Dr. Gizmo Column

"Dr. Gizmo"
By Phil Arendt

Repair Attempt Unsuccessful

Question 1
About one year ago the check engine light went on and my local mechanic found a code for oxygen sensor/mass air sensor problems.  My SUV is a 2000 Toyota 4Runner with 100,000 miles.  They replaced the sensor with the proper Toyota sensor.  They have been unable to get the trouble light to stay off.

The engine will stall very infrequently.  I have noticed a definite lowering of my gas mileage.  Does this make sense to you?  R., email

Answer 1

Yes but from your description it’s difficult to know which sensor was replaced.  Your letter describes two.  One is the mass air flow sensor and the other is an oxygen sensor.  Additionally, there is more than one oxygen sensor in the system. 

Since the fuel economy is dropping more than likely the engine computer is adjusting the fuel trim to compensate for a lean fuel mixture condition.  Generally, lean fuel mixture problems are caused by air leaks in the intake plenum, exhaust system and air induction system somewhere between the air filter and intake manifold.  Even a loose vacuum hose could cause such a condition.    

It’s time for more tests.  A smoke machine, lab scope and proper scan tool should find the cause of the trouble during test drives under normal driving conditions and static testing in a shop.  Perhaps a trip to a different repair shop is necessary as sometimes a fresh set of ideas from another technician will find the cause of the trouble.

Drain Hides From View

Question 2
I want to change the antifreeze in my 2007 Dodge Grand Caravan SXT.  It has a 3.8-liter engine.  I don’t want to pay a shop $90 to do the task. 

I went to an auto supply store to find out where the drain is but they were not able to help me.  Where is the drain?  H.M.H., Minneapolis, Minn.

Answer 2

Draining the antifreeze can be accomplished by loosening the drain plug on the right side of the radiator just below the location where the lower radiator hose connects to the radiator.  Be sure to collect all of the coolant in a container for transport to a recycler. 

Once the fluid has drained, refill the system with a fresh supply of antifreeze and distilled water so it protects against freezing to around minus 40 degrees.  Also, be sure to purge all air from the system so there is no trapped air in the engine or heating system.  This important no air can remain or engine cooling and heater performance will be impaired.

Torque Builds In Four-Wheel-Drive On Dry Roads  

Question 3
Recently, I purchased a 2007 Ford Expedition Limited with a 5.4-liter engine, automatic transmission and four-wheel-drive.  It has 96,000 miles and is in great shape inside and out.  When four-wheel-drive high is engaged when I slow to a stop from cruising speed I hear a thumping noise from the front.  If I disengage four-wheel-drive the noise stops.  Also, I don’t hear the sound when I have the 4-wheel-drive in auto mode.

I took the vehicle to a repair shop.  The mechanic checked over the suspension, steering and four-wheel-drive but did not find anything loose or wrong.  He suggested that I keep the selector switch in the automatic mode.   

Have you ever heard of anything like this?  H.B.D., email

Answer 3
The fact that you don’t hear the sound in automatic mode indicates that the running gear is okay.  Perhaps the trouble is caused when manual mode is selected and the system is used on dry pavement.  Under these conditions torque builds in the four-wheel-drive gears.  When this happens pressure releases and makes noises.

Use the system according to recommendations in your owner’s guide.  Never use the system on dry pavement.  When in doubt use automatic mode when driving on paved roads.  Engage manual mode if you so desire when traveling on ice or snow covered roads or when driving in muddy conditions off-road.

Intake Plenum Springs A Leak

Question 4
In a recent column you suggested that an air leak in the engine was causing problems.  I had a 2001 Mazda Tribute with a 3.0 engine.  At 85,000 miles it idled poorly and stalled.  My shop found an air leak and had to replace the gaskets on the upper and lower plenums.  I also owned a 1993 and 1997 Ford Taurus with a 3.0 engine.  I never had a problem with them. 

Now I own a 2010 Dodge Journey.  No problems yet.  Why did plenum gaskets fail in my Tribute and not the Taurus?  R.H.R., Chippewa Falls, Wis.

 

Answer 4

Basically, the 3.0-liter engine in the Tribute and Taurus is the same engine that was used in the old Ford Escape.  I can only speculate why the plenum gaskets failed in the Tribute but differences in the materials used in the construction of the engine, driving habits and engine temperature fluctuations play a role in such failures.  It’s a condition that might develop in any vehicle.  It happened a few years ago in my General Motors vehicle at 18,000 miles.  Thankfully the factory warranty picked up the repair tab.  Let’s hope it doesn’t occur in your Dodge.

 

Engine Won’t Crank To Start

Question 5
Intermittently, the 3.8-liter engine in my 1998 Ford Windstar will not start.  It won’t even crank.  I asked my shop about the trouble but they said that many problems could cause the trouble.  They asked me to bring the car in for diagnostic tests or they would come to my work place to check for the cause of the problem when the trouble surfaces. 

Do you have any suggestions?  D.D., email

Answer 5

Intermittent conditions are difficult to diagnose especially when the vehicle is operating normally.  Your shop’s recommendation is sound.  If at all possible have them check for the trouble when it occurs.  This will give a technician an opportunity to experience the problem and run diagnostic tests at the same time.

What you describe might be caused by the Passive Anti-Theft System or PATS.  Under certain circumstances a glitch in the system prevents the engine from cranking.  If tests determine trouble in this system, reprogramming may be the cure.

Starter Spins But Engine Does Not Turn

Question 6
I own a like new 1994 Dodge Dakota with a 3.9-liter engine.  It’s my baby.  I go to cruise nights in my area and people always comment on how nice it is but there is trouble. 

The starter quit.  It was making a whirling sound and the engine did not crank.  I installed a new starter but the same trouble remained.  I removed the starter and bench tested it.  It worked fine.  I returned to my auto supply store and they tested it.  It worked okay for them.  I reinstalled it and the starter still did not crank the engine.  I removed it and checked the teeth on the flywheel and everything looks fine.

Is it possible that the crankshaft is broken?  What am I missing?  T.C.T., email

 

Answer 6

This is just a temporary setback for your baby.  Once it’s back on the road perhaps you should enter competition and win a trophy or two for the best Dakota. 

As for the trouble, it’s doubtful that the crankshaft is broken.  More than likely the cause of the problem is a broken flex plate.  Remove the starter and check it.  You might find it is not secure.  If so, replacing it should have your truck back on the cruise night circuit.

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 mailto:drgizmo@hotmail.com  04/29/2013 ® DR. GIZMO © 1989 - Present