Diagnostic strategies for problem vehicles

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What you will learn:

• Have a plan of attach to make easy work of driveability issues

• Engine mechanical faults can be detected via a relative compression test

• Thermal imaging is a viable way to determine if an excessive parasitic draw exists

When faced with a variety of vehicles and the issues they are experiencing, having a solid diagnostic plan of attack will not only allow for a proper diagnosis, but also an increase in efficiency. With both of those results combined, the confidence in your diagnostic abilities soars as well.

2010 Ford Escape 2.5L

Our first problem vehicle has 130,767 miles on the clock along with an illuminated MIL. After interviewing the vehicle owner, we were informed that the vehicle started running rough, followed by the check engine light coming on when she was driving up a hill. We performed a visual inspection and noticed that the ignition coil had burn marks and rainbow-colored markings on the sides of them. We continued our plan by connecting the Ford IDS. We scanned for DTC:

P0301 “Misfire on cylinder #1”
P0316 “Misfire on startup”
P052B “Cam start intake, camshaft position timing over retarded bank 1”

Figure 1- The Freeze Frame data offered a clue as to how the vehicle was being operated at the time of the failure. this saves time on road-tests to reproduce the symptom of concern.

With the data at hand, it was time to review the freeze frame information and see if we could come up with any clues that would help us with a diagnostic strategy. The freeze-frame data indicated the ECT temperature was 50 degrees F, rpm was 2279, TP 31 percent, VSS was 21 mph, and the load was 100 percent (Figure 1).

That information informs us that this misfire happened when the engine was cold, part-throttle as the vehicle was pulling a hill (noted by the 100 percent load value). This confirmed what the vehicle owner told me during the interview. Now I had to make a game plan and come up with a test plan, solution, and repair.

One of the first and most important steps after checking the battery, starter, and alternator is to check if the problem is a mechanical issue. Ford made it easy to check mechanical conditions using their relative compression test. We performed the test and the results that did not indicate a problem (Figure 2).

Figure 2- the relative compression test quickly determines if a mechanical fault is present in one or more cylinders.

Our next step was to perform a power balance test. The results confirmed that a misfire was present. Logically, we followed this test by performing a manual injector balance test that cleared the fuel system of any issues.

The next logical deduction was a fault due to an ignition system problem. We repaired the ignition system which included replacing the original spark plugs and ignition coils. After the parts were replaced, the engine ran smooth and strong, along with no MIL illumination on our test drive. We checked DTCs, scan data PIDs, and Mode 6, and all passed the test. It seemed that the vehicle was now repaired so we billed it out and sent the owner on her way. Unfortunately, that was not the last time we were going to see this vehicle for a rough running issue.

It was an "Oh no" moment when the vehicle returned with the same complaint of rough running and an illuminated MIL. With eggs on our faces, we had to check for DTCs and recheck the work we performed. Being the techs with dirty faces, my colleague and I had to make a new game plan and find out what was the cause of the rough running engine.

Our new direction led our investigation a bit deeper, we researched in Identifix and found the exact DTC P0301 and P0316 that had recommendations for replacing spark plugs and ignition coils as some of the top fixes. Since we had already found those defective parts and replaced them, we had to move on.

The next test we performed was a visual inspection inside the cylinders, using a video scope that did not provide a definitive answer to a valve or cylinder problem. What next? Compression test dry, wet, followed by a cylinder leak down test that was marginal. Our next move was to perform an in-cylinder pressure transducer test that has never failed us. The results were very minor when we compared the number 1 misfiring cylinder to the other cylinders, but enough to recommend the removal of the cylinder head.

Figure 3- The cylinder heads was sent to the machine shop for inspection and issues with valves/seats were present and corrected.

The vehicle owner took my suggestion to remove the cylinder head and sent it to the machine shop. The machine shop test found that the intake valve on the number 1 cylinder had a slight issue. They suggested that we replace all the valves since they have seen issues with this cylinder head. This machine shop does all the work for us besides the local Ford dealer. Feeling confident that this was going to fix our problem we ordered all the parts from Ford to go along with the recondition cylinder head (Figure 3).

The install job included the reconditioned head, new timing chains, tensioner, head bolts, crankshaft bolt, VVT cam phaser, and VVT solenoid. We torqued every fastener to spec followed by an engine start. Thinking we had this engine issue fixed was a mistake since after our test drive the MIL was back on. Even though we performed and checked every special procedure using all the special tools to align and lock the crank and camshafts, we still had a problem. This was one of those, “What the heck?” moments. We no longer had a problem with a number 1 misfire, but we had other issues:

P0016 “Crankshaft position correlation bank 1 Sensor 1”
P052B “Cam start intake A camshaft position timing over retarded bank 1.”

My colleague had to remove the valve cover and timing cover; install all the engine lock tools and install the crankshaft alignment tool, only to find everything was on the money (Figure 4). He called me over to make sure he was not missing anything — he wasn’t. We even checked the screen in the cylinder head oil passage, and it looked good (but we replaced it just in case since it was inexpensive).

Figure 4- Common on today's vehicles, special tools are required to maintain the position of the camshaft(s) and crankshaft during timing component service and repair.

We followed that up by pouring the ATS 505 CRO oil pour-in treatment into the engine and running it before draining the oil. We concluded since there was no longer an issue with any DTCs that there must have been something in the oil passages. The engine was running smooth and did not exhibit any more codes or issues, so we shipped it.

Case study: 2014 Ford Edge 3.5L

Our next vehicle came in with a recommendation from another shop that usually diagnoses their own problem vehicles for their customers. This one was going to be a bit different since it was an intermittent parasitic drain. When we first received the vehicle, we found a high draw that lasted for one hour after the key was off. The high draw was most likely a result of the NVLD (natural vacuum leak detection) system that is normal until it goes to sleep.

After one hour, the draw dropped down to 50-60 mA then later went up over 1 amp. We tested all the fuses for a draw, performing the VD (voltage drop) fuse method at all the under-dash fuse boxes and Underhood fuse box. The results were nothing out of the normal range, no VD. We even pulled fuses and relays that could not be reached with the voltmeter, but there was no change.

Figure 5- A defective switch was the root cause of the parasitic drain.

We looked up TSBs and common issues for this year's make and model, finding that the rear window motors are a common issue for intermittent high current draw. We proceeded to use our thermal imager and though there was some draw, we removed the rear trim panels to access the motors to double-check. Since that was not the source of the draw we had to move on. During our search for the problem, we discovered two add-on aftermarket modules under the dash. Thinking we hit pay dirt finding these aftermarket modules, we unplugged them just to rule them out but there was no change.

Next, we parked the vehicle inside (overnight) so we could check it in the morning when the vehicle was cold, and all the computers were asleep. The vehicle was checked on five different days with no excessive draw from anywhere. We know that the other shop said that it was intermittent, but this was a real kicker.

On the sixth morning, the vehicle started and was driven out of the bay and parked, then we tried to restart it, only to hear clicking from the solenoid. We tested the battery, and it failed the test, so we charged the battery and retested it. The battery test indicated another fail on the new battery that the other shop had installed. We called the shop to inform them of the defective battery, so they sent us a new replacement that we installed.

Knowing that the replacement battery was not going to solve the problem we still had to continue our search for the drain. Starting with a new battery was an important step before moving on. We drove the vehicle, making sure we turned on all the accessories and parked it in the bay overnight to monitor the current draw. The next morning, we struck out again since we did not find any draw.

The second night we got a hit! We found an intermittent 2 amp draw that lasted 15 seconds and reoccurred every 10-15 minutes. Unable to pinpoint what circuit the 2-amp draw was coming from we, had to keep searching.

One night while parking the vehicle, we noticed the PRNDL lights remaining on after the vehicle was parked. Using a thermal camera along with the Fluke i30s low current amp clamp (connected at the battery) we discovered a 300 mA draw. Our next step was to remove the instrument cluster fuse to check what level the draw was at. With the fuse removed the draw went down to the acceptable level of 50 mA. We did a bit more research on the system and found the shifter has a redundant park switch that can fail (Figure 5).

We decided to bypass the switch and let the vehicle sit for two days, the result was the battery never went dead. Since we were confident that we solved the parasitic draw on this Edge (that had us on the edge), we recommended a Ford shifter assembly. We found another odd thing; the aftermarket remote start module was causing the dash to lite up if the lock button on the fob was clicked twice. We kept the vehicle another few days with the remote system installed making sure it did not cause a draw. From experience, we thought it would be better to remove the system since we have seen many problems with add-on systems.

We left the vehicle owner a message concerning the removal of the remote system and did not hear back from him for a few days. With the system connected for over a week, there were no issues found. Since the owner’s daughter was driving the vehicle to college (far away), he took our suggestion and had us remove the system.

This Ford was a difficult problem since it was intermittently draining the battery down. I am happy to report that it has been over four months without a problem on this Edge. We used our game plan and made modifications to come up with a solution to the parasitic draw problem.

2013 Subaru Outback 2.5L

This vehicle, with 178,350 miles, was towed in as a no-start. The engine cranked but would not start. Using our "game plan," we checked for air, fuel, spark, and exhaust backpressure. The engine had two out of the four in the good range.

Figure 6- A Cranking vacuum test is a great way to infer engine breathability and uncover restrictions.

The cranking vacuum was an issue (since it was not at a bouncing 3" to 4" while cranking) and the exhaust back pressure was not under a half-pound while cranking. This led us to remove the air-fuel sensor and install a backpressure gauge (which displayed a high reading). As I always say in my classes, “You can’t get five pounds of dew out of a one-pound bag." Or in this case, 4.5 pounds (Figure 6). The excessive back pressure was the result of not one, but two defective catalytic converters. The front converter had come apart and blasted pieces of debris into the second converter, which broke that substrate. We were very surprised since we had replaced both converters not all that long ago, due to a defective air-fuel ratio sensor that was out of range. The defective sensor caused the converters to overheat preventing the vehicle from being driven over 60 mph.

The cause of the low power complaint was high backpressure which caused the loss of power on this Subaru. Our solution for this problem was to install a new air-fuel sensor and two new Subaru OE converters at 165,008 miles (that was only 13,000 or so miles on the converters before our current problem occurred).

There is no way (even if there was an abundant amount of fuel being dumped) that the converters should have had this issue. The problem was not fuel or sensor related but rather a defect in the reduction (first) catalytic converter. The problem with this converter was due to a matting issue that protects the converter substrate from being moved around.

Figure 7- Seen surrounding the substrate is the matting which is there as a vibration insulator. If the matting becomes displaced, it can become restrictive and prevent the engine from preforming correctly.

Maybe you have never seen or noticed catalytic converter matting but I can assure you that all converters have this matting (Figure 7). When there is an issue with a broken converter substrate, that has no external shell damage, the problem is most likely due to matting.

The first converter was so badly damaged that it broke my backpressure gauge, blocking it with the fine powder that can be seen on the floor; along with broken substrate from the same converter. The broken pieces went into the second converter and destroyed it.

After our discovery, we called the dealer that informed us they would warrant both converters without any questions. When they arrived, we only received the front converter and were told that the other converter had to be replaced at the dealership. After both converters were installed, the engine ran fine.

A few months after that problem, the customer called us saying they were losing power again. We had them come in to check it out and found that the problem was not an engine or exhaust issue but rather a transmission problem. The Subaru owner decided that enough was enough and made a deal with the dealership, and traded it in for a new one.