Plug Unknown 6000 RPM Limit
 

Hi Guys & Girls,

Car is 1989 NA RX-7 Coupe , Australian Version and I have one problem which I will soon fix with a match and some petrol if I can't sort it out. I rebuilt the standard motor two years ago and have had this problem since. As I am now using the car only on the weekends I want to fix it.

Here Goes
When engine is revved during driveway test i can rev to redline so long as I don't give too much throttle (ie I slowly build up revs)

When I do it any other way the engine misses and seems to be rev limited to about 6000rpm or so. Also happens when driving.

Checked TPS, AFM, etc etc. Have added extra grounds as per other posts and no luck.

After testing everything I found that O2 sensor is not working, fitted voltage divider to give 0.8 volts to fool ecu - still not working.

Pulled off inlet to check wiring and found plug as per pic (Blue with Black trace), what is this for?

I have tested ecu voltages and found this problem occurs when VDI solenoid is activated, however no power to secondary solenoid or secondary injectors(from ecu) occurs at all. Also noticed reversing lamps do not come on when I put car in reverse.

The questions are:- What does the ecu need to activate the secondary ports and injectors? What effect would the reverse switch have if it didn't work? What is this spare plug for?

Help!!!!!

Checked for vac leaks? Perhaps a leak that occurs when there is load on the engine...

Also have you checked timing?

Are both coils working?

Checked both coils and timing ok, set timing using procedure from FSM. Also made up led indicator lamps to check ecu codes and found no problem, tested by removing air temp sensor and code flashed as per manual.

Engine will rev to limiter (approx 8500rpm) IF the engine is in neutral (no load) and I slowly depress throttle. Once it is there though, if I put any more throttle it misses and drops to around 6000rpm.

Don't think it's a vacuum leak as most of these have been removed to test and idle speed always goes up slightly when I do it. I have manually checked all solenoids by adding + & -ve wires to see if VDI and 6th ports are working and all ok. Air pump is ok too.

Am still working on it, need to know what plug is for so I can re-install manifold and try some other things.

DOZ

Have you checked the fuel pump voltage? Low voltage will cause problems.

2ndary ports do not work unless the engine is under load. You need to be driving or on a dyno for them to work.

You reverse lights are probably either a bad reverse switch on the tranny or disconnected reverse wires at the tranny

I figured out that the unknown plug goes to a yellow multi pin connector in the footwell near the ecu, from here it goes nowhere (there is no wire connected to the other side).

So the question/s are now:-

When do the secondary ports open? (under load I can test) ie what conditions must be satisfied (rpm/temp/gear/etc)

When does the VDI port open, as above?

When do the secondary injectors start to function?

I know that guys on this forum have probed their ecu's to tell them this sort of info, I want to know so I can see what I am getting is consistent with something thats known.

Thanks

DOZ

I think sec injectors come on around 3500-4000 somewhere there..

Interesting problems I'll keep thinking about it lol...

3850 RPM with engine under load, warm, tranny not in neutral, and air pump hooked up.

5200 RPM w/ engine warm, and under heavy load.

3500-3800

Its all in the FSM, no need for probeing, Mazda has already done it for you.

the unknown plug looks like the plug that plugs into the back of the water pump, check and see if there is a sensor with nothing connected to it on the back of the water pump housing

Thanks for the help, I found the plug is not connected to anything, This may have been for an option or Automatic maybe, in Australia we only had turbo, NA and convertible, the only option/s were A/C and Auto trans (so far as I know).

Icemark, as you said the secondary ports operate at 3850 in gear etc, I would have thought that both the ports and injectors would operate at the same time? Saying that, maybe I am not getting the out of neutral condition (switch broken or what ever will have to check). It's unsual though as I remember that I could easily rev the car in neutral before I took the engine out.

I still plan to add led indicators to check switching of VDI etc. As I stated earlier, I had probed the ECU and found the miss/rpm limit occurs when the VDI valve is operating, this happens at slightly different rpm depending on load.

Will keep working on it and hopefully fix it soon.

DOZ

I found the problem was caused by faulty fuel injectors. For some reason, while the motor was apart, two of them (the secondaries) decided to stop working, they were open circuit.

What I actually think happened was the fuel turned to jelly (jello) inside the injectors and caused them to stick. This burnt out the coil and made them go open circuit.

The problem of fuel going to jelly was involved with a similar issue on my two stroke bike, the choke mechanism gummed up over summer and didn't work. Using acetone cleaner solved that problem so I suspect if I had cleaned the injectors before starting the engine they may have been ok.

Anyway, runs good and this was fixed ages ago now

Cheers

Daniel