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NA6 PNP V1.1 injectors 2 & 4 permanently open

Posted: Fri Aug 21, 2020 1:17 pm
by Jaimyy
Hello guys,

Since december I am succesfully boosted with the NA6 PNP V1.1 ecu and really had no issues with it until last weekend. I was driving to the Nurburgring for a couple of laps but my trip was cut short when the car suddenly ran badly with afr's pegged at 8 on my aem. I smelled alot of unburned fuel so I cut the engine and coasted of to the side of the highway worried the car was leaking fuel. But as the afr's lead me to believe the engine was floading itself so badly a very distinct unburned fuel came from the exhaust. The car was recovered eventually and it was delivered to me back on monday.

I pulled the sparkplugs and cilinder 2 & 4 were full of fuel what lead me to believe that there is an electrical issue on the "bank" that controls those injectors. After measuring with a multimeter with the ignition on the plugs on injector 2 & 4 have constant 12volt so if the fuel pump primes it dumps fuel in the engine. Measuring the other injector plugs I saw 1.6 volts aka off. To rule out the wiring from the injectors to the ecu I measured the wires and it seems there was no premature grounding before the ecu. So I think the ecu is shorted out on that bank of injectors but I can't really see anything wrong on the pcb or the arduino mega. I don't have alot of knowledge on pcb's and how to check for faults so if anyone has a suggestion(s) I would greatly appreciate it :D

Kind regards,
Jaimy

Re: NA6 PNP V1.1 injectors 2 & 4 permanently open

Posted: Sat Dec 05, 2020 9:05 am
by Chris Wolfson
If transistors burn out, they often stay low ohm, so you got to find the defective drivers and replace it. To make sure it is the power stage, you can simply measure the injector output to negative (ground) on the disconnected board. If they are burned they show close to 0 Ohm. If not, the problem is with the pre-stage driving the power stage. Return for sevice!
Depending on which board you have, the driver are large transistors or a small SMD with 8 legs for two (!) outputs. It seems crazy that these small parts can switch 2x 13 Amps.
You can easily fry them if you inject 12 Volt. Touching ground is no problem. Unplugging injectors while powered on can do the same, as it often occurs with bad wires and connectors. Most probable cause if they fail while driving.

Re: NA6 PNP V1.1 injectors 2 & 4 permanently open

Posted: Sat Dec 05, 2020 6:49 pm
by PSIG
How to test? Logical diagnostics. You are already on this path (remove injector grounding and injectors should close), with your first basic test for stuck injectors and wiring faults. Everyone has their own perspective on diagnostics and mine is to break-up the basic primary functions categories, finding which category the fault is in, then working on a focused path to the failure. The primary categories in this case are:
  • Control (processor, code, settings, tune, etc)
  • Hardware (ECM components, board, connectors, wiring, etc)
From these two, I can find if the failure is in one or the other, then develop tests specific to that category.

So first I conceive tests that can help determine in which category the failure is occurring. With your symptoms, I find the division between control and hardware, which is roughly at the junction between the processor output and the functional hardware (control vs hardware). From the diagram below, you can see where I would test for a control signal to the injector FETs (powered ECM and fuel pump disconnected).

If there is no signal (0V), then the processor is doing what it should, and the failure is beyond the control category and in the hardware category. If the signal is present (±5V), then the failure is in control, the hardware is just doing what it is told, and presumably the remaining hardware is OK. Keep in-mind there are a few minor components and board traces that are in this gray-area of division. ;)

[EDIT] As a verification example and next-steps, if you found V+ on R15, you could pull the Mega from the board and re-test, verifying D10 is hot or not, confirming the voltage is either from the Mega (control) or from a short on the board or hardware. Stuff like that.

Anyway, pick you path by what makes sense to you and follow it until you find the fault. Good luck, and try to have fun even though the situation sucks, as you will eventually find the problem and solve your issues.

David

I find points that are physically easier or safer to probe, such as resistor ends versus IC pins:
NA6_v1.1_INJ_schem.jpg
NA6_v1.1_INJ_schem.jpg (109.63 KiB) Viewed 2896 times

Re: NA6 PNP V1.1 injectors 2 & 4 permanently open

Posted: Sat Dec 05, 2020 9:52 pm
by LPG2CV
Are the leds for the channels that are not working flashing? if they are flashing, then probably the Fets are working.

The injectors work by supplying 12v to them, and the Fet provides the ground at the correct time. Equally, a signal wire from the injector shorting to ground, could cause the injectors (if paired) to be continuously on.

Eliminate the simple stuff before looking for anything complicated. Check what you may have disturbed first.

Good hunting :)