immobilised injector pulse problem

Hi All,

I've just finished installing my Mongoose M80 alarm system. I used 2 of the 3 immobilisers to neutralize the injector pulse wire on injector 1 and 2.

The problem is the car seems to run a bit rougher, a little richer and not as smooth as it use to be.

(The injector circuit for this car works by negative pulse from the ECU.)

I'm thinking the alarm module is changing the signal somehow. Is it possible the immobiliser circuit in the alarm has short to ground when not armed? Or is there something else I'm missing

I haven't had the chance to diagnose it yet as it was getting late and I packed it up. But anyone with ideas or suggestions before I tackle it again would be appreciated

Cheers

Mostly replying to subscribe but I believe more information would be needed here? Car, wires used etc

You are sending out a ground pulse to interfere with the injection pulses? Not sure what you mean there..

Post a bit more info and I am sure you will get a better answer

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To master and control electricity is perfection. *evil laugh*

Sorry I probably should have worded it better.

So the alarm has 3 point immobiliser, instead of wiring it up to the usual Fuel pump, Starter or Ignition circuit I wired it up to disable the injector signal.

However, this has caused slight issues with the car idling and possibly engine performance. The car is definitely running a little more richer than normal.

I believe somehow the immobiliser circuit from the alarm is altering the injector signal.

The car is a Honda Civic '99

Hope this makes more sense

If you have "shorted" the injector instead of "opening" the injector it is possible that the injector is firing at all times. This will cause it to run rough at idle, it will be hard to start, and it will run rich. It can also bend rods (excess fuel won't compress and something will have to give) and cause massive engine and catalytic converter problems.

Why would you cut two injectors? I would guess that your motor will still fire with two injectors cut, just with a heck of a miss and little power.

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Kevin Pierson

It's not running excessively rich so I don't think it's shorted or causing the injector to stick open. It's only a very slight hesitation, a slight roughness that I could pick out. The car still starts as normal and drives ok.

I also have another 3rd point of immobilisation in the ignition system so car definitely won't start.
I thought it was a good idea to do the injectors as it wasn't your typical fuel pump/starter circuit that are pretty easy to find and bypass.

In reality if it has affected performance you have either open or closed the circuit. There is no way your alarm system would affect the PWM of the fuel injector control circuit. Your immobilizer is most likely a discreet set of contacts on a relay that opens when ignition and ground when armed are both present.

If you feel that your alarm system has caused the problem I would immediately return it to stock and see if the problem goes away.

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Kevin Pierson

If you are "disabling" the injector by adding a connection, then you are "shorting" it to GND and keeping it open. No system would do that - it would ruin injectors and bend conrods.

Injector interrupt must be done by breaking the injector connection, else shorting some other sensor.

the injector signal wire was cut and the immobiliser wires from the alarm were used to intercept it. It was not piggybacked on

Good.
Maybe convert back to standard and see if that makes a difference. Maybe the extra wiring & contacts are increasing resistance and inductance and effecting the pulse or ECU's injector readings.

Ran a few tests today

- Immobiliser circuit tested okay. Open circuit when armed and continuity between wires when disarmed

- Immobiliser wires no short to ground

- All injectors pulsing when run through alarm (via immo circuit). Tested using screwdriver as a stethoscope

- Back to back tests with immobiliser connected and disconnected. Definitely slight noticeable difference in engine note and exhaust gasses out of the muffler. Sort of sounds like the timing is off


The only other test I can think of is to measure the injector pulse width, this should give me a definite answer.. if only I had the equipment to do so


Until then I've reverted it back to stock so I can have it running nicely.. I'll just have to keep pondering in the mean time

Probably long wires etc effecting the injector waveshape.

Better to interrupt the injector +12V using an inverting relay if necessary.

^^this ^^^

If the relay contacts are even slightly resistive, it will affect the pulse duration and firing characteristics. Best to interrupt the voltage supply, not the controlled side of the injector. Even a 4 cyl engine will run on 2 cyls. And a 6 will definitely run on 4. You need to disable all of them.

I'm not familiar with Honda EFI, but most contemporary port injected engines are sequential fire, ie the PCM controls each injector individually. BUT the other side of the injector is almost always +12V. Check wire colors at the injectors. If you find each injector has one wire of a color common to all the others, that's the +12V side. Go far enough up the harness towards the PCM, and you should be able to find the splice where they all come together. Make your interrupt there.