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Old 01-03-2010, 07:31 PM
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Default How Diesel IP Timing Affects Performance.

Thought I might post some fundamental/first principle information regarding diesel IP timing.

Bit of background:

After researching for my lift pump install I wanted to find out about diesel engine timing and use this information to see if i could detect any changes in any of the engine parameters that I could measure. Namely EGT's.

But even before fitting the lift pump I noticed some interesting observations after leaving my fuel filter on for a bit too long.

Before changing my fuel filter I noticed the following:

1) Engine not reving out cleanly.
2) Significant lack of power with aircon on.
3) Poor off idle performance
4)Struggled to rev over 3000rpm (Well it did rev but made a lot of noise and didn't achieve very much.)
5) Generally not as smooth or refined as it was.

I also noticed that after fitting my $550 ARE bonnet scoop that my EGT's were virtually no different.

Now symptoms 1 to 5 are easily explained as lack of fuel due to clogged filter.

But how does a lack of fuel cause an INCREASE in EGT's??????

Well after changing the filter symptoms 1 to 5 all gone and its running 100% and

REDUCED EGT's around 30 to 50 degrees normal driving and more importantly struggled to get to 550 degrees (Alarm set point on the Fox Shooter EGT Gauge) 550 was possible but you'd really have to try.

The question is why did the clogged fuel increase EGT's?

The answer:

As with any internal combustion engine the timing of the ignition is important to gain maximum energy from the fuel and air mixture.

Assuming that timing is non optimised/retarded from optimum (not necessarily factory setting)

This is how it works:

Advanced Injection Timing results in:

1) Hotter Combustion Temperatures.
2) Colder EGT.
3) More Power.
4) Decreased fuel consumption.

Counter Intuitive I know however the reason is not complicated. The earlier fuel is injected the more pressure will be generated/heat and more complete combustion. The extra combustion energy is converted into useful work rather than being partially blown out the exhaust.

Therefore Retarded Timing results in:

1) Lower Combustion Temperatures
2) Hotter EGT.
3) Reduced Power
4) Increased fuel consumption.

Rather than pushing the piston down with maximum force the energy goes straight out the exhaust.

And this is why modern emission compliant engines have factory set retarded timing, or the ECU deliberately retards the timing.

(Keep in mind thats retarded from optimum)

The main method of controlling NOX emissions is retarding the timing giving a High EGT but a low combustion temp. High combustion temps create NOX, not high EGT. (chemically just not hot enough compared to combustion temps)

Most tuning chips actually advance the timing and generally void the emission requirements. (AFAIK, But Please correct me on that)

CONCLUSION For my 2.8 GU: (Applicable to 4.2 Owners as well)

A blocked fuel filter can retard your ignition timing, and therefore the standard fuel pump relies on the correct amount of fuel to deliver the optimum timing to a measurable extent. If the flow of fuel is restricted or insufficient at higher revs timing will be less than optimal.

A lift pump can ensure that timing is correct across the entire rev range of the engine.

Further Reading:
http://dodgeram.org/tech/dsl/FAQ/timing.htm

http://www.dieselpowermag.com/tech/d...tion_pump.html

Source: http://www.feldmanbd.com/Thesis.pdf

So there you have it.

I hope that made sense.

Cheers

Justin
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Last edited by parscheese; 01-03-2010 at 07:38 PM. Reason: Spelling
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  #2  
Old 01-03-2010, 09:37 PM
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Nice post Justin and a good bit of research. I have another thought for you, maybe the blocked filter caused higher egts simply because you were giving it more welly to compenstate for the lack of fuel ? Bottom line is, with a blogged fuel filter the IP is just not going to work at its optimum so anything could be happening.
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Old 01-03-2010, 10:04 PM
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Quote:
Originally Posted by Tracteur Tom View Post
Nice post Justin and a good bit of research. I have another thought for you, maybe the blocked filter caused higher egts simply because you were giving it more welly to compenstate for the lack of fuel ? Bottom line is, with a blogged fuel filter the IP is just not going to work at its optimum so anything could be happening.
isnt that what he said ??

how i understand the ve pump is that it has 2 pumps inside it , a lift pump which sucks the fuel from the tank and the pressure pump to inject the fuel through the injectors , the pump timing is controled by the lift pump , the higher the revs the more presure is made to advance the timing , if there is a restriction in the fuel creating a vacume or a greater vacume than the lift pump can overcome then the lift pump wont build the pressure to advance the timing , this is why an electric lift pump helps older ve pumps perform better as the built in lift pump is worn and not building the pressure needed
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Old 01-03-2010, 10:26 PM
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Quote:
Originally Posted by ITS A FORD NOT A NISSAN View Post
isnt that what he said ??

how i understand the ve pump is that it has 2 pumps inside it , a lift pump which sucks the fuel from the tank and the pressure pump to inject the fuel through the injectors , the pump timing is controled by the lift pump , the higher the revs the more presure is made to advance the timing , if there is a restriction in the fuel creating a vacume or a greater vacume than the lift pump can overcome then the lift pump wont build the pressure to advance the timing , this is why an electric lift pump helps older ve pumps perform better as the built in lift pump is worn and not building the pressure needed

Not really and in any case the specifics in the case above relate to a VP pump were the timing is electronic and not a VE were the timing is hydraulically controlled.

However, Itsa, your explaination of the timing control on a VE does help expalin why a blocked fuel fiter could keep the timing at base setting. I wonder if there is more to the electronic control on the VP ?
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Old 02-03-2010, 07:46 AM
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Well done justin.
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Old 02-03-2010, 01:01 PM
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Interesting research Justin.
Have you now fitted an auxiliary pump? If so, what kind and where?
I'm still chasing better performance from my 2.8 and lower than its current 17l/100km drinking habits.
Thanks

Darren
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Old 02-03-2010, 06:45 PM
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Quote:
Originally Posted by fits5 View Post
Interesting research Justin.
Have you now fitted an auxiliary pump? If so, what kind and where?
I'm still chasing better performance from my 2.8 and lower than its current 17l/100km drinking habits.
Thanks

Darren
Hi Darren

Yes lift pump installed but no fuel economy figures yet, had just started with a full tank but I left my lights on this morning and flattened the battery which reset my trip meter

But the lift pump did make a seat of the pants difference to drive ability and all round engine response. Especially above 3000 rpm.

Before lift pump I averaged about 14l/100km on my norma run to work.

Cheers

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Old 10-06-2010, 10:18 AM
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I have advanced the timing on one of my rigs and it made a noticeable increase in power and response. Next I want to install and EGT and measure from standard vs. advanced.
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Old 10-06-2010, 03:43 PM
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Fitting and external supply pump helps maintain correct internal pressure. If pressure drops off for whatever reason, injection advance decreases, so does power. This allows for retarted injection pump timing. In a Ve pump generally injection advance is hydraulically controlled, td42ti and vp44pumps have a duty cycle controlled solenoid that controls pressure going to the pressure side of the advance piston.

Td42ti pumps have a closed loop injection advance system, where it uses a needle lift sensor to tell the ecu where the injection point is. I believe vp44 use a map to determine this as there is no feed back to the computer.

Hope this helps

Andy
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Old 11-06-2010, 07:21 PM
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How does disconnecting the control solenoid on a Td42ti pump affect pump timing? Does it default to advanced/retarded. Does the internal hydraulic control still work to allow timing to change or does timing remain stationary once the solenoid is disconnected?
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Old 11-06-2010, 08:47 PM
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i think someone mentioned the ti pump stays in advanced position. it still mechanically changes timing as per normal VE. the control is more of a trim when required.

just on the VP44, pump ecu has internal pickup for TDC and compares it to crank sensor to adjust for slack in the drive gears. obviously there is some feed back between ecu's.
also while it has solenoid to control timing, the actual timing control is still hydraulic by fuel pressure. so fuel pressure still influences timing, importantly, how fast it reacts to ecu demands and if it achieves the required timing or not.
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Old 11-06-2010, 08:54 PM
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I though the Nissan base timing set-up for the VP pump was full retard and the electronic control advances it ? I think it's Toyota that have the base timing at full advance ?

and again I'm not sure about the VP retaining the hydraulic timing advance - why should it? But then, there are probably versions that do and ones that don't for all I know.
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Old 12-06-2010, 03:35 PM
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Quote:
Originally Posted by Twinotter600 View Post
I have advanced the timing on one of my rigs and it made a noticeable increase in power and response. Next I want to install and EGT and measure from standard vs. advanced.
I have done the same.

On all my Mitsu's, advancing the timing gave an increase in performance, less smoke and better fuel economy.
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Old 13-06-2010, 01:04 PM
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Thanks for the feedback regarding the Td42ti pump solenoid disconnection. May have to do a couple of tests to actually see the outcome.
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Old 13-06-2010, 02:42 PM
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Quote:
Originally Posted by Tracteur Tom View Post
I though the Nissan base timing set-up for the VP pump was full retard and the electronic control advances it ? I think it's Toyota that have the base timing at full advance ?

and again I'm not sure about the VP retaining the hydraulic timing advance - why should it? But then, there are probably versions that do and ones that don't for all I know.
VP doesn't really have any base timing like the VE's as such. all timing is electronic. it self corrects for any difference between crank position and pump position.

it needs the hydraulic side of it as a small electrical solenoid cannot make the power required to shift the cam ring, especially as it has to fight the plungers pushing against the cam.
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Old 13-06-2010, 08:58 PM
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Quote:
Originally Posted by tweak'e View Post
VP doesn't really have any base timing like the VE's as such. all timing is electronic. it self corrects for any difference between crank position and pump position.

it needs the hydraulic side of it as a small electrical solenoid cannot make the power required to shift the cam ring, especially as it has to fight the plungers pushing against the cam.
Well you learn something every day. Merci beaucoup.
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