Missfire Cylinder #4 - Please Help! - Ford Powerstroke Diesel Forum
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Old 02-17-2008, 12:53 AM
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Missfire Cylinder #4 - Please Help!

I am a newbie and have been on this forum less than a week. I have an F-250 Super Duty super cab with 7.3L PSD, 203K miles, build date is 02/01. Truck is blowing white smoke from exhaust that smells like diesel and feels "missing". Took it to dealership for cam position sensor recall. Replaced CPS did NOT correct the problem, computer diagnostics revealed "missfire on cylinder #4". I was quoted $175 to do a compression check.

My questions:
  1. Is compression test the same as contribution test?
  2. Is it possible to perform a compression check using this Harbor freight diesel compression tester for $25? Or perhaps this $149 kit from the same vendor?
  3. What is the best procedure to perform the compression test?
  4. What is the acceptable pressure range for 7.3L PSD for the above truck?

More specifically to my problem:
  1. What are the odds that the truck has a failing injector on cylinder #4? Is it possible for injector to deliver fuel to the cylinder but not result in combustion?
  2. Is there a way of testing an injector for its functionality?
  3. Can injector O-rings and copper seals result in observed symptoms?
  4. Can poor compression cause a "missfire" even if glow plug and injector are working?
  5. Will glow plug resistance and glow plug relay tests be sufficient to rule out a faulty glow plug?

My first steps:

It's best to probably get small stuff out of the way, so tomorrow I am planning on replacing the fuel filter and putting in a cetane booster from walmart. I am also planning on testing glow plug resistance and wiring to the glow plugs (assuming I can get the right set of instructions).

Also, is there a recommended manual for 7.3L PSD motor? Wiring diagrams, troubleshooting flow-charts, etc?

Excuse me for all these questions, I hope this learning curve will not last forever. Thanks for your help in advance.
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Old 02-17-2008, 02:30 AM
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here's a bump for you bud
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Old 02-17-2008, 02:40 AM
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yes an injector can be stuck open causing cylinder wash and white smoke also if the computer is showing a misfire on #4 then it is more than likely an injector. if it where a dead cylinder with low comprstion the computer would still sence the injector functioning properly.
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Old 02-17-2008, 09:13 AM
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Quote:
yes an injector can be stuck open causing cylinder wash and white smoke also if the computer is showing a misfire on #4 then it is more than likely an injector. if it where a dead cylinder with low compression the computer would still sense the injector functioning properly.
I was under the impression that "missfire" trouble code simply meant absence of proper combustion, be it a glow plug, air in the fuel, injector, bad piston compression, etc. Is this code seen only in the event an injector is stuck? I will go through little maintenance today and will attempt to eliminate several things. In the mean time, if anyone can shed some light on some of the above questions that would be fantastic.

Best regards to everyone!
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Old 02-17-2008, 09:21 AM
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There are things that break easier than rings, pistons and valves. More likely is the wiring that fires the injector. There is a connector at the edge of the valve cover gasket and a harness under the valve cover gasket that can come loose or melt due to vibration and dirt and water. Check those first (Cost $0).
The engine harness can also loose insulation or short causing the same problem.
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Old 02-17-2008, 09:29 AM
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in my opinion, if you are sure its cyl. 4 , i dont think a compression test is necesary at this point, reason why i say thats is , if it were low compression is wouldnt be white smoke , it would be more blue , i think you will find that the injector is bad or has worked loose and burned the copper washer on the end of the injector, if that happens the injector on the end will be black and washer missing , thats what i usually find , but by all means make sure cyl. 4 is the verified bad cylinder , jerk the injector out and visually look at it , cylinder no. 4 is the second one back on the drivers side or left side ,let us know what you find
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Old 02-17-2008, 09:37 AM
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take the oil cap off and see if there is any white smoke coming from under it if there is then you might have a ring broke and has scratched the cylinder wall at least thats what mine did had to have my motor rebuilt
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Old 02-17-2008, 10:51 AM
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Quote:
take the oil cap off and see if there is any white smoke coming from under it if there is then you might have a ring broke and has scratched the cylinder wall at least thats what mine did had to have my motor rebuilt
I did that and it's blowing a little bit of white smoke at the same frequency as it is coming from the exhaust. Here are the pictures:



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Old 02-18-2008, 01:12 AM
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Today I decided to buy an OBDII Scanner - Innova 3100 from WalMart for $95. Incidently I was unable to reproduce the same "misfire on cylinder #4" that diesel mechanic at Ford dealership told me. At the same time, my OBDII scanner is capable of reading manufacturer specific trouble codes - and I was expecting to see at the very least the P0304 but no luck. Is it possible that these codes have to be retrieved by a specialized OBDII reader/scanner, or do I need to drive around a little bit to retrieve these codes?

It is also worth mentining that the "Check Engine Light" was never present.

Any ideas, guys?
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Old 02-18-2008, 07:02 PM
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the cheapy obdII scaners wont pull the codes on our trucks. hope you get er fingered out.
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