Checked when I did the full UV vacuum system smoke, got nothing. No leaks anywhere, its truly been almost a decade long headache.

 

Did some data analysis at work today. Once the truck is up to temperature, it is a misfires on cylinder 2. It’s not a constant miss, it’s intermittent at best, but happens often enough to cause the truck to file surge and bog down. When it misses it seems the computer tries to over correct and compensate for the miss, causing the idea to surge, then it misses and it bogs down. This has no effect on drivability, but does cause the truck to idle weirdly when sitting still or in park.

Since the misfire is only in cylinder 2, I pulled the cylinder 2 plug and coil (brand new OEM Ford coil I installed last week). The plug appears fine, the coil is fine also. I put a bore scope down the cylinder, everything looks good. No oil buildup, valves have minimal carbon deposits on them, good crosshatching on cylinder walls still, everything mechanically seems to be sound. I am going to treat this as an electrical issue now, since I have found no vacuum leak and no indication inside the cylinder of a failed mechanical component. First thing I will do is replace the plug with a new Motorcraft plug tomorrow, then the pigtail for the coil and see if this solves the issue.

It is important to note that the coils for cylinder 1 and cylinder 3 seem to seat much better than this one. When I seated it on the plug an bolted it down, I noticed that it will twist about 1/2 inch left to right, where as the other to coils do not shift as there seems to be a lip on the intake manifold that prevents and back and forth movement. I will try holding the ignition coil steady when the engine is up to temp, but I doubt the coil is shifting side to side and I also doubt that will cause the issue I’m having.

 

You can try swapping the coil & plug from 2 with the ones from cylinder 1 and see if the problem moves to 1.
Also, trying swapping the fuel injector from 2 with 1.

 

Did the injector swap from cylinder 1 to 2, if anything the truck runs worse now. Misfire code is gone since the new cylinder 2 ignition coil was installed, hooked it up to IDS today at work with one of the truck techs. Everyone also says vacuum leak. It ACTS like a misfire, but injectors, coils and everything seem to be firing perfectly. As far as I have tested, I have not been able to find the source of the leak. The whole thing started when I had the intake manifold off to do the spark plug threaded insert, so I'm wondering if the intake gasket didn't get pinched on install and is opening up a vacuum leak once the engine is up to temp. I am going to remove the intake again tonight. I will inspect every vacuum line I can get my hands on along the way to see if any of them are cracked/dry rotted/collapsed and replace them accordingly. I'm hoping to soon fix this issue, its been happening since March of 2017 and love to resolve it and have a smooth idling truck again that doesn't rev like it has a cam in it and stall at lights or when the steering is at full lock

 

Smoked the system again today, found a leak in the air intake where the ribs are just before the throttle body. Went to the junkyard, found a good one and swapped it in. Put everything back together, no change. Did some more looking around, plugging and unplugging various vacuum lines, found the line from the Vapor Management Valve to the back of the throttle body was missing and capped on the throttle body side. Replaced VMV, added hose back in to the system, no change. I’m at my wits end with this vacuum leak. It’s GOT to be a vacuum leak, but from where? I checked and rechecked the known issue spots on the throttle body, all those hoses are solid and doing their job.

 

Have you tried another smoke test since the last one?

 

Did a vacuum test today. Got the engine up to temp and running where it would idle surge, and hooked the vacuum gauge up. I can’t upload the photo or video because the file size is too large, but it held steady at 19.5 inHg even when the idle was surging. Based on this and my previous attempt to smoke the system not showing any leaks, I am pretty convinced at this point that it is NOT a vacuum leak. The question now is, what? Electrical? Mechanical? It doesn’t knock or tick, all injectors show to be firing, all sensors appear to be working fine, wtf is there that could cause a vacuum leak-like symptom that ISNT a vacuum leak?

 

Have you ever done a compression test on all 10 cylinders?

Denny

 

Yes we did a compression test on every cylinder, all cylinders have compression, that was one of the first things we did after originally ruling out a vacuum leak.

 

Is the misfire in cylinder 2 gone now? Was that the common denominator through these last 7 years? Have you pulled valve cover and inspected cam lobes?

I had a surging issue on my truck. The MAF was aftermarket and I monitored the MAF readings and saw they were out of spec. I got another new MAF, it ran worse and barely idled, and the readings were even worse than my original. On the 3rd try I just pulled a MAF from a salvage yard truck and its been good now. I'm assuming you've already checked MAF and O2 sensor output data as they play a large role in how the truck runs.

 

Were they even across all of them.

Denny

 

yup, even compression. I even checked cylinder 2 specifically with a leak down test on that cylinder because of the misfire.

 

I thought it could be the MAF. I grabbed a MAF out of the truck I got the air intake off of, just to be safe, I had an aftermarket that we thought might’ve been the culprit 7 years ago and replaced it with a known good Motorcraft one. The cylinder 2 misfire appears to have just been a recent thing, resolved by the new ignition coil. Now the engine shows no issues as far as misfires, just all readings sporadic across the board when idling, which one of the master techs said looks just like a vacuum leak.

 

I know you've changed the IAC.
The IAC controls all airflow into the engine at idle and there are no codes for it performing poorly.
Maybe try a known good one from a good running engine.
I think I read quite awhile ago about a similar surging problem and their issue was a lot of gunk under the throttle body butterfly which is hard to see without removal.
(Not related - If you take the throttle body off consider replacing it with an Accufab, I've been very impressed with the improved response - see thread "So I installed the Accufab SCTB96-98" )
You've said this happens when it gets up to temp, I'm trying to remember what happens at that point.
I seem to recall something about closed loop vs open loop and O2 sensors.
Maybe do some research on that.

 

I’ll do you one better, I have a brand new IAC in stock at my dealership, I’ll slap it on tomorrow and see what happens