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Cardoctor71, ASE Master Technician
Category: Lexus
Satisfied Customers: 672
Experience:  35 years experience in the automotive and Lt truck repair business, owner Cardoctor LLC Guthrie, OK
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Cylinder 5 misfire, 270k it misfires sometimes and other

Customer Question

cylinder 5 misfire
JA: How many miles are on the car? Is it a steady misfire? Or random?
Customer: 270k it misfires sometimes and other times it doesnt new plugs new wires new coilpack
JA: What is the model/year of your Lexus?
Customer: 1998 gs300 3.0
JA: Are you fixing your GS300 yourself? What have you tried so far?
Customer: new plugs new coils new wire just changed VVT solenoid changed the injector too for number 5
JA: Anything else you want the mechanic to know before I connect you?
Customer: thats should be enough i believe
Submitted: 6 months ago.
Category: Lexus
Expert:  Todd M replied 6 months ago.

Hello. My name is ***** ***** I will be attempting to help you today. Have you had the coil pack pigtail tested for proper voltage? Have you had the pressure on that cylinder test. You could have a weak piston ring. What could also be happening is a valve for the cylinder may not be closing properly at all times.

Expert:  Todd M replied 6 months ago.

I'm going to check some information. Give me a few minutes.

Expert:  Todd M replied 6 months ago.

You may also have a problem with your ignition control module. This should be tested for proper function/resistance.

Customer: replied 6 months ago.
I have not tested the pigtail end yet. What voltages am I looking for?
Expert:  Todd M replied 6 months ago.

I'm here. Give me a few to take care of another issue. I will be with you shortly.

Customer: replied 6 months ago.
Expert:  Todd M replied 6 months ago.

I'm back. I took the liberty of pulling up these diagrams... As far as the pigtail voltage goes, I would compare them with the rest to be sure, but I'm assuming 14v while care running, 12v while the vehicle is off but in the on position....

Expert:  Todd M replied 6 months ago.
Customer: replied 6 months ago.
My tps only reads a max 75% on full throttle on my scanner
Expert:  Todd M replied 6 months ago.

I don't believe that would be the cause of the backfiring and misfiring. Other than the miss, there vehicle was accelerating properly correct?

Expert:  Todd M replied 6 months ago.

I believe you should have a pressure test done on the #5 cylinder. Lower pressure will cause skipping also.

Customer: replied 6 months ago.
ok the coilpacks are new and so are the spark plug wires.i just replaced the coil pigtails since they were frayed and still same issue. the car accelerates fine when easing on the gas but on certain abrupt accelerations it skips and you have to ease off the accelerator for it to stop skipping
Expert:  Cardoctor71 replied 6 months ago.

New expert ,Because of the extremely high mileage on your car, i would suspect carbon build up issues on the throttle plate as well as the back of the valve stems not only on cylinder 5 but all cylinders, a professional fuel injection cleaning that includes air induction cleaning as well, should remedy your vehicles problems, a great product to search out is called BG Fuel Injection and air induction cleaner, available at your Lexus Dealer. The cleaning should be performed using specialized equipment at the dealership, and performed by an experienced technician , that will take the proper precautions to insure the vehicle does not catch fire . The cleaning solvents are introduced into the combustion chamber while the engine is running at 1500 rpm. The solvents are extremely flammable, a small leak on the equipment while under pressure can spell disaster very quickly. Typically dealerships charge about 200.00 for this complete service and it does not require any engine tear down. Please rate my service, If you have any additional questions I will answer them until you are completely satisfied with my answers.

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