A little stumper for the wrench-turners

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  #1  
Old 06-22-12, 09:20 AM
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A little stumper for the wrench-turners

Caught this while drinking coffee at my tow buddy's place and perusing one of the trade magazines. He was bemoaning the insanity of some modern automotive engineering and showed me the article. Let's see if anybody hits the tricky little potential problem (no fair cheating if you read the same article or Google for clues):

2003 Chevy Malibu, 3.1L engine, has a constant misfire on #6 cylinder. Has good spark, switched injectors and plugs, good compression, and no vacuum leaks, no loss of coolant or other signs of head gasket problem. Carbon-treated and no apparent valve hang-ups.

So what item might be overlooked in the troubleshooting/diagnosis?
 
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  #2  
Old 06-22-12, 09:24 AM
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Bet it's something crazy like a friend's mustang - it had a high speed miss he couldn't track down. Finally took it in and had it hooked up to a diagnostic machine. Turned out he had a faulty starter - but it started fine! - replaced the $200 starter and the miss was gone.
 
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Old 06-22-12, 09:35 AM
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Wow, that is crazy. Not the problem in the case study.
 
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Old 06-22-12, 01:58 PM
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All right, Master Guns, how long are you going to leave us (me) hanging?
 
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Old 06-22-12, 02:16 PM
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Sounds to me the ignition unit for the bank was not firing in the proper order, although you had "spark" if it wasn't at the right time it would misfire. Hey, what do I know?
 
  #6  
Old 06-22-12, 04:35 PM
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good possibility

I would check for pulse with a noid and check and make sure the ground on #6 injector was good.
 
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Old 06-22-12, 07:41 PM
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Answers:

1. I suppose I'll spill it tomorrow (Saturday). Probably precede with a BIG hint that will give it away.
2. Nope.
3. Nope.

Hint: It's not an ignition or injector issue. Hmmmmm.
 
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Old 06-22-12, 08:28 PM
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Yeah, you're going to say something is wrong with the brakes or something like that, right?
 
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Old 06-23-12, 04:50 AM
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Nope :NO NO NO:, and here's the BIG hint:

The camshaft is not a one-piece cast/ground unit.........
 
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Old 06-23-12, 10:15 AM
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Change the spark plug ..........
 
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Old 06-23-12, 01:43 PM
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See original post; not a spark/ignition issue.

Figured mitch would be on this by now since he was chomping at the bit yesterday.
 
  #12  
Old 06-23-12, 05:54 PM
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The camshaft is not a one-piece cast/ground unit.........
Are you trying to trick us with a play on words because it is a one piece COMPOSITE camshaft so I would say that you are pointing to a damaged camshaft which would have been diagnosed by a compression test are a cylinder leak down test.
Jim
 
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Old 06-23-12, 07:09 PM
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cam position sensor?......................
 
  #14  
Old 06-24-12, 06:37 AM
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Okay, here's the answer. Jim was on the right track, maybe, but then derailed.

It's not a one-piece shaft.

Quoting from the article:

"The camshaft is a hollow tube design with pressed on lobes [emphasis added]."

The trouble can arise is a lobe "slips" which most often happens when "the engine had been overheated prior to the event".

SO, you over heat, the camshaft and the lobe get squirrely with the cam lobe rotating slightly on the shaft and voila! You get a single cylinder with an out-of-timing valve.

The diagnostic steps are pretty involved, so unlikely something an average backyard mechanic would ever track down.

Now, one piece cast/ground cams have only been around for about 100 years and suddenly the auto engineers decide it needs to be improved on? Not sure what the benefits are; the only thing that comes to mind would be that it's cheaper to make a bunch of hollow shafts and an assortment of lobes to be pressed on depending on the design of whatever engine it's going into than to have one-piece finished cams made for each engine type.

Crazy.
 
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Old 06-25-12, 04:28 AM
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No comments. Hmmm.
 
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Old 06-25-12, 07:47 AM
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Couldn't get on over the weekend, just seeing this now.

Ok, I never would have come up with that one.
 
  #17  
Old 06-25-12, 08:52 AM
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Yeah, my tow buddy who originally read the article, greeted me next time I saw him with, "Have all the automotive engineers gone insane?". Granted, the article does say it usually follows an overheating event, but still. I wonder how the price of one of those compares with an old-school one and fixing one that's "slipped" would be impossible, so you'd have to replace.
 
  #18  
Old 06-26-12, 07:34 AM
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Back in the "old days" you never heard of camshaft trouble. In the 50s they started to fail I suppose due to more spring pressure. I had a friend who wiped a lobe off a new cam in his drag car before he got it out of the garage. I wonder if the "press on lobes" might be hardend steel which should be better than cast or forged one peice?
 
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Old 06-26-12, 11:17 AM
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Could be. Like putting carbide tips on a saw blade; the base is cheapo steel and the important part is the higher priced material.
 
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Old 06-26-12, 07:36 PM
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soooo.... there is no bevel to hold cam lobe in place on the shaft?
 
  #21  
Old 06-27-12, 03:46 AM
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Automotive engineers aren't the brightest bulbs in the pack (apologies). They have a certain amount of space to put things cheaply. Remember the 1966 Chevy Nova with a V8? It fit, but you couldn't replace #8 plug without lifting the engine 6". Surely they could have thought of a keyway or, as ukrbyk said a bevel or offset to hold the lobe in place.
 
  #22  
Old 06-29-12, 03:01 PM
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Time for ScannerDanner on Youtube

Check out ScannerDanner on YouTube. HE would find it.

My guess is a bad connection somewhere. Need to put the Verus or Pico on it...
 
  #23  
Old 07-12-12, 04:55 PM
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I've helped some of the engineers who designed this shaft. If you haven't seen such a camshaft, it's essentially individual lobes with splines in the ID, A tube is swaged from the inside onto the splines of the lobes. This allows for individual lobes to be manufactured with material that is extremely wear resistant, yet the tube is soft for machining the journals and it makes for a lightweight assembly.

The lobes I've seen are made of powder metal and hardened. Changing the cam lobe profile for production is a cinch compared with cast or forged cams.
 
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Old 07-13-12, 04:55 AM
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RFlagg, you didn't read the entire thread?

Splines would make sense as that would prevent slippage; the stumper question would seem to indicate no anti-slip provision.
 
  #25  
Old 07-20-12, 10:04 PM
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Just saw this topic and it is interesting. Ah yes, progress or some bean counter has to justify his job!
 
  #26  
Old 07-25-12, 07:09 PM
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I just read the "V8 in a Chevy II post".

I remember helping a friend on an old Chrysler with the big block V8. One of the plugs near the firewall was just about impossible to get to so we cut a hole in the inner fender well!

I had an older Nissan Pathfinder with a V6 that took up the whole engine compartment. Trying to change the oil filter would require an unusually long arm to reach it from the top of the engine compartment. It was not reachable from under the car as it was just above the starter and it's hot lead! I finally figured out that turning the steering wheel all the way to the left allowed me to reach the filter through the wheel well! That was the only car I ever had that needed the battery to be disconnected to change the oil!
 
  #27  
Old 07-29-12, 09:00 PM
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umm hold up a minute how could a cam lobe be off enough to cause a consent miss, but not though off compression?
 
  #28  
Old 07-30-12, 04:42 AM
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Beats me, I was only repeating the info from the article. I thought it a bit odd when I read it.
 
  #29  
Old 07-31-12, 11:05 AM
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In keeping with the "engine-too-big-for-engine-compartment" theme, I presently own a 1989 Dakota with a 2.5 OHC 4cyl....no power steering. A good sized man...or woman...could easily sit on the inner fender well and work on this thing...like the "old days", before the hoses, wires, sensors, etc. (Vehicles certainly do last a lot longer now for sure).
 
  #30  
Old 08-09-12, 06:18 AM
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I had an Oldsmobile one time that had a lobe wiped off but the comp was still within limits.
 
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