2000 RPM miss/stumble?

[mransr]

2000 RPM miss/stumble? - solved maybe

I just replaced my well worn (200,000+ mile) 4.6 with a brand new, "old stock" 2004 4.6..the new engine was complete from oil pan to throttle body (even a belt and oil filter)

after the swap I have a significant miss/stumble/vibration right about 2000 RPM...I thought it might have been the Energy Suspension motor mounts, but it seems worse once the engine gets up to temperature so I'm thinking it's not a mechanical issue

a couple other things; the place that did the swap* didn't use the new engine's wiring harness and may not have used the new injectors...I have blocked off the hoses to the heated PCV because it wasn't plugged it, and that may have made a slight improvement (by that may be just in my mind)

any thoughts guys?


*I intended to do the swap myself, but the place I had planned to do the work disappeared and my chronic back issues picked a really back time to re-appear so I had to farm it out...the place is a Mustang shop and they seem to know what they are doing :-/ )

 

[2002BLGT]

I just replaced my well worn (200,000+ mile) 4.6 with a brand new, "old stock" 2004 4.6..the new engine was complete from oil pan to throttle body (even a belt and oil filter)

after the swap I have a significant miss/stumble/vibration right about 2000 RPM...I thought it might have been the Energy Suspension motor mounts, but it seems worse once the engine gets up to temperature so I'm thinking it's not a mechanical issue

a couple other things; the place that did the swap* didn't use the new engine's wiring harness and may not have used the new injectors...I have blocked off the hoses to the heated PCV because it wasn't plugged it, and that may have made a slight improvement (by that may be just in my mind)

any thoughts guys?


*I intended to do the swap myself, but the place I had planned to do the work disappeared and my chronic back issues picked a really back time to re-appear so I had to farm it out...the place is a Mustang shop and they seem to know what they are doing :-/ )

pcv needs to be hooked up or vented , not plugged , other than that , you might have a coil taking a crap on you if you didint replace those with the engine

 

[poindexternasty]

This might be the "hitching" issue. I think it may relate to the EGR valve or something. In theory, the ratio of exhaust gases to clean intake air may be higher at low RPMs, while when you're at 5500 rpm, the exhaust gas makes up a smaller share of the overall air being sucked into the engine.

I am no expert, I am merely repeating what I read on this same forum. Search for "hitching."

My 02 GT vert 100k miles does the same thing from 1200-2000 rpms when in 4th or 5th gear going 35-55 mph.

Does the whole car shake or is it a stumbling of acceleration? Does it happen at WOT, idle, half throttle?

 

[mransr]

the coils are new

it doesn't make much difference what gear it's in, although it seems worse in 1st and 2nd...and I really haven't done much at WOT, I have less than 100 miles on the new engine

 

[mransr]

it doesn't seem to be the "hitching" issue...

I unhooked and plugged the EGR vacuum line and that didn't change anything

anybody have any suggestions on what else I could try? maybe a 'tune'?

 

[poindexternasty]

I have heard of the hitching issue being solved by changing the upstream o2 sensors, I dunno if they have anything to do with your issue though.

 

[mransr]

I'm cautiously optimistic...'cause when I'm wildly optimistic I usually end up getting kicked in the teeth ....but I think I got rid of that nasty miss/vibration/hesitation my car had...

I changed the plugs and that helped a lot, there were a couple pretty nasty looking ones but it still didn't fell 100%...

then I changed the oil, it was wildly overfilled (my 12 quart drain pan was FULL after the drain) and now it seems like it's running just right :thumbs:

I'm not so sure how it got so full (well obviously they put too much oil in, but I only provided them 6 quarts) and to be fair the dip sticks on our cars are crap, but at least now I know exactly where it should read when it's full