Boost Bucking
 

My son's FD seems to buck when he steps down on it. He showed me the other day in 3rd gear, he stepped down probably around 3000+ rpm's and it started bucking. He said he can go fast and it won't buck as long as he slowly presses down on the pedal.
It seems to run OK other wise. I tried to clean all the grounds I could find. Cleaned the air filters, Fixed one crack hose that had fallen off. He said he used the power fc and checked the tps and he said it was good. New plugs about 3 days ago. Any ideas?
Thanks Duder

Either you are getting knock or ignition break up. What are the mods done to the car?

Try resetting the ECU. Disconnect the positive battery cable from the post and set it aside. Step on the brake for 30 seconds. Reconnect the battery and try it again. This may fix it. Mine does this from time to time and that is how I fix it.

could be a fuel pump issue...... if he can increase his speed slowly increasing throttle but he gets a bucking under WOT it may be an fuel delivery issue.


might be something as simple as a new fuel filter is needed.


Has the car been maintained well?

When you come get those A/c lines I could plug in my datalogit and wideband and see whats going on.

How many miles do you have on the car?

Is the exhaust system stock or aftermarket?

First off this is not how you reset a power FC.

Secondly, you don't need to step on the brakes. Disconnecting power is all that's required.

Thirdly, disconnect the NEGATIVE terminal.

-Geoff

check the rest of you vacuum lines as well. I'm in the process of troubleshooting this right now and I've narrowed it down (I think) to vacuum lines. How is the idle?

Long winded and long shot theory. Hitting wot suddenly causes boost spike and/or over boosting of the primary turbo due to either flow mods or a broken precontrol line/solenoid, and hits fuel cut on the primary. Slowly increasing throttle position yields an easy transition and a solid 10psi on the wastegate.

Again, long winded and a long shot theory. More than likely something more simple though like plugs, wires, coils, etc.

Matt

So my bad. I read the post quickly and didn't see the fact that the car had a power FC. Sorry. I was referring to the factory ECU and the reset and Yes it works the way I described. I was just trying to be helpful. I stand corrected.

This car is non seq, so no transition.

plugs have been changed.

Not likly a coil or wires as it runs fine except when you punch it. Easing in to the throttle it doesn't buck.

Check battery voltage. Mine did that when a couple of cells went bad. Started OK but anything over 1/4 throttle would cause bucking.

A coil or wires can be the issue for this exact reason.

I went through a bucking and hesitation problem under WOT that was caused by a dying leading coil.

New coil, problem solved.

There may be enough spark to handle idle and cruising, but not enough to handle all the air/fuel at boost.

-Geoff

I'd kind of reccomend getting a wideband , and a boost gauge so you can better diagnose as now people are just throwing randoms at you . if its a fuel issue you can blow theengine so try not ot drive it hard until its fixed.

Go back and read the 1st post in this thread

"He said he can go fast and it won't buck as long as he slowly presses down on the pedal."
I am assuming this means at some point he is going WOT just not punching it. Will see tomorrow.

Term120- its happening tomorrow...

I don't interpret that as going to WOT, I interpret that as getting up to speed by going half-throttle or whatever...

Would be nice if the person who is actually having the issue was on this thread...

-Geoff

He was coming to pick up an A/c line from me tomorrow, have been talking to his dad in Pm's so I have a little more info then mentioned in the thread. Going to check out the map as it was never tuned, and see whats up.

Damn SNOW BIRDS

Cold pump- think you were right. My apologies, miss interpeted what he said, no he can't get to WOT.

Car has an intake, front mount ic. Downpipe, stock mid pipe with original cats, cat back exhaust and a Pfc. Stock base map in ther ecu(tune is not causing the issue) Stock ports.

Here is what I noticed-

-3rd gear starting from 3,000 rpm when it builds boost .45 bar it misses, totally falls flat on its face.

Steady cruise it has a slight miss (25-60mph range), you can feel it slightly "bucking", not horrible but you can feel it.

Under Vacum acceleration its smooth even at 4,000 -5,000 rpm, but when you build boost it starts missing.

It will free rev to 6-7,000 rpm with no load, no noticable missing.

Car starts and idles fine.

He said the car ran fine until he took it to a body shop to get painted about a year ago. After that this issue occured.

Thanks Sean!
I was just coming back to update the thread. I checked with O'rielly's and they ordered some plug wires. I will start with that and see what happens and go from there.
Duder

Well I changed the plug wires and the car does not start now. The wires I ordered from O'rielly's look like they came from a dollar store!
I did find another disconnected vacuum line and reconnected it. There is black thing about 4 inches long that is bolted to the bottom 2 screws on the intake, not sure where the vacuum lines run. I did a search for it and seen something called a catch tank, but not sure if that's what it is.
I'm taking a break and doing something else for awhile and will come back to it later.

Took it apart and checked the wires again. I pulled one wire from a plug and could not get a spark to ground. I put a timing light on there and still dead. The car turns over but not even a single sputter.

Seems like maybe a fuse is blown but I don't know why that would happen, I am getting tired of this car pretty fast.

You most likely knocked some thing loose.

If you like I can come out and give you a hand.

I tried to jump it and it almost started. The battery is getting drained a bit. I also forgot to pull that vacuum hose back off and try it. I'm think ing the same thing. I removed the intake and checked everything again. I'll try starting in agian in a bit.

Check the map sensor line.

We got it running!
Earlier I had unplugged the connector for the knock sensor by acciedent. I was going over with my son what I had done and noticed a broken wire on another connector going to an air selonoid. It looked like it was bairly touching, so I got a jumper wire and jumped it and the car started. It also happens to be the same vacuum line but other end that I found unplugged from my post above. Any way the car sound like it idles much better. I will wait until morning to fix the connector. I just can't believe how a simple plug wire change turns into an absolute disaster!!