Bent Intake Valve?

[gunrac]

94' 5.0L TBI, Original 82,000 mi. Dad bought the truck new.
My bad for not making a more thorough inspection, I know, but it is, what it is and could use a bit of help confirming my suspicions.

Recently. I made another run from Oh. to Tx. "1,200 mi." Rain all the way. Approx. 1/2 down, the muffler blew a 3"x4" hole on top, toward the rear of the muffler. Muffler was only 3 mo. old at best. I pulled over, yes it was loud and idle was very rough. Also there was a light dull knock, I knew right off it was not a lifter tap and didn't make the loud noise I've heard w/a rod. I needed to make another 12 mi. to get off freeway. As the RPM's built up, the engine smoothed out, an seemingly, was running great, other then the noisy muffler. I also never seen a smoke trail either.

 Pulled in an got fuel, idle was still rough. Checking my fluids, water level was fine, temp. was 190*, oil pressure was a bit lower then usual, maybe 25 PSI at a barely running idle. I could tell it was running a bit rich, at idle. I was concerned, but hit the road again. At a nice cruisin speed, oil was running the normal 50+ PSI. I still needed to run another 500 mi. I made 2 more fuel stops after that, nothing had changed and I did make it to Temple.

Thinking valve all along, I still had to eliminate the obvious with what little tools I had. Tune up.  Plugs, rotor, cap and after a bit of searching on here, I changed out the  Idle Air Control (IAC) valve.

K' I seen how it happened, but still unsure of the complete damage it caused. #7 plug had burned or broken off the  electrode at the bend. The plugs were all in bad shape, but no oil on any of them. I had NO compression on #7 and only 90 PSI. on #5. This is what makes me think it is the intake valve has suffered the damage. I think I read that #5 and #7 intake valve's work   together. Thinking this may be why I'm losing compression on #5, not sure. I also have very good spark on both cylnders in question.

I have not located a leak down tester to use, I may end up having to buy one........Please chime in for other possibility's that should be addressed......THX

[Stewart G Griffin]

i'm thinking the pushrod will bend before the valve------maybe.

Have you removed the valve covers?

[gunrac]

i'm thinking the pushrod will bend before the valve------maybe.

Have you removed the valve covers?

I'm not that lucky to catch that easy of a fix. I'll be gettin into it over the weekend. Local machine shop is not expecting the head till 1st. of next week, if need to be.

[bd]

Can you post a pic of the spark plugs in order by cylinder - especially #5 & #7, but prefer all of them if you can.  Plan on performing a cylinder leak-down test to focus your diagnosis, before teardown.  In the meantime, remove the left valve cover and inspect for bent/loose pushrods and/or valves hanging open, as suggested. 

Your compression test indicates that #7 is the cylinder with possible valve issues.  The "dull knock" could be a piece of spark plug embedded in the crown of the piston or a valve kissing the crown.  Low compression on cylinder 5 also maybe due to poor valve sealing, but could just as easily result from compression pushing past the head gasket bridge between #5 and #7.  Since cylinders 5 and 7 don't share a common plane of the intake manifold, it is unlikely that debris from #7 ricocheted into #5.  Essentially, you might have more than one problem.  Ultimately, however, you will need to pull the cylinder head to see exactly what occurred and determine the extent of damage.  Because of the accumulated mileage, it would be prudent to check valve lift/cam wear while you are at it.

[gunrac]

Can you post a pic of the spark plugs in order by cylinder - especially #5 & #7, but prefer all of them if you can.  Plan on performing a cylinder leak-down test to focus your diagnosis, before teardown.  In the meantime, remove the left valve cover and inspect for bent/loose pushrods and/or valves hanging open, as suggested. 

Your compression test indicates that #7 is the cylinder with possible valve issues.  The "dull knock" could be a piece of spark plug embedded in the crown of the piston or a valve kissing the crown.  Low compression on cylinder 5 also maybe due to poor valve sealing, but could just as easily result from compression pushing past the head gasket bridge between #5 and #7.  Since cylinders 5 and 7 don't share a common plane of the intake manifold, it is unlikely that debris from #7 ricocheted into #5.  Essentially, you might have more than one problem.  Ultimately, however, you will need to pull the cylinder head to see exactly what occurred and determine the extent of damage.  Because of the accumulated mileage, it would be prudent to check valve lift/cam wear while you are at it.

bd.....Plugs are gone. As mentioned, the break was in the center of the bend on #7. The other plugs were all dry with heavy brownish-gray corrosion. There was still a gap, but in very bad condition. I will go ahead and pull cover tomorrow and have a look. Will update.

[bd]

Was the "heavy brownish-gray corrosion" a fluffy, sort of glazed appearing coke buildup coating the insulators and electrodes?  Any idea of how many miles were on the plugs?  You weren't clear on this one point - was the ground electrode burned/eroded away or physically broken off?  Any other evidence that the electrodes were hammered, such as electrode dimpling or a fractured/shattered insulator?

[gunrac]

Was the "heavy brownish-gray corrosion" a fluffy, sort of glazed appearing coke buildup coating the insulators and electrodes?  Any idea of how many miles were on the plugs?  You weren't clear on this one point - was the ground electrode burned/eroded away or physically broken off?  Any other evidence that the electrodes were hammered, such as electrode dimpling or a fractured/shattered insulator?

Was the "heavy brownish-gray corrosion" a fluffy, sort of glazed appearing coke buildup coating the insulators and electrodes? YES. The electrode was burnt off, not beat down. {the hook was still there} There was also a couple other plugs that showed heavy deterioration at the same point on the electrode., pretty thin at the bend.

After thinking, these numbers are very accurate, plugs would have had 15,000 mi. installed 3 yr. ago. The truck also set nearly 1 yr. during this period. (cosmetic issue)..
Any other evidence that the electrodes were hammered, such as electrode dimpling or a fractured/shattered insulator? NO. Will admit, I was runnin er' pretty hard until I hit bad weather........seen a lot of 90 mph on several long stretch's, till muffler blew and w/the rough idle. After I felt comfortable that she was gonna finish the trip.....speeds average 70-75mph after the rains slowed down. Even after making a few short trips after being here, the engine still acts an sounds the same as it did when the incident happened.

[gunrac]

i'm thinking the pushrod will bend before the valve------maybe.

Have you removed the valve covers?

Wasn't expecting this........not enough clearance between the front Alt. and PS pump bracket and another bracket that bolts on the back side of head keeping wires and booster hose clear of heat......I'm assuming the PS pump must come off and will also need a puller to remove pulley off, then disassemble. ugh

[gunrac]

pulley was a bit stubborn, but finally gave up, cover is off. looks very clean under it......had to run an lost daylight, will pop push-rods in the morn.

[gunrac]

#7 is far right

[bd]

Opinion:  The spark plugs are running much too hot - #7 is torched from detonation, not a simple case of erosion from chamber swirl.  It appears that #7 was not properly seated, which could have caused it to retain excessive heat to the point of preignition and melting.  Nonetheless, switch to AC #CR42TS spark plugs and chase all of the spark plug holes.  Check the base ignition timing with ESC bypassed, check fuel pressure, and check for vacuum leaks.  Check MAP calibration using the information posted in Troubleshooting sensors and how to test in our Technical Pages and use a timing light to verify the injector spray patterns.  You should proceed with a cylinder leak-down test and inspect the valve train.  Are there any trouble codes stored in memory?

[gunrac]

Opinion:  The spark plugs are running much too hot - #7 is torched from detonation, not a simple case of erosion from chamber swirl.  It appears that #7 was not properly seated, which could have caused it to retain excessive heat to the point of preignition and melting.  Nonetheless, switch to AC #CR42TS spark plugs and chase all of the spark plug holes.  Check the base ignition timing with ESC bypassed, check fuel pressure, and check for vacuum leaks.  Check MAP calibration using the information posted in Troubleshooting sensors and how to test in our Technical Pages and use a timing light to verify the injector spray patterns.  You should proceed with a cylinder leak-down test and inspect the valve train.  Are there any trouble codes stored in memory?

Hoping I'm not getting into more then I can handle. I'll go w/it as long as I can.
#5 and #7 push rods, very straight, w/no restriction. Head was very clean, no sludge turds. No broken springs.
Wondering, since the compression gauge never moved on #7, can I just use the compression hose hooked to compressor, to see where leak is going? Or, is it vital that I do the leak down, as to gauge it? Also, do the  AC #CR42TS run a bit cooler? Everything I read says #CR43TS. Curios.

 I'll be reading into your other suggestions, as I have little to no clue about most of it. I don't mind spending a few bucks to get this truck up in good running condition. Providing it's fees able. I don't want to get buried into a lot of specialty tools that may go years before I use them again.

Quotes I got was 1000. to go thru both heads and 600. for the 1 in question. Probably not real hateful, if I was positive it would stop there. I'm fairly certain I can tear down an remove the head and reassemble.
Went thru exhaust manifold, my biggest worry, all the bolts broke loose. Time I have, just knowledge in the finer tuning, is pretty weak.
THX for all the help fella's.......Ron        Keep it coming, if you would

[gunrac]

hit  #1   #5    #7........no leak off on 1.........5 blew some air thru backside of TBI.......on 7, air flat busted out thru TBI.......will hit the rest this afternoon, if it doesn't rain

[bd]

In general, the better approach to a solution is to figure out what went wrong and why, before dumping money into a "blind" repair.  Invest only what is minimally necessary to determine what happened and its resolution.  Discovering after-the-fact that you prematurely invested in a bottomless money pit is no fun when you wake up to being hopelessly committed and unwittingly trapped into a repair that seemingly has no end.  Hence, my advice is to make as complete a survey of the situation as reasonable, so you can remain in control and manage your costs.

Reading the plugs:
Spark plugs cool primarily by transferring heat to the cylinder head casting where the heat, in turn, can be absorbed by the coolant and, ultimately, rejected to atmosphere.  Referring to the previous image, there is visible evidence that the #7 spark plug wasn't properly tightened against its seat (look at the narrow witness mark at the top of the taper and compare it to the witness marks on the adjoining spark plugs).  That reduced area of contact functions like a thermal dam to prevent the spark plug from cooling.  Consequently, the spark plug continues to absorb heat to a maximum limit that it cannot shed.  As a result, its electrodes progressively melt and burn.  Unfortunately, the excessive concentration of heat at the end of the spark plug invites detonation.  Detonation can be grossly destructive to an engine, breaking valves, pistons, rings, cylinder walls and hammering rod bearings.  This potential damage is where the leak down test that you are performing comes in - to help determine the upper cylinder condition and the extent of damage before teardown.  Since you already know the engine has low compression, a formal leak down test is unnecessary.  Injecting 40 - 80 PSI of air into the cylinder as you are doing should be adequate to determine how the cylinder is compromised.  I suspect something along the line of a cracked/burned intake valve in #7 and a leaking head gasket bridge between #5 and #7.  Eventually, you will need to remove the cylinder head.

Supplemental clues pointing to the spark plugs running too hot is the absence of color change from light to dark in the radii of the ground electrodes.  They are light in color all the way to their intersections with their bases.  Generally, the ideal spark plug temperature range will produce an abrupt color change from light to dark, mid-radius of the ground electrode.  In addition, although sometimes indicative of excessive combustion temperatures and running slightly lean, the white color of the spark plug insulators in your engine, in fact, borders between significant and circumstantial.  A white insulator in itself is not alarming unless it also appears blistered and/or fractured.  But with 15,000 miles of use, I expect to see a light coating of modifier deposits, which are largely absent from the spark plugs in the image.  To help compensate for higher spark plug temperatures, the CR42TS run cooler than the CR43TS and should help suppress chronic light preignition. 

Chasing the spark plug holes will help ensure that the spark plugs properly seat in the heads for optimal heat transfer.  While verifying correct ignition timing simply ensures that the timing isn't working against you by exacerbating preignition.  Checking the fuel pressure, injector spray patterns, vacuum leaks and MAP calibration are simply precautions against running too lean once the engine is placed back into service.  Under the circumstances, however, checking for stored trouble codes is fundamental to your diagnosis.

[gunrac]

Thx for your support Rich......ideally I'm thinking of gettin the heads off, rebuilding as  needed, then start going thru  the ignition, timing cycle......thinking, while I'm down that far, will open up front end an contemplate on replacing gear an chain. Did Chevy still start with nylon gear in 94'? In addition, I'll go over cam an lifters..........If u have a moment  to comment.......throw me your best scenario after head job, and or before as needed........need help
Thx......Ron