03-11-2008, 04:18 PM
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Registered User
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Join Date: Sep 2007
Location: Long Beach,CA
Posts: 58,366
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Quote:
Originally Posted by pimpernell
I definetly feel that you are on the right track. I did my delivery valves, and prior to the repair, the engine could not be heard at idle. After the repair, there was slight nailing at idle and when going about 15mph and taking your foot off the throttle. There was no issue with smoke, nailing, or power at highway speeds. I redid the valves, and the nailing has almost gone away. In almost every post you read about the delivery valve repair, the writer indicates that after the job, nailing that was not present suddenly appears. The other area that would support your idea is the fact that when the engines are started from cold, as long as the glowplugs are active, the nailing is not heard. Once the glowplugs dissengage, the nailing immediatley follows. That would correspond with the idea of extra fuel getting to the injectors. As long as the glow plugs are activated, this extra fuel is no problem, but when they are deactivated, this extra fuel causes the nailing sound.
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Thank you for your comment. I am surprised more people have not said anything even if it was to disagree with me.
I do not think that the nailing is being caused by too much fuel; I think it is being caused by a change in the timing due to the delivery valves not seating well and allowing some fuel to seep back (causing less fuel delivered and at less pressure) causing the fuel to be injected later starting ignition later and causing the nailing.
I believe that when the glow plugs are on it speeds up the ignition to the extent that less fuel is burning later. In the same way the glow plugs on a cold day if used long enough stop the injectors from nailing during a cold start.
I do not recall the specific details (I have seen several threads on this) there are at least 3 stages of the ignition of the fuel when it is being injected. If for some reason; like a spray nozzle with a worn seat is not atomizing well there is a lot of unburned fuel left at the last of the 3 stages. When an abnormal amount of fuel burns at that end stage you get the loud knocking or nailing sound and this is what I think is happening due to the delivery valves not seating due to being disturbed.
Another aspect is that the delivery valve helps to regulate the shock wave that is created when fuel injection stops. The whole injection system from plungers and barrels to the spray nozzles is engineered to produce specific results. If something along the line changes it can cause unforseen results.
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84 300D, 82 Volvo 244Gl Diesel
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