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john -aka eauto
john -aka eauto, The Car Guy
Category: Ford
Satisfied Customers: 16917
Experience:  ase tech over 15 years in the field
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I have an 04 F150 4.6 sohc with 235K. K&N air filter. Around

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I have an 04 F150 4.6 sohc with 235K. K&N air filter.
Around town it seems to do fine but, if I get on the interstate and get on the gas. I enbd up with a check engine light and the codes read misfire on cylinders 4 and 7.
I have new coils, new plugs, new pvc valve, new pcv valve hose, and nerw camshaft position sensor.
I have heard other guys with this problem, but not the solution.

have you checked compression?

Customer: replied 11 months ago.
No, I did think about that. However, the engine seems to run strong and has been well-maintained. And why only throwing the codes in high rpms?
Customer: replied 11 months ago.
a compression test makes sense though, but it seems more fuel system related.

well only a few things cause miss fire codes...ignition (plugs/coils) fuel injectors or internal motor step would be injectors if compression is good

Customer: replied 11 months ago.
I have heard these misfire codes for a lean mixture on 4 and 7 from other owners with the same engine. They seem to be quite common. Have you heard of this before? It seems to be the placement of the cylinders in relation to the intake or that is what I have heard.
Customer: replied 11 months ago.
What about crank sensor, egr or o2 sensor?

yes it will

Customer: replied 11 months ago.
Also, running lucas injector cleaner and a higher octane has reduced the frequency of the codes, is this simply the reduced knock factor of the higher octane?

it is likley clogged injectors

Customer: replied 11 months ago.
If it is the injectors, and I swap them with another cylinder, the problem should follow the injector, correct? Anyway to test the injector without pulling it or swapping it?

not really any esy way to test other then swapping to another cylinder

Customer: replied 11 months ago.
oh, also. I just got this truck, and before I replaced all the coils, plugs etc.. I was getting LOTS of codes, 6 of 8 cylinders were misfiring, cyl 8 injector was supposedly stuck open, engine running lean bank 1 or 2, etc..
Customer: replied 11 months ago.
They all disappeared except for the misfire on 4 and 7.
Injectors was my next move, but testing the compression seems easier.

well if compression is weak ya narrowed it down to internal failure....if its good then its pretty good odds a couple injectors will fix it

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