04 Navigator Not Reaching 2x RPM or accelerating past 50mph

I have a 2004 Lincoln Navigtor with 183887 Miles on it and am currently having issues getting it to accelerate past 50mph. The truck was just stickered a week ago and this past weekend I was on the highway flying at 80 and above no issue. However I just filled the tank up using supreme after I used all the gas that was previously in the tank. FYI the vehicle was sitting at the mechanic shop for 6 months with this same tank of gas. On my way home tonight I noticed that I could actually pass 50mph if the RPM were at 2x and above and that when I did not accelerate higher than 45mph the RPM would not reach 2x. Im trying to pinpoint my issue as best I can before going in for service. Ive been told this could be a fuel filter maybe a tranny issue even an exhaust problem. Another FYI I did have a hole fixed in the exhaust and I notice that it has gotten louder since Saturday. However I did have the fuel pump replaced last summer and Im not sure but I assume most mechanics would replace the fuel filter especially if they were already servicing the fuel pump… please help!

That is quite a story that didn’t tell us much that can help you. A few questions answered might help us.

Is the check engine light on? For how long? Why was it in for service for 6 months? For what?

I would suggest you aren’t the one to pinpoint the cause. That is the mechanic’s job. If you take it in and tell him what to fix, they will. In that case the problem won’t be fixed and you will have spent money for nothing. Tell the shop how it reacts, not what you think causes it. They may charge you a diagnostic fee. Pay it, it will save you money in the long run.


As far as generics like the check engine light I would have included that in this post. I know if the light is on codes are in the system and to have them checked. That would’ve been my first option if the check engine light was on lol. It is NOT. As far as the 6 months at the shop it was for initially a timing chain which turned out to be a few pulleys. The time frame was just the mechanic being extremely busy and not having time to fix it for a few months. Ultimately Im just unsure as to what could cause my truck not to hit 2000 RPMs when I accelerate. Im assuming it needs to do this for the tranny to be told to switch gears but Im not sure. Im thinking either fuel filter or exhaust but as usual… it could be ANYTHING or EVERYTHING until I take it to the shop and get it fixed.

No way for us to know that. Many, many, many people post here looking for help and never mention the CEL was on for days, months or years.

I don’t quite understand the symptoms exactly… It will not go over 2k rpm if you floor it? Or is it just shifting early?Will it go above 2k rpm in park?

First off I want to thank both of you guys for responding to this post. At this point my check engine light did come on today… finally and I took it to a shop to have it quick diagnosed. The codes read misfire in cylinder 7 and an emission break or something. The mechanic asked if I recently put gas in the truck while it was running and unfortunately for me the last time I fueled up I did. This is what he believes is the cause of the emission break or whatever. The misfire however may be caused by a need for a tune up. Ill find out for sure in the morning when the truck will receive a full diagnostic and service. What do you guys think? Does this sound like a resolve to my issue based on your expertise or should I plan for something worse?

I haven’t tried in park but what I was trying to say is when I accelerate when I notice its not going past 45mph the rpms are not going pass 2000 no matter how hard I step on the gas it just keeps sputtering. However it did manage to go pass 2000 rpms as long as I delicately accelerated then eventually it creeped up past 50mph. It was like it would not let it shift to 50 if the rpms did not reach 2000.

Yeah… Im not that dense. But I understand the reason for the question. Sorry if I came off condescending.

Ok, so it’s running so poorly it doesn’t go beyond 2k rpm’s. Yes, I think the misfire is the first thing to resolve. It’s good that you got a code.

The emissions code might resolve itself after enough drive cycles and not filling the tank with the engine running again.

I agree with Scrapyard_John. Fix the misfire and the driveability problem is likely to go away. Normally, it takes multiple faults to set a code. One time with the gas cap off while fueling would be unusual to set a code. It would be good to know the exact code that was read…