Mystery Misfire – Already Checked the Usual Suspects, Help!

I recently purchased a 1999 Toyota Tacoma (2.7 engine) with 186k miles. It was in storage for 7 years so I installed new belts, battery, catalytic converter, fuel filter, fuel strainer, fuel level sending unit, fuel tank, fuel pump, and had the injectors professionally rebuilt/cleaned. After this, the truck started right up and has run great for the past 300 miles until….

Last week when, in the middle of the drive home from work, it started to run rough at idle and lacked power. The check engine light was flashing too. I made it home (slower than usual) and checked the OBD-II codes. P0301 – Misfire No 1 Cylinder. Since then I have done the following…

• Swapped coils even after checking their resistance which was within spec
  
  
• Swapped the number 1 and number 2 spark plugs
  
  
• Added fuel injector cleaner to a ¼ tank of gas about 10 miles ago
  
  
• Checked spark plug resistance on the # 1 and # 2 plug wires (both between 6k and 7k ohms)
  
  
• Cleaned out the fuel rail
  
  
• Swapped the number 1 and number 2 fuel injectors
  
  
• Compression tested the No 1 cylinder. Reads out to 170 psi
  
  
• Sprayed starting fluid at the vacuum hose connections (which would primarily effect the number 1 cylinder) while the truck was running
  

The truck now runs smoother at idle but still flashes code P0301 (and no other codes) when traveling at any speed over idle. The code and symptoms do not manifest themselves at idle. The truck starts immediately whether hot or cold. It will drive faster than 50 mph and still pulls beyond 4,000 rpm but is sluggish and runs rough.

I’m afraid the issue is related to spark at higher rpms.

Any help troubleshooting this fun truck would be greatly appreciated. Help!

 

Hey, did you ever figure out the P0301 issue on your Tacoma? I've got the exact same thing going on, except the car runs perfectly. I've checked all the things you listed, plus the harness from ECU and the P0301 comes back. Dealer said I need a new engine, which is ridiculous. All tests have been good. Compression 205psi on all 6.

Any insight?

Thanks.

 

Do you have a timing light? If so, hook it to #1 and then slowly rev the engine. If the light "skips" you have an ignition issue. If not, then at least you know the plug is firing, so on to the fuel side. Next step would be to check pressure, and possibly the fuel rail where it might have some sort of trash or obstruction near the #1 injector.

Note that inductance-type timing lights are problematic here, you need old school...

 

He is relying on the ignorance of the customer. Almost 200K + misfire == new engine, if you are dishonest and you believe your customer is an idiot.

 

Could be the valves on that part of the head

 

Possible of course, but the chances are very remote. If a valve is damaged, it would be unlikely to have a smooth idle also...

 

Yes but still possible. My 06 Colorado ran great and had 2 valves on a cylinder busted

 

"ran great" with two valves busted??? What does that mean? If the valves are damaged, it is NOT going to "run great". It might run. We drove my son's mustang home from the drag strip with four bent valves. He missed 3rd gear. We drove about 70 miles from Steele AL to Pelham doing 50mph up hills, 70+ going down. That was not "running great" was "just barely running". In general, a valve will kill a cylinder. Would take really odd circumstances to make it idle smoothly but run rough at any speed off-idle...

 

Google "Chevy colorado head failure", it was an issue on the 2004 to 05 and some 2006 engines. Off my skull I believe the valves were burning.

My 2006 Colorado did it and ran smooth but threw a misfire cod

 

did you try swaping coil packs and see if it follows to the swapped coil?

 

Yes I did. I started a new post showing what I've done. Nothing has helped. Dealer said they have no idea what's causing the CEL and agrees the engine runs near perfectly, but still concluded that the engine needed to be replaced. Not buying it. https://www.tacomaworld.com/threads/p0301-stumped-as-to-cause-5vz-fe.445748/