Engine stumbling on mild acceleration

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Bob McDonald

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I have been experiencing some strange engine performance problems lately.



The engine wants to stumble when I try to accelerate moderately using just a small increase of the throttle. This may occur either from a stop, or when just trying to increase my speed while under way. I can't seem to determine if it is an ignition problem or a fuel problem. Often, when the engine is actually stumbling, if I ease off the throttle, the stumbling smooths out. Other times I need to go to wide open throttle (WOT) to get it so accelerate normally. It does seem a little engine load sensitive.



The Trac is an '02 with over 209K miles on the original fuel filter, but there is no fuel starvation symptom at high speed or high revs. I have been wanting to change it but have been too lazy to crawl under to determine if it has a two tube, or three tube filter installed.



It also has the original plugs installed, except for one plug. Years ago (at 100K) I started to change them but had so much trouble removing the first plug that it broke. After that, I just left the rest alone. I am not seeing any missing at WOT nor at stong acceleratiom (once past the initial stumbling). I am also not seeing any CEL light at all. I am will to have the plugs changed but I wonlt be able to do that myself. Getting to old, fat and stiff jointed to do that anymore.



I did try cleaning the MAF sensor and the throtle body, but that did not seem to have any effect. Of coures, since that was the first time I ever cleaned those items, there is no guaranty that I did it correctly (other than to not touch the sensor with my bare fingers).



Does anyone here on the site have any thoughts or suggestions?
 
First off I would do basic maint. Spark Plugs, spark plug wires and a fuel filter.. you have waited way too long time to get this stuff done:banana:
 
Ditto Roamer. At 209K with original plugs, wires, fuel, and air filters are absolute priorities.



Original engine oil and filter too? Surprised your Trac is even driveable. :banghead:
 
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The oil and filter are changed regularly (between 3 & 4 K miles). When I cleaned the MAF I put a new air filter in at that time too. The wire were replaced several years ago when I installed a high performance coil pack. Can't remember when that was.
 
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Uncle Bob, your spark plugs are Junk! they are way over due, Not to mention going to be a lot of fun getting them out. One of my many jobs at FOMOCO was a powertrain calibrator, Spark plugs begin to fail badly at around 100k its a wonder you can even get it started on cold days. The required voltage to fire the worn plugs is getting near the max your coils can put out. Your fuel mileage is getting much worse and your emission's are very high, hydrocarbons' are through the roof. Spark plug wires are good for two to three years then they begin to fail and leak voltage. Get a good tune up change your fuel filter and you will think you have a new trac..
 
Bob, I don't think your problems are strange at all - I find it strange that your Trac even starts and runs. Trans and diff fluids original too?
 
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The only thing strange is. How long you have waited for all the above maintenance.

Wot running good has nonthing to do with, not needing a tune. You may have colapsed the fuel filter, and riped an opening in a pleat. Therefore no lack of fuel.

Suprised you havent pluged a cat. I bet your cylinders are full of carbon.



Your HI-PO coil might be what has kept you running. Might be what is failing, amongst other things. Mine failed after one year. It was stumbling so bad I could hardly drive it. Went back to the oem coil. Realized buying the coil was useless. Ran just as good stock. Bought the hi-po coil used so I couldnt warranty it.



There are some things you can ignore and actually ruin a motor. When I first read your opening of this thread. I thought you were joking, sort of pulling our legs.



Bob I dont want to sound mean,but. If I asked why My tires were flat. After I told you about running over a pound of roofing tacks. I would be ashamed to even ask..



Good Luck and peace brother......:driving:
 
The spark plugs are fairly easy to change with the right tools and a little patience. DEFINITELY remove the passenger tire and splash guard to get to the ones in the rear of the engine. You may be able to access the driver side plugs easier that way too, but I got all of mine from up top. Get plenty of extensions (i have locking craftsman extensions) and universal swivels as well as the proper spark plug socket.
 
OP Uncle Bob lives in Southern Cal, corrosion shouldn't be too bad even at 209K although they may screech coming out. Highly recommend repeatedly spraying PB Blaster or equivalent one week prior to, and when removing. Make sure the engine is cold and blow compressed air around the plugs as you loosen. Use Motorcraft SP-500 plugs gapped .054 or at the "high performance" coil spec, and remember to use a light coat of copper or nickel anti sieze on the threads. GL, wishing you the best.
 
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I'm having the EXACT same issues with my trac. Original plugs, wires and fuel filter. 80,000 km. I guess I should change those things.
 
Canadiantrucker502,



Definitely change the fuel filter (every 30,000 miles; ~48,000 km) - it is due.



The replacement interval for plugs is 100,000 miles (~160,000 km). I'd change the fuel filter first and then, if the problem remains, pursue other remedies.



Regardless, if you do nothing else, you must add that rice can muffler. Not only will it have that authentic lawnmower sound, but it will be faster, too.
 
I'm having the EXACT same issues with my trac. Original plugs, wires and fuel filter. 80,000 km. I guess I should change those things.
 
I'm having the EXACT same issues with my trac. Original plugs, wires and fuel filter. 80,000 km. I guess I should change those things.
 
My '03 ST had the same problem & I found out by changing the vacuum elbow the stumbling stopped. The ST has a strong vacuum & my rubber elbows kept imploding. Look behin the alternator at the vacuum line when Ur ST is running & check the top elbow for softness or suction.:grin:
 
^ Good point. Chances are with original plugs in there at 209K, the PCV elbow is also.
 
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Years ago, I did have the infamous elbow crack and replaced it. It did throw the usual error code at that time (don't remember what is was). That's not to say it 'couldn't' be the same problem and I will check it.



In the mean time, the Trac will be getting new plugs and fuel filter tomorrow. I dropped it off at the mechanic tonight for them to work on it (getting too old and stiff to do the work myself any more). At the same time, I hope to have them replace the oil seal for the pinion shaft in the differential. I have had an annoying drip coming from that area.



I will advise of any success (or not) regarding the symptom.
 
I got the Trac back after having new plugs installed along with a new fuel filter installed and the stumbling seems to have been resolved. Personally, I think it was the plugs and the filter replacement didn't contribute, other than some peace of mind since it had over 200K on the filter.



I also had them replace the pinion shaft oil sleeve along with a new crush sleeve. Now I can go about cleaning up the oil spot in my garage that was under the differential.



Thanks for all the input. I am also going to update the thread on the thermostat.



 
I guess that was a little confusing. What I meant was I think the plugs were the fix and the filter wasn't. But, replacing the filter gave some peace of mind since it was way overdue to be replaced.
 
The only way you'd know the fuel filter wasn't an issue is if you had cut the old one apart for examination. Very few of us are going to do that - my preference is for regular replacement (I use 30K miles/every 2 years, whichever first) for reliability. I want my cars to run right with no surprises; so far it's worked for me.
 

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