about a week ago, my car started getting a tick then got a miss in the upper RPMs - after 4000 basicly I had all kinds of bad thoughts on what may be wrong - mostly focusing on the cam & lifters..... anyways, while looking around, I found a header bolt loose. yay - found my tick. tightened it back, and was also hoping that the exhaust leak may have caused a "scavenging" problem, and maybe was creating the upper RPM miss. nope. just the tick.
so, now I am looking for reason for a upper RPM miss/stumble. my worst thought sofar is a broken valve spring. I have the crane springs, and they are dbl springs, so maybe the inner spring broke, and my valve is floating but, it does feel more like ignition. but, I'd expect that to be full time. maybe the exhaust leak melted some insulation from the spark plug wire. but, again - should be a full time miss.... maybe a clogged injector, just cant deleiver enough fuel. yes, remind of another part of this: its only when loaded. doestn happen if I just rev it unloaded. this is what makes me think clogged injector. the miss is predetonation, from a super lean cyl.... another thing that changed recently - replaced the tach filter. previously, the tach got wierd after 4000 rpm. kinda funny. change the filter, and now the tach reads good - but the motor now runs funny after 4000....maybe I just have a lousy tach signal to the ECM....
the worst part of all of this...I just finished my modified upper plenum. opened the neck & reduced the runner length....so, now I should be able to breath out to 6000....grrrrrr
A couple things that I've run across were a clogged fuel filter and a weak coil. Another person had a spark plug wire problem that only acted up at higher RPM's. Unfortunately, you can't check these things unless its on a dyno and I hate just replacing parts until you find the right one.
I've heard of ionized air causing high RPM missing. The air inside the cap gets charged and causes all kinds of stumbling/missfires. Check your cap for carbon tracking and general servicability. I'd bet it's something simple and not internal engine breakage.
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ARCHIES JUNK IS FASTER THAN SHAUNNA'S JUNK
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12:29 PM
pontiacman63383 Member
Posts: 819 From: warrenton, mo Registered: Jun 2007
I have seen warn out valve springs cause the same problem, under that faster movment of higher rpms thay cant close the valves quick enough
yes, one of the things I am worried about. a bad valve spring. the springs are recent Crane Cams springs. I've had cams problems in the past, until I finally discovered "spring install height". I've wrecked a few cams. anyways, they be dbl springs, and I am concerned that maybe the inner spring is poo-poo'd and giving me with valve float. and, the big worry with this, is eventually a peice of the broken spring will get jammed in the outer, and bind....and then I will add bent rod to my list of the many things I have broken in my motor......
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08:24 AM
Oreif Member
Posts: 16460 From: Schaumburg, IL Registered: Jan 2000
If it's an ignition miss it could also be the ignition module is starting to go bad, the pick-up coil inside the distributor could be corroded, or the ignition coil is getting weak. Does the miss happen when the engine is hot and cold or just when hot?? Is it worse during high humidity like on a rainy day? If it is worse when the engine is warm, The ignition module or coil could be going bad. If it is worse on a high humidity or rainy day the pick-up coil would be more suspect. Also spark wires and plugs could be bad as well.
If it's a air/fuel miss then it could be a bad valve spring, slightly bent pushrod, or a bad lifter. Usually if the valve floats and causes a miss there usually is a little more noise coming from the valve train. A broken spring should be detectable by sound even at lower RPM's even though it isn't causing a miss.
Since the Tach filter seemed to have issues, I would suspect the ignition is causing the miss. When you changed to a new tach filter it was less susceptible to a noisy signal. Starting with the ignition module and pick-up coil would be what I would look at first. Usually a mechanical problem like valve train related, will happen even in neutral (without a load). It may not be as severe as loaded, But you can still detect it.
------------------ Happiness isn't around the corner... Happiness IS the corner. ZZ4 Powered !!
[This message has been edited by Oreif (edited 08-15-2007).]
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10:24 AM
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
well, it is a recent thing, and recently we have had higher humidity. also, earlier this year, I had my dist gear wear out, and I replaced the pickup coil & ignition module while there and got the dist shaft nice & smooth spinning. I guess I'll start with a new set of wires. these old Accell 8.8's have been on for 4 seasons now anyways.
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11:09 AM
Aug 30th, 2007
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
well, finally was able to get back to this. replaced the wires, didnt help. tho, listening to it - it sounded pretty ticky. I guess ya hear it differently, when you dont drive it everyday....took off the valve covers. loose rockers. sofar - at least 3 of them. I have seen this before - when I had cam failures due to valve spring binding. I havent removed the inatke manifold yet - just the upper & lower plenums. but, I am sure I will find lifters with bowl'ed out bottoms & a cam with wrecked lobes. of course, I still have hopes of collapsed lifters - but 3? the 3 near the dist gear that failed? or did one start failing, and wreck the other around it & the dist gear...ug - dunno. I think the failure chain is: high volume oil pump on old dist gear wore gear out, the shrap from the gear wrecked the oil pump and started the cam lobe failure.
either way - dropping the cradle. fully tearing down motor. new cam bearings. plastigauging crank & rods. while this is happening, I will meld in my original winter project - the 7730 ECM. so, I will add the existing cam, crank & knock sensor to the wiring harness, while deleteing the automatic trans, egr & cruise control wires from the harness. if I can - I will just transfer the functions.
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12:44 PM
lacelles Member
Posts: 298 From: Rockland Ontario (Canada) Registered: Nov 2004
In my 84 Iron duke the problem was finally traced to a bad 24 year old fusible link, my stumble started at 3200, then 2700. Then the car might start after sitting or might not. Turns out the furiable link was totally fryed, just wouldn't carry the juice for the higher RPM requirements. I already had the new coil, new rebuilt distributor, cap, wires, plugs to begin with. Just my one cents worth.
