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Old 04-09-2013, 08:57 PM
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97 chevy 1500 major loss of power

i have a 97 chevy 1500 that to say is way down on power would be an understatement. it started as the truck had overheated and burnt the head gasket which has been fixed. have done all the basic tune up plug, wires, rotor etc. the #4 cylinder is getting spark but no fire. when driving coming up to a hill you lose all speed and momentum even if you mat the pedal. running outta ideas. Anyone got one? much appreciated

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Old 04-09-2013, 09:53 PM
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If it's stock you should be able to run a scan. Is the check engine light on?
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Old 04-10-2013, 12:03 AM
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There's quite a few things it could be. Is it a 4.3L, 5.0L or 5.7L? What do the plugs look like? Gap? Have you checked fuel pressure at the rail? Is the no fire plug on the side of the previous burnt head gasket?
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Old 04-10-2013, 01:25 PM
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I'd suggest a complete compression test dry/wet as you may have softened the rings when it overheated and now are down on compression. It could be that, or you mistakenly bottomed out a lifter when you adjusted the rocker arms and number 4 is not producing compression due to a valve not allowed to close. On the other hand it may be all fuel related and you are simply not getting fuel to that cylinder. Never the less though, after an engine has overheated like that its very wise to do a compression test to see what condition the rings are really in now.

Was the head itself checked out when it was off, for warping, cracks or valve condition and so forth ?.
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Old 04-10-2013, 07:04 PM
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i had the heads checked and they came back fine. fuel pressure also was fine. its the 5.7. yeah the no fire cylinder is on the burnt side. i hadnt thought about checking the compression. a friend of mine said it could be the egr valve or a burnt valve. the only code it was throwing was random misfire and o2 sensor.
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Old 04-10-2013, 07:26 PM
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If the valves were not cracked open to inspect or any leak test done on the head, then you would have no way of knowing what condition they are in. Yes, that compression test is in order and to have the correct procedure in your lap before you would perform one. Its definitely a handy tool to have around if you don't happen to have one and pays for itself in one test vs brining the vehicle to a shop $$$.

It sounds like you might have some other issues going on too, the 02 sensor ... actually your engine most likely has more then one sensor.
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Old 04-10-2013, 08:26 PM
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Compression is a likely culprit. The fuel injection poppet could have failed for that cylinder as well.
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Old 04-11-2013, 08:33 AM
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The L31 Vortec 350 will have 4 O2 sensors,
Bank 1 Sensor 1 Precat drivers side
Bank 2 Sensor 1 Precat passenger side
Bank 1 Sensor 2 Post cat drivers side
Bank 2 Sensor 2 Post cat passenger side

Only the 2 Precat O2 sensors will cause bad running. But since the O2 sensors are NOT read when in open loo or when in Power Enrichment Mode(PE Mode) like when at WOT(wide open throttle). So when you hold the throttle open, if O2 sensors were the issue, it should run fine at WOT.

So 100% for sure, when you hold teh throttle open when in gear, the truck doesnt run well?

You say fuel pressure is fine, the spec is 62-66 psi at KOEO(Key On ENgine Off), or just under 60 psi at KOER(Key On Engine Running).

You stated you changed the rotor, I hope you changed the cap as well, these are notorious for cross fire.

How do you know that #4 is NOT firing?

peace
Hog
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