No ground signal to injectors - 720 DOHC swap

[720Joe]

As some of you may remember I talked about swapping a ka24de into a 720.

Well, it's done and in the engine bay, but i am having one problem.

 

I am running a 240sx(S13) harness, I get a beautifully strong spark but no ground signal for the injectors to fire.

I am thinking the ecu is bad but im not sure. Does anyone have any suggestions?

[720Joe]

Here's a pic for proof, lol.

 

[Icehouse]

Unplug all 4 injectors and see it one side has power. If so you can hook a LED (or a test light may actually work but the pulse will be very dim) to check for injector pulse. My guess is your fuel lines are backwards.

 

Nice truck.

[720Joe]

Yes the constant power is there, but the ground does not get switched.

The fuel lines are not backwards, I've gone over that already, lol.

 

Thanks(assuming you meant it), but it needs alot of work.

[Unclejesse88]

You need to go to the injector ground terminals at the ecu and check for grounds there. If no grounds then you need to look over what inhibits injector firing. Things like cam/crank position. Also, make sure the ecu has all of it's grounds hooked up. Load test the grounds.

[720Joe]

I have checked for grounds at the ecu and there is nothing.

All 3 grounds are hooked up. The one near the intake manifold, one on the valve cover and one near the igniter.

I get spark and I can turn the disributor which triggers the fuel pump, which tells me the CAS is working.

[datsun brat pack]

check the crank triger it sounds bad it will do that if it is bad .:D

[720Joe]

By crank trigger do you mean the CAS?

[Icehouse]

Yes the constant power is there, but the ground does not get switched.The fuel lines are not backwards, I've gone over that already, lol. Thanks(assuming you meant it), but it needs alot of work.

 

 

HAHA yeah I just had to add backwards fuel lines because that seems to be a common problem so I figured I would throw it out there :)

 

It is a cool truck! I would put the ECU in the cab just to keep it out of the weather.

 

 

 

You need to go to the injector ground terminals at the ecu and check for grounds there. If no grounds then you need to look over what inhibits injector firing. Things like cam/crank position. Also, make sure the ecu has all of it's grounds hooked up. Load test the grounds.

 

Grounds are a good point. But if it's getting spark from my experience the CAS is good.

 

 

I have checked for grounds at the ecu and there is nothing.All 3 grounds are hooked up. The one near the intake manifold, one on the valve cover and one near the igniter.I get spark and I can turn the disributor which triggers the fuel pump, which tells me the CAS is working.

 

 

Shouldn't there be 4 grounds? One from each injector back to the ecu? Did you check for pulse at each injector? I would, an LED would be best, so much easier to see than a incandescent bulb.

 

 

check the crank triger it sounds bad it will do that if it is bad .:D

 

 

Every time I've ran across a bad CAS the engine won't have spark either. I could be wrong though.

[jesusno2]

First off did you use a 240 motor and what did you do about oil pan clerance. I'm thinking of swapping my kc 720 soon. Also have you checked fuel pressue? From what I'm seeing all the injecters grounds are all inline. Is the motor grounded to the chassis well? I'm guessing it must be if you have spark though.

[720Joe]

HAHA yeah I just had to add backwards fuel lines because that seems to be a common problem so I figured I would throw it out there :)

 

It is a cool truck! I would put the ECU in the cab just to keep it out of the weather.

 

Shouldn't there be 4 grounds? One from each injector back to the ecu? Did you check for pulse at each injector? I would, an LED would be best, so much easier to see than a incandescent bulb.

 

Every time I've ran across a bad CAS the engine won't have spark either. I could be wrong though.

 

The ecu will be going in the cab, it's just temporary.

The grounds I was referring to are for the harness, not the actual injectors themselves. At the moment I am trying to figure out which actual ground point for the harness the ecu uses to ground out the spark plugs.

 

jesusno2 - It is actually a frontier KA block. I have not checked fuel pressure but the fuel pump is a brand new 255lph unit. Even if pressure was low, the injectors would still get a signal to fire. The injectors power source are all in-line but each has a seperate ground. The engine should be grounded fine, the negative wire still goes from batt-chassis-engine block.

[Icehouse]

The ecu will be going in the cab, it's just temporary.

The grounds I was referring to are for the harness, not the actual injectors themselves. At the moment I am trying to figure out which actual ground point for the harness the ecu uses to ground out the spark plugs.

 

 

What do you mean ground out the spark plugs? They ground out through the head. How did you wire the KA? Did you use the diagram in the How to section?

 

Check the injector pulse on all the plugs and let me know what happens.

[720Joe]

What do you mean ground out the spark plugs? They ground out through the head. How did you wire the KA? Did you use the diagram in the How to section?

 

Check the injector pulse on all the plugs and let me know what happens.

Whoops, typo, I mean the actual ground that is switched by the ecu to ground the injectors, making them fire.

I have checked for the pulse, that's the issue, there is none... :unsure:

 

Pretty much used the diagram in the how-to section. Ecu has its own relay, fuel pump has its own, and all the engine sensors are all on one.

[Icehouse]

Whoops, typo, I mean the actual ground that is switched by the ecu to ground the injectors, making them fire.

I have checked for the pulse, that's the issue, there is none... :unsure:

 

 

Are you assuming that or did you test each one with a light?

[720Joe]

Are you assuming that or did you test each one with a light?

Each one was tested with a light.

[Icehouse]

And you are sure they are getting 12v while cranking? How did you wire in the power for the injectors?

 

I've never seen all the injector drivers go bad. I've had ECU's where the CAS was bad and not was there no spark but no injector pulse. I've also seen a injector driver go bad but never all of them at once.

[Unclejesse88]

Is the MAF plugged in? I don't know about the KA, but some japanese engines require "X" amount of airflow before the fuel pump turns on. Maybe the ecu also doesn't fire the injectors until that airflow is reached. I know the diag is leading towards a ecu, but I find it hard to believe that four injector drivers have failed at the same time.

[Icehouse]

Is the MAF plugged in? I don't know about the KA, but some japanese engines require "X" amount of airflow before the fuel pump turns on. Maybe the ecu also doesn't fire the injectors until that airflow is reached. I know the diag is leading towards a ecu, but I find it hard to believe that four injector drivers have failed at the same time.

 

 

KA's don't need the MAF signal to run, just to run in open loop and above 2500 rpm's. I know I don't know how the injector drivers went bad all at once. I would double check all the wiring. Do you know anyone with an extra ecu you could try. Or have them try yours?

[720Joe]

Unclejesse88 - Trust me, the fuel pump turns on, it's an audible unit :D

 

Icehouse - The guy I purchased the ecu from said if there were any issues with it, that he had like 6 laying around and I could come grab another if need be. As far as my 240 friends, all of them are sr or rb25 now =/

 

And you are sure they are getting 12v while cranking? How did you wire in the power for the injectors?

 

I'm positive they are getting 12v while cranking.

 

What ground does the ecu use to switch the injectors?

[720Joe]

Update #1:

Multimeter now confirms ground from ecu to injectors while cranking.

Found out two of the injectors were bad, swapped those with ones that ohm'd out ok.

It's started twice, but on starting fluid.

 

MAF is currently disconnected, just trying to get it to idle at the moment.

Not sure where to look now...

 

Update #2:

Started it again with starting fluid it won't start on it's own. Once it's running it will continue to run if i throttle it, even after the starting fluid has worn off.

[Icehouse]

Didn't we talk about checking each injector plug for a pulse? :)

 

 

Should idle fine with the MAF unplugged if it's not there is something that isn't hooked up. Check for vacuume leaks. Make sure the IACV is wired up as well.

[720Joe]

Didn't we talk about checking each injector plug for a pulse? :)

 

 

Should idle fine with the MAF unplugged if it's not there is something that isn't hooked up. Check for vacuume leaks. Make sure the IACV is wired up as well.

Mhm, and I was also telling you from the beginning that was my problem, I didn't have a pulse. :P

IACV and all that jazz is hooked up, I made sure of it before it was together because of it's location.

I checked voltages on sensors today and everything seems fine.

All gaskets are new on the intake.

 

I pulled the #1 spark plug, turned it over and don't see any fuel in the cylinder at all.

[720Joe]

Ok, well the injectors are not firing. I pulled the fuel rail off and turned the engine over, no squirt. Then, to make sure they functioned and wernt clogged, I jumped them to 12v and they sprayed perfectly.

 

Sooo, at this point, my next move is to try a different ecu.

Any other ideas?

[datsun brat pack]

I had one do the same i went and got a ecu and put it in and it did nothing come to find out it was the crank trigger if this is not working it will not work. It control's the pulse to the injectors in the ecu .:)It also work's with the fuel pump.

[720Joe]

I had one do the same i went and got a ecu and put it in and it did nothing come to find out it was the crank trigger if this is not working it will not work. It control's the pulse to the injectors in the ecu .:)It also work's with the fuel pump.

Yea, I was told tonight that if the CAS is on it's way out you may still get spark but no pulse to the injectors. I'm going to try another distributor I have tomorrow and possibly another ecu.