2 & 6 (batch ) not firing. ECU issues? help is appreciated!

[brett]

some background here:
1jz in a 240sx
wiring was done in house
had resistor pack on car and wouldnt run at all (no fuel somehow & yes it was wired properly)
removed resistor pack and here is where we stand....

so...its been quite a while now and finally got it running a lot better. something was up with the resistor wiring. i double checked the wiring and the order and all that, everything checked out fine. i was still having issues so i just took the resistor pack off and put the stock injectors back in......and.....

wha-la, it started and idled very rough. now its running but only firing on 4 cylinders. 2 and 6 are not firing. i know this by the temperature of the manifold runners...and its very noticable (trust me, my finger tips hurt).

now, these are on the same circuit/firing order (one of the batches). so...what could be the issues?

it seems the only difference between these two plugs and the others firing is the fact that the ecu side of the clip does not have continuity to ground. could this be an issue with the ECU?

i have done some preliminary research on this but many topics i have read dont really address the batch firing issue. i feel it is more than likely the ECU but will not rule out the plugs being fouled. i am getting spark on those cylinders its just not getting fuel to those two.

any additional help would be great. thanks,

brett

 

[tlo86]

what injectors did you have in there w/ the resistor pack?

 

[annoyingrob]

it likely is the ECU.

When you say there's no continuity between the ECU pin and ground, what exactly do you mean? The ECU is supposed to hold all three injector pins at 12V, then when it wants to fire, it pulls the pin to ground briefly.

What I would do, is check the signal with a light, at the injector. Un-plug the injector, and put a light bulb into the connector. If it lights up, the injectors are at fault. If it doesn't light up, check the injector signals right at the ECU, to eliminate your wiring. If there's no signal at the ECU, open it up, and look for cracked solder joints, and leaky capacitors. Re-solder cracked joints, and replace leaky caps.

If the problem persists, my only advice is wire the injectors into another injector signal. I did this, and while it did eventually burn out another injector driver, it took about 18 months before it did.

 

[brett]

thanks guys...i'll get to it in a few days. i appreciate the input thus far.

as for the resistor pack i had MKIV 550's. i used a 7m resistor (which now i am thinking was at fault). wired properly but still no fuel.

thanks again,
brett

 

[brett]

ok so here is where i now stand.

i tried the whole light bulb thing and it did not light up.

when you say "signal" at the ECU, what do you mean? there is about 9V on the ecu pins themselves. there is 12V on the plug of the ECU for the respective wires as well.

i used a noid light and there is no action on it on the two cylinders that are not firing. the other 4 cylinders show on the noid light.

on the plugs that work, there is continuity to ground on both wires at the injector plug and 12V on each as well.

on the plugs that do not work, there is 12V on each, but no continuity to ground on either side. any ideas? the ecu's (both) do not appear to have cracks or leaks. one was repaired previously and came off a known working shop car.

what are my options? should i send the ecu's out to someone who has experience checking/repairing them? what kind of re-wiring can i do to get the injectors to fire and work properly? if i do wire them into another injector signal (say into the 1&4 batch) wouldnt it still not fire at the proper time?

i guess i dont understand this all, but would certianly love too...so i too can pass the information on to others. thanks a million,

brett

 

[annoyingrob]

if i do wire them into another injector signal (say into the 1&4 batch) wouldnt it still not fire at the proper time?

You would be surprised how un-important injector timing is.

If your injectors are running anything more than about 25% duty cycle, at some point they'll be spraying on closed valves anyways.

 

[brett]

yeah thats what i figured, but i'd rather get them running the way they are supposed to be instead of forking money out for another ecu...especially if i end up running the stinger unit.

any other things to explore?

thanks rob

 

[brett]

so, you are saying that i can just splice into the signal wires on 2 of the four that are working and this should resolve my issue, no?

is there a way to help prevent the system from burning that driver out? use smaller wires, etc.??? just to help with longevity...though a year and a half is a decent amount of time, but you never know. thanks again rob you have been most helpful,

brett

 

[XMasta19]

Ok...can you clear some things up for me:

You've put a noid light on all the injectors while the car was running, and it doesn't light up for two of them?

Have you used a stethoscope or simple screwdriver to listen to the injectors?

Also, please explain by what you mean when saying you have no continuity to ground on some of them? As stated...each of the injectors has constant source voltage (ie: 14v), and then is supplied ground by the ECU.

Do you have access to a lab scope to view the injectors' signals?

 

[brett]

the noid light: two of the injector plugs do not light up while cranking/running

i have not listened to the injectors recently...i do believe i have spark on those two (did a few weeks ago), though i will verify this evening. i did try and listen to them last time i was diagnosing everything and you couldnt hear shit...but i will try again for sure.

no continuity to ground: using an ohm-meter i get a beep when touching one probe to the injector wires and ground = cont. to ground and this is usually on both the signal side and 12v side. i am not sure if this is an issue or not though...we'll leave this issue for last because it seems to be a weird one.

no access to the lab scope...where might one be sourced or borrowed?

thanks,
brett

 

[XMasta19]

Well listening to the injectors is like a backup of verifying that they are working/not working. The noid light lets you know that the signal is/is not being sent. Just to be clear, you have spark in all cylinders, just have 2 injectors not spraying correct? A lab scope would be found at a shop, or possibly some guys that may have one of their own at home.

 

[annoyingrob]

so, you are saying that i can just splice into the signal wires on 2 of the four that are working and this should resolve my issue, no?

Yes it will.

It's a 'temporary' solution, as what you're doing is running one of the three injector drivers at double its rated load. They're pretty robust, but it could fail on you in the future. Of course, then you would just be back to where you are right now.

Like I said, I ran my car like that for quite a while before it finally blew the injector driver, and even then, it was only 'flakey', it still ran with two shoddy injector drivers. I suggest if you have the ECU out, re-solder every point within the ecu. The cracked solder joints are where a lot of these problems stem from.

 

[brett]

thanks guys. i did get it running on all 6cyl, but only by doing the splicing like rob had mentioned. it runs well now, but has a coolant leak - poop...on the driverside near the back of the block (i'll figure it out).

i am getting spark on all 6, just two injectors not spraying (2&6). it is like this when using both of the ecu's i have. there is continutity from the ecu plug to the injector plug from the 2&6 pin location....so i dont think its wiring. i will verify this and any cracks/openings when i get the harness back off the car.

thanks a lot guys. when i upgrade to the stinger EMS i will have to make sure i undo the splicing...and see if it works on that ecu.

brett

 

[XMasta19]

Good to hear you got it ok for now. For the record, doing continuity tests on cars really doesn't help out much. Your best bet is usually a voltage drop, then maybe an available voltage test, and the occasional resistance reading on a load when it's disconnected from the circuit. The way to verify an open/short in the wiring would be to verify if and/or where you're dropping the voltage.