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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 22660
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I have a 2000 Hyundai Elantra that has a P0301 code. I've replaced

Customer Question

I have a 2000 Hyundai Elantra that has a P0301 code. I've replaced the spark plugs, checked the electrical connections with spark plug lights, there is normal voltage at the injectors, normal resistance across the injectors, changed the fuel filter, swapped the injectors from cylinder 1 and 2 with no change in the code. The car idles normally but runs very rough and with decreased power.
JA: Spark plug problems can be challenging. So many causes, some simple, some complicated. Fortunately, the mechanics we work with have tons of experience dealing with all of them. Are you hoping to fix this yourself?
Customer: If possible
JA: Is there anything else the Mechanic should be aware of about your car?
Customer: Not that I can think of, it was running just fine up to this point.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Car
Expert:  K. Wiggins replied 1 year ago.
Hello, it looks like you've covered most of the bases so far. Have you checked the injector to see if it's being fired using a "noid light"? Also have you performed a compression check?
Customer: replied 1 year ago.
yes on the noid light, all injectors were firing normally, have not done a compression test yet, don't have a gauge at this point.
Expert:  K. Wiggins replied 1 year ago.
Thanks, ***** ***** Is where I suggest going next, I often see these vehicles blow the head gasket between cylinders resulting in a misfire like this. Let me know how the test goes.
Customer: replied 1 year ago.
sounds good, I've read about bad intake gaskets causing this problem as well, will a compression test identify that as well? I was also wondering if you can tell me where to connect a vacuum gauge to check for vacuum leaks? Thanks for your time.
Expert:  K. Wiggins replied 1 year ago.
Usually intake gasket leaks result in a PO300 code which is random misfire as well as a lean code. Compression test will not identify the intake leak vac test will. The best place to check manifold vacum is the hose at the brake booster. The link below explains how to iterpret your vac gauge readings. Let me know how things go.
Expert:  K. Wiggins replied 1 year ago.
Hello, I was just wanting to follow up and see how things went.
Customer: replied 1 year ago.
Compression was 210 on cylinders1,2,3, and 215 on 4, all cylinders built up pressure at the same rate, first around 95 and then by 7 to 10 cycles of the engine were at max pressure.
Customer: replied 1 year ago.
Vacuum is steady at 17, elevation here is 3500 feet. I can hear a hissing around the hose that connects the idle speed control actuator where it connects to the intake manifold, is that normal?
Customer: replied 1 year ago.
Vacuum on the pcv hose bounces between16 and 18, same thing on the fule pressure regulator.
Expert:  sprinkles08 replied 1 year ago.
Hello and welcome to JustAnswer!Have you checked for vacuum leaks using carb cleaner while the engine is idling?