Our first vehicle is a 2006 Acura MDX 3.5L, with 178K miles on the clock. I was called on for some help by one of my students, Mike Pegan from New Jersey. His concern on this vehicle was a complaint about a bad hesitation from a stop and poor fuel-economy of only 11 mpg. Mike started his diagnostics on this MDX by connecting the ATS EScan to the vehicle. The scan of the vehicle revealed that all the Monitors were Ready, there were no DTCs but, a “time to temperature” warning was displayed. Not thinking much about it, Mike assumed the problem was something else since, the engine temperature did indeed reach 195 deg-F. The engine was not overheating but, did provide good heat.
The history on the MDX cooling system was that it had been serviced about a year ago, flushed and refilled with Acura antifreeze/coolant. Mike decided to contact me for a second opinion since, two heads are better than one. I suggested to replace the thermostat as, a good place to start since, the Escan flagged it as a problem (Figure 1).
If you know something is wrong, and you have checked all the basics (the battery condition, engine mechanical, DTCs, etcetera), then fix any simple issues (in this case, the thermostat).
The result of that decision to replace the thermostat changed the fuel mileage from 11 mpg to 18 mpg. A great improvement for replacing an inexpensive part (Figure 2). Since one problem was out of the way, Mike continued his diagnosis by running the fuel trim test (Figure 3). The test results did not look good so, he started to analyze the performance of the catalytic converter. During his investigation, he found that the converter did not have any physical damage but, the catalyst efficiency was down, at 50%. Knowing that a possible cause of the hesitation could be from a catalytic converter issue, he was going to check it out, thoroughly. The next step in that process, was to check the exhaust back-pressure. The results were within specification so, that ruled-out the converter as the cause. This was followed by an important and typically-overlooked step (especially with fuel trim outside of specification), a PCM-reset. This will bring the PCM-adaptations back to their starting point. Mike filled the vehicle with premium-fuel then, drove home and back to work again. The results of the reset, fill-up and test drive moved the efficiency reading of the converter to a passing level but, there was still something wrong.
Mike’s decided to contact ATS tech support where they log-on to your computer and review the scan tool data so, they can help guide you through a diagnostic process, to repair the problem. Mike explained the vehicle’s situation, what he had tested, and the repair he made. He knew that even without any DTCs, it did not mean that the engine, sensors, and actuators were operating as designed but, he could not condemn anything, yet.
During the tech support call, it was observed that the MAP sensor was not in the correct range, during various engine RPMs. ATS tech support suggested that Mike carefully check the load sensor, to make sure it stayed within specification, at all rpm ranges. Taking their suggestion, he double-checked the data PIDs when he noticed the MAP engine vacuum reading was not in the correct range. His findings uncovered that the MAP was reading 22 inches of mercury, while the actual reading was 18 inches of mercury (Per vacuum gauge). Since this engine does not use a MAF sensor, the load commands all come from the MAP sensor. If the MAP vacuum reading is skewed, the PCM will respond to the erroneous information and send the wrong commands to the fuel injectors. The MAP was replaced, and the fuel trim reading was positively affected but, still not perfect.
The hesitation still existed. This could be caused by an APP (Accelerator Pedal Position) sensor malfunctioning. I contacted Mike and told him that I had read-up on the APP (in Identifix) on the location, specification, and testing procedure. I suggested to Mike that, he follow their test procedure for the APP. After he located the APP sensor on the firewall, he checked the accelerator cable that runs to it, along with a 6-wire black connector. He verified that pin #1 (the Yellow/White wire) had 5-volts on it, (with KOEO) from the PCM and, that the Black wire (pin #2) had a good connection to ground. He proceeded to check the APP #2 sensor-sweep on the Pink/Black wire (pin #3) to make sure the voltage-sweep was in the range of 0.2 - 0.3 volts. It was able to reach roughly 2.2 - 2.3 volts, without any drop-out on the graph of the scan tool or lab scope. Since this part of the test checked-out, he moved on to checking APP #1 sensor, to verify the Black wire (pin #6) had a good ground path and, Pin #5 (a Yellow/Black wire) had 5 volts available. Mike ran another sweep-test on the Green/Yellow signal wire (pin #4). The specification indicates it should rest closed at 0.5 volts and, should sweep up to 4.5 volts, as the pedal is depressed, without a glitch or drop-out (when testing at both the sensor and PCM). If any of the signals drop out, the APP sensor will need to be replaced. Neither of the two signals indicate a fault. Leaving no stone unturned, Mike performed a throttle body cleaning and engine decarbonization process, using the Run Rite chemicals. As a result of the cleanings, there was a slight improvement in the engine running-condition but, the hesitation still existed.
With the engine-side of the equation out of the way, the only remaining possibility was an issue with the transmission. Mike asked me if I could get in touch with Wayne Colonna (from ATSG/ETE), the transmission expert. I contacted Wayne and asked him about the hesitation on this MDX. Wayne was able to shed some light on the hesitation issues that this transmission has, due to a common sprag-clutch problem. He also sent along a particularly important ATSG Service Bulletin titled, “Five Speed Neutralizing Downshift To 1st Gear”. The bulletin goes on to state:
before or after an overhaul, Honda and Acura vehicles equipped with a five-speed transaxle may exhibit a neutralizing condition on a downshift into 1st gear, or a 3-1 passing gear neutral. This condition may be intermittent. This neutralizing condition can be cleared up simply by placing the selector in the Manual 1 position. The cause may be, a worn low one-way clutch, or a worn inner race for the low one-way clutch. Honda and Acura vehicles equipped with a five-speed transaxle utilize a low one-way clutch that locks in 1st gear for take-off. If the low one-way does not hold in 1st gear, there will be no engagement until the selector is placed in manual-1st. In this position, the low hold clutch is engaged, and 1st gear can be attained. The low hold clutch is used to provide engine braking in manual low as well as backing up the sprag by holding 1st gear, should the sprag fail. This sprag failure is commonly overlooked, as the low-hold clutch hub must be driven out to inspect the sprag and races.
This important information from ATSG goes on to state (with pictures) what parts to replace, how to install, and retest. This information can be purchased from the ATSG hotline or by purchasing one of their great transmission troubleshooting manuals. The problem with this Acura, boiled down to the transmission. Mike informed me that the vehicle owner decided to live with the hesitation since the owner’s uncle (that has the same vehicle with about the same high mileage) has the same hesitation. Go figure!
Carbon bound
Our next problem-vehicle came in from Patterson Auto Body. They had an issue on a 2016 Honda Pilot 3.5L with 126K miles on the odometer and, a P0300 DTC. The shop told us that their customer complained of engine misfiring. This was confirmed by the P0300 they found stored when they scanned the vehicle. The shop performed a tune-up, spark plug, and air filter replacement. It seemed that the shop made all the right moves by replacing all the worn-out components that have a major effect on engine misfires. The misfire was still an issue after the repairs, so the shop decided to run a fuel system cleaning, using a national brand. They performed the GDI cleaning twice (with a company representative present) but, did not see the results that they expected. When they looked inside the engine with their video scope, they noticed that carbon build-up was just as heavy after the cleanings, as it was prior. After the cleanings were performed the engine still misfired. The fuel-system cleaning-product representative thought that the GDI injectors were causing the problem and must be replaced. The shop followed the company’s recommendation and ordered all 6 GDI injectors from Honda. After the shop installed the injectors, they drove the vehicle around, only to find the same misfire issue. This was when Fred Byron (from Patterson Auto Body) called me and asked if I could diagnose this misfiring Honda. I told him to come down and we would check the vehicle out.
Our diagnosis revealed the engine misfire exhibited, was not mechanical, ignition, or fuel related. So, we waited until the engine cooled down. We then, looked into the engine via the plenum and found a heavy carbon build-up on the intake valves and seats (Figure 4). We suggested an ATS Chemical carbon cleaning on this GDI engine, to clean the carbon up. Fred was not 100 percent sure that the cleaning was going to prevent the engine from misfiring but, he trusted my recommendation. We performed the ATS Chemical cleaning and noticed a heavy amount of black smoke coming out of the tailpipe, as the cleaning was being performed. Once the cleaning was completed, the valves and seats were noticeably cleaner, allowing the Honda to run as it should, performing well and free from misfires (Figure 5). I called Fred and told him to come down and pick up the Pilot. Fred was so amazed at how well the engine was running, he is waiting until the pandemic is over and will then, purchase the ATS Chemical machine, himself.
Noisy 3.5L Honda
A 2011 Honda Pilot 3.5L, driven 172K miles, came in with a complaint of noise when the engine was at idle. The noise would worsen, during acceleration. We needed to confirm where the noise was originating from by using a stethoscope to listen, all around the engine. We found that the noise was from the right-side of the engine and could be coming from a belt, pulley, water pump, or alternator. We played the disconnect-game to narrow down and locate what was generating the noise. What we usually do is remove the belt(s), depending on the system. If the noise goes away, we install our Grizzly make-a-belt (Figure 6) and attach it from the crankshaft, to either the alternator, pulleys or water pump (not available since it’s under the timing cover on this engine) or any other of the auxiliary rotating devices, to pinpoint the problem. On this engine, we did not need to use the Grizzly to make a belt, since the noise was still audible with the belt removed.
Our next step was to call the Honda owner and suggest that we remove the timing cover and inspect all the components of the timing belt system. With the Pilot owner’s OK, we removed the timing belt cover to expose the two camshafts, crank gear, water pump, idler pulley, and adjuster pulley (that the timing belt goes around). We carefully started up the engine and used the stethoscope once again, on each component. Our results concluded that most of the noise was coming from the water pump and the adjuster pulley. We recommend the timing belt, pulleys, water pump, thermostat, drive belt be replaced, along with a cooling system flush. Once we completed the job the engine ran noise-free.
Unfortunately, this was not the end of this story. A few months later (now with 174K on the clock) the vehicle was back in for the engine not running well, along with an oil leak. Our technician Bill, checked out the engine area and found that the oil was leaking from the VTEC (Variable Timing/Electronic control) solenoid spool valve assembly on Bank 2, for cylinders 4, 5, and 6 (Figure 7). Since oil was leaking from the unit, we knew that the VTEC system was not operating correctly. There was no need to check the pressure switch or scan data to make sure it was functioning properly. Instead, it was time to call the owner and suggest a new spool valve. The fix for this spool valve entails removing the intake plenum, valve cover and the rocker assembly which, allows access to the spool valve. Bill removed and installed the new spool valve, followed by adjusting all the valves and performing an oil and filter change. Now, the Pilot’s repairs were complete and it’s running like a top.
Clogged Honda
Our next problem is a 2005 Honda Accord 2.4L, that logged 203K miles and stored a DTC P2646, for a VTEC Pressure Switch Circuit, Voltage Low. The first place to start is to make sure that there is the proper voltage and ground at the pressure switch. This was followed by removing the VTEC pressure switch and installing a pressure gauge, to determine if there is a pressure problem or just a bad switch. On this engine, Bill found that it had a good switch so, he proceeded to check the VTEC solenoid’s functionality. When he removed the solenoid, he noticed that the screen assembly was clogged with RTV.
Bill installed a new solenoid and started the engine up only to have the MIL illuminated again, with DTC P0011 Timing Advanced Bank 1. He removed the VTEC solenoid again and, found more RTV in the small screens of the solenoid. The RTV was a result of a head gasket repair, that was previously performed by a different shop. Bill cleaned-up all the RTV that he could see but, he knew that there was more in the engine. He suggested to the Accord owner that the engine be flushed and oil/filter changed. The vehicle owner refused to perform the engine flush and paid only for the repair that we performed on the vehicle.
This was not the last time we were going to see this Honda, either. It was back in less than 300 miles, with the same DTC, due to another clog. Bill recommended the engine flush and oil change as, he had done before, at the previous visit. The Accord owner wanted to know what was wrong, so Bill explained the problem again, then suggested an engine flush and oil change was a good starting-point. Bill made sure to explain that the flush and oil change may not remove all the RTV (Figure 8) causing the problem. If the flush and oil change did not clear the issue up, the oil pan would have to be removed. Believe me, we do not like flushing engines, especially with 204K miles on it. We did provide the Honda owner with the pros and cons of the oil flush. Our choice of engine flush chemical was the ATS 505 CRO additive that we poured in the engine and ran for 20 minutes. This was followed by a drain and replacement of the oil and filter. The outcome of the cleaning left engine was running well, without an illuminated check engine light. This turned out to be an easy fix.
My hope is that these case studies help you take a path in making your diagnosis easier. By opening your mind up to potential failures, the logic involved in uncovering them, and the available tools and solutions to alleviate them, I also hope to assist you and your shop to remain profitable and efficient, in future-encounters.
