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TPI Tuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.

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Old 02-12-2003, 10:54 PM   #1
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My Iroc misses at 3500:(

Please look at my signature. My car misses at 3500 rpms and I can't figure out why. I just go new accel 8mm wires and I have an Accel Supercoil. I know I have a bad MAF which I will replace in a couple of weeks. Could that be the problem? Also, the Mafs at Oriely's are only $150. How come? I saw teh botch ones on the internet for like $300. Has anyone tried the Autozone or Oriely's stuff and whats the difference in performance?
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Old 02-12-2003, 11:35 PM   #2
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I'm experiencing a similar problem. I'll get an occasional miss around 3500... sometimes its quick, and continues to pull hard, other times it'll kinda contiune to miss some as the revs climb, the majority of the time its perfect. It'll also do it around 1500 pulling hard. I haven't chased it down yet, I just got her... but I'll hoping its the little 7mm wires the previous owner has on there. Thoughts anyone?
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Old 02-13-2003, 09:19 AM   #3
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Check your spark plugs and see if any particular one is cracked or corroded or showing signs of age or failure.

If it's only missing at 3500, I'd be inclined to think there's a defective component in the ignition system. At 3500 rpm (about peak torque in TPI engines) the cylinder pressure is astronomical, and the higher the pressure, the more energy the spark needs to jump the gap on the plugs. If anything is defficient along the current path from the distributor to the spark plug, it won't fire and you'll get a miss. You can also look under the hood at night and have a friend rev the engine to 3500 and look for arcing- that is, a spak leaking out of the wire boot (usually the sign of a cracked ceramic on a spark plug).

Also, check your distributor cap for cracks, or carbon tracking inside. Sometimes, the spark from the rotor may find an easier path to a different cylinder than the one it's supposed to fire because there's dirt or carbon build up, or one of the terminals is deteriorated from age.
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Old 02-13-2003, 09:39 AM   #4
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Couple things...
To me it sounds like your coil is going bad, or is bad. If you have a haynes manual, it will tell you how to check it with a volt-meter. A digital one is better.

If it isn't there, it might be the cap and rotor. How old are these.

Also, how do you know that your MAF is bad? If you are getting trouble codes for your MAF there are many ways to test the wiring and relays
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Old 02-13-2003, 12:36 PM   #5
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my was doing the same thing and t was a burnt wires that was arching. it had the ac delco 7mm wires. i then replaced all of it with msd gm blaster coil, msd cap and rotor and msd 8.5mm superc conductor wires along with new ngk plugs

theve been on the car about 1500 miles now iand i havn't had it happen to me yet.
but i've also ben taking it easy due to the fact that the weather has ben bad here for the last month or so.
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Old 02-13-2003, 12:43 PM   #6
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I know I have a bad maf because I took it to my mechanic the other day and he read the error code. The rotor and cap are about 8 months old. I will check those tonight and see if I see any corrosion. I want to put the msd 6al box but I want to see if I can fix the problem first.
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Old 02-13-2003, 02:43 PM   #7
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Quote:
Originally posted by madmanups
I know I have a bad maf because I took it to my mechanic the other day and he read the error code.
Don't go replacing the MAF just because a code was set for it, there are a multitude of other things that can wind up setting a MAF code. Those codes are there to give a starting point for troubleshooting.
you wouldn't want to replace that expen$ive MAF just to have the same code reappear.
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Old 02-13-2003, 09:31 PM   #8
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do u have a friend with a 3rd gen tpi.. if so borrow his MAF for a sec if the "service engine soon" light goes on u knowits not the wiring or relays, its your maf
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Old 02-14-2003, 03:04 PM   #9
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Thats true. Today I found out that I'm not getting enough voltage to the fuel pump. It was at 11.8 and I'm not getting any fuel in the fuel rails when I turn the key. I believe its code 36. I want to find out if the burn off relay is faulty. Maybe that is why my car is missing at high rpm.
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