My problems seem to be multiplying at the moment [:(] …
Shocking misfire with clouds of smoke from the exhaust, almost total loss of power, and whisps of smoke under the bonnet when I get some revs going.
Eventually found there seemed to be a leak from the exhaust manifold around pot 4, so I whipped off the turbo and the manifold, hoping a new gasket and would be the solution. Actually the gasket doesn’t look particularly damaged, but one bolt wasn’t really tight, so maybe it just wasn’t torqued up properly.
However, I may have more of a problem; with manifold off, this is what I see -
It looks as if I not only have the exhaust leek, but also some oil getting out there! This must mean oil in the cylinder, I guess.
So, does this mean piston rings are knackered, or is there any other way to get oil in the chamber?
Hi Dave, the amount of oil showing in the exhaust port looks as though it my be more than just a valve stem oil seal, more likely piston rings or as it is turboed even piston failure which could be caused by pre-ignition from weak/lean mixture or from the ignition timing too far advanced. The smoke from under the hood is caused by the loose manifold bolt where blow-by has left a witness on the cylinder head. A compression check on the cylinders should confirm if it is major or not. Hope this helps, would like to know the outcome. Mozza
There is some sign of oil in the pipe from the turbo to the intercooler, although no copious amounts (does this mean turbo is on the way out, or would one expect some oil seepage?). However the pipe from intercooler to throttle body looks clean, and peering into the throttle body with butterfly open all looks clean. In any case, if oil’s getting in from intake side, I think I’d expect all cylinders to be the same. Thanks for your input.
Of your 3 options, I definitely prefer 1 and 3 [:)] - so those may be my first lines of investigation.
Exhaust smoke was blue-ish (I think - engine now partially dismantled, so can’t confirm).
No sign of splits in boost pipework that I can see.
Thanks for input.
Sounds grim - “piston failure” has a particularly nasty ring to it (no pun intended) - what exactly does it mean? [::(]
Interesting you mention timing too far advanced, as I’m currently also pursuing possible timing set up problem - see my other thread “Cannot adjust timing less than 14 degrees” http://www.mx5oc.co.uk/forum/forums/t/2903.aspx
Generally with pre-ignition, detonation or pinking type problems the temperature generated in the cylinder can get so high to the point that the piston can be holed (melted) or suffers from piston blow-by at an edge usually next to the exhaust port but could be any where around the circumference of the piston producing a gap where the oil can be sucked up past the piston.<o:p></o:p>
A very simple check to make. Get hold of a compression tester, screw into the back plug hole, and spin the engine over [pull all the plug leads to make sure that the engine doesn’t fire]. Should read 180-195psi. much less and it’s either rings, valve guides or a piston failure. The last will show a big drop in pressure.
As an aside, I’m puzzled by the 14 deg timing thing, I’m sure that my car [supercharged] has a base timing of 8 deg, and the changes are made by the Megasquirt ecu??? I guess this is done to avoid any chance of detonation.
I’d certainly go along with the compression test idea, but would also add one warning;
Remove the plug from the CAS before starting the test to avoid injecting fuel into the engine, and, more importantly, to eliminate the danger of damage to the coil packs. There have been several occurances of owners damaging/destroying a coil pack by spinning the engine over with no plugs connected to the leads.
Without the plugs there is a risk of the coils having to generate too high a voltage to create a spark across a large gap, this can cause a breakdown within the electronics contained in the coil packs of all models except the early 1.6, which has the electronics contained in an external ignitor module. Even here its still a good idean to remove the CAS plug to stop the fuel injection squirting fuel into the engine.
Do you have oil on the spark plug of that cylinder? Like already mentioned it could be the rings or the valve stem seals. Do a compression test, take note of reading if it is low on that cylinder, add a small amount of engine oil through the spark plug hole, do the compression test again, if the reading increases then its the piston rings and the oil you have added will temporarily sealing the piston rings, if no change in compression reading then it points more the valves stem seals or guides.
Yes, it looks like the injector fuse does the same thing on the early models, not so sure about later ones as the wiring changes quite a bit. Removing the CAS plug seems to me to be the easiest way of guaranteeing there’s no spark or fuel.
I’ll do a compression test as soon as I’m able – right now, I’m not in a position to “spin the engine over” as I’m pursuing my timing anomoly (http://www.mx5oc.co.uk/forum/forums/t/2903.aspx), though not with any great success.
Good job this car is a hobby and not essential transport [:D]
BTW, when I went to my Mazda dealer for a new exhaust manifold gasket, he persuaded me that in addition to the two-part gasket that I removed, I also needed another thin gasket (making in effect a three-layer gasket) - anyone got any observations on that?
Thanks to everyone for all the input so far. I’ll keep you posted on any progress.
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