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Keeping the good vehicles going

The vehicle keeps giving oddball problems. Is it worth fixing?
Sunday, May 1, 2011 - 00:00

The vehicle keeps giving oddball problems. Is it worth fixing?

Motor Age Garage 200 C1500 low idle concerns vehicle idling old vehicles fixing vehicle repair shop training technician training automotive aftermarket

Those of us who have owned vehicles and driven them for more than a dozen years can think of at least a few vehicles we wish we had never sold. There was the '55 Chevy pickup I drove as a young teenager and sold for $150 to a guy up the road. It had vacuum windshield wipers that stopped their wiping at wide open throttle and a burned out exhaust system, but I loved that old truck, and a part of me wishes I still had it to restore. I have no idea what it might be worth today.

Some customers will have vehicles we wouldn't give $100 for, but they think they can't live without them, and trading or selling the old bomb is the last thing on their minds. These folks will sometimes spend obscene amounts of money on repairs.

I once diagnosed an early 1980s Renault 18i that needed a $1,700 engine controller, and to my surprise, the customer didn't even blink before he gave the go ahead. I wouldn't have given him $50 for the car, but he loved that old bomb enough to dump a large amount of cash into keeping it on the road. One man's trash is another man's treasure, and this fellow turned loose of a lot of treasure that day. What's a good ride to the customer might seem pretty worthless to us, but then, good is generally in the mind of the person paying the bill. One caveat on jobs like this would be that the money for really expensive parts to repair an old car should be collected up front, else you might get stuck with a vehicle you can't sell that isn't even worth driving.

Doing fleet maintenance work, I've maintained some vehicles like that as well, and the bean counters like that – keeping existing units in shape is, in some camps, more sensible than buying new ones, at least from an accounting standpoint. And there are some vehicles in every fleet that tend to give more interesting problems than other ostensibly identical units. Every vehicle has its own personality, particularly as the vehicle grows older, and the stubby little Chevy pickup (our title vehicle for this article) has given some really interesting problems, but in my mind, it still has at least 100,000 good miles left in it. But while this lively little work truck was in the shop, there were some minivans that came in and we'll peruse those first.

The Aerostar

The retired deputy sheriff's primary ride was a very nice late-model SUV. I don't know how many other cars he has besides that one and this 1994 Aerostar, but from my perspective the little van appeared to be kind of used up. Be that as it may, the Aerostar must have been sentimentally valuable to the deputy, because at some point several thousand miles ago he had seen fit to spend $4,400 having a remanufactured engine installed.

I've seen more than a few of these situations through the years – like the Renault situation, somebody will put thousands of dollars in parts in a $300 vehicle to get it going only to find that they wind up with a $500 vehicle. A customer simply can't get dollar for dollar back on a deal like this one unless they drive the money out of it.

The deputy's major mistake was that not too many thousands of miles after the engine was replaced, he had chosen to have the radiator repaired rather than replaced when it started leaking. In trusting that second rate radiator repair, he overheated the $4,400 rebuilt engine and warped the heads to the tune of .010 inch.

We had the heads machined and valve jobbed and got that one going, but there was a wrinkle in the process. The owner claimed the van wouldn't start when he brought it in, but it started right up when Casey, one of my students, pulled it into the shop, and it was blowing steam out the tail pipe like a fog machine.

After we got the heads back on along with a brand new radiator, we filled the cooling system and got the Aerostar fired up initially. But when we began ironing things out, the spark was here one time and gone the next. This situation was apparently the cause of his earlier no-start and that always makes for a confusing end to a job as intrusive as this one. True to form, Casey kept thinking he had a bad connection somewhere, but that wasn't the case.

Checking the coil's primary feed (which comes from the module) I didn't see the expected pulse, and so it was time to make sure the Profile Ignition Pickup (PIP) signal was present at the module. If I had seen a pulse but no fire, the coil would have been at fault. My trouble tree goes this way on Ford's TFI. First, if the module is powered and grounded; and second, if it gets a PIP signal (which is generated by the distributor stator) but the module won't fire the coil, then the module is bad. This module wasn't bad, it was only doing what it was told. With my O-scope connected to the PIP signal, I saw that it flat-lined during the no-spark incidents with the engine spinning even though the power and ground feeding the distributor's PIP sensor were constant. We could find no shorts to ground on the PIP circuit between the distributor and the module, which is mounted on the passenger side of the engine compartment near and above the air cleaner.

With the distributor removed and in hand (we didn't examine it as closely as we should have the first time it was removed), we discovered that the driven gear was showing enough wear that it was time for a reman replacement, which comes with a new stator. After ironing out the bugs and clearing puddled coolant out of the exhaust system, the Aerostar was test driven and stamped ready.

Overheating Town & Country

The 2002 Town and Country belongs to a guy who had replaced the thermostat and the radiator and vigorously flushed the cooling system in an attempt to fix an overheating problem coupled with a lack of cabin heat. There had been no engine damage yet – this man and his wife are both avid gauge-watchers. This one merits mention because the couple was considering replacing the vehicle because of the overheating problem, but it is a beautiful van that would be worth fixing by just about anybody's standards, and so we tackled it with fervor.

While the lack of heat/overheating situation can indicate an airbound cooling system, this one had been properly bled, but it wasn't circulating water. The heater hoses were cool. Wondering if the water pump impeller might have melted away during the pre-flush miles, I had one of my guys yank the pump to find an aluminum-bushed plastic impeller spinning freely on the water pump shaft.

I could hold the shaft still and move the impeller with one finger. I could also pull it off the shaft very easily. That was a straightforward fix and not a very high dollar ticket.

C1500 No-Frills Work Truck

We bought this truck used from an agency that was liquidating some vehicles. It ran OK for a while, but it developed an intermittent low idle stalling concern. The IAC came to mind and I happened to have a new one in my supply stock for that truck, so I replaced it without checking much of anything else. While that shotgun repair seemed to help, the truck still wasn't right.

Checking for water damage due to the ever present A/C low pressure line dripping condensate on the distributor cap, I found nothing, but the scan tool cam retard offset PID (you have to check it at an rpm greater than 1,000 or it won't be accurate) was at nearly 20 degrees and on a really high mileage truck that can mean the timing chain has a fair amount of stretch, but it doesn't always mean that.

The Cam Retard Offset (CRO) reading is supposed to be nearer to zero than that. Some earlier GM engines with the Central Sequential Fuel Injection system had adjustable distributors for making a CRO adjustment. This one didn't, but we slotted the hold-down clamp and fiddled with the indexing a bit just to see what we could see. Because this truck putters around the campus most of the time, the driver and vehicle were usually within easy reach if something went wrong. Please note that it is very difficult to find what the CRO reading is supposed to be without factory shop manual information – the spec on some of these units is zero and on others it's 16 degrees. If the PCM loses the cam signal it fires the injectors in banks instead of sequentially, a maneuver that keeps the vehicle on the road, but firing the injectors that way can cause fuel economy to drop considerably.

A few days later, I was changing the oil on this truck and installed a new distributor in this unit on a whim. The parts store had one in stock and it didn't cost much, so why not? Further, GM's procedure calls for distributor replacement if the CRO isn't right on one of these. With the new distributor installed, the cam retard number was down to around 12 degrees and the truck ran a lot better.

A few weeks went by and suddenly the no-idle problem was back in full force. Initially, I noticed that the temp gauge and the scan tool were reading bone cold (77 degrees) but my infrared temperature gun was reading 193 degrees at the sensor. While that might not be the cause of the concern, it needed addressing. Replacing the ECT sensor fixed the gauge and the scan reading, but the truck still wouldn't idle worth a toot.

The scan tool indicated that the PCM was calling for some really high Idle Air Control (IAC) step numbers — it does that when it wants the engine to idle up — but the IAC stepper motor apparently wasn't responding. With the air cleaner horn removed and a look into the throttle body, I could see the passage where the air is supposed to circumvent the throttle plate and I could tell that the IAC pintle was totally seated. This made no sense at all.

Book procedure calls for disconnecting the IAC connector and checking each of the three driven wires for pulsing voltage. We did that and saw the pulse on all three control wires. It was time for another new IAC. When I removed it from the throttle body, however, the plastic end of the IAC was gone. It had screwed itself off and its spring and sleeve had held it in place, effectively causing the low/no idle concern. The pintle had been forced by spring pressure to remain in place until I removed the IAC, which released the spring pressure and allowed it to drop into the intake. This kind of thing is really disgusting. I call these situations circumstantial land mines.

I wanted to see if I could locate the missing pintle, so I yanked the throttle body off and peered into the intake with a bright light and an inspection mirror. No dice. Not to be outdone, I pulled the upper intake, revealing the spider assembly in all its glory. I used two different borescopes looking for the end of that IAC in the intake passages and never did locate it. I realized that I was being outdone after all, and it didn't feel good. One thing that did give me a little comfort was that this particular pintle was soft plastic. The aftermarket supplier may have chosen to make it that way for this reason, who knows? I thought about how some automakers with bolt on air cleaners and throttle body injection tended to make the air cleaner nuts out of plastic.

Irritated at my inability to locate the missing part, and after burning about an hour and a half fishing for it, I decided to take a chance and hope for the best. After all, it was a company truck with a lot of miles on it anyway. I reinstalled the intake with new seals, replaced the IAC valve with a new one, and put that truck back on the yard. It has gone a few thousand miles since that repair with no ill effects, so apparently the tip of that IAC is still dancing around in those curvy air passages somewhere if it didn't blow through the engine to make its way to the converter, where it will melt onto the strata. I halfway expected it to catch under a valve and cause a compression/skip problem, but it hasn't yet, and the truck still runs great.

The next time I change one of those, I'm going to yank the throttle body first. It isn't a lot of trouble and this kind of thing is less likely to happen.

Conclusion

The age and condition of the vehicle should always be factored in when a job is being considered. The Ford service department where I used to work failed to do that once and wound up with $1,200 worth of engine work invested in a rusted out piece of junk truck that was bone yard material even after the work was done. The owner knew the truck was junk and when it was to be auctioned off several months later as an abandoned vehicle, he showed up at the auction and tried to buy it really cheap. It was a "no sale." We kept the truck at the shop and used it to haul scrap iron and garbage.

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. Email him at rwm19@mail.com.

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