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2003 Ford Focus ildes funny, sucks gas

Tiny
BOTTLES0
  • MEMBER
  • 2003 FORD FOCUS
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 109,000 MILES
I just had a timing belt changed, and motor runs somewhat better. Have changed every sensor I can think of, and all 4 injectors. I have an after market coil and wires from Davis Unified ignition, over a year old. Car has a very rough idle when cold, and really sucks gas. Even if I drive 50-60 mph. It runs better when warm. I am also using Pulstar spark plugs, with a.045 gap. This is fixed. Car will idle smooth when stopped, and then start acting as though it is missing on one or two cylinders. It also sucks gas after 65 mph. I can watch the gas gauge go down! The local garage cannot diagnose the problem. No codes. Car ran rough before the coil and wires. They helped a little. Any suggestions, please? Thank you.
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Friday, April 11th, 2008 AT 2:51 PM

9 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
If you have a scanner that can read the ect and iat in degrees, get a reading from these two sensors in the morning after the car sat overnight, turn the key to on, do not start it, readings should be within 5-10 degrees of each other. My money is on the ect. But if you have a bad idle at all temps, even warm, remove the idle air control valve and clean or replace it. You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
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Friday, April 11th, 2008 AT 3:12 PM
Tiny
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You say that the ect may be bad. What is the ect? I have already done the spray around the manifold routine. No result. A co-worker, who is a mechanic, says that it sounds to him like it may be the crank position sensor? Is this the ect? Please let me know. Thank you.
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Sunday, April 13th, 2008 AT 1:10 AM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
No, if the crank sensor is bad the car won't start. The ECT= engine coolant temp sensor, while your at it, the IAT= intake air temp sensor, and both the MAF= mass air flow and MAP=Manifold absolute pressure sensors could be the ptoblem. Turn the key to on, but dont start it, does the check engine light come on?
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Sunday, April 13th, 2008 AT 5:37 AM
Tiny
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I have already replaced both the ECT and the MAP sensors. When I changed the MAP sensor, the problem went away for one day, and then returned. My car doesn't have a MAP sensor, or AIT sensor. Could it be either a cracked crankshaft position sensor or a camshaft position sensor? All the normal dash lights come on when I turn the key. No check engine light, and no codes ( I had it scanned at Auto Zone). It seems like the engine is pulling back on the timing, if it runs rough when I start it. And the gas mileage seems to change after I hit some big bumps on I-94, on the way to and from my job in Flatrock, MI.
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Sunday, April 13th, 2008 AT 1:08 PM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
On yours the MAP is called the barometric absolute pressure sensor. It will have vacuum and electrical connections to it. Test the CKP with a volt meter should put out 2-4 volts when cranking. Some IAT sensors are built into the MAF. It's also possible the CPS wasnt installed right. Actually looking into yours further the MAP/IAT is a single sensor.
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Sunday, April 13th, 2008 AT 6:08 PM
Tiny
JESTR
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I had the same problem with mine and spent alot of money tryin to fix it, even as far as replacing the cat and exhaust! The culprit was a loose wire on the coil! The factory harness was a bit short and made the wire for cyls 2-3 crack and corrode! Check the harness and see if the wires are pulled too tight! That was the fix to mine. A plug the junkyard gave me for free and added 6 in to the harness and presto it was fixed, I did spent a month and hundreds tryin before that! Good luck!
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Monday, April 14th, 2008 AT 10:39 AM
Tiny
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I checked with the garage that worked on my car. They said that they checked all of the sensors out, and changed the spark plugs. What does the manifold pressure control look like? I changed one on the firewall that has two vacuum lines going to it; one of which goes over and around the front of the engine, and then down. I am going to try and replace my custom ignition wires, and see if that makes a difference. I also checked the wire connection to the coil, as suggested by the other person, and it is tight. Also, the idle gets rougher when the defroster is turned on. I turned it off, and it smoothed out a little. Any other ideas?
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Monday, April 14th, 2008 AT 12:58 PM
Tiny
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I went to my local Auto Zone on Monday, in order to purchase another bottle of Techron fuel system cleaner. While looking at the shelf, I noticed that they now carry CRC MAF sensor cleaner. I was told more than once that it couldn't be cleaned! I bought a can, and followed the instructions. What a difference that made. It now gets great gas mileage, and runs very well. But when cold started, it still has a rough idle. And once warmed up, the rough idle comes and goes. If I stop, it will idle rough until it reaches the base idle (750 rpm). Then it smooths out. Any suggestions, please?
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Thursday, April 17th, 2008 AT 2:53 PM
Tiny
MERLIN2021
  • MECHANIC
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Cold running rough will be the ECT I mentioned earlier and or the idle air control.I think the other poster was refering to the wires to the coil are TOO tight! And not quite long enogh for comfort, and as a result, they crack, break, fray, or corrode. Check inside the harness for these conditions first! The other thing is although the MAF works better cleaned, a bad one will give ALL your symtoms! The car thinks it's operation in barometric pressures that are not correct, thus it tells the PCM false info, and the PCM tries to solve the problem by adjusting fuel mixture. And incorrectly!
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Thursday, April 17th, 2008 AT 4:45 PM

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