87 T2 Violently cuts out underload at higher RPM
 

87 T2 Violently cuts out underload at higher RPM1987 Mazda RX7 Turbo II.
I bought the car a ten years ago after it had been parked behind a building with under 40k miles on it. I put it back on the road, but for the past couple years it's spent most of it's time parked.

Fuel pump, plugs, wires (among other thigns) were are replaced in '09 and have about 5k miles on them. Fuel filter was replaced again two days ago. Fuel should be good, it's only had ethanol free fuel treated with Archoil, it's recently been drained and refilled with 93 octane from Mobil.

It's idling around 1200-1500. It's intermittently going from a slight miss to rough. And now, occasionally, underload at high RPM, it feels like the fuel is cutting out. A sound kind of like it's violently hitting a rev limiter, backfiring. I'm just not sure what the problem is or where to start looking. I swapped the fuel filter, I'll check the plugs and replace them again, but unsure what else to do. I'm hoping someone recognizes my the symptom I've described and can help point me in the right direction. Randomly replacing parts could get very expensive, so I'm hoping others can share some wisdom.

You sure the secondaries are coming online?

What kind of exhaust do you have on the car and does the exhaust have any leaks? If the ecu detects an overboost condition it will cut fuel...violently... Lets start there.

It really feels like fuel is cutting and I think the first thing to do is put in a new fuel pump, replacing the one I put in and has largely sat dormant for the past few years. It's a stock ECU, injectors, and exhaust, so I think I'll just get a stock replacement pump and test it out.

It didn't have any problem reving high in the low gears, but it was in the high gears. It was running fine earlier then progressively got worse tonight, just a little while ago I was having misfires and bucking at 3k too.

Exhaust is stock, needing replacement, but the only 'holes' are right before the two mufflers. Temperature-wise, the pipes were uniform in temperature, hopefully confirming that there aren't any obstructions or dead animals stuck in there.

it sounds like limp mode to me..
you get an error code sequence from the engine light after grounding the green plug under the hood?

No check lights. It really did feel like the tank was empty and the condition became worse, the symptoms creeping lower and lower into the power band. I'm wagering it's just a dead ten year old fuel pump. I swapped it after pulling the car out of the weeds in '08, and then it spent most of it's time sitting for the past 8 years. I'm waiting for a new fuel pump to arrive tomorrow. I'll swap that out, along with a new set of plugs, and see how it works out.

Do you have a fuel pressure gauge? It's pretty easy to confirm a faulty fuel pump. Just saying, it could be something else. Guessing can get needlessly expensive.

It was the fuel pump.
Installed a new one and now, after cleaning the terminals, I have a fuel gauge that works too.

Bad plug wires will miss under load.

it was the fuel pump.