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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8594
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi 3000GT SL: I have a 93 3000GT SL that is having

Customer Question

I have a 93 3000GT SL that is having idling problems. Its idling under 1000 RPMs and sounds like crap if I give it gas.
Submitted: 2 years ago.
Category: Mitsubishi
Customer: replied 2 years ago.
it sputters when I give it gas and seems to have a hard time gaining RPMs
Expert:  Doug replied 2 years ago.
Is the check engine light staying on while driving, and if so can you retrieve the codes from it?
What is the current mileage, and when was the last time the timing belt was serviced?
Customer: replied 2 years ago.
The check engine light is on and it has about 180,000 miles on it I recently purchased the car fro a friend who had it sitting up for a while. It had ran fine for the last couple of months with no issues but now its doing this. I don t know when the last time the timing belt was serviced.
Customer: replied 2 years ago.
And I do not have a scan tool so I wont be avble to retrieve the codes.
Expert:  Doug replied 2 years ago.
Hmm, that is certainly going to complicate matters.
When the engine is idling and revving, does the exhaust feel normal out of the tail pipe or does it feel like very little is coming out?
Customer: replied 2 years ago.
I would have to get back to you later on that one Im currently at work. but i didnt have any smoke coming out of the tail pipe.
Expert:  Doug replied 2 years ago.
I'm not concerned over smoke, but just the feel of the exhaust as it exits... if it feels like a reasonable amount of exhaust exiting or if it feels extremely minimal (you can compare versus another car if necessary). A lack of exhaust pressure would at least point us in a direction if that was the case. Beyond that inspection, we are going to need to get it to a shop to perform some more in depth checks.
Customer: replied 2 years ago.
O the heat shield did come off of catalytic converter also.
Expert:  Doug replied 2 years ago.
That is not of too much consequence. Though the catalytic converter is what I am interested in with regard to exhaust flow... a reduction in exhaust exiting the tail pipe would indicate a catalyst clog which will cause idling issues, abnormal noise, and lack of power.
Customer: replied 2 years ago.
One of the ignition coil packs isn't firing
Could this be the reason for my drop in RPMs
Expert:  Doug replied 2 years ago.
Thanks, ***** ***** is going to be of concern!
With one coil not firing we need to figure out if this is intentional (computer requested shut down) or if it is due to actual malfunction/component failure (bad coil, bad PTU).
Are you able to swap the coils around and see if the same coil location does not fire, or if the problem follows the coil you move?
Is checking the belt alignment something you are able to do (if the timing belt slips a tooth or more, the computer shuts down one coil)?
Customer: replied 2 years ago.
Which one would happened outta now where??
Expert:  Doug replied 2 years ago.
The coil or PTU failing are more likely to occur out of nowhere like that. While belts slipping aren't necessarily uncommon, they generally are only a concern if the timing belt is long over due for replacement. The coils and PTUs failures would be completely random.
Customer: replied 2 years ago.
Where is the PTU located
Expert:  Doug replied 2 years ago.
The PTU is located underneath the coils. It is the flat electronics part right underneath them, around 4" square and flat.
Customer: replied 2 years ago.
Okay I see it is there any way to test if that is the problem
Expert:  Doug replied 2 years ago.
Here is what I would be doing, in this order:
1) Disassemble the coils and swap them around to see if the problem moves. If the problem follows the coil, then you know the coil is at fault. If the problem does not follow the coil then:
2) Check for signal to the PTU. This requires a volt meter and to unplug the six pin connector and measure the voltage on pins 1 2 and 3 while cranking. Good voltage would be anywhere from 300mV to 3V, pulsing on and off while cranking. If all three are within normal range, then the PTU is bad. Be aware aftermarket PTUs are very hit or miss... if this is the case, I would strongly recommend getting a Mitsubishi PTU.
If one of the three wires (there is one for each coil) is 0V or high voltage (5V+), then there is a problem originating at the ecu and so:
3) I would check the timing belt alignment. If it is off a few teeth it will shut down one coil and you will only get two good signals at the PTU, so only two coils will work. If the belt is off position, of course re-aligning it would be in order... and at that point if you don't know the history it would be wise to just replace it with new. These are 60k mile belts and if they fail it will wreck the engine.
If the belt is aligned perfectly, then:
4) I would pull the ecu (under radio, near gas pedal) and inspect it for visible signs of damage inside. 91-95 ecus are somewhat known for internal failure (leaking capacitors, burned out diodes, etc) and are usually visibly verifiable. There are many ecu repair shops that will fix these if this is the case... it is a common failure on this model
Apart from something out of the ordinary (rodent damage to wiring etc), one of the above will be the issue, and following those steps will identify it.
Customer: replied 2 years ago.
Expert:  Doug replied 2 years ago.
You're welcome, good luck!

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