Ms3 fuel cut/aftermarket turbo surprise

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Rustyms3

Rustyms3

Greenie N00B Member
So I bought my first gen about 4 months ago knowing it needed some work. I just pulled the transmission to do a clutch and flywheel job. When doing so I noticed an aftermarket turbo. This car has no tune and is bone stock all the way around. Its a mahle 627 TC 20002 000 which is a twinscroll aftermarket replacement turbo. I've been experiencing a fuel cut at 5.5k rpm. I diagnosed it as a fuel octane issue and started being overly careful with the word "premium" at the pump. The issue lessened, but power between 5.5k and redline isnt there. What im trying to figure out here is do I have a turbo that is "over-boosting" my stock ecu? Will I have to buy hpfp internals and get a tune? I didnt plan on modifying this car since this would just be transportation while building my other mazdas.
Any input is greatly appreciated.
 
You're going to have to get something to monitor. Whether it's an Accessport or a bluetooth obd thing from Amazon, that's the only way you're going to know. You could definitely be overboosting and at a certain point you will be getting fuel cut, but that will feel like you're hitting a brick wall. You're probably getting throttle cut, which you still do not want.

You should honestly get yourself an accessport and a decent tune. You don't have to go for power or anything crazy, but even just getting the car tuned for your climate/elevation might help with everyday performance and even fuel economy if you tell your tuner that's what you're most interested in. You should also consider hpfp internals if you're getting into it like that and have an aftermarket turbo. I know you say this is just a getting around car, but if that was the case I'm not sure why you're going WOT to redline lol. Don't get me wrong, I get it, but if you're going to be driving hard you should get the basics done so you can monitor and have reliable fueling.
 
VashEXE said:
You're going to have to get something to monitor. Whether it's an Accessport or a bluetooth obd thing from Amazon, that's the only way you're going to know. You could definitely be overboosting and at a certain point you will be getting fuel cut, but that will feel like you're hitting a brick wall. You're probably getting throttle cut, which you still do not want.

You should honestly get yourself an accessport and a decent tune. You don't have to go for power or anything crazy, but even just getting the car tuned for your climate/elevation might help with everyday performance and even fuel economy if you tell your tuner that's what you're most interested in. You should also consider hpfp internals if you're getting into it like that and have an aftermarket turbo. I know you say this is just a getting around car, but if that was the case I'm not sure why you're going WOT to redline lol. Don't get me wrong, I get it, but if you're going to be driving hard you should get the basics done so you can monitor and have reliable fueling.
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I appreciate the input. This is what I was afraid of. I do drive her pretty hard for a getting around car. I have access to a snapon scanner and I'm pretty sure it has a data logging feature. I'll post back my findings when I get the trans put back in. If i do find that my ecu is struggling I dont know if ill go the cobb ap or the versatuner route.
 
Rustyms3 said:
I appreciate the input. This is what I was afraid of. I do drive her pretty hard for a getting around car. I have access to a snapon scanner and I'm pretty sure it has a data logging feature. I'll post back my findings when I get the trans put back in. If i do find that my ecu is struggling I dont know if ill go the cobb ap or the versatuner route.
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Cobb is easier honestly. With VT you'll need a laptop and it also logs slower than Cobb does. If you're just going to have one for monitoring and flashing tunes a used AP is what I'd go with personally.

It's important to note that this isn't "the ECU struggling". The ECU is just following the rules that have been laid out for it by the tune. You could set your tune to not have any throttle/fuel cut until 50 PSI if you really wanted (don't do this), but this is a safety measure obviously.
 
VashEXE said:
Cobb is easier honestly. With VT you'll need a laptop and it also logs slower than Cobb does. If you're just going to have one for monitoring and flashing tunes a used AP is what I'd go with personally.

It's important to note that this isn't "the ECU struggling". The ECU is just following the rules that have been laid out for it by the tune. You could set your tune to not have any throttle/fuel cut until 50 PSI if you really wanted (don't do this), but this is a safety measure obviously.
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Yea i know just enough to get myself in trouble with the whole ecu thing. I have a little experience since I soldered and tuned my miatas ecu. I dont like the limitations of the cobb since you can't change the tune directly by yourself. Im still doing alot of research on the topic and haven't came to a decision. I'll look around for a used AP and see if I could pick one up cheaper. Really what it comes down to is if I feel comfortable with boosted tuning or not. Since this car has a knock sensor and monitors alot more engine variables than my miata im sure it would be a little easier.
 
You can certainly self tune on the Cobb what are you talking about? You just have to do the online course for the basics for Cobb to cover their ass then you get access to access tuner.

Of course you cannot change a professional tuners tune as they lock it because you're paying them to do the adjustments.
 
Awafrican said:
You can certainly self tune on the Cobb what are you talking about? You just have to do the online course for the basics for Cobb to cover their ass then you get access to access tuner.

Of course you cannot change a professional tuners tune as they lock it because you're paying them to do the adjustments.
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He is talking about the limitations that you have with flash tuning - and he is absolutely right. He is likely using Megasquirt on his miatas which is one of the most open source stand alone tuning options. Compared to the megasquirt, cobb offers very limited control over the ECU.

That being said, you actually benefit from the flash tune because you don't have to tune the things you dont want to tune like idle, emissions control systems, etc. And I would also not transfer the same tuning knowledge from stand alone to flash tuning, because you are locked into the manufacturers tuning solution, which is usually based on a target based closed loop system (a lot easier to tune than you think).

IF this isn't your main project, just get an oem replacement turbo and call it a day.
 
Well I believe i found the problem. I apologize for not writing back. I've been swamped with work and putting this contraption back together. The boost controller thats mounted on the turbo is not hooked to vaccum. That would explain the over boosting conditions right? I'm guessing (correct me if I'm wrong) that the bypass valve on the ic isn't big enough to regulate boost. Thanks.

The_big_dill said:
He is talking about the limitations that you have with flash tuning - and he is absolutely right. He is likely using Megasquirt on his miatas which is one of the most open source stand alone tuning options. Compared to the megasquirt, cobb offers very limited control over the ECU.

That being said, you actually benefit from the flash tune because you don't have to tune the things you dont want to tune like idle, emissions control systems, etc. And I would also not transfer the same tuning knowledge from stand alone to flash tuning, because you are locked into the manufacturers tuning solution, which is usually based on a target based closed loop system (a lot easier to tune than you think).

IF this isn't your main project, just get an oem replacement turbo and call it a day.
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Well whats fishy to me is that the turbos have all the same mounting locations (wastegate, steel water line, oem boost controller). Can anyone confirm whether or not the oem turbo has two sets of impellers. The pictures I could find looked to be only single scroll. Like I just stated i believe this is now just a boost controller issue. I'll update yall when I get her back on her feet.
 
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Rustyms3 said:
The boost controller thats mounted on the turbo is not hooked to vaccum. That would explain the over boosting conditions right? I'm guessing (correct me if I'm wrong) that the bypass valve on the ic isn't big enough to regulate boost. Thanks.
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If the controller is not hooked up correctly, it will not function correctly.

Don't confuse wastegate control with bypass valves, they control different modes of operation. The BPV releases the pressure once you let off the throttle to allow the pressure to escape. The WG controls your boost tagets, whether its mechanical or electrical.
 
The_big_dill said:
If the controller is not hooked up correctly, it will not function correctly.

Don't confuse wastegate control with bypass valves, they control different modes of operation. The BPV releases the pressure once you let off the throttle to allow the pressure to escape. The WG controls your boost tagets, whether its mechanical or electrical.
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See this is what I needed to know. One more thing. On further research I've come to find out my knowledge on boost control is rather limited. The factory boost controller (which is a 2 port) should be plumbed how exactly? The way its plumbed right now is the hose running from the wastegate is on the connection closest to the boost controllers plug in. The hose coming from the intake pipe is going to the farthest connection. Thanks
 
Okay I have an update as I've got the car back together and did a few pulls with the snapon scanner. It seems my fuel rail pressure is steady at 1900psi at 4500rpm to redline. Even when the car looses power at 5500 rpm. The ignition timing is right around 5 degrees in the same conditions and doesn't retard when it falls on its face. So I'm stumped. On a side note the new clutch and aluminum flywheel feels wonderful and definitely helped rev matching and 0to60 times. I couldn't figure out where the boost psi was on the scanner as it could be overboosting still. But if it overboosted it would cuase it to run lean which would lead to knock and ignition retard right? Is 5 degrees pretty normal with 56 degrees intake temps, full throttle, around 5500 rpm?
 
Are you logging fuel pressure orjust monitoring live? When it drops it will only do it for a cell or two and cause a stumble. You have to log as it will not be obvious just looking at the display
 
Easter Bunny said:
Are you logging fuel pressure orjust monitoring live? When it drops it will only do it for a cell or two and cause a stumble. You have to log as it will not be obvious just looking at the display
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Sorry for the late response. I was just monitoring by watching it. It has a graph and a current value. So I belived It would show it on the graph if it was.
 
Just an update. I've since installed an accessport and in the process of declaring husband and wife it said that it has a "previous tune". At first I thought that the person may have tuned it terribly or put a stage one tune without hpfp internals. I set it back to the stage 0 tune and it still does it. I also ordered HPFP internals and began instalation today only to find out autotech internals already installed. So that throws out the stock internals conclusion. I plan to change the plugs to factory denso plugs as I could only get autolites in town when I first got the speed. I've heard a few things about mzr engines not liking autolites so that may very well be the issue. Im still running circles around this car. Never broken just never fully fixed. The ap doesn't see any fuel pressure or afr issues so I'm steering further away from fuel and more into electrical or ignition. There's lots of wiring falling apart on this car for some odd reason.
 
I got done with a little bit of maintenance and finnaly drove her tonight. I installed denso plugs factory heat range gapped at .27. I loaded the stage 1+sf map and the car has come alive. No more skimps and skuters above 5k. It pulls smoothly all the way to redline. I used a cheap worn out spark gapper on the autolites. When I checked them with the feeler guages they were all gapped way over what I had intended. Now time for meth injection
 
Awafrican said:
NGK> deno
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Well after installing a test pipe i went for a little drive. There is a little controversy over whether or not you run a stage 2 OTS map with one cat deleted. Some have success some dont. I loaded it up "stage 2 91" just out of curiosity. It didnt over boost but it did detect a little more knock than i like. I data logged it a few times and switched it back to the "stage 1 Plus SF" map. To my surprise but not yours its back to bucking at 5k. The AP detected knock MUCH worse knock. Here are the data logs. Converted to PDF for your viewing pleasure. Im really beating my head on a wall with this car.
 

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I apologize I brought it up in google sheets to trim off the excess overrun and non boosted cells. Here is the stage 1 sf data logs. The Stage 2 maps weren't as bad.
 

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