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DM_climber
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Sep 10, 2010, 3:43 AM
Post #1 of 10
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Cylinder#5 misfire
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97 GMC sierra 4x4 Truck, I have a cylinder # 5 misfire according to the code reader. I have replaced spark plugs,wires,distr cap and roter. I can not figure out what to do next.
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Hammer Time
Ultimate Carjunky
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Sep 10, 2010, 5:02 AM
Post #2 of 10
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Re: Cylinder#5 misfire
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The next most likely suspect would be an injector. You would need a bidirectional scan tool and a fuel pressure gauge to perform an injector balance test
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DanD
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Sep 10, 2010, 5:11 AM
Post #3 of 10
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Re: Cylinder#5 misfire
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Considering that you’ve replaced ignition components, we’ll assume (not the best thing to do) that the misfire is not ignition related.
Before doing anything else, confirm that this cylinder has compression; without compression nothing externally will get that cylinder running.
Next would be fuel control; this engine is likely using Central Sequential Port Injection (CSI)
CSI systems use a single electric fuel metering valve that is opened and closed by the computer and is common to all cylinders. So we know that it is working because we’re only dealing with #5.
Leaving the metering valve are 8 individual tubes with poppet valves/nozzles at the end of each tube; one poppet valve per cylinder. The poppet valves are a form of mechanical injector; fuel pressure is applied to the base of the valve’s nozzle to open it and spray fuel. Once the valve/nozzle is opened the fuel pressure in the tube drops and the valve closes with spring pressure.
These poppet valves are famous for sticking.
If this is the case with your misfire; you can attempt having them professionally cleaned. Don’t waste your money with the pour in the tank cleaners; if this is a stuck/dirty poppet it’s to late for that stuff. They need a very aggressive cleaner if it’s going to work at all.
Again if this is the issue and cleaning didn’t work; there is an up dated retro fit CSI unit that does away with the mechanical poppet valves and uses 8 electric injectors. No modifications are needed to install this unit; it’s plug and play; but it’s not cheap to buy.
Dan.
Sorry HT I wouldn’t have replied to this thread if I saw that you already had. Don’t take offence please.
Dan.
Canadian "EH"
(This post was edited by DanD on Sep 10, 2010, 5:13 AM)
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Hammer Time
Ultimate Carjunky
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Sep 10, 2010, 7:56 AM
Post #4 of 10
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Re: Cylinder#5 misfire
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No offense taken......
I was however under the impression that this was an SFI (sequential) injection system with individually controlled and serviceable injectors that could still cause a miss on #5 only and can be replaced independently.
These images are from the 5.7 but the 4.3 is the same
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DanD
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Sep 10, 2010, 9:48 AM
Post #5 of 10
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Re: Cylinder#5 misfire
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I agree with all that you have said about both types of fuel control systems and yes the poppet nozzles can be replaced individually but in my pass experience with these things; it’s a make work project, just replacing one; let alone one of the same design.
If one has become plugged/stuck, the others are close behind; they’ve all seen the same heat soaks and dirt.
So if after having the CSI unit assembly cleaned and #5 is still not operating; I would suggest the up-dated unit.
Again assuming that this is the cause of the problem and that the vehicle hasn’t already had the up-date done?
Dan.
Canadian "EH"
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Hammer Time
Ultimate Carjunky
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Sep 10, 2010, 10:30 AM
Post #6 of 10
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Re: Cylinder#5 misfire
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I'll agree on those points. My intention was for diagnostic purposes to verify that the injector is actually the problem.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DM_climber
New User
Sep 10, 2010, 11:56 AM
Post #7 of 10
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Re: Cylinder#5 misfire
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Ok guys I really appreciate the help! I messed up by not including the size of the motor. Its the 5.7 vortec, and no it dosent have individual injectors, so popet valves are on the board to replace. I am also wondering if a cleaner like "sea foam" might be worth a try? it is a rather aggressive cleaner, or will i be waisting my time? I am not oposed to up dating to the new style so I will look into that. But I guess I am clueless as to what is involved or where to get it. Any suggestions?
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Hammer Time
Ultimate Carjunky
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Sep 10, 2010, 1:20 PM
Post #8 of 10
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Re: Cylinder#5 misfire
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Yes, you do have individual injectors. They are just all contained in a central unit but they are individual. Forget the cleaner. It won't do a thing.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DM_climber
New User
Sep 10, 2010, 4:15 PM
Post #9 of 10
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Re: Cylinder#5 misfire
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I understand about the idividual injectors I was thinking in terms of a fuel rails and each injector. How hard is it to pull it out and clean it? The other question I have is the cylinder numbers,in terms of the cpu numbering the cylinders and the print out for the firing order are they the same? in one book the cylinders are counted down one side and up the other, on the firing order they are alternated accross the block. which is correct?
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Hammer Time
Ultimate Carjunky
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Sep 10, 2010, 4:32 PM
Post #10 of 10
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Re: Cylinder#5 misfire
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No, you can't manually clean these injectors. They are not even accessible without removing the upper manifold and then they are a sealed unit. As I stated earlier, the way this is diagnosed is by doing an injector balance test using a professional scan tool and a fuel pressure gauge. Once you identify that it is actually an injector causing the problem, then you make the decision to change that one or all of them. As the discussion with the other tech noted, it is recommended to replace all of them at once although it would be quite expensive.
The only attempt you could possibly make at cleaning them would be using a pressure system with professional cleaner but I can tell you from experience, this rarely works on this type of injector and would set you back about $150.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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