I just completed my install of an older Flyin Miata FM2 turbo kit on to my 99 Miata. I am using the FM2 with the red intercooler piping. For engine management I am using the Xede from BEGi.

Once I was able to get the car to idle somewhat smoothly with decent AFRs, I took it for a test drive. The car will not rev past 4000 RPM in any gear. At full throttle in second gear, as the car hits 4000 RPM, it suddenly lurches like I have just slammed on the breaks. Once the car lurches, the BOV will then release even though my foot is still on the gas. Trying to continue to rev past 4000 RPM results in jerky car movement and a very slow increase in RPM. As soon as I shift up a gear the problem goes away. AFRs during this are around 14. The car will also rev fine in neutral. The problem only occurs under load.

I contacted Stephanie at BEGi and she thinks my problem might be a bad CAS, even though I have not thrown any CELs. She is certain it is not the Xedes fault. I took the senor off and examined it. It looks fine, just a little dusty. No frayed wires or anything, which is what Stephanie told me to be on the lookout for. I also doubt my CAS has gone bad as my car only has 60,000 miles on it and was running flawlessly before the turbo install.

Has anyone ever experienced this problem before? If so what did you do to remedy the situation?

 

The MSPNP has something called overboost protection. Which makes the described your symptoms. Does it do it at full boost? Let the wastegate open freely and see if it does it. If it still does it the problem is something else.

 

The Link has a similar protection mode, both for boost and temperature. I've hit it a few times at the track - essentially, once the water temp hits a predetermined point, it won't let you go into boost or rev beyond a certain point.

 

+1 on the overboost protection. Sounds a lot like fuel cut. Also, do you have new plugs/wires?

 

Im am using the Xede, not the Link though for engine management. I have contacted Stephanie at BEGi and she is sure the Xede is not the problem. I just ordered some new plugs, and they are in the mail as we speak, can old plugs really have this dramatic of an affect. How do I check for the overboost protection?

 

I dont think the xede has any sort of overboost cutoffs or safeties. What injectors did you install? What gap on the plugs?

 

From personal experience, when I first installed my megasquirt, the car wouldn't go past around 3.5-4k under load. Turns out the " tune up " the previous owner did was actually... well.. nothing at all. The plug gap was .065, which would run a stock car, but under load it was blowing out.

 

I have 550 CC injectors installed, and the maps to support them. I decreased the gap of my stock spark plugs to .030 as per Flyin Miatas directions. I have ordered NGK IRIDIUM BKR7EIX-11 as recommended by the previous owner of the kit. These are gapped at .044.

 

I'm not familiar with the xede, but from there website it looks like there is datalogging functionality. You should post a screenshot of a log during the cut-out event.

 

While not a miata, my turbo 99 Accord (back in the day), did something similar, I think it ran to 4400 RPM. Injectors, fuel pump, wires, plugs and all looked good. Turns out the tune in the Hondata for the injector duration was too short causing it to run lean as the turbo hit full boost.
The Xede can be tricky in how it "masks" the signal, it may be you do not have enough fuel.

 

I will do this once I get a chance to work on the car again. I am leaving town and will not be back till Monday.

 

I was never able to get datalogging to work.

Sounds like you need to decrease plug gap and/or add more fuel.

 

14's afr are not going to cause this problem but you should be at 12-11 afr at 4k. Asuming your talking about at full wot and not cruise.

 

Absolutely do not use any spark plug you cannot gap. You must gap the plugs to 0.030 to 0.035 with the Xede.

The Xede does not have an over boost protection wired in right now.

The Xede data logging might help. Chances are it will not tell us anything new.

I still think you need to go back and check the Crank Angle/Position Sensor wires. What you are describing is an exact replica of damaged wires. I have seen it twice. And just because it was fine prior to turbo install does not mean jack. You might have moved the wires during the install by accident and not known it. Just remember, this sensor is on the front, driver side of the engine. The CAM position sensor is on the passenger side. I e-mailed you the diagram from the service manual.

Just 'cus I am super paranoid, please check the Crank wires again. Very carefully. Remove the plastic shroud and inspect each wire.
Stephanie

 

Just out of curiosity, how is your BOV hooked up? If it's hooked up properly, it won't release pressure until the throttle closes. Just wondering if you have some major vacuum problem going on.

 

had those symptoms. intake air temp sensor not properly grounded in my case. cut boost then fuel for intake air over-temp safeguard.

 

There are no apparent Vacuum leaks, I have double checked all my work. I don't think my air temp sensor is bad. I simply unplugged it from the stock air box and then plugged it into my new intake piping. Plus a bad air temp sensor would probably throw a CEL

 

So I will not be able to use the Iridiums? This is exactly what Joel was using, and he said they have been highly recommended by this site.

 

Iridiums are far too hot of a plug for turbo setups.

By the way, how much boost are you hitting at 4000rpm?

 

So what is a good spark plug choice? I hit around 4 PSI of boost before I get cut off.