Weird studdering
 

I have this weirdness going on with my turbo setup. I call it studdering but it's kind of a hard duh, duh, duh sensation that only happens at certain boost levels. See if anyone can help me figure it out:

I can run 12-13 psi with my little Mitsubishi 14b no problems, but if I turn up the manual boost controller so I go over 14 psi, I get this hard studdering sensation and immediately have to back off the throttle. At first I thought it might be detonation, but I haven't killed my motor after doing it a bunch of times... ;D

It's most obvious and has the hardest studder when I really punch it. If I kinda sneak up on 14 psi like on the highway, I might get to 16 psi and not get the sensation.

Dialing back timing or adding fuel doesn't seem to matter. I've looked everywhere I can think for vacuum or exhaust leaks.

Basically it spooks quick and pulls strong until it hits that one spot and then -- duh, duh, duh, duh.

I'm running the MegaSquirt EfI system and can datalog just about any parameter and can see no change in A/F ratio. I do seem to get sudden variation in boost pressure, with a 2-3 psi flutter up and down.

I have pressurized my intake track using a compressor. The turbo itself starts leaking air above about 14-15 psi. If I pressurize the track after the turbo to the engine, it will easily hold 20 psi.

Any ideas on what's happening?

Re: Weird studdering
 

My car has been doing the same thing. I think it might have something to do with the manual boost controller. I'm going to disconnect the mbc and see if it makes any difference. Maybe the ball in it is fluttering back and forth. I don't even know if this is possible. :-\

Re: Weird studdering
 

Plug gap

Re: Weird studdering
 

needs tightened up you think?

Re: Weird studdering
 

The 14b wastegate opens on its own at 9 psi. Since I can dial up the mbc to 12-13 and run fine, I'm assuming my cheap ball n spring controller is working like it should.

I posted this question on some other boards last night and a few people have suggested problems with ignition -- plug gap, bad wires or weak spark -- which is something I hadn't considered. I'm using basic Bosch plugs from O'Reillys and my plug wires are several years old. I did an ohm test on the wires and they check within spec, but maybe time for a change there.

Any other ideas?

Re: Weird studdering
 

anyone bother to upgrade octane?

Re: Weird studdering
 

map sensor?

Re: Weird studdering
 

Spark plugs did it. I went a step colder and slightly smaller gap and no breakup topping out at just under 17 psi. ;D

Re: Weird studdering
 

Get some vids ;) That little MR2 sounds like it'd be a ball to drive.

Re: Weird studdering
 

Plug gap and weak spark is a good probability. Your problem is basicly what used to happen to me on my old single cam builds at over 12psi.