High-load, low RPM misfire(?)

Car:     1995 Camaro Z28 (LT1) M6 with ~69k miles     Hurst shifter     SLP intake & exhaust (dual conical K&N air filters)
    Intake airfoil     Performance Friction race pads - front (they dust too much)     Performance Friction street/track pads - rear (I prefer these)
Symptom: When the engine is at low RPMs (~<2k) and throttle position is greater than 3/4 in a higher than ideal gear (a co-worker of mine referred to this as "lugging the engine") the vehicle car starts to shake. I think that some of the cylinders start missing as the source of the shaking appears to be from the engine.
Other indicators: None; this is what is confusing me since the engine should set the "Service Engine Soon" indicator if it detects a misfire.
Troubleshooting steps: I did add some fuel injector cleaner but it doesn't appear to be helping. I think the problem has more do with spark. This condition is reproducible every time I'm on the highway cruising in 6th gear and then mashing the throttle. Shaking galore! Lower gears also work but RPMs have to be low. Hard accelerations from a stop (ex: 0 to 60) do not cause this to happen and the car's 0 to 60 performance appears to be the same as it ever was. I've noticed no decrease in fuel economy. I tried getting the local AutoZone to pull the codes from the ECU but their reader was not able to link up.
My request: I have a service manual, but it's buried somewhere in my storage and I have not been able to locate it. I would appreciate troubleshooting suggestions or possible causes for this symptom. Thank you very much for your help!
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I also had this problem with a recently acquired V-6 (3.4) 95 F-bird. Around 1500-2000 Rpm in overdrive...the shakes/missing. It would also sometimes miss at a red light at idle. Dropping out of O/D would clear it , until it was under a load again in O/D.
My cure was replacing the plugs and wires....( 3 plugs were only in hand tight )
My guess is it was blowing by the plugs on my car under a load.
Hope this helps........Stan

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could be plugs&wires need to be changed. Also the cap&rotor. Make sure your water pump is not leaking antifreeze on your cap. That could cause it to crack, letting antifreeze in and causeing a missfire. good luck

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wrote in message Correct me if I'm wrong, but I think that year LT1 has a distributor-less ignition (ie. no cap or rotor). Good luck with the plugs... they're impossible to get to by mortal men.
-O
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"> Correct me if I'm wrong, but I think that year LT1 has a distributor-less You are in fact wrong. Lt1's use what it called an "OptiSpark" distributor. It mounts on the front on the timing cover, behind the water pump. This setup was used only on the LT1 and LT4 engines. If they used the standard rear mounted distributors in the 4th gen cars you would have to remove the engine just to change the cap and rotor. - Gary
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Gary - KQ6RT wrote:

LOL - I never even thought about that. I thought changing the plugs on an LS1 was a bitch.
Changing the distributor cap & rotor on an L98 93 Camaro: option a) drop engine option b) remove windshield and top of dash pad. Sawzall a hole in firewall.
Sometimes I miss my 70 Buick. Enough room to pull the tranny out from the top - no need to remove the engine. ;)
--
Ray

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I don't beleive that a L98 was availible for a 1993 Camaro.

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Thanks for the suggestions guys. I'll get to work on this tomorrow after swaping the front brake pads. Do you think that I should still try to get an OBDI diag tool reading or just jump into replacing the plugs/wires and perhaps cap and rotor? Any suggestions on replacement parts (speciflically the plugs and wires?)
Thanks again, Wayno
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You are indeed right, but it works the same.
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I should have said, Cap and rotor as we once knew them. The Optispark works the same way.
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I found my service manual this weekend! Woohoo. Bad news is that it looks like changing these plug wires is going to be a major PITA. Have to take off the PS pump and drain the coolant! I think I'm going to call around to find out how much the local places will charge me to do this before I spend a whole weekend on it.
Anyone know where I can find a Tech 1 to borrow for a few minutes? Auto Zone has OBD readers but the will not link with my car due to the OBDII connector (I think). I'm currently in the Detroit area.
Also, I looked into replacement wires this weekend AZ had the MSD wires but I hear that they do not find into the stock guides. The other choice was Bosch, which also were custom wires. Any comments? Also, has anyone tried the Platinum +4 plugs? Are these worth the $ or are iridium (sp?) the better way to go? Thanks!
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Darn, I was just quoted $695 for changing the plugs and wires by Midas. 6 hours labor!!! How much time should this take them to do really?
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At 50.00 per hour, and I am not sure what the going rate at Midas is. That leaves 395.00 for parts! That in my opinion is A little expensive. Do you know what there rate per hour is? A couple of years ago I had a new water pump, optispark, plugs,wires and fuel filter installed at the Chevy garage here in town and if I remember the labor required was a little over six hours. The bill came to 900.00.

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The dealers in town charge $75/hour. Midwas is supposedly at $65/hour if I remember right.
I've been thinking about this issue that my car is having and am confused to the logic why this would be caused by either the plugs or wires. Wouldn't I have problems all over the RPM range if that were the case? Why only at high loads at near or at WOT? Just trying to get it straight in my head. Thanks!

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High loads and WOT demand more from the ignition system. Therefore if your spark is weak then you will encounter a misfire.
-Zuhalter

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I was able to change all my plugs and wires by getting to several of them from underneath by dropping the pipes. No need to do anything with the ps pump or coolant.
Superman

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Thanks.... I noticed that this is what was stated in the F-Body FAQ, I'm surprised to see that it conflicts with the service manual.
Question... If I get an 8.5mm wire will it fit in the looms? What about an 8.0mm? If no, how does one get around this? I hit the local Auto Zone last week but was lost at which plug wire I should purchase. I'd like to get the High Performance MSDs but I don't want to make this job any harder that I already know it is going to be....
Thanks!

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Well I tried my luck chaning the plugs/wires yesterday. What a PITA. I ended up braking the first two bolts when I tried to take off the Y-pipe, even after soaking them with liquid wrench overnight. After that point i decided to give up since any more broken bolts would have left me with a car that I couldn't drive. Instead I ended up chaning the oil/ air filter/ PCV valve. Looks like I'll be paying a shop to do the plugs/wires for me.
Thanks for all your help! -Wayno
snipped-for-privacy@yahoo.com (Wayno) wrote in message

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