SOLVED! Vortec 5.7 - Cyl 8 Misfire - Valve Adjustment?

shovenose

Well-Known Member
#1
Just picked up a 97 Suburban. Many issues, first thing I have to take care of is the blinking/on check engine light. P0308: cylinder 8 misfire. You can really feel it, especially at idle. I'd say it's a dead miss (as in, it feels like that cylinder is doing nothing)...

Anyway, guy I bought it off of says his mechanic did a tune up and it didn't help, and thinks the problem is the valve adjustment.

I'm going to do a compression test on Monday, to see if the problem really is mechanical. If it is, any idea whether a misfire could be caused by a valve adjustment problem, and if so, I've never adjusted valves before... if compression is fine then that rules out the valves, right, and I should focus on fuel or spark.

Thanks for any input!
 
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Reprise

Lifetime VIP Supporter
#2
You may find the following helpful; @MRRSM posted it in my thread from yesterday re: rough idle...
http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/how-to-troubleshoot-a-misfire-1
Yes, yours is a little older, but except for yours not being coil-near-plug, the principles are largely the same - and, yes, once spark & fuel are ruled out, the conversation does turn to things mechanical.

If it does turn out to be the valves, I'll guess they're too loose, rather than too tight. Of course, yours could just be a loose plug wire, as mine turned out to be!
 
#3
Valves are non-adjustable hydraulic. Usual suspects for misfires in order of probability and expense:

1. Dead coil/plug wire/spark plug
2. loose spark plug
3. wiring to coil
4. fuel injector/wiring to it
5. loss of compression due to burnt valve, dead lifter, damaged rocker, blown piston
 

littleblazer

Gold Supporter
#4
You'd hear rocker clatter if the valve needed to be adjusted...
 
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shovenose

shovenose

Well-Known Member
#5
You'd hear rocker clatter if the valve needed to be adjusted...
So now I'm confused. Is it possible it's a valve adjustment issue? I'm trying to understand whether or not this engine (Vortec 5.7) has adjustable valves or not.

The engine doesn't make a ton of abnormal noise when running, but I would say it is ever so slightly noisier than other (3+) Vortec 5.7s I've owned and about as noisy as the (4?) Carbureted or TBI 5.0/5.7s I've owned. Just by doing a "compression test by ear" as in cranking the engine with gas pedal all the way down it doesn't sound great but also my battery was pretty much dead so only cranked for a few seconds before I had to give up. Charging battery now.

Tomorrow the plan is to pull all the plugs for visual inspection of plugs and wires, do a dry and wet compression test. If the problem is compression but the bottom end is fine (as in, wet compression test is similar to dry) then I could pull the valve cover. While I have the plugs out I do plan to use my borescope to inspect inside of cylinder as best as possible. If I pull the valve cover can I turn the engine on to inspect how valves are working or otherwise check the valves?
 
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littleblazer

Gold Supporter
#6
It is my understanding that the valves on the l31 can be adjusted like a traditional sbc. The ls cannot? I think... you're just adjusting the preload. You know. Loosen until it ticks tighten until it just stops then do your half turn. Unless I missed something on the late model vortecs. I am not that familiar with the mechanicals of them.
 

MRRSM

Lifetime VIP Supporter
#7
EDIT: Unfortunately... It looks like 1999 was the last year for the production line of your Gen I Version of the 5.7L Motor... so while much of the physics described below hold true... YOUR engine DOES sport Solid Base, Hydraulic Lifters and would STILL require only a Single Valve Lash Adjustment per Valve. This requires that you first Rotate the engine Clockwise to allow BOTH Valves to CLOSE so that BOTH Camshaft Lobes (per each cylinder) are on their Base Circles when being adjusted via first loosening the Adjustable Rocker Arm Locking Nut in the Center Post of each of the Rocker Arms and then GRADUALLY tightening down the Locking Nut while turning the Push Rods until they just stop turning...AND STOP TIGHTENING FURTHER! What follows for the amount of tightening after this part is achieved depends upon whether your Service Manual demands 1/4, 1/2, 3/4 or a Full Turn of the Socket starting with the handle set at 12:00 High... and ONLY THAT AMOUNT OF PRE-LOADING SHOULD OCCUR! This process is performed for EACH Pair of Rocker Arms and Push Rods... per All (8) Cylinders.

CAVEAT EMPTOR: RTFM ...AND FOLLOW ALL PROCEDURES TO THE LETTER!

This type work is usually done by Mechanics with a Good Deal of Experience ...because getting this WRONG and causing ANY of the Valves to be Adjusted TOO TIGHT... will cause some of them to remain open as the Pistons arrive at TDC ...effectively bending Valves and Breaking the Valve Stems...and then it is "Bye-Bye Motor". Here is an "Old School Method" on a 327 CID in the same Family technique wise for Adjusting your Hydraulic Valves:


If you are going to attempt this yourself.... you must be very aware of doing the job perfectly for each and every Valve. If you do not feel confident of doing this task.... Try Flushing the Engine as per the Last Video... AND DO NOT TOUCH THE INSIDE OF YOUR ENGINE! Only run the engine with (1) Quart of Flush and use Brand New Inexpensive Organic Oil and Filter for ONLY (5) Five Minutes...at IDLE... Do NOT Race The Engine! After this period... Shut Off the Engine and Replace the Flushing Oil with a HQ Motor Oil to Spec and an HQ Oil Filter and Start the engine to warm it up for a short test drive after the engine has reached the upper operating temperature. This is the 1995 Version of the 5.7L Motor with an intrepid, inexperienced mechanic trying to adjust this engine dynamically... A Very Stupid Thing to Do For ANYONE Without a LOT of Experience... SO THIS IS NOT A RECOMMENDED METHOD... AND YOU SHOULD NOT BE ENCOURAGED TO TRY THIS OUT!! But ..at least you get an idea of what this Gen 1 5.7L Engine looks like... Under The Valve Covers:


These are the General Dynamics of Modern GM V8 Engine Valve Train Oiling:

When the job of installing the Roller Rockers and Push Rods happens... Assuming the Motor is the GM 5.3L Motor OR >... the Camshaft inside of this engine is using neither a Solid, Flat Tappet Lifter nor does it use a Solid Base, Hydraulic Lifter... The Camshaft actuation Profile is designed for Roller Lifter and Roller Rockers and is NOT of an Egg Shaped design with dramatic peaks on each Camshaft Lobe...but it is rather Elliptical...with a gradual incline that mate with a bottom roller bearing surface pinned into the bottom of each lifter. They are oriented squarely by Tappet Guides and with the needle- bearing style rollers mating with the Elliptical contact surfaces. This allow the Roller Rocker Arm Assemblies to run at much higher RPM...with much less contact friction in all contact locations.

Nonetheless... they still have a concave, spring loaded hydraulic plunger on top of each lifter where the Ball Ends of the hollow push rods insert and which must be slightly tightened at the Rocker Arm locations to slightly depress the plungers inside. The lifters get plumped up when the engine oil pressure rises and pushes with enough hydraulic force that the resistance allows for lifter plungers inside to make small squirts of engine oil to get pushed upwards inside of the hollow push rods...and lubricate the Upper Rocker Arm Assembly.

This process of 'pre-loading" the lifters is called, "Adjusting Valve Lash to "0" --> PLUS the Proper Fraction of a Turn " and once this done correctly.. .no further adjustments are needed... nor should they be tightened down any further, The problem of noisy lifters in these engine is that if the Engine Motor Oil gets Dirty or lacks a proper cycle or Regular Oil and oil Filter Changes every 3,000 Miles ...the very small oiling holes drilled into the sides of each Lifter will become plugged up solid...and then the oil which should enter into the lifter body and get squeezed into the push rods...is blocked. Without fresh oil constantly refreshing their 'innards'... the Valve Lash disappears and the Valve Train becomes very noisy and clatters as the Rocker Arms mate-up points with the round upper ball ends of the hollow push rods become loose.

The solution might be as easy as flushing the engine after first Draining out the Old Oil and Changing the Old Oil Filter and using either one (1) quart of Transmission Fluid ...or actual Motor Flush and get the rest filled with Inexpensive, Organic Motor Oil, and then Start and Run the Engine for only (5) Five Minutes at IDLE. This will generally be enough time for the high detergent flush to loosen and purge the Dirty Clogs hiding inside the Oil Galleries and from inside of the Lifter Bodies. This action will allow the hydraulic hollow areas inside of the lifters and push rods to once again become "plumped up" and the Upper Valve Train will Quiet Down once it is being better lubricated.

Briansmobile1 on Youtube has the perfect video that shows you how to do this "Noisy Lifters" Engine Flush:

 
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shovenose

shovenose

Well-Known Member
#8
Hey, thanks for the info - you've scared me out of messing with the valve adjustment :smile: Oil is very dark and nasty in the truck right now, I might give the flush a shot. I have a ton of oil and filters floating around lol.

Today I spent quite some time on the truck. Here was my process:

1. Checked with scantool to be sure CMP retard is set correctly (it is)
2. Checked to be sure all plug wires are hooked up in the right order and go to the right cylinder (all good here)
3. Pulled the plug on cyl8, looks like they used Bosch Iridium (ew), plug had strong fuel odor. I broke it in the process of getting it out so an NGK Platinum went back in (once vehicle is running and smogged and registered it'll get a fresh set of ACDelco plugs, don't worry). Also while I was messing with plugs I used an inline spark tester and spark was present.
4. Compression test on cyl8 showed 180psi. I didn't check any others because the compression tester broke. Oops.
5. used a cheap borescope I had floating around to look inside cyl8. Didn't work very well, i could see only part of the piston, but the part I saw didn't have a hole in it or something.
6. Removed valve cover, started engine, everything looked fine - all the things went up and down with engine running. You know what I mean.
7. Reassembled everything. Symptoms persist.

So, uh, what's next? I'd say it's a bad injector but there was a ton of fuel on the plug and it smells really bad like raw gas when running so I don't think it's a fuel delivery issue?

If it matters, the engine seems to sound fine, no abnormal noises.

If I had to pick what was next I'd get a working compression tester, have a helper, and do a proper compression test (pull all plugs out) and compare the numbers. If that is good then I would do new fuel injection spider... But that's expensive and a lot of work if that's not the problem.
 

littleblazer

Gold Supporter
#9
180 seems a little high to me? You could double check the simple things like checking the firing order. (seems like you have) 8 is passengers side rear right? Only other thing could be a spun bearing. If the plug is wet it is not burning right either. IE too rich. Maybe a leaking injector?
 
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shovenose

shovenose

Well-Known Member
#10
180 seems a little high to me? You could double check the simple things like checking the firing order. (seems like you have) 8 is passengers side rear right? Only other thing could be a spun bearing. If the plug is wet it is not burning right either. IE too rich. Maybe a leaking injector?
ok, i will use a different compression tester and do it right in terms of pulling all the plugs first and then testing each cylinder... any suggestions for a good compression tester that isn't a total pain to use like the rental parts store one or the similar bosch branded ones sold at the parts store?

all plug wires are hooked up in the correct order, that's one of the first things i checked. yeah the cylinder in question is pass. rear

as for a spun bearing, would the vehicle run with no abnormal noises with good oil pressure in that case?
 
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littleblazer

Gold Supporter
#11
ok, i will use a different compression tester and do it right in terms of pulling all the plugs first and then testing each cylinder... any suggestions for a good compression tester that isn't a total pain to use like the rental parts store one or the bosch branded ones sold at the parts store?

all plug wires are hooked up in the correct order, that's one of the first things i checked. yeah the cylinder in question is pass. rear

as for a spun bearing, would the vehicle run with no abnormal noises with good oil pressure in that case?
Our 3500 just ran rough and had no power. Like 40psi at idle with a spun bearing. Allegedly. I started it a few weeks ago and it seemed like a bad injector to me... I'd imagine you'd hear a knock. As for the 180 I thought about it and it could be right. All the 350s I've worked on personally had smog heads and 160 cold was normal.
 
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shovenose

shovenose

Well-Known Member
#12
OTC 5606 any good?
https://www.amazon.com/gp/product/B000R5CPAQ/

Our 3500 just ran rough and had no power. Like 40psi at idle with a spun bearing. Allegedly. I started it a few weeks ago and it seemed like a bad injector to me... I'd imagine you'd hear a knock. As for the 180 I thought about it and it could be right. All the 350s I've worked on personally had smog heads and 160 cold was normal.
It's obviously down on power compared to other Vortec 350s I've owned but it's not bad by any means.
 

littleblazer

Gold Supporter
#13
I mean mine are Macs and matcos that are older than me so I'm not 100 percent. That otc looks like the mac I have. The two piece is nice since you just thread it in then clip the gauge on.
 

MRRSM

Lifetime VIP Supporter
#14
OP... You mentioned seeing or smelling Raw Gas after pulling the Spark Plug(s)... If your engine is NOT using a TBI (Throttle Body Injection) Fueling and/or carburettor set up and sports the "Spider" design of a Fuel Injection System for that series of 5.7L Vortec Engines... like this one:

https://www.summitracing.com/parts/...year/1997/make/chevrolet/model/k1500-suburban

...then be aware that when a Fuel Injector is seriously clogged.... instead of literally atomizing and "misting" the gasoline into the cylinder head intake ports/valves... it will start to spray a straight...stream of fuel... which is NOT as easily mixed with the air ingested through the intake manifold...and which will collect and puddle down inside the cylinder. It will also serve to ruin Oil Lubricity by watering it down after passing the piston rings and invading the oil pan and oil in the crank case.

If you pull the Dipstick and you can smell Raw Fuel there with the oil on the end of it... this is probably happening. Remember... Liquid Gasoline will NOT burn very well ...unless it gets VAPORIZED first. So if the EFIs in that Old Engine are in Real Bad Shape, the description I just gave you could explain why there is so much unburned fuel present inside those cylinders...and perhaps thinning down your Motor Oil, reducing cylinder-to-piston sealing and causing lower compression as a result.
 
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shovenose

shovenose

Well-Known Member
#15
OP... You mentioned seeing or smelling Raw Gas after pulling the Spark Plug(s)... If your engine is NOT using a TBI (Throttle Body Injection) Fueling and/or carburettor set up and sports the "Spider" design of a Fuel Injection System for that series of 5.7L Vortec Engines... like this one:

https://www.summitracing.com/parts/...year/1997/make/chevrolet/model/k1500-suburban

...then be aware that when a Fuel Injector is seriously clogged.... instead of literally atomizing and "misting" the gasoline into the cylinder head intake ports/valves... it will start to spray a straight...stream of fuel... which is NOT as easily mixed with the air ingested through the intake manifold...and which will collect and puddle down inside the cylinder. It will also serve to ruin Oil Lubricity by watering it down after passing the piston rings and invading the oil pan and oil in the crank case.

If you pull the Dipstick and you can smell Raw Fuel there with the oil on the end of it... this is probably happening. Remember... Liquid Gasoline will NOT burn very well ...unless it gets VAPORIZED first. So if the EFIs in that Old Engine are in Real Bad Shape, the description I just gave you could explain why there is so much unburned fuel present inside those cylinders...and perhaps thinninbg down your Motor Oil as well.
Yep, I do have the notoriously unreliable spider injectors, and yes, the oil smelled a little like gas, but not that bad. I guess I need to buy a new injector :'(
 

MRRSM

Lifetime VIP Supporter
#16
As a “Topping Off” to this Important Thread… This video proves that when the Prior Owner of this GM Truck “Just Started Hearing The Valves Ticking...” More than likely… THIS condition had been gradually building up over time; either because he was just being lazy... or because it may have seemed more important to him to squeeze an extra 2,000 to 5,000 Miles out of the Engine Oil. What he failed to realize is that in engines that have teeny-tiny Oiling Holes in their Valve Lifter Bodies… or engines capable of reducing fuel consumption when (4) out of the (8) cylinders shut down via AFM, the Motor Oil is being COOKED to DEATH inside of the Engine Crankcase. Modern Engines have unique problems develop when they are not treated to regular, 3,000 Mile Oil and Oil Filter Changes:


But don’t despair if similarly, your Engine has been “Tick...Tick...Ticking” away under the hood… THIS is the same truck about (4) months later after this VOP performed his very effective Transmission Fluid Clean-Out:


If this were my vehicle… I would have been tempted to use a small Garden Hand Pump Sprayer and after filling the Plastic Tank with pure Kerosene… and with a modified Rubber Stopper-Grommet placed around the Plastic Spray Nozzle… I'd have pumped up the Sprayer and delivered a few quarts of Kerosene sprayed up inside and all over the the Bottom End via the Drain Plug access and then allowed the stuff to sit inside of the Crankcase for an hour or so and then let it all drain out until nothing flowed freely from the Drain Plug Hole. THEN… I would have followed up by using that Transmission Fluid Clean-Out Technique, and finished the job with pouring in some HQ Mobil1 after changing to a HQ Mobil1 Oil Filter. If those clean-out actions did not quiet down the Noisy Lifters after all of that… then nothing else would do it.
 
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shovenose

shovenose

Well-Known Member
#17
Just to update, I replaced the fuel injector assembly with an upgraded spider unit from BWD (not ACDelco, but it's what we sell at work and the employee discount was too good to pass up) and it solved the misfire problem. I have yet to actually drive the Suburban since the steering and brakes need attention and that's not all of it but the misfire and "service engine soon" are gone! So the fuel injector was the issue. Compression tested with the new OTC tool I bought wasn't exactly consistent but good enough for my purposes. Thank you everyone for your help!
 

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