Mysteries Solved

My mom’s 91 Chrysler had an MIL illuminated, and the flash-out code indicated a cold running engine.  Dad replaced the thermostat and got it running normally warm again, and she drove it for a day or two before he got around to changing the oil.

With new oil in the crankcase, it wouldn’t idle, and dad (an old-school mechanic) was so mystified by that development that he called me on the phone to ask about it while he still had the car in his shop.  I told him to remove the battery cable for awhile and let it forget what it had stored in the fuel trim tables.

As a cold-running engine, it had also run rich long enough to lace the engine oil with gasoline, the vapors of which were making their way through the PCV system.  With no gas in the crankcase, the air-fuel mixture was all fouled up, and until the screwball numbers were dumped, it just didn’t idle worth a toot.

Stories Number Two and Three

My sister once drove a 1977 Chevy Caprice that mysteriously developed an inoperative radio right after my dad replaced the brake pads.  She grumbled about the radio and how he must have caused that problem somehow (my dad knew better and turned a deaf ear to her complaints).  Finally, I got tired of her tirade and troubleshot the radio problem to find that the radio had a shorted capacitor in it that was causing it to blow the fuse.  How did replacing the brake pads cause the radio problem?

They didn’t, obviously.  Why the failure happened when it did is probably a Murphy’s Law deal the likes of which we’ve all seen.  Customer logic is simple (a little TOO simple sometimes): The item in question was working fine before the car went into the shop and it had a problem after they got the vehicle back, so it had to be something the technician did wrong, and it should be fixed for free. Right?  Well, sometimes, but not always, and many a shop has chosen to eat the cost of repairs that were actually the customer’s problem so as not to alienate the customer.

Still, there are times when the customer’s complaint is legitimate, no matter how seemingly unrelated it may be.  One of our problems in this business is that with so many customers trying to get piggy-back freebies, we tend to roll our eyes at complaints of related issues when in reality we should be giving them the benefit of the doubt.

For instance, I personally saw my brother’s 1977 Cadillac develop radio static immediately after the tires were rotated. Sound ridiculous?  As it turned out, the steel belted tires on that car were older radials that weren’t friendly to being cross-rotated, and when they were placed back in their original positions, the radio static was gone.  Really, it was!

The Blazer

This gentleman was qualified to have work done in my department because he has a government job; he had a few concerns he wanted checked.  To begin with, the engine was a hard-start long-cranker, and he had the idea that the fuel pressure regulator needed changing. This Blazer was equipped with one of those delightful CSFI fuel systems GM dumped after only a couple of years or so, and at his insistence I had the guys replace the fuel pressure regulator, which was no small feat on that engine.  The upper intake had to be removed, and with it a part of the fuel system.

I had my doubts as to whether the regulator was the problem, and we replaced it just to satisfy the customer.  The fuel pressure wouldn’t hold steady at engine shutdown, and I was fairly certain it was the pump rather than the regulator, but it didn’t hurt the students to tackle the job.  With the regulator replaced, the fuel pressure decay wasn’t any better (not surprising), so I sold him a fuel pump, which handled that hard-start problem.  His second complaint was a fairly serious oil leak, which turned out to be a rear main engine oil seal, and I had a different student handle that repair.  The transmission was removed, and the rear main seal was replaced along with the transmission pump seal; it would have been a bad bet not to replace that one as well.  After all the work was done, everything seemed fine, the bill was paid, and the Blazer went home.

A few days later, the Blazer owner called back to say that his electric rear hatch release no longer worked after we performed our repairs.  I have to confess to some eye-rolling here, but I gave the customer the benefit of the doubt and told him to bring the Blazer back so we could have another look.  When I spoke to him at length, he explained that the key lock cylinder hadn’t opened the hatch for years, and so he had been accustomed to opening the hatch with the pushbutton switch up front.  We were studying electrical systems at the time, and even if the problem wasn’t something we had caused, it would be good for the students to track this one down.


Checking the Hatch from Scratch

First we checked the fuse, then we followed the circuit to the next easiest place; the pushbutton release switch had good power and the power would pass through the switch with the button pressed, but there was no activity in the hatch.  I know of one guy who has a short piece of 2×4 with two nails in it.  He has a long wire connected to each nail so he can connect the wires to the battery and with the wired-up 2×4 in hand, he takes power and ground with him wherever he goes.  Shifting the test light to B+, we checked the circuit feeding the hatch release solenoid and found that there was no ground.  Studying that side of the circuit we found that the hatch release solenoid gets its ground through the neutral safety switch; GM didn’t want some yahoo punching the hatch release button while driving down the road.  Think about it: You could lose ice chests, camping equipment, dogs, and even kids that way, if they’re riding back there.

To make a long story short (if it isn’t too late), the transmission range sensor connector wasn’t properly seated. As unlikely as it may sound, with that connector poorly seated as it was, everything else that went through that switch would work except the hatch release.

Mustang with a Buzz

This isn’t about a half-drunk horse; I saw a 1996 Mustang that belonged to a retired Air Force fighter pilot, and the car had developed a buzzing noise coming from behind the instrument cluster.  I fiddled around for awhile trying to find something and couldn’t pinpoint the noise.  The shop foreman noticed that if he held a balled up jacket up at the top of the windshield area, it muted the noise, so we applied masking tape to all the chrome around the windshield, but to no avail.  We explained what we had found (or rather hadn’t found) to the old fighter pilot, who told us that he needed the car that afternoon and said he would bring it back later so we could do more checking.

When he did bring the Mustang back, it was to report that he had found the source of his noise.  He had been driving with his left elbow on the door and the fingers of that hand on the rain trough when he heard the noise and felt it on his fingers at the same time.  He used his finger for a pointer until he felt the strongest disturbance, then held his finger there and pulled off the road.  When he stood up to look down his finger, he saw that he was pointing at the edge of the brand new bug shield he had mounted on the front of the hood.  The old pilot built some V-shaped aluminum braces and used Velcro to mount them in such a way as to brace the bug shield.  The bug shield had been creating an oddball noise that was being telegraphed through the windshield and actually sounded to all of us as if it was coming from behind the speedometer.

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