2005 Ford F150 King Ranch Edition 5.4 Misfire

This vehicle came into the shop with a customer complaint of a rough running engine, a misfire.  Customer said he was driving along on a trip and all of a sudden the truck started to misfire and run poorly.

First things first, we verified the customer's complaint.  Took the truck for a test drive and confirmed the misfire.  Next, we connected our diagnostic tool and checked for stored codes.

We pulled three DTC's.  They were P0171 System Too Lean (Bank 1); P0303 Cylinder 3 Misfire Detected; P0316 Engine Misfire Detected on Startup; and P0353 Ignition Coil C Primary/Secondary Circuit Fault.  We checked the freeze frame data and started our diagnostic.

We weren't concerned with the first code, with an active misfire on that bank, the lean code is explainable.  We needed to know what was causing the misfire.  Just a head up, on the last code P0353, the Ignition Coil C . . . C is number 3 cylinder.  Ford uses letters to correspond to the cylinders.  So "A" is 1, "B" is 2, "C" is 3 . . . "H" would be cylinder 8.  Okay, you get the idea.

Another FYI for you, Ford commonly mistakes cylinders.  So it may throw a cylinder 3 misfire, but when you start investigating you determine it isn't number 3 that actually has the misfire.  So be careful with that too.

Now, we needed to see what was causing this misfire.  Was it a plug, coil, wiring, or PCM?  With the P0353 code, any of these could be possible.

So, we hooked up our lab scope and sync probe and did some investigating.  First, let's rule out the PCM and wiring.

We checked battery voltage at the PCM with key off and with at KOEO, both showed good.  So wiring seems to be fine.  What about the driver in the PCM?

That's where our lab scope and amp probe come into play.  The picture below shows two traces (one red and one green).  The red trace is through the amp probe connected around the power feed.  This wire was accessible in the steering column and was fairly easy to get to.  It is a dark blue wire with light green tracer.  The green trace is our sync probe, allowing us to know which cylinders are which.  In this case, we were connected to number one cylinder.  With that info we could go by the firing order if we saw any problems in the patterns.  Here, what matters, is that all 8 cylinders are accounted for.  You will notice there are 8 red "lines" between each green "line".  This would suggest the PCM is onboard and functioning.

Now, we need a closer look to see where the problem lies.  The below pic shows a zoomed in view of the above pic.  Notice the difference in appearance of the two sets (3 spikes each) of red traces.  The first is nice and pointed, the second image (to the right) sort of curves over to a point and then drops straight down and then straight back up.  The first one is a known good pattern.  The second is a view of a shorted secondary ignition component: either plug or coil.  I know these trucks and engines are known for bad coils, but you have to follow the evidence to make a proper diagnosis and the right repair.

The next pic is an even more zoomed in look at the known good pattern.

The pic below is the faulty pattern . . . again, notice the differences between these last two images.

As I said earlier, these vehicles are known to mis-identify the offending cylinder.  So, we moved our sync probe from cylinder number 1 coil (control wire) to cylinder 3 coil (control wire), the cylinder that is supposedly the misfiring cylinder.  Below is the pic of this.

Based on the above pic, we knew it was indeed cylinder 3 that was the misfiring cylinder.  So, in this case, the PCM had the right cylinder pegged all along.  Now it was a case of determining if it was the spark plug or the coil that had shorted.

It turned out to be the spark plug.  The plugs had been replaced about a year ago.  So, we removed that one plug and replaced it with a new one.  We also ended up replacing another coil because it showed signs on the scope of weakness.

Started the truck and it ran like new.  Took it for a test drive, allowed the monitors to run, double checked no misfires being reported, lean situation straightened out with the misfire no longer present, cleared the codes, and shipped the truck.

The Little Things Matter

This is just a quick post to remind everyone (including myself) that the little things matter.  And not taking care of the little things, or paying attention to them can cause a lot of unnecessary headaches down the road.

Case in point, I ordered some new OE (AC Delco) spark plugs for a 2006 Chevy Cobalt 2.2.  If I had not taken the time to pay attention to the little things, in this case checking the gap on each plug, I would have had a problem as soon as I started up the vehicle.

I would encourage you to always, always check the gap on any new plug you get.  I know the argument about them being pre-gapped and all that, but humans are involved, which means errors can creep into the equation.

It doesn't take but a couple of seconds to give each plug a visual inspection.  Simply put, use the diagnostic equipment God gave you, your eyes, and look over each plug.

Here is what I found on the plugs for the Cobalt.  This first picture is the proper gap:

No problems with that plug.  In fact, three out of the four looked like the above plug.  Good and ready to go.

However, one of the plugs looked like this:

As you can see from the above picture, this gap is far too low.

Again, this is just a quick and simple reminder.  Be sure to do the little things, it can save you a lot of time and hassle down the road.

Just because something is new or right out of the box, doesn't mean it is good.  Always check it.

2007 Chevrolet Colorado LT 3.7 2WD, P0128 Code

Just FYI, the Colorado pictured above is not the one this issue occured.  I did not take a picture of it, but I thought this one (another customer's) would do.

This vehicle came in with a customer complaint of the CEL being illuminated.  I ran the codes and discovered it had a P0128 DTC.  P0128 is a Coolant Thermostat code.  However, some tests need to be performed before relacing a thermostat.

I first performed tests on ECT and its wiring.  Everything checked out okay.

I then started the vehicle and let it idle for several minutes, long enough to reach normal operating temperature.  Below you will notice the temp hand has hardly moved even though the truck had been idling for several minutes.

I then connected my diagnostic tool to see what temp the sensor was showing.  Again, as with the temp hand, it was woefully low.  Sorry for the glare, but the temp is reading only 140 degrees. 

After taking it for a short drive, the temp remained very low.  It only got as high as 150 degrees.  Obviously, there is a problem in the coolant system not allowing the vehicle to reach normal operating temperature.

After gathering the evidence, I decided it was time to take a look at the thermostat.  To easily reach the thermostat on these vehicles, raise the vehicle and go through the driver's side wheel well.

After removing the left tire, the inner fender trim has to be removed. 

Here it is on the floor.  It has six retainers holding it on.

Now, the thermostat housing can be observed.

In order to drain the coolant on this vehicle, the lower radiator hose must be removed from the radiator.  There is no drain plug on these models.  It can be a bit messy, but not too difficult.  In the picture above, you can see the lower hose connected to the thermostat housing.

There are two 10 mm. bolts holding the housing on.  Below is the entire assembly (lower hose still attached).  On these models the thermostat, housing, and gaskets come as one assembly.

Upon inspecting the thermostat it was obvious what the problem was.  Notice below (I'm pointing to it) that the gasket has come out of place.

This was allowing coolant to bypass through the opening.  As a result, the thermostat was partially open and not allowing pressure to build in the system or allow the coolant to reach normal operating temp.

Once the new one was installed and the coolant was at full, the temp hand at idle came up as it is suppose to do.  The difference in temp can be seen below on the scan data.

Now the temp is reading around 200 degrees.  This is where it should be based on the amount of time it was idling. 

A quick test drive and check for leaks and a recheck of coolant level (after the vehicle had cooled) and the repair was verified.