Originally Posted by Redbul (Post 12650532)

The car is LHD, so the USDM FSM can be used as a guide for the hooking up of spark plug leads and the coil harness.

I usually chime in when the car is JDM Version 4 or newer, because Mazda changed the mounting order of the coils, and if an owner is unaware of that, they could hook things up the old way, and cause big problems.

(The coil harness for the LHD cars is a bit complex, with its own wired in grounding lines - probably best to replace. Note that the newer JDM coil harness is more simple, but will not work well on the USDM set-up. Make sure you have the correct coil harness.)

Meanwhile, it is very brave to try to retain the original set-up with all sequential twin turbos and all the emission stuff.

A very large number of owners will have given up that effort long ago.

There are just too many gremlins. Also consider that your stock ecu may be over 30 years old.

One of my first questions, these days, is, "how old is your gas?"

Ethanol in the gas these days means it attracts water if sitting too long.

Next, is the check engine light on?

If yes, don't ignore it, you need to check codes.

There may be up to 50 different malfunctions the codes can make you aware of, and save you going through the engine bay checking all the solenoids, sensors and other components one by one.

Even though it is a new motor, run a compression test.

The dash wiring has two grounding points, those could affect the gauges.

There is new diagnostic software for PFC, that may be able to analysis and essentially self tune the PFC to your set up.

Originally Posted by Redbul (Post 12650533)

In certain cricumstances the ECU will put the car into "Limp Mode". The ECU might not like that you removed the EGR valve.

Originally Posted by Redbul (Post 12650551)

Here is a pic of the earlier version of coil harness. Note grounding wire. This grounding wire formed a direct ground for each of the coil wires.

https://cimg4.ibsrv.net/gimg/www.rx7...899897acc.jpeg

Originally Posted by Redbul (Post 12650563)

Looks like Nengun sells both versions, old and new.

https://www.nengun.com/oem/mazda/n3f1-18-051

Originally Posted by scotty305 (Post 12650530)

I haven't double-checked this myself, but the factory wiring diagram says that the tachometer ground comes from 'ground point 3' on the engine harness, which is a ring terminal that bolts to the upper intake manifold near the firewall. It's a spot that would be easy to miss if you're not careful. That part of the engine harness is somewhat near the downpipe so it might have gotten brittle with time and heat. The ground signal wire for the tacho also goes through connector X-14 which is one of the rectangular connectors inside the cabin behind the dash near the ECU. There are at least two of those connectors in that area that usually get disconnected when removing an engine, so it would be a good idea to look up in that firewall/dash/ECU area to make sure everything is connected.

If you're confident the tacho ground is good, I would take a close look at the CAS (crank angle and cam angle) connectors and sensors, and their brackets, and the trigger wheel on the crankshaft pulley. The ECU sends the engine speed signal to the tachometer, and it measures engine speed using the two CAS sensors near the crankshaft pulley. If those wires have problems, or the sensors are not mounted securely, or the crankshaft pulley is not installed correctly that could cause problems.

Other problems I've heard that cause rough idle could be a MAP sensor vacuum line unplugged, or the MAP sensor itself not plugged in to the harness. The coolant sensor is the same plug as the fuel temperature sensor, and the harness is just long enough that the plugs could be connected to the wrong sensors. That would give the engine the wrong fueling which could make it run rough.

I'm surprised Redbul hasn't mentioned spark plug wires, if those are not installed properly the engine might run rough. It's hard to see that area without removing the intake pipe near the throttle, but the wires from the two-post leading coil need to connect to the lower (leading) spark plugs. The leading wires can go to either front or rear rotor, with the stock two-post leading coil both the front and rear leading plugs fire at the same time. The single-post trailing coils go to the top (trailing) spark plugs. As a test, you could disconnect the trailing spark plug wires and see if the engine runs any better or worse. They shouldn't make a huge difference, and having the trailings connected should not make the engine run rough.

Edit, here's a video showing that ground location on my car: https://youtu.be/6SzsJq_0KpE

Originally Posted by despistao (Post 12650583)

Regarding the ground connections on the upper manifold, one I think is connected underneath (it's anchored, but I haven't lifted the manifold to see where). The other ground connection is different from yours; I've attached a photo.


Could the air conditioning compressor be the problem? I've disabled it since it seized up, and I have the impression that the engine is running more smoothly

Originally Posted by scotty305 (Post 12650610)

The ground connection on my car is Mazda part number FD02-67-E70 , it is was part of an update that was intended to address the '3000 RPM hesitation' that people talked about on this forum 15-20 years ago. I didn't notice any change in my car's behavior when I installed it, but that was back in 2005 when all the parts were less old than they are today.

If you think the AC compressor is causing problems, it should be possible to temporarily remove the belt that drives the AC and the power steering. I would not drive the car with the power steering disabled, it will be very hard to turn the wheel with the pump in place but not spinning.

Originally Posted by Redbul (Post 12650623)

Is the pulley for the A/C pump turning freely? If not it could be resisting the fan belt that runs over it.