1998 Chevy Tahoe only 2 plugs fouled

Tiny
MAXXMAN04
  • MEMBER
  • 1998 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 165,000 MILES
Did a FULL tuneup with quality parts, new fuel pump, new fuel injection "spider" unit (the new mfi conversion for the vortec motors), new upper gaskets. When I bought rig few months ago, #3 and #5 cylinder plugs had ash deposits on them. Rest of plugs were fine. Still had a rough idle problem, changed fuel pump, checked plugs. New plugs were fine except #3 and #5 again, so changed all 8 again. Bought the mfi conversion injection unit, idled and ran alot better, but still had a slight miss. Checked plugs. #3 and #5 again ashed. Replaced just those two as rest were good. Drove 250 miles, with the last 50 or so motor ran very rough. Heavy miss, stuttering. Pulled plugs next morning, again #3 and #5 fouled up after only 250 miles. Ran compression test, all cylinders 160-170 except #3 at 120. Did not do wet compression as I have never ever seen any smoke whatsoever at any time, thus assuming that there is no blow by on rings. Pulled head off, head gasket SEEMS ok, can't see any indication that head gasket was the problem. Did find quite a bit of carbon deposits on top of #3 and #5 pistons as well as in the combustion chambers. #1 and #7 look great, really clean. Valves in 3 and 5 do have carbon build up but do not appear burnt or cracked. So my question is, what would cause the plugs to keep fouling in just 3 and 5? Is it possible that head gasket could have been issue, but just can't really tell? Is it possible that maybe valve guide seals are leaking? Is it possible to have the guides leak without actually burning oil? Anything else I should check or look for?
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Friday, February 19th, 2010 AT 9:56 PM

12 Replies

Tiny
MERLIN2021
  • EXPERT
I can tell you if you still have the heads off, tip them upside down and fill them with alcohol, if it leaks out, valves or seats need reshaping. Straight edge the heads and block to check for warpage. Migh be a good idea to send heads to a machine shop, they will check valve springs and guides, and plane it flat if needed, they will also check for small cracks that you might not be able to see without special test equipment.
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Saturday, February 20th, 2010 AT 8:37 AM
Tiny
MAXXMAN04
  • MEMBER
Thanks merlin. Sorry for delay. New addition to family. Soon as I can, i'll check heads with method you suggested. Hoping it is just valve stem seals, tho it seems odd I don't burn oil. But I guess it's possible.
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Tuesday, February 23rd, 2010 AT 5:36 PM
Tiny
MERLIN2021
  • EXPERT
Could be seals, but I did say guides, or seats.
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Wednesday, February 24th, 2010 AT 12:51 PM
Tiny
MAXXMAN04
  • MEMBER
Replaced drivers side head gasket, now it smokes heavy. Started motor up, heavy white/blue tint smoke pouring out. I know white is usually coolant, blue is oil, but with a new head gasket, it shouldn't smoke. Should it? Shop SAID head was ok. Maybe they were wrong? Could it be cracked head, cracked block, or just excess water burning off? Only let it run for few minutes, to avoid damage. It seemed to run and idle fine. What might it be?
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Monday, March 1st, 2010 AT 4:34 PM
Tiny
MERLIN2021
  • EXPERT
You followed the directions on the head gasket? Some need sealnt applied, most do not. Did you use a chemical decarbon solution on the pistons? And some require a sealant on some of the head bolts? Some want light oil, some dry, and this will make a hugh difference in the torque! Try pulling 3 and 5 plugs again and check em out. I sent you a PDF on installing the heads, read it and see if this is how you did the job, check email! Did you install new valve stem seals? This is the proper way...


http://www.2carpros.com/forum/automotive_pictures/62217_tahoeguides_1.jpg

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Monday, March 1st, 2010 AT 4:47 PM
Tiny
MAXXMAN04
  • MEMBER
Thanks again merlin for all your help. I did follow instructions for putting head gasket on. I have since taken head back off, sent it to a better shop. No cracks, good. They think that #3 exhaust valve may not be seating centered. Gonna do seats, valve grind, check for cracks, pressure test, send it back to me. Meantime, i'm gonna pull the other head, have it checked, tho the numbers were good. This rig has to go cross country soon, I feel better knowing it's done. Fingers crossed that it's just the valve causing my low compression. New stem seals will be installed to stop oil usage. I will update with results soon as it's all done. Thank you again greatly merlin for all your help.
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Tuesday, March 2nd, 2010 AT 8:36 PM
Tiny
MERLIN2021
  • EXPERT
Have that other head sent to the shop too! Good luck, let me know.
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Wednesday, March 3rd, 2010 AT 2:26 AM
Tiny
MAXXMAN04
  • MEMBER
Heads are almost ready to go on. I've heard conflicting stories about using oil and sealant on bolts. I have new head bolts for both sides that have some type of compound on them already. Should I apply silicone to the water jacket bolts still? Should I apply oil to any other bolts? Which bolts are considered the "blind" ones? Thanks again for all help.
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Saturday, March 6th, 2010 AT 11:58 AM
Tiny
MERLIN2021
  • EXPERT
Installation (4.3L, 5.0L & 5.7L)

Page 1 of 1
Clean gasket surfaces, bolt threads and bolt holes. Position NEW head gasket on cylinder block. Ensure all holes align. Coat head bolt threads with GM Sealant (1052080). Install cylinder head with bolts finger-tight. Tighten head bolts in sequence to specification. See Fig. 8 - Fig. 10. See TORQUE SPECIFICATIONS. Lubricate the valve tip, rocker arm pivot and push rod socket with a high viscosity oil containing Zinc (1052367) or equivalent. To complete cylinder head installation, reverse removal procedure. Adjust the valves. See VALVE CLEARANCE ADJUSTMENT under
No oil, just sealant on the bolts
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Saturday, March 6th, 2010 AT 4:33 PM
Tiny
MAXXMAN04
  • MEMBER
Thanks again merlin! Got it mostly together. Fingers crossed for tomorrow!
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Saturday, March 6th, 2010 AT 8:17 PM
Tiny
MAXXMAN04
  • MEMBER
Thank you merlin for all your help. Both heads got redone, followed install to the t, got all hooked up. She runs great now, no stumbling, no codes, all is good. Thank you again for all your help.
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Thursday, March 11th, 2010 AT 12:30 PM
Tiny
MERLIN2021
  • EXPERT
Your welcome!
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Thursday, March 11th, 2010 AT 12:53 PM

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