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Old 08-26-2008, 17:33   #1 (permalink)
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Low Pressure in engine after gasket work

I did a head gasket job, and everything seems to run well at acceleration and cruising, but struggles at idle. I have two cylinder misfire codes for cylinders 1 and 2. I was afraid I had an issue related to either the block or the heads (heads were pressure checked and machined). I took it to Pep Boys (mistake) and they said it was plug wires. I changed them and no change. I went back, a different tech ran some tests and came to the conclusion that there was nothing wrong with the ignition system or the emissions system. He checked the engine pressure by placing a pressure gauge in the back of the intake manifold (in the bottom of the sensor to the side of the EGR solenoid). The pressure was 5-8 at idle, and he said it should be around 20. When we reved the engine, the pressure went up to 20. He said that it's definitely mechanical. Any ideas on what the issue could be? I checked the pushrods and rocker arms again, and made sure that I reset them with the valves closed. Help please!!
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Old 08-26-2008, 17:39   #2 (permalink)
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Re: Low Pressure in engine after gasket work

You mean engine vacuum not pressure. I wonder if it could be a timing issue? Did you have to remove the "dummy distributor" synchronizer assembly?

What year & engine?
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Old 08-26-2008, 18:26   #3 (permalink)
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Re: Low Pressure in engine after gasket work

It's a 3.0L 12 Valve OHV engine. It's got an ignition coil that's mounted on top of the front valve cover. I'm not sure what you mean by "dummy distributor". Would that be on the 3.0 OHV?
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Old 08-26-2008, 18:27   #4 (permalink)
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Re: Low Pressure in engine after gasket work

Sorry, forgot the year, it's a 2001.
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Old 08-26-2008, 18:38   #5 (permalink)
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Re: Low Pressure in engine after gasket work

You probably didnt have to remove it to R&R the heads. I was thinking if you did the timing could be off.

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Old 08-26-2008, 18:45   #6 (permalink)
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Re: Low Pressure in engine after gasket work

Yeah, I didn't have to remove or unplug anything there. I'll check it though. The wiring harness is a pain in the ass to work around, and I might have done something to that while I was wrestling around the harness.
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Old 08-27-2008, 18:09   #7 (permalink)
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Re: Low Pressure in engine after gasket work

Here is the update: car still running, but still rough at idle. Did a pressure check today, and got from between 100-150 psi for cylinders 3,4,5,6. 1 and 2 (the cylinders with the misfire codes) only come up to 60. Bad news. I did the oil check where you add a few drops of oil to the spark plug holes, and the pressure rose to 75. So that means there is some piston ring wear, but I don't think that's the main problem. When I did the head gasket replacement, I pulled the heads and took them to the machine shop where the machinist said that the rear head (1,2,3) was out .006 which was the outermost range of tolerance, but still in tolerance. So he re-surfaced them and he pressure checked the valves and said they were ok. I'm 99.9% sure there was nothing wrong with the re-installation of the gasket and heads. I torqued them in the order and to the specs provided by Ford. My main question is this: assuming the machinist didn't screw up the resurfacing, is it more likely that I've got a problem in the block or a problem in the valves? I'm leaning towards the valves, thinking maybe the valve seals are cooked which may cause the loss of compression. I don't think it's likely that the block would be worse than the heads and visually inspected it for cracks and didn't see any. What else should I be thinking about here?
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Old 09-01-2008, 19:43   #8 (permalink)
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Re: Low Pressure in engine after gasket work

Valve seals won't affect your compression. My guess would be that the gasket was leaking between 1 & 2, especially with them both at the same pressure.
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