SonofaMitch

The title gets the gist across, the car has a fairly noticeable vibration at idle after it warms up and the idle drops down to the 850 range but is perfectly smooth across the rest of the rev range and at the cold start idle range.
I am new to the car so I'm not sure how much vibration is normal, also no cel.

Just rebuilt the car with a new reman about 50 miles on it rn, did coils plugs wires, MAF and o2 sensors over the course of the engine out.
The only thing that gave me trouble was the injector wiring, my car came to me in pieces and I couldn't find a reference that matched the wire colors I had so I had to make educated guesses on which wire went to each injector based on the shape of the loom, could that have any bearing?

thanks!

Loki

iTrader: (1)

Some vibration is normal, especially when the air conditioning compressor cycles on. Difficult to express how much is too much, maybe make a video? Do you feel it in the seat, the mirrors, the shifter?

Automatic or manual?

SonofaMitch

Alright so I went to go record some video of the idle and I had a check engine light for misfire and bank 1 running rich and the car was really misbehaving, it picked up a hunting idle and really wants to die on tip-in and won't catch the RPMs after you let off.
Pulled out my OBD scanner and looked at AFR and fuel trims, short term trims were -25 and long term were -14 or so across 800-6000 rpm. The MAF and both o2 sensors are new so I trust their readings.
I had just done the 20 pedal stomp yesterday because the battery had run flat.
I'm kinda in over my head here tbh.
It is a 2007 MT if that helps at all.

Loki

iTrader: (1)

What was the airflow g/sec at idle? Ignore anything that happens above idle for now.
You could have miswired your injectors, your coils, or left a vacuum leak in the intake. All of those are common mistakes when putting an engine in.

Since it's trimming full back and still running rich, my bet is injectors.

SonofaMitch

A few data points at idle immediately after resetting fuel trims.
I had to reset the fuel trims to get the car to run ok-ish, it looks like the maf was reading between 5.1 and 5.5 g/s at idle.

Loki

iTrader: (1)

The airflow is right but you're way overfueling. It's at -24% fuel trim and still running 12 AFR. I really think the injectors are misplaced or misconnected, with the secondaries firing in place of primaries. It's an easy mistake to make, the wire colour coding is like beige and yellow.

mazdaverx7

iTrader: (6)

Also, check for vacuum leaks. A vacuum leak will throw off the fuel trims quite a bit and you will see numbers like that.

SonofaMitch

I checked the injector wiring against the schematic by checking which connector went to which PCM pins and it was correct, I also didn't find anything that looked like it could be a vacuum leak, all the gaskets were in place and all hoses connected.
Personally I suspect a leaky or stuck injector? so I'm looking for a set of injectors to swap in to see if that helps.

CaymanRotary

you need to do a smoke test to see where the leak is. Everything would look normal just visually inspecting because you won’t see the leak without the smoke. Don’t waste money guessing what’s wrong and swapping parts. You want to run tests to help you find out what is actually wrong.

Loki

iTrader: (1)

A vacuum leak would give you + fuel trims, not -. So I don't think it's that. Leaky injector would do it. You might pull the spark plugs to see if one rotor is burning richer than another, and cut your list of suspects in half. If they're both equally rich, perhaps the wiring is correct but the injector sizes are flipped.

mazdaverx7

iTrader: (6)

Ah, good call, I just looked again and saw he had negative numbers. Also good call on the possibility of the injectors being in the wrong spots. I could see that happeneing!

SonofaMitch

Its a six-port so I should have four yellows that are the same and two reds right? And the four yellows are one the same rail with the reds on a second shorter rail?
I went off this post for the positions, https://www.rx8club.com/series-i-tec...r-info-150432/
and matched the pins to these references https://www.rx8club.com/series-i-tec...iagram-118627/

I'm going to pull the plugs and take a look today thanks!

SonofaMitch

I got around to pulling the plugs today, and both trailing plugs had carbon deposits and smelled of fuel. I also borrowed a full set of known good injectors and with them swapped in the problem persisted identically.
Could a fuel pressure regulator failure cause the issues I'm seeing if the regulator fails high?

Loki

iTrader: (1)

That sounds like further symptoms of overfueling but not the root cause. I doubt it's the FPR either, it's in the pump and not really a common point of failure, but of course is fuel pressure test would confirm.
Seeing as both trailing plugs are wet, the issue is upstream from injectors so it's not a bad idea.








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SonofaMitch

Does the Rx8 report the fuel pressure to the PCM in a data point that I can get over obd2? or would I have to get a pressure tester from somewhere?

SonofaMitch

So I got ahold of a fuel pressure tester and the fuel pressure tested at 58-62 psi which from what I found is where it should be.
I don't know the history of the car but could something have been done to the PCM to cause this issue? I may just cut my losses and send it to a local mechanic at this point lol.

Loki

iTrader: (1)

There isn't a fuel pressure sensor. So if the pressure is right,and the ECU is pulling fuel as much as it can and still running rich, there's only one explanation I can think of : the injectors are still miswired. I know you said you checked them, and tried other injectors, with same result, so it's not the injectors themselves. They might be in the right positions but have the wrong wiring harness connections. Probably not what you want to hear, but I can't think of another way to explain this. We've eliminated everything else.

The ECU could have been messed with but it would be very strange to increase the fuel supply at idle. That would mean someone had fitted smaller than stock injectors and was trying to compensate.

JoeBlow

Check for spark before you worry about fuel injectors. I had the exact same symptoms and it was a bad coil. If the fuel is not igniting then theO2 sensor is going to show too rich.
After fixing the spark issue and resetting ECU it took a while to start running right. I had to take the air filter out and drive around the block. Put the air filter back in and drove for a bit and everything was back to normal.