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blown motor / rebuild and misfires at idle

1998 s10 with 4.3 v6 5- speed 2wd. 92k miles here is my story. driving to work one day. service engine light comes on, check gagues light also comes on. temp gauge was fully tached out, overheated. engine started wraping louder and louder as cylinders started dropping and finally temp gague went all the way back to cold. pulled over and truck died with not restart. opened hood steam pouring out and light smoke from..... well a damed dirty engine thats burning up. the head gaskets blew out due to a very neglected cooling system. pulled heads and had them maged, milled and pressure tested. rebuilt using felpro gasket kit. cleaned the hell out of the cooling jackets, core, rad, ect.. replaced block temp sensor. distributor rotor ,cap, wires and plugs. also replaced all coolant hoses and lines , thermostat, waterneck, and water pump. other mods i have made are cold air intake, removed throttle blade wedge limiter, removed and capped off the smog tube from the exhaust and capped off at the intake manifold. my problem is that now it idles horribly rough. engine thrashes around. tech 2 says p0300 wich is a random cylinder misfire. #4 is misfiring from idle up to around 2200 rpm. #1 misses from idle to 1000rpm at ramdom times. #6 is missing random from idle to about 800 rpm. also had code p0103 which is MAF sensor high input voltage. i dont care about the MAF sensor right now but the misfire is driving me nutty. did i mention that the dead cylinder wraps loudly when it cold starts. engine run smoothly at freeway speeds but is still under powered. and all cylinder will fire clean over 4000 rpm with no misfire.

CAN ANY ONE HELP ME!!!!!!! any tips or advise would be greatly appreciated. what do i check next??

Reply to
stroker-rc
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You drove it till it got so hot it quit running and all you did was basically head gaskets? Next time you got money to throw away, mail it to me. bearings shot on engine, crankshaft goosed, damaged pistons from extreme heat, and trying to compress a solid (water is a solid as far as an engine is concerned) probably a bent rod or two.

Whitelightning

Reply to
Whitelightning

=========== ===========

ANY..???...???

okay.....

~~TIPS~~ when run hot enough to fubar a set of heads....... engine blocks will fubar toooooo.

~~ADVICE~~ theres a guy in another thread hunt'n a deal on a 4.3 injector setup.......post a forsale ad.

~~UNSOLICITED SUGGESTIONS~~

Check for vac leaks around the intake and heads...

Check compression...

Define "wraps" loudly...... (maybe you oughta do this one first...the other 2 steps may be mute)

~~RANDOM THOUGHTS~~

this is some good smoke i got today.....

this crown-n-coke is tastey......

this guy's jest wasted enough money on a shot-gun diagnostic repair....to buy a good used engine...

this guy diagnosed his own problem when he typed the first two words of the title of the post.....

oh wellll....... that don't mean we can't charge him to tell him he's right....

^^

** L O

~:~ MarshMonster ~wonders why the OP spent all that time and money...... AND NEVER CHECKED OR CHANGED THE OIL~~ (maybe he jest didn't mention it....)

Reply to
Marsh Monster

uhhh ...i dunno.? sounds like it broken?... wow thanks for the concern and help.......... by the way -wraping- dead cylinder piston knock. if you ever had a no fire cylinder or misfire then you heard it. no vac leak. block surface planeed out good. comp pression is good and cylinders all leaked down less than 8%. when engine was apart i checked crank and rods all good. no piston fractures. one more time... this problem only exsists from idle up to about

1850 rpm. then it runs good and quiet. also engine starts easy, every time.
Reply to
stroker-rc

Maybe stuff you already checked and I missed so I'll just ask anyways and see if I hit something.

1.) Did you check..... a.) Crank bearings? b.) Crank straightness? c.) Pivot pins. e.) Exhaust flow. (Plugged converters can make a lot of noise at lower engine rpm. Puts to much back pressure in the cylinders.) f.) Listened to motor to see if it's a particular cylinder? g.) Crank end play? h.) Correct valve adjustment?

When you think of the mechanics of an engine and what could be "Thumping" at a lowere engine rpm. Most items get louder as the engine speed increases. So I'm leaning towards something that as the power increases it ovepowers the noise. So I'd start by unhooking the exhaust system and give it a run. You never know what sort of trouble comes from to much heat!

Reply to
Daveman

hey thanks daveman. it very well could be the exhaust. the cat took a load of nasty engine coolant and mud when the gaskets blew. i would imagine the o2 sensors are packed with garbage as well. i did check all the push rods for trueness via vee blocks and a dial indacator. the valves are not out. they are self aligning rockers with hydraulic roller lifters on the cam. all valves were with in a few hundred thousandths of and inch of lift from each other. the #4 cylinder (middle on passenger side ) is haveing the most misfire count on my scanner. that cylinder running dead is what is causing the rattling sound. i have been to overly thurough in checking every think in the engine that i am haveing trouble with the simple stupid things like exhaust blockage. thanks again daveman.

Reply to
stroker-rc

======== ======== (the following is what you have written..and what you've led a bunch of guys to believe to be true) . . You have 2 adjacent cyl's that have a misfire symptom.

Albeit one of the cyl's seems ok above 800 rpms, the other ok obove 2200 rpms, and no probs at all on the hiway or above 4000 rpms.

The entire engine assembly has been either rebuilt or all parts disassembled and inspected, and were good at time of reassembly.

(you have led us to believe by your posts that the following diagnostic steps have been taken)

The engine has been checked for vacume leaks. There are NO..no..no..no..vac leaks on the 2 adjacent cyl's that are throwing a "LEAN MISFIRE" code in the computer.

Compression has been checked. All cyl's are within specs.

~~RANDOM THOUGHTS~~

does he know what i meant by checking for vac leaks?

why would someone in the thread suggest that a stopped up cat convertor would cause only 2 cylinders to misfire, and one of them to be dead?

whoever suggested the cat conv as the prime cause of the symptoms (as listed)....ain't gotta clue.

why...would a cylinder be dead.....under idle, but be okay during normal hiway driving?...on an engine with good compression and no vacume leaks

what would cause a misfire on 2 adjacent cyl's on an eng with good compression and no vac leaks?

~end random thoughts~~ (sip of coffee) (toke on joint) hmmmm

OK.....here's what we can eliminate based on what you've posted.

everything except for.......

improper reassembly of the engine system secondary ignition system fuel supply computer

because..based on the facts as you've given them... ANYTHING else would cause more than what you've listed as the symptoms.

~:~ MarshMonster ~thinks he shudda been a dentist~

Reply to
Marsh Monster

Reply to
none2u

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