Fuel injection signal - Mk1 MR2 4AGE engine

[itiejim]

Folks, I'm trying to help my Dad resolve a frustrating problem with a Mk1 MR2 engine which refuses to inject on cylinders 2 or 4.

The injectors themselves have been swapped over and shows that all 4 are working fine - but not when attached to cylinders 2 & 4!

I can only assume that it's not receiving a signal in open the injector, does anyone know where this comes from? I thought it was from the dizzy and have tried an alternative, but no joy. I have also tried a different ECU yet the problem persists.

Any 4AGE folks out there who can help?

[stevieturbo]

itiejim said:

Folks, I'm trying to help my Dad resolve a frustrating problem with a Mk1 MR2 engine which refuses to inject on cylinders 2 or 4.

The injectors themselves have been swapped over and shows that all 4 are working fine - but not when attached to cylinders 2 & 4!

I can only assume that it's not receiving a signal in open the injector, does anyone know where this comes from? I thought it was from the dizzy and have tried an alternative, but no joy. I have also tried a different ECU yet the problem persists.

Any 4AGE folks out there who can help?

So have you actually conducted the most basic of test to see if the injector plug is getting a signal ?

With an LED, multimeter, scope ? Why would you just assume it isnt receiving the signal when it is so easy to test ?

[Steve_D]

Injectors are normally powered directly and then earthed by the ECU.
So first thing is to see if they have power at the injector plug. They are normally fused in banks so there may be a fuse out.

Steve

[itiejim]

stevieturbo said:

So have you actually conducted the most basic of test to see if the injector plug is getting a signal ?

With an LED, multimeter, scope ? Why would you just assume it isnt receiving the signal when it is so easy to test ?

All injectors have power, the two which fire normally oscillate when the engine is running, however, the two which don't fire remain steady at 12v.

FI wiring isn't my thing I'm afraid, hence the request for help

[stevieturbo]

itiejim said:

All injectors have power, the two which fire normally oscillate when the engine is running, however, the two which don't fire remain steady at 12v.

FI wiring isn't my thing I'm afraid, hence the request for help

So are you saying you have tested with a multimeter for frequency, pulse width, duty cycle, any of these ? and are not getting any signal whatsover ?

If so, that would be very very strange. You would then need to test the wiring from injector plug to ecu pin to ensure wiring integrity

[anonymous-user]

are sure that:

a) all injectors are seeing 12v power feed when ignition is on (and that needs to be 12v under load, as some cumbly wiring can show 12v at now load (i.e. just the minimal current that the test meter draws) but due to a high resistance joint or contact, that 12v will fall close to zero when actually loaded etc)

2) the is proper continuity between the low side of the injectors and the engine control ecu (engine ecu will "earth" injectors to fire them (again, resistance check is worthwhile)

[itiejim]

I haven't done any more complicated checks than to see that there is power at all of the injectors. Sunds like I need to check the earth going back to the ECU then?

[Diag]

As someone already said, the injectors are supplied 12v and grounded by the ECU. The 12v supply is common to all 4 and comes from one fuse. In this case, the grounds are linked in pairs, ie both injectors of one pair (aka bank) fire at the same time. The pairs are 1&4 and 2&3.
Your fault is with 2 and 4. That’s 2 banks, not just 1. If it was a grounding fault in the ecu that would knock out all 4 because of how they are linked. Since 1 is working and 4 (its pair) is not, you could swap the wiring between them and see if the fault moves from 4 to 1.
If what you said is right, then its not an ecu problem and its not an injector problem. If the fault is lack of injector signal then it must be a wiring fault. Swapping the wiring as I suggest would prove that for you in the absence of a better way to check the signals (oscilloscope).
It may not be an injector fault. If you haven’t already, swap the ign components to see if the fault moves and do a compression check, or preferably a leak down check.

[stevieturbo]

itiejim said:

I haven't done any more complicated checks than to see that there is power at all of the injectors. Sunds like I need to check the earth going back to the ECU then?

no, you need to check for a signal at the injector plug as already described with either a test LED, multimeter on frequency, pulse width or duty cycle, or using an oscilloscope

[Steve_D]

As most people don't have a scope or fancy test equipment some more simple tests are required.

If (as has been stated) 1 & 4 are paired then start with a multimeter and see if you have continuity and low resistance between those two injector leads for both the +12 side and the earths. If you don't then you have a broken wire somewhere in the engine loom.

You could strip the ends of some wire and insert into the connector terminals of the working injector and with the wire still in the contacts push the connector back onto the injector pins. Do the same with the other end of your wires on the dead injector. This has now connected them together.

Has it brought the injector back to life? If so then you know for sure that you have a broken wire.

Steve

[stevieturbo]

An LED is not fancy or expensive. And any half decent automotive multimeter should have a dwell or duty cycle/pulse width feature.

But a test LED would be the easiest and cheapest way to check for a signal

[Diag]

The problem with testing using an led or a meter is that it takes very little current to get a result but a lot more to open an injector. A positive result with an led means nothing.

[Mr2Mike]

IIRC the Mk1 with the 4AGE uses low impedance injectors driven via a resistor pack. You need to make sure the resistor pack and associated wiring is ok.

[stevieturbo]

Diag said:

The problem with testing using an led or a meter is that it takes very little current to get a result but a lot more to open an injector. A positive result with an led means nothing.

Test with the injector in place of course.

[Diag]

stevieturbo said:

Test with the injector in place of course.

Even with the injector in place, which was what I meant. A faulty circuit could have, for example, .1 amp. That will flash an led but not open the injector so what does it prove? All it proves is that there is some attempt to switch it, not that its ok.

Mr2Mike said:

IIRC the Mk1 with the 4AGE uses low impedance injectors driven via a resistor pack. You need to make sure the resistor pack and associated wiring is ok.

That could change things slightly. The diagram I looked at didnt show any resistor but it wouldn't be the first time I have seen wrong diagrams.

Steve_D said:

If (as has been stated) 1 & 4 are paired then start with a multimeter and see if you have continuity and low resistance between those two injector leads for both the +12 side and the earths. If you don't then you have a broken wire somewhere in the engine loom.

You could strip the ends of some wire and insert into the connector terminals of the working injector and with the wire still in the contacts push the connector back onto the injector pins. Do the same with the other end of your wires on the dead injector. This has now connected them together.


Steve

The pair being 1 and 4 was an error on my part. That should have been 1 and 2.

you would need to be sure what way the current limiting is achieved before linking any injector wiring as you could double the load and damage the driver circuit. There would be no harm is swapping the injector wiring though.