P38A Modulation

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wammers said:
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.
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It's got nothing to do with electric fans and everything to do with variation within the normal temperature range. "Up to temperature" is not going to give an accurate modulation reading on diagnostics. I run within what I see to be the normal temperature range.
 
Datatek said:
It's got nothing to do with electric fans and everything to do with variation within the normal temperature range. "Up to temperature" is not going to give an accurate modulation reading on diagnostics. I run within what I see to be the normal temperature range.
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Ok carry on, take no notice do what you want to. No skin off my nose.
 
Datatek said:
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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I would say needle slap-bang in the middle is up to temperature. That is where the system is stable.
 
It would seem some like to vary the tension of the belt around their waist. Then when their pants fall down wonder why. :D:D
 
Grrrrrr said:
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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That is all about engine temp. When the thermostat opens the engine cools slightly as coolant starts to move through the system. When the rad and engine temp equalise and the gauge is central that is the time to check modulation. As said, up to temp. The gauge is damped not to show small temp changes. So slightly up or down temp changes whilst driving and the needle stays central. At idle the temp should stay pretty static as the viscous fan does it's stuff. Normally whilst driving the engine is cooled by ram air and the viscous fan does little at all, it is only when the car slows down in traffic for instance that the viscous fan will anything like engage.
 
wammers said:
That is all about engine temp. When the thermostat opens the engine cools slightly as coolant starts to move through the system. When the rad and engine temp equalise and the gauge is central that is the time to check modulation. As said, up to temp. The gauge is damped not to show small temp changes. So slightly up or down temp changes whilst driving and the needle stays central. At idle the temp should stay pretty static as the viscous fan does it's stuff. Normally whilst driving the engine is cooled by ram air and the viscous fan does little at all, it is only when the car slows down in traffic for instance that the viscous fan will anything like engage.
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At idle in cool temperatures even without the viscous the temperature remains stable for considerable periods.
As you say, the gauge does not indicate small temperature changes, so at exactly what temperature do you consider to be "up to temperature". It matters because small temperature changes make a big difference to the modulation as displayed by diagnostic.
 
Datatek said:
That can easily be anywhere from 82 to 90C and the variation in modulation is significant over that temperature range, so it would be easy to be misled as using diagnostics.
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I only did a short trace of the General section but mine seemed pretty stable at 89. Is that the same signal used for the needle?
 
Keith do yourself a favour and fit a viscous and shroud, use your fan mod as an over heat system. Return the engine to how it was supposed to be cooled and save yourself a lot of trouble.
 
wammers said:
Keith do yourself a favour and fit a viscous and shroud, use your fan mod as an over heat system. Return the engine to how it was supposed to be cooled and save yourself a lot of trouble.
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How would that be doing me a favour? It has no bearing on the modulation/temperature relationship, I'm sorry you are unable to see that.
 
Datatek said:
How would that be doing me a favour? It has no bearing on the modulation/temperature relationship, I'm sorry you are unable to see that.
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Your engine is NOT running as it should be because YOU have changed it's method of cooling to one it was not designed to use. The designed cooling is progressive, yours is on or off. I am sorry you are unable to see that.
 
wammers said:
Your engine is NOT running as it should be because YOU have changed it's method of cooling to one it was not designed to use. The designed cooling is progressive, yours is on or off. I am sorry you are unable to see that.
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With a viscous it runs at 90 to 95C, without a viscous it runs at 90 to 95C kindly explain how that is different. According to you the viscous does nothing when moving as RAM air does the cooling how is that "progressive" and different from no viscous?
 
Datatek said:
With a viscous it runs at 90 to 95C, without a viscous it runs at 90 to 95C kindly explain how that is different. According to you the viscous does nothing when moving as RAM air does the cooling how is that "progressive" and different from no viscous?
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I have explained it in previous posts read them.
 
Datatek said:
With a viscous it runs at 90 to 95C, without a viscous it runs at 90 to 95C kindly explain how that is different. According to you the viscous does nothing when moving as RAM air does the cooling how is that "progressive" and different from no viscous?
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Oh dear me. We are talking checking modulation at idle. With a viscous fan fitted the temp does not go up and down at idle like a brides nighty, is is stable. When the thermostat opens at 80 degrees the coolant temp will drop slightly until the coolant is circulated around the system. Then it will stabilise and it will be held stable by the viscous fan. Then you check modulation. Your car cannot do that.
 
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wammers said:
Oh dear me. We are talking checking modulation at idle. With a viscous fan fitted the temp does not go up and down at idle like a brides nighty, is is stable. When the thermostat opens at 80 degrees the coolant temp will drop slightly until the coolant is circulated around the system. Then it will stabilise and it will be held stable by the viscous fan. Then you check modulation. Your car cannot do that.
Click to expand...

wammers said:
Oh dear me. We are talking checking modulation at idle. With a viscous fan fitted the temp does not go up and down at idle like a brides nighty, is is stable. When the thermostat opens at 80 degrees the coolant temp will drop slightly until the coolant is circulated around the system. Then it will stabilise and it will be held stable by the viscous fan. Then you check modulation. Your car cannot do that.
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You are just going round in circles ignoring the fact that I measure with a stable temperature. According to you the viscous fan does nothing most of the time. When modulation is checked with diagnostics needs to be done relative to coolant temperature as displayed on the diagnostic device, just saying up to temperature as indicated by the gauge can be misleading. I suppose as a garagist, near enough is good enough for you, it's not for me. Clearly you have never done any temperature analysis with or without the viscous fan fitted.

I'm wasting my time, you either don't read or don't understand, seems there are 2 options. Wammers way or no way. With your attitude problem, lord knows how you ever ran a garage. End of conversation.
 
Datatek said:
You are just going round in circles ignoring the fact that I measure with a stable temperature. According to you the viscous fan does nothing most of the time. When modulation is checked with diagnostics needs to be done relative to coolant temperature as displayed on the diagnostic device, just saying up to temperature as indicated by the gauge can be misleading. I suppose as a garagist, near enough is good enough for you, it's not for me. Clearly you have never done any temperature analysis with or without the viscous fan fitted.

I'm wasting my time, you either don't read or don't understand, seems there are 2 options. Wammers way or no way. With your attitude problem, lord knows how you ever ran a garage. End of conversation.
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It's you that doesn't understand my friend. As for your last remark i would think a lot more people on here would prefer me to be repairing their car than would be happy with you doing it.
 
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