn't the cause of the misfire.
Thanks again for the help

Frustrating result. But we still appreciate the update! Whoever gets to diagnose that truck next is in for a fight. :lol: