Overboosting?

[Cpl_Bryant]

Hi gang. It has been a while since I've given the MX-3 any attention and I'm finally able to start again. The car has the BPT engine and ECU, FMIC, 8,5mm wires and a few other goodies (probably not relevant to this question). Here's what I'm experiencing: During acceleration, I can hear the turbo spool and boost (fairly loudly). After only a second or two under boost, it feels like I'm hitting a wall. Is this the fuel cutting out? Also, when cruising in top gear, and attempting to go up a hill or accelerate/minorly boost, the engine studders and will not produce any power.

What could be causing this? A vacuum leak? Intake leak? Poor spark? Lack of fuel? (still using the original 1.6 SOHC injectors)
I'm trying to see where to attack this from: New plugs and wires and dist cap? Bigger injectors? I probably should just go through the whole intake piping first. Your thoughts?


I really miss the MX-3 and I want to get it back in shape. I have a Mazdaspeed6 now. Honestly, its experiencing a similar stumble, but has been running on the same plugs and wires for about 50k miles.

[onlytrueromeo]

Sorry I can't help but you're in albany NY? I will be moving back there permanently in december and will be there from june-august. I've only seen 2 mx3's around the area and never seen yours! (I live in guilderland)

[Cpl_Bryant]

I just brought the car up from downstate. I'm right of Western near the entrance to SUNY. Not that I'm trying to get off tpoci here. lol We'll have to meet up sometime then.

[projectzemx3]

perhaps fuel filter. or the pump.

[RS_OBD'oh_2]

poss lack of fuel. you should upgrade injectors to the 330's (?think those are stock BP?) if not the RX-7 if you have a good ems (not safc). + Fuel regulator such as NRG.
sadley there could be a few issues that are causing your issue like. wastegate sticking. What are your boost readings normally and under these conditions?
if it has been sitting, for how long? Bad gas? what octane you runnin? have you checked the VAF? poss bad coupler/pressure leak.

many options.. just trying to help. the boost readings will narrow things down.

[Cpl_Bryant]

Fuel pump in the gas tank is relatively new, it is the Walbro 255 or whatever, put in during the engine swap July 2005. I have refueled the tank since it had been sitting to the usual 93 octane. I guess I need to get a boost gauge, been running blind since the beginning. I'm hesitant about the injectors since it did run fine once upon a time, but maybe they're just dying. I don't even think they are the BP ones, they are from the original engine I think? The 1.6 SOHC L4. I can't remember. I had considered the wastegate. How would I know if it were sticking? Can it be tested? I realize there are a lot of things that could cause this. I appreciate the responses. Keep them coming.

[RS_OBD'oh_2]

if you take off the downpipe and give the wg actuator the 6-8psi (guessing again.. btw no more than 10psi) it needs to open you'll be able to see how well it's functioning. I'd really like to say you need to go to the local parts store and just get a realy cheap, autometer boost guage just to see how it's acting up. I think these are dirt cheap and it will save you soooooo much time. you can just put a T in by the WG actuator to get a reading.

I really hope you are not using the soch injecties.. iirc they are smaller then the dohc and the dohc's are ~205cc. You are in danger of running lean. esp if you don't have a boost guage and or uego.

[Cpl_Bryant]

Yeah, I guess I need to start there. Where can I get one?

[RS_OBD'oh_2]

pepboys, auto zone.. I'm not great with the shops in the states.. sorry..

[Cpl_Bryant]

Well, this stupid boost gauge doesn't appear to be working. It reads 10" of vacuum when nothing is even hooked up. I didn't notice when I bought it, but it looks like it has been used and returned. Sigh... back to the store tomorrow.

The air/fuel gauge might have to wait. I can't be welding any new bungs on this thing, or dropping $300 for a damn gauge.

[ElectricEnergy]

Air/fuel is a MUST for any custom boosted system IMHO. You could be destroying your engine without even knowing it. Just don't waste any money on a narrow band sensor, they give you a nice light show but don't actually tell you anything useable. You could be running way lean and it'll still read rich.

I'd also recommend an EGT and fuel pressure gauge if you really want to know whats going on with your motor.

[colinsmx3]

Yea WHY are you running the stock 1.6 B6 injectors anyway?? I would asume that would throw it way off right away!

[Cpl_Bryant]

I can't remember which injectors I'm using. I don't think they came with the engine honestly, but maybe they did. In any case I think I found and fixed my leaks. It's boosting between 10 and 15 psi. When I let off the gas, the boost spikes as the bypass valve line I think is too narrow, not allowing quick bypassing. Still, under steady boost of over 10 psi, eventually I get a fuel cut like jolt where it feels like it misfires. This could be me leaning out and needing new injectors. What do you all think?

The gauge is also not picking up any vacuum. I have it tapped into the wastegate line. Is that ok?

[RS_OBD'oh_2]

hmm.. suspect bov/bypass valve. it is getting it's signal after the throttle booty, correct? if that is the case you may just have to adjust the valve.

can you see the tops of your injectors, and tell what colour they are?

[Cpl_Bryant]

There's definitely a bottleneck condition in the bypass piping, I'm working on it.

What color should the injectors be? I just changed all the O-rings as one had broke and was leaking. I want to say... green? like a dark green maybe? Help me out here. They seem to be handling the fuel delivery alright, so I'm guessing they can't be the stock 1.6 SOHC ones right? Must be the GTX? But I seem to remember having to keep the original ones for some reason. I'll have to go back & read my swap journal lol.