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Me again! I recently peformed a home service on my 1999 stock Coupe. Changed oil & filter, drained-flushed-refilled engine coolant, replaced spark plugs, replaced spark plug leads, cleaned and re-oiled K&N air filer, changed PCV valve. Started her up expecting all to be well, and initially it was but within a day I noticed her running with an acceleration lag and more noise from the BMB tail pipes. I only use the best fuel, but suspecting a fuel problem ran some cleaner through the tank, but saw no improvement. In fact, over the week the drive quality worsened. If I accelerate without dropping a gear the car is initially unresponsive and then when it does pick up it's accompanied by a crescendo of pops and crackles as the unburned fuel ignites in the exhaust system. Monitoring my mpg, I've lost about 5mpg average, have a lot of soot deposits equally distributed across both sides of the tailpipes (previously never experienced any soot on the polished stainless!), know I'm not burning a drop of oil, and it feels like the situation is worsening each day. I tried the idle re-learn procedure and whilst this improved things marginally at first it's as thought the car is re-tuning itself for very fuel-rich / air-lean operation. I'm recording no DTC codes from the engine, and it's not misfiring. I don't see any arcing from the leads, and at steady idle I'm not suspecting a plug gap problem on a cylinder as it's smooth and even. Last night I unplugged the mass air flow sensor whilst the engine was running and was surprised that the engine didn't respond one bit. Maybe I have a problem with this, but I don't know how to confirm. Also, when I unplugged the mass air flow it didn't throw a DTC code which surprised me.
Never had a problem with the vehicle until 2-months afetr my extended warranty ran out; now plagued by them (see EBCM thread)! Before I lose complete confidence in my abiltiy to keep this vehicle on the road and running well, can someone please help point me in the right next direction?
Posts: 6 | From: Louisiana, USA | Registered: Nov 2007
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Thanks for the reply. I'm not getting any new codes other than the traction control ones, so the DTC isn't pointing me towards any specific problem with the running condition.
The plugs I went back with were'nt AC Delco. I went with the NGK's, and probably regrettably opted for the iridium plugs over the platinum, or as some posts recommend just go back with simple copper replacements as they are more forgiving. I don't think I disturbed the gap as I fitted them, but it's a tight squeeze getting the plug into some cylinders so I can't be sure. The leads are new and on good and tight as far as I can tell. I wondering if the iridium plug was a mistake?
In terms of the MAF and security of the air piping you may have a point. I disconnected this to work on the EBCM replacement. Don't think I mistreated the assembly to cause damage to the MAF, but have not checked properly to ensure I got the clamps back on properly/tight. Thanks for the tip. I'll check tonight and see if it makes a difference. Really appreciate the help!
Posts: 6 | From: Louisiana, USA | Registered: Nov 2007
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Maybe you got the wrong plugs. I've seen a couple of cases where the partsman either got the wrong number or grabbed the wrong box off the shelf. Did you compare the new plug against the old for reach, etc?
Posts: 799 | From: arizona | Registered: Nov 2001
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Another possibility could be if you over-oiled the air filter. That could cause a problem with the MAF. You can buy cleaner specifically for cleaning MAFs from auto part stores.
Posts: 799 | From: arizona | Registered: Nov 2001
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Sounds like wires to me. Are you sure all are connected correctly? The MAF as stated before check for leaks and excess oil
Posts: 2845 | From: Pennsylvania | Registered: Jul 2001
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My vehicle had a similar problem after a header install. Some people call it "tractoring" and has similar lack of power rough idle symptoms.
Mine was accompanied by a O2 sensor trouble code (my sensors were crossed after the headers were thrown in) I'd check the O2 sensors. They're part of the regular tune up anywho. Oreilly's carries Sensors for ~$50 ea
-------------------- Every day, I beat my previous record for consecutive days I've stayed alive. Posts: 99 | From: Spring, Texas | Registered: Sep 2007
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As mentioned already start with the MAF. You're looking either a leak from a bad/loose connection or possibly excess oil from the K&Ns. Over oiling the filters is fairly common.
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As the others mentioned, check the plugs, wires, and MAF. It's not uncommon for a wire to pop off the plug, a plug to be cracked on install, or overoiling the filter and the oil getting on the MAF.
You might also want to check the codes stored in the DIC to see if there are any misfires or something else going on.
[ January 05, 2008, 03:24 PM: Message edited by: BruceF ]
Posts: 4449 | From: Long Island, NY | Registered: Nov 2000
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Apologies - long time logging back in, but just an update if it helps others in a similar situaiton. I replaced the wires, cleaned the MAF, checked and re-prepped the K&N, then pulled and replaced the plugs (again) - this time with AC Delco iridiums. As soon as I started to pulle the NGK's the problem became obvious. The ceramic broke on six of the eight I removed upon replacement. They had only been in the vehicle a couple of weeks. I know they were not over-tightened because I torqued them, and used anti-sieze compound. In assesing the two that were "OK", is was obviuos on inspection they too had lots of cracks in the ceramic. I strongly suspect the shop I bought them from had dropped or mishandled the box and cracked or weakened the ceramic befor sale. I installed them carefully/surgically, but right form the get go on re-starting the car it was arcing and misfiring. The AC's I replaced them with (after a thorough inspection pre install!) are running fine and the problem has been compeltely eliminated. Leson - check the plugs before install!!!
Posts: 6 | From: Louisiana, USA | Registered: Nov 2007
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