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Discussion Starter · #1 · (Edited)
Hi All,
I am new to the forum, but know plenty about cars. My grandfather has been a ford mechanic all his life. Recently I bought an 03 Taurus SES DOHC with only 83,000 on it. To get it running correctly, we put in a new radiator support, and pretty much everything in the ac system has been replaced. Recently though, I have been having a problem with some hesitation.

About a month ago, my car threw a random p0306 misfire code, and another for misfire during first 1000 revolutions. OK, so I replaced all front spark plugs. That went away, but about a week later, it came back some without a CEL. What happens is when you step on the gas in 4th gear, about half way (when the engine is under a load), it hesitates. Also a little rough at idle when cold. Drive it and come home and the idle will sometimes be perfect. It is also more random, because when it is colder out, like today, it is barely there!

Also, there is alot less power when you step on it. It seems like if you let it shift to a lower gear, there is almost a "surge" of power, but not much (very gradual, when in gear 3 or 4. I have had the plenum off more times than you can count.

I have also replaced
EGR Valve and gasket, IAC, misc. vacuum lines (Which helped, and a new pcv with line, oem, which somewhat helped). New "cam position sensor", or thats what i think its called. I have cleaned the plenum good. Broke two of my uim bolts but dont seem to be leaking.
I HAVE ALSO TAKEN THE FUEL RAIL OUT! It is clean, and when the car is on,you can feel injector 6 making more noise than the rest. . Now on the original 3 spark plugs, the sixth one was carbon-fouled. I have had these new ones on for several weeks, and they all look fine.
The only thing is that on 4 &5 there is oil on the spark plugs, which I was told was caused but a bad intake gasket. i really dont want to get into that since I broke the middle bolt when "suggested by a thread" to "tighten" it, but I really don't think that would cause this problem.

Would a coil really cause this, or could the injector be bad? It seems that the colder the weather, the less hesitation. i can just feel that the car doesn't have enough power though. its not bad, unless you step on it. Over 4000 rpm when cold to get to 40. Other times, it is fine.

Next is to change the rear spark plugs, but I dont think that would make a difference. Again, it only has 83,000 miles.

***I fill the fuel rail w/ sea foam and had each injector off. I noticed that for a few miles, the problem went away, but came back. Is there a better way to clean the injectors??? Hoping to not take them off again, but will need to if necessary. Just trying to spend as little as possible seeing how much I have already spent. **Plus recent tranny flush for all who think transmission- done at Midas w/ a ,machine. I watched them).
Thanks, for quickest repsonse--Im hoping its just a sensor.
James
BTW THIS ALL STARTED AFTER MY GRANDFATHER SPRAYED BRAKE CLEANER ALL UNDERNEATH CAR TO CLEAN OLD OIL. THE HESITATION STARTED SLOWLY AND GRADUALLY GOT WORSE. COULD A BAD OXYGEN SENSOR EXPLAIN ALL MY PROBLEMS? IF SO WHERE IS THE ONE UNDERNEATH?
 

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So, it is still throwing the misfire code? I agree, plugs probably won't help but since your an expert at remove the plenum, why not change the rear plugs anyway. They are almost due.
I'm not familiar with the UIM on a '03. Do you have the plastic manifold? Are the 2 broken bolts close to each other? Either way, it might be possible you have a vacuum leak due to the UIM not having the correct clamp load. Maybe try running an unlit propane torch around the intake and see if your idle increases.
Keep us posted.
 

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Discussion Starter · #3 ·
no, No misfire code, but I think it still may be misfiring, becuase it is still hesitating, which would be caused by the misfire. No CEL is on.
 

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Discussion Starter · #4 ·
Because i didnt have the right extension. So i didnt bother. Changed pcv and now i have to go through removing that to get the uim off again.
 

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Discussion Starter · #5 · (Edited)
So, it is still throwing the misfire code? I agree, plugs probably won't help but since your an expert at remove the plenum, why not change the rear plugs anyway. They are almost due.
I'm not familiar with the UIM on a '03. Do you have the plastic manifold? Are the 2 broken bolts close to each other? Either way, it might be possible you have a vacuum leak due to the UIM not having the correct clamp load. Maybe try running an unlit propane torch around the intake and see if your idle increases.
Keep us posted.
\
Sorry for all these postbacks, still new here.
The bolts aren't close, the end ones are tight. This is very little/ no space. I have felt around and feel no air. Besides, Im sure that would cause it to run lean, right? When warmer, in 4th gear ( or under load), the hesitation is pretty severe, causing the car to shift back into 3rd, too.
Yes the intake is plastic. AND THE MISFIRE/HESITATION SEEMS TO GO AWAY SOME FOR A LITTLE BIT W/ LUCAS UPPER CYLINDER LUBRICANT.
 

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Hi All,
I am new to the forum, but know plenty about cars. My grandfather has been a ford mechanic all his life. Recently I bought an 03 Taurus SES DOHC with only 83,000 on it. To get it running correctly, we put in a new radiator support, and pretty much everything in the ac system has been replaced. Recently though, I have been having a problem with some hesitation.

About a month ago, my car threw a random p0306 misfire code, and another for misfire during first 1000 revolutions. OK, so I replaced all front spark plugs. That went away, but about a week later, it came back some without a CEL. What happens is when you step on the gas in 4th gear, about half way (when the engine is under a load), it hesitates. Also a little rough at idle when cold. Drive it and come home and the idle will sometimes be perfect. It is also more random, because when it is colder out, like today, it is barely there!

Also, there is alot less power when you step on it. It seems like if you let it shift to a lower gear, there is almost a "surge" of power, but not much (very gradual, when in gear 3 or 4. I have had the plenum off more times than you can count.

I have also replaced
EGR Valve and gasket, IAC, misc. vacuum lines (Which helped, and a new pcv with line, oem, which somewhat helped). New "cam position sensor", or thats what i think its called. I have cleaned the plenum good. Broke two of my uim bolts but dont seem to be leaking.
I HAVE ALSO TAKEN THE FUEL RAIL OUT! It is clean, and when the car is on,you can feel injector 6 making more noise than the rest. . Now on the original 3 spark plugs, the sixth one was carbon-fouled. I have had these new ones on for several weeks, and they all look fine.
The only thing is that on 4 &5 there is oil on the spark plugs, which I was told was caused but a bad intake gasket. i really dont want to get into that since I broke the middle bolt when "suggested by a thread" to "tighten" it, but I really don't think that would cause this problem.

Would a coil really cause this, or could the injector be bad? It seems that the colder the weather, the less hesitation. i can just feel that the car doesn't have enough power though. its not bad, unless you step on it. Over 4000 rpm when cold to get to 40. Other times, it is fine.

Next is to change the rear spark plugs, but I dont think that would make a difference. Again, it only has 83,000 miles.

***I fill the fuel rail w/ sea foam and had each injector off. I noticed that for a few miles, the problem went away, but came back. Is there a better way to clean the injectors??? Hoping to not take them off again, but will need to if necessary. Just trying to spend as little as possible seeing how much I have already spent. **Plus recent tranny flush for all who think transmission- done at Midas w/ a ,machine. I watched them).
Thanks, for quickest repsonse--Im hoping its just a sensor.
James
BTW THIS ALL STARTED AFTER MY GRANDFATHER SPRAYED BRAKE CLEANER ALL UNDERNEATH CAR TO CLEAN OLD OIL. THE HESITATION STARTED SLOWLY AND GRADUALLY GOT WORSE. COULD A BAD OXYGEN SENSOR EXPLAIN ALL MY PROBLEMS? IF SO WHERE IS THE ONE UNDERNEATH?
If you have not changed the fuel filter, that can cause hesitation and loss of power. Fuel pump also. On that and later models, the fuel pressure is managed by varrying the voltage to the pump. (pulse width). A fuel pressure test would be in order.

And as an aside. The upper intake bolts have spacers to control the pulldown. Tightness is not an issue. Tighter does nothing but risk breaking the bolts. The plastic could not take much pressure, so the spacers keep you from crushing the composite. (plastic)

There is the possibility of cat converters being plugged.

-chart-
 

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being an 03. check the battery and alt also. im sure the factory battery hasnt made it this far. ( would be shocked if it is original )
i would take care of the intake gasket and bolts. its only getting colder outside
 

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Discussion Starter · #8 ·
If you have not changed the fuel filter, that can cause hesitation and loss of power. Fuel pump also. On that and later models, the fuel pressure is managed by varrying the voltage to the pump. (pulse width). A fuel pressure test would be in order.

And as an aside. The upper intake bolts have spacers to control the pulldown. Tightness is not an issue. Tighter does nothing but risk breaking the bolts. The plastic could not take much pressure, so the spacers keep you from crushing the composite. (plastic)

There is the possibility of cat converters being plugged.

-chart-
Thanks. There is a new battery, orig. alternator (which i cleaned many times, it works fine). However the fuel filter may be original. I have my Haynes book so I'll check that. I'm just up on whether it is a fuel or electric (spark issue). Today i am planning on changing the orig. coil (still $50) with the rear plugs, and I will also do the fuel filter. i will let you know how I make out. Thanks all,
James
 

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Discussion Starter · #10 ·
I had a similiar problem with my '93 Vulcan. It was a plugged cat.
Is there anything to help clean the cat?

Which one went wrong on you? I do get occasional white smoke on start up (Think its condensation), but no egg smell. Again, it only has 83,000. I wonder how much that would cost.
**btw. The colder weather today seemed to help a little. Again, this is what happens.
When it shifts into 4th gear, and you put your fut on it a little in that gear, the rmps go down about 200, then after a few secs. you will get the hesitation. It is almost like a sensor.
 

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You may have more than one problem.

I agree you need to address & fix the broken upper intake manafold bolts.
As composit parts expand more with heat, it may be sealed when cold, but open up when the engine is at operating temp.

But lets think about this some more. You said that the #6 fuel injector sounds Much louder than the others & that you've briefly gotten positive results with filling the fuel rail with SeaFoam & after using a Lucas product, so it seems to me you need to look into the #6 fuel injector some more, to investigate the possible root cause of the P0306 & other random misfire code some more, as you indicated you had them before breaking the uim bolts.
Also measure the injectors resistance to see if #6 value is different, as they all should be closely matched.

Maybe monitor the long & short term fuel trim & & O2 sensor numbers, as you said the miss started after your helper sprayed the under neath with a strong solvent to clean off oil deposits, so maybe it's messed with the O2 sensors wiring or such as you suspect & post the O2 sensor switching speed & fuel trim number results.

Since you got some brief positive results with fuel detergents, maybe consider a 20 oz dose of Chevron Techron Concentrate Plus in the tank, at the pump, before filling up with Chevron, Texaco, or CalTex gas so you get good mixing.
They already have some Techron in them, so the additional 20 oz will raise the treat rate 10X above that of pump gas alone & will usually get the job done in one tank, if cleaning is all thats needed.
It'll also clean the combustion chamber heads & piston crowns, so if CCDF is causing some of the missing mischief, the Techron can address that while cleaning the injectors!!!!

A dirty MAF sensor can cause a hesitation too, so maybe consider removing it & cleaning with a non residual product formulated just for that, like CRC, or Valvolene MAF sensor spray cleaner. Let it cool before cleaning, Don't touch, or poke the sensor with the spray wand & keep it squeeky clean upon re-installation.

Have a look at the TPS resistance range, paying close attention to what happens in the upper range where your having the hesitation problem. It's resistance value should be within the specified range & change smoothly, from closed to WOT.

Check the fuel pressure & pump flow rate over time, so you know pressure & delivery volume are ok.

A bunch more thoughts for consideration, let us know how your trouble shoot goes.
 

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Since you "know alot about cars" and have a Ford mechanic in the family, I am surprised at your attempt at diagnosis and the shotgunning parts at it trying to solve the problem. Ford EGR valves almost never go bad. Why was it replaced? The CMP on the Tec basically never fails, unlike the CMP/syncro assy on the Vulcan. Why was it replaced?

The first thing to do when diagnosing a problem like this is use a scan tool and have a look at the long term fuel trims. Are both banks within +/- a few % of zero? Are they the same bank to bank or is one bank significantly different from the other?
 

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uif its coil on plug make sure theres no cracks on the top of the coils if its not make sure the coil packs arent corroded, sand down all your electrical grounds and make sure theres no oil in the back plugs
 

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Don't mess around with the cat until you verify that other problems are resolved. Cats don't fail on their own, they are destroyed by the engine running out of tune. As stated in the earlier posts, check the fuel pressure, and replace the fuel filter (if it is replaceable). A dirty or fouled MAF can also cause hesitation. Check the air filter too.

At 80,000 miles, you need a full tune up.
 

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Discussion Starter · #15 ·
Since you "know alot about cars" and have a Ford mechanic in the family, I am surprised at your attempt at diagnosis and the shotgunning parts at it trying to solve the problem. Ford EGR valves almost never go bad. Why was it replaced? The CMP on the Tec basically never fails, unlike the CMP/syncro assy on the Vulcan. Why was it replaced?

The first thing to do when diagnosing a problem like this is use a scan tool and have a look at the long term fuel trims. Are both banks within +/- a few % of zero? Are they the same bank to bank or is one bank significantly different from the other?
My grandfather is a garage mechanic.He's restored over 50 thunderbirds. The car was stalling going down hills. Researched this properly and replaced the egr valve after cleaning it 3x. No longer stalls going down hill.
 

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Discussion Starter · #16 · (Edited)
You may have more than one problem.

I agree you need to address & fix the broken upper intake manafold bolts.
As composit parts expand more with heat, it may be sealed when cold, but open up when the engine is at operating temp.

But lets think about this some more. You said that the #6 fuel injector sounds Much louder than the others & that you've briefly gotten positive results with filling the fuel rail with SeaFoam & after using a Lucas product, so it seems to me you need to look into the #6 fuel injector some more, to investigate the possible root cause of the P0306 & other random misfire code some more, as you indicated you had them before breaking the uim bolts.
Also measure the injectors resistance to see if #6 value is different, as they all should be closely matched.

Maybe monitor the long & short term fuel trim & & O2 sensor numbers, as you said the miss started after your helper sprayed the under neath with a strong solvent to clean off oil deposits, so maybe it's messed with the O2 sensors wiring or such as you suspect & post the O2 sensor switching speed & fuel trim number results.

Since you got some brief positive results with fuel detergents, maybe consider a 20 oz dose of Chevron Techron Concentrate Plus in the tank, at the pump, before filling up with Chevron, Texaco, or CalTex gas so you get good mixing.
They already have some Techron in them, so the additional 20 oz will raise the treat rate 10X above that of pump gas alone & will usually get the job done in one tank, if cleaning is all thats needed.
It'll also clean the combustion chamber heads & piston crowns, so if CCDF is causing some of the missing mischief, the Techron can address that while cleaning the injectors!!!!

A dirty MAF sensor can cause a hesitation too, so maybe consider removing it & cleaning with a non residual product formulated just for that, like CRC, or Valvolene MAF sensor spray cleaner. Let it cool before cleaning, Don't touch, or poke the sensor with the spray wand & keep it squeeky clean upon re-installation.

Have a look at the TPS resistance range, paying close attention to what happens in the upper range where your having the hesitation problem. It's resistance value should be within the specified range & change smoothly, from closed to WOT.

Check the fuel pressure & pump flow rate over time, so you know pressure & delivery volume are ok.

A bunch more thoughts for consideration, let us know how your trouble shoot goes.
Hi, again, thanks. I rpelaced the fuel filter (easy) and not much, if any change. And what I mean by noise is that you can "FEEL" it making more noise inside than the rest. The hesitation only happens at the right time, usually up hill, in 4th gear about half way. So I will ateempt to put a new injector in. I think that that would cause this problem. I will post back results.
Thanks,
James *I will also replace rear plugs since I will have the uim off too.
Alrady cleaned maf sensor with maf cleaner too. 3x Ran plenty of techron in it with NO CHANGE. Only with that lucas stuff, and since it is a cylinder lubricant thats why I'm leaning towards that #6 injector.
Thanks again for your input,
James
 

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Discussion Starter · #17 ·
uif its coil on plug make sure theres no cracks on the top of the coils if its not make sure the coil packs arent corroded, sand down all your electrical grounds and make sure theres no oil in the back plugs
Thanks
There is oil on the front plugs. Hoping that that isnt causing this. Really dont want to open that lim yet (As I am not that familiar with it_. Thanks for the coil, too. I will take a look after replacing injector and back plugs.
 

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Thanks
There is oil on the front plugs. Hoping that that isnt causing this. Really dont want to open that lim yet (As I am not that familiar with it_. Thanks for the coil, too. I will take a look after replacing injector and back plugs.
Is the oil on the firing tip or the threads? If the threads are oil coated then you need to replace the intake gaskets.
 
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