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Ron Z.
Ron Z., - Auto Tech -
Category: Car
Satisfied Customers: 19037
Experience:  18+yrs. experience diagnostics & repair of all makes/models.
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I have a Mitsubishi Montero sport. The engine runs rough it

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I have a Mitsubishi Montero sport . The engine runs rough it idles rough . It throws a code p0306 . I have replaced spark plugs wires coil . And ithrows 2 codes both p0306 .
JA: Is the rough idle intermittent or consistent?
Customer: Consistant
JA: What year is your Montero Sport?
Customer: 2003
JA: Are you fixing your Montero Sport yourself? What have you tried so far?
Customer: Yes I have replaced spark plugs wires #3-6 coils new gaskets
JA: Anything else you want the mechanic to know before I connect you?
Customer: When driving runs sluggish no power

Hi! Welcome to JustAnswer. Thanks for coming! I'm Ron and I'll be working with you on your question today.

Does your vehicle have the 3.0L or the 3.5L engine? And roughly how many miles are on the vehicle?

Customer: replied 2 months ago.
I'm thinking its a 3.0 . It has 117,000 miles

Great Larry, thanks. Give me one moment to type out some info for you. Sit tight one minute... I'll be right back!

My apologies. There are only a handful of Techs that take phone calls. Unfortunately, I am not one. If you'd like, we can continue here in Q&A chat and I can provide you with the information and help you need, and I can handle any follow-ups you may have.

Customer: replied 2 months ago.
Online

Great. Give me one moment to type out some info Larry. Be right back!

Customer: replied 2 months ago.
Give me a call

My apologies. There are only a handful of Techs that take phone calls. Unfortunately, I am not one. If you'd like, we can continue here in Q&A chat and I can provide you with the information and help you need, and I can handle any follow-ups you may have.

Customer: replied 2 months ago.
Continue

Thanks for holding, Larry!
The next thing to look into here will be the fuel injector for cylinder #6. With the engine running, unplug the electrical connector to the injector, the engine should respond with a worse idle. If not, inspect the electrical connector and wire harness for any loose, broken or damaged wires. If no problems are found, the injector will need to be replaced.

If the injector checks ok, next an intake air leak test should be done. With the engine running, carefully and sparingly spray some throttle cleaner around the base of the intake. If the engine responds, this is a sign of a leak and the intake gasket will need to be replaced (make sure to visual inspect the manifold itself for any cracks at this time as well).

If the intake test proves no leaks, then ultimately, a cylinder compression test will need to be done.

Please be kind enough to leave a rating for our Q&A using the 'stars' at the top of the page or click 'Accept' when I have answered all your questions. A 5-star rating is very much appreciated! Rating or accepting my answer does not cost you extra.

Customer: replied 2 months ago.
How can you disconnect # 6 fuel injector with engine running

On the 3.0L you should be able to access the electrical connector with the need to remove anything.

Customer: replied 2 months ago.
I'm sorry the engine might be another size . I thought the Montero sport LS had a 3.0 engine . The only fuel injector I can get to is #3

Ah. Ok. If that's the case, then the upper intake will need to be removed and you can test the injector with an Ohms meter. The resistance should be between 13 - 16 Ohms. Might be a good idea to run the compression test and intake leak test first before pulling apart the upper intake. Get the easier tests out of the way first.

Customer: replied 2 months ago.
Can't do a compression test with ou t removing intake

I believe you can. Pull the spark plugs. Disconnect the crankshaft position sensor electrical connector so the spark and fuel injectors will be shut off. Then crank the engine with the throttle wide open. Should be around 127psi with no more than a 14psi difference between cylinders.

Ahhh. I see what you're saying... right... so the upper intake will need to be removed either way....

Sorry Larry... it's been a long day...

Customer: replied 2 months ago.
The only plug that can be removed is #3 without removing intake . I under stand it could be #6 injector or compression . Is there any thing that it could be other than that . I would like to check something else before I tear the intake off again

Unfortunately, if the plug and coil have already been done, then the only other things that can cause a single-cylinder misfire is an intake air leak, a faulty or clogged injector or low cylinder compression.

Customer: replied 2 months ago.
How about the e.c.m.

If the ECM were faulty, you'd get a P0300-Random Cylinder Misfire, because it would affect all cylinder equally. Not just one. And the ECM's in these vehicles are pretty solid. Very rare to see one fail.

Customer: replied 2 months ago.
I think you for your time . You have given me places to start . Thank you,

You're welcome, Larry! Glad I could be of some help today! Please remember to leave a rating for our Q&A using the stars at the top of the page! Have a great day!

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