Taurus Car Club of America : Ford Taurus Forum banner

1 - 20 of 34 Posts

·
Registered
Joined
·
202 Posts
Discussion Starter #1
I'm still poking around trying to find the cause of my symptoms, which are: hesitation/stumble at dead-stop tip-in and poor performance during times of low/medium throttle, particularly noticeable under load.

I'm examining the TPS more closely this time (using an analog multimeter). No dead spots are noted when performing a resistance test. However, I do notice what appear to be plateaus in the readings as I slowly open and close the throttle. These appear at several spots within about the first 1/3 of it's travel; then from 1/3 open to WOT, readings become quite linear.

I was of the understanding that failed segments would manifest themselves as "dead" spots, as in the resistance reading would suddenly become very high indicating one or more open segments.

Is it possible for a failed unit to exhibit the readings described in paragraph 2?

Regards... Mike
 

·
Premium Member
Joined
·
1,318 Posts
Maybe if certain parts of it were shorted together? Not really sure.
 

·
Registered
Joined
·
202 Posts
Discussion Starter #3
To briefly paraphrase: Are apparent "flat spots" in the TPS considered a fault as well as "dead spots"?

Incidently, I performed the same test on my '91 Town Car's TPS as a comparison and it also displays similar flat spots within the 1st portion of it's travel. However, that engine is not experiencing the symptoms that my Sable is.

Regards... Mike
 

·
Premium Member
Joined
·
14,126 Posts
Yes the readings should smoothly and continuously increase as the throttle opening increases. There should be no plateaus.

Another way to test is to monitor the voltage output of the TPS (KOEO). It should start at just under 1V (.90v to .99v) then increase to under 5V.
 

·
Registered
Joined
·
202 Posts
Discussion Starter #5
SHOZ123,

I tested the voltage; it seems to be smooth & linear, but I'm using a digital multimeter for that test, and I find it kind of hard to follow it as well as an analog readout, so I may be missing any inconsistencies that could be there. Would it be safe to use my analog meter for this test, or would I introduce too much current, thereby risking damage to the computer?

I did notice, however, that at closed throttle, I'm reading only .750v, which is at least 150mv below the range that you mentioned. I get 4.50v at WOT.

Is it possible that the voltage is too low early on, then eventually "catches up", becoming closer and closer to specs as the throttle is progressively opened, finally winding up on target at WOT? If so, that would coincide with the symptoms I'm seeing.

Regards... Mike
 

·
Premium Member
Joined
·
14,126 Posts
You can use the analog meter. .750 is too low though if that is at closed throttle KOEO.
 

·
Registered
Joined
·
202 Posts
Discussion Starter #7
OK, thanks Paul.

I drilled the mounting holes out as much as I dared in order to gain a little adjustment. I also turned the throttle stop in just a smidge. Doing those two things got me to .860v with CT/KOEO. It also bumped the voltage at WOT up just a little.

If that doesn't help, I may just install a replacement.

Regards... Mike
 

·
Registered
Joined
·
202 Posts
Discussion Starter #8
Update:

I elongated the previously drilled out holes to get it to .957v at CT/KOEO (I have to wonder why it was so far off to begin with). I've been told that the CT voltage is not too important, as the computer reads whatever the voltage happens to be upon start-up, then uses that as a baseline for further calculations.

I also tested the voltage curve again, this time using an analog meter. Again, readings were consistent with a correctly operating sensor, so I have opted not to replace it, as I hate to throw parts at the car unless there is proof of a fault.

However, the symptoms remain; the quest to hunt down and crush those evil gremlins continues.

One other thing I should mention, and it may very well be unimportant, but this engine has never "popped right off" upon start-up like all my other cars, past and present (various makes, including Fords). It has to turn over what seems like a couple of revolutions before it starts. It almost acts like there is no fuel or ignition for a few seconds (hot engine or cold engine, it doesn't matter). I've tested FP... it's within specs with no leak-down. It is in a good state of tune, and I always cycle the ignition on/off a few times first just to make sure the fuel rail is pressurized.

Thanks guys, for taking the time to help.

Regards... Mike
 

·
Premium Member
Joined
·
14,126 Posts
Yes they "say" the PCM will read the voltage and adjust. I've found it is important to be within .10v under 1.0V.

Sounds to me like you need a new one. A good working TPS does not need the holes drilled out.
 

·
Registered
Joined
·
2,449 Posts
Update:

I elongated the previously drilled out holes to get it to .957v at CT/KOEO (I have to wonder why it was so far off to begin with). I've been told that the CT voltage is not too important, as the computer reads whatever the voltage happens to be upon start-up, then uses that as a baseline for further calculations.

I also tested the voltage curve again, this time using an analog meter. Again, readings were consistent with a correctly operating sensor, so I have opted not to replace it, as I hate to throw parts at the car unless there is proof of a fault.

However, the symptoms remain; the quest to hunt down and crush those evil gremlins continues.

One other thing I should mention, and it may very well be unimportant, but this engine has never "popped right off" upon start-up like all my other cars, past and present (various makes, including Fords). It has to turn over what seems like a couple of revolutions before it starts. It almost acts like there is no fuel or ignition for a few seconds (hot engine or cold engine, it doesn't matter). I've tested FP... it's within specs with no leak-down. It is in a good state of tune, and I always cycle the ignition on/off a few times first just to make sure the fuel rail is pressurized.

Thanks guys, for taking the time to help.

Regards... Mike
[/b]
You may have more than one problem & I agree, the TPS readings sure sound suspicious & it shouldn't require messing with to get it's output readings within tolerance.

If you have a good quality high impeadence analog multimeter, that says it's ok for solid state circuits, you should be good to go for most testing. A good scantool is even nicer!!!!

Where are you on past & present due scheduled maintenance items, like fuel & air filters, plugs, wires, distributor cap, rotor, ect.

Have you tried removing & cleaning the MAF sensor with a non residual cleaner like CRC maf cleaner????

Long but true story:

Back in the late 90's my 94 3.8L had become "lazy" off the line, had poor overall throttle response & mpg was poor.

I suspected intake side deposits, as it had low mileage & was up to date on all scheduled maintenance.

I began a fuel brand search for better mpg & tried several gas additives, none of which worked & all the local fuel brands & the last one I tried, one that I hadn't used for many years, "Texaco Clean System-3", proved to do what they were then advertising, "give us 5 tanks & we'll gaurantee you'll feel the difference"!!!!!

But they lied!!!!!

It only took ONE tank to begin to "feel the difference"...lol & by the end of that first tank the city mpg was up from the low 17's to the low 19's & throttle response was beginning to return & both cotinued to improve with every following tank, with mpg topping out at 24.5 around town.

I was blown away, as I had never had fuel make THAT much difference in a engines performance & mpg & the bull had never turned in that good a city mpg since new.

Moral of the story, keep the scheduled maintenance up with quality parts like Motorcraft & use a really good top tier gasoline, that says it's add pack wll clean up the injectors, intake, valve AND combustion chamber deposits WITHOUT adding to the combustion chamber deposit load & or regularly use a good gasoline additive like Chevrons "Techron Concentrate Plus", that'll clean up the intake side, as well as the combustion chamber, WITHOUT adding to the combustion chambers deposit load.

For years, Ford has also had a 4.0L "decarbon" TSB out, that calls for ingesting 3 cans of Motorcraft PM-3 through a vacuum line & a good high rpm (above 3500) 3 mile run, to blow carbon out of a clogged up engine, but we are supposd to change the plugs, oil & filter afterward.

IMO a tank of Texaco, Chevron, or CalTex fuel, thats already dosed with Techron & a can of Techron Concentrate Plus, at the recomended oz/gal, (it raises the treat rate 10X above pump gas), along with Fords "Blow-It-Out above 3500 rpm for 3 miles" daily, part of the TSB, has worked well for me on the Rangers CCDI problem & the Taurus throttle response lazyiness & I don't have to replace the plugs, oil, or filter afterward.

I keep a copy of the TSB in the glove box to show the officer that I'm just doing as Ford said to do!!!!! lol

Anyway, make sure the plugs, wires, distributor cap & rotor are in good repair, the MAF sensor is properly cleaned, use gas with a good add pack & or decarbon your 3.8L with a good product & you'll likely be as surprised as I was, when my bull WOKE UP!!!!!

A whole bunch of thoughts for pondering!!!!
 

·
Registered
Joined
·
202 Posts
Discussion Starter #11
SHOZ123 & pawpaw,

Thanks for the input.

I think I will take your advice and buy a new TPS; that way I can rule that out for sure.

Yup, I've recently done all of that maintenance stuff... plugs, wires, cap, rotor, checked ignition timing, fuel & air filter, pcv valve, cleaned the MAF sensor. Also, just last year I decarbonized the heads, piston tops and intake manifold, and cleaned the throttle plate area when I replaced the head gaskets. I also installed new injectors at that time. I've used top tier gasoline since I've had this car, around 3 years.

While I did the above stuff for reasons other than to try to fix those symptoms, none of it made any difference.

On a lark, I've been experimenting with the ignition timing. I advanced it a few degrees from specs and drove it for a day. Unlike many other cars I've owned, it ran a little worse... felt like it was "fighting" itself a little, and fuel economy dropped somewhat. No hint of detonation was noted though.

Today I drove it with it retarded a few degrees; "normal" performance was restored and fuel economy seemed better than when the timing was at specs (but I'll need to drive it more to know for sure). This kind of surprises me.

Other family members hate to drive this car because it's such a "gutless wonder" (their words). It's my daily driver and perhaps I've come to accept it's spongy responsiveness as normal. When I think about it though, I've driven similar size/weight cars with smaller engines that seemed more powerful and were more responsive, so maybe that ties in with the other symptoms.

Regards... Mike
 

·
Registered
Joined
·
2,449 Posts
Well with all the work & maintenance you've done, it seems you'd have noticed some improvement in performance.

When you cleaned the MAF sensor, were you mindeful to use a "non residual" cleaner, who's recipe says it's formulated just for cleaning the MAF sensor & did you remove it for cleaning, so you could get to all sides????

How many miles on the O2 sensors & how is their switching rate????

A 3.8L thats running right, sure isn't a "gutless wonder", even the Vulcan 3slow doesn't meet that criteria, so it'll be interesting to hear how changing out the TPS does, or what ever you finally discover the performance problem to be.
 

·
Registered
Joined
·
4,022 Posts
hey i have a 3.8 and it run right lol

but for that i had to use some carburator cleaner on the iac and the main thing was the egr valve when my performance are gettign low i have to remove egr and let it soak into carb cleaner for 10 min then put it back together and enjoy a real nice ride after ward

oh and once in a while i do seafoam that really really put back the kitten into the engine oh and the tps is wrong cuz mine is 0.902 and 5.0 a woot
 

·
Registered
Joined
·
202 Posts
Discussion Starter #14
pawpaw,

Yes, I did notice subtle improvement in performance after I fixed the gaskets, decarbonized and put in new injectors. No difference was noticed after I did the other more routine stuff.

I cleaned the MAF sensor in the manner that you described with a dedicated MAF sensor cleaner. However, the sensor looked very clean to begin with, so I was not surprised to notice no improvement.

I did a routine replacement of the 02 sensors not long ago as well. Again, performance remained unchanged. How does one test the switching rate... can it be done with a multitester?

mooby,

I've looked at the EGR valve as well. It has only light deposits on it and it moves freely.

I tested it by manually applying vacuum, which correctly stalls the idling engine.

Thinking I had an overly ambitious EGR valve, I temporarily disconnected it and drove the car. No difference was noted; not even a hint of ping with a warm engine. Again, I'm somewhat surprised at that.

I plan to round up a TPS this weekend, then I'll go from there.

Again, thanks guys for your input.

Regards... Mike
 

·
Registered
Joined
·
2,449 Posts
Yup the O2 sensor can be checked with a digital multimeter, but a scantool that'll read PID's is much quicker & easier, as we can just sit in the front seat with our scantool plugged into the diagnostic port!!!!

Check out AutoZones web site on testing O2 sensors with a multimeter. Lazy O2 sensors won't help performance at all.

I plan to replace the O2 sensors on my 94 3.8L tomorrow. One as gone to sleep & the other is lazy, both just like me!!!! lol
 

·
Registered
Joined
·
4,022 Posts
lol my egr work 100 % according to the vacum test but still after some cleaning it made a hell off a difference with carb cleaner

and when you pour liquid into it you can be sure theyre is no leak inside the diaphramg if you have this could still be ok on vacumm teste but make you loose performance
 

·
Registered
Joined
·
202 Posts
Discussion Starter #17
I tested the O2 sensors; the one on bank 2 cycles within factory specs and seems to be responsive as best I can tell... I don't have access to an oscilloscope. I could only get the one on bank 1 to rise to a max output of around .5v, and it arrived there only sluggishly.

However, replacing it had no effect on the afore-mentioned gremlins.

Now I'm looking at the EGR again. I previously stated that applying vacuum to the EGR valve while the engine is at idle correctly stalls the engine. However, my Haynes manual contradicts this; it states that if either V6 engine stalls, the valve should be replaced. Incidently, it goes on to state that the opposite is true for the 4 cyl engine.

I tried to confirm that by looking it up in my official Taurus/Sable service manual, but emissions are not covered there. Can anyone who is reading this confirm whether or not this assessment is correct?

I'm not fully trusting of what Haynes tells me, as I've encountered errors in the past. For example, it states that this test should be done with the IAC wires disconnected. My engine will not even run with it disconnected (which I believe is a correct reaction).

The valve is seating completely; on a cold engine at idle, no heat is felt on the EGR supply tube. When vacuum is then applied, the tube warms in an instant.

Regarding the improvements I thought I was getting by altering the ignition timing... that was evidently a figment of my imagination... more driving tells me that the engine runs about the best at the factory recommended setting.

I've resisted purchasing a new TPS, as I just can't bring myself to do it knowing that my multimeter tells me that it's output is within factory specs.

Regards... Mike
 

·
Registered
Joined
·
4,022 Posts
i dont want to be a pain but those are the repair and test sheet



and it say not ajustable an dshould be from .39 v idle and 4.89 full open

so check and see





it seem it need to be replaced anyway you have all the info to do the proper testing
 

·
Registered
Joined
·
2,449 Posts
Nice post on the TPS parameters mooby I saved that in my Taurus Favorites!!!!
 

·
Registered
Joined
·
202 Posts
Discussion Starter #20
Hey, thanks mooby!

My TPS was pretty close to specs then, before I elongated the holes. So, I need to put it back to where it was... perhaps even adjust it a little the other way, as, according to the charts you provided, the voltage was ranging too high, especially at the low end of the throttle plate travel.

I may still need a new one, because when I adjust CT voltage to specs, it may lower the WOT voltage output to well below specs.

The specs I was using earlier are evidently for a different model year than the 1991, perhaps for an OBDII system.

By the way, I'm still trying to learn if Haynes is correct in telling me that the 3.0 and 3.8 engines should NOT stall when EGR is manually applied at idle.

Regards... Mike
 
1 - 20 of 34 Posts
Top