Help me diagnose these Coils please :|

[shadowarrior]

I picked up a new multimeter today and wanted to test the coils off my Mrs' Pajero to check for that misfire issue.
(Although there is no stutter while driving, I can sometimes see the rpm needle take a quick dip while idling.) Just wanted to make sure if the coils are ok anyways.

So according to my engine's manual, and Bennoz's link (http://www.ehow.com/how_4912368_check-c ... meter.html) this is what I am doing:

Engine Manual:


The Coil in question:


To get the primary resistance of the coil am touching the middle pin and the 3rd pin in the plug A as named in the diagram. (Reads .578 k ohms)
To get the secondary resistance of the coil am touching the Spark Lead connector C and the Spark Plug connector B metals. (Reads 10.3 k ohms)
(Both measurements are taken on an autorange meter)

Am I doing it the right way?
So according to the manual my primary resistance should be between .7-.86 ohms and secondary resistance should be between 11.3-15.3 k ohms. My readings are lesser than that, therefore my coil is bad?

This is my first time with a multimeter and learning things..so sorry for the noob question

[PHIL069]

Well to start the pic you have out of the manual is not the same as the coil you have.
The manual is showing a complete coil pack which would be bolted beside the engine and have 4 leads running to the 4 spark plugs.
The coil you have is like the FTO ones that sit above one sparkplug and run a lead to a second spark plug.

You must have the wrong manual.

[shadowarrior]

Hmmm... yeah sensed something was odd in that picture. Had searched for 4G93 1.8L 4cyl SOHC and that's the result I came up with..apart from the other ones with 6 cyl.

Is my method of testing the resistance correct though?

[PHIL069]

Yes your method is correct, but you need to find out the actual pins/terminals to test and the correct specs.

[shadowarrior]

Thanks mate. All the manuals am finding now have coil-on system. :\
Urgh!! Off to the abyss of Google search

[shadowarrior]

Btw, this is a SOHC and not a DOHC right?
(couldn't see any groove in the middle of the cam head like DOHC engines usually have)

[PHIL069]

Yes it is a SOHC as there is only one cam pulley as you can see from the timing belt cover.

[shadowarrior]

Thanks

[shadowarrior]

Hey Phil,
Is this what am after?

Does match the engine specs and coil/lead wire type.

[PHIL069]

That looks like it.
Is it for your engine?

The "secondary resistance " you have already done is in specs

The primary coil check, you will need to connect a "AA" battery to "2(-)+3(+)" and read the continuity across "1+2" should be 000 or not far above and your multimeter should "alarm".
Disconnect the "AA" battery and you should not have any continuity.

[shadowarrior]

Manual said 4G93 SOHC, only thing it said was 2002 M/Y... which I think is for a 2002 model But that's the only one out of 8 Pajero IO manuals I downloaded which matched the coil and spark lead combo
Whew so secondary resistance was all good

I put the coil back on before I saw your post but I had done this test yesterday:

Checked continuity/resistance between 1 and 2....got OL and no beeps, checked continuity between 2 and 3 got .578 k ohms, checked continuity between 1 and 3 got OL and no beeps. (This was on an autorange, so definitely didn't matter if I had a lower range selected).

This is what I understand from the test, correct me if am wrong -->

2 and 3 has a working circuit with some resistance hence my continuity test worked giving me the result of .578 k ohms; and connecting the 1.5v battery on 2 and 3 passes power through them. 1 and 2 do not form a complete circuit unless you manually connect those two points and have a battery (some form of connection) on 2 and 3. This completes the circuit between 1 and 2 and 3. Disconnecting the circuit between 2 and 3 (with the battery in this case) will also break the circuit between 1 and 2 or 1 and 3.

[PHIL069]

It's like a relay or switch
Power (battery) to 2+3 switch is closed (turned on) = continuity (flow) 1+2
No power to 2+3 switch is open (turned off) so NO continuity (no flow) 1+2

[shadowarrior]

Ah..makes sense
Thanks mate. I will pull it out and check it again.

[PHIL069]

The ECU will send 1.5v to 2+3 to activate coil (send specified power to coil and onto spark plug through 1+2), then ECU will send no power to 2+3 to stop spark.
This will happen constantly (on,off,on,off....) as the ECU wants each plug to spark

[shadowarrior]

So there wouldn't be any way where I can change all the 4 as coil on spark instead of the current coil and lead system? I would need to alter how the ECU handles and fires the spark? I have heard all coil on spark plug systems have better spark/ignition than the ones with lead wires branching off from a coil?

[PHIL069]

Unsure, may need to ask an auto electrician.

I would assume you would have to change the ECU and wiring too, but don't quote me on that