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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8598
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Replaced fuel pump car ran great next day car won't start?

Customer Question

Replaced fuel pump car ran great next day car won't start?
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.
Was anything changed apart from the fuel pump?
Was the original problem intermittent, where you had periods of operation and periods of failure?
Can you check for fuel pressure while cranking (or listen for fuel pump operation while cranking)?
Customer: replied 1 year ago.
The car had low fuel pressure and was low on power, changed pump and she fired right up and test drive with great power and response, went to start it yesterday and it tries to start then just cranks over
Expert:  Doug replied 1 year ago.
Lets check to see if you can hear the pump running while cranking (not just key on, it has to be cranking), and if you do lets get another fuel pressure reading.
Customer: replied 1 year ago.
Pump is not running while I'm cranking the motor but runs just in the key on position till I crank it over
Expert:  Doug replied 1 year ago.
Can you clarify, the pump is running any time the key is on?
Customer: replied 1 year ago.
When I turn the key on the pump starts but I don't hear it when I'm cranking the motor over
Expert:  Doug replied 1 year ago.
Please pull a spark plug and see if you have spark while cranking.
Customer: replied 1 year ago.
Is there a fuel filter on this vehicle? If so where is it located? I will check for plugs firing as I said after I put the new pump in the car ran great
Expert:  Doug replied 1 year ago.
The fuel filter is part of the pump assembly.
The reason for checking for spark is that there is a common ailment that will cause both the fuel pump and spark to stop working while cranking... And it is highly likely this could be your issue, so we need to check the spark.
Customer: replied 1 year ago.
Car had low voltage so I jumped it and it fired right up, I can hear new fuel pump working the service engine soon light is on, what do you recommend I'm gonna check alternator voltage now
Expert:  Doug replied 1 year ago.
Check your charging voltage for certain.... if the problem all along was just that it didn't have enough juice to spin it over that fast, then you would suspect the battery is faulty or the charging system isn't working (And upon last shut down the battery is fairly heavily depleted from running).
If the charging is normal... then it is possible that the battery ran down from trying to start the engine and is unrelated to the actual no start condition previously.
In that instance, I would go with my previous assumption (regarding losing spark at the same time as fuel pump operation) and check out your crank position sensor while the problem is occurring. It is highly likely that it is intermittently cutting in and out at that point based on the symptoms. The crank sensor is the origin signal for the fuel pump, without it you will lose fuel pump operation during cranking only, and you will lose spark too. This is a VERY common failure (partly due to the use of aftermarket crank sensors that have compatibility issues on these cars, but just natural failure as well too), and it is extremely common to get misdiagnosed because of the unusual feature of killing the fuel pump when it malfunctions and randomly coming back etc.
Customer: replied 1 year ago.
The car is running again without any CEL lights but two different scanners say I have a faulty camshaft positioning sensor? Are those something that would cause intermittent start stop CEL codes?
Expert:  Doug replied 1 year ago.

Absolutely would... it would not cause the fuel pump to not run, however it would prevent more than a single fire from occurring at most during cranking.
It is of utmost importance to note that you can not use aftermarket cam sensors on this car. They will not work properly... best case scenario you may get a few weeks/months out of them, but realistically they often are inoperative right out of the box.
If you are getting a cam sensor fault (P0340) on a 2.4 and you are certain your belt timing is correct, the cam sensor is going to be at fault. If you are unsure about the belt timing, it would be wise to check that first just in case... it usually sets a P0335 and P0340 at the same time when it is wrong, but not always.

Customer: replied 1 year ago.
Timing belt is fine, the local Napa store said their sensors are good, you recommend going to Mitsubishi for the sensor then?
Expert:  Doug replied 1 year ago.
Absolutely... in fact the NAPA ones are one of the least reliable.
The problem is that the same sensors are used for Hyundai as well as Mitsubishi, and the Hyundai systems are WAY more lenient when it comes to signal quality. Because of this, the manufacturers have no real interest in improving things for the Mitsubishi portion of sales which accounts for next to nothing... consider that Mitsubishi has a 0.4% market shared, then you consider what that looks like next to the goliath that is Hyundai now... they have a 99% success rate, it would cost them a fortune to improve the design to Mitsubishi standards for basically no real profit.
You can certainly try them... just be forewarned is all. These cars get towed in from other shops all the time with aftermarket cam or crank sensors and the other shop is at wits end unable to solve a problem that they diagnosed right the first time, just the new parts were rubbish.

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