Timing is everything

Here we have a 2005 GMC Envoy 4.2 Liter engine. The vehicle is fairly clean and has 112,361 miles on it. The complaint is the MIL Lamp is on and is setting a P0017 code. This code indicates an issue between Crankshaft and Camshaft correlation. The truck runs well and the shop owner was hoping there was a reprogramming that would solve this. A quick check of present calibration and available updated calibrations yielded nothing for this code. Time to roll up the sleeves. First step is to look at the code and more importantly code set criteria. While we are at it check for pertinent TSB's.

Here is the code P0017. I love the code set criteria. A calibrated amount. What is a calibrated amount? Time to dig a bit. I look for TSB's and PI's on the OE site.

I come up with this document. A world of information including the specified calibrated amount as well as a wealth of causes for this code. A little background on these engines. They utilize a camshaft actuator or phaser on the front of the exhaust camshaft that is loaded to a neutral/base position. When the PCM wants to actuate this actuator it duty cycles an oil control solenoid that will in turn feed oil to the actuator and in this case will retard the exhaust camshaft. Basically, this operation takes the place of EGR operation and it also improves overall efficiency. Like all engines that utilize this type of design it is very reliant upon proper oil level, viscosity, and pressure.

Here is the front view of the engine. The oil control solenoid is in the head right by the power steering pump. The camshaft sensor is also on the front of the cylinder head right by the upper radiator hose.

Here is a close up of the oil control solenoid. I see plenty of issues with these. They clog up, the portion inside the head gets clogged up and doesn't allow the oil solenoid to do its job properly. Typically, when this happens the vehicle runs really poor at an idle but runs decent raced up. Think of a vehicle with a stuck open EGR valve. This vehicle runs rather well at an idle. Scantool data is only going to give me a small portion of what I need to know. My play is to scope crank and cam sensors.

 

 

Well here is Crank sensor on channel 1 in yellow and Cam sensor on channel 2 in Green. Is it good? Is it bad? I don't know. This is where it is nice to have a known good. It just so happens that there is another similar vehicle on the lot. This vehicle is running fine and is just in for servicing. Lets take a look at that one and see if we can see any differences.

 

 

Hmmm. Waveform interpretation can be daunting at times. I usually zero in on one portion. If you look closely at the crank sensor pattern you will notice a double spike. This is the signature portion of the waveform. The PCM uses this signature pulse to determine piston position. I am going to zero in on that portion of the waveform.

 

 

  Notice how the first signature starts after the second trailing portion of the short camshaft sensor pulses and the second signature is on the trailing edge of the second long pulse of the camshaft sensor. Lets look at our suspect pattern.

 

 

A definitive difference indeed! Looks like the whole crank pattern is shifted to the left or is the camshaft pattern shifted to the right?

 

 

 

Here is a comparison of the two waveforms. At this point I inform the shop owner of my findings. I tell him definitively that he has a true blue issue with correlation. At this point it could be a stretched timing chain, timing chain alignment, an actuator/phaser not returning to base position, an oiling issue inside the head, an oil control solenoid not operating correctly, etc. I ask the shop owner if he wants me to delve deeper. He refuses citing he has to get approval from customer for more diagnostic time. He was really hoping there was a calibration update to solve this. I advised the shop owner I don't think it is crank endplay or a loose crank bolt. Because I don't see major differences in the amplitude of the crank signal when raced up, etc. Unfortunately, the customer refused more diagnostic time and the vehicle was released. This happens sometimes. What is ironic just last week a buddy of mine called me asking if I had a known good 4.2 liter crank/cam scope pattern that I could send him.

Just a little math here as well. One crankshaft rotation (from signature to signature) took approximately 100ms. That would mean 3.6 degrees per 1ms. The code set was 16.31 degrees which is approximately 4.5ms.  Looking at the bad pattern it is real close to being about 4.5ms out. If memory serves me these cam sprockets have 48 teeth that would yield 15 degrees per tooth. So a tooth out with a little stretch is a possibility here as well.

Details, Details, Details......

In the automotive diagnostic world details are everything. Missing a vital piece of scan data can lead to a misdiagnosis or missing a step during a programming event can cause issues. You have to pay attention at all times. It is something I strive for. To be a detail orientated person and that translates to my business as well.

A shop owner called me one day frantic about a 1999 Ford F150 pickup truck with 78,820 miles that he could not get rid of a P0401 EGR code. I arrived at the shop to see a very clean low mileage Ford truck with a 4.6 liter. Lifting up the hood I could see a new EGR valve, a new EVR (EGR solenoid), a new DPFE (Delta pressure feedback egr) sensor, a new exhaust tube for the EGR, and new DPFE hoses. Some parts the shop put on and others the customer installed. I quickly ran a KOEO (Key on engine off) test there was a P0401 (EGR low flow) code in KAM. No on demand codes. I moved on to the KOER (Key on engine running) test but first I hooked up an old fashioned vacuum gauge on the vacuum hose between the EVR and EGR valve. When you run a KOER test the PCM will activate certain outputs such as EGR and look for change. I was interested in if there was any vacuum going to the EGR valve during the test. During the test I indeed saw vacuum going to the EGR valve. The control side of the EGR system seemed to be in order. The test completed and a P0401 was set in KOER. Next step was to actually put vacuum to the EGR valve at an idle and see if it caused the engine to run rough indicating the EGR was opening and that the exhaust and intake passages for EGR were not clogged. Putting vacuum to the EGR valve didn't cause the engine to change at all. I could physically see the EGR valve diaphragm opening. I unbolted the EGR valve and started the motor the intake port were completely clogged. No vacuum could be felt. Considering the low mileage and the common issues with this issue I instructed the shop to remove the throttle body so I could show him the clogged ports. 10 minutes later the throttle body was off and sure enough the ports were clogged solid. Leaving the shop I gave the shop owner a quick rundown of how the system works and how it tests itself to see if it fully functioning.

A couple of days later I get a call from the shop owner saying he gave the vehicle back to the customer and the MIL (Malfunction illumination lamp) came back on and it has a P0401 again! Huh? This was a slam dunk diagnosis. I asked the shop owner if he ran a KOEO/KOER tests before releasing it to the customer. His reply was "I scanned it". I also asked him if he put vacuum to the EGR valve did the motor run rough or stall? Again, I got a reply "I think so". I told the shop owner I would stop by later in the day. Those that know me already know that this vehicle would be gnawing at me all day until I got there. I take things very personal. Did he clean the passages completely? Did another issue crop up?

I arrive at the shop and first thing I do is apply vacuum to the EGR valve and the engine ran very rough almost to a stall. Well, he has the passages clean now. Now, lets retest to see if it still is getting vacuum to the EGR during a KOER test. It was. Ok, does the PCM actually know the EGR is opening and flowing. How the PCM knows this is from the DPFE sensor. It senses flow across a controlled orifice in the EGR tube via those two brand new hoses. I hooked up my scantool and graphed the DPFE voltage. On a plastic DPFE such as this one KOER with no EGR flow you should be at 1.00 volt as EGR flow increases so does the voltage. I normally can get upwards of close to 4.0 volts or more when adding vacuum to the EGR valve.

 

 

As you can see from the graph I started out at close to 1 volt. I then added vacuum, took it away and reapplied vacuum. But, my voltage went down. Way down to .14v. What is going on? I know the hoses at the DPFE are reversed. I reverse the hoses and redo my vacuum test.



 

 

 Totally different story here.

 

 

 

We are flowing now. The DPFE hoses have a large and small opening and have to be orientated correctly at the EGR pipe and the DPFE. Somehow, someone managed to mix these up. You really have to try really hard to mix this up. Now, were these hoses like this on my first visit? I really can't say for sure. I didn't check-shame on me. I was so caught up on diagnosing the clogged passage I didn't see if the hoses were orientated correctly. To be honest this is the first time I have ever seen this. However, I won't be making this mistake ever again. I ran a KOER test and all was well.

 

 

Some details you don't see on the scantool. Some you have to see or feel.

 

Here is a 1999 Ford Expedition with a 5.4 liter. Shop has installed a new oxygen sensor for a P0135 (O2 heater circuit) code. New sensor and still same code. Now they are thinking it may have a bad PCM. I got called in and inspected the wiring. The connector for bank 1 sensor 1 is in an awful spot behind the passenger side of the engine. The clue that it may be a wiring issue is the newly installed remanufactured transmission. Bad things can happen to wiring when a transmission is installed especially to oxygen sensor wiring.

 

 

 

   Well here it is the lock portion of one of the terminals for the heater circuit was broken. The terminal itself was also damaged. The terminal was being pushed out when the oxygen sensor was connected causing the heater circuit code. 

 

 

Here is another one found with the eyes. Mitsubishi Montero with oxygen sensor codes. My first tipoff was the two different color connectors. Then a close inspection of the harness connector showed the locator tab was filed off. They used a left side sensor in the right side. They are all the same aren't they? Wire orientation was different. Very dangerous. Shop was lucky no PCM damage occurred.

 

 

A good technician not only uses his scantools, voltmeters, etc. He or she also utilizes sight, sound, smell, feel, etc. Pay attention to details and learn from your mistakes. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                                                                                                                                                                                                                                              

 

 

 

 

 

 

 

 

 

 

 

 

Technician Training

This is a real sore subject with me. Almost every technician gripes about the lack of training in our industry. It is something I hear almost daily. I am often asked "When is the next training event?" I give information, hand out flyers, and even remind techs of upcoming training. Then why is it that I see the same familiar faces at every training event I attend? I will tell what I think.

It all comes down to sacrifice and commitment. If you want to become the best in whatever you do these two actions are paramount. When I ask the same people that were wondering about training why they weren't at a recent event. I get the usual excuses "I forgot", "It was on a Saturday and I couldn't swing it", "It was after work and I didn't feel like it", "It is too expensive". These aren't as bad as the people in this industry that think they don't need any training. They know it all, just ask them. I often say the minute you think you know everything in this industry you should walk over to your toolbox lock it up and look for another job. There is no one person in this industry that knows it all. You can always learn something. If you are not learning something everyday in this industry you are not paying attention.

Some training events are better than others. No doubt about that. However, I always pick something up no matter what. It is vital if you want to become a better tech you will need training. You will also need to do some self training. This can be looking at known good vehicles for scantool data, scopeshots, or maybe "bugging" a vehicle to see how it reacts. If you are not willing to do this you will not advance in this field.

The same people I see at training events all have some similar personality traits as well. Typically, we are perfectionists, inquisitive, some degree of OCD (Obsessive Compulsive Disorder), headstrong, and willing to sacrifice to be the best.

Think about it. What separates an athlete from an elite athlete? An elite athlete identifies his weaknesses and wants to improve on them. Then he/she does the work and improves. Same thing applies to our field. If you want to become a more proficient tech you will need to identify your weaknesses and take steps to sure them up. Part of that is to get as much training as possible.

So the next time a training event is around. Attend and invest in your future.