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My very own hesitation/bucking thread

I

iBrent

Veteran CEG'er
Joined
Oct 13, 2005
Messages
568
Location
Northborough, MA
So I have the same hesitation/bucking issue that many people have. I've done a lot of thread hijacking but never started my own thread. I figured its about time. It started about a year ago, back then it was very slight and almost unnoticeable. It has since been getting progressively worse. Its so bad now that my whole body moves front to back in third gear while accelerating. Its worse around 1500 RPM. For example, i'll be cruising around ~35mph in 5th gear (1500 RPM) and it will buck with our without throttle. When the throttle is slightly opened, it will get worse. At WOT, it's still there, but not as bad. Another example, I was in 2nd gear and revved it up to about 4500 RPM. Then I let go of the gas and let the engine slow me down. Once the RPM's got to 1500 it started bucking and got progressively worse until idle. It feels like when you're learning to drive a stick and the car bucks back and forth. Its not quite that bad, but you get the idea.

I've done lots of searching and replaced a lot of stuff. Its really bothering me. Help please!

Here's what I've done over the last year (in order).
Had a CEL, replaced fuel filter and pump. Fixed other problems, but the bucking was still there.

Replaced plugs/wires with APP764's and motorcraft wires - NO CHANGE (not better or worse)

Cleaned K&N and re-oiled - NO CHANGE

Tested coil pack, tested out of spec, thought i had something, replaced with autozone brand...- NO CHANGE

Checked spark plugs for carbon tracking and checked gap, all tested fine.

Rebuilt intake and cleaned IAC (yesterday) - NO CHANGE

I thought I had it with the intake rebuild...but 'twas not the case. Also, when the car is warm it seems my IMRC is malfunctioning and the bucking is worse. I bought a replacement transistor and will be replacing it this afternoon. That may fix the IMRC issue, but probably not the bucking.

Any help would be greatly appreciated...and if you successfully diagnose the problem, perhaps rewarded.
 
iBrent said:
.... I bought a replacement transistor and will be replacing it this afternoon. That may fix the IMRC issue, but probably not the bucking.

Any help would be greatly appreciated...and if you successfully diagnose the problem, perhaps rewarded.
Click to expand...
Send the money my way. :laugh:

It is the IMRC. Get it fixed and post new experience.
 
Sorry Tony I'm taking the reward on this one...it's the roll restrictors. Take a look at them, they're probably worn out and loose as ****. I had the EXACT same problem, precisely as you described it, and I just replaced the rear with an 80A poly-filled, which made it a lot better. I just ordered an Energy Suspension insert for the front, should have it on Tuesday and then hopefully it'll be totally gone.
 
rollinstylee said:
Sorry Tony I'm taking the reward on this one...it's the roll restrictors. Take a look at them, they're probably worn out and loose as ****. I had the EXACT same problem, precisely as you described it, and I just replaced the rear with an 80A poly-filled, which made it a lot better. I just ordered an Energy Suspension insert for the front, should have it on Tuesday and then hopefully it'll be totally gone.
Click to expand...

You're going to have to help me with this one. I understand the role (hehe) of the roll resistors but where are they and what should I look for? How much am I looking at to replace them?
 
I went through 2 sets of plug wires to fix my bucking/hesitation on my '99 Mystique. One set was brand new... ended up getting a set of $10 plug wires from a salvage yard and presto - all was well.
 
fornetti14 said:
I went through 2 sets of plug wires to fix my bucking/hesitation on my '99 Mystique. One set was brand new... ended up getting a set of $10 plug wires from a salvage yard and presto - all was well.
Click to expand...

Everyone keeps saying that, but when I replaced mine, it didn't change anything. It didn't make it better, or worse. Which leads me to believe it has no effect on my situation.
 
No man, trust me it's the roll restrictors. My symptoms are literally what you described to a T. Right down to the RPM descriptions (approximately). The rear roll restrictor is at the back of the engine hanging down, it's circular and if stock, has a rubber insert with a bunch of holes in it that are probably cracked and all kinds of distorted. Just look under the car, you can't miss it. 4 easy bolts to get out, piece of cake. The front roll restrictor is behind the cooling fan and is a little harder to get to and in fact, I'm having trouble extracting it from its bracket. I've got all the bolts out and I can move it around but can't clear it from the trans bracket. Does anyone know if you have to remove the trans bracket to get it out??? Anyway, I got an 80A poly filled rear restrictor from Pole120 for $60 ($120 with a $60 core refund) and just today ordered an Energy Suspension urethane front restrictor insert for $19 from Autozone.
 
iBrent said:
Everyone keeps saying that, but when I replaced mine, it didn't change anything. It didn't make it better, or worse. Which leads me to believe it has no effect on my situation.
Click to expand...

It didn't make sense to me either. I had brand new wires on the car at one point and it was the same.
I like the roll resistor idea. Bill J. has great prices on those. New ones make the car feel alot better too - not as much drive line play.
 
I don't think it is the roll restrictor... but give it a shot - here is what a bad one looks like.....
nevermind, photobucket not working right now
 
So here's my rear roll restrictor...How does it look?

IMG_0218.jpg
 
That doesn't look too bad to me, but someone w/ more experience with them can chime in, too. Can you get a hold of a noid light to check to see if your injectors are getting a good signal from the PCM?
 
...and btw, I got the energy suspension insert in the front along with the poly rear and my bucking is GREATLY reduced, only a teeny bit left sometimes when you hit it from low RPM in 3rd.
 
Any other ideas? I think it's getting worse. Another experiment I ran was shifting early into 2nd gear, then applying very LIGHT throttle. The car bucked every 150 or 200 RPM or so, but randomly up until the secondaries opened. The bucking was slight, not as bad as in 3rd gear, but still noticeable. Also, I have noticed the 5th gear 1500 steady rpm is bucking worse. At first it would buck for a few seconds, then stop for a few seconds, then come back, etc. Now its constant. Once again, lighter than while accelerating in 3rd but still definitely present, and still noticeable and annoying.

TPS maybe? Cause at 1500 rpm in 5th gear I'm either giving it very light throttle or its idling. I've done the autozone website check by backprobing the TPS with an ohmmeter but it checked out fine. I have an occasional moose as well, but that's very random.

Help me out guys! This really sucks!
 
Well with this additional information, it's starting to not sound like what my problem was...my bucking didn't come back once it went away at a certain RPM or if throttle was constant. Mine was definitely the worn roll restrictors allowing too much driveline play in transient acceleration or deceleration. Sorry I don't know what to tell you from here on out, at least it was easy to check right?
 
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