5th injector not working. Where do I search for the problem?

[dikidera]

As you all probably know, after the first electrical short that "disabled" my VVT I had issues with 5th injector on my S60 2005(facelift) 2.4i 140hp bifuel until it starting working again by itself way back 2 months ago. Inside the ECM injector 5 and VVT share the same chip and traces/pins are next to each other.

Last night it stopped working again after a 1hr drive and the car misfires, BUT the car works normally in CNG mode. So I am ruling out coils, spark plugs and even timing problems.

I measured injector resistance, 15ohms-14.7 like the rest. I used 12v on it and it is clicking. I start the car and use a stethoscope, I do not hear it click whilst injectors 1-4 are all clicking. Pulling the 5th injector plug does nothing indicating it is indeed the problem. I then measured the voltage of the injector harness and there is voltage to it while the car is running.

I then used my multimeter's frequency measurement but word of caution, I am not sure how trustworthy it is for my UNI-T unit. It shows 1Khz for all injector plugs at idle, including 5th injector. This is higher than VIDA says, it should be 2-3ms or 500-333hz but maybe it is because the car is warming up keeping a higher idle thus higher frequency.

Next thing I did was install the replacement ECM I have for my car. I copied over the immobilizer EEPROM data. The car did start but the problem persisted, additionally it stored error codes about SW mismatch so I reverted to the old ECM, although the sw mismatch may make this test NULL.

So now I am stuck scratching my head. There is voltage/pulsing to injector 5 with the original ECM, but the injector isn't firing. I press the switchover button so that the car work in CNG mode and all of a sudden all symptoms go away, but it is using a distributor for this so it bypasses injectors.

If anyone has any ideas what might be going on I am all open to suggestions.

[cn90]

Swap with let's say #2 (label which is which first) and see what happens.

[volvolugnut]

Swap with let's say #2 (label which is which first) and see what happens.

Yes, this should be instructive.
Perhaps some trash stuck in the misbehaving injector?
You can test an injector with a 9 volt electronics battery or 12 volt car battery. Just make and break the connection to pulse. Use a short hose on the inlet side to make a supply of gas for the injector. Without pressure you won't get a spray pattern, but you can tell if it opens and closes.
volvolugnut

[dikidera]

I can't explain it. Two days ago I started the car, it was still only working on 4 cylinders, I wiggled the ECM+TCM wiring as well the wiring around the injectors and it magically started working when it warmed up. I cant say if it just started working by itself or me wiggling the whole computer wiring/socket did the trick. I can tell you the ECM and TCM are in there snug.

Obviously the root cause has not been fixed.

[MoVolvos]

I can't explain it. Two days ago I started the car, it was still only working on 4 cylinders, I wiggled the ECM+TCM wiring as well the wiring around the injectors and it magically started working when it warmed up. I cant say if it just started working by itself or me wiggling the whole computer wiring/socket did the trick. I can tell you the ECM and TCM are in there snug.

Obviously the root cause has not been fixed.

.
Regardless, don't wait and swap injector 5 with 2. If it happens again with cylinder #5 you'll know it's not the injector. If it happens with injector #2 it's the injector. Without doing this you still wont' know if it's the injector, wiring or something else if it acts up again.
.

[scot850]

Have you removed the ECM and TCM to check for pin corrosion? Wiggling those and connectors could simply have cleaned some corrosion or oxidation on the pins to get it working again. Glad it is working!

Neil.

[dikidera]

It isn't corrosion as I have since the problem occurred in the first place, removed the ECM multiple times and even sprayed the ECU itself and the breakout box with contact cleaner.