Rough engine between 2300-3000 rpm under acceleration. Why? Need help

[Drcoffee]

Recently, I noticed the truck accelerated fine and smooth until I hit 2300rpm. Then from there up thru 3000rpm the engine seems rough. This happens in all gears and not speed related. It will cruise at 70mph very smooth. At first I was thinking U joint and replaced the rear most joint but the rough acceleration is still there. The good news though is the clunk from Reverse to Drive is gone which is why I initially thought of the U joint.

When it first started I wanted to see how it would respond at WOT so I floored it and it smoothed out above 3500rpm but still not what I would consider smooth. Then a strange thing happened. After I let off the gas and the engine idled down it stalled. It was hard to restart and I had to press the gas pedal slightly to keep it running and then a few minutes later it recovered and drove normally again without stalling. The rough acceleration at 2500rpm was still there though.

I'm thinking fuel pump now. I bought a new Denso pump and just need to empty the tank. What else should I be checking. I have no codes from the computer. It otherwise drives fine and I get 18 mpg which for around town is about average.

Motor mounts? What else can you think of?

FYI: I did a full tune up last March (plugs, wires, (3)fuel injectors 2,4,6 plus much more).

 

[HCurphy]

sounds kind of like a bad ignition coil. could be crank position sensor.

Why did you end up replacing half the injectors? (possible one of the three you didn't replace is taking a **** on you?)

Weird you don't have a CEL. I'm guessing the engines actually missing? Is that what you mean by rough?

edit: or is it not missing? just saw that you think it could be a motor mount, does that act like a missfire?

 

[Kung]

I had the exact same thing happen in my '95 F250, and I believe there was another gentleman here who had much the same thing....and in both cases it was the CPS, as Hcurphy above says.

 

[Drcoffee]

Back in March I has a bad coil on number 4 so instead of having to rip down the whole intake again I just replace all 3 on the drivers side. It seems like a miss but not really. Its not like a cylinder is dead miss, but more like just a gritty not smooth feeling.

Okay, how do I trouble-shoot it? Where is it located? If someone has the FSM page for this I would greatly appreciate it.

 

[PitbullRescuer]

Couple things:

1.) (just an observation) you don't have to remove the intake to get to the coils. They come out pretty easily with it in place. Although with 3 new ones, probably won't be an issue for you again.

2.) It doesn't sound like a fuel pump only because it smoothes back out over 3500 RPM. If it was the fuel pump, I'd think it would be starving more at higher RPM's.

3.) When you say no codes, did you scan it for codes or are you assuming no codes because no Check Engine Light? Reason I ask is it may have pending codes that you're not aware of if you didn't scan it.

4.) What injectors did you use when you replaced them? Seems to be some debate about the quality/performance of different brand injectors. (probably not your issue since you say it's not missing but something to consider.)

5.) Unfortunately, I'm not sure if you can test the CPS. But I do think these guys are on the right path with suggesting it as the culprit. Might want to try buying one from a local parts store, doing your best to keep it clean while installing it and see if it does the trick. If it doesn't, return it.

Good luck man.

 

[Drcoffee]

Couple things:

1.) (just an observation) you don't have to remove the intake to get to the coils. They come out pretty easily with it in place. Although with 3 new ones, probably won't be an issue for you again.
A What I meant was a broken coil inside the #2 injector. It died. sorry, it was a bit confusing the way I phrased it. The ignition coils seem to be fine

2.) It doesn't sound like a fuel pump only because it smoothes back out over 3500 RPM. If it was the fuel pump, I'd think it would be starving more at higher RPM's.
A tend to agree but its also taking longer to start and more so after its been running

3.) When you say no codes, did you scan it for codes or are you assuming no codes because no Check Engine Light? Reason I ask is it may have pending codes that you're not aware of if you didn't scan it.
A I scanned it for current and pending codes

4.) What injectors did you use when you replaced them? Seems to be some debate about the quality/performance of different brand injectors. (probably not your issue since you say it's not missing but something to consider.)
A I used GB reman injectors. I bought 3 and sent the other 3 to witchhunter for a tune up.

5.) Unfortunately, I'm not sure if you can test the CPS. But I do think these guys are on the right path with suggesting it as the culprit. Might want to try buying one from a local parts store, doing your best to keep it clean while installing it and see if it does the trick. If it doesn't, return it.
A where is it? Is it down on the timing cover on the pssenger side? How hard is it to get at and replace?

Thanks for the suggestions everyone.

 

[cj80cruiser]

Back in March I has a bad coil on number 4 so instead of having to rip down the whole intake again I just replace all 3 on the drivers side. It seems like a miss but not really. Its not like a cylinder is dead miss, but more like just a gritty not smooth feeling.

Okay, how do I trouble-shoot it? Where is it located? If someone has the FSM page for this I would greatly appreciate it.

FSM in my sig

 

[Drcoffee]

Just to be clear. You mean Crankshaft position sensor and not Camshaft position sensor?

 

[LittleCaesar]

Because it is not running on Dunkin......

Blocked fuel filter. Crank bolt tightness (217ft/lbs). Clogged kitty. I would think that such was the problem, the engine would not smooth out at 3000 rpms+.

If it is taking longer to start, then it could indeed be the pump.

 

[Drcoffee]

Because it is not running on Dunkin......

Blocked fuel filter. Crank bolt tightness (217ft/lbs). Clogged kitty. I would think that such was the problem, the engine would not smooth out at 3000 rpms+.

If it is taking longer to start, then it could indeed be the pump.

It has a new fuel filter last March. Wouldn't a clogged Cat stop from me accelerating? I have good power, its just a little rough in the mid range.

Now the crank bolt is curious. I'll have to check that in the morning.

If it was the crank position sensor, wouldn't it set a CEL?

 

[jamess]

Dr Coffee, did you solve this problem? The reason I ask is I just picked up a 1999 4Runner and I am experiencing the rough running from around 2500-3000 rpms. I was going to start with plugs, wires and fuel filter since it is at 142k and I it appears those parts are all orginial.

Please let me know what you discovered.

Thanks.

 

[Drcoffee]

Not yet. I have done the full tune up, new tires, new rear U joint, new bearings. It seems to be engine speed related under load. I have a new exhaust waiting to be installed and new motor mounts ready to go in. Just waiting for warmer weather.

I did add some Mystery oil 1500 miles ago and it could be my imagination but it seems to lessen the vibration a little. Who knows?

 

[Illicitdream]

Just a thought, but did you check to see if you MAF sensor was clean? A dirty or faulty MAF can cause this problem.

 

[jamess]

Not yet. I have done the full tune up, new tires, new rear U joint, new bearings. It seems to be engine speed related under load. I have a new exhaust waiting to be installed and new motor mounts ready to go in. Just waiting for warmer weather.

I did add some Mystery oil 1500 miles ago and it could be my imagination but it seems to lessen the vibration a little. Who knows?

That's a bummer man. I was hoping you had solved the mystery. Please keep us posted with what you try and any associated results. I will do the same. I cleaned my MAF and TB last night but have not driven it since.

 

[Drcoffee]

Just a thought, but did you check to see if you MAF sensor was clean? A dirty or faulty MAF can cause this problem.

Oh yes. That was one of the first things I did. Other than the vibration from 2500-3000 it runs strong and smooth. Its some type of resonance.

 

[slapdappy]

me newby.
purchased 99 limited 2 weeks ago. 179,000 miles. seems well cared for. I have the same roughness at same RPMs. Looked under hood. revved it up. fan blade wobbling. clearly some fins are following a slightly different path. turn engine off. pull fan blade back and forth/up and down looking for any obvious play or looseness in bearings. Nope. solid. turn it on, look at shaft (which spins the blade), rotating perfectly, no deviation or wobble or anything but a straight shaft spinning true. new toyota fan, $100 at dealer (they were willing to make me a price), easy install, definitely running smoother. Original fan had a couple of slightly warped blades. it is a piece of plastic trapped in an oven for 14 years/180,000 miles. like i said, def running smoother, but…..
still an obvious (to me) but not alarming engine roughness [MENTION=105273]2500[/MENTION]-3200 RPMs. New plugs and wires. cleaned MAF and throttle body. engine peppier but….
thinking maybe injectors need cleaning (BG 44k in the gas tank or the machine (MOC or BG) induction system cleaning)
still the engine roughness. today i installed a new fuel filter. the stuff that came out of the old filter was watery brown mud. gritty brown mud water. it was shocking. Thank You Filter. You have been doing your job. I commend you for your service.
Besides the immediate obvious improvement in throttle response, acceleration, and overall engine performance, I notice the roughness is greatly reduced. Substantially reduced. Obviously reduced.
I surmise the filthy filter was impeding fuel flow within that RPM range. The fuel demand of the engine below 2000 RPM was low enough that the impeded flow through the dirty filter wasn't an issue. But when the RPMs start increasing as 3.4 liters of V6 start producing some real power to get our 4000lbs of truck really moving, it demands more gas at a faster rate. it is gulping that stuff down. the straw it is sucking through is clogged, so it sucks harder. no matter how hard as it sucks the dirty filter limits the flow. It cannot get the quantity at the rate it needs. I think the engine is trying so hard to do its job with an inadequate supply of fuel that is is simply stressing out. its trying but just can't quite get it done, so it isn't running smoothly. It is stressing and straining and experiencing disharmony.
Or not. Just a theory. Not sure how to explain the roughness diminishing above 3000 RPMs, which seems to put the lie to my ill informed conjecture.
But I'm telling you, so much smoother with a new filter. Ill try to post of foto of the vile bile spewed by the old filter.

 

[Drcoffee]

Good post. I had changed my fuel filter last summer but i am glad it helped.

I had been dealing with a sudden loss of mpg for the past 6 months, down to 16.5 mpg. Once the ABS and battery light came on I found a small signal wire to the alternator had broken in the harness causing the alternator to drag at full power continuosly. Fixed the wire and replaced the alternator and the mpg jumped back up. Still waiting to fill the tank again to know current mpg.

The roughness has almost gone away. Its hardly noticeable anymore.

 

[slapdappy]

jittery bullets, PhD,
reread thread and now see you had changed your fuel filter. I'm getting the same kind of MPGs as you were. My engine seems to be in excellent working order, no weak links.
very interesting about the alternator. did you recently discover this? how? diagnostic codes? tracing connections with a meter? visual inspection? How did you know what to look for? where is this wire, what color?
Do you think RPM roughness was the engine stressing as it fought the drag of the alternator. Why did you replace the alternator after repairing the wire? I suppose i could remove my belt from the alternator temporarily and see if it solves the remaining roughness.
Is the remaining (hardly noticeable) roughness in same RPM range? to what do you attribute this residual roughness? Is it possible the roughness has actually disappeared but you are hyper attuned to any tiny hint of disharmony within this range?
I am so curious about this stuff. Love learning about solutions and the paths which lead to them. I am so happy when things work as they are supposed to.

 

[Drcoffee]

jittery bullets, PhD,
reread thread and now see you had changed your fuel filter. I'm getting the same kind of MPGs as you were. My engine seems to be in excellent working order, no weak links.
very interesting about the alternator. did you recently discover this? how? diagnostic codes? tracing connections with a meter? visual inspection? How did you know what to look for? where is this wire, what color?
Do you think RPM roughness was the engine stressing as it fought the drag of the alternator. Why did you replace the alternator after repairing the wire? I suppose i could remove my belt from the alternator temporarily and see if it solves the remaining roughness.
Is the remaining (hardly noticeable) roughness in same RPM range? to what do you attribute this residual roughness? Is it possible the roughness has actually disappeared but you are hyper attuned to any tiny hint of disharmony within this range?
I am so curious about this stuff. Love learning about solutions and the paths which lead to them. I am so happy when things work as they are supposed to.

What is your record for asking the most consecutive questions in a row?

My mpg dropped by 3 about 6 months ago and couldnt figure it out. Then a month ago my battery and ABS light came on. I tested the battery and alternator and it wasnt charging so replaced the alternator with a denso reman unit. 2weeks later my lights started blinking. Tested again and got 16v(regulator is toast). Sent the alt back for a brand new TYC alt and in the process I read a thread that mentioned testing the harness that plugs to alt. checked for continuity on red yellow and white wires but norhing registered on the white wire. So check for voltage. The white wire is a signal wire. No voltage found. So i pulled and pushed on the harness and got an occational spike. So i dissected the harness and found a break in the wire. Cut out the corroded section and soldered a new wire in and it works again. To test it, unplug the plastic plug from alternator and the other end from the base of the fuse box. Test using the oms setting on the meter. Each wire should have some resistance. Mine tested at 1.3ohms. Then plug the fuse box end in again and test for 12v on the white wire from the alt end with engine off. Should show 12-13v.

The extra load from the alternator was making the normal v6 engine vibe as it entered the powerband more prominant. Its better now. The mpg went from 16 up to 19 which tells you how much drag the alternator can put on the engine when running full power.

 

[slapdappy]

372. it was a NY state record until 1997 when they held the the next championship. I was disqualified after they discovered I had moved to Colorado. Escorted from the premises by an armed guard all hopped up on starbucks and jujyfruits.
exactly the info i was looking for. great detail and description of process. Merci mon frère.