Hi guys,

I have left to check Camshaft retard settings as Captain hook wanted me to do as a NEXT STEP to diagnose my misfire that occurs at idle and I believe in upper RPM's too. I also have yet to check fuel pressure at filter area too.

However I have the following information from scantool regarding the o2's at idle.

Does anything stick out to you, did I take screen shots of the right info, I may not off.

Anyway just throwing it out there. 130 000 km truck.
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Here is a copy/paste of a post from another user regarding this question I have, I thought it would be beneficial for the thread

Be lucky you don't have the dreaded p0300 code!

Anyway, your cylinder misfire is narrowed down to #4. I doubt highly that a weak fuel pump would cause a one cylinder misfire. Not even a lazy/leaking Fuel Pressure Regulator. More than likely, those cause the p0300 codes, or just a rough idle, no start condition. It however doesn't hurt to check the Fuel Pressure and leak down anyway.

Life is much easier if you have access to a scanner that does live data. You can get them at harbor freight for a decent price. In case you don't have a scanner like this, or cant not easily source one, I will give you two ways to diagnose this;

With Scanner:

Under live data, take a look at the STFT1 (Short Term Fuel Trim) and STFT2 (bank 1 and bank 2 respectively).

Under idle when the car has went into closed loop watch these values. If the numbers are positive or negative more than 5% you have an issue.

Positive STFT means the engine is running lean, not enough gas, or too much air. This could be from a vacuum leak, misfire in the ignition system, or fuel problems. Excessive positive STFT on both banks normally lean towards a vacuum leak. Let us narrow it down to either fuel or igntion or vacuum leak;

Hold the throttle in park at 2000 rpm's while looking at this value of STFT. If the values start to drop, then you are looking at a vacuum leak. As the engine RPMs increase a vacuum leak becomes less effective on the engine performance. If your numbers do not drop at all or very little then you are dealing with a fuel delivery issue. In my experience, once a fuel pressure test and leak down test is done, and numbers are good, you are looking at a faulty or clogged injector.

Negative STFT is when the truck is running to rich, i.e. too much fuel, not enough air. This could be from bad ignition components, to engine mechanical issues like a bent valve, leaky injector, cracked head, too much fuel pressure, etc.


Without Scanner:

Obviously this method is not as accurate as using a scanner, but you can get an idea of where to look.

On cylinder number 4 (middle cylinder on passenger side of motor, while the engine is running, carefully use a spark plug wire puller, and pull the wire off the cap. Be extra careful here as you can get a bad electrical shock that will send you into another world. Make sure you are grounded. If there is no change in the Engine performance, i.e. the engine runs the same, then you know that your problem is likely ignition related. Check the cap/rotor, wire, and spark plug. This can also be safely done with an inexpensive inline spark tester sold at most auto parts stores. The old school screw driver trick is risky, dangerous, and inaccurate. You are looking for a very hot spark, a blue flame as we like to call it.

If the engine performance does change, it shakes more, etc. Then you know that more than likely your issue is elsewhere, i.e. fuel delivery. Check fuel pressure, leak down, etc. If that is all good, you may have a messed up injector.

In all cases, I always recommend a fuel pressure test, leak down test, spark test, and a compression test. Just to give you a base idea of where to start looking next, and to be sure that the basics are covered.

A really good article on fuel trims is here: Fuel Trim?

Let us know, and good luck!