Changes in diagnostic strategies

Jan. 1, 2020
When we technicians employ a test procedure that works well, we don’t change it and we don’t expect different results when we use it. That would just be crazy, right? 

Some say the definition of insanity is doing the same thing over and over, yet expecting different results. When we technicians employ a test procedure that works well, we don’t change it and we don’t expect different results when we use it. That would just be crazy, right? Well, what happens when the vehicles change but we don’t?

Ford F-Series trucks may use a 5.4 Liter engine, like the one having problems as described in this article

We work in an industry where change itself is prevalent. As an automotive technician, I’ve sometimes wondered who the engineer was that decided to do “such-and-such” when the way it was done before worked just fine (almost every technician can fill in the blank for “such-and-such”). On more than one occasion I’ve tilted my head, perked my ears and raised an eyebrow all at the same time while asking aloud “why didn’t they do so-and-so instead?” Sometimes though, I asked that even when no one was around to hear the question. Proof positive the engineers were temporarily driving me nuts trying to figure out their logic.

Wiring Diagram which includes (among other things) both Knock Sensors, the PCM and their connecting circuits

I understand. It’s human nature to resist change. But it seems as if the auto manufacturers detest keeping things the same, even when things work well already. I abhor changes done simply for the sake of change! I hate change worse if I’m unprepared for it. I hate change because *I* have to change. I have to change my attitude and try to consider the benefits of this latest change (whew, what a bunch of “changes”!).

I recognized early in my career that the auto repair industry is dynamic. By that I mean it has never NOT changed, at least not since I joined it. It seems that almost daily new technologies are developed therefore new diagnostic strategies and techniques must be developed as well. Due to 

The “Lacks Power” Symptom Chart mentions abnormal engine noise as a possible culprit for causing this complaint but offers no dynamic component testing procedure

that inherent nature of the business, I’m committed to embracing change because of the exciting learning experiences we gain from it. Once I get over the initial despising the changes response, I look at it as an opportunity to expand my knowledge in other ways of doing things and as a way of viewing circumstances from a different perspective.

Here’s an example of a design change I encountered recently which took quite some time before I changed my attitude…

Feeling Powerless
I was asked to come to a shop to help them diagnose a vehicle whose owner complained it “lacked power”. This vehicle was a 2006 Ford F-250 with a 5.4L with 108,506 miles on the odometer. Before calling me, the shop had already performed “all the basics” but hadn’t come to any conclusion for a cause of the complaint.

When learning of newly designed components one should consider reading the “Description and Operation” section of the manual. Unfortunately in this case, that section was not very helpful.

The customer first authorized performing the maintenance that the manufacturer recommended based on the vehicle age and mileage, including replacement of the spark plugs, a new air filter and fuel filter, oil and filter change, etc. The shop also did a fuel injector flush and an air induction system cleaning. When the maintenance was complete and the vehicle ran no differently, the shop was authorized to perform an initial assessment including fuel and exhaust back-pressure tests, scanning of the powertrain systems and they performed other tests - none of which answered the question of why this truck lacked power.

This is the point when they called me. Just as you interview your customers, I did the same with the technician and the shop owner to ensure no steps had been skipped and nothing obvious was overlooked. I’d made a few other suggestions over the phone for them to try but their test results were inconclusive.

I went to work immediately after receiving the Vehicle Identification Number (VIN). First, I researched the important information I keep on hand. That’s stuff that I’ve encountered in my mobile diagnostic business and throughout my career. Whether it was me or it was the technician in the shop contracting my services who came across the findings, a magazine article I thought may be helpful in the future, or anything my customers may have shared with me about a car that nearly drove them nuts, any and all “diagnostic dilemmas” tests and results (cause of complaints) I’ve saved for future use, such as at a time like this. I have an extensive collection that can even be cross-referenced where I store the details of those hard-earned victories. It’s like having my own “Identifix” database - and I feel all techs should have one of their own.

I didn’t find anything pertinent in my own information so I performed a systematic and extensive web-based search. I started by searching the archives and forums on the International Automotive Technician’s Network (www.iATN.net). There one can broaden or narrow their search query and read through the results in hopes of seeing a common cause of a problem. I also use the search results to remind me of what I may have forgotten to check too. In fact there are many uses for searching the iATN archives but in this case, I was focused on this one problem vehicle so I didn’t need to use the extensive capabilities it offered.

The PCM connectors have unique purposes. The connector on the far right is called Connector “E” (Engine), the center one is called “B/C” (Body/Cowl) and the far Left connector is called “T” (Transmission).

I then searched for possible solutions in the information available for members of the Ford Truck Enthusiasts forum, the Mobile Diagnostic Group and I looked at suggestions from Identifix. I even subscribed to the Ford service information site in hopes there was a TSB or other piece of information (possibly an internal memo) that might give me ideas about what to look for on this vehicle. No such luck.

By the way, this research – this time spent before wrenching – is all necessary when the “basics” don’t properly address the customer’s complaint. The procedure I follow is similar every time no matter the vehicle problem I’m addressing but I’ve found most of the time, someone else may have already “been there and done that”. Therefore, I suggest everyone associate themselves with however many forum(s) you feel will help you diagnose problems. You’ll most likely find not only a lot of company in your misery, but sometimes your misery is greatly reduced due to someone else’s efforts.

In order to test the Knock Sensor(s) and their circuits, one must back-probe the PCM Engine connector after disconnecting it from the PCM, then read the resistance between pins E48 & E49 (KS1) or pins E30 & E31 (KS2). Resistance tests are the only component tests found for these sensors. There wasn’t much room for the back-probes as seen in this image.

Going in Armed
So, after researching this complaint, I was ready to approach the vehicle armed with some possible causes, and some testing ideas I’ll use to try to prove or disprove each one. As I do with every diagnostic routine, the first step is to duplicate the customer’s complaint. A short test drive was all that it took for me to agree with the owner. This truck was almost scary to drive away from a stop and into the flow of traffic! After returning to the shop I reviewed what tests they had already done and verified the results so that I was sure I wouldn’t duplicate any efforts.

I’ve learned the importance of making sure the PCM has the latest calibrations loaded in it because so many problems can be resolved with a flash and sometimes there’s no amount of wrenching you can do to fix them. I found this PCM had revisions available that were newer than what was presently loaded and received permission to reprogram the PCM. Ford doesn’t inform us what they are adjusting with their flashes, like some other manufacturers do, so I wasn’t sure programming the module was going to resolve the owner’s complaint until it was done. It didn’t.

I then recorded the data stream (the Ford IDS software calls it “Datalogger”) while attempting to accelerate. During playback I noticed the variable camshaft timing phasers were slow to return to a zero degree position on deceleration. I also noted the spark timing PIDs showed negative numbers at any throttle position that was not closed throttle. I decided it was time for a visual inspection and maybe a functional test.

Upon arriving back at the shop we opened the hood and I immediately heard noises coming from the front of the engine. I heard tapping around the right front valve cover area and I heard some sort of knocking from the front of the motor. Funny, I thought, there’s been no mention of engine noises when I asked if there were any other symptoms!

As seen on another vehicle’s IDS Datalogger, this vehicle’s KS activity was well below 100 off idle – indicating no engine noise was detected.

The crankshaft pulley (balancer) key was known to shear on these trucks, which would cause the CKP signal to be generated at a different time than originally intended. When that occurs the engine becomes lethargic. It’s relatively easy to determine if this happened by using an oscilloscope to show both the CKP and CMP relationships at the same time and comparing this image with one that is a “known good” image. This one looked textbook perfect. To be 100% sure it had not sheared the shop owner insisted his tech remove the pulley assembly and visually inspect it. NPF (No Problem Found) here.

The next test was done to see if the camshaft timing phasers worked as designed. I was able to monitor their actual position on the scanner while controlling them. The only indication of a problem during this test was an unusually slow response when I commanded less pulse width modulation. The camshaft position was slow to return, which can be attributed to sludge build-up. But the rattling noise was hardly noticeable while the phasers were commanded on, so this helped us determine the cause of some of the noise. I couldn’t help but wonder if the negative timing PIDs I saw were caused by the cam phaser rattle being detected by the knock sensor so I tried controlling them while the technician drove the vehicle. We soon knew those noises, and maybe some of the others, contributed to the PCMs decision to retard the spark timing which resulted in poor performance.

Here’s where it should have been an easy confirmation that is, had the engineers not changed the design. I would have grabbed my scope, back-probed the KS signal wire at the PCM, monitored the spark timing PID whilst tapping the block near the sensor with a long socket extension at the same time watching the PCM’s timing control response. That’s the standard procedure I’ve used for “ever”. Upon looking up the wiring diagram I realized this system of knock detection was different from previous versions. This vehicle not only has two knock sensors (no big deal – lots of carlines have that setup, I thought) but each of these sensors has two wires! Back-probing any of the four wires and tapping near the sensor produced no signal! Yikes, I better read up on this, I thought.

This capture of the IDS Datalogger at idle shows excessive KS activity

Wrapping it Up
I won’t get into too much detail about how many methods I used researching these new-fangled knock sensors. But, after many frustrating hours, I ended up not knowing any more about the proper way to test their performance than when I began. I do know there are KS PIDs in the datalogger and I’m aware when those PIDs show an increase above a certain number then the timing gets retarded. But I never found any accurate (dynamic) component testing procedures or specifications, even in the Ford O.E. service information. All I ever found were resistance specifications.

I read the 2006 F-250 PC-ED Manual from front to back, I looked through all of Ford’s KS DTC and Symptom charts, I researched part manufacturer’s sites for knock sensor information, read numerous articles written by renowned diagnostic authorities, re-read the pertinent manuals I received in the training classes I’ve attended and even tried the incorrect method of testing listed on a particular auto parts supplier’s site intended to help techs. I challenge you (readers) who want to occupy your spare time productively, to find the accurate information I was unable to find. I want to know, when a knock is sensed, what kind of signal is generated by these knock sensors and what should my oscilloscope show me?

Under a load this IDS Datalogger capture shows a great deal of excessive KS activity

Since I wasn’t able to use conclusive testing methods, the only way of knowing with certainty that the engine noises contributed to the poor performance complaint was to get the vehicle owner’s permission to repair the mechanical faults and see how well the truck runs afterwards. How easy is it for you to sell a customer a costly repair that may not address his complaint? Well, this shop owner was able to convince the customer the noises would only get worse over time and that the truck had many years of service left if we can get it running correctly so the following repairs were performed: both camshaft phasers, all timing components and one rocker arm were replaced. With the engine noises gone the truck ran like new!

Our jobs are sometimes frustrating enough - even with complete and accurate information. I’ve learned many things on this job - mostly because of how long my research took in an attempt to thoroughly understand what I was seeing. I learned we now use “smart” knock sensors that will only produce a signal when a SPECIFIC noise is detected so therefore, the tried and true method I’ve used for decades won’t work on these systems. I’ve also learned my trusty diagnostic routine, the one I’ve followed for “ever”, has to change. I can no longer include the “component test” every time when there isn’t one published.

What is the end result? I found that doing tests on these “smart” knock sensors the same way we always have - and expecting the same results – will just about drive one insane. 

Subscribe to Motor Age and receive articles like this every month…absolutely free. Click here

Sponsored Recommendations

ZEUS+: The Cutting-Edge Diagnostic Solution for Smart, Fast, and Efficient Auto Repairs

The new ZEUS+ simplifies your diagnostic process and guides you through the right repair, avoiding unnecessary steps along the way. It gives you the software coverage, processing...

Diagnostic Pre- and Post-scan Reports are Solid Gold for Profitability

The following article highlights the significance of pre-scans and post-scans, particularly with Snap-on scan tools, showcasing their efficiency in diagnosing issues and preventing...

Unlock Precision and Certainty: TRITON-D10 Webinar Training for Advanced Vehicle Diagnostics

The TRITON-D10 lets you dig deep into the systems of a vehicle and evaluate performance with comparative data, systematically eliminating the unnecessary to provide you with only...

APOLLO-D9: Trustworthy Diagnostics for Precision Repairs

The APOLLO-D9 provides the diagnostic information and resources you need to get the job done. No more hunting through forums or endlessly searching to find the right answers. ...

Voice Your Opinion!

To join the conversation, and become an exclusive member of Vehicle Service Pros, create an account today!