Misfire... Need help badly.

T

The-Kid

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#1
Hi guys. I have a 2002 Mitsubishi Galant ES 4cyl AUTO. ~127k I have done all the maintenance and more. Beginning at like 75K, the car started shaking at idle when in drive. at like 120K, timing belt broke and was brought into a NOOB shop. No bent valve. No damage. Though now, the car's engine sounds unbalance at 3000RPM. (Sounds REALLY LOUD) The car had misfire at like 95k. Though the misfire was very little back then, it has gotten worst. So here's the whole story. (Check engine light is on)

Trying to fix the misfiring I have replaced the following things.
-Ignition coil
-Spark plugs (to OEM)
-cleaned the fuel injectors (switched it around)
-replaced the pre-cat O2 sensor.

When it was misifring, the check engine light comes on. So I went to Autozone and got the code. P0302 and another time P0304. To I thought something was dirty or something is not right in the #2 or #4 cylinder. (Only happens in the even # cylinder) So I went ahead and replaced the spark plugs. It was fine for a while, but it came back after a mile or 2. Then I replaced the ignition coil and wire. I guess it got better. Then we took out the fuel injectors and cleaned them with CARB spray at the tips. We even put the even # injecotrs in the odd number cylinder. STill misfiring in the even. Got better, but still misfiring. So then, just because of desperate reasons, we replaced the O2 sensor. Nothing changed. We checked the connectors and they were still good.

So my theory now is the EGR valve (going to test it with the vacuum pump). So my question is can a EGR valve cause a misfire. and can a compression test tell me anything?

*on a side note, the misfire happens when in Reverse (stopped) and in drive. It seems like it only misfires when im accel. from 0mph. If you need any more info please tell me.

I'm desperate and any probable causes are accepted. So please reply soon!!!
 

2POINTautO

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#2
A compression test would not be a bad idea but you are going to have to be very specific on how you do it. Watch the very first pulse, lets say it goes up to about 50 psi on the first pulse, you need to be aware of this, if a cylinder seems to be low on the first pulse, release pressure and start over again. For the rest of the test you need to count that first pulse and then pick a stopping point, as in reading the gauge, lets say five pulses. You need to compare all cylinders in the same way, lets say five pulses. I would use a friend to turn the key while you watch the gauge. He may keep turning the engine more than five pulses so keep a close eye on the gauge. Some people like to pump up the cylinder to the max reading, lets say 8 to 10 pulses, a weak cylinder may pump up just fine like this so be aware of this false reading possibility.

There is a dry test, like you already know how to do, then there is a wet test by adding a little oil into the cylinder for round number two if weak rings are suspected, this is evident by a low first pulse.

I would opt for a leak down test on your engine, this requires a special compression type tester and I would pay to have it done by a reputable shop, you seem not to mind spending a little money on your car for troubleshooting from the hip. I would not be suprised to find a slightly bent valve. If the shop knows how to read spark on an oscilloscope, the bent valve should show up there also. Another piece of special equipment is a vacuum transducer that goes with the scope but this one will be used by someone who uses it on a regular basis, it takes experience more than the other tests.

Maybe someone else can explain a running compression test better than I can, you can perform that one by yourself also. I think you install the guage like normal, start the engine, only pull one plug at a time for this one, release pressure, check the reading at idle, goose the engine real fast all the way to the floor and check the reading again. The idle reading is lower than a normal compression test, go figure.
 

jjm

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#3
You need to do a compression test. It is very UNLIKELY valves weren't bent on the 2.4 motor. Since the engine is running, you're lucky the damage wasn't worse, but it's likely there IS valve damage. Compression test should tell all.

My question is why the timing belt broke to begin with. You indicate you do all the maintenance, but did you forget about the timing belt? Most Mitsu 2.4 motors are supposed to have the belt replaced at 60,000. So if yours broke at 120,000 you were REALLY pushing it.

Joe

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T

The-Kid

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#4
LOL I know. Its bad for the engine. *SIGH* I knew that we were suppose to get the timing belt replaced, but we were short on money. And the fact that we're short on cars too. LOL! Anyways it won't happen again.

Anyways I'll try to buy a compression tester this weekend or something. How about the EGR? Do you think that could cause the misfire?
 
W

Will Mackey

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#5
The E.G.R. valve will have an effect on all cylinders. Replacing the egr will not help your situation. You say you have the misfire while accelerating. The egr would cause a problem at idle, no acceleration. The egr (exhaust gas recirculation valve) opens when you accelerate and allows exhaust gas to flow back into the intake manifold. This gives 3 results: 1)decreases combustion chamber temp (by about 600 degrees) 2) Gives better fuel mileage (burning gas twice) and 3) Cuts out pinging. If it was stuck open while accelerating, you may get a hesitation, but you would'nt experience a misfire.

You say it got worse after the timing belt was replaced. I am going with the thought that this is dohc? It has been my experience that a lot of mechanics have a hard time getting the exhaust cam lined up properly when replacing the belt. It is possible to be a toothe off and still have a good idle, but you would experience other problems (missing and such) while accelerating.

Do the compression test as the other fellows have suggested. If it comes up weak, I would still check the timing belt and make sure it is on right. This would also give you low compression in those 2 cylinders.
 
T

The-Kid

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#6
It's a SOHC. Sorry. Ummm I might do the compression.

I thought misfire and hesitation are the same. Well I guess hesitation in accelerating. When fuel is in demand. Like if I'm accelerating hard through a yellow light, it hesitate, but recovers.
 
W

Will Mackey

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#7
Yes, as soon as I posted I realized it was sohc. Unfortunately there is no edit function here :(

No, misfire and hesitation are not the same. Most people who come into my shop describe a misfire as a hesitation, but to a mechanic they are seperate things. If you have doubts about the quality of the tech who replaced your t-belt and feel it got worse after it was replaced, I would still go ahead and do the compression test, but I would also have the nagging feeling that I should check the t-belt for proper alignment.
 

Dave

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#8
I've worked on allot of these 2.4L mitsu motors and every time i have one come in with a broke timing belt there is valve damage it might only be slight damage but there was always some. also Mitsubishi's always have missfire and hesitation problems and it could be allot of different things i have a 00 galant in my shop right now with these symptoms some times it will be easy to figure out and some times it will be really hard to figure out.

so on your car I'm going to say i wouldn't do a normal compression test you need a leak-down test cause i think your going to find a bent valve in there. this is the first thing you need to do then after you get some results from that you will know if you need to go back into the motor or start diagnosing the misfire

post back the results and let us know each step you took
 

Dave

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#9
just as Joe said earlier in the posts i cant stress it enough on a Mitsubishi the timing belt needs to be changed every 60,000 miles. this is no joke Ive seen them go only a few miles over 60K. Mitsubishi's are really good cars in my book i love them but they require tighter maintenance intervals than most cars
 
T

The-Kid

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#10
Aite thanks guys. I don't want to sound rude or anything, but does a bent valve(even a tiny little one) can cause hesitation? I just want to work on the hesitation problem.

And where do I go to get a leakdown test?

I'm kinda short on $$$ right now. I've spent lots on this car, its just makes me frustrated to spend more money. =(
 

Dave

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#11
yes a bent valve could cause misfire & hesitation. also Will Mackey had a good point in his post that you need to check your timing belt for proper alignment, that could also result in hesitation. any shop in your area should be able to do a leakdown test as for prices I'm not sure for your area.
 
T

The-Kid

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#12
Hey guys. I forgot about this. =( anyways, I didn't get the test yet. How much would is cost. Around how much. Between $30-60???

And also the problem has gotten worst. So I don't know what is going on...
 
T

The-Kid

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#14
The car has 2 coil packs. So no distributor cap. I replaced 1 of them, and switched it around. Both are good.