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Discussion Starter · #1 ·
I've gotten 28-30 mpg with this car, driving in traffic it will drop to 25.
I log all my mileage: recently had one tank out of four that was back to 25 mpg, but am only getting 19-20 mpg now.

Also, fwiw, occasionally loads up and stalls at idle. Will always immediately restart and generally be fine. It has to sit for a minute before the idle speed drops and it ultimately stalls.

No engine light, starts and runs ok. Crappy power - I've been thinking that was probably a clogged catalytic converter.

I have been having cooling fan issues and the guage has been to the AL (NORMAL) range on the gauge.... at that point the high speed fan would finally kick in. I've since installed a toggle switch so I can run the fan manually... this summer in Philly, that means pretty much full time.

This car has been trouble free until the last 6 weeks. Since June 1st, I've been dealing with the heating fan, had to replace the alternator, and now this mpg problem really has me worried.
Suppose I dropped a valve seat?!?! :(
 

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if you dropped a valve seat it would be making lots of nasty sounds...

to me it sounds like there is a problem with the coolant temperature sensor. i know there are several so i cant tell you exactly which one lol. the ecu adjusts fueling and controls the fan based on the signal from one of these sensors, so it seems reasonable to me.

it sounds like the ecu thinks the engine is running a lot colder than it actually is, so it runs rich and doesnt kick the fan on
 

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Discussion Starter · #3 ·
GREAT!! I'm relieved about what you said about the valve seat. No bad noises, the car is fine that way and rock solid reliable other than the mpg having gone into the cellar. No leaks and oil consumption is virtually zero.

Looking in the how to section I see lots to tend to... cleaning the egr and MA? sensor, to start. I'm sure the intake needs cleaning anyway.
At 190K, I'm sure any number of overall tuneup/EFI topics could be covered and improve things.

I'm tempted to replace the O2 sensor, just becuz... I know on many cars that can ruin the mileage if the O2 is off. Now there's a question... does my '94 1.9L have one sensor or two?

FWIW, I went to Pep Boys to have them just pull the codes -I thought. The quy wanted $100 plus to do an overall diagnostic. He said pre '96 he couldn't pull anything from the computer.
This doesn't sound right to me. Can ya'll shed any light on this?

As for engine temp sensor, I know there is one right near the thermostat. It shares a small manifold with the sending unit for the dash temp guage.


I may seem all over the map with my topics but I have some knowledge and some ignorance. Perhaps a dangerous and often confusing combination.
Thanks for this and any future advice.
 

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If you had a dropped valve seat, you'd have bigger problems than you describe.

Get a compression tester and check each cylinder dry and wet. That will at least allow you to sleep at night.

Somewhere in this forum, many years ago, I wrote an article about each of the sensors and how to check them. If you are even the slightest bit handy with a multimeter, find that thread, read it and start troubleshooting. Don't just start replacing parts via the shotgun method.

What year is the car? For posterity sake, there are two temp "sensors" - only one is used for engine management. The other has a single wire that feeds your dash guage. The ECU does not need multiple, redundant coolant temp signals.

Don't forget that vehicle speed is used by the ECU to determine engine speed. Thus, idle won't drop down instantly if you come to a stop. I find that the idle takes longer to settle down and even dips a bit low at times when there is higher relative humidity, but it is not a significant issue. The relative humidity will be affecting the IACT.

PS - you posted again while I was posting. There will always be an O2 sensor upstream of the cat. It's electrical connector is attached to the rad fan housing. If you have a second O2 sensor, it will be after the cat and the only thing tapped into the exhaust downstream of the cat. Get under your car - you can't miss it if you have one.
 

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Discussion Starter · #5 ·
My car is a '94 Merc Tracer/Trio Wagon. 1.9L with Auto and a/c.
As for the two temp sensors, yep, I know where they're at. The single wire unit feeds dash guage, and the other then must be the ECU sensor.
So that is the only one? That's useful info.
I will see what I can find in old threads about testing that ecu sensor. Thanks.

What about the Pep Boys assertion that there are no codes to pull from the computer? Is that correct?
 

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Discussion Starter · #7 ·
Nope. Oil is fine. and no coollant loss.
I am super paranoid about overheating, having been through that nightmare years ago. In fact, I checked those both just this morning, but not for the first time in recent weeks.
I am due for an oil change, just by the odometer but after the high temps in traffic, I'm sure the oil is overdone anyway.
 

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Most Autozones have a Ford OBDI reader they can hook up and pull codes. Typically these only pull them if the check engine light is already on, but sometimes you luck out.

The primary controllers for fuel trim are going to be your IAT (Intake air temp sensor) and your ECT. Many repair manuals will give resistance readings for a variety of temps but in general the resistance is lower as the temp goes up. If either of these is reading a low temp the computer will richen the mixture to compensate.

A dirty MAF will also cause a change in fuel trim but these are a bit harder to test, so I typicaly give them a few shots of MAF cleaner and see what happens.

The forward O2 sensor also plays a big factor in fuel trim so if it's contaminated and reading lean you'll have an overfueling issue as well.

One other issue I'd check is for a hanging fuel injector, if the resistance is off or something is mechanically causeing it to hang up it'll kill the economy as well. I had this happen on a Subie I had, and I was lucky to get 18MPG in it.

Good luck!

Pat
 

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You can easily read your own codes, especially pre-OBDII. There are many posts on here about how to do so.

Doesn't take anything more than a jumper wire.
 

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Discussion Starter · #10 ·
Cover the basics!!

I have to say, last week I did use most of a can of spray cleaner around the intake looking for a leak.
However, after so many references here to that common malady, I went back at it. I started going over the hoses and quickly found a problem child.

BINGO! What I found was a vac hose pulled free from the vac reservoir that supplies the cruise control. I am sure that got pulled while I was doing the alternator swap; I had to take the cruise control unit and the (?)Power Steering Resevoir loose to get the alternator in and out.
The idle is better, and the stalling is gone. I'm hoping my mileage picks back up too. That remains to be seen.

I did pick up relays to redo the set up for the cooling fan, as well as a can of MAF sensor cleaner. I have limited time at this late hour but I'll take all that on tomorrow a.m.
 

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Gat a MityVac and check for vacuum leaks elsewhere. How many miles on the O2 sensor? I don't trust them past 100K miles.
 

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zzyzzx said:
Gat a MityVac and check for vacuum leaks elsewhere. How many miles on the O2 sensor? I don't trust them past 100K miles.
DITTO. Not to mention that with the car running as it was, the O2 sensor has most likely, lost it's ability to compensate anyway. Cheap and easy replacement and can only help the overall performance.
 

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I'd get your cooling issues fixed ASAP and if it's an automatic do an ATX oil change. Unless you are using Synthetic ATX or Dexron 6, temperatures like that are terrible for your transmission too.
 

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Discussion Starter · #14 ·
I did the relays today, but am leaving my trusty toggle wired in. As I said earlier, I'm very paranoid about overheating and having the option for manual operation of the fan brings peace of mind.
As for the AT service, that is coming very soon. So far so good with it and I want to keep it that way.
I've had the car for two years and have clocked roughly 50K doing only oil and tires. I shipped it across country and suddenly things have bitten me in the backside.

Today, I sprayed the intake, cleaning the butterfly up a bit. My MAF sensor wasn't secured with basic torx screws, but instead has the tamper proof that features a little stud standing up in the center of the star: I had to settle for spraying the prongs through the 1/2" inlet.
It seems to run a little smoother but wasn't terrible previously.

But back to the point, oil and AT fluid are both due for a change.
I'm thinking I"m gonna have Jiffy Lube or a similar outfit do a flush. As I understand it, that gets more actual fluid changed, while dropping the pan and changing the filter still leaves the torgue converter full.

Money is an issue so I'm not sure what exactly will be next. Am gonna price an O2 sensor with the 4 wire plug on it. Changing that will probably start saving me money as soon as I change it.
 

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Rainman19154 said:
My MAF sensor wasn't secured with basic torx screws, but instead has the tamper proof that features a little stud standing up in the center of the star: I had to settle for spraying the prongs through the 1/2" inlet.
It's easy enough to just get the right bit.
 

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If I were you I would do the oil and atf change myself. Right now Auto Zone has a sell for about $15 that gets you 5qts of motorcraft oil and a motorcraft oil filter. I will run great with that. I would just change the atf fluid and filter. I have heard that flushing sometimes causes problems.
 

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Discussion Starter · #17 ·
zzyzzx said:
Rainman19154 said:
My MAF sensor wasn't secured with basic torx screws, but instead has the tamper proof that features a little stud standing up in the center of the star: I had to settle for spraying the prongs through the 1/2" inlet.
It's easy enough to just get the right bit.
And I will, but was getting started with the time frame I had to deal with it. I can unplug the harness and pull that sensor off for a better cleaning another time.
 

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While you're at it, do a full tune up. plugs, wires, fuel filter, air filter, oil & oil filter.

you'd be surprised how many MPG a tune up can recover.
 

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i got 20mpg for about 2 months one time and it was caused by a clogged fuel injector.

my car died from running out of gas as i was entering a gastation, rolled in neutral and thats when it started. tryed a bunch of injector cleaners and nothing fixed it until i put seafoam in it.

i remember hearing an exhaust like tap/click sound at low rpms when i was doing it. thats about all i noticed while it was doing that. i think i averaged 20-22, it was a stick.
 

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Discussion Starter · #20 ·
UPDATED progress:
I know people have success and don't followup, so I will try to keep this thread current.

So far, I've clean MAF and IAC. Especially doing the IAC really made a seat of the pants improvement. The MAF seemed to improve idle. Meh.

Over the weekend I changed out the O2 sensor.

Today I treated the intake and oil with Seafoam, ran it til fumes cleared from exhaust (engine was all ready well warmed up from morning commute), and then changed the oil.
The balance of the seafoam went into the fuel tank. I have a fresh fuel filter for change out once this full tank of gas is expired. My daily driving is typically less than 20 miles, so this tank of fuel will last quite a while.

Following other threads, I also took time to make sure my caliper pins and pads were properly lubed with high temp grease, so I'm not dealing with sticking brakes.

So far, the general runability of the car is well improved.
Previous to initiating this thread I'd done plugs, wires n air filter... these items made virtually no change. Cleaning the intake butterfly and sensors made a very noticeable improvement in general engine operation. However, checking mileage after only 33 miles, I saw only a negligible change. From 19.5-20 mpg recently, I showed 23 mpg. Meh. Until it's back over 25 mpg, I still have a problem.
I'd really like it all the way up to 28+. I have a gas log going back to '06 so I know what I should be getting. Reviewing that log, this mileage issue has been developing for a while but something recent pushed it over the edge from degraded to terrible.

I will continue to post my results here. This forum when researched offers a lot of great info. Thanks a lot.
 
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