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My LT1 is out of a 94 Z28. 6 cyl test at 180-195 2 test at 240. Engine idles rough yet smooths out at 1500 rpm and power falls off after 2500 rpm. Need help diagnosing this. Thanks
 

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You need to test all the cylinders.

But, having said that, you need to put car on an obd 1 scanner that reads codes & does running sensor data scans. I suspect your problem could be found in this area.

But, don't forget the basics. I hope you installed new spark plugs, dist rotor & cap. Plus plug wires. Note that LT1 plug routing is different from SBC.

While on basics, get a fuel pressure tester. Screw it on to fuel rail fitting. Do key on prime. Pressure should be around 43 psi. Crank engine and let idle. Pressure should be at least in mid 30's psi. Take a drive. Tape gauge to windshield. Except for idle pressure should be around 40 psi. Have you put a new fuel filter on?
 

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Discussion Starter · #3 ·
My LT1 is out of a 94 Z28. 6 cyl test at 180-195 2 test at 240. Engine idles rough yet smooths out at 1500 rpm and power falls off after 2500 rpm. Need help diagnosing this. Thanks
We did everything but the fuel gauge. 6 of the cylinders tested at 180 psi with two at 240. Looking at changing the lifters for TV those 2 cyl. Mr Google said it could be exhaust lifters collapsed and won't allow the exhaust to escape and the pressure just builds. Only other option is rebuild everything. It's got new wires and plugs, egr valve, torque converter, and horn - I'm telling you we tried everything.
 

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The higher readings in 2 cylinders can indicate a blown head gasket in those cylinders. The reason that pressure is higher is that coolant can be entering the cylinders.

Since water does not compress, the water in the cylinders could cause higher psi. Check your tail pipes for water vapor oe the sweet smell of antifreeze.

Also remove radiator cap when engine is cold. Run engine, and when it warms up, check for air bubbles in coolant.

If blown head gasket is problem, don't run engine anymore until problem is fixed. Doing so as hg blowout area gets worse can hydro lock the engine causing all sorts of damage.
 
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