What can cause bucking below 2k rpm?

OrangeMustangGt · Jul 4, 2006

MY car seems to be doing this more and more lately. it gets worse after the car is hot, but it will start bucking quite badly when im crusing below 2,000 rpm. Also, my wideband shows quite a lean spike when this happens. any ideas? if i cruise at say 2,500 it is fine, and full throttle is fine also.

I dented a 02 sensor s small bit with a wrench, and possibly one of my plug wires is arcing somewhere.....could any of these cause the problem?

JJ95GTID · Jul 4, 2006

Dirty or broken MAF sensor element(s). This happened to me and was fixed after I replaced the MAF sensor.

final5-0 · Jul 4, 2006

From a tuning perspective ... here is a thought or two

When you are driving under that kind of condition, the spark value is quite high.

More so on GT's than Cobra's.

Most of us jack up the spark with the dizzy for maximum wot power.

Some of the time, that can cause what you speak about as the value is now too high for optimum dirvability.

however

If this is something that just started and you have made no changes lately, as you pointed out, there could be a mechanical issue of some kind starting to develope.

Grady

94-302-vert · Jul 5, 2006

My car was doing that below 1500 rpm. Running higher octane gas got rid of it. Then changed plugs last week and saw signs of detonation (white residue on the plugs). I am thinking too much timing down low. Maybe lower the inital timing and then run less boost related retard?

IEatRiceGT · Jul 5, 2006

hmm...mine does that too around 2k'ish and mine just got dyno tuned.

OrangeMustangGt · Jul 5, 2006

well, it wasn't the plug wires. OK, question. is there any way to test an 02 sensor? I had one go bad the same way, by denting it as i did this one when i was removing it, and it didn't trip a CE, but it was reading values out of wack.....could this be my issue.

Another question: shouldn't the computer's adaptive adjust my fuel, etc to stop the bucking, assuming all my sensors are in working order? BTW it runs great otherwise, but on light cruising and decel it bucks badly....and this is my daily driver so i would like to address the issue.

mo_dingo · Jul 5, 2006

GreenMustangGt said:
well, it wasn't the plug wires. OK, question. is there any way to test an 02 sensor? I had one go bad the same way, by denting it as i did this one when i was removing it, and it didn't trip a CE, but it was reading values out of wack.....could this be my issue.

Another question: shouldn't the computer's adaptive adjust my fuel, etc to stop the bucking, assuming all my sensors are in working order? BTW it runs great otherwise, but on light cruising and decel it bucks badly....and this is my daily driver so i would like to address the issue.

Yeah mine does this to. Even though it's running in CL the O2's cant seem to compensate. But I think that is from timing more than anything. I need to reset my dizzy back to 10* and start messing with the tables some.
Scott

OrangeMustangGt · Jul 6, 2006

i may have been wrong about what i said above. If i listen, i can hear static in my radio that goes to engine rpms.....Now, i this leads me to believe that i may have a bad spark wire somewhere. The reason i am questioning the wires, is because my bronco had a similar issue and i fixed it with another set of wires and a stock coil.

So, if this sounds accurate, does anyone know where i can get a QUALITY set of wires that have tight 90deg end boots?

mo_dingo · Jul 6, 2006

summit I am sure has them. The ones from autozone, etc shouldn't be that bad. They seemed like pretty decent quality wires.

1slow95 · Jul 7, 2006

Taylor 409's, you can get them from Summit.

ProKiller · Jul 7, 2006

i don't know what your cam curve is but i know some cams just don't like low rpms.

95Vert · Jul 7, 2006

This seems to be a pretty common problem I'm having this same issue as well as another friend of mine. I'll be switchin out my o2s tonight or tomorrow, I'll let you know.

loudpedal99 · Jul 7, 2006

My car does this also, but I am untuned. Have you tried watching it run in the dark?

OrangeMustangGt · Jul 7, 2006

well, after finding a nice dent on my driver's side 02' sensor, i replaced it yesterday.....dident cure the problem, but my a/r ratio seems better while cruising so it may have been bad anyway.

Yesterday in the dark, i misted my engine and didn't see and sparks. So, maby my wires aren't bad.

Now, i may have observed the root of my problem today.

As you may know, while moving our cars have a higher idle then when at a dead stop.....When my car is stopped it idles at around 1000rpms. Now, i pushed my clutch in while i was driving and noticed that my idle hovers at around ~1700-1500rpms.....this is the area that my car like to buck.....SOOO.....Im going to try and close down my IAC screw and drop the idle, see if it goes away.

OrangeMustangGt · Jul 7, 2006

...i don't know if anyone is still reading this, but......

I went and turned down my idle so that while crusing it idles low, down at 1,000 rpm. whell, the car still does it's bucking thing.......I noticed that it does it worse after about 20mins of driving, and ONLY when im giving it the slightest amount of throttle while in say 4th or 5th.......If i give it a bit more throttle, it goes away and drives smooth.....Now, tommorow im going to clean the MAF(which is a PITA because it is in the fender)....And if it still does it, i guess its a tuning issue, and i will finally have to break down and get a chip-burner so i can tune myself.......
BUT, what is making the car do this? I mean, the a/f ratio stays pretty straight when it happens, and the car cruises close to 14.7,,,,so that seems ok. Could it be spark? .......my car is running a base of 10 deg, and i think only has a total of say 15deg if i remember correctly...... If i were to pull the spout, and take it for a drive.......that would tell me something right?

95Vert · Jul 10, 2006

I don't have the answers to your question but I want to know that solution. So I'll kep reading this.

94-302-vert · Jul 10, 2006

Try pulling the SPOUT because it is so easy... But I would also think to try turning the base timing up or down too... Maybe try 8* and 12*... if you stay out of it jsut to look for the bucking I don't think you will hurt anything...

final5-0 · Jul 10, 2006

When you get your chip burner all setup

You'll be able to make some headway with the bucking as you will then have access to the spark tables

Just dial out a bit of spark in the mid load rows.

Grady

95mustang_gt · Jul 11, 2006

Im having the same problem,But im also untune with my car .Let us know if you solve your problem.

Therian · Aug 3, 2006

Just noticed this today as well...only in the low RPM ranges and only at slight to no throttle

I'll be putting in some 93 and I'll see if that does anything. I must say...it can be quite annoying driving around parking lots...

What can cause bucking below 2k rpm?

OrangeMustangGt

JJ95GTID

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final5-0

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94-302-vert

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mo_dingo

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1slow95

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