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2008 6.2 No Compression in two cylinders


mbfireboat

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My 2008 Yukon Denali with 105K miles suddenly started running really bad this week. The traction control/stabilitrac light came on at the same time.

I took it to a local shop which said I need to take it to a dealer. They felt possibly it was a bad fuel pump module (which has physical damage) and a new one would have to be programmed by the dealer.

I drove it a few miles to Williamson Cadillac here in Miami. The service advisor called me the next day and said that diagnostics points to no compression in cylinders in 2 and 4. He said that he has seen this several times before with the 6.2 where it is a broken valve spring. However, it will be a week before they can fully check out the engine.

I have always cared for my Yukon with regular maintenance and do not drive it hard.

Obviously the engine is out of warranty but I was wondering how big of an issue is the broken valve and/or spring with the non-AFM 6.2 engine?

I haven't seen much on the internet as everything seems to be related to the AFM engines.

I am hoping it is just a simple valve spring replacement but I am aware that if a valve dropped and hit a piston, I am looking at a new engine. I'll keep you guys posted as I find out more. Thanks.

 

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Extremeley easy to change a valve spring, without using rope. Take your compression tester adaptor, screw into plug hole, loosen both rockers so valves are not being held open, and connect air line to adaptor. Quality compression testers have a standard air line fitting on the adaptor.

 

The only time I would expect to see a stock engine have a valve spring fail by breaking is on first run in. A defect that causes a break will be in manufacturing, and will show up right away. Stock valve springs are one of those parts that is not where there is any money to save. Cost per failure is far too high.

Yep - that's how I was taught. Much easier than feeding a dirty rope into #7 & #8 ...

 

I agree with that failure pattern you described, however, we used to run cars and trucks for hundreds of thousands of miles, and I've worked on cars with hundreds of thousands on them ... and never seen a valve spring break on a stock engine - every one I saw that broke had a big, lumpy cam. Not to say that it's impossible, but it just seems to happen much more these days than I ever remember it happening. I would expect one to break at 250 -300, or 400 -500k miles ... but 100k these days? There's just something wrong with that ....

 

So my question is ... why did valve springs last forever in vehicles that were around when we were kids, and now we're seeing failures WELL below 200k miles? New cars have aggressive camshafts? We know that's not true with today's emissions standards, and how smooth (usually ... but that's another topic for another day!) they idle ...

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Good stuff Doug. :thumbs:

 

Yeah, that's the main reason I've always been a big Edelbrock fan - cheap, and, easy & quick to work on. One screw for each metering rod, and your in. Whole top comes off for float adjustment in less than a minute. I put a 500 CFM on the '00 Jimmy engine - thing runs great, although a 500 is still too big for that engine. Throttle response is awesome.

 

Being used to Eldelbrocks, the first time i got into a Quadrajet, I was saying ..WOAH .. WTF ... :lol:

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When did they stop using the wheel sensors to detect wheel speed difference (as in spinning)? Can't see how monitoriing the tach feed will ever show wheel slippage when the vehicle has a torque converter that is not locked up.

I misread the post thinking he meant the traction control was turning on, not a TC fault condition.

 

I also poorly worded my original post. The tach sensors at each wheel were originally used only for ABS but are now being used for traction control. I meant the ABS tach sensors at each wheel send data back to the PCM for traction controls.

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Yep - that's how I was taught. Much easier than feeding a dirty rope into #7 & #8 ...

 

I agree with that failure pattern you described, however, we used to run cars and trucks for hundreds of thousands of miles, and I've worked on cars with hundreds of thousands on them ... and never seen a valve spring break on a stock engine - every one I saw that broke had a big, lumpy cam. Not to say that it's impossible, but it just seems to happen much more these days than I ever remember it happening. I would expect one to break at 250 -300, or 400 -500k miles ... but 100k these days? There's just something wrong with that ....

 

So my question is ... why did valve springs last forever in vehicles that were around when we were kids, and now we're seeing failures WELL below 200k miles? New cars have aggressive camshafts? We know that's not true with today's emissions standards, and how smooth (usually ... but that's another topic for another day!) they idle ...

 

Anyone that spent anytime working in a Chrysler shop in the 60's, 70's and 80's learned how to change valve seals in the 383-440 engine using this method, along with pulling the oil pan to retrieve all the pieces of the old broken up valve seals from inside the oil pickup tube.

 

Operating temps are much higher now than they were before emissions were invented. The changes to engines have also taken a toll on some parts. Engineers have tried to reduce the weight of all internal engine parts to help reduce friction, so the metal used in springs are of a different composition. They are also revving these engines higher than they ever did before. Cam profiles are a fair bit more aggressive now as well. Lift and duration may be lower than aftermarket, but with roller cams and lifters, the ramps can be more aggressive.

 

I worked at Cummins OER a few years ago in their rebuilding plant(the place that made the Chrysler crate performance engines) and would spend one day every month or so inspecting and measuring valve springs. Also spent couple of days every month or so disassembling core cylinder heads(everything from original style hemi to 1.9L VW TDH diesels). Those two jobs were about the worst jobs, so they spread the work around. Near as I can recall, the only time I would see an issue with a spring was when it was completely missing. Almost always due to either keepers failing, or popping the head off of the valve. There was one job that someone had to visually inspect every spring for any nicks or scratches in the wire. Spring was tossed if there were any marks on them that actually moved metal.

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First, those older vehicle would need rebuilding of the carbs around the 80k where EFI allows for 300K+. Then the cam would be junk around the 100K mark because the exhaust lobe was gone and the motor wouldn't shut off for a minute or two. The timing events might have been more ideal, but the were low lift at slow rates. The motors didn't rev up so, you could use a suspension spring on the valves, most diesels can still do this with 3,500 max rpm. The way you make torque is valve velocity and that is why the overhead cam motors need more revs or forced induction. So, the springs are compressed more often (higher rpms) at a faster rate (more aggressive ramp rates thanks to roller lifters) on refined springs (to ensure valve train can keep up with the revs) and they stay on motors that run up to 3 times as long without being serviced. The Beehive springs are a great concept as they do work better, but do have more failures so they have to be quality parts. Broke the first 3 variations of inCompetent Cams attempts and won't run them again. If it's not a GM beehive then it has to be from PAC or some other serious quality part or I won't use them. Mostly just run updated old school style doubles on anything above .550 because they never have problems. I've built about 100 motors with just little .550 lift cams, so the GM LS2 yellow and GM LS3 blue springs and not had one issue. GM however has built (guess) 10,000 to each of mine and that means they can have a lower percent of failure and it will be noticed by the internet as it pass dirty laundry faster than any real info.

 

You would think that overhead cams wouldn't have issues since they can be aggressive on the ramps, but I've seen it on stock Fords. Find it funny when Ford guys call the push rod motor old and out dated compared to their dual overhead cam motors since the first one was the 1921 Duesenberg with the straight 8 engine.

 

First DOHC car was a 1912 Peugeot, and Duesenberg DOHC did not appear until 1928. You have the logic reversed though in regards to rpm requirements. DOHC's main advantage is that they can rev higher than a cam in block design. This is simply due to simple layout, with far fewer parts having to start and stop while engine is running. All that weight in the lifter, push rod, rocker arm, and valve train all add together and will limit engine speed because they cannot stop the parts fast enough for them to change direction. OHC typically has cam on follower. Only two parts have to change direction when engine is running, assuming they are using a hydraulic follower. A main advantage to overhead cam is you can control valve action a lot easier, and it reduces frictional losses. I have yet to hear a Ford guy start a conversation by saying push rod engine is outdated. Need only look at NASCAR to see a cam in block 358 cu inch engine put out over 800 horse power to see that push rod engines are not dead yet. They also run those engines over 9000 rpm for 500 miles, and it is still running at the end, and will likely be run a few more times.

 

This sort of a chicken and egg story about what came first. The reduced number of parts, and weight reduction allowed manufacturers to rev engines higher, and that gives you a higher HP number(for some reason consumers are brain washed into thinking HP is real). Early roller cams used a rev kit, that added another spring to ensure that the roller lifter would stay in contact with the camshaft. Without that rev kit, it was not hard to get the pistons to aid in closing the valves due to roller lifter floating off of the camshaft lobe instead of changing direction to allow the valve to close. They rev the engine higher with DOHC because they can, not because they have to.

 

Those engines that were wiping out cam lobes on number 5 cylinder (usually it was number 5 cylinder) were usually the 305 Chev engine. There were a couple of other GM engines that were prone to this as well.

 

You are confused when it comes to failure rate numbers. Just because GM builds more engines than you does not mean they have a lower failure rate. If CompCams has a failure rate of one in a thousand, it is always one in a thousand, regardless of number of engines built. You can build a thousand and have one failure, GM can make 10 thousand and will have 10 times the number of failures you had. The rate is the same. That is why they use rates in statistics. It makes it all relative.

 

Intake velocity is what helps build torque. And that has little to do with "valve velocity". Intake velocity is important due to the ability to get more air into the cylinder when it is at a high velocity. The faster the engine runs, the less time there is to fill the cylinder with air. Long duration, and high lift helps overcome the time open issue. This is all basic engine 101 stuff. BTW, the reason for the double spring is simply due inherant spring resonance at about 6k rpm. The internal second spring on stock engines is usually a damper spring that will help control the outer spring from resonating.

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The L92 did have some valve drop issues at one point, but didn't hear a lot of it happening. bobejones is right, if it was not running very rough at idle then you were not down two holes and you need to make sure your not getting screwed.

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If GM is making 100k-mile valve springs now, I'm putting my truck up for sale TOMORROW. :throwup:

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First, those older vehicle would need rebuilding of the carbs around the 80k where EFI allows for 300K+. Then the cam would be junk around the 100K mark because the exhaust lobe was gone and the motor wouldn't shut off for a minute or two. The timing events might have been more ideal, but the were low lift at slow rates. The motors didn't rev up so, you could use a suspension spring on the valves, most diesels can still do this with 3,500 max rpm. The way you make torque is valve velocity and that is why the overhead cam motors need more revs or forced induction. So, the springs are compressed more often (higher rpms) at a faster rate (more aggressive ramp rates thanks to roller lifters) on refined springs (to ensure valve train can keep up with the revs) and they stay on motors that run up to 3 times as long without being serviced. The Beehive springs are a great concept as they do work better, but do have more failures so they have to be quality parts. Broke the first 3 variations of inCompetent Cams attempts and won't run them again. If it's not a GM beehive then it has to be from PAC or some other serious quality part or I won't use them. Mostly just run updated old school style doubles on anything above .550 because they never have problems. I've built about 100 motors with just little .550 lift cams, so the GM LS2 yellow and GM LS3 blue springs and not had one issue. GM however has built (guess) 10,000 to each of mine and that means they can have a lower percent of failure and it will be noticed by the internet as it pass dirty laundry faster than any real info.

 

You would think that overhead cams wouldn't have issues since they can be aggressive on the ramps, but I've seen it on stock Fords. Find it funny when Ford guys call the push rod motor old and out dated compared to their dual overhead cam motors since the first one was the 1921 Duesenberg with the straight 8 engine.

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Loss of power coupled with traction light??? Something smells off in the loss of compression diagnosis. ABS sensors use a tach feed back to the PCM to determine wheel slip and retard timing until slip condition resolves.

 

If the you are down on 2 cylinders, the engine will run VERY rough. Not just loss of power, but ROUGH!!! Like shaking because the engine is no longer balanced. You will also have abnormal sounds from the engine.

 

If your engine idles smooth, go find another mechanic and tell that dealer to refund you for wasting your time.

 

Also, you can run a leakdown test on those cylinders at TDC for those cylinders to determine where the leak is. Not rocket science. [/quote

 

 

Reread his original post, and yes for whatever reason when ecm picks up misfires it shuts traction control down, tcc engagement and some other functions to somewhat "mask" horrible drivability.

 

 

Sent from my iPhone using Tapatalk

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Two cylinders cannot lose compression from one broken valve spring. Each cylinder has 2 valve springs, neither of which is shared with another cylinder.

 

Personally I would be asking which valve spring was broken? Along with show me the broken spring. Should be very obvious with the valve cover removed. Would also want to see why the cylinder nexxt to it was also showing 0psi compression. What was the cause of that? Given todays technology, there should be pics available showing the damage.

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First, those older vehicle would need rebuilding of the carbs around the 80k where EFI allows for 300K+. Then the cam would be junk around the 100K mark because the exhaust lobe was gone and the motor wouldn't shut off for a minute or two.

 

...............

 

80k? LOL!! Where the hell did you pull that number from?? Maybe in the early 80's just prior to FI - those carbs were bandaids for a problem that didn't exist .. but that's another topic for another day. Even recently I've had Edelbrock carburetors 12 - 20 years old that needed NOTHING to run right. I've run Rochester Quadrajets (and they had the nickname QuadraJUNK back in the day too ... go figure) that were OVER 40 years old with who knows how many miles on them, than ran fine ... aside from vapor lock when hot. Just hold pedal to the floor on a hot summer day, and it would start up within 10 seconds. With maintenance those old V8's will last every bit as long as a modern engine, and probably longer. Those cars/trucks didn't burn oil and tick right off the showroom floor either ...

 

Doug is right about the 305 too - they closer you get to today, the more you start to see failure prone components. It's been a gradual decline. The 305 was the economy engine - the 350 rarely saw issues like that, that weren't due to lack of maintenance.

 

FYI my family has personally run carbed vehicles WELL OVER 150k miles WITHOUT a SINGLE failure back in the day. That's towing tag-along campers too. NEVER used or leaked a drop of oil either. Oil changes, points/condenser adjustment/replacement when needed, cap/rotor replacement, spark plugs, wires, and air filters. All those vehicles were sold and continued on long after we were finished with them. It wasn't until my ol' man traded his '76 Torino for a '83 Escort did the problems start. That car had 3 COMPLETE carburetors on it before it hit 40k miles. By the mid 70's, it was common knowledge that the smaller cars were typically unreliable, and the bigger luxury cars were more reliable - that's just how it was. By the late 70's into the 80's, government meddling had turned that into a hit or miss affair.

 

I know a guy that got well over 300k miles on the ORIGINAL Chrysler slant 6 in Dodge Dart - carb & points. Thing had hit everything but the lottery, but was still running and driving when it was finally retired by a telephone pole that jumped out in front of it ... :lol:

 

Government meddling has caused just as many reliability issues as greedy manufacturing practices. Remember - the entire WORLD was getting by with carburetors and POINTS ignition for 75+ years before solid state ignitions, and 85+ years before fuel injection. Just because the only carbureted cars you've ever seen are now 30 -40 + years old, neglected, and worn out, doesn't mean that's how they were when they were new. American cars USED to be the envy of the world. We built the BEST. Thanks to the government, the rest of the world has had plenty of opportunity to play catch-up - decades, in fact.

 

Prior to '73 cars were all built like tanks - that's why most of them are still here 42 years later - take a browse on eBay for pre-'73 vehicles. People are too spoiled now to deal with adjusting points or even waiting for a car to warm up. They'd melt down! There was a time for DECADES where this was just the way it was. Even in those days there were plenty of guys that didn't get it. Our family never had a problem. You checked them at certain intervals, and replaced them when needed - it took a half hour tops to do a dual point Ford with the distributor right out front, AND it didn't cost an arm and a leg.

 

Don't get me wrong - I'm not 100% against FI and computers -- I AM 100% against UNRELIABLE FI & computers. So far in that respect I can't complain about my truck .... but it's only got 75k miles on it, so I should hope the hell not!

 

Ford got it right in '86 with their sequential fuel injection in the Crown Vic/Grand Marquis, trucks, and the Mustang. It's well known that those injectors AND fuel pumps will run WELL NORTH of 300k miles. Lets see any of our vehicles today pull that one off ....

 

It can be done, if they would just build them correctly ....

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Valve spring do fail from time to time. Even the insanely expensive ones on top fuel motors. The valve springs are made in Germany and they are the only not expensive beehive spring I'll put on a motor I build.

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Correct, when the ecm sets a code for misfiring, it also sends a message to abs module And will set the traction light on.

 

A broken valve spring is obviously a very easy thing to visually see, so if you doubt the dealer get them to show you. Broken springs are not uncommon. It's a moving part, parts fail, weather you maintain or not. I would be hoping all that is wrong is the spring, will cost you some labor but atleast it shouldn't be any real expensive parts involved.

 

Good luck, let us know what they come up with.

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