Folks,

I have an Mercury Villager 1993 - great shape except for strange engine problem. Ford Dealer not able to diagnose. They have changed plugs, wires, fuel filter, distributor. No luck. Here is the problem. Car starts fine and runs perfect until temperature gauge reaches the top of the "L" within "NORMAL". Then it is like someone throws a switch and the engine starts missing terribly - very poor engine performance. Chug chug chug. It almost stalls. After 3-10 minutes, the temperature gauge reaches "M" (engine is fully heated), the problem disappears. Problems has occurred for 1 year. Happens rarely in summer, but almost without fail in winter. Never happens when the car is plugged in overnight (block heater). However, return trip home from work (not plugged in during day) it will happen. I live in Ottawa where the winters are very cold. On very cold days, when the temp gauge climbs very slowly towards "M", problem can persist for 15 minutes or so. I have discovered that turning off the interior heater allows the engine to heat up more quickly and reduces the problem time. Problem also happens if I start the car and leave it in Park in my driveway. It is not the transmission.

Dealer has done an engine pressure test. No problems. Antifreeze levels are stable. They hooked it up the diagnostic machine which reports everything is fine.

Any guesses? ECT sensor? I have no idea - I just read that from my Haynes book - purely a guess. Anyways - any help is much appreciated as unnecessary repaires at dealer have exceeded $1000. Thanks Tim.

 

ECT or ACT or the temp compensation valve in the air cleaner(providing heated air from around the exhaust manifold).
Going from open loop (cold) to closed loop seems to be the situation you are describing. The ECM finds out what is going on after reaching a certain temp, and given bum info, decides to cut the fuel ... Chug CHug gulp... til the engine actually reaches the temp the ECM is seeing..
My $2 guess for the day.
tom

 

I would #1. check the voltage output of the oxygen sensor to see if the voltage the ECU is reading is correct....a worn unit will mess readings up
upon cold start....

#2. Have the thermo time switch (or air temp sensor)checked....it is located on the thermostat housing, air cleaner or radiator itself.. If the sensor is bad....it may not be telling the ECU to enrich the fuel mixture at cold startup thus causing the bucking and jerking....this is your engine starving for fuel....

#3. Have the TPS sensor checked or proper voltage as well....if it is erratic
the wrong signal may be sent to the ECU.....causing it to tell the injectors to
lean up......thus the bucking....

Some vehicles have a cold start injector at the intake....I know older Nissans do....if it is bad and not working (check by trying to start the car cold and having the cold start injector out....to check for spray patterns) this can cause a lean problem at startup....

Check all parameters that entail the cold startup phase of the engine's operation....When starting cold....do perform a vacuum leak test...

Grab a small can of propane with the twist valve outlet installed....clamp a hose over it and bleed some propane around vacuum controlled sensors...
especially when engine is cold during start up...if there is a vacuum leak...perhaps one of the vacuum controlled sensors may not be activating due to that vacuum leak during cold start...

If the motor speeds up while leaking propane on the vacuum connection then you have a leak....if not then you don't.

Perhaps an OBD reader while cold would be the best bet.....

then perform a wiggle test during the same test...

CHeck all sensor connectors and apply DIELECTRIC grease before plugging them back in (this keeps oxidation at bay)

I can garauntee you it is one of the reasons above

Another thing to think about is condensation causing the air bypass
in the tbassembly

I have access to Nissan techs so...let me know if you don't find the problem...

good luck..

 

Have you replaced the thermostat lately? Is the L hotter than the M, or is it the other way around on the guage? I would definitely start by pulling the codes when the miss occurs. There shouldn't be any heat riser to the intake, so I don't think that is your problem. My best guess is that it is related to the coolant temp sensor (ECT), so I would test that sensor too, to see what it is telling the computer.

 

Folks,

I really appreciate your help with this. To answer one of your questions. The word NORMAL appears on the dashboard temperature gauge as follows:

N
O
R
M
A
L


When cold, the needle points well below the L. When fully hot, it points to the M. I never goes past M. When the problem occurs, it always occurs without fail at the top of the L.

The thermostat has not been changed recently - most likely not ever.

By the way, Ford Parts department say a new ECT is $31. I might just as well order it. I've already spent $1000 trying to fix this - $31 won't hurt.

The MAF (Mass Airflow Sensor), on the other hand, is $450.

Thanks
Tim

 

You can clean the heating element in the mass air meter with a q-tip and some rubbing alcohol. Be very gentle so the wires don't break. Usually that causes it to run lean, most of the time across the range of temperatures, so I don't know if that is your problem, but it can't hurt.

 

Jeez...I just realized I threw the wrong brand of car out....heheh

late nights doing homework will take their toll....

nonetheless the tests still apply the same way.....

sheesh....gotta get some shuteye!!!

 

No wait!!! Nissan Quest and Merc Villager are the same!!! Doh!!!

Anyhow....you would need a voltmeter and an OBD reader to check the above tests.....

OBD readers are available at your local parts store for a nominal fee....they come with the instruction booklets...and code key.

You'd probably need the OBD2 seeing that your van is newer.

 

'93 should still be OBD. OBD-II wasn't federally mandated until '96. I think two years before that would have been the absolute earliest they would have been installed.

 

Followup: I purchased a new ECT sensor and installed it. Did not solve my problem. I intend on doing the following test: Since I now own 2 perfectly good ECT sensors, I will use both as follows: I will unplug the wire from the sensor that is installed and plug it into the spare sensor - I'll tape it down securely but the important point is that the extra sensor should stay relatively cold. This will trick the computer into thinking that the car is running cold at all times. The purpose of the test is to determine whether the problem is really the O2 sensor. My Haynes book says that the computer ignores the O2 sensor until the engine reaches 600 degrees Far. The fact that the input from the O2 sensor is ignored until the car heats up fits nicely with the symptoms that the car displays. So the idea is to fool the computer into thinking that the engine nevers heats up - thus should result in the O2 sensor being ignored at all times. I'll post the results of this test soon - send me your thoughts on the validity of this test - I'm grasping at straws here.

 

Conclusion: My problem is fixed. Capone was correct. The problem was the oxygen sensor. Had it replaced. Car is running so smooth now. Just a quick note: I ended up going to the Nissan dealership at Ford's recommendation. The Ford computer is messed up when it comes to Villager parts. Nissan charged me $109 Canadian dollars while Ford had it listed at $200 Canadian. They mentioned that their part numbers for the Villager are wrong in the computer.

The Nissan folks were very welcoming even though my vehicle was a Mercury.

What I found surprising was that only 1 of the many dealership mechanics I spoke with mentioned the O2 sensor as the possible culprit. Too bad I didn't run into him earlier. By the time I spoke with him, Capone had already got me on the right track and I was pretty sure it was the O2 sensor. So kudos to Capone.

Anyways - that's it. Thanks for the advice guys.