Datatek
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they fit them with superchargers insteadProper engines don't need turbos
P38A Modulation
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Datatek
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Mine is literally a guzzler on gas, not petrol no HC or CO
Be interested to know the variation from cold to hot.
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I need to get my lpg fixed
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Why?
Datatek
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Modulation is set mechanically, I want to know why it varies with coolant temperature and how much variation would be considered normal.
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I guess the chains will stretch as they heat up. The pump itself will expand a bit, especially as the fuel is heated. I did a long trace when I first got the Nanocom and it took ages for the fuel temperature to stabilise.
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Modulation is about point of injection adjustment. Static timing is set slightly advanced, timing returns to this position every time the engine is switched off and the internal pump pressure bleeds away to aid next start. On a cold engine the the point of injection will be slightly higher in degrees before TDC with a cold engine than it is with a warm engine when it should be within 1 or 2 degrees before TDC. It makes no difference whether the engine is EGR and MAF equipped or not it is the same for all M51 engines. Modulation adjusts point of injection, it has nothing at all to do with injected fuel quantity if that is what you are thinking.
Datatek
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I'm not thinking that it has anything to do with fuel quantity. I want to know how much variation there is to be expected between cold and hot water temperature.
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There will be some but it will not be great and as long as all is well at engine up to temp at idle all should be well.
Datatek
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That is not what I have found.
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What have you found that bothers you?
Datatek
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Nothing that bothers me as you put, just a wish to know how and why there is a very considerable variation in modulation with respect to coolant temperature.
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As said, as long as everything is ok at normal engine temp at idle it does not matter.
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Just to add that with a cold engine the ECU restricts power output until the engine is at a set working temp, maybe that is what you are seeing.
Datatek
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There is a big difference in the modulation between 88C and 95C, so checking the modulation with diagnostics can be very misleading is just going by the dash gauge for assuming the engine is up to temperature.
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80c is when the thermostat opens, maybe it would not get to 95c at idle with a viscous fan fitted. Checked at 750 RPM idle only. If you rev the engine the modulation will increase.
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Be interested to know the variation from cold to hot.
When started my modulation was about 80%. It then gradually dropped and by the time the temperature needle came out of the blue and hit the first white bar it was down to 65%. Oddly enough, as it climbed to the second bar (middle of the dial) the modulation crept back up to 70%.
Not analysed on computer yet, that was just looking by eye. Fuel temperature started around 2 and ended about 35 degrees centigrade. Not sure where the coolant temperature started but it ended at about 89 degrees centigrade. Air temperature 31 degrees centigrade which seems a bit high but maybe it was hot under the bonnet. It was certainly sunny today.
That's on a '95 with no EGR and 161k miles on the clock. Original chains but had a refurbed FIP.
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Try putting an egg in a pan of cold water, then put it on a lit hob and time it for three minutes and see if you get a perfectly boiled egg. My guess is you won't. If you want good results use proper methods.
Datatek
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Exactly why just saying "modulation is checked with the engine idling and up to temperature" What is "up to temperature? There is a significant difference over a relatively small temperature range so people could be misled when using diagnostics to check the modulation, a temperature check needs to be done at the same time.
I intend to post a small table showing modulation against coolant temperature with the FIP timing correctly set mechanically.
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Because that is how it is done. Because you have modified your cooling system to run electric fans puts your engine out of normal temp ranges. With a viscous fan fitted the engine would possibly get nowhere near 95 degrees at idle. The thermostat opens at 80 degrees and coolant circulation begins. Without the viscous fan no air is being drawn through the rad to cool the engine. So the engine temp will rise above what is normal at idle. If you modify things you have to accept the changes that mod causes. Modulation is a function of internal injection pump pressure control against the timing device piston. With the engine stopped and the internal pressure bled off the timing device piston returns to and is held at the mechanically set static position by spring pressure. When the engine is running the internal pump pressure varies between 3.5 bar and 4.5 bar dependent on RPM. At above 4.5 bar a pressure relief valve opens and directs fuel back to the internal pressure pump inlet side. At idle 750 RPM engine up to temp, the modulation to balance fuel pressure against spring pressure on the timing device piston and set point of injection at 1 or 2 degrees before TDC should be between 45% and 55%. The amount of modulation increases as the RPM increases and the internal pressure rises to maintain the point of injection set point throughout the entire rev range.
