Bucking under 2,000RPM

[digitalslacker]

Hey All,

I've been chasing this issue for the past 5k miles or so but never really posted up so here goes.

When I am in pretty much any gear except first, i get bucking under 2,000 rpm with part or full throttle. I have some pretty nasty speed bumps in my townhouse complex and normally roll over them clutched-in in 2nd gear then just give it some gas on the other side. I am coming over the bump about 1500 rpm and the car bucks like its missing until it hits 2,000 rpm. Anything over that and it runs fine, pulls to red line smoothly without any hint of missing. I have a new set of plug wires and coil packs on it within the last 5,000 miles and I've just been replacing plugs every oil change since that seems to help for the first few miles. I have a blue-tooth code reader and i don't see anything when i go to read it.

Anyone have ideas on what it could be? I am at 210k miles with, I believe, about 130k on the replacement engine.

 

[chrisrob]

Need a little more info here.
Is it a case where the car hesitates like a misfire or is it a case where the car feels like its being 'thrown' back and forth? If it feels like a bronc horse doing his thing then, the problem could be your engine mounts. Proteges are known to have the bucking problem. With new mounts there will be some small amount of bucking but if the mounts are worn or torn then the problem will be more pronounced.
So check your mounts if they are ok.

 

[digitalslacker]

It feels like a misfire. I will check into the codes again tonight.

I replaced two of the mounts this summer, the rear is still the original but it didn't look ripped last time i checked.

 

[digitalslacker]

Double checked for codes today: No pending or historical codes according to torque.

 

[chrisrob]

Wow! Well... that misfire could be anything. I've experienced misfires a couple of times. Here are a couple of things to check:

1. Coil packs or plug wires need replacing. You have already done this.
2. Small leak in the head gasket, somewhere in the cooling jacket. Small amount of coolant may be getting in the cylinder which may cause a bucking in low rpm. Note that even if there is a small leak here, it most often does not result in overheating. You may notice that you have to top up on your coolant level once in awhile.
3. A vacuum leak somewhere(vacuum lines, intake manifold, intake pipe) can cause a bucking under 200 rpm. This means excessive air coming in after the MAF.
4. Fowled or dirty fuel pump filter screen(intank) can cause hesitation, mostly under high load situations.

 

[rit14623]

You replace the spark plugs at every oil change? Why don't you just clean and re-gap them?

Have you cleaned/replaced the EGR valve?

 

[larson701]

How about just a throttle issue? Some manuals have a real on/off action at light throttle loads. Sorry, but I do no have a solution for this type of problem. Maybe others might.

 

[Maroon]

In my experience, bucking is caused by O2 sensors. I have not had that experience with this car, but with others. You can try unlplugging the O2 sensor to see if that will help.

 

[digitalslacker]

I actually haven't replaced the EGR on this engine. I may have to try that.

Due to a header install I have the o2 pulled out of the stream with a spark plug non-fouler. Think that still may be an issue? I can get another o2 sensor if need be.

Funny thing is it doesn't seem to start doing it until the car is warmed up. I noticed the last two mornings when i left and it was cold it didn't seem to do it. I replaced that accordion tube around the TB earlier this year, maybe there is still another leak?

 

[JesseM]

My bucking was caused by a crack in my intake hose. Wrapped electrical tape around it, now smooth acceleration in 1st gear.

 

[Maroon]

Am I reading that right? You have the O2 installed into a non fouler and then into the exhaust? Regardless, try unplugging it from the harness (but leave it installed in exhaust) and see what happens. If the computer knows there is no O2 plugged in, it will stop taking input from it and trying to adjust the air/fuel mixture. If the issue goes away, you know it's either the non fouler or the O2 itself.

The computer does not take input or give output from/to some devices until the engine is warmed up; the O2 sensor and EGR are two of them. This may explain why you only experience issues after warm up.

 

[digitalslacker]

Am I reading that right? You have the O2 installed into a non fouler and then into the exhaust? .

That is correct.

I cleaned the EGR tonight, man was it bad. I guess 200k miles worth of gunk really makes it bad. I filled it with berrymans for about 45 minutes then scrubbed the heck out of it, then flaked off thick carbon deposits with a screwdriver... then more soaking then more scrubbing. Its somewhat clean now and idles at lights a tad bit better.

I'll try unplugging the O2 tomorrow and run it for a day or two and see if its better. If it is i'll order a new o2 sensor.

 

[Maroon]

I would not assume that the O2 sensor is bad if the issue goes away after unplugging it. If unplugging it fixes the issue, then there is still the possibility that the non fouler is causing it. The non fouler is essentially changing the output of that O2 to the PCM.

You installed the non fouler on the downstream (after cat) O2, right?

 

[digitalslacker]

You installed the non fouler on the downstream (after cat) O2, right?

It is installed after the header which may or may not contain a cat.