Low Compression (engine random misfire)

Jimny 2008 M13A engine 140k miles
I reported on a small problem a while back .- engine misfire when cold - where I replaced many parts and eventually came to the conclusion that the problem was solved. Turns out it was not.. and it appears far from it. 3 months ago as the weather started to get colder, the EML would come on even when I would let the vehicle idle and warm up. Once warm I started to just slightly detect the faintest of misfires when driving, so as I have finished getting the rest of the vehicle pristine, I decided to get to the bottom of this misfire problem. It passed through my trusty garage who could not find an issue so I took it to 4 Paw Racing, a specialist tuning company in Huntingdon. They have tested and checked all the sensors, electrics and EMU and found the following:

• Engine running excessively lean
• Compression on all 4 cylinders now sitting at around 110 psi and less (3 months ago it was checked as up in the 130/140 psi range by my garage) 

According to the Suzuki workshop manual that they have access to (they are registered to get this info from Suzuki), this very far below what it should be.

This deterioration seems to have taken place over the past 3 - 4 months, when I have driven less than 200 miles due to my travels. 

They have recommended replacing the engine. They are vehicle enthusiasts at heart, so I have no reason to doubt them.   

But this is so far outside my comfort zone I feel like they are talking heart transplant here.

I cannot face the thought of dumping this vehicle, I have spent countless hours and quite a few pounds on getting it looking super nice, it has been my hobby vehicle completely. MOT is in January and if the light comes on, thats it, fail. 

Not the Christmas news I wanted, so I am posting this for comments and suggestions. 

What now?... Where to from here?

If you are asking whether the advice to retire the engine is reasonable, then my answer is yes: everything has a service life, and at 140k it should not surprise that the motor is rather tired.

If you are asking *how* to deal with retiring the engine, I assume that you are not the @yakuza type who would rebuild it on the kitchen table over the weekend just for a larf. But that does not mean a "heart transplant" has to be a traumatic or expensive undertaking!

The good news is that secondhand engines are readily available and can be very cheap indeed. Especially with a "hobby vehicle," you can take your time until your network turns up a good replacement motor for you. The swap itself is quite straightforward, and I doubt your preferred tech will charge you as much as you might be fearing.

Bottom line: if you want to keep that particular Jimny, put out some feelers now to help find a replacement (good used) engine. Sit back and wait until you have found the one you want, SORN it for a bit if needed, but don't worry-- a good, reasonably priced solution is out there.

Either way, don't give it much thought for the next two weeks. The holidays are not a time to worry about such things, and the problem will not seem so bad after you have let it mellow for a bit.

Just my halfpenny worth having been in such situations before. Good luck and keep us posted.

That's very sad news.

Low compression is usually piston rings have worn, especially in a high mileage engine, but if it has happened very quickly then it's not just wear it is something which has failed, like a split ring.

Rings can be diagnosed using a borescope to look at the cylinder wall, but you might need to get your garage to do the test and analyse the results as it might not be obvious on a low cost eBay scope.

Running lean is much more of an issue as a lean engine will suffer two problems, the first is 'knocking' or multiple detonations as the fuel doesn't burn correctly, the second is excessive heat which causes wear to valves, cylinder head gasket failure and in extreme cases a hole in the top of your piston.

The two could be linked, a very lean engine which has caused rapid [exhaust] valve seat wear and this has led to a lack of compression.

My suspicion is the garage has suggested an engine swap as it is cheaper than finding out what is going wrong and then fixing the issue.

Did they give you an indication of cost to replace the engine?

Robin

Long block swap to a 1.6?

On a M13a engine, Suzuki considers 'normal' as 199 psi, and the acceptable limit as 156 psi, I mention this so that you understand that the engine did not suddenly deteriorate in the last three or four months, three months ago with 130~140 psi compression numbers, that engine was well past it's prime.

As has been mentioned, the primary cause of low compression is wear, worn rings, worn bores, there can be other causes and the quick way to determine this is a properly done compression test, dry & wet compression tests - these should be reported on a "cylinder-by-cylinder" basis, so you get two compression numbers per cylinder, eight for a four cylinder engine.

The value of the compression tests lies in the way the numbers vary from cylinder to cylinder and between the dry & wet tests for the individual cylinders.