K Series Cold Running issue

[COLVERT]

Originally Posted by mbonwick

Or it could just be that the spark gets drowned more easily at the larger distance.
As it's two different sets of plugs I'm using (Bosch/NGK) I don't think we can directly conclude it's an ignition issue.


If it was spark related, I'd expect to be seeing issues at higher revs/hard acceleration which there just aren't. I also find it hard to imagine that I've got 2 failing coils, especially as they're only 3-4 years old.

Are the plugs sooty when you check them ??

You think it's running rich. Normally a rich mixture is necessary to start a cold engine but your engine is harder to start from cold. Odd.

Large plug gaps normally make an engine easier to start but the spark can fail to jump the gap at high revs and cylinder pressure. It just tracks down the electrode surface.

The standard gap should work perfectly at all revs.

Your need to modify the gap could mean the mixture is too weak or too strong so I guess you need to find out the cause of the varying mixture.

Best of luck with it.---

[sworks]

Originally Posted by mbonwick

The cold running problem did start at the same time the VVC manifold was fitted, but then the ported cylinder head also went on that day too, so can't point the finger definitively anywhere.

I Remember a few of us looking at options at Gretna. The uneven firing pulses through the exhaust at the time suggested cam timing to me, was this rechecked and ok, has that stopped? The oxygen sensor obviously wasn’t working in current data but you’ve now fitted a genuine one. I’ve just seen the mention of the head and manifold being changed at the same time the fault started. Was the ported head your original or a replacement? I’ve seen an issue on the K series where the symptoms were similar to inlet manifold gasket failure but not caused by the gasket. You have a VVC manifold so can discount the gasket. It was a 400 tourer and I found on removing the head there was a very small mark on the head by the fire ring, upon testing it was a hole. Once the car had been parked up overnight the coolant would leak into the cylinder and the car would start with a misfire for a few seconds then clear. There was no indication of wet plugs and this was in the days before borescopes. The head was drilled threaded, a threaded plug fitted and skimmed level and the result was instant. It was my own car so nothing to lose as it potentially needed a new head anywhere and the fix lasted a good 12 months before the car was traded.

[mbonwick]

Yes, after Gretna I completely stripped the cams down and put the originals back in. Turned out that the offset dowel on the inlet cam had rotated, so was retarding it rather than advancing - leading to too much cam overlap. How that happened I have no idea, but the dowel is now completely wedged in the cam and will need drilling out.


Anyway, that plus the o2 sensor has it running properly when it's warm, can see the sensor working on the live data now too.


The head was a new one that went to DVA power for building up. Other than some of the valve guides being slightly oversize there was nothing noted (and even then, Dave's words were "not suitable for a race engine but more than OK for normal use").


We're not talking a few seconds of rough running here, like you get with a coolant leak, but several minutes - before lockdown, my normal routine was to start the car, go in and have breakfast, and then it would just about be running smoothly by the time I'd eaten (around 10mins probably).

[COLVERT]

Heat seems to cure you cars engine performance so what is it that heat can cure ???----


Perhaps the sensor to the flywheel gap changes with heat ??? Only a good signal when all the surrounding parts expand with heat.--and the gap closes.

[mbonwick]

I have wondered that, the crank sensor is one of the few that I haven't changed.


The other option I considered is it being in closed loop control - but then it's not like it suddenly runs fine, it's a very gradual improvement.

[mbonwick]

Bit of a bump, any suggestions/ideas other than possibly replacing the crank sensor?

[mbonwick]

Well, bit the bullet and ordered new crank and throttle position sensors. Don't know what else to do if its not that.



Felt very bogged down below 3000rpm driving to work today, not sure if that's me not being used to it or if it's real.


As always, if anyone has any ideas...shout up!

[mbonwick]

Well, new crank and throttle position sensors haven't made a difference.

Completely stumped for what to do or where to go now.

[breakfastinsmethwick]

Is the earth lead to the engine intact?

[mbonwick]

Yes, earths are all connected tight and in good condition.