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intermittent misfire, no codes.

C

cetroutt

Veteran CEG'er
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Feb 16, 2009
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just like the title says, i'm having an intermittent misfire and there are no codes. it usually happens after i've driven more the 40 miles or so. i've had it stall out twice at stop lights. anyone have any ideas as to what could be causing this? it's happening to my 98 zetec with the ATX. thanks
 
My check engine light bulb was missing when i bought my svt from previous owner. Maybe yours burnt out or is missing. also if thats not the case, mine stalls out if im below a quarter tank of gas and it bucks and jerks a little bit when im in 4th gear going like 35-45 miles per hour so to avoid this i keep it at above quarter tank at all times
 
update
i finally had a code, p1131, i took it to a reliable shop and had them pull the code. their computer showed that i had 7 thousand misfires on #2 cylinder and almost 8 thousand on the #4 cylinder, but zero on cylinders 1 and 3. no misfire codes. the plugs have less than 8k miles on them but the plug wires had an unknown number and they were replaced. i pulled all four plugs and they all looked clean however the #4 plug had evidence of carbon tracking (? is that what it's called?) i cleaned the ceramic on all four plugs, rechecked the gap and reinstalled them. i also reset the timing because the belt tensioner for some reason backed off some and there was almost 3/4 inch deflection in the belt between the cam gears. the bucking doesn't seem to be as bad but it's still there sometimes. the TPS is within range and both O2 sensors checked out. the guy at the shop suggested changing plugs, wires and fuel filter. changed wires and filter and inspected plugs. what else could this be? could the plugs really be bad or MAF need cleaning? thanks in advance for any help.
chris
 
i changed the plugs. it's a better now, but there is still some hesitation when taking off from a stop. every once in awhile while sitting at idle it will stumble and the rpms will drop and then seems to catch itself and the rpms go up and then settle back down to normal. some one suggested a vacuum leak but i can't find one or should i say can't hear one and all of the hoses seem to be okay. i look in the TB and it's looking pretty dirty, i'm thinking i need to clean that out. any one have any suggestions?
 
are you still using the wires with unknown miles? the carbon tracking effects the plugs and the wires. once it occures, as far as I know, it can not just be cleaned up and it will be ok again. get some fresh wires and now maybe another set of plugs.

however when I had carbon tracking on my 95 the idle was fine, just off idle power was gone.

P1131 - Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1

looks like its time for a new O2 sensor also.
 
both plugs and wires have been replaced. can the O2 sensor be bad if the code is gone? i thought that if it's bad then the code would come right back after it was cleared? thanks
 
possibly. it might take a few drive cycles. generally a O2 sensor code like that means that the sensor is done and needs to be replaced. however i suppose bad miss fires for a long time might cause issues.
 
Unless you want to spend the money I would just change the indicated sensor until you have a code for the other sensor. The sensor in question is the one that control the a/f ratio, so it would be good to make sure that one isn't a problem. the other sensor just monitors the cat.
 
right at 120 miles with no code. i ordered a new O2 sensor and coil (just because it was on sale) this morning. i still have a little hesitation and a stumble at idle once in in a great while. i'm over due for an oil change and i'm thinking i probably ought to clean the TB and MAF and triple check all of the vacuum lines while i'm in there. i should have all of my parts by FRI so on SAT i'll get all of this done.

any particular brand of cleaners i should look for when cleaning the TB and MAF?
 
fedex dropped off the parts about an hour ago. i installed the new coil. started and let it run for a few minutes. and it idles smoother and it's quieter now. i still need to pick up oil and filter and the stuff to clean the TB and MAF. looks like it was the plugs and wires and possibly the coil. i also need to pick up a O2 sensor socket so i can get that changed. thanks for the advice BrApple.

one question, does the coil have any kind of oil in it? when i pulled the old one there was oil between it and the mounting bracket. i do have a slight leak on the valve cover and i suppose that's where the oil came from but i'm just wondering. thanks
 
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