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Dealing with pattern failures that are anything but

Saturday, December 1, 2018 - 08:00
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I did some bench grinder work on one side of an old chopped-up 1-1/16 wrench I had already modified for something else, and we used that modified wrench to work the sensor around, getting it indexed so we could finger the trigger and remove the connector. We continued to use that same wrench to worry the sensor out, because even with the connector disconnected the harness prevented the use of the sensor socket. We finger-started the new sensor and worried it back in until it was good and tight, then we reinstalled the previously removed oil temp sensor and reconnected all the wires. Then we went back together with it using new intake gaskets and whatnot.

The job was a victory, but it took a couple of dedicated students just about an entire day to make it happen. That surprisingly annoying task was behind us, and so was the Durango and its MIL light.

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The 2005 S10

This 4-cylinder S10 was a beat-up little farm truck that came to us with the owner complaining of a hesitation, and sure enough it stumbled on takeoff. But even after acceleration this dog was anemic at best. We applied the fuel pressure gauge to determine that the pressure was always steady and strong. We got a P0300 code, and on the scan tool misfire screen, cylinders 1 and 4 had recorded LOTS of misfires – thousands of them. Initially, I’d have believed there was a coil pack issue, since coil packs fire companions and 1 and 4 share the same coil on those. But this one is fitted with COP coils. What else could cause multiple misfires on companion cylinders? Was the valve timing skewed?

This misfire counter led us in the wrong direction on the S10 – at the end of the day, the farmer drove it home with the MAF connector swinging free. The truck ran good enough to chase cows that way.

Just for grins I had the students check compression, and they found that the firing cylinders actually had less compression (175 psi) than the ones that were reporting misfires (210). The two rear spark plug wells were awash with oil, so we did the valve cover while we were there. Those higher compression readings might have been due to surface quenching from unburned fuel, but it was strange, and we couldn’t see a lot of difference in the spark plugs on the misfiring cylinders and the plugs on the ones that weren’t reporting misfires. Just to be sure there wasn’t a cam/crank issue, we PICO scoped the cam and crank traces to check for a timing situation, but everything lined up perfectly so we moved on.

After the valve cover gasket was in place, we tossed a couple of coils in the reportedly misfiring holes along with a full set of plugs, but nothing changed – misfires were still being recorded on 1 and 4, but it honestly didn’t feel like it was misfiring – it only seemed sluggish and a holding a rag in hand by the exhaust didn’t show any puffing. And the ACE Misfire Detective was confusing enough as to be no help at all on this one.

At this point, I decided to focus on the MAF sensor, because, according to my professional eye, the airflow readings didn’t seem to reflect reality, even when MAF was the only PID being traced. Interestingly, when we unplugged the MAF and did a test drive, the truck ran like brand new, and as I peered through the sensor with my streamlight the hot and cold wires seemed dirty – but cleaning the sensor only helped a little. This one needed a new MAF, but when we showed the farmer how good it ran with the sensor disconnected, he opted to drive it that way and ignore the MIL, since most of the time he’s using this truck to herd cows. His call, I guess. But the surprisingly annoying part of this job was that the misfire counter pointed us in the wrong direction initially.

The Edge

One of my colleagues drives a Ford Edge – awhile back we had to replace the brake booster (which was dreadfully annoying). Speaking of brake boosters, for a short side story (annoying) we had to replace the booster on a 1998 F150, and after we changed the booster, the brake lights were always on because the booster pushrod had some flashing on it that had to be ground off so it wouldn’t keep the switch closed all the time – didn’t see that coming!

This stoplight switch on the 98 F-150 wasn’t giving a problem until we replaced the booster – I ground some flashing off the molded-and-cast booster pushrod on the rebuilt booster to fix this one

On the Edge this time around she was having issues with her A/C. She reported that it’d run for about 30 minutes and then get hot on one side (dual zone), so, after we duplicated that and saw erroneous readings coming from the blend door actuator on the driver side, we replaced that actuator with a Dorman unit and let her try that, but after a few days, the Edge returned with the complaint that the A/C that would totally stop cooling after about 30 miles of driving.

In addition to that issue, her radio would always begin to search wildly for no reason after a few minutes – obviously an APIM problem (the 2012s are problematic this way), which we figured might have something to do with the A/C issue, but it didn’t. We did that wacky Ford PTS software update/reflash with the IDS (with some guidance from Joey Henrich’s AE tools guy), but the APIM radio function still wasn’t fixed, so on her orders, we ordered a rebuilt replacement APIM from Ford. The core charge is $500 on one of those, by the way, and replacing that unit fixed the radio – but by the time the APIM came in, we had already figured out the A/C problem.

These were the readings we got on the Edge after it stopped cooling (with the A/C running, no less). After the expansion valve was replaced it was good to go with limitless cold air.

After letting the A/C run in the service bay with the recycler connected so we could watch the pressures, we noticed that when the register got warm, the low side had drifted into the negative and the high side was hung at just over 150 psi – much lower than it had been when the A/C was cooling. That was our smoking gun.

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