I have a 1997 Mitsubishi Mirage with 93,000 miles on it. It idles rough when the engine is cold and when braking it will die if I don't give it some gas or put it in neutral. Once the engine is warm it runs fine though. It starts up alright most of the time, but occasionally dies at start. I have taken it to a mechanic and they can't seem to pin-point the problem. I've had a lot done so far and it hasn't helped the problem. They replaced the catalytic converter and MAP sensor for free, since they weren't able to fix the problem with the other items. I'm not sure how many more things they will replace for free though. Here is a list of services and parts I've had replaced.

- spark plugs
- ignition wires
- distributor cap
- distributor rotor
- PCV valve
- fuel filter
- air filter
- transmission flush
- fuel induction treatment
- catalytic converter
- MAP sensor

If you have any ideas as to what my problem may be please help!!

Thanks!

 

Well my mechanic said he found my problem today. He says that the engine compression pressure difference between cylinders is too great. It should have a maximum of 14 psi at an engine speed of 300 RPM. My cylinders have PSI's of 175, 155, 175, and 150. So he says that my engine needs overhauled, but recommended I trade it in. Does this sound like an accurate diagnosis? Does it really need overhauled or should I get a second opinion? He also said it would be about $3000 ot overhaul it. It this an accurate estimate?

Thanks for your help!!

 

That's a maximum difference of 14 PSI.

 

Since your compression varies between cylinders, I would have your mechanic perfom a leak-down test which will determine exactly where the leak in compression is coming from. What hes told you so far is correct but you need to know where the leak is coming from. It could be Piston Rings or something to do with the valve train in your cylinder head. If the leak is from your head and valve train then thats alot cheaper to fix than a whole engine overhaul. Also I dont know what order you listed the compression ratings but the two with the lowest, if they are next to each other then that could be a blown head gasket. You would probably have more problems if that were the case, but a small crack in the HG could affect performance the way you are describing. I personly think it could be worn exhaust lobes or lobe on your cam. That will cause the symptoms you've described and compression readings you listed.

 

Thanks antomx for your reply.

The compression ratings are listed in order. So perhaps it is a leak or worn lobes. Do you have any idea what either of those would run me?

Thanks again.

 

Again, I would ask your mechanic to find out where the leak is. Rings or valve train? If he dosent know what you're talking about or cant do it then run from him like hes spoiled poo.
If its coming from the bottom end (pistons, rings) If it were my car, I'd dump it. Unless you plan on souping it up, in which case this would be the prime time to rebuild the engine and make it stronger and a little faster. Not sure what engine you have though. Is it the 4G15 1.5 liter 12 valve? If you love your car and want to go through the hassle of rebuilding it, a stock rebuild engine kit at www.importperformanceparts.com would cost $550 and includes the following:
Contains complete gasket set, set of pistons and rings, main bearings, rod bearings, thrust washers, timing belt, balance shaft bearings (if applicable), and a set of expansion plugs and oil pump
I would call about 5 or more different mechanics and get an estimate of pulling your engine and building it with this kit, this way you can get an idea of who's trying to rip you off and who's trying to be reasonable. You would have to also pay to have your head milled and perhaps go ahead and put some new valve seals in. Most shops where I live will take a head that you bring to them and mill it, put new seals in that you provide (which are in that kit) clean it up, check it for cracks ect. for about $100-$150.
The same company that has the rebuild kit also has a high performance kit for about $900.
Some mechanics might tell you to just re-ring it if thats the problem and not to do anything else. The problem with that is now you have a bottom end thats as strong as the day it was new and a head thats not which can cause alot more headaches for you.
You could do all this or find a used engine and price having it put in.
This is for if you want to fix it right and it wont be smooth sailing and might prove to be a pain in the *** for you. Thats why I'd say dump it.
If it is just the valve train then you can get a rebuilt head that has good cams for I would say between $250 and $400 dollars. You would then need a head gasket and someone to do the swap for you. Here again, I would call 5 or more mechanics to get an idea of what it will cost. You should be able to find someone who could do it for around $200-$300 dollars.