Power cutting out, now a boost issue, need advice!
 

I need some help with some boost issues. It started out as one problem and has now turned into something else, or there is a second issue cropping up. First off here are some details on the car:

93 R1, 130k on chassis, unknown on motor and turbos (the engine has definitely been replaced at least once). Stock turbos and I assume stock motor.
Corksport Turbo back exhaust. It was hacked up and a high flow cat was put in. I added a ~2.3” exhaust restrictor plate put in. I added it to help with a boost creep problem.
New sparkplugs 4,500 miles ago, and JUST replaced them again last night.
Stock intake and inter cooler.
Stock ECU. (I do have a PowerFC on the shelf, but I have no idea what kind of map is on it so I have hesitant to use it. It came from the previous owner.)
Most of the safety mods (koyo radiator, silicone vacuum lines, fuel recall kit, freshly rebuilt and flow matched injectors)
TurboXS D-TEC boost controller. I left the pre-control on the turbos stock.

Over the last couple of weeks I have noticed an issue where the car just cuts out. While getting on it at high rpms and high boost, it will just cut the power out. It doesn’t sound like a rev limiter bouncing back and forth. It’s smooth, almost like its pulling spark or fuel. It happens very consistently at~7200 rpm in 2nd, ~6600 rpm in 3rd, and ~5800rpm in 4th. It has never happened in first or 5th but it’s likely due to me never driving fast enough to find out. I have noticed a fireball once or twice when it happens, so I’m working on the assumption that its spark related since plenty of fuel is getting out the back.

I thought it might be hitting fuel cut due to boost. Looking at the logs on the boost controller, I don’t see it getting close to that limit. I have it set to mimic the stock boost pattering (10psi tapering down to 8ish at redline) and its doing a very good job of hitting that target. (or at least, it was)

I thought maybe it was fouled plugs so I replaced them last night (I went ahead and did an oil change at the same time). I went to test drive to see if it had made any difference and after the first 2nd gear pull it repeated the same issue. It also has now decided to start overboosting. I was seeing it climb up to near 14psi now. I hadn’t touched the boost controller, any of the vacuum lines, or wiring on the passenger side of the car. I tried setting the boost controller down to 8psi with a 5% duty cycle (as low as it goes), and the boost acted exactly the same! I pulled the intake out and spent an hour checking lines and wires to see if something had gotten disconnected. So far everything looks normal.

Here is what I plan on doing tonight:
• Hook the wastegate directly up to vacuum bypassing the boost controller to illuminate it as a possible cause of the problem. It should run off the spring and boost to 7-8psi.
• Hook a mightyvac up to the wastegate and build some pressure to see if I can get the wastegate arm to actuate on its own. I assume I will be able to see/feel the actuating arm. I hope this is the case.
• Pop the ecu out and make sure all the wiring around the ecu and boost controller looks good.

What are some other things I should be testing or looking for? I’m totally lost on the cutting out issue. Are there any issues that would cause both these symptoms?

TIA

Here are the approx numbers for fuel cut off:
https://www.rx7club.com/showpost.php...95&postcount=3

It is possible you are hitting it in the upper rpms depending on what the MAP sensor is reading verses your boost controller sensor.

That's good to know. Also, I could confirm its not a boost cut issue if I took the boost controller out (and ran with no pill). That should keep it at lower boost and certainly prevent it from hitting the cut.

Alright, its definitely a boost control issue. I took it out of the loop and hooked the wastegate back up directly too the niple on the turbo. 8-9psi. No cutting out at all. Went all the way to redline in 2nd and 3rd no problem. As soon as I plug the boost control back into the mix, uncontrollable boost. The map is completely the same as before, I wonder if something shorted. It seems likely that my first problem is boost cut.

I think my real solution here is just to get a dyno tune on the PFC ;).

It should be a lot easier to troubleshoot now.