Hey everyone, looking for some diagnostic help with my '98 Ranger 4.0L 4x4, 180k miles.

Initial codes: P0305 (cylinder 5 misfire), P0306 (cylinder 6 misfire), P1151 (O2 sensor issue)

Work performed:

• Complete tune-up: new spark plugs and wires on all cylinders
• Cleaned MAF sensor
• Replaced driver's side O2 sensor
• Oil and filter change
• Cleared codes

Current situation: After the tune-up, P0306 and P1151 are gone (great!), but now I have:

• P0305 - Cylinder 5 misfire (still there)
• P0174 - System too lean bank 2 (new code)

So the tune-up fixed the cylinder 6 misfire but cylinder 5 is still misfiring. I'm wondering why one cylinder cleared up but not the other, and why I'm now showing a lean condition on bank 2.

Has anyone dealt with a similar issue? I'm thinking maybe vacuum leak at the lower intake manifold, bad injector on cylinder 5, or possibly a compression issue. The fact that cylinder 6 cleared up makes me think cylinder 5 has a different problem beyond just plugs/wires.

Any suggestions on what to check next would be appreciated. Thanks!

 

Driven daily? Dose it with injector cleaner.

A '98 would need all O2 sensors replaced, no? Otherwise you're asking for...imbalances!
What quality/brand sensor did you buy?

 

Hi George,

I changed the drivers side O2 sensor with a Bosch brand. It seems now that the P0174 code has gone away and only the P0305 code remains

 

Give it a healthy dose of Techron before a stint of local driving. They say the PEA works on injector nozzles upon shutdown.
Throwing Techron into the tank before a long trip is not the way.

Besides something freaky, like a weird condition inside the coil pack or a bad valve spring, checking compression, wet and dry and maybe cold and hot too, might be a good idea.

 

Update from the mechanic:

Confirmed Findings

• Active code: P0305 – Cylinder 5 Misfire
  
• P0174 (System Too Lean – Bank 2) is not currently active, but mechanic notes it is very likely to return based on fuel trims
  
• Cylinder #5:
  
  • Has good spark
    
  • Shows 145 PSI compression (healthy)
    
  • Has proper injector signal (confirmed with noid light)
    
  • Spark plug was fouled, cleaned and swapped with #6 — misfire stayed on #5
    

Live Fuel Trim Observation

• Bank 2 (driver side) is running at +25% fuel trim, meaning the computer is adding a lot of fuel to compensate for what it thinks is a lean condition — a classic sign of a failing or clogged injector.
  

Mechanic’s Recommendation

• Replace Cylinder 5 Fuel Injector
  
• Additional Notes
  

• Mechanic noted an unusual binding or crunching noise from the engine while running
  
• Recommends removing valve covers to inspect further
  

 

The mechanic "noted an unusual binding or crunching noise from the engine while running".
- At 28 years of age and 180k miles, have you considered accessory belt and bearings aging?
-- Are the front hubs "always engaged" on your truck? Is your front driveshaft spinning at all times? Lots to inspect.

Do get back to us with the cause of that noise.

Truck on the road ?
Replace the fuel filter and drive a bit before doing any injector work.
You've the option to drain the gas tank. Disturb the system ahead of your work first.
Replace injector #5 and maybe service / clean the others?
Like they say with older vehicles: Don't patch. Do the whole system.

 

Thank you very much for your reply! I did change the fuel filter before the mechanics diagnosis.

I ended up replacing the #5 fuel injector. But I did not notice a difference.

I'm going to go ahead and pull the heads and see what they look like. I'm afraid after the mechanic mentioning a "binding or crunching" that is maybe be a cylinder head valve.

Crossing fingers 🤞 🤞

 

"Recommends removing valve covers to inspect further".
Good luck

 

Thanks Georgeandkira!

I did pop the valve covers and I found no obvious problems. I know I should crank the engine but I don't feel comfortable doing so with all the components off of the motor.

One thing I found interesting is that Cylinder #5 looks especially clean compared to the rest. Any thoughts? Please see photos. Thank!

 

An