If its banks 4,5,6 - you can essentially eliminate everything from the intake manifold back to the the MAF....except those knock sensors?

Prime suspects live between (and including) the oxygen sensors and the exhaust manifold. How does that manifold look? Take the shield off and see if it's not in really bad shape.

 

A bad manifold or sensor would only cause over-fuelling wouldn’t it, not missing spark? Fuel is present, and it was running ok a couple of days ago except missing on one cylinder, I haven’t touched the sensors or manifold. What’s absent now is the spark to those three cylinders. I’ll double check the spark and injection is happening and I’ll have a look at the manifold while I’m there.

 

A cracked 1 bank of exhaust leak could account for a bank of mixture being off and possibly misfiring from mixture ( overfueling )

Your cylinders 4 . 5 , 6 are the aft bank

But not missing spark

Your ECU pin side looks in good shape externally but ,,,,,,,,,,,,,,,,,,,,,,,,

There is only 1 input pin for the timing ( CKPS )

2 pins for ECU power

6 separate pins for coil timed grounds

 

Perhaps timing or lack of power to the ECU then? I’ll give the connectors another clean out. The connector and face of the CKPS also, even though it’s brand new.

Ok, forget the whole bank. It’s only missing spark on cylinders 5 and 6. Cylinder 4 has spark, but isn’t firing presumably for the same reason as it was previously. Compression maybe. Anyway, so narrowed it down to 2 cylinders to focus on first. Will start by moving coils from 1 and 2 to 5 and 6.

Ok, I’ve swapped the coils, still no spark. So we have two cylinders not sparking, and one with a still undiagnosed misfire.

In other news, the Plenum was full of dirt, so I’ve cleaned that out and (hopefully) put the rubber back in the right place. It’s quite hard to get it to sit flat. Maybe that’s solved the leak, I don’t know.

 

When I see that much water, I immediately distrust the wet equipment.

Did you open up the ECU case? I don't know if I could ever get comfortable with the ECU ever again!

I believe the x300 ECUs are plentiful on eBay.

 

" It’s quite hard to get it to sit flat. Maybe that’s solved the leak, I don’t know."

The rubber is probably warped but best it can be , leaves probably degenerate and fall through there and then block

The British most likely have there own ECU part version

 

I felt the same way, the ECU was certainly scary. I took one side off, it looked alright inside. The other side's screws were rusted solid, so I didn't dare force it. Safe to assume the other side internals are more... questionable. Payday tomorrow, so I think I'll treat myself to a 'new' ECU and see what happens.

Just to be sure, I've cleaned the connectors specifically for controlling the sparks for cylinders 5 and 6, just waiting for it all to air out before I reconnect. The wires seem solid in the case, and the actual connectors in the plug look ok. Strange that until I removed the ECU it was functioning fine, despite the significant water presence.

In all the diagrams I've read, the black connector seems upside down to how it appears in the car. Is it at all possible to connect the plug the wrong way round? I assume not, it's just odd the pictures seem different.

 

I'll hit it with a hose and see if it holds water. I'm not quite sure if the rubber flap is meant to do... If it's meant to hold water, why not just make it a solid plastic bottom? If it's meant to let water out, why worry about the flap being perfectly seated? When I was pushing it up into the plenum, one side kept folding up and sticking, then I couldn't get it back down again.

There are quite a few ECUs on eBay. I'll keep an eye out for a 4.0 from my year without any visible water issues, just to be safe. They seem to be around the £150 - £200 mark, so not unbearably expensive.

 

" Is it at all possible to connect the plug the wrong way round? I assume not, it's just odd the pictures seem different."

You would have to look at the keys or male / female channels inside the connector rim

 

Today's testing will be to check the continuity of the ECU to coil wiring. I think either the ECU, connector plug, or wires to the coil have broken since I took the ECU out, I can't think of any other reason why the cylinders would suddenly lose spark other than that.

The ECU would be easier to replace so I'm hoping it's that. Need to restore some cylinders then get back to trying to work out why cylinder 4 is dead. Still thinking it's compression in that one, but I'm stuck for now with 5 and 6. At least I'm getting better at diagnosing misfires!

 

I know it seems like a long time ago, but this car did run well before you parked it for a few days. Despite being untouched by human hand, it ran poorly when you went back to it.
To my mind that would be a clue and would in the first instance point to flat battery, water ingress or rodent damage.
It would seem that you have now eliminated the flat battery possibility, and with the voltmeter reading between 13 and 14 with the engine running, that sounds right.
Water ingress has been confirmed at your ECU, although water in the fuel was my own first suspicion. The seemingly illogical point is that you had isolated the misfire to a single cylinder which had power to the coil and injector, and a working spark plug. I am wondering however whether you carried out a valid test of the injectors and the coils as from memory do at least one of them not have switched earth rather than switched +ve? You could attach a test light/ meter to earth and probe for power successfully without actually establishing that the injector or coil was working as it should.
The fact you could track it to a single cylinder, and can still isolate the fault to specific cylinders is a huge clue, and the wet ECU a smoking gun for sure. It is interesting that your problem switched from a single cylinder to multiple after you tried to dry the connectors, and this is surely another clue. Opening the ECU and looking for moisture would seem like a sensible step ahead of buying a replacement, and drying it thoroughly with a hairdryer would be a good idea.
You say you adjusted the throttle cable earlier to adjust the idle, and this will need to be revisited once you have her back on 6 cylinders.
As a matter of interest, can you remember whether it rained heavily during the initial parked up phase?

 

Hi County, thanks for your thoughts. You seem to be on the same page as me generally. The car ran well as I recall before parking, however it may have always been misfiring on the one cylinder as it's not particularly noticeable at cruising RPM or with the high idle the car had, so I'm not 100% sure if the one cylinder misfire occurred due to being parked or if it has been there since I bought the car two weeks ago. One thing I've since thought about is that the estimated range in the trip computer was very low even after filling up, so perhaps it's always had a cylinder out confusing the trip computer? But then again it was reluctant to start and idling very low on 5 cylinders only after sitting a few days, whereas before it always started easily. So maybe that one cylinder misfire was from sitting.

Battery has indeed been ruled out. It's been charged, jumped, measured while cranking, and it seems above the low limit of 10.4 (I think) volts. It has enough to generate a spark on four cylinders at least, so it's probably fine.

Water in the fuel was a possibility as it had rained since parked, not exactly heavy rain but showers here and there. The filler area was dry and clean when I checked it, so presumably the drain is unclogged. I was also confused why having water in the fuel would cause a consistent dead miss on one cylinder, regardless of plug, coil, or injector. For now I have ruled out fuel, but when she's running again I'll burn through it all and put some super premium in to help flush things out.

The coils and injectors do have a timed earth. I tested for the constant voltage supply to the coils and injectors, all are ok. I know cylinder 4's coil is getting the timed earth as it does generate a spark with the plug outside and grounded on the exhaust manifold heat shield. The injectors I did not test for timed earth, but as there was a strong petrol smell from the exhaust I assumed cylinder 4 was getting fuel and just dumping it out the exhaust valve, unburnt. Also, petrol smell and vapour was present when I removed the plug in cylinder 4. I may remove the fuel rail and injectors again and crank them into a towel to observe timing and spray pattern.

I do suspect the ECU for causing the 6 for 6 misfire and non start, and now the 2 rear cylinders. I'll try and crack it open for a clean and a dry on both sides, as you suggested. I only managed to reveal the black side, which seemed ok. I'll try and get the red side open too without rounding the screws.

The initial misfire on cylinder 4 still vexes me. I know I have spark, I am confident I have injection as it smells so strongly of unburnt petrol, and I have yet to test compression as I've been unable to start the engine to warm everything else up.

Cylinders 5 and 6 are almost certainly caused by a dodgy ECU or ECU connection. The ECU is wet and rusty, and they only started playing up after I fiddled with the ECU and removed it for the first time. I just hope it's not the wiring or the ECU plug, I don't trust my shaky hands to re-solder a new plug on correctly.

Thanks for the advice and apologies if this long old thread seems to be going in rambling circles, that's how it feels on my end too. I don't know how many times I've had the coils and plugs out... Hopefully a bit more cleaning and testing of the ECU and wiring and I'll at least get 5 and 6 back, then it's back on to the elusive cylinder 4. Probably, 4 is down on compression, or maybe not getting injection. Any further advice and suggestions always welcome.

 

I’ve prised open the relay, pics attached. It looks alright, slightly dusty and a spot of corrosion in one corner so that’s been cleaned out.



Not as bad as I’ve seen from other users.

A small patch of blue corrosion.



Connectors from black plug look ok? Whole thing cleaned with contact cleaner, currently drying out.

One thing I’ve noticed is the connector pin in the black plug no. 18, for the ECU controlled relay, is looking a bit worse for wear. Could this be a cause of my troubles?



Just west of my thumbnail. There’s not as much copper showing, could the connector have snapped off, or is it just crooked?

Is there a way to test the relay to see if the ECM is powering it properly?

Once all this has dried out again I’ll reconnect everything and see what happens. In the meantime, continuity checks to the coil. I hope my tester can reach.

 

Well. Here’s number 18 from the plug.



The tongue (?) of the connector fell out of the slot. It’s sitting on top of the spanner in this pic.

So I’ll have to work out how to replace a connector then. It’s an important one I assume, the power relay. Not sure what it powers, but it must be something significant if it’s on the black plug.

Apparently it powers the injectors. So it wasn't broken before, or at least it was holding on enough to send power to the injectors. Now though, it needs replacing.

 

On the run at the moment, so just a quick thought, you have nt mixed up numbers 5 and 6 coil connectors have you? The way the loom is set up, it almost invites you to connect them the wrong way round. Ask me how I know……

 

I wish it were that simple, but I’ve triple checked and they are correct. That would at least generate a spark, but at the wrong time. I’m not getting even a whiff of electricity out the 5 and 6 coils at the moment. Definitely something wrong with the timed ground, either ECU or wiring.

 

Can you put a test light on the White / Pink power sitting wire on the # 5 and 6

You won't be able to use the ECU provided grounds as they appear to fast for light to respond

This would verify half of the 5 and 6 plugs needs

There are wire splices from it's source , but probably not disturbed , maybe inside the harness as you lift it out of the way

The power source is the right engine bay fuse box relay and may be compromised to the edge of badness but good enough for the other coils

This test can be done without the engine running , but key in run position

 

I've tested continuity from the ECU connector plug to the coil timed earths on cylinders 5 and 6, they were both fine and unbroken.

I know they're getting the constant 12V power supply. The wires from the ECU are unbroken to cylinders 5 and 6. It must be the ECU not sending the timed ground signal to them then, surely? They are powered, they are connected to the ECU, but they are not receiving the ECU's signal. That's my theory.

I'll see if I can rig up a test light with some wire and a spare bulb.

 

The 12 volts is not provided by the ECU

You can see 12 volts with a meter but still may be current limited

 

So the meter's 12v reading may not be a true indication of power reaching the coil? But if it illuminates a test light, you can confirm power is arriving? I'm not familiar with current limiting. I assumed 12v at the coil meant good power supply.

I will order a test light and see if it illuminates.

Today's good news is that after cleaning the plenum, and after some rain overnight, the ECU plugs were dry. Hopefully that means the leak is resolved, or maybe the rain wasn't heavy enough.