White Smoke at start, Low compression in #4 cylinder - Ford Powerstroke Diesel Forum
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Old 02-23-2014, 06:35 AM
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White Smoke at start, Low compression in #4 cylinder

Hello everyone, so this last summer my truck had the #4 injector head crack and had to get it replaced (belching black smoke, ticking, knocking, etc). Had it tested after the repair and was told it was at 95% compression. In the last couple months i've noticed some white smoke from the exhaust at start up, which would stop after 10-15 sec. Had the glow plugs replaced and new batteries installed (due to a non-starting issue). Took it into a local shop and they told me the #4 injector was sticking causing fuel to leak into the cylinder. Thinking it was a warranty issue with the injector i took it to the ford dealer and they told me they had were getting a "low performance" code from the #4 injector (no check engine light) caused by the low compression and had to do the $250 compression test.

My question:
Will a cylinder with low compression cause an injector to stick open? Which is what the dealer is telling me (seems like they're trying to avoid honoring the warranty). Because my understanding is that a stuck or damaged injector can cause severe damage to the cylinder therefore lowering the compression.

The shop who gave me the 95% compression reading indicated that it was not a problem (nor would it become a problem), just a small loss in power. Sorry for the long post, just trying to avoid paying a ton when the problem could be a warrantied injector. Thanks!


03 6.0 F250 Crew Cab Short Bed
4" Magnaflow Exhaust
Stock Intake
New Turbo at 181K
New Glow plugs at 190K
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Old 03-15-2014, 11:05 PM
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An injector stuck open will melt a cylinder out... "Fuel Knock" will knock chunks from the cylinder, and the heat from it dumping fuel will melt valves and pistons.... If a diesel is fuel knocking, do not run it. Pull the glow plugs out and jump the starter over, then see which cylinder is spraying fuel.
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Old 03-17-2014, 01:36 PM

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The shop that gave you the 95% compression number was not quite right. What they did was a relative compression test, done using the scan tool. The suspect cylinder was down 5%. Unfortunately the "glass is five percent empty" is more accurate than "glass is ninety five percent full" when it comes to this test. Anything that is more than 2% is considered suspect and warrants a manual compression test, comparing the suspect cylinder to at least the remaining cylinders on that bank. The fuel correction strategy will compensate to some degree, which is bad for those who cannot run an enhanced power balance test. An enhanced power balance test will remove the fuel correction, giving a much clearer picture of whats happening in the engine. So, you could just have a faulty injector, but you could also have a base engine issue. Only a manual compression test will tell you for certain.
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