Northwest Herald Dr. Gizmo Column October 12, 2012

10/12/2012

"Dr. Gizmo"

By Phil Arendt

Cost Of A/C Repair Exceeds Vehicle Market Value

Question 1
I have a 1998 Chrysler Town & Country with 190,000 miles.  Recently, the air conditioner went out.  I took it to a repair shop where they found the pressure is low.  They thought a new compressor might fix the problem but they are not sure. 

The cost to fix the van is high.  I don’t want to sink a lot of money into this vehicle even though it’s in great shape.  Do you think installing a new compressor will fix the trouble?  R.L., email

Answer 1
Air conditioning repair can cost a bundle.  There are many reasons for an air conditioning system to have low pressure.  A low refrigerant level due to a leak could be the cause.  The compressor might have failed.  Also, it is possible there may be a restriction somewhere in the system such as a clogged evaporator or condenser.  It also is possible a valve has failed.

No matter what is causing the trouble the cost to return the system to full function could equal or exceed the market value of the vehicle.  Of course if your vehicle is in excellent condition repairing it is without a doubt less expensive than purchasing a new vehicle.

Electric Solenoid Impairs Cylinder

Question 2
After driving through a puddle the 5.7-liter engine in my 2006 Dodge Ram 1500 TRX4 developed a misfire.  I took the truck to a repair shop where they determined that cylinder seven only has 75 p.s.i.  They did not know why the compression pressure was low.  The mechanic working on the truck said the pressure should be around 170 p.s.i.  He thought the trouble might be caused by a faulty solenoid on one of the valves but when he removed the valve cover the valves were working.  He checked the compression again and the pressure was around 175 p.s.i.  Once he reassembled the engine it ran fine for a few minutes but the misfire returned.  Now he does not know what to do next.

I take great care of my truck.  I change the oil every 3,000 miles.  Do you have any suggestions?  M.R., email

Answer 2
The V-8 engine in your vehicle is designed to run on four cylinders when cruising and under light loads.  This saves fuel and cuts down on exhaust emissions.  To do this the engine control module closes valves in up to four cylinders at one time.  In this mode normal cylinder compression is around 75 pounds per square inch in disabled cylinders and 175 p.s.i. or so in cylinders that provide power.  This keeps the engine running smoothly when the computer takes a cylinder off line.

Electric solenoids control the valves but when a solenoid fails the valve the solenoid controls does not open to place the cylinder back on line to develop power.  It is possible a solenoid has failed.  Your description indicates the valves are not excessively worn on the afflicted cylinder. 

To return normal function, ask your technician to consider disconnecting the battery for at least five minutes.  Once the battery is connected reprogramming the control module might return normal function to the valve system and the misfire should be cured.  If not, the solenoid likely needs replacement.

Blown Fuse Causes Poor Engine Performance

Question 3
The other morning my 2008 Ford Fusion with a 3.0-liter engine cranked but would not start.  Thankfully, I live close to a train station so I walked to the train so I could get to work. 
When I returned home I checked over the battery terminals and cleaned them.  I also found an ignition coil had melted.  When I had time, I replaced it.

Now the engine runs but not very well and the check engine light is on.  I’m still taking the train to work.  What else should I look for?  K.D., email

Answer 3

Apparently, you have do-it-yourself skills and luck.  The fact an ignition coil melted provided you visual cues of an obvious malfunction.  If it had failed and not melted you might not have seen the problem.

Since it melted, more than likely it created a short circuit.  Check the engine compartment fuse panel for blown fuses.  You might find a blown fuse.  If so, replacing it might return the engine to normal operation. 

Additionally, if a new fuse returns the engine to normal function take the car to a shop to have the engine control module cleared of trouble codes.  This will turn off the check engine light as long as there are no other faults in the system. 

If you do not find a blown fuse it is time to take the vehicle to your favorite repair shop for further diagnostic work.

Excessive Wear Stalls Engine
Question 4
I have a 2007 Chevrolet Trailblazer with a 4.2-liter engine and 110,000 miles.  Once in a while when braking hard the engine stalls.  When this happens the engine is hard to restart.  I took the vehicle to a repair shop where a mechanic went for a test drive with test equipment connected.  When he slammed on the brakes the engine stalled.  The mechanic found several trouble codes in the engine computer that indicated that the engine had misfired when it stalled.

The mechanic also checked the engine oil and found it very dirty.  He suggested an oil change.  I told him that I didn’t think it was necessary because the oil change monitor had not turned on.  He suggested that according to a windshield sticker it was 10,000 miles since the last change.  I authorized the service.

When the mechanic removed the drain plug he found fine metal in the oil.  Once he discovered this he did some checks on the engine and found that the crankshaft is sliding forward and backward too much in the engine.  He said this is causing the stalling problem.  He says to fix the trouble the engine needs replacement.
Except for the stalling the engine runs fine and does not make any unusual noises.  A friend who knows a lot about cars says that if the crankshaft was bad the engine would make knocking sounds.  My engine sounds normal.  Is the mechanic trying to rip me off?  W.J., email

Answer 4

Apparently, the cause of the stalling is exactly as your technician diagnosed.  There is too much play in the crankshaft.  When this occurs the crankshaft moves to far forward as you brake.  As a result the crankshaft sensor at the front of the engine does not send proper signals to the powertrain control module.  When this happens the module cannot fire the spark plugs at the proper time.  This causes the engine to stall.

To fix the trouble the cause of crankshaft fore and aft movement needs repair.  This could be caused by an excessively worn engine block, thrust washer or crankshaft.  The location of excessive wear determines the course of repair.  Additionally, since the engine oil contained excessive metal that has circulated throughout the engine there are multiple concerns with excessive wear of bearings and other parts.  The likely course of repair is a complete overhaul or engine replacement.

This type of repair is premature.  If your guide to oil change intervals is the oil change monitor, in the future consider ignoring the monitor.  Instead, change the oil and oil filter at 3,000 miles but no later than 5,000 miles depending upon your driving habits.

Additionally, frequently check the oil level.  Depending upon driving habits, it is typical for an engine to consume a quart of oil in 3,000 miles.  Add oil as needed.

If you reside in the Chicago Metro area 3,000 mile intervals should keep your engine clean and reduce engine wear such as the wear that presently exists.  Usually, an engine that is treated to oil and filter change intervals of 3,000 to 5,000 miles lasts 200,000 to 300,000 miles before major wear takes its toll.                  

Temperature Plays Big Roll In Powertrain Performance

Question 5
The automatic transmission in my 1995 Ford Mustang with a 3.8-liter engine does not shift from third to fourth gear for the first few miles of driving.  Twice in the last two years the transmission has been rebuilt.  The shop that did the work says there is nothing wrong.  That’s somewhat true because by the time I bring the car to the shop the transmission is working fine.

In addition to the trans problem, the heater is not blowing as hot as it used to.  My transmission shop says they don’t repair heaters.  They referred me to a shop that does repair heaters but I want to get the transmission fixed first. 

My car has 187,000 miles.  I’ve owned it since it was new.  It’s in great condition.  I change the engine oil and filter every 3,000 to 3,500 miles and follow factory recommendations for other services.  Do you have any idea what might be wrong with the heater?  Do you know what’s causing the transmission to stick in third gear? E.T.F., email

Answer 5

Both conditions might be related.  Since the emission control and engine management systems rely a lot on engine temperature to make decisions such as transmission shift sequences, the engine thermostat might be faulty.  If so, the failure would account for a lack of heat from the heater and prolonged engagement of third gear. 

Ask your favorite technician to consider this possible cause.  If indeed the thermostat has a fault, replacement likely will cure both concerns.     

Oil Leak Repair, No Easy Task

Question 6
There is oil leaking from the 6.6-liter turbo diesel engine in my 2006 Chevrolet Silverado.  I’ve narrowed down the leak to under the turbocharger, but due to limited space I can’t see what’s leaking.
Is there a gasket on the turbocharger that can leak?  I’m pretty good at fixing things.  Can I repair this at home?  Is it necessary to remove the truck body to remove the turbo?  B.G., email

Answer 6

The turbocharger has oil supply and drain lines that could leak.  To remove the turbo does not require removing the truck body, but this is a big job without removing it.  The inner fender liner, exhaust pipes, intake ducts, heat shields and a lot more need removal before there is enough room to examine the oil lines and remove the turbo.

I applaud your willingness to attempt this repair, but this is suited for a repair shop with ample tools, a vehicle hoist and experienced technician.  

Thanks for all of your great questions.  Dr. Gizmo can’t wait to answer more.

Phil Arendt is a columnist, consultant and A.S.E.-Certified Master Technician.  Readers may send questions to Dr. Gizmo at P.O. Box 548, Cary, IL. 60013 or e-mail address drgizmo@drgizmo.ws. 10/12/2012 ® DR. GIZMO © 1989-2012