Technical Fiat 500 Rough idle/ crankcase pressure?

[Telephonepole]

Hi,
My friends Fiat 500 (4 cylinder) has some weird symptoms.
It runs fine on cold start, but as soon as the engine gets warm it starts to shake and “puff” from the exhaust like one cylinder isn’t firing right.
Additionally, there seems to be a ticking noise similar to a header leak.
The idle also noticeably drops when electric load is applied (turning on the lights/ rolling down the window)
However, it revs up just fine...the slight miss seems go away once the engine gets reved past idle.

So far we installed new Spark plugs and wires, one plug was completely trashed and the top part of it remained stuck to the wire during removal, but the new components didn’t change anything.

After replacing the parts we test-started the car without the airbox on, and there was lots of pulsing air coming from the breather hose (valve cover to airbox). The throttle butterfly was also pretty gunked up, like there was lots of oil being pushed through the breather pipe.
When removing the oil cap with the engine running there’s is a loud sound and lots of oil splashing, so it seems like the crankcase pressure is a bit off...
Right now I think it might be either a blown headgasket or broken piston ring...or do these engines just run rough with high crank pressure? Never worked on one...

Thanks!

 

[varesecrazy]

If its losing fluids.. that needs investigating

DO remove the spark plus again.. and compare them.. cylinder to cylinder

its possible its running on 3 cylinders

 

[Al D]

typecastboy may have some advice....??

 

[typecastboy]

Have you changed the coil pack and leads (£25 on ebay). I had spluttering, rough running on a car recently and it took me ages to figure it out. Ended up being an air seepage in the inlet manifold. Was overfuelling and the plugs looked like they had been in there since the old king was on the throne.


Diagnostics is clearly needed. Anyone near you with MultiECUScan or invest in the software and cables and plug it in yourself. You're never going to get to the bottom of it except playing parts roulette unless you get it plugged into diagnostics.

 

[jrkitching]

@Telephonepole, welcome to the forum.

Remember the OP is in the US. The generic advice is sound & relevant, but it's unlikely there'll be someone round the corner with MES (does it even cover the US engines?). The OP sounds mechanically competent and has started out doing all the right things.

I'd do a compression test before proceeding further, just to be sure there isn't a serious mechanical fault like a broken piston ring, leaking valve or failed HG. If it's ever had any cooling issues, the latter is certainly a distinct possibility; HG failure is likely if run low on coolant. After that, you really need diagnostics to narrow down the possibilities.

 

[chris3234]

Have a check of a vaccum pump on the right side of the engine at the top on the end of the cam Shaft a few people have reported issues with this leaking on the US engine's

 

[varesecrazy]

Good spot there JRK

Being a multiair ..

Irregular running has yet more possible causes

A 'dead' sparkplug doesnt hint at top notch service upkeep..
And these motors do need some care

Again

Pull the plugs.. that may well tell a story

 

[Telephonepole]

Hi,
thanks for all the input!

I just performed a compression test today...unfortunately cyl. no. 1 is low on compression, the others are almost equal...a drop of oil improves the reading, so dead rings it is....


This is also the cylinder from which I pulled the broken spark plug, so I think running the engine for a long period of time without proper ignition caused a fuel wash-out in the cylinder bore and now the rings can't seal properly...

Seems like this engine is in for a full rebuild -.-

 

[jrkitching]

Seems like this engine is in for a full rebuild

Not sure about availability of parts (both new and used) in the US, but here in Europe, lots of mechanically sound cars get written off by insurance companies after relatively minor accident damage, so buying a secondhand engine from a breakers is often a more cost effective option.