Mechanic Misdiagnosed P0300

4Runner is a 2002 with 344K miles. Had the spark plugs and head caskets replaced a year ago. Now a fuel pump and fuel filter.

Had the CEL come on and with a cold start would idle rough. After a few minutes it would seem to subside. While driving it was OKish, and then upon acceleration would be slightly hesitating. Checked with the ODBII scanner and it was code P0300, took it to a shop and they said it was the fuel pump and filter. OK done.

Picked it up and next day it had the same issue. Checked with the ODBII scanner and now it has added the P0304 with the P0300. Random misfire and #4 Cylinder. Took it back and now the shop is saying it is the Fuel injector on the #4 Cylinder.

After reading some posts about these codes and similar issues, it could be a lot of different things. Now the shop does have a professional type of ODBII scanner, and can read a lot more information then I can. But shouldn't they have done a compression test first and then a leak down test second?

I am not trusting this shop and I do not have the tools (testers) to DYI. I live in a small town in the desert and these guys are the only shop. Another shop would be 60 miles away. I am mechanically inclined - but can only do so much. My fear is a blow head casket.

 

Did the same shop do the headgasket work? A good shop would have compression checked and leakdown tested the engine. You can swap components over to see if the problem follows specific parts like if #4 is missing you can swap injectors with another and see if the misfire follows or the same with the coils. It sounds like this shop isn't very good at diagnostics and are just throwing parts at your Runner. How do they know the fuel pump was bad? Did they check fuel pressure?

 

They said they did a fuel pressure test and that is why they replaced the fuel pump and filter.

I am having do the compression test and leak down test tomorrow.

Thanks

 

so the shop did a compression test and leak down test and said it was the #4 cylinder fuel injector.

I drove it home and swapped the coils on #4 and #5…
Rough start and idle…checked codes…now I have P0300, P0303, and P0306. ??????? Totally confused. Any help would be greatly appreciated