Heres a bit of a backstory, I rebuilt the engine in my FD put it back in started it up drove it for around 1k miles and it had oil consumption issues which ended up being the oil control rings. My first time rebuilding one of these I was expecting to have to re-do something.

So I removed the engine harness draped it over the side and pulled the engine, replaced the oil control rings, re-installed the engine. Reconnected the wiring harness and no fuel injector pulse, no spark = no start. All I have done is unplugged the harness and plugged everything back in. The car ran perfectly fine and was driven into the garage to do the engine work.

What I know so far
- the car had a weak spark and once I fiddled with a few wires around the CAS sensor it went away.
- cas sensor sends rpm signal ok
- injector circuit fine (noid light illuminates when I ground the circuit myself) but when cranking no injector pulse from a noid light.
- fuel at the injectors
- heres a very confusing one - injectors fire when in a bottle out of the engine. but when installed after cranking spark plugs are dry.
- good continuity from the connector at the cas sensor to the ecu

any ideas for things to check that I might have missed?

 

First, just FYI, pull the harness with the engine. It makes life SO much easier. You just have a handful of connectors to unplug by the ECU and you can easily pull the whole harness out. Then you can work on everything on the engine stand instead of bent over the car.

What exactly was wrong with the oil control rings? Just curious.

All that said, the first thing is to look for the tach bouncing as you go to crank the car. If you see that then the ECU is seeing a timing signal which is good.

The crank angle sensor connectors, when looking from the front of the car, should have the white connector on the left side, grey on the right.

That could be the root of things. Either that or you aren't getting any fuel to the injectors.

Dale

 

Thats a good point, and will definitely do that in future.

Oil control rings - I didn't replace the o-rings in them. Rookie mistake I am told.

So my dash has always been completely dead (apart form the oil pressure gauge, weirdly) so I've not been able to check if the tach is bouncing but the car is running a power fc and it shows and rpm when cranking, I'm assuming thats the same signal as the dash would be getting?

Connectors were the correct way around but the wiring was falling to bits at the connector so we've just got the wires on pins at the moment whilst I'm waiting for replacement connectors. And I definitely have fuel in the rails to the injectors - a split injector o ring when I first tried to fire it back up verified that.

I'm honestly totally stumped by it, I took the case off the power fc and it all looks brand new inside theres no obvious issues with the board in it to me anyway.

Are there any other connectors on that main harness that if they weren't connected would cause the car not to start? (single turbo set up)

 

Got a stock ECU to verify just to rule out the PFC before you dive into the harness?

 

I haven't unfortunately where I am in the UK I don't know anyone else with one and there aren't any rotary specialists anywhere near me.

Is there any other way of testing the pfc without swapping out a known good ecu?

 

If you have a patch harness you can potentially probe the pins to see if you are getting any injector signal right out of the ECU. Probably a small chance it is the PFC, but it is nice to rule it out first if you have a spare ECU.

 

I don't have a patch harness unfortunately, I'm going to try and find an ecu to test it with though and see if it is the power fc. I mean I drove it into the garage, unplugged the harness on the engine, haven't touched the pfc had it all connected back up within about 3 days and now something has gone wrong but I'm at a complete loss as to what ...

 

As inferred above, the 1st rule of troubleshooting is "inspect what you did just before the issue." So I'm suspecting something that has failed in the wiring harness just due to disconnecting and reconnecting.

 

I'm no expert with Rx7 and still new to understanding their diagrams. If i were in your situation i would isolate the injectors circuit and start testing everything. I've done my best to highlight the areas i would check. This is a 94 diagrams and im not sure if its different from the UK models.

Without power i would disconnect the connectors and start testing continuity and resistance to trace out what pin goes where and make sure it isn't internally touching a wire it should not. This is also a good time to test the each wire for a connection to ground. This helps verify that no shorts are present and your actual ground is proper as well.

Connector X-05 will be a good place to look to make sure its actually plugged in. And of course just rule out the simple stuff like fuses and relays.

Once you feel confident in the circuit you can hook up the battery and start testing the voltage flow. This is where it gets challenging for me since im not sure if you'll just need to be key on or cranking to get a proper reading.

Best of luck to you.

 

Did you attach the 2 ground terminals on the engine harness to the top of the motor? Yes the cas may be plugged in (white plug on top and gray on bottom) but are the mount tabs for the sensors broken? Is the trigger wheel installed correctly? Are the primary injector plugs on the correct injector? Is the fuel temp and water temp plug switched around? Did you reconnect the ground on the charge harness and on the back of the uim? Is your map sensor vacuum line installed correctly? Are all your vacuum lines installed correctly?

There are quite a few simpler possibilities here outside of the big stuff. Can we start by ruling out the basics?

 

Thanks for the suggestions and the attached diagrams, really appreciate it.

I ended up buying another engine harness replaced that and the car fired right up. I'm assuming that there were some issues with the wiring internally in the harness and when I've moved it around to get it off and back on the engine its not been very happy about it.

New issue though is a lumpy idle, hesitation/stuttering at partial throttle.Unplugging the AWS helped a lot with the idle, I'm assuming the connector on my old harness never worked looking back. My TPS is also pretty out of whack I think, we tested it and it read around 2v fully closed and 10v fully open... Thinking that might be the issue with the weird running conditions.