Hello,

Looking for some help - this is kind of a long post but I am trying to provide all the info I can. I'm new to this forum so I've been forced to post this here.

I'm using a 13b engine with manual transmission from an 86 N/A in my home built car. I have the stock ECU sensors - atm. pressure sensor, boost sensor, water temperature sensor, air temperature sensor and air flow meter. Also using the original solenoid valves except for the egr one which I got rid of (using block-off plate where the egr was). Fuel pump is stock. I rebuilt the engine using an Atkins rebuild kit and some used rotor housings + irons from rotary resurrection. I set the timing using the “yellow” mark on the front pulley as instructed with a simple timing light. The engine runs good once it is up to operating temperature but I have to fiddle with the throttle (open slightly) to start it from cold and keep the throttle open slightly with the engine rpm up over 1k to keep it running until it is up to temperature. Once up to temperature it idles fine at around 800rpm and revs up fine too.

So I'm trying to figure out why it won't start and idle when cold.

I cut some wires from the original ECU wiring harness. Here is a list of wires that I cut at the ECU (terminal names according to the factory service manual)

1A: Self Diagnosis Checker
1B: Self Diagnosis Checker
1D: Self Diagnosis Checker
1E: AC switch (input)
1F: AC main relay (output)
1G: Neutral switch (input)
1H: Water temperature switch (input) - grounded this
1J: Initial set coupler (input)
1K: Shift indicator light (output)
1L: Clutch switch (input) - wired 12V to this
1R: Power steering switch (input)
1W: Heat hazard sensor (input)
2N: EGR solenoid valve (output)
3B: Starter switch (input)

I started checking things according to the fsm;

Throttle sensor - I don't have a checker lamp but I adjusted this to 1k-ohm when resting.

Anti-afterburner valve - air is not sucked into the air control valve when decelerating from high rpm's like it should.

Switching solenoid valve - air is sucked into the port opening of the solenoid valve at idle and at increased engine speed. If I remove the throttle sensor, air is not sucked into the port opening at idle or at increased engine speed (fsm says it should not suck air over 1000-1200 rpm).

Relief solenoid valve - when I disconnect the throttle sensor and increase the engine speed, air is sucked into the port opening all the time - it doesn't stop sucking air after 120 sec like it's supposed to. Decreasing the engine speed to idle, air continues to suck in continuously.

Split air solenoid valve - with ignition on but car not running voltage is 12V at LB terminal when in 5th gear even though it should be below 2.5V (I am getting the correct reduced voltage input ~1.5V at the ECU when in 5th gear).

Port air solenoid valve - voltmeter reading while idling is 2.0V and is 13V with throttle sensor disconnected (this is correct according to fsm.

Purge valve (on oil filler pipe) works correct.

Fuel cut operation (deceleration control) works correct when the throttle sensor is pushed in.

BAC Valve - with the initial set coupler jumped (I actually removed this coupler so I just ground pin 1J), when I disconnect the BACV connector the engine speed is not decreased, so I'm not sure if it is doing anything.

Pressure regulator control solenoid valve (for fuel pressure regulator) – This is apparently part of a hot start assist system. I put a 2-3k-ohm resistor to the terminals of the temperature sensor connector to simulate a hot engine - air is sucked into the solenoid valve continuously even though it is supposed to not suck air for 90 seconds after starting the engine.

The air bypass solenoid valve never opens as it is supposed to for the first 17 seconds after start up. The wiring is good from the bypass valve to the bypass relay and there is 12V at the valve, but the ECU never grounds the relay as it is supposed to. I get a 12V reading at the BrY terminal all the time.

I checked each one of the solenoid valves individually, the BACV and the air bypass valve with 12V supply and ground and they all operate fine.

Water temperature (thermo) sensor - replaced with a new one and it works fine (getting 0.52V at pin 2I when at operating temp).

Air flow meter - I did not check resistance across any of the terminals, but I know the fuel pump switch works since the pump comes on when the measuring plate is opened and I get 2.5V on pin 2E at idle (4V when not idling).

I checked for continuity all the signal wires from these various components to the ECU and they are good.

The thermo wax unit that controls the throttle diaphragm is working correctly.

The air pump seems to be working, it blows plenty of air.

The auxiliary port valves and actuators rotate smoothly, I cleaned everything before reassembling the engine, the actuators work fine with compressed air put to them.

Voltage from the alternator is around 14V when idling.

I checked the ECU voltage readings at idle and with just the ignition on and the only ones that are not within the ranges listed in the fsm are;
1L: wired 12V to this so it’s 12V always
2K: 12V always, even in 5th gear (should be below 2.5V in 5th)

So my questions are;

Are any of the wires I cut required to properly operate the various solenoid valves? As far as I can tell, these inputs are mostly to increase idle speed slightly but I’m not sure about that starter switch pin.

Why are the solenoids not working as they should?

Is there a way to test my ECU to make sure it is functioning properly?

Why won't the engine idle when it's cold?

Here are a couple pictures - one of my build and one of the ECU.

 

This is the longest Tech question I have ever Approved.
Help this Guy out,before he writes a Novel!

 

Atleast they wont be short on info!

 

Cutting pin 3B from the equation causes the ECU to rely on the AFM for guidance relative to how much fuel is used upon start up and this amount is very, very small. Normally, a cold engine requires more fuel than a hot one. Repin 3B and see how it changes anything.

 

And w/regards to pin 2K you have a 5th gear switch known as the Over The Top Switch. This switch is responsible for causing the voltage at the Split Air ECU pin to drop to the required levels.

 

The 5th gear / over the top switch is working - I'm getting the correct reduced voltage input ~1.5V at pin 1I when in 5th gear, but not getting the reduced output at pin 2K. 2K is always at 12V.

Thanks for the info on the starter switch 3B - I'll have to reconnect. Looks like it's just jumpered to 3D the inhibitor switch pin. Do you think this will effect the bypass air valve function too?

 

The Air Bypass Valve that is instrumental in the 17 second high rpm warm up can be averted by starting the car in gear I believe so perhaps the ECU believes that this is occuring in your case.

 

And the Air Bypass does not cause the 17 second high rev start up on its own as the BAC also is involved w/this process. If the Air Bypass were to be disconnected, the 17 second high rev could still occur, but if the opposite were to occur such that the Air Bypass was connected, but the BAC was not then the high rev cannot happen.

 

why would it think it's in gear? maybe because I ran 12V to the clutch switch pin?

 

Both the BACV and the bypass valves are connected. I wired the starter switch pin back in and now it starts without touching the throttle but only stays running for maybe 3-4 seconds, then starts to cough and stalls. If I disonnect the wires at the air bypass valve and run 12V and ground to it, it runs great at the fast idle like it's supposed to, but the ECU still won't do it.

 

Possibly, but as noted, if the BAC is not working properly then the engine cannot goes through its normal warm up process. Another possibility, albeit remote, would be the ground wire in the thermoswitch wiring is really not grounded.

EDIT: Are you grounding the temp switch directly at the ECU pin 1H or via the wiring related to the system?

Double EDIT: Is this an NA or Turbo? The NA incorporates an Air Bypass Relay while the turbo does not.

 

It's grounded right at the ECU. Would cutting the neutral switch make it think it's in gear? I am getting 12V at that pin (1G). If I want to make it think it's in neutral should I should probably ground that.

It's a N/A

 

That could be the cause because by receiving 12 volts at pin 1G the ECU is being told the car is being started in gear as opposed to neutral, which then cancels out the 17 second process as I understand it.

 

so now the question is, if I ground that pin, the ecu will think it's always in neutral so how will that effect the ecu output when I'm actually in gear - like the 5th gear/split air solenoid? Maybe I should look into re-wiring to the actual neutral switch.

 

The Neutral Switch affects many things as explained in the FSM, but it does not go into detail as to what extent the affect is. There's a post in the following link which specifies which things it affects by Hailers. You probably should rewire the switch back to a more normal approach.

https://www.rx7club.com/2nd-generati...tch-do-125743/

 

OK, since I last posted and Satch gave some advice, I've wired the neutral switch back in and while I was doing that I found that the reverse/over the top switch was bad so I replaced that with a new one and rewired it. Now I'm having other issues. The cold start system seems to be working since the air bypass valve opens when I try to start it, but now it's flooding badly. I thought maybe it was a bad fuel injector so I replaced all of them with remanufactured ones. It's still flooding as soon as I go to start it. I can only get it to start if I disconnect my fuel pump and turn it over for a while, then it will eventually start and run ok until the fuel is used up, then I go an reconnect the fuel pump and try again but always have the same problem - it fires maybe twice and then its flooded. So much that there is fuel dripping out of the exhaust. The injector replacement did nothing. Any ideas on what to check? Could it just be too much fuel pressure? I'm using the original fuel pump and regulator that's mounted on the fuel rail.

 

Maybe this is your problem.

"Pressure regulator control solenoid valve (for fuel pressure regulator) – This is apparently part of a hot start assist system. I put a 2-3k-ohm resistor to the terminals of the temperature sensor connector to simulate a hot engine - air is sucked into the solenoid valve continuously even though it is supposed to not suck air for 90 seconds after starting the engine.

Your hot start assist system migh be assisting your starts regardless of whether the engine is hot or cold. The system is normally supposed to add more fuel on hot starts. If it's working all the time then it's adding more fuel than needed during your cold starts. This is just a thought."

 

well I can try to disconnect the hot start assist and try again. I didn't think of this before but after some searching, maybe my spark plug wires are bad? Do you know what the resistance should be for plug wires?

 

I believe the FSM states 16k per meter of wire.

 

I checked the fuel pressure and found that it is a bit high. I'm getting 42psi injection pressure and the fsm says 34.1-39.8, so I'm thinking maybe that is causing the injectors to leak. Even the reman injectors that I just put in are leaking. I noticed something; when I stop the pump, the pressure in the line drops quickly to about 25-30psi and then slowly down to about 5. I'm pretty sure this shouldn't happen. Shouldn't the pressure stay up around 34-39 psi even after the pump stops? I'm doing this without running the engine (jumping the connector to the air flow meter). I'm going to put in a new pressure regulator and see if that helps. I know the injectors are leaking because after my testing, I turned over the engine by hand and fuel gushed out of the spark plug holes. I'm assuming it's because the pressure is too high, but why would they leak all the way down to 5psi?

 

Post #25

https://www.rx7club.com/2nd-generati...-1012775/page2

Could also be a leak in the tank as also mentioned in the thread.

 

Were you directing me to post #24 in that string? I see there RotaryEvolution said " ...fuel pressure between the fuel filter and the hard line to the engine. it should read about 32psi with the engine running idle and about 40 psi without the engine running, clamp the return hose and it should read about 90psi."
I'm getting 86 psi with the line clamped, so that's good, and 42 psi without the engine running, so maybe it's not too high? I can't get it to idle so I can't get a reading when idling.

 

I linked the wrong thread.

https://www.rx7club.com/2nd-generati...roblem-995917/

 

I don't have a check valve in the fuel line so that's the reason pressure wouldn't be trapped. (I don't think I need one). I did clamp the fuel line right after the fuel filter (pressure gauge downstream of the clamp) and the pressure dropped quickly to about 25psi, so its either leaking through the injectors or the pressure regulator. Shouldn't the injectors be able to take up to a little over 40 psi without leaking?

 

^The injectors should be able to handle it. And are you aware of the compression of your engine for low compression causes hard starts and could contribute to a flooding situation w/o it necessarily being the fault of the injectors.