What happens when you pass the point of no return?
Our customers' trust is the oil that greases these otherwise galling situations. Nobody can truthfully claim that every job in every service bay goes smoothly every time. Furthermore, there are some customers who think everybody who handles a wrench is a shyster, and there have been plenty of genuine shysters out there to reinforce that stigma.
With those observations behind us, let's peek under the hood and behind the wheels of a few vehicles that have managed to produce some gray hair during the summer of 2011.
The Altima
Some jobs seem doomed from the beginning. This 145,000-mile Altima had briefly visited a dealership in a big college town a couple of hours to the north for oil leaks and an intermittent no-start. While the owner rejected a ridiculous $2,000 dealership estimate on repairing the oil leaks, he did pay the dealership $500-plus to repair the no-start problem. That was just dandy, but the problem reoccurred less than a week after they replaced the cam sensor and its pigtail.I have no idea what else they did to the car for that sizeable wad of cash, but because the owner lived in our town and the his mother is a colleague of mine, the Nissan came into my shop to have the oil leaks repaired and for us to provide an opinion as to the cause of the sometimes no-start. We repaired the timing cover oil leak first, which involved removing the oil pan. That's not a simple job.
With the oil leaks done, we tackled the no-start. Whenever the no-start occurred, disconnecting the cam sensor would usually (not always) enable the 2.5L to fire up, which is a fairly common occurrence on these units. Remembering thane out of line cam/crank scope pattern I saw on a PT cruiser (only to find that the crank sensor pigtail was the problem and the scope pattern was a rabbit trail), we nevertheless performed a scope test of the cam and crank that appeared to indicate that the timing components were indeed out of line.While this platform sports a chain rather than a belt, it's fairly common knowledge among Nissan gurus that these timing chains can stretch on these Altimas and can cause oddball no-starts of this nature. That stretched chain condition would also cause the cam/crank traces to be out of sync on the scope. Had that happened here?
Rather than ripping the timing cover back off to check for gear alignment (kicking ourselves for not checking while the cover was off), I decided examine the pigtail repair. The cam sensor wires were in the right cavities and the solder joints were well done and shrink wrapped, so I decided to try an aftermarket cam sensor just for grins. It was very easy to do and didn't cost much at all. To my amazement, the scope pattern straightened up and the car started every single time. I had not seen a Hall Effect sensor do that, but in retrospect, I have replaced more than a few Hall Effect sensors on various platforms that might have shown tattletale patterns if I had scoped them.Why the dealership's cam sensor and pigtail repair left this problem untouched always will be a mystery to me. We drove the car repeatedly to make certain the intermittent no-start was fixed and the oil leaks were gone. But the Service Engine Soon light came on, and so I plugged in the scan tool to see what code was stored. A P0420 code was in the memory, and that was troubling, because the engine side of the light-off catalyst strata loves to come apart on these cars.
Because those little pieces of ceramic can't go past the honeycomb, they generally swirl around and find their way back into the combustion chambers to ruin the cylinder walls and piston rings. This car was going to need a catalyst. Well, that wasn't all it was going to need. On the next test drive, the 2.5L started knocking, and locked up. I'm not kidding. It had hammered one of its bearings out and beat the rod cap off for a dandy catastrophic failure. What started out as a simple repair morphed into a full-blown engine replacement.
With the new engine, the Altima also got a new catalyst and a pair of new O2 sensors. Peering through the upper O2 sensor hole in the old cat with my pocket flashlight, I could see where the catalyst's honeycomb had been eroding, and I wasn't going to take any chances with the 45,000 mile replacement engine.Because the mileage was so high, the owner had us replace the transmission as well. Then, to get rid of the low profile tires that were on the car, he brought the original tires and rims. In replacing those, we had two lug nuts that were galled to their studs on the rear, so the Altima got a couple of new lug studs and a new set of lug nuts. We washed the car, re-checked everything (including tire pressure) and put the Altima back on the road. The bill was about $4,000, which was a rather large snowball. The customer, however, was happy with his ride and still is.
Ranger No. 1
This red 1997 Ranger came in with an A/C concern. The customer said the compressor had locked up, but I found that I could move the compressor hub by hand.First connecting the refrigerant identifier and then the recycler to the high and low side ports, I found about 100 pounds of static pressure, which actually means very little; there aren't any good numbers for static pressures. But I did notice that when we started the engine and fired up the A/C, the unit seemed to cool well with normal numbers on the gauges, then the pressures began a stratospheric climb that was sure to jitter the compressor's pop off valve. When the high side passed 350 psi, we shut the engine off and went searching for the problem.
When we unbolted the radiator and moved it away from the condenser, we found enough fuzzy plant fiber stuff trapped there to fill a soccer ball. It's amazing how that stuff can go completely through the condenser to clog the radiator fins. It happens all the time to vehicles that are driven through tall weeds a lot.The shop vacuum cleaner took care of most of that fuzzy stuff, but we followed up with a water hose, rinsing from the engine side. The pressures were normal after the wash and the A/C was frosty, but now we had another problem. The high side charge fitting was leaking (isn't that just peachy?). On this vehicle, as on so many, it's part of the discharge line, and it's one of those silly ones that doesn't have a replaceable Schrader valve. The entire suction/discharge manifold would need replacing.
That otherwise simple repair snowballed into a monster when we found that the hose was going to cost almost as much as a new compressor would. Three hundred dollars later, the Ranger was cooling again and while the customer wasn't angry, nor did he blame us, it was evident that he felt like he'd been the victim of a raw deal.Ranger No. 2
The second Ranger was a serious snowball job. It came to our door with a low power concern; another shop had tentatively pinpointed the problem as a fuel pump, but I felt a misfire. But even with the misfire, the truck drove poorly, like something was holding it back. The brakes had a nasty pulsation as well, and when we pulled it into the service bay, I could feel heat radiating from the front rotors. My temperature gun showed that the disks were at a blistering 450 degrees.This truck had been driven repeatedly through high water and mud and left to stew in those juices. We also found the wheel cylinders showing leakage inside their dust boots. The wheel cylinders would need to be replaced. Well, thanks to the "rode hard and put up wet" habits of the owner, the flare nuts where the brake lines fed the wheel cylinders were frozen solid and wouldn't budge, not even with Vise Grips.
Another problem with the flare nuts was that they were a size larger on the outside threads than normal: The brake lines on this truck are 3/16, but the outside threads of the flare nuts at the wheel cylinders are the size of ¼ inch tubing flare nuts. What that meant was that it wasn't as simple as cutting the line, double flaring it, and installing a new flare nut. We had to upgrade the wheel cylinders, obtaining some for a later year model, which solved the flare nut issue. By 1998, Ford had downsized the threads in the wheel cylinders so that normal aftermarket replacement brake lines could be used.
Under the hood, we found factory OEM spark plugs. These had been screwed into the heads at the assembly plant when the engine was new (paint spot on top of the plug), and one spark plug had developed enough internal resistance that the homemade ignition lightning was traveling down the outside of the ceramic next to the spark plug boot to find the plug's metal shell. This situation creates carbon tracks inside the spark plug boot, and so the plugs and wires were replaced on general principle. When I mentioned this to the owner, he told me that the engine had been replaced with a 60,000-mile salvage yard engine, so the bottom end could probably be considered reasonably healthy. We replaced a partially clogged fuel filter as well.
With the brakes fixed and bled, we started the engine for the first time after replacing the spark plugs and found we had black smoke and questionable engine vacuum hovering down around sixteen inches. The low vacuum bothered me; could the timing chain be stretched? Well, if the 60,000-mileage info was accurate, it wasn't likely, and V6 timing chains aren't as stretch-prone as their V8 cousins. Fuel pressure was between 30 and 40 psi, even when I gently tapped on the fuel pressure regulator. I tapped it because sometimes the pressure regulator on Fords of this vintage will intermittently fail and cause the fuel pressure to be really high, and tapping the regulator can trigger that intermittent mechanical anomaly.
On the scan tool datastream screen, the injector pulse width was initially more than 5 milliseconds at hot engine idle (it drifted back to 3.5 ms when the fuel trims began to subtract), and the MAF sensor, which should have been reading about 1 volt, was reading 0.02 volt. A known good MAF sensor showed exactly the same reading, so we got a replacement MAF sensor pigtail I had on hand, connected it to the sensor, applied power and ground to the appropriate terminals, and measured .86 between the MAF signal and return wires at idle. Revving the engine raised that voltage appropriately. When this sensor was out of the PCMs loop, it read normally. We needed to gather data on the integrity of the circuit between the PCM and the sensor.
Disconnecting the PCM, we went in search of a pin assignment chart on ALLDATA – every single pinout we found there showed the MAF signal at pin 50 on this 60 pin PCM, but that cavity was empty on our truck's PCM connector. Dipping into the Ford OEM schematics I had on hand we discovered that this 4.0L Federal Emissions vehicle received its MAF signal on pin 14. Go figure.
Checking PCM connector pins 20, 40, 60, and 16, I found good strong grounds being fed to the PCM on all the appropriate terminals. Reference voltage was a healthy 5.0 volts and all the sensors except MAF were reading as expected and required. The MAF wire had good continuity and wasn't shorted to power or ground en route to the PCM. It was evident that something inside the PCM was driving that signal low and miscalculating the injector pulse width as well.
A replacement PCM cost just more than $200 from the parts store, solving the black smoke and low vacuum problems. This low power concern had snowballed big time.
Conclusions
This Ranger started out with a low power concern that snowballed into a monster repair order right before our eyes. And I have to hand it to the students that handled this beast. While they had help from me, both of these guys are still in high school, and they hung in there like a cat on a cashmere sweater until the job was done, all in a hot shop where fans that were supposed to be cooling us off were doing nothing except moving 100 degree summer air that couldn't melt the snowballing repair bills.
Hard work was what eventually did the job. In the end, nothing makes us sleep better than knowing we finally won the fight against a bevy of monsters that dominated three of our service bays until they were done. The Rangers and the Altima are back on the road.
Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. Richard is now an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. E-mail Richard at [email protected]
