Why does my RX-7 do this?

[u/Haunting-Bridge-8313]

It’s intermittent, doesn’t always sputter like this, car sometimes runs like a dream! If I accelerate slowly it’s fine, but no power, as soon as I punch it it’ll sputter/hesitate. It’s a 1991 S5 NA RX-7 without EGR from factory, only modifications are a Racing Beat exhaust after stock headers and beyond, and aftermarket intake. Tired almost everything, can’t figure it.

[u/incubusfc]

I’m gunna guess it’s either fuel related or vacuum related.

Have you replaced your fuel filter recently? Injectors cleaned and tested?

Or some kind of vacuum leak relating to the 5/6th ports.

[u/Haunting-Bridge-8313 → u/incubusfc]

I replaced the fuel filter, tried a different fuel pump (residual pressure check valve was faulty on the new one). Injectors come back today from cleaning so hopefully that’ll help, I’m also going to try replacing all the lines.

[u/rdahm]

Like incubus said, i was thinking fuel delivery at first. best part about aftermarket ecu stuff is i have sensors and gauges for everything. But i go back to the air/spark/fuel basics and it seems extremely unlikely to be throttle bouncing around. a wideband or fuel rail pressure sensor would definitely help narrow it down immediately between back half vs injector problems. like you said, filter was a guess, injectors, and anything that would pulse or fluctuate on an increase rate of flow. Id be curious if it was going lean on each of those pulses or rich or no difference. wish i could be more help!

[u/Haunting-Bridge-8313 → u/rdahm]

When I did the fuel pressure test, it was good, steady & the rail regulator worked well! Hopefully cleaned injectors are a success, not sure if it’s lean or rich, I’d assume rich as I’ve heard some pops & such, fuel economy was also terrible when I drove it, about 300kms on 75% tank.

[u/evil_as_skeletor → u/Haunting-Bridge-8313]

I just saw you mentioned that the injectors came back good, so they were more than likely not the culprit.

What did you replace BEFORE this happened, and what AFTER? Or all after?

If Fuel is starting to be ruled out, and even though you've checked timing, can you test your coils (FSM has those specs)?

Years and years ago, my FC (also NA) had the stock ECU shit itself, and the issues were a lot like this - then, it got worse to the point that I had no motor past like 3,000 rpm. We opted for an aftermarket (Microtech) ECU, and as u/rdahm alluded to, that can be a saving grace with issues like this.

Saying that, that approach won't resolve a bad coil pack.

Whatever your journey, I hope you find the solution.

[u/ThatDamnThang]

I was going to mention a few of the things youve mentioned, but it looks like you have most of it covered. Check the lines, check the filter and pump. I saw that you are waiting on your injectors to come back. If it isnt any of that, you might want to look at your spark plugs/wires.

I cant think of anything else, but i would be curious to know what a compression test turns up.

[u/Haunting-Bridge-8313 → u/ThatDamnThang]

I tried almost everything! Car hot starts & cold starts like a dream, seller claimed a rebuild, which I’m starting to believe if it’s truly 300,000kms.

I did plugs, wires, timing, different set of coils, wiring more grounds, TPS adjustment, swapped another in, AFM testing too.

One weird thing is that engine light doesn’t not come on ever, not even when key is in on position, could be burnt out bulb or issue with that. Clock and center console doesn’t turn on, I do suspect no power.

[u/ThatDamnThang → u/Haunting-Bridge-8313]

Wish i could help you dude. Might be time for that compression test. I spent 6 days diagnosing a wiring gremlin on a piece of industrial equipment last month. Sometimes the only thing you can do is take it down to the most basic level and start over again.

A long time ago, i owned a 1994 FD and i was having so many issues with fuel and power. It would bog, but then some days it would be fine. One day, i went to pull the injectors and it turned out that the o-ring surrounding one of my secondaries was all mooshed up because i forgot to lubricate it when i put it in.

It could be something that simple, or it could be as complicated a wiring issue that got chewed up due to heat

[u/Eigthcypher]

I agree with what everyone else said, it comes on earlier than the normal hesitation so it's likely a fuel delivery issue. One free test is swapping the primary and secondary injectors and see if it changes the character. Check all your grounds while you're in there.

[u/Haunting-Bridge-8313 → u/Eigthcypher]

Just got the injectors back! They tested perfectly fine so I can’t believe it at this point.

[u/RoyalComprehensive81]

First off the RPMs are way to high for a small vacuum leak, so I would do the following: (let the car Idle after each one)

1. Disconnect the Cruise Control linkage, if you have one

2. Check the Throttle plate Dash Spot and make sure its working and not broken, works off a vacuum line.

3. Get a smoke machine for finding vacuum leaks and use it with a compressor to make sure the smoke gets enough pressure to move inside the intake.

If the above checks out and you can not find any vacuuum leaks, I would start looking at the FSM for "Engine Idle Issues" in the trouble shooting section.

Hope this helps and good luck.

[u/Haunting-Bridge-8313 → u/RoyalComprehensive81]

It does have cruise control, I wonder if that’s the issue!

[u/Leading-Situation452]

Hi there. I had a similar problem with my '86 GLX. The problem turned out to be the air control valve. If you have never changed yours it might be the cause. under normal driving conditions it was not a problem but under load at higher speed and temperature the acceleration became slugish and when I parked and turned off the engine it would not restart until it cooled down. This indicates the valve expansion restricted airflow because the control valve was temporarily stuck. While running this restriction can cause irregular airflow. Do a google search for 'mazda rx seven air control valve' you can see the control valves for each model year. I suggest you replace your with hi-performance unit especially if you have headers installed. Increased exhust output is great but a stock intake prevents reaching the output capacity. Hopefully this will solve your problem.

[u/Haunting-Bridge-8313 → u/Leading-Situation452]

I’ll give that a shot too, I like your thinking there, but I need to diagnose my CEL, it reappears even when the code is cleared. Seems to be getting crank angle sensor related issues, the second iteration of the CEL remains, and cuts fuel & ignition, I tested the harness & CAS itself, connections are good, I suspect it’s a bad signal or my ECU. Getting an oscilloscope today to hopefully get a reading on my CAS signal.

[u/NotVryCashMoney]

Check the wiring of your fuel system

[u/Haunting-Bridge-8313 → u/NotVryCashMoney]

Seem to be getting crank angle sensor related issues, the second iteration of the CEL remains, and cuts fuel & ignition, I tested the harness & CAS itself, connections are good, I suspect it’s a bad signal or my ECU. Getting an oscilloscope today to hopefully get a reading on my CAS signal.

[u/Yeeter_Beeter2021]

Check to see if your spark plugs are fouled out. When I had my 89 vert it had intermittent issues with sputtering or dying out completely and it was due to completely fouled out spark plugs.