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Ask Doug Your Own Question
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8604
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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I just got a 2000 GT with 123k on it. No check engine, of

Customer Question

Hi Doug...I just got a 2000 GT with 123k on it. No check engine, of fault codes, but misfires on acceleration between idle and around 2000 rpm...very rough.
Submitted: 2 years ago.
Category: Mitsubishi
Expert:  Doug replied 2 years ago.
Can we start by pulling the front spark plugs to check brand and condition?
Customer: replied 2 years ago.
NGK BKR6EIX-11 is 0.040 inches. Looks clean (middle plug)
Expert:  Doug replied 2 years ago.
Thanks that's good. How is the porcelain on the top, is it brown/orange at all at the base?
Are you comfortable checking compression and or belt timing?
Customer: replied 2 years ago.
Porcelain is clean. I'm not so good on the compression and timing, but I have the compression tester and the manual...
Expert:  Doug replied 2 years ago.
Compression testing is very easy, we can just do the front back. Remove the three plugs and install the tester into one plug hole, then crank the engine 4-5 revolutions and take a reading, then move to the next cylinder.
Customer: replied 2 years ago.
Working left to right, looking at the front bank, the reading is 145 - 145 - 135 PSI
Expert:  Doug replied 2 years ago.
Thanks, ***** ***** good right there. Spec is 120, and accounting for gauge accuracy I'd say you probably right on point so we can skip the rear bank.
Look at the intake hose carefully... are there any cracks in it, or a baffle broken off or anything like that?
Take a can of brake cleaner and spray around the intake manifold at all sealing surfaces, vacuum hoses, etc while the engine is idling... is there any point where you can influence the idle by spraying?
Customer: replied 2 years ago.
Cannot see any crack...the intake is new. Could not influence the idle with the spray.
Expert:  Doug replied 2 years ago.
Do you have access to a scan tool that reads live data or even that logs?
If not, would you be comfortable pulling the distributor cap to inspect the condition of its contacts, the rotor contact, and the coil cover for cracks?
Customer: replied 2 years ago.
I have an ODB2 reader?
Expert:  Doug replied 2 years ago.
Yeah a code reader won't help you with anything other than if there is a code set or pending.
Customer: replied 2 years ago.
Pulled the distributor is new and does not look to be faulty...
Expert:  Doug replied 2 years ago.
Thanks, ***** ***** behind it? Under the rotor there is a black plastic cover, do you see cracks in it?
Customer: replied 2 years ago.
No...but there is a small rubber seal that is broken and fell off ,when I removed the cap
Expert:  Doug replied 2 years ago.
Thanks. That is of no concern with regard to the running condition.
Last thing we can check before we are going to need some professional equipment...
Put the cap back on and reinstall the wires (make sure you use the numbers on the cap if you didn't leave them attached) and get the battery/intake etc reinstalled.
Pull one plug wire and plug and reinstall the plug into the wire, then ground the plug to the valve cover or other grounded piece of metal and run the engine so you can observe the spark quality to make sure it is intense and white/blue rather than red/orange.
Note you may set an engine light doing this, you can clear it by unhooking the negative cable for a second.
Customer: replied 2 years ago.
All back together and the spark looks strong...only did the front 3...
Expert:  Doug replied 2 years ago.
Thanks. The purpose of that was that we see the coils get weak in these distributors which causes blowout in the mid range, and is usually orange and intermittent when it occurs.
At this point we've ruled out a good bit of items, and are at the limit to what we can do with consumer level tools.
What I would recommend at this point is getting it to a shop that can run a data log while the vehicle is driving so that the sensor values can be read while the problem occurs. This can help identify for example a throttle sensor that is skewing at certain pedal levels, a MAF sensor that is not linear with air input etc, and of course fuel trims.
Beyond that, a running fuel pressure test (requires a Mitsubishi specific adapter that goes in between the fuel line and the task) would be in order in case there is a supply pressure issue, and finally an exhaust check to make sure there is no restriction in the exhaust.