High Tech Techniques Don’t Fail

Chevy Equinox Failing Inspection

Aside from diagnosing hard to fix cars for other shops, we get our fair share from the general consumer. Sometimes they are referred to us by another garage, but we also get some referred to us from the State of Delaware’s Department of Motor Vehicle Inspection Division. In Delaware, all safety and emissions inspections are handled centrally by state employees. As a citizen, you drive to the inspection lanes where as a drive through process your car is inspected for both safety and emissions and you are issued a pass or fail slip. Vehicles that fail are given paperwork that includes a list of certified emissions repair technicians that the State of Delaware has qualified as meeting a specific minimum standard in regard to emissions and diagnostics.

We met the owner of a Chevrolet Equinox about 4 months into her emissions failure odyssey that included stops at 3 other independent repair shops and one dealer.

Once she dropped her truck off to us and I spoke with her and her husband, we found out that the issue was a failure for a cylinder #2 misfire code that was causing the check engine light. Further inquisition determined that she had previously had spark plugs, injectors, coils, a few sensors and at least one catalytic converter replaced over the past 4 months and across several shops. She was last told that either the engine was bad or it needed an ECM and felt that likely a solution could not be reached at any cost.

Our inspection of this 2005 Equinox, with a 3.4 engine and 145,000 miles on the odometer, showed the truck exhibited a steady misfire at idle, had a consistent tick that sounded like internal valve train noise and an audible exhaust leak.

Scan tool check with our Tech2 showed a P0300 and a P0301 and that all monitors were complete except for the EVAP monitor. Because of the misfire we opted to perform a relative compression test that we hoped would indicate if the issue was internal engine or otherwise.

The results confirmed a low contributing cylinder at cylinder number 2. This indicated to us that we likely had in internal engine concern of some sort that was causing low compression on cylinder 2.

A relative compression test is a fast and easy way to check if one or two cylinders are low or high of compression by simply using an inductive amp clamp on the starter positive or negative cable.

At this point, we have roughly ten minutes into our testing and probably know as much as the other shop who recommended an engine. In fact, we could

Relative compression testing with a scope is a fast way to rule in or out the engine’s mechanical state of health.

confidently say replacement of the engine would solve the number two misfire. Because the engine didn’t sound like it had catastrophic bottom end issues, we opted to test a little further in hopes we could offer an option that salvaged most of the original engine. We removed the number 2 spark plug and installed our Pico WPS500 then fired up our Pico 4425.

Test results showed cylinder 2 cranking compression at 153 psi and running compression is 54psi. The resulting engine running pattern showed an intermittent, but semi-repeatable, minor disturbance at the very top of the compression stroke and at the very beginning of the exhaust stroke. We suspect it was very slight exhaust valve leakage, but not enough to call this an issue so we analyzed further. After some debate, we decided that there was not enough valve leakage to cause a misfire. We believed if there had been, it would have shown up in the compression portion as a lean to one side.

Based on our low running compression and otherwise good looking in cylinder pattern and good cranking compression, we determined that the intake valve is not opening sufficiently enough to fill the cylinder 100%. This is resulting in incomplete combustion and the cylinder 2 misfire. We probably looked at this wave form a little bit longer than we should have, but after about 35 minutes of total diagnostic time we had a path forward. We advised the customer that we had identified the fault as either a loose intake rocker, a bent push rod, collapsed lifter or a wiped lobe on the camshaft or a combination of these items. Major tear down was going to be necessary. The vehicle owner was advised of her worst case scenario (camshaft replacement) and given a day to contemplate her options.

In cylinder pressure testing is gaining popularity because you can glean so much more information from the resulting picture beyond just cranking and running compression numbers. In this case the low compression and lack of lean on the compression towers told us we had a filling issue on cylinder #2.

We receive the authorization to proceed and we found the #2 cylinder camshaft intake lobe severely worn due to a failed roller on the intake lifter for cylinder #2. This was causing the valve to not reach max opening and resulted in not enough air being pulled into the cylinder. All other lifters were in usable shape, but we opted to install a new camshaft and lifter set to prevent any break in issues with the new camshaft. We also replaced the leaking EGR tube as, for sure, once the misfire was resolved the EGR monitor would end up turning on EGR related codes.

Where did things get so off track for this vehicle owner? It appears that the vehicle owner had not been keeping up with her maintenance and that led to at least one of the previous shops equating a misfire with old spark plugs. Another shop saw the then new plugs and assumed it must be an injector or a coil problem. Because we never saw the old parts it is hard to say. Maybe this truck did need the tune up. Maybe it needed a coil and maybe it even needed one injector. When this number of parts are installed to fix a single #2 misfire it screams to me that proper testing had not been performed.

None of the customer’s previous paper work showed any legitimate testing was performed. The customer understood that guessing was not going to fix her truck. This resulted in her bouncing around shop to shop until she found us. An expensive endeavor for her, but eventually she bounced into our shop. In the end her truck is fixed and legally tagged once again. All she could say was thank you and “I wish I had found you first”.

Take the time to make sure you are performing the correct test for the symptoms presented to you in the bay.

Originally published in Auto Inc Magazine, a magazine geared towards independent repair facilities with the sole goal of improving the automotive trade.