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Motor Mystery for gearheads

rnet

rnet

New member
This is accually an on going problem and I thought I would present it as a mystery game and see if you would have done the same things that I did. Last friday on my way to tug hill towing a 4 place snowmobile trailer the motor started missing going up a steep hill and the service engine soon light came on. Then when I,d crest the hill it would run better and the light would clear. It would do this intermitently the rest of the way to tug hill. (lot of hills) Got gas as I left on sunday to come home and after I gased up it ran fine all the way home, (180 miles) shut off for about a half hour, then started it back up to park the trailer and it started missing again and engine light at idle. What would you do? Here are some of specs; 2002 Chevy Avalanche 8.1 liter with 60,000 miles. Used primarily for towing. Plugs were change about at 40,000 miles (worn out) Always use overdrive and do not use tow haul 12,000 pound towing package, 410 rear. After I get a few answers I will let you know what I did and go on.
 
water in your gas?
cracked spark plug, plug wire ?
gas cap aint on properly ??
pooched fuel injector?
gas filter?
pooched alternator?
02 sensor?
need emission service
 
As we go along I will tell you what I observed so as to throw you the same curve I got and not comment on anyone post who might be close or not so we all have fun tell the end of which I don't know absulutely yet. Ok, since it wore out a set of plugs at 40,000 miles, I went ahead and changed out the plugs and wires (theses are 100,000 mile plugs). Noticed plug # 7 had black hard crust on it. The rest were worn but ok. No luck, still missing. Now I put on the computor reader, it tells me I'm missing at random, clear codes and it comes back # 7 missing. I've spent $110.00 What do you do next?
 
rnet said:
As we go along I will tell you what I observed so as to throw you the same curve I got and not comment on anyone post who might be close or not so we all have fun tell the end of which I don't know absulutely yet. Ok, since it wore out a set of plugs at 40,000 miles, I went ahead and changed out the plugs and wires (theses are 100,000 mile plugs). Noticed plug # 7 had black hard crust on it. The rest were worn but ok. No luck, still missing. Now I put on the computor reader, it tells me I'm missing at random, clear codes and it comes back # 7 missing. I've spent $110.00 What do you do next?
Click to expand...

trade it in on a toyota. At least if the gas pedal sticks you 'll know why:2thumbs:
 
Read thread 'agree or disagree' reply by grumpyBob, that is me. Give you an idea of what went on with my truck. Good thing it was covered by warranty yet. took almost 2 months to get it finished. Parets were hard to get, dealer that worked on it was great.
 
ferno said:
trade it in on a toyota. At least if the gas pedal sticks you 'll know why:2thumbs:
Click to expand...
Does Toyoda make something that can tow 12,000 pounds?

grumpybob said:
Read thread 'agree or disagree' reply by grumpyBob, that is me. Give you an idea of what went on with my truck. Good thing it was covered by warranty yet. took almost 2 months to get it finished. Parets were hard to get, dealer that worked on it was great.
Click to expand...
Yes, sometimes these things are a pain in the a$$. This is my truck and my story, but my son is doing the troubleshooting and repairs, as my mechanical skills were from the sixties and seventies and todays cars and trucks are way more reliable I feel. So we decided to do a little investigating online and are next step was to change out the crankcase sensor. Now spent $170 and still missing. then a quick change of the coil and still missing on seven. What do you do next? the end is near I think.
 
Hmmmm the more I drink the better my answers will become.

ok so a coil swap and it still misfires, so Im back at a bad spark plug, wire or cap..
You have a seperate coil for each cylinder right?
 
ferno said:
Hmmmm the more I drink the better my answers will become.

ok so a coil swap and it still misfires, so Im back at a bad spark plug, wire or cap..
You have a separate coil for each cylinder right?
Click to expand...
Yep, Now were both puzzled, so we decide to do a compression test on seven. Walla, 40 pounds compression, don't believe the gage, check another cylinder 150 lbs. Any guesses to what's wrong yet?
 
spyryder said:
Broken valve spring?:popcorn:
Click to expand...
you've been just ahead of me right along and now guessing in the right direction with the information that you have. Pulled the head yesterday to find a brown sandy looking grit on # seven exhaust valve and some specks on the intake valve. The intake valve on seven is concave more so than the other intake valves. The head is now at a race motor shop and i am awaiting there say so, but what I believe happened is that the injector is restricted somehow, ran lean and warped the valve, therefore not closing all the way. Have not heard from my son yet about the head. What through me was the intermittent missing.
 
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I'll keep you posted as to the final results, but until then, on to another Hardy Boy mystery.
 
rnet said:
you've been just ahead of me right along and now guessing in the right direction with the information that you have. Pulled the head yesterday to find a brown sandy looking grit on # seven exhaust valve and some specks on the intake valve. The intake valve on seven is concave more so than the other intake valves. The head is now at a race motor shop and i am awaiting there say so, but what I believe happened is that the injector is restricted somehow, ran lean and warped the valve, therefore not closing all the way. Have not heard from my son yet about the head. What though me was the intermittent missing.
Click to expand...
I had a similar problem once (well sorta) with a '55 Plymouth V8! It would misfire at idle and only when cold. A compression test was pretty even across the board. Changed wires and plugs etc etc...still misfiring! Pulled the valve covers and found a broken spring. My guess is that with a cold engine and higher oil pressure, the hyraulic lifter would keep the valve opened slightly when the engine was running, but it would close fully during a compression test as there wasn't any oil pressure during cranking. That one had me scratching my head for a while.:gaah:

But ya, I'd have a good look at the injector for that cylinder...or maybe swap it with another one and see if it moves to the other cylinder.;)
 
NancysToy said:
It was a whole lot easier with a single coil and an AFB, wasn't it?
Click to expand...

That one just had a 2 barrel, a Carter BBD I believe....a 259 Hy-Fire poly-head if I remember correctly.:thumbup:

Ah yes, '55 Plymouth Belvedere....called it "the bruise", black and blue and a few dents! It was already 30 years old when I owned it.

(sorry for the hijack RNET....just reminiscing:D)
 
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