Thank you, I do not live in the the US and I have a spare connector to the ECU. But thank you anyways.

 

Hi Connor,

I think you've covered it. To check for shorts between the ground wires I would disconnect the ECM and all the coils, then measure for infinite resistance between one ground and all the others, then repeat the test until you've tested all possible pairs of wires. If you find any resistance lower than infinite (even, for example, 10,000 ohms), you could have a short between two or more of the ground wires.

Cheers,

Don

 

Thanks for the clarification. I don't seem to have any shorts anywhere. I checked the fuel injectors as well but they seem fine. Maybe theres something wrong with the ECU I bought. It does look good as new though outside and inside.

 

I attached a multi meter to the coil connectors and cranked the engine. I could see that for the working cylinders, the multi meter would fluctuate between 0.00V to 0.9V. But on the ones that didnt work it just stayed around 0.00 (Maybe this means something?). All the wires have good connections and none of them seem to have a short. I'm starting to think that my problem lays in the ECU. The ECU I bought did have the same code as mine (LNB1410CC/3--) but theres no way that I know of to confirm that we have the same numbers after the 3, ie --.

I also dont know of a way to check if this ECU works fully. It looks good but maybe theres something wrong with it anyways.

Im thinking about buying another ECU just to see if the problem stays....

Any advice on this is appreciated.

 

With the ECU connected I've now realized that for the three working cylinders, their respective coil grounds all have resistance to the engine. The three that dont, well their grounds dont have resistance. This really feels like it could be my problem, I'm unsure though of where to look: what wires that could be at fault.

 

How are you measuring for this resistance?

 

With a multimeter on the ohm setting. One end into the green wire on the ignition coils connector and one on the engine.

 

The Light Green wires are grounded by the ECM to fire the coils, so the resistance you are measuring may be through the circuitry in the ECM. I'm not sure if this tells us anything, since the wiring schematics don't show the internal circuitry. But it definitely could be a clue.

While I'm thinking about it, could you please visit your User Control Panel and edit your signature to add the year, model and engine of your car? That will help us be sure we are consulting the correct wiring diagrams.

Cheers,

Don

 

Ill go ahead and do that, in the mean time, it's a 1995 Soverign AJ16 ROW

 

Sorry for going AWOL for a while, I ordered a new ECU and waited for it to test. With the new ECU, all but one cylinder sparks; number 6. This is a cylinder that had a spark with the first ECU I fitted.

I can only think of three things that could cause this mystery: 1. Both ECU's I purchased are in one way or another broken. 2. The ECU's have to be recoded somehow (I've tried the original PROMS's in both). 3. Theres something wrong with the car that causes similar but not the same issues with the two ECU's.

Nota that ECU #1 caused a failed spark in cylinder 1, 4, and 5. ECU #2 causes a failed spark in cylinder 6.

I'm amazed at this mystery...

 

Hi Connor,

That is definitely a mystery!

One thing to bear in mind is that the OBD system in the X300 is primitive and while it is fairly good at telling you when one or more cylinders are misfiring, it is not very accurate in telling you exactly which cylinder is misfiring, so don't assume that the current misfire is really in cylinder 6. You can swap ignition coils between 6 and another cylinder to see if the misfire code moves.

I think I recall that you have inspected your ignition coil harness wiring for insulation damage and potential shorts, all the way back to the rear of the cylinder head inside the harness wrapping?

Cheers,

Don

 

cylinder specific misfire codes (P0301-P0308) should always be ignored and are a very unreliable diagnostic tool in most vehicles, especially these cars

 

I havent used an OBD. I pulled out each coil as the car was running. The engine reacts to all coils being removed except for coil 6. You can also hear a spark comming from each coil except for #6. The coils are all good. I'm fairly certain that the issue lies with the ECU. I'm just not sure as to exactly what or how to go about fixing it.

With the other ECU, doing the same test. Three coils are clearly reciving no spark. But coil 6 is.

So I really dont believe that theres any issue with any of the wiring/coils/sparkplugs/fuel injectors. As I can get all of them to work, just not with the same ECU at the same time.

Does this make sence, or am I missing something obvious that I havent thought about?

 

You're doing well in your diagnosis!

One further test you could do is to measure for the proper power supply voltage at the coil #6 electrical connector with the ignition in the ON/RUN position. If you have voltage, back-probe both wires in the connector and connect your meter on its lowest AC voltage setting. Start the engine and see if you can measure even a small AC signal, which would indicate that the ECM is pulsing the coil to ground.

(P.S. Not to argue with xalty, but on later cars, from the X100/X308 onward, the P300 series codes are actually quite good at identifying specific misfiring cylinders. Just not on the X300 with its first-generation OBD II)

Cheers,

Don

 

This sounds like a tall idea, Do you think you could wire the #1 ignition coil to operate the #6 ignition coil at same time? And the #5 ignition coil to operate the #2 ignition coil at the same time. Then operate #3 ignition coil and #4 ignition coil at same time. I would try this with the ECM that does not fire # 6 ignition coil,

Thank you

Larry Louton

 

I find myself continually drawn back to the integrity of the wiring / connector at the ECU. To fit the new ECU, you have to disturb it, which might, at least temporarily, make good some poor connections, explaining the apparent improvement. Are you 110% happy with your repairs to the wiring and connector?

 

Well I have checked each connection and they all have resistance. Maybe this test isnt good enough? Is there anything else I should check for?

(When I put the other ECU back the old problem of three cylinder missfires comes back, and when I put the new one in again, It's only one) So the problem stays consistent which it wouldn't if it was just poor connections made good again...

 

Interesting idea, Im not sure how id make that work though. Would I have to rewire the fuel injectors to so?. Isnt there a firing sequence I that has to be timed with other components?

 

I'll go ahead and try that, might have to wait until I can get a helper though to start the car as I look at the multi meter.

 

If your meter test leads are standard length (1 meter), you may be able to connect the leads, then lay the meter on the windshield or stand it on the windshield cowl where you can see it when you start the engine.