Motor Age Garage: Weak Links

Jan. 1, 2020
Weak links abound in just about all vehicles; some more serious than others. Some are covered by technical service bulletins (TSBs) and some aren't. Late 1990s Ford single overhead cam (SOHC) Explorers came with intake gaskets that leaked air when th

Weak links = broken chains. Weak parts = broken vehicles.

Weak links abound in just about all vehicles; some more serious than others. Some are covered by technical service bulletins (TSBs) and some aren't. Late 1990s Ford single overhead cam (SOHC) Explorers came with intake gaskets that leaked air when they were cold. Early to mid-'90s Toyota Camrys tend to develop messy oil leaks around the cam gear and oil pump. Those little four-cylinder KIA engines like to burn at least one valve at about 100,000 miles. The tendency of late-model General Motors (GM) cars to have bad radiator caps is legendary.

This list could go on indefinitely across a myriad of vehicle lines and year models, and no manufacturer is immune. TSBs are a good thing, but they don't cover all the weaknesses, and sometimes it seems that the manufacturers deliberately keep quiet about recurring concerns, especially when safety or emissions aren't affected but their bottom lines might be.

When we, as technicians, discover a situation where several similar vehicles are having the same problem, we know there's a weak link in that car's chain of parts and processes. Discovering that weak link is like money in the bank. Working on a vehicle without knowing that unit's weaknesses can cause a guy to rebreak old ground troubleshooting, effectively losing his shirt on a job that would be "duck soup" for somebody aware of a known concern with that platform.

One of my jobs as an instructor is to show my students how to find those weak links, particularly the ones that don't appear in TSBs.

THE INVISIBLE AIR LEAK

For several years, my former employer handled all the maintenance on the local telephone company's vehicles. The nasty thing about these jobs was that we didn't have any literature on most of the stuff they drove – the least of which was a group of those annoying mid-'80s K cars – and the telephone company people who drove those cheap little bombs were tough to please.

One of the most annoying problems we dealt with on these units was a rough idle/stumble condition that would coincide with the air conditioning (A/C) clutch cycle. Carburetors were cleaned and resealed, adjusted, checked and double-checked, and nothing really seemed to help much. I spoke with Chrysler instructors, tech reps and other techs, and I generally got pat answers that led nowhere.

Then came the glorious day when I finally found the weak link that was causing the problem. I happened to be monitoring O2 voltage and noticed that the O2 signal dropped to zero for a few seconds every time the A/C engaged.

I decided to hit the carburetor base gasket with a brief and tightly focused shot of carburetor spray. I immediately saw the O2 signal respond. Although the carburetor base mounting nuts were tight and the gasket appeared to be sealing, there was obviously an air leak there.

I carefully flat-filed the base of the carburetor and found a serious warp factor there that wasn't visible to the naked eye but was effectively preventing a proper base gasket seal. I finished the flat-file job to true up the carburetor base and reinstalled the carburetor. The first time I did this, I don't think I even replaced the base gasket, but the car ran like new. Finding that one weak link made fixing all the other rough-running cars in the fleet simple.

KNOWN CONCERNS = LABOR HOURS

VEHICLE: 1996 K1500 DRIVETRAIN: 5.7L engine, 4L80E transmission MILEAGE: 157,654 miles COMPLAINT: Check water leak from under cylinder head.

A HUGE COOLANT LEAK

Initially the Air Force soldier who owned this truck contacted the Toyota T10 school, but for obvious reasons they weren't interested in tackling a nuts-and-bolts job on a 350 Chevy engine. The guy described his problem as a water leak from under the cylinder head.

But as I questioned him, I began to realize that he was assuming a lot. Water was literally gurgling out as fast as he poured it in, and no cylinder head gasket is going to cause a leak that severe on an engine that runs as well as this one did. He also spoke of some peculiar transmission activity that had developed not long after the transmission was replaced.

When he finally brought the truck in, we added liquid to the radiator and found it rushing out of the driver side front corner of the intake manifold underneath the A/C compressor bracket. That location made the source of the leak hard to spot, thus the owner's erroneous conclusion.

GM's V engines seem to have a fair amount of intake gasket trouble, sometimes leaking coolant externally and sometimes leaking it into the engine oil.

It was time to yank the central (point) sequential fuel injection (CSFI) intake, which would entail removing the A/C compressor and bracket. In order to make that happen, the power steering pump pulley needed to be removed. The distributor had to come out as well. Pulling the intake on a 350 isn't nearly as much fun as it used to be, but at least the intake was plastic and aluminum instead of heavy metal. It took two guys to get some of those big-block cast-iron intakes back in place.

The gasket had disintegrated at the water passage on the guilty corner of the intake. After everything was cleaned and checked out, James started putting everything back together. It was to be an interesting endeavor.

HOT SOAK NO-START

While James was working his way through the intake manifold job on the '96 5.7L, I was investigating a mysterious concern one of the college pickup trucks had developed. The maintenance men drive a 2001 Chevy pickup — one of those basic, no-frills units with a 4.3L and a CSFI fuel system.

As they were driving the truck around the campus doing their work, they would experience a hot soak no-start at least twice a day that would require about 20 minutes of cool-down time, after which the truck would start normally. I'll bet somebody who's reading these words has probably seen more than a few of these and may know exactly where I'm going with this one.

Well one day, the truck was right outside my department when the concern surfaced. I rushed out there with spark tester and a fuel pressure gauge to find that the engine was giving me the classic symptom that generally points to a fuel problem.

The engine would try to start but wouldn't stay alive, which told me it had ignition — at least during the time the key was in start — but that there wasn't enough fuel delivery to keep it going when it did start. Installing the spark tester, I saw a strong, hot spark that was popping normally all the way down to the last wheeze during one of these start and die cycles, so I discarded the idea of a spark problem.

Reaching for the irritatingly hard-to-access fuel pressure port (it was a hot engine, and I was in a hurry to do the test while the problem was present), I connected a pressure gauge and found 62 pounds of fuel pressure. I was leaning in the direction of a fuel metering body issue, especially because it seemed like a fuel starvation no-start. A few minutes later, it started normally, and when it did start, the fuel pressure hadn't changed until engine vacuum acted on the regulator diaphragm.

There is an interesting GM service bulletin (00-06-04-003A) that outlines a procedure whereby the injector poppets should be unstuck first by applying 150 pounds of pressure with a special tool and operating the injectors with the Tech 2. If that doesn't work, the TSB then calls for running a mixture of 5 percent top fuel cleaner and 95 percent gas through the poppets from an outside fuel source. That is a dandy TSB, but it was for a cold start/misfire concern and didn't line up with my symptom. This wasn't a misfire; it was a no-start hot.

At the local GM dealer, the service manager sometimes doubles as the parts manager, and when I called to inquire about a CSFI metering assembly, he told me to try a cap and rotor, because the A/C suction line likes to drip condensate on the distributor and cause weird problems.

While I had yet to examine the cap and rotor on this truck, my prognosis didn't seem to support it. A fouled up cap and rotor don't usually cause problems like this, but in the interest of doing the cheapest thing first, I ordered a cap and rotor.

What did I have to lose? With money and labor as an issue, I'd have tried the same repair even if the truck had been my own ride.

A JAW-DROPPER

My skepticism seemed ill-founded initially. Five weeks passed after I replaced the distributor cap and rotor – both of which looked fairly pristine – and the no-start hot soak problem didn't happen. Then one day Gene the maintenance man called me out to the truck to tell me the problem had reared its head once more.

My skepticism, it turned out, was on the button. Using my scan tool, the truck showed me a P1631 (theft deterrent start-enable signal not correct), one of those "I forgot the key for a few minutes" deals, I guess. The dealer would need to use the Tech 2 to solve this problem.

I have since discovered that the Chevy truck we use on the other campus (15 miles away) is giving the same problem and has been towed to the dealership in that city about 10 times. I haven't looked at that one yet, so I don't know what's going on with it.

LEAK FIXED – NO MAF SIGNAL

James got the manifold back in place with a new thermostat and a new heater quick-connect fitting (another weak link on GM cars). He had enough trouble starting the fuel line because he had fouled up the threads on the return line and had to fix the nut with a file.

As we watched the scan tool during engine warm-up, another problem surfaced: the mass airflow (MAF) sensor and the camshaft position sensor (CMP) sensor were both dead and they were both tossing codes. I was in my element now. A quick check of the circuit showed no power at the MAF sensor on circuit 539, and the CMP sensor was fed by this same wire. Checking the schematic, I found ENG fuse 1 to be a logical check, and it was blown. Inserting another fuse prompted an instant replay: that fuse blew too. At least the problem was there all the time and could be pinpointed.

With an 8-amp self-resetting circuit breaker temporarily wired into the ENG fuse 1 cavity, we found the breaker tripping. Further research revealed that circuit 539 fed the EGR valve, the canister purge valve and all the oxygen sensor heaters. I moved around the circuit path disconnecting components and found the heater shorted in HO2S 1/2. Replacing that sensor and the ENG 1 fuse, we found all systems go on the 1996 Chevy.

WHY THE PLASTIC FITTINGS?

Those pewter quick-connect fittings are pretty lousy, but they don't hold a candle to the egregiously silly plastic hose fittings. How many people are on the verge of enduring a record-breaking repair bill because of a plastic fitting that should never have been used by anybody?

There are plastic heater control valves, plastic radiator tanks, plastic intake manifolds, all carrying precious pressurized coolant for years and hundreds of thousands of miles. Those plastic fuel filters seem a bit dangerous until you cut one open; that plastic filter housing is about ¼-inch thick.

Ford uses a plastic heater hose tee on some of their late '90s Taurus platforms, but GM is just as guilty.

Rebecca is a student at my college whose car developed a coolant leak that was just as aggressive as the blown intake; as liquid was added, it gurgled out from behind the alternator and all the way to the pavement at the rate of about a quart every five seconds.

Removing the alternator, we found a plastic fitting screwed into the lower intake for the bypass hose connection. What a time bomb.

The term "planned obsolescence" comes to mind, and it goes this way: Let the plastic fitting pop (inevitably, it will), dump the coolant, and if the circumstances are right, you have a pretty good chance of totaling a 13-year-old vehicle. How many people will want to pay for a replacement engine on a 1993 Park Avenue, with all due respect?

In doing any type of cooling system service or preventative engine maintenance on a high mileage GM 3800 like this one, wouldn't it would be wise to remove the alternator and see if it has one of those plastic hose fittings screwed into the intake? If so, there are metal replacement fittings available that will strengthen that link and probably save the engine.

CONCLUSION

Some weak links aren't such a big deal; the DPFE sensors on Ford cars is an example of a weak link that doesn't cause much of a problem. But as technicians, we should be acutely aware of the potential risks involved in leaving a critical weak link in place, especially in today's dog-eat-dog world.

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, AL. E-mail Richard at [email protected].

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