xantos wrote:Yep disconnected the injectors and then crancked engine and measure... So I did it wrong. That's me. If there is a way to do it wrong then thats my way
So I should strip a bit of insulation on the injector connection and do the measuring again with engine running?
I would avoid stripping insulation or poking holes in the insulation because unless you repair the insulation with an air/water tight seal the wire will eventually corrode and fail. (Although it might take years)
As sparksie says, the best way is to "back probe" the connector - it's very easy to do so on most 2/3 pin connectors where you can see the wires individually go down into the back of the connector - surrounding the wires is a flexible rubber like material, you push something sharp and very small in diameter (a sewing needle is ideal) down BETWEEN the insulation of the wire and the rubber that surrounds it.
When you push it far enough down into the plug it will make a reliable contact with the wire at the bottom. Sometimes more than one attempt is needed to get a good contact if you don't push it in straight. When the needle is withdrawn the rubber around the wires expands back into place and there is no exposed wiring to corrode so nothing to repair.
I actually made up a special test lead for semi-permanently back-probing connectors for long term diagnosis - I've used it mainly for the oxygen sensor but I have also used it on the MAP sensor and TPS as well. It's made of two cut off sewing needles soldered to the end of some high temperature shielded audio cable and then carefully heat-shrinked for insulation and mechanical support:
Shown above pushed into the back of the TPS connector before reconnecting the connector to the TPS. It's very tidy and reliable - I had it connected to the oxygen sensor for months and there is no risk of short circuit as the needle lengths were chosen such that they are not significantly exposed when pushed into the connector.
For your test all you need to do is carefully push four sewing needles into the negative wires of each injector, test that they have a good connection (by putting your test light from battery positive to each one in turn with the engine running to make sure they flash) and then carry out the test as described.
It's important that the injectors remain connected for my suggested test to work. The way it works is that if you connect the bulb between the negatives of injectors 1 and 2, if they both fire at the same time both will go from 12v to 0v at the same time so there is no voltage differential to light the bulb.
If injector 1 fires by itself the ECU will ground the negative of injector one and thus one end of the bulb, the other end of the bulb (which only requires about 100mA) will be powered from 12v via the series resistance of injector 2. (About 12 ohms) The same happens in reverse when injector two fires. So if they fire at different times the bulb lights but if they fire at the same time the bulb doesn't light. From this you can work out the firing scheme.
One other important note - checking how the injectors fire MUST be done when the engine is idling normally. You can't test it during cranking because most injection systems switch to an "unsynchronised" batch fired mode during cranking and only revert to their normal pair fired or fully sequential mode of operation once the engine starts.
Some engines also temporarily switch to firing all the injectors at once if you press the throttle rapidly then revert to their normal sequence a fraction of a second later. This is done for instant enrichment to avoid lean stumble. This may show up on the bulb test if you snap the throttle during the test.
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It hurts...
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