Join 3,516 readers in helping fund MetaFilter (Hide)


Unknown car troubles
March 8, 2014 6:34 PM   Subscribe

I bought a second-hand Mitsubishi Magna a month ago, and it's having a weird loss of power issue. I've gone to two different mechanics and spent more than I paid for it on repairs, but nothing's changed. Has anyone had this issue before?

It's a 1996 Magna V6 'Executive', with 173000 km on the clock, and in fairly good condition (in terms of exterior and so forth).

It starts fine, but 5 - 10 minutes into a drive (in the country, up to about 100km/hr) there will be a sudden loss of power - it feels exactly as if I'd suddenly stopped pressing the accelerator. The engine doesn't stop, and the car will roll for 5-10 seconds. I'll normally have the accelerator down wherever I had it before the problem, and after coasting it will suddenly jump forward with a burst of power and drive normally for another 5-10 seconds before suddenly losing all power again. If I pull over and turn off the engine for a few minutes, it will start fine and drive normally for another 5-10 minutes before the problem starts again. When I stop, there is a fairly acrid burning smell, and occasionally wisps of dark, non-exhaust smoke from the exhaust pipe.

One mechanic did a lot of work on the ignition system and cleaned the throttle body and so forth, but that didn't change anything. The second one said the exhaust system, from the catalytic converter backwards, was very old and blocked. He cleaned it out, and the car ran fine for a few days before the problem started again. He then replaced the whole exhaust, but the problem was there the next day.

Has anyone had a similar problem before? Do you know what it could be? I spent $750 (AUD) on the car, and the repairs so far have cost about $1600. I don't want to pour any more money into this car, unless I could be relatively sure that it was a single, <$500 job that would fix the problem. I can't afford to keep experimenting with fixes. Which I guess is the second part of the question - is there any way to salvage any value from this car, if I can't get it repaired, short of lying to someone and selling it to them? (Which I will not do).
posted by twirlypen to Travel & Transportation (11 answers total)
 
Google says the 1996 Mitsubishi Magna has a fuel filter. Your symptoms (minus the exhaust stuff) sound exactly like what happened to my 1982 Datsun 310 GX, back in the day. Stumped several mechanics, until one figured out it was a clogged fuel filter. If it is your fuel filter, that's a cheap fix.
posted by mon-ma-tron at 7:20 PM on March 8


Wikipedia list the magna as possibly coming with a carbauretor in early 96. Is your car carberouted or fuel injected? (your questions implies fuel injection, but it matters as to your problem).
posted by bartonlong at 8:12 PM on March 8


My husband owns an auto repair / tire shop (in the US) and he says it sounds like your transmission.

He said the first mechanic was an idiot and the second mechanic should have tested his theory better. He said the first thing the mechanic should have done if he thought it was the exhaust (to differentiate it from a transmission problem because they have similar symptoms) would be to remove the exhaust ahead of the catalytic converter and drive it and find out if that was causing the loss of power. It sounds like he didn't do that and just changed the parts instead so now you have no way to know.

My husband says a transmission is likely to be very expensive and you are "pretty much shit out of luck." He said your best bet for extracting value out of the car is to find someone with the same car with a good transmission and a bad engine and sell them your engine.

He says that in general, buying cheap cars is too expensive if you don't want to / don't know how to work on them yourself.
posted by Jacqueline at 8:19 PM on March 8


I don't know how much value you need to salvage to consider it okay, but about five years ago I got $250 for a 1988 Hyundai Excel from a wreckers in Canberra. They were willing to pay that much because I could drive it to them instead of having them pick it up, and all the big parts worked fine (engine, gearbox, etc). It just had enough small problems and worrisome unidentifiable issues that I couldn't get a pink slip, wasn't worth the repair costs, and I didn't feel comfortable selling it on under false pretences.

So if you feel like you can't sell it on, and you can't get it repaired, start calling around the wrecking yards, and emphasise that you can drop it off and that it actually runs.
posted by lollusc at 11:53 PM on March 8 [1 favorite]


Oxygen sensor? Especially once it's heated up. Could cause all sorts of odd fuel mixture problems, which could well cause the dark exhaust on restart.

New one could cost $70-$90 or so (AU) and only take a few minutes to fit if you have some basic tools.
posted by nonspecialist at 12:52 AM on March 9


it feels exactly as if I'd suddenly stopped pressing the accelerator. The engine doesn't stop, and the car will roll for 5-10 seconds. I'll normally have the accelerator down wherever I had it before the problem, and after coasting it will suddenly jump forward with a burst of power and drive normally for another 5-10 seconds before suddenly losing all power again.

So, the engine doesn't stop, but what *does* it do? Does it falter and slow down? Does it continue smoothly at the same RPMs? Does it suddenly rev up higher?
posted by jon1270 at 5:44 AM on March 9


So, the engine doesn't stop, but what *does* it do?

Absolutely the right question to ask and there is no way of diagnosing whether or not it is fuel or transmission without that answer. If the engine revs up (makes more noise) and then surges forward or jumps forwards then it is most likely transmission. If the re-appearance of power is sharp or jerky (even jarring) then it is likely transmission.

If the engine is still running but not revving wildly (beyond where it was when it was pushing the car along) the 'sudden burst of power' could just be the engine getting fuel again and suddenly producing full power again. This will feel like a surge of power because you didn't have power a minute ago.

If the revs drop (despite you not moving your foot) during these periods, then it is most likely fuel pump or filter. If the revs rise, it is almost certainly transmission.

Google says the 1996 Mitsubishi Magna has a fuel filter.

Every car that has fuel has a fuel filter.

Wikipedia list the magna as possibly coming with a carbauretor in early 96.

No car with a catalytic converter has a carburettor. It's not possible to achieve the emissions control that a catalytic converter requires to function without fuel injection.
posted by Brockles at 7:24 AM on March 9



No car with a catalytic converter has a carburettor. It's not possible to achieve the emissions control that a catalytic converter requires to function without fuel injection.


That is completely untrue - catalytic converters were mandated by (US) federal law in '75-76, long before most cars got fuel injection.
posted by 445supermag at 9:49 AM on March 9 [1 favorite]


Apologies - that must be a UK centric viewpoint. Everything had long gone to injection before catalytic converters came to our shores.
posted by Brockles at 1:31 PM on March 9


Thanks everyone! The first mechanic did a general service on it, and replaced the fuel filter, so it shouldn't be that. Could be the pump though, I guess.

Jon1270, the engine essentially idles - not revving at all, despite pumping the accelerator pedal, but not stopping either. That made me think it wasn't a fuel pump issue, since there's still enough fuel getting through for it to idle?

I'm dropping it off to the second mechanic again today, who said he'd have another look for free, given that his first attempt didn't change anything. Thanks for the help!
posted by twirlypen at 7:06 PM on March 9


That made me think it wasn't a fuel pump issue, since there's still enough fuel getting through for it to idle?

Not necessarily. The transmission would likely be backfeeding enough torque to keep the engine turning over at idle or above. The fact that the revs drop despite the accelerator not moving neatly rules out the transmission being the issue, though.

It still could be electrical, sensor, fuel related though. Possibly fuel pump, but without some fairly serious diagnostics and being able to force the fault to happen it may be hard to find.
posted by Brockles at 6:49 AM on March 10


« Older A friend and I are taking a sh...   |  When I was younger I wanted to... Newer »

You are not logged in, either login or create an account to post comments