Car runs lean

So when I drive my car for a while let’s say like 10 mi?
She’ll run good for the 10 mi but then after that she’ll start running lean and she’ll start misfiring and lose all power and then at some point she’ll just die. How do I diagnose this?

How do you know it is running lean?

If the check engine light is on have the codes read and post them here, the code will look like P0123


I don’t remember the codes but it did say it was running lean on bank one and two

There are a lot of possible causes, ranging from a bad MAF sensor, or clogged injectors, or a bad fuel pressure regulator, or a vacuum leak, or bad O2 sensors–all the way up to a bad ECM. You need a good mechanic who can diagnose this in person, before you wind up damaging the engine.

Well then I guess my car sitting in my parking spot for a while cuz it cost hundreds of dollars just for them to diagnose what’s wrong. Thanks for the help

A diagnostic is not usually hundreds of dollars , most range from 100 to 150 . Many shops will waive that fee if they get to do the work . Now if you are one of the 3 people in the world who don’t have a credit card then maybe a relative will help you .


3.3 or 3.5 motor? Could be heat related sensor. Crank sensor?
Side note. When you start car are cooling fans off?

It’s a 3.5l v6 And no, my cooling fans are working correctly. My car is actually perfect when it comes to running temperature

Nobody wants to perform work w/o being paid, so mechanics will charge a diagnostic fee in order to not be holding the short end of the stick if the customer says… Thanks… I’ll think about it… and then drives away. If the shop performs the repairs, they are likely to waive the diagnostic fee.

Does your dentist do the exam and X-rays for free if you have the root canal done? Does the restaurant take the appetizer off the bill if you order a full dinner?

No well-run shop can give away the most valuable item they sell. Generally speaking, the shop will have the most experienced and talented mechanic diagnose the failing fuel pump on this Concorde, using thousands of dollars of scan tools, fuel pressure/volume gauges, amp probe/lab scope, and experience. Then once the repair is approved one of the lower-paid line techs will replace the fuel pump.

If a shop tells you they are waiving the diagnostic charge, they are making up for it somewhere else in the ticket. There are only 8 hours in a working day, and they all need to be accounted for. The only shops that have to give away their products are the ones that are hurting for business.


There is a test port on the fuel rail, rent or purchase a fuel pressure gauge and monitor the fuel pressure while you experience the lack of power.

Actually mine did - Aspen Dental - a chain. First visit only though.

Good looking car in nice setting, thanks for photo. 10 miles driving, runs ok, then it starts running too lean? My guess is fuel system problem. Faulty fuel pump, evap vacuum switch system problem causing vacuum developing in gas tank preventing fuel flow to engine, something like that. Any change to symptoms if gas cap is on, but slightly loose? Unsafe to operate vehicle that way, so not a solution, only a test.

Cranks sensor problem noted above, another good possibility. Crank sensor faults often don’t cause P-codes though.

Next time CEL turns on, suggest to immediately obtain diagnostic P-codes from engine computer and post the numbers here.