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Discussion Starter · #1 ·
Just completed rebuilding the 4age after doing it first time in the spring. Struggled with the main harness and found a few points that needed to be refreshed and fixed. Bought spare ECUs and other parts but didn't help.

That was after the igniter mysteriously stopped working (no spark) and no signals going to the ECU.

Then got it running after weeks of digging into the various systems and trying different ECUs - now have two or three working ECU.

However I did not follow the coolant bleed process correctly and overheated the engine, spun a bearing and did rebuild 2.0. Sourced a 'new' crankshaft, took to shop and checked for straightness, magnaflux for cracks and polished.

That all said, got into the heads/ valves more during rebuild 2.0. Got timing just about perfect and checked the gaps between the cam lobes and valves. A couple were out of spec and lucky i had a spare head so replaced a couple of the shims and happy with the timing and valve clearances

After all the work and getting engine 2.0 back into the engine, I hooked up all the bits except coolant and bang started after running the engine with igniter disconnected. Idea is to move the oil and build up pressure.

So short story, long, i'm now getting on start up, immediate start (got fuel and spark) rev to 3,000 rpms then dies....

Checked COR relay, Spare ECU, spare COR relay and next going to dig into the engine codes.

Also using the gas pedal, there is no fuel (or feels that way) going in.

I've replaced new fuel filter, have 50 psi at the rail and injectors all firing. I had tested this and actually caught the car on fire... yeah... burned up a few parts and managed to put out fire, clean up and replace all the burn bits... only the third car I've caught on fire...

My problem is no fuel... could it be fuel relay? in the engine bay fuse box. Anywhere else to check?

Any thoughts on the start up, runs for two seconds, then stalls out?
 

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... have 50 psi at the rail and injectors all firing...

... I had tested this and actually caught the car on fire... yeah... burned up a few parts and managed to put out fire, clean up and replace all the burn bits... only the third car I've caught on fire...

My problem is no fuel... could it be fuel relay? in the engine bay fuse box. Anywhere else to check?

Any thoughts on the start up, runs for two seconds, then stalls out?
50 psi is too high. The spec is 24-31 psi idling, and 33-40 psi max, with the engine stopped or the vacuum compensation disconnected.

Are you bragging or complaining?

Is the fuel pump running? If you jump out the crash interlock, Fp to +B, then the pump will run with the ignition on, and you will be able to hear it. You can also check to see if the engine runs in this state.

When you are cranking, the starter signal turns on the fuel pump. As soon as the engine starts, the AFM takes over fuel pump control. This is the function of the COR relay. So, if the AFM or the COR is defective, then the engine may fire and then stall as soon as you release the starter. The jumper Fp to +B completely bypasses the COR, and so that is the first diagnostic for this sort of situation. You don't want to drive in that state, because the system is designed to prevent you from burning to death in the event of a crash. Although, that may be water over the dam to you.
 

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Discussion Starter · #3 ·
okay, will check out the afm and related wiring. and will confirm the idle and standing psi on the fuel rail... need to get idle first!!

and will perform the jump later this week...
 

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Have you checked that you're getting power at the injectors? Poke the afm door open a bit with the key set to ON. You should hear the fuel pump running and you should get 12v on one of the pins of each injector connector.
The initial start is probably from the cold start injector fuel being burned, it's a separate circuit from the main injectors. You get behavior like you described if something is up with the injectors or the circuit

If you have power at the injectors, make sure you have continuity from the other injector pin to the injector pins on the ecu.

If you don't have power at the injectors, make sure the injector resistor is getting power, it's the heat sink looking doober behind the battery. If you have power there, check to see if you have connection from it to the injectors.

If you don't have power there..... I'd have to look at the schematic, but I believe the circuit opening relay is what feeds the resistor.

In any case, your problem sounds injector power or wiring related.
 

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Discussion Starter · #5 ·
Excellent advice and amazed that there is the safety and technology in this 1980s (designed in the late 1970s??) beast...

Agree the initial start is just a squirt of fuel then no more juice from the injectors. Will definitely try the afm door

Checked two different (known working) COR relays with the cover off to watch the action. Looks like the relay 'closes' on cranking then opens again...

My harness quite old and brittle and did a thorough continuity check with all the circuits from ecu to the various inputs/outputs and grounds. So just the act of putting the harness back in all the twists and turns then putting some weight on the entire harness while installing the afm may create problems.

I did have it running for over half an hour bleeding the cooling system and going for multiple spins around the block. Ran well while my two buddies were taking it out then when I took the wheel, the MR tanked 250 feet from my house and started this crank and then die program!

Hope it's something minor and will go thru the injector power checks as well.

Super advice and will report back with my findings..
 

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...If you don't have power at the injectors, make sure the injector resistor is getting power, it's the heat sink looking doober behind the battery...

... I believe the circuit opening relay is what feeds the resistor...
The '88 cars did not have injector resistors. Around '87, the low impedance injectors were replaced with the high impedance injectors that had that new connector that did not break when you looked at it.

The injectors are powered direct from the ignition. The COR feeds only the fuel pump. It is there to shut the pump down if you crash the car.
 

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Discussion Starter · #9 ·
jumpered the Fp and +B and instantly fired up and stayed running...

disconnected and instantly cut out

tested the resistances and voltage on the afm - need to open and close the barn door and measure the voltage at the ecu.. this is our next check.. ran out of time tonight. Is there an easy way to do this?

Also did continuity check on the COR to the relay in the fuse box - EFI or fuel pump relay? What is the correct name for that large black relay?

Meantime, I'm planning a airplane type of jumper for the Fp circuit (manually turn on fuel pump like a race car while having a switch on the dash turn off - could be a good anti theft.. trick is not to forget otherwise will come out to dead battery? Main thing now is I can drive the car and not get stuck. It's winter here so just a few drives around the block for the next few months.

Earlier this week, when i got the engine in and started, it kicked to life with two cranks (after cranking for awhile without the igniter plugged in to circulate the engine oil) we got it running and no problems beside high idle and some hunting
for about 30 minutes... then started this cycle of start for two seconds and the die.

Any creative ways to fix this? What would be the first area to look in the harness? COR to the circuits. AFM to the ECU. Any other suggestions?

We did the power to injectors test also. They fire when told to fire... possible problem with the #10 and #20 fuel injector circuits? they wouldn't both be toast... and the jumper confirmed they fire and run so long as fuel is sending...
 

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jumpered the Fp and +B and instantly fired up and stayed running...disconnected and instantly cut out

tested the resistances and voltage on the afm - need to open and close the barn door and measure the voltage at the ecu...

Also did continuity check on the COR to the relay in the fuse box ..
Well, good. Now you have some useful information.

The ECU is not involved in this. Neither are the injectors. The AFM has a separate switch to keep the fuel pump running, and that is wired direct to the COR The next test to do is to get the engine running, and then hold the "barn door" cracked open while you pull the jumper. If the engine keeps running, then the problem is only with the AFM or the intake. The switch is out of calibration or there is an air leak that prevents air from opening the barn door. If the barn door does not keep the engine running, then the problem is with the COR or the wiring.

-OR, the switch in the AFM is non-functioning. Sorry that I left out that obvious possibility.

Generally, you do not want to do resistance or continuity checks on a connected circuit. You are likely to get misleading results for a number of reasons. There are almost always multiple paths that you don't think of, and you are counting on your meter to tell you what the right answer is. The right way to do circuit troubleshooting is to power the circuit up and measure voltages to chassis. If you read different voltages at points that are supposed to be connected, then you have poor continuity. Remember to also test points that are supposed to be grounded.
 

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Discussion Starter · #11 ·
Amazing advice!! We did do the barn door voltages and could see the open, closed and partially open barn door working as it should. And I did experience, earlier in the year, the car running no problems, and then when I tucked in the COR onto the ECU bracket, it stopped running. I 'untucked' the COR and car would run again. Last week I had the harness on the bench and tested for breaks in the wiring and continuity and couldn't find any issues - checking while it was easy to reach everything...

I'll do the barn door test with jumper in while running...
 

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The ground for the fuel pump circuit is located on the intake manifold in the injector "valley". An easily missed connection to be sure. If you missed that one it will be the first and last time you do. Yeah, I did that on an AE86 I had a while back.
 

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Discussion Starter · #13 ·
The ground for the fuel pump circuit is located on the intake manifold in the injector "valley". An easily missed connection to be sure. If you missed that one it will be the first and last time you do. Yeah, I did that on an AE86 I had a while back.
I think the fuel pump has good ground... and i definitely have the ground to the intake on nice and snug... and yeah, i did forget this ground first time i reconnected the harness!

planning to run a fresh direct from afm pump switch to COR... think there's a problem there...

Product Rectangle Schematic Font Slope
 

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Check the wire before you go and do a bunch of work. With the key in the ON position, you should measure around 12v on the B+ and Fc wires of the circuit opening relay, with the relay connected.

You should also see 12v at the other end of the Fc wire, at the Afm.

Be systematic about measuring where you have power when the system is connected and turned on, otherwise you're flailing around replacing things that probably don't need to be replaced. Electrical systems are simple chains, you can measure the voltage at the end of each link to know if that particular link is broken.
 

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Discussion Starter · #15 ·
testing the mr2 for connection and possible broken wires/weak connections, i found six suspect wires and one harness pin, depinning itself. might have been in there replacing the harness wire in the spring when we were cleaning up the harness and pinning out.

main issues found is the COR harness have five connections and car will start, run with the Fp - +B jumper in and once we jiggled the wires a little, it would stall. problem with this set up is likely the five wire (actually 8 because 3 are doubled up) has been damaged from being bent for 30 years and gotten brittle/weak so when we pulled the harness through the firewall, perhaps it damaged the connections. Is this common?

so I have 'fixed' seven connections (and suspect maybe need to do more with this 33 yr old harness) and will report back once i got it running again.

@teran checking the FC at both ends for 12V and regarding the measure of voltages of the wires
 

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Sounds like the wiring to the circuit opening relay is compromised. I've seen cases where the wire is broken inside of the insulation, causing issues like you are talking about. In one position the wire will contact and conduct, but if you move the wire or the device, it will separate and break the coin connection.

It sounds like the problem is near the circuit opening relay. You may get away with cutting back a foot or so of the harness, splicing on fresh wire, and then reconnecting the relay.
 

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Discussion Starter · #18 ·
the break in the wiring seems to be right near the

plan B on the COR, run a wire harness into the interior and setup aircraft style flip switches and manually turn on
1. activiate Fp - fuel pump
2. fuel relay - the one in the engine bay fuse box
3. activate Fc - fuel pump
4. maybe Fuel switch in the Air flow meter
5. black wire to air flow meter, tvis vsv, cold start injector, throttle position sensor....

flip off the switches (that need to be off) after car starts... race style... am i missing anything?
 
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