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Old 09-05-2010, 09:56 AM   #1
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Default Idle miss...driving me crazy?

This problem is an obsession at this point, and basically taking over my life! While the wife is yelling about the siding falling off the house, I'm stomping back out to the garage to give locating the engine miss...yet one more try. It's gone on and on like this for weeks now.....help!
Basic situation: Engine fires right up strong. Good throttle response. Runs cool (160 thermo), hardly ever going over 180 deg. When the engine has been sitting overnight, it idles fine...but once it's at operating temp, sitting at a stop light, I get this "miss" in the right bank exhaust, and the idle is rough.
I've checked for VAC leaks, till the cow came home. Changed plugs, changed gap (50 to 45). Spark checked each cylinder has a steady spark. Check for exhaust leak as best I could with stock manifols shields installed. Iac counts at lest 10, with TPS set @ 60. Throttle body is clean. What am I missing?
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Transplant LT1 5.7L using stand alone harness with no MAF, only MAP
Bosh III 24lb injectors (even switched injectors to opposite banks, same problem) Sock rebuilt engine, stock cam Thanks, Jimmy
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Old 09-05-2010, 12:33 PM   #2
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how do you know its a cylinder miss on the right bank? throwing a code? check compression on all cylinders, check fuel pressure and fpr. i have been tracing down a similar issue only i stall out randomly. i am going to pull the tb and check tps voltage - you want a smooth transition from closed to wide open. also pull the iac to check the condition, sometimes it will stick.
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Old 09-05-2010, 02:00 PM   #3
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How about your O2 sensor on that side. Sounds like as soon as it's going in to closed loop is when you're having issues.......
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Is the drivetrain free wheeling? Something as little as a broken pinion gear would make the car not spin the rear wheels.

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Old 09-05-2010, 02:30 PM   #4
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Thanks for the input guys, but already been down that road....Changed O2's from Bosh, to ACDelco (LTFT readings seemed better with AC's), but "miss" still there? Even switched O2's to opposite sides...still there? New IAC, new TPS (set@ both .57, and .67) still there? Did not do a compression check, but the engine is fresh rebuilt by a trusted machine shop, and my VAC reading @ idle, is a steady solid 21? I know it's probably gonna turn out to be something stupid that I'm just missing, but can't figure out what? Left side exhaust steady @ idle....right side pop's/ misses. One more clue: I can watch the oil pressure gauge and it seems to fluctuate in rythum with the miss, +/-3psi, or so? Jimmy
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Old 09-05-2010, 03:23 PM   #5
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Have you verified or double checked your lifter preload? Maybe you're a little heavy on one causing the miss......

Also I see you changed the plugs, how about the wires?
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Is the drivetrain free wheeling? Something as little as a broken pinion gear would make the car not spin the rear wheels.

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383--AFR Heads--12.2:1 scr--58mm TB--LT w/X TDs--23X/24X @ .050--3800 Edge Stall--TH400 w/RMVB trans brake--3.73's--Next up 150 Shot and 9"(after I twist the 10 bolt in half)

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Old 09-05-2010, 04:22 PM   #6
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Check, check, and check. Switched wires, for testing, changed plugs, and checked pre load, already....pop still there? As a matter of fact, that's how I dropped the bolt, down through the head, through the intake oil galley, into a crevice in the block (another post)..checking the preload.....Jimmy
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Old 09-05-2010, 04:29 PM   #7
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By the way....I checked the pre load (which ended up taking 3 days of tearing the intake, and oil pan off looking for the lost bolt), even after getting a steady VAC reading of 21! This "popping is driving me nuts!.....Jimmy
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Old 09-05-2010, 04:30 PM   #8
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How old is the cap and rotor???
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Old 09-05-2010, 06:42 PM   #9
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Brand new MSD. Again, runs fine on hwy....come to a stop light when it's warmed up and the oil pressure (which is normally 50-65psi) drops and fluctuates between 20-25, in rythum with the miss/popping? H2O temp stays steady (170-180) all the time reguardless? I realize oil press will drop, and 20-25 @ idle is normal, but there's no inbetween. It's either 50+, or fluctuating between 20-25, in rythum with the miss @ idle?....Jimmy
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Old 09-05-2010, 06:48 PM   #10
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I know it's something with the right bank because not only can you hear it, but when I put the palm of my hand on the exhaust , you can feel it. I can also sit in the drivers seat and feel a pulsating/vibration/miss, and watch the oil pressure gauge stay in perfect time, with the vibration. Timeframe on the pulsating at idle is lets say every "one, one thousand". Jimmy
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Old 09-06-2010, 03:54 PM   #11
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Most obvious thing is spark arcing to ground. You'll need a very dark location, and very closely look for it. When I say very closely, I mean VERY CLOSELY since the arcing may not be easy to see.

This is one of those Attention to Detail things.

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Old 09-06-2010, 04:05 PM   #12
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You should also wet down the spark plug wires, one agt a time, with water from a spray bottle to ID any that are deterioriated.

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Old 09-06-2010, 04:35 PM   #13
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Sounds good Jake. There new MSD wires, but I'll give it a try. By the way, what exactly am I looking for?...Thanks, Jimmy
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Old 09-06-2010, 06:25 PM   #14
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Quote:
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Sounds good Jake. There new MSD wires, but I'll give it a try. By the way, what exactly am I looking for?...Thanks, Jimmy
You're looking for spark arcing to ground.

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Old 09-06-2010, 09:29 PM   #15
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Roger that Jake. Thanks, Jimmy
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