Whats up all,

I have a slight concern with my new evo. I have noticed that if I step out of the gas at partial boost, say around 4000 rpm mid throttle, the car bucks hard. I have experienced this before in my 2nd gen rx7 turbo and never got it sorted out but I went through two motors in less than 1 year before I gave up on it.

I try to avoid this as much possible, but sometimes you get cutt off ya know...

I think I need to take it by the dealer and have them look at it, but I wanted some feedback first.

 

I don't think there's a problem w/ the car. I think that will happen with any car when you suddenly lift off the throttle. The more torque there is, the worst the bucking would be. I would experience the same symptoms you listed in my stock engine Type-R even.

If you're still concerned, try talking to the dealer just to feel more assured that nothing is wrong. Make sure they have knowledgable techs though.

Mark

 

hmm, thanx for the feadback kk. I may not be doing a good job of describing what happens, then again I may just be a tool and you may be correct . Let me elaborate just a bit more.

It does not feel like taking a stab at the breaks or anything, and it is deffinetly not a good feeling. In fact I make a very unpleasant face every time it happens.

so i'm tooling along at say 3000 revs, roll into the throttle (not full throttle) and as the boost is building step off, like to tap the brakes cause someone just cut me off, and wham the car bucks and stumbles for a second. It feels like the BOV is sticky and not opening quick enough or at all.

If I can get a few more folks to say thats normal and they can reproduce the same thing then I won't worry too mauch and I'll wait till I have some free time to take the car back to the dealer.

 

The Evo engine isn't the smoothest thing I've ever driven (nor is it designed to be). It's a small displacement, high output little beastie. Frankly, I'm amazed it's as civil around town as it is. To answer your post, I get that same buck if I come out of the gas quickly while on boost. Rightly or not, I attribute it to the abrupt change in pressures within the engine. One second it's happily on boost, then you lift off the gas and boost is quickly vented causing the buck. My turbo MR-2 did the same thing. Also, because the Evo is so sharp edged, I think we feel things that a softer, rubber isolated car might be doing as well, but wouldn't transmit to the driver... particularly driveline lash. I just try to mitigate some of the harshness by using smooth throttle inputs. It doesn't eliminate the bucking, but it makes it better. All in all, a little driveability harshness is a small price to pay for a fantasic car.

Hope that helps.

 

Yeah, I'm starting to feel better now, or at least like it is "normal" behavior. I was worried becuase my turbo miata never did this, but my 7 did and it went through 2 motors in a short time with no real explanation as to why.. that was one of the things that never felt right about the car. I'll see if the behaviour goes away after a few mods (upgraded bov).

Thanx again for the feedback guys.

 

I usually disengage the clutch when I have to lift quickly during these situations. It helps take the strain off the driveline as well.

 

Yup, good point. I'm quickly learning that this car is unlike any other I've owed.... biggest problem is that I had to sell my toy (turbo miata) to come up with the down paymebnt for my house, so I was stuck driving an open diff front drive contour for the past two years...

Oh well, those days are over now for sure

 

I believe the system in this car is a not a BOV (blow off valve) but a diverter type such as the type on the 1g Eclipse turbo. Meaning, the compressed air is not being blown off to atmophere but rather is diverted back to the compressor side of the intake. This is done to help avoid what you are describing. When boost is high in the intake and you slam the throttle plate shut, that air has to go somewhere. In this system it's gets diverted back to the compressor/intake side which is before the IC.

Now, what you're describing seems odd. Is the car actually "bucking"?
And, your foot is off the throttle and the trans is engaged in gear?
Thus, your throttle plate is closed and the clutch is engaged (you foot not on the clutch pedal)?

If this is what you're describing, I once had a problem on my 1g Mits Eclipse.
I had done some throttle body cleaning and did not set the plate stop accurately. I had this type of "bucking" as the plate was closing too far.

I don't know if this is the problem that you describe, but just throwing out some ideas. If this is what is causing this, then your idle would be a bit off as well as mine was.

It's possible that the diverter/blowoff is malfunctioning, but you're saying the problem is happening as you let off the throttle and your foot is off the gas.
I could see if you have some odd "bucking" once you got back on the throttle partially, as that could mean your diverter is acting up. But, I'm not sure that is what you're describing.

Sorry if I confused you more.

GR-VIII

 

Well, I don't know what else to call it but yes it is off throttle and in gear, and it only happens if you have to let off during spoolup. This kinda worries me cause imagine what happens if this occurs as you are modulating the throttle mid corner near the limit of adhession.....

In my 2nd gen turbo, I did have major hesitation if I tried to get back in the throttle after the buck, and this normally showed up when merging onto the interstate where you have to do a few on then off throttle moves..

Once I get past the 600 mile breaking (425 now) I'm gonna go see if I can take a mechanic for a ride and show him what I'm talking about.

I do plan to put a true BOV on the car, but I will set it up to recirc since the air is already accounted for by the engine management, though it would be interesting to see if venting to atm stopped the "issue"

 

I get the same thing to on my Evo most of the time when I am stuck in stop and go traffic, But yeah I wouldn't worry to much about it if I was you.

 

I've also noticed this issue, or a version of it. For me it usually appears when I'm starting to build boost, need to break or step off quickly for no more than a second or so, then re-appy the throttle, but not wot. I will get one quick "buck" and then everything settles out. Feels alot like engine management is trying to figure out what I'm trying to do.

I've got a bit over 2k miles and have only seen this a few times, so it's not been much of an issue for me. My car has also always been fully warmed up, but then I don't get on it until it is.

 

Your symptoms are typical for the boost leak around the BOV (or should be correct and say CBV ), or connection hose between the valve and the intake that gets attached before the turbo. Check those hoses and connections!


Fedja

 

i agree.

try letting off around peak horsepower instead of peak torque engine speed and see if there's a difference. i haven't tried myself but understanding TQ vs HP makes think there will be.

 

First, I think the behavior you are describing is normal. If you lift totally out of the throttle when the RPMs are up, the engine goes from a big power source to a big power sink. This applies a significant braking force through the drivetrain. In an AWD car, the car will buck more than a RWD car (like your RX-7), because the engine braking is hitting the front wheels as well. Like wkehn said, pressing in the clutch pedal should eliminate the bucking.

If what you are describing is the normal behavior like my car has, don't worry about the throttle modulation near the adhesion limit. I autocrossed my Evo yesterday, and did quite a bit of 1st gear driving at the limit of adhesion, and the car never "bucked" once -- I was actually quite surprised when I finished my first run to realize that I had just driven so much of the course in 1st gear, and so smoothly. Very smooth cornering, very throttle steerable, and that's with the tires squealing like stuck pigs. Totally unlike 1st gear driving in stop and go traffic, which is just a tad painful in the Evo...

 

I have only had this problem in stop and go traffic where I was in first gear. But like someone else said if I pushed the clutch in I find it solves the problem. But luckily it has been very rare I have about 3300 miles on mine so that may have a little to do with it. Good luck