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  • TDC - Technical Questions & Answers - June 2004

TDC - Technical Questions & Answers - June 2004

Questions and Answers

Bruce Caldwell
Jun 1, 2004
Photo 2/3   |   tdc cranky When Cold
Cranky When Cold
My '89 Chevy Silverado pickup seems to take way too long to start in the morning or any time that it's been idle for several hours. It seems worse when the weather is extra cold, but I don't think the problem is strictly temperature-related. When I'm doing errands and starting and stopping the engine frequently, it starts right up, although it tends to idle a little fast. It did register a trouble code for the idle motor. I installed a new idle motor, but I didn't notice any big improvement, although the trouble code went away. Can you suggest anything other than the idle motor or a related problem that could be causing the symptoms that I have been experiencing? Thanks for giving it a shot.
Lyle Davis, Charlotte, North Carolina
A: Check out the fuel pump relay. A fuel pump relay problem can manifest itself in overly long cranking times. This is the relay that serves as the middleman between the truck's computer and the gas tank-mounted fuel pump. There is an oil pressure switch that serves as a backup to the fuel pump relay. That means that if the fuel pump relay isn't working correctly, as soon as there is sufficient oil pressure, the fuel pump will receive current. In your case, the extra cranking time is most likely the time it takes for the oil pressure to build to the point that the fuel pump kicks in. Once your truck has warmed up and been driven, it will take much less time for the oil pressure to build. That explains why you don't seem to have the problem when you're doing errands.
You may want to have a shop check out the functioning of your fuel pump relay, but it sure sounds like that is your primary problem. You can get an idea of whether the problem is the relay by listening to the engine compartment when the key is turned on. Open the hood and position yourself on the right side. Have someone turn the key from Off to Run. An audible click (when the key is first turned) followed by a second click a couple seconds later indicates that the command has been given to the relay switch. The first click means that the command was sent to the fuel pump relay; the second click indicates that the relay operation was canceled because the relay wasn't working.
A vacuum leak is the most likely cause of your fast idle problem. If that leak exceeds the idle air control's (IAC) ability to correct itself, the idle will remain too high. Common sources of vacuum leaks include faulty vacuum hoses or ones that have become disconnected. There can also be vacuum leaks around the base of the throttle body. Inspect these hoses carefully for any signs of problems.
A way to check for the problem is to put your finger over the air intake port for the throttle-body injection. This small hole should be on the top right side of the throttle body (with the air cleaner removed). Idle the engine and put your finger over the hole. If the idle drops, the IAC isn't responding or the ECM is incorrectly asking for higher idle speed. If the idle speed stays constant, there is probably a vacuum leak.
Slow To Go
I have a '93 Jeep Cherokee Sport with the 4.0L six-cylinder engine. The automatic transmission has trouble moving in the morning. It's like it doesn't want to go into gear when I first try to put it into Drive. After a while it will get going, but it's annoying. Once it does get going, it seems reluctant to upshift at first. This problem is particularly noticeable on cold mornings. I've also noticed some transmission fluid where I park the Cherokee. I don't seem to be losing a great deal of fluid, but it's definitely leaking. Could these problems be related, and how can I fix them?
Lindsey Powers, Dallas
A: Your problems are all transmission-related. You will probably need the help of a transmission shop to resolve them. The first problem sounds like torque converter drain-down. You didn't mention if the vehicle is driven daily or if it sits unused for several days. The longer it sits, the greater the odds are that converter drain-down is the culprit. Ask the transmission shop about installing a check valve in the fluid line that goes between the transmission and the transmission cooler. That usually fixes the problem.
As for your second problem - the slow initial upshifts - these transmissions have been known to exhibit slow shifts in cold weather. The problem has been traced to defective cast-iron seal rings in the governor drive. The transmission shop can fix this. A common source of minor leaks in '93 and '94 Cherokees is the transmission's speed sensor.
Photo 3/3   |   tdc leaks In Dakota
Leaks In The Dakota
I've got a couple of leakage problems with my '95 Dodge Dakota. The truck has the 5.2L V-8 and automatic transmission. It has about 95,000 miles on the all-stock engine. I've done a pretty good job of following the recommended service schedules, but not exactly. I've got two leakage problems. The most troublesome one is water on the floorboards. The carpet is wet most of the time, but I can't figure out where it's coming from. I know it isn't the heater because it doesn't smell or look like coolant. I've left white paper towels on the floor to see if green coolant was the problem, but it wasn't. It seems like the water is coming from the upper firewall area. I've inspected the windshield gaskets and they look to be in good shape. Do you have any suggestions about where the water could be coming from?
My other leak involves oil. It seems to be coming from the oil filter or in that area. When I last changed the oil and filter, the leak continued. I put the filter on as tightly as I dared. Could I be using the wrong filter or something? Thanks for your help.
Andrew Hutton, Davenport, Iowa
A: Dodge Dakota pickups circa '93-'95 have been known to leak at the roof seams. The water then seeps down behind the dashboard and onto the floor. You should have the seams checked by a body shop. The oil filter leak problem has been reported on '95 Dakotas fitted with the 3.9L V-6 or the 5.2L and 5.9fL V-8 engines. The problem is a warped filter adapter plate. A new plate should stop the leak.
Low And Loud
I recently bought a low-mileage '96 Tahoe that had been largely used as a tow-behind vehicle on a big motorhome. The sellers were the original owners and the truck had only 38,000 miles on it. I don't know if those were all driven miles or driven and towed miles. Regardless, the low mileage and excellent condition were key reasons for buying it.
My concern is over what I think is too much noise coming from the engine when the truck is cold. It sounds like loud lifters or loose connecting rods. After the engine has warmed up, the noise subsides. The Tahoe is primarily used by my wife for local errands and such. She rarely takes it out on the freeway, so it doesn't get a lot of hard use. Since I bought the truck from the original owner, it came with all the service records. One of the repairs was replacing the connecting rod bearings while the truck was still under warranty. The listed problem for bringing the truck in was similar to what I'm experiencing.
My question is, do you think the rod bearings are going bad again? How can this happen to such a low-mileage engine that's mostly driven on short, easy trips?.
Stan Cistallias, Paterson, New Jersey
A: It's reasonable to think that since the engine had this problem before, it could be happening again. It's not unusual to hear a little rod bearing noise when a cold engine is first started, but it should go away quickly. If it seems like the noise is getting progressively louder, that's an indication of rod bearing trouble.
If there is a problem with the rod bearings, they should be replaced before the damage goes beyond the bearings. Take your truck to a shop you trust and bring along the old service records.
As for a reason why these types of problems can happen to relatively low-mileage, lightly used vehicles, it's because short, frequent trips can be harder on a vehicle than long, sustained trips. The myth of low mileage is that vehicles need to be used to keep everything lubricated and functioning properly. On short trips, the engine doesn't always get warm enough to dissipate condensed moisture and corrosive gases. The result of this condition is sludge. There are acids in sludge that can attack, corrode, and weaken bearing material. Weak bearings tend to be noisy and prone to premature failure.
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