I hope this is in the right section. I am experiencing some pretty violent bucking with my evo, seems to only be at part throttle. The problem surfaces within about an hour and a half of interstate driving and to me has no rhyme or reason to when it does it, but it is bucking some at part throttle situations. The only facts I know of are that the car has not thrown any CEL and is registering a really lean AFR when it starts bucking. Like the car is just cutting injectors for whatever reason. It was so bad at one point that the car would not gain speed at all, because all attempts to give throttle would just buck harder.

The car was put on SD about a month ago, stock turbo, stock internals. It made great power and had no issues until recently. Im not too sure if it coincides with the colder weather or if there is a developing problem with something else. I replaced the Walbro 255 with a Deatsch Werks 301 today and seemed to help a bit with this problem (not quite as frequent), but the problem is still present.

Does anyone have any ideas on what could be plaguing me?

The car has all basic bolt ons, FIC 900CC injectors, DW 301 Fuel pump, stock computer with Tephra v5 SD tune on 93 octane.

Thanks for any input!!

 

It will be eather spark or fuel related.

I would guess at your maf ( air flow meter ) is crapping out.

 

Wrong section! You should have posted this thread over in the Evo Engine/Turbo/ & Drivetrain area, me thinks.

 

My general diagnosis is thinking something is telling the injectors to cut....as for the MAF, its on speed density so it doesnt have that anymore.

Only reason I posted it here is because I was wondering if it could possibly be a tuning fix?

 

So, the problem does not manifest itself during stop and go driving around town? It is only during steady state driving, or cruising on the turnpike?

 

You may get someone to help you on here. The problem that there are some special requisites for starting a thread on this sub-forum I think. So, the mods may move it over to another section.

 

Thats it! It seems to be so random that I dont think the tune is at fault, but the car performed just fine on the maf just before the SD tune.

I havent noticed it at all except on the interstate cruising in 5th. Goes WOT just fine, just at times will decide to start bucking part throttle.

 

Sorry mate should have finished reading the last few lines

Could it be something as simple as a sticking t/b?

 

What size injectors? Mine does it in 1st an 2nd say going through a parking lot at low speed I'm also on sd I've heard cop greatly helps this problem but I have no exaperiance with it

 

I dont think so, because it gets really lean.

You can hold the throttle constant and you'll feel it cut fuel and re apply with the same throttle modulation.

 

Yup that's my car too lol I think it has to do with sd IMO and having a bigger injector can make it worse

 

Does your car just have random spells like mine? Any other symptoms you've experienced?

 

Cold temps outside gradually gets more vilolent if I don't adjust normally shift or push the clutch in I'm heading back up to English racing soon I've heard that this is a pretty commen thing with bigger injectors and sd and posibly big cams i have s2s but like i said mine only happens in low gears at parking lot speeds

like I said some say cop help with it but im sure a good tuner can tune it out I watched tom from tscompusa he has a video of just smooth driving so I'm just guessing it can be tuned to be a little less aggressive

 

it shouldn't buck with speed density at all. if it dropped over 40F colder since you were tuned, then it could effect it yes. assuming o2 feedback is non existent.

 

This.