Slow acceleration then it feels like power kicks in. No check engine lights

[ynottruth]

I have a 98 Mountaineer 5.0 AWD, and during acceleration from a low speed, and from a stop, it feels like I only have half power, and halfway through 1st gear the power kicks in until it shifts to 2nd, and then low power for half the gear, then full power. If I'm already going a decent speed it will accelerate fine. And sometimes when I accelerate from a stop power completely drops for a slit second and kicks back in.

 

[Mbrooks420]

Any codes? What’s the transmission fluid look like?

 

[ynottruth]

Any codes? What’s the transmission fluid look like?

Bank one O2 sensor code, but I changed it. Figured it might be 'cuz its got duals with muffler delete, but idk. Tranny fluid looks good, and shifts super smooth

 

[Mbrooks420]

I ran with no muffler at all for a few days, and it was totally fine. What’s the actual code? Do you possibly have a clogged cat?

 

[ynottruth]

I ran with no muffler at all for a few days, and it was totally fine. What’s the actual code? Do you possibly have a clogged cat?

I'll have to run the scan tool again to get the specific code, but it could be a clogged cat. I dont think that's it, but maybe. Worth checking

 

[CDW6212R]

How old is the fuel filter and the pump? How about the plugs and wires, and the two front O2 sensors? Replace any of those which you don't know how old they are, and check the fuel pressure. You need to have about 35psi of fuel pressure with the FPR vacuum hose off.

Transmission shifts should not be super smooth, you should feel them, firmer is better for less wear, for a better lifespan.

 

[ynottruth]

How old is the fuel filter and the pump? How about the plugs and wires, and the two front O2 sensors? Replace any of those which you don't know how old they are, and check the fuel pressure. You need to have about 35psi of fuel pressure with the FPR vacuum hose off.

Transmission shifts should not be super smooth, you should feel them, firmer is better for less wear, for a better lifespan.

Fuel filter is new. Plugs and wires are new. Front 2 O2 sensors are new. Transmission feels perfect. Fuel pressure is the next check. I was thinking maybe the fuel pump too.

 

[CDW6212R]

That's a good start. Go through the main basic items, and see how it is after new fluids and filters etc. My last 98 had a worn out front suspension, so I tackled that first. Then the old and possibly original plugs said hello, and after new plugs, a coil pack was bad(the old plugs killed it). You go at it until it's working the way it should, then it's reliable for a long while.

 

[ynottruth]

That's a good start. Go through the main basic items, and see how it is after new fluids and filters etc. My last 98 had a worn out front suspension, so I tackled that first. Then the old and possibly original plugs said hello, and after new plugs, a coil pack was bad(the old plugs killed it). You go at it until it's working the way it should, then it's reliable for a long while.

I've had this 98 for about 4 yrs and I've rebuilt the front end, replaced front driveline, variable rate suspension. Rear 2 in. shackle lift. Dual exhaust. Air Intake. Plugs and wires. Replaced ac comp. Egr. Cam shift position sensor. Camshaft synchronizer. Fuel filter. A few other sensors. 30 x 9.5 ko2's on 2 in. spaced 15 in. American Racing wheels. I've done more but can't think of everything. For the most part it runs great. Its my daily, and I do construction. Tows and pulls amazing. Other than the accel issue

 

[CDW6212R]

Very good, excellent. That kind of care makes it easier to diagnose any issues and fix them. Forgive me for the basic questions and suggestions, a ton of people buy these and don't think of those basic items to do. People want to buy a car and drive it, if they didn't run out of gas, they wouldn't even buy gasoline.

You issue sounds more like fuel given the care you've done to it for four years. My 98 Mercury had a similar issue that was both a coil pack and lean condition due to gas tank corrosion. Power was randomly normal and off too at times. So be sure it has good fuel pressure, and the other stuff already done, then there isn't much left. I had to go back through my stuff a 2nd time to get around to checking the almost new coil packs.

The error codes will be helpful too, to narrow down what's left, possible.

 

[ynottruth]

Very good, excellent. That kind of care makes it easier to diagnose any issues and fix them. Forgive me for the basic questions and suggestions, a ton of people buy these and don't think of those basic items to do. People want to buy a car and drive it, if they didn't run out of gas, they wouldn't even buy gasoline.

You issue sound more like fuel given the care you've done to it for four years. My 98 Mercury had a similar issue that was both a coil pack and lean condition due to gas tank corrosion. Power was randomly normal and off too at times. So be sure it has good fuel pressure, and the other stuff already done, then there isn't much left. I had to go back through my stuff a 2nd time to get around to checking the almost new coil packs.

The error codes will be helpful too, to narrow down what's left, possible.

Yea, I'm thinking its gotta be fuel related. Timing is perfect, and I fixed all vacuum leaks and its breathing good, in and out, from intake and exhaust work, so fuel has got to be the culprit. Thanks for the advice. Its very much appreciated.

 

[Jamjr4887]

I have a 98 Mountaineer 5.0 AWD, and during acceleration from a low speed, and from a stop, it feels like I only have half power, and halfway through 1st gear the power kicks in until it shifts to 2nd, and then low power for half the gear, then full power. If I'm already going a decent speed it will accelerate fine. And sometimes when I accelerate from a stop power completely drops for a slit second and kicks back in.

I had this same issue. I swapped my 1999 ranger with a 98 explorer 5.0 and it runs amazing just feels like im dragging an elephant behind me until i hit higher rpms then it lets loose. Almost like a 2 stroke powerband. Like turbo spooled and shoots like a rocket. But only after i wind out about 3/4 a gear. Its not transmission related because im a 5 speed. But i believe its fuel related. I just changed my pump and haven't driven it yet so ill let you know tomorrow my diagnosis. Only code was a lean bank 2

 

[Jamjr4887]

Yea, I'm thinking its gotta be fuel related. Timing is perfect, and I fixed all vacuum leaks and its breathing good, in and out, from intake and exhaust work, so fuel has got to be the culprit. Thanks for the advice. Its very much appreciated.

This might sound stupid, however, this May have been my problem also, while in the process of changing my pump, i decided to check my BRAND new o2 sensors like yours, i believe i had downstream and upstream plugged in backwards. Which will make it run like that. So make sure your Up stream's are grey and green and downstreams are blue. Atleast one grey anyway. I think i had one upstream plugged in to a downstream connector and downstream in the upstream plug. Damn plugs all the same and all right near each other. When i did my swap i didnt know which was pre and post and i obviously didn't pay attention. So double check yours. Ill know tomorrow if my issue is fixed when i drive it more then around my house one lap lol

 

[ynottruth]

This might sound stupid, however, this May have been my problem also, while in the process of changing my pump, i decided to check my BRAND new o2 sensors like yours, i believe i had downstream and upstream plugged in backwards. Which will make it run like that. So make sure your Up stream's are grey and green and downstreams are blue. Atleast one grey anyway. I think i had one upstream plugged in to a downstream connector and downstream in the upstream plug. Damn plugs all the same and all right near each other. When i did my swap i didnt know which was pre and post and i obviously didn't pay attention. So double check yours. Ill know tomorrow if my issue is fixed when i drive it more

I had this same issue. I swapped my 1999 ranger with a 98 explorer 5.0 and it runs amazing just feels like im dragging an elephant behind me until i hit higher rpms then it lets loose. Almost like a 2 stroke powerband. Like turbo spooled and shoots like a rocket. But only after i wind out about 3/4 a gear. Its not transmission related because im a 5 speed. But i believe its fuel related. I just changed my pump and haven't driven it yet so ill let you know tomorrow my diagnosis. Only code was a lean bank 2

Yea thats exactly how it feels. It's so hard to describe. It feels like after it spools it launches.

 

[ynottruth]

5.0 swapped Ranger is cool. I wanna 5 speed swap my Merc.

Yea thats exactly how it feels. It's so hard to describe. It feels like after it spools it launches.

 

[Jamjr4887]

Yea thats exactly how it feels. It's so hard to describe. It feels like after it spools it launches.

Check your 02 sensors. Make sure they are plugged in to the correct plugs and not swapped. That was my problem. Fuel and 02 fixed it. Drove it today and had 2x the amount of power its ever had simce i swapped it.

 

[ynottruth]

Check your 02 sensors. Make sure they are plugged in to the correct plugs and not swapped. That was my problem. Fuel and 02 fixed it. Drove it today and had 2x the amount of power its ever had simce i swapped it.

Awesome thanks. I'm gonna try it tomorrow