Fluctuating Idle RPM -Diesel P38

Grrrrrr said:

To be fair the marks are already there. You can always put it back again.

As N2O says it is tens of millimeters. When I did mine the act of tightening was enough to take it out. In the end I left the bolts ever so slightly loose and with a piece of wood just tapped ever so gently so it just moved then tried again. In fact in the end I did it with the engine running and a mate in the cab to turn the engine off as soon as revs went too high.

CPS is probably safer to play with though!

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One problem at a time. Modulation has nothing to do with fuelling. Moving pump mid section will not change that. I want to see 45% to 55% modulation at 750 RPM first, then we can move on from that.

kapilamuni said:

Message centre says 5.4 L/100KM (without AC- I don't use AC since this idle problem), which is absurd. Even my small Toyota 1.5 Dturbo was doing 10L/100KM under similar conditions with AC.
Actual usage is about 18-19L /100KM which is in fairly heavy traffic. I figure this is too high but has been the position for the 8 yrs of my ownership.

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It should be at around 13-15l/100km with normal town use or within 1l/100km error.
To me it's clean that middle section position is set wrong.
And timing modulation can't be set with unstable idle - it will go nuts because ECU cuts fueling to prevent engine runaway with too much fuel and no load.
Search for "hammer mod" on VW forums, it's the same construction of pump and quantity adjuster.

N2O, tell me why it's not a constant occurance , if it's the center section?

N2O said:

It should be at around 13-15l/100km with normal town use or within 1l/100km error.
To me it's clean that middle section position is set wrong.
And timing modulation can't be set with unstable idle - it will go nuts because ECU cuts fueling to prevent engine runaway with too much fuel and no load.
Search for "hammer mod" on VW forums, it's the same construction of pump and quantity adjuster.

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Timing modulation has nothing to do with fuelling.

It's strange, but it has.

N2O said:

It's strange, but it has.

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Modulation is about point of injection timing, nothing to do with the fuel quantity being injected. The pump mid section being out of place CANNOT influence modulation, only fuel quantity.

It's all dependant of each other.
Last time i've changed only quantity on one of mine, and modulation went from 43 percent to almost 60.
And when you bump fueling too much, modulation jumps across full range(10-90%).
It's not that simple as you think.

You will never have stable timing modulation with badly adjusted fuel quantity - it behaves in totally unpredictable manner.

N2O said:

It's all dependant of each other.
Last time i've changed only quantity on one of mine, and modulation went from 43 percent to almost 60.
And when you bump fueling too much, modulation jumps across full range(10-90%).
It's not that simple as you think.

You will never have stable timing modulation with badly adjusted fuel quantity - it behaves in totally unpredictable manner.

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Is this the one you changed the pressure piston size, so that the fuel injected was far greater than the ECU fuel map was setup to encompass. No bloody wonder it ran rough. The more fuel you inject the faster the engine runs. It is not a good idea for this guy to play with pump centre section at the moment. He has no working stop solenoid fitted. Normally the quantity servo shuts the engine down, the stop solenoid is just a back up in case the servo fails and the engine runs away. Playing with pump centre section without a working stop solenoid would be seriously stupid.

Last saturday I replaced the stop solenoid too after adjusting static timing.
Now waiting for the CPS .
N2O's suggestion will be last resort, hopefully.

Also, now I can start her immediately after shut down, say within 5 -10 seconds.
How is it possible with hot start issue?

kapilamuni said:

Last saturday I replaced the stop solenoid too after adjusting static timing.
Now waiting for the CPS .
N2O's suggestion will be last resort, hopefully.

Also, now I can start her immediately after shut down, say within 5 -10 seconds.
How is it possible with hot start issue?

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Because the internal pressure has not bled off after 5 or 10 seconds that is why. .

kapilamuni said:

Last saturday I replaced the stop solenoid too after adjusting static timing.
Now waiting for the CPS .
N2O's suggestion will be last resort, hopefully.

Also, now I can start her immediately after shut down, say within 5 -10 seconds.
How is it possible with hot start issue?

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The good news is that we're all watching your progress and learning from it!

I'm watching Wamsy Wams, if he were an olympic figure skater he'd get my 10, only downside to that weird thought would be having to squirm every time he cocked a leg doing sexy skatery crotch reveals, but with the yardage of undergarment material seriously under-estimated....yeek

Wams, you da man.

Wammers said:

Because the internal pressure has not bled off after 5 or 10 seconds that is why. ..

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I guess the internal pressure bleed off through the pump's return line on top.
If that's correct, if one can control the return line, say by a 12v fuel control valve or similar ,to close it with engine, then the 'hot start' issue should not be there.

kapilamuni said:

I guess the internal pressure bleed off through the pump's return line on top.
If that's correct, if one can control the return line, say by a 12v fuel control valve or similar ,to close it with engine, then the 'hot start' issue should not be there.

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Not a good idea, wait until you get everything right then see what you have.

Hmmm....
will wait for CPS, then.

Today checked the EDC system with nanocom. Strangely, there are no faults recorded. Yet, timing modulation remains within 40 and 93-fully warmed engine, idling. Also, randon fluctuations at idle is there, no change.

Should receive the CPS by next monday or tuesday. Hopefully, it will solve the issues.

kapilamuni said:

Today checked the EDC system with nanocom. Strangely, there are no faults recorded. Yet, timing modulation remains within 40 and 93-fully warmed engine, idling. Also, randon fluctuations at idle is there, no change.

Should receive the CPS by next monday or tuesday. Hopefully, it will solve the issues.

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If the static is set correctly, the only possible reason modulation can be anything like 93 is that the ECU is trying to correct a discrepancy between the point of injection indicated by the number four injector and the CPS. Difference in RPM indicated by the needle sensor and the CPS should NEVER be more than 40 RPM.

please! CPS?
Crank position sensor?

Mark Piercy said:

please! CPS?
Crank position sensor?

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Yup.

cheers wammers..