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Hi, I have a 2001 Taurus, and some days, it just runs like crap. but only for a while. I plugged in my code scanner, and I can watch the timing at idle go from 19 degrees, up to almost 40 degrees, then jump down in the 20's, and back up to the 30's, before top dead center. The car has 220,000 miles. since it has so many miles, early this year I started changing parts that could fail and leave my wife stranded. I changed, crank position sensor, can position sensor, Throttle pos sensor, EGR valve ( it was sticking) and the cam synconizer, Idle air valve. the car runs good most of the time. I did put in a new timing chain , when I changed the water pump at 150,000 miles. and it was a good cloyes true roller, not a cheap one. Thoughts ? I think its the computer.
 

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I actually did change the cam syncro after it started acting up. and it still acts the same, so I dont think its that. I also believe that if my code reader says 38 degrees, its not the sycro, because it would say 19 degrees , but really be at 38, and run bad. The bad thing is, some times, it runs just fine. Intermittent problems are the worst to diagnose. Thanks
 

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Timing is off the crankshaft sensor that sees the harmonic damper. Check the condition of your harmonic damper and make sure the rubber between the outer ring and inner hub is in good shape. If it isn't the timing ring could shift and change the timing.
 

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Different engine but: mine ran bad but no codes, no true misfire. I used Ultragage and could see timing all over the place even at idle. (timing as advance) I replaced the cam and crank sensors with JY units and no change. I talked to the shop at local Ford garage and they showed me a bulletin from Ford indicating the things to check before considering the PCM. Stated PCM fail rare. I let them have the car and they seemed to know from experience what to look for. As in the pic, bad plug wires, 2 rear bank. Called arc tracking. So they still fired but they said the radiation from the arcing messed with the PCM signals. New wires fixed the issue. I let them do the wires, new OE wires.

But I figured the plugs must be damaged and so I changed the plugs and the 2 cylinders they found had bad wires, had bad plugs, arc track and they were nearly new plugs. One year later, same issue and I replaced the plugs again but NO Autolite ones this time. OE plugs and I replaced only the one bad wire as in the pic. 4 years later and it runs fine.

Now my tinkering. I have an induction timing light. With the DOHC there is a hex on the shaft to the crank pulley. I put different color paint marker on every other flat. Then idled it and used the timing light to look at the hex. Timing was all over the place. I used each front wire and same results but different color hex flat.

This is an issue with only coil pac (waste spark) systems. Only the rear bank where you have reversed polarity spark.

-chart-
 

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Thats a good Idea to check. Iv'e seen the outter ring slip on v8's. but not familiar with the the way the toothed ring attaches. It seems hard to believe that it would slip, making the car run bad for a while, then go back to the correct placement and run fine. But, Iv'e seen odd stuff happen before.
 

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I changed the plugs and wires about 3 weeks ago, when a plug fouled. I think the engine is pretty worn out. But I would like to try your method of marking the teeth on the ring.
 

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Timing at idle will not be rock steady. PCM uses timing to "fine tune" the idle speed to maintain a stable idle. If idle drops a bit, PCM advances timing to bring idle speed increases a bit, PCM pulls timing to bring idle speed down. PCM controlling idle via timing is much more responsive (i.e., smaller time constant) than changing the IAC duty cycle. Virtually all modern computer controlled engines built in the last 35 years use this strategy.

With that said, your timing variations seem excessive. How stable is the idle? IAC clean and operating properly?
 

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The IAC is new, the idle went 921 at 19 BTDC to 864 at 38.5 BTDC. these were readings on the scanner, that I took pictures of. Thanks
 

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Yes, the only IACs that function correctly are the Motorcraft. All other brands are junk, and do not work well, if at all.
 

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Nearly everyone has minor to major issues with a non Motorcraft IAC.

Search IAC here, and read the hundreds, if not thousands, of posts about idle problems going away when a Motorcraft IAC was used to replace another brand IAC.
 

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Anyone else have this happen with an off brand IAC ?
I had a IAC valve on my 2006 that was moaning at cold idle and I decided to cheap out, 40% off, and buy a Advanced Auto store brand, not sure what the brand was. I installed it and instantly noticed idle shot up real high on start up much higher than OEM. Then it did not respond right trying to keep idle. Things really went bad when you put the AC on. It just responded too late and dropped idle then shot idle up after the initial load of the AC. The worst issue was on the highway, it kept feeding air when I left off the gas and car would take longer to slow down forcing me to use more brakes in stop and go traffic. I returned it to AP and went to the Pull a Part and got a used IAC from a 2006 and everything was fixed.

The aftermarket one that I had was just not tune to respond the same as the Motorcraft one.
 

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I had a IAC valve on my 2006 that was moaning at cold idle and I decided to cheap out, 40% off, and buy a Advanced Auto store brand, not sure what the brand was. I installed it and instantly noticed idle shot up real high on start up much higher than OEM. Then it did not respond right trying to keep idle. Things really went bad when you put the AC on. It just responded too late and dropped idle then shot idle up after the initial load of the AC. The worst issue was on the highway, it kept feeding air when I left off the gas and car would take longer to slow down forcing me to use more brakes in stop and go traffic. I returned it to AP and went to the Pull a Part and got a used IAC from a 2006 and everything was fixed.

The aftermarket one that I had was just not tune to respond the same as the Motorcraft one.
I have JY spare for my DOHC bulls. I cleaned the JY one, oiled it and switched it out, works just fine. I would rather have a used one cleaned than a new one unless it was JY priced. So I have a good spare, proven. Switching one out takes minutes.

-chart-
 

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Discussion Starter #18
OK, today I switched out the AIC, back to the one I took off. ( I save the old parts in the new part boxes) I didn't do much driving , but monday will tell. Thanks to all for the suggestions. I will post the results.
 
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