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350tbi bad idle. Knock, but non-existent under deceleration

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Old 12-21-2010, 10:45 AM
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Default 350tbi bad idle. Knock, but non-existent under deceleration

Replaced intake manifold gasket (appeared to be leaking oil out the back). 2 miles down the road, knocking sound started during hard acceleration and exhaust manifold was glowing in the dark when I stopped. I thought the exhaust manifold gasket burned (it did), but the noise is still present with new exhaust gaskets.

Engine sounds normal under deceleration. Sounds almost like a mild rod knock at idle and accelerating. No change with 1357 plug wires unhooked.


Won't idle right (stalls), have to open throttle a bit for it to start/run. No vacuum leaks found with starter fluid. It only idles with brake booster unhooked or throttle cracked open after started.

Replaced IAC with napa part, new delphi MAP and CTS (probably my initial problem sensors causing lean condition => hot exhaust).
 

Last edited by helo; 12-21-2010 at 11:38 AM.
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Old 12-21-2010, 02:03 PM
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Well, n/m for now. I pulled the valve cover and took some video. Noise is in-time with 3rd pushrod/rocker, so I'm pretty sure it's a valve issue based on my vacuum leak symptoms.

Solution? I'm ordering vortec-tbi intake manifold and taking a trip to u-pull-it for a pair of $35 vortec heads. If this doesn't fix me up for the winter it'll be time for a 383 shortblock.
 
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Old 12-21-2010, 02:50 PM
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Those heads will give you a nice boost in power.

I would replace the cam and lifters while you are in there. The noise could be due to a collapsed lifter.

And all of that will need to be followed closely with a tuned chip for the ECU so it doesn't freak out.
 
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Old 12-21-2010, 05:21 PM
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Don't the Vortec heads have reverse flow coolant? I'm not sure from your post what setup you are running. Can you set Vortec heads on an 87-95 Block? Or older generation small blocks?
 
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Old 12-21-2010, 06:08 PM
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They will definitely bolt up and work just fine on the older blocks.

Only the LTx engines had reverse flow cooling systems where the coolant flowed through the cylinder heads first before flowing through the block. You may be thinking of the reverse rotation water pumps. A lot of engines with a serp. belt setup used reverse rotation water pumps because the pulley rotated "backwards" compared to older "V" belt systems.
 
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Old 12-23-2010, 10:51 PM
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Why do you have to change the chip if you put vortec heads on?
 
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Old 12-24-2010, 08:03 AM
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If you put a different cam in, you would need to have it tuned, especially if you get a more aggressive grind.

The heads and intake alone may be enough to cause some concerns with the stock tune. The stock ECU's don't learn too well and don't like having things changed. For the best possible results, you really should get a tuned chip.
 
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Old 12-24-2010, 08:03 AM
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You don't need to tune a chip, but it's highly advisable. Air/fuel needs differ.
FYI: TBI DIY performance and PROM tuning - CK5 Forums

Vortec heads are only sold for the price of the entire engine at my u-pull-it (Horseheads, NY), and I couldn't have loaded an engine in my 97 blazer, so I'll be going back for a complete '96 motor on monday with a pickup (hopefully it didn't get pulled yesterday, I'll be pissed!).

In the meantime, I'll be taking a peak under the head =)
 
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