2005 E350 w/5.4 engine, just over 145K on everything except the engine---Ford reman'd installed just over 350 miles ago. Oil pressure and coolant temps perfect (as expected), plugs, boots and injectors all new too. Throttle body cleaned, used new gasket when reinstalled.

This feels very much like a low grade misfire but there's no MIL, no pending codes. Two different scanners show Kv and burn time for each COP is perfect too; misfire counter showing just one single incident, not recurring. The only thing discovered was a relatively slow reacting Bank 2 downstream O2 sensor, the other three performing normally.

This same minor roughness was present before the engine was replaced (8 PSI oil pressure at hot idle). Could the EGR system cause this? No pending or set codes for that either.

Appreciate any help or direction to head from here---TIA!

 

Does it do this just on cold start up ? or hot idle? mild load? or always, don't matter weather it's sitting or driving?

 

Doesn't matter---that minor shudder is full time regardless of engine temperature, engine RPM's or load/no load.

Naturally its most noticeable when idling to warm things up or when stopped for traffic lights, etc. It doesn't seem to have poor performance for a vehicle with the TPS system, the "fly-by-wire" throttle control.

 

Well....Considering that you just put a remanufactured engine in & I'm sure you've been over the engine several times.....could it be the torque converter being lazy/weak?? or maybe a sticky shift valve in the trans??

 

Well I didn't mention the entire transmission was rebuilt less than 500 miles ago, new torque converter. This is the 4R75, feels stout to me.

This roughness is most obvious while parked idling and when in drive and brakes are applied. RPM's somewhere between 600 & 700.

 

Have you hooked up a smoke machine to check for vacuum leaks? Does this have a FPCM on the rear axle? Also might be worth pursuing that lazy O2 sensor

 

Did you use a vacuum gauge? Have you replaced the orings on every orifice?

 

Haven't (yet) used a vacuum gauge but that's one of the next tests. Injectors are all new Motorcraft with o-rings, throttle body cleaned and the spacer plate was replaced with a new part---the only gaskt/o-ring not replaced is the one between the back part of the throttle body and the intake---I'll use some sort of aerosol spray to see if short blasts affect the idle.

I will say my Actron scanner shows COP's for the #1 & #5 cylinders show misfires but each less than 10 times since codes and last data was cleared out. Thinking to myself since this minor rough idle was present before the engine swap it might be due one or both of those. I don't care to disconnect a COP while engine is running but might disconnect one, start the engine and see if that affects idle. Reconnect COP and repeat the test once again.

 

I just had a remanufactured 5.4 installed. It had a ever-so-slightly rough idle as wll that turned out to be a slight vacuum leak in the evap line from the intake manifold to the vapor management valve.

 

I'll add that to the list of specific things to check. As I say this rough idle might have been present before the new engine was installed so any transferred part or connection could be the culprit.

Thanks Rumble Phish!

 

 

Not loosing coolant now--when first started I had a small coolant leak from the intake just behind plug #4--retorquing the intake stopped that and its not recurred.

This miss isn't intermittent---its constant and feels like a minor misfire but can't find much amiss with my Actron scanner that'll do live data. I see a very small number of misfires on cylinders #'s 1 and 5 but both show less than 10 incidents over 400+ miles since engine was first installed.

I'll check for vacuum leaks and perhaps pre-emptively change the COP's for #1 & 5. I'm not fond of disconnecting COP with engine running as it might be hard on the PCM.

IIRC this same miss was present before the new engine; because the old engine was running noticeably poorly this was ignored thinking it was just a part of the larger problem.

Thanks guys---always open to opinions or advice.

 

Just wanted to comment: The first WON'T work. The PCM is much too fast to react with adjustments to fuel trim, timing advance, throttle plate etc. I assume you have already checked fuel trims - which are far the best indicator of a vacuum leak. It's also best way to isolate one while blowing an unlit propane torch all around hoses, injector 'O' rings, intake manifold etc.

Second: You will not harm the PCM by unplugging COPs while running. The PCM just 'passively' pulls the COP control wire to ground. In fact - it will detect the 'open circuit' in the COP and shuts off that fuel injector for THAT cylinder - to protect cat, KNOWING that it could not possibly fire.

It would help to 'isolate' which cylinder(s) is or are responsible for the idle roughness. Monitor IDLE RPM with your scanner 'very carefully' for a minute or so and log it. Then remove COP wire, monitor RPM another minute or so and log that. Do all 8 cyls and note the one or ones that make the 'LEAST' difference in idle RPM. (( My poor-man's Power Banance Test)).

BTW. It is also important to consider the OBDII Theory of Operation's description of a 'MISFIRE'. It may/or/may not be electrical at all. Don't condemn COPs 1 & 5 just yet. The PCM (fast little devil it is) accurately times the pulses from the CKP sensor (crankshaft tone ring), and a misfire is registered if the rotational speed of the crankshaft fails to register a 'boost' when ignition spark is commanded for that cylinder. SO it certainly may NOT be a COP or plug. There remains too many other 'possibilities'.

One thing that comes to mind (since you say it is there ALL the time, cold - hot - light load - etc), The 3 valve engines will run - pretty much fine but not perfect - with one intake valve not functioning. All it takes is a brief stiky valve stem, or sticky lash adjuster to spit out a roller/follower out. Frequently they will just lay there not interfiling with anything else other than degrading breathing on one cylinder. Not saying this is it (given the reman) but it will produce the symptom

 

Massively helpful reply F150Torqued---great info that and thanks for contributing.

This engine is a 2 valve as they vans never received the 3v gassers.

I have a forgotten resource I'll have diagnose this possible misfire---he's a former Ford technician and very experienced with my era of engines. Now working at one of my big truck customers he has access to the more sophisticated diagnostic gear, is great with hands on diagnosing too. I'm shocked at myself for not recalling him sooner--had he not called for my windshield replacement services last evening I'd have never thought of him.

Once I have this sorted out I'll reply here---could be helpful to others.

Thanks again!

 

Hummm. Thanks - I did not know that. Limits the possibilities a lot on rough idle possibilities. You report it is pretty much always present - If it was really electrical, seems like it would show in misfire counts. But you report no MIL and only nominal misfire counts. ??? Seems it (somehow) has to be a breathing issue, compression issue, OR fuel volume delivery issue (which should show up in Fuel Trims)

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