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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Lexus
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Lexus ES300: I have an intermittent running engine...starter

Customer Question

I have an intermittent running engine...starter engages ok, at times engine intermittently will not start. The under hood fuse/relay box has a space labeled "fuel pump relay". There is no relay in place. Should I hear the pump running? Could the engine run w/o that relay?
Submitted: 1 year ago.
Category: Lexus
Expert:  Juan Crespo replied 1 year ago.
Hi there. Welcome to our site. The fuel pump in your ES300 works off the Circuit Opening relay, which gets its power from the EFI Main relay. Word of caution: When diagnosing an intermittent fault, it's easy to get sidetracked by all the electronic circuits. Instead, it is best to focus first on the basics: For example, when the engine won't start, check to find what's missing; fuel (pressure and injector pulse) or spark. Once you know what is the basic cause of the no-start, then I can help you formulate an efficient diagnosis. Best Regards.
Customer: replied 1 year ago.
Would appreciate help on determining the right " basic cause of the no-start".
Expert:  Juan Crespo replied 1 year ago.
Great. The easiest way to eliminate lack of spark as the possible culprit when the engine won't start is by spraying a bit of starting fluid down the throttle. If the engine then starts, we'll know fuel is the issue. If it still won't start, then you would need a Noid light (about $15 at your local parts store), a ignition tester (about the same) and a fuel pressure tester (available as a loaner from most parts stores). Once you have these tools, I can guide you through a systematic diagnostic process. Best Regards.