Engine will not exceed 2000 rpms
Thread Starter
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Trailering
Joined: May 2022
Posts: 18
Likes: 1
Engine will not exceed 2000 rpms
Hey y'all I got an 02' f250 with the 5.4L 4x4 with 235,000 miles. While driving home the other day I started having problems with acceleration. My truck wouldn't exceed 2000 rpms and when it got to 2000 it would start bogging down. I stopped in a church parking lot for a few minutes and I started it up and drove away. It acted ok at first but it didn't take long and it started again. I since have changed the fuel filter and TPS and it's still doing it. Please help!
Cargo Master
Joined: Jul 2009
Posts: 2,538
Likes: 54
From: Des Moines
1) Check for codes, even if the CEL isn’t lit.
2) With the engine at operating temperature (thermostat open), check the vacuum using a gauge on either the brake booster or EVAP port on the manifold. It should be 15 in-Hg minimum, but ideally 18-22 in-Hg and the needle should be holding steady with little, if any, fluctuating.
Less than 15 in-Hg or a rapidly fluctuating needle indicates a restriction in the intake or exhaust.
2) With the engine at operating temperature (thermostat open), check the vacuum using a gauge on either the brake booster or EVAP port on the manifold. It should be 15 in-Hg minimum, but ideally 18-22 in-Hg and the needle should be holding steady with little, if any, fluctuating.
Less than 15 in-Hg or a rapidly fluctuating needle indicates a restriction in the intake or exhaust.
Cargo Master
Joined: Jul 2009
Posts: 2,538
Likes: 54
From: Des Moines
The issue you describe indicates a problem with either the throttle controls, fuel delivery, or a breathing problem with the engine.
It’s certainly possible the PCM is to blame, but the only way to know is to diagnose the problem.
I’d start with checking codes and vacuum readings because they’re the easiest places to start and will define the direction of diagnosis.
If you’re not equipped/prepared to read codes, check vacuum, or perform other diagnostic tests, I’d recommend taking it to a shop.
If you’re willing to buy the tools and learn, I can help walk you through the testing.
It’s certainly possible the PCM is to blame, but the only way to know is to diagnose the problem.
I’d start with checking codes and vacuum readings because they’re the easiest places to start and will define the direction of diagnosis.
If you’re not equipped/prepared to read codes, check vacuum, or perform other diagnostic tests, I’d recommend taking it to a shop.
If you’re willing to buy the tools and learn, I can help walk you through the testing.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
There should be a test port on the fuel rail passenger side.
Can you rev it briefly to 3000 rpm when not in gear?
But, if you drive it the rpm won't go over 2000 rpm.
Our 2003 Exped had a restricted exhaust when the cat honeycomb disintegrated and clogged the exhaust.
If you pound on the cat housing can you hear anything rattling inside?
I had a Ford van where the cat internals broke into pieces, went thru the muffler and collected just before the exhaust pipe bent upward to go over the axle.
Clogged the exhaust and had similar symptoms, wouldn't accelerate over 2000 rpm or so.
There is an exhaust pressure test kit available to check for clogs.
It plugs into the fitting used for an O2 sensor.
Cargo Master
Joined: Jul 2009
Posts: 2,538
Likes: 54
From: Des Moines
Diagnostic tools that will be the most useful/versatile:
1) OBD2 code reader or dongle & phone app.
2) Digital multimeter.
3) Incandescent test light.
4) Vacuum gauge.
All of these should be available at any auto parts or tool store. Be aware that you often get what you pay for - not that cheaper is necessarily bad, but cheaper tools may not have the functionality to make the process easier. For example, most code readers only read powertrain codes, but if you want capabilities in the future to read ABS, air bag and body codes, the cheapest code reader won’t be able to do that.
That’s not to say you should go for the most expensive either. My primary recommendations for off the shelf brands are Gardner-Bender for meters and Innova for code readers.
For the test light and vac gauge, harbor freight or equivalent should do fine.
1) OBD2 code reader or dongle & phone app.
2) Digital multimeter.
3) Incandescent test light.
4) Vacuum gauge.
All of these should be available at any auto parts or tool store. Be aware that you often get what you pay for - not that cheaper is necessarily bad, but cheaper tools may not have the functionality to make the process easier. For example, most code readers only read powertrain codes, but if you want capabilities in the future to read ABS, air bag and body codes, the cheapest code reader won’t be able to do that.
That’s not to say you should go for the most expensive either. My primary recommendations for off the shelf brands are Gardner-Bender for meters and Innova for code readers.
For the test light and vac gauge, harbor freight or equivalent should do fine.
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Thread Starter
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Trailering
Joined: May 2022
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So I beat on the cat with a hammer and didn't hear anything. My exhaust is separated between the cat and muffler and I put my hand over the exhaust and it seemed to have good steady pressure. Does that not mean the cat is not clogged? Also I cleaned the MAF sensor twice. After the second time it seemed to help and I was able to drive it on the highway but it's still severely lacking power. Before this problem began I noticed an unusual vibration between 45-65 mph. Not sure if that has anything to do with it. I was thinking it's a U joint. I pushed the rpm to 3000 while in park briefly this afternoon a few times and once when I let off it backfired. Not a big backfire but noticeable.
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Fleet Mechanic
Joined: Oct 2017
Posts: 1,704
Likes: 164
From: Southwest Ohio
Remove the oxygen sensor that resides before the catalytic converter, then test drive. Improved? Then you have excessive back pressure.
A backfire means you have unburnt fuel getting into the exhaust (which will kill a catalytic converter). You might want to view the fuel trims while driving.
— Dave
A backfire means you have unburnt fuel getting into the exhaust (which will kill a catalytic converter). You might want to view the fuel trims while driving.
— Dave
Thread Starter
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Trailering
Joined: May 2022
Posts: 18
Likes: 1
Dave I'm a little confused. I've read that a bad oxygen sensor will produce similar symptoms. Is that true? Also I've found that after sitting for a while it will start and run fine for a little bit and then start acting up. It gets to the point where if you just gently push the gas it bogs down but kinda sounds like it's backfiring but not a full loud backfire. When it does that it loses all power and I got to shut it down. After shutting it down I can fire it up within 30 seconds and it'll start and drive away but only for a short way. I've also read things suggesting a bad torque converter. I'm just extremely confused. Maybe I can take a video so y'all can hear it. I'll try but I'm not sure if I can post it.
Cargo Master
Joined: Jul 2009
Posts: 2,538
Likes: 54
From: Des Moines
1) O2 sensors are monitoring devices only and have limited effect, if any, on driveability. The PCM uses O2 sensor data as part of a calculation for fuel delivery but it’s not the only determining factor. Engine speed, temp, load, throttle demand and other factors have a more direct influence.
2) The only way to verify excessive back pressure in the exhaust is or is not affecting driveability is to either measure it with a gauge or, as Dave said, remove the upstream O2 sensors and see if it smoothes out while driving.
2) The only way to verify excessive back pressure in the exhaust is or is not affecting driveability is to either measure it with a gauge or, as Dave said, remove the upstream O2 sensors and see if it smoothes out while driving.
Thread Starter
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Trailering
Joined: May 2022
Posts: 18
Likes: 1
Ok so I pulled the sensors and drove it and it seemed MUCH BETTER! So now we know. So my next question is if I remove the cat and reinstall the O2 sensors will it be safe to drive without fear of tearing something else up? I know it's gonna be loud but I'll replace it ASAP.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
A test pipe replacing the CAT is another way to determine if it is bad.
The test pipe will tell if the honeycomb is broken into pieces clogging the CAT and/or if pieces got into the muffler.