P38A M51 Diesel - Lumpy idle after rev - Setting the top section of the pump?

MikeFl4 said:

Hello everyone,

I have been working on my P38 to try and make the engine run as it should pretty much since I got it. Its had a heap of work done to it - summarised below:

Full service of every single oil and filter in the vehicle
Refurbished injectors x 6
Intake manifold gaskets (1999 model so rubber type)
Cleaned/flushed intake manifold
New glow plugs
New leak off pipes
Cleaned / swapped MAF (for testing purposes)
Cleaned / swapped MAP sensor (for testing purposes)
Pipes free from crap going from manifold to MAP sensor
EGR bypassed – one of those straight through pipes
Intercooler swapped (original one was leaking oil so I assume had a hole in it)
Note: Ac system has been removed from the car.

Things ive tested:

Turbo wastegate – I was able to move the rod so I assume its not stuck
All hose clamps are tight and pipes seem to be good with no obvious splits
Engine power is O-K, I’ve never driven a “good” M51 so I don’t really know what to base it off of
Removed cam cover and cleaned the oil sponge thing (engine seems to have high-ish top end pressure – no pressure from crankcase testing through dip stick – only what I would consider as slightly excess pressure coming from the cam breather hose

I have made some improvements to my engine since my last post, I will give a quick summary below:
1. I got a Nanocom.
2. I removed the viscous fan and was able to get the engine to reach operating temperature - actual issue must be something to do with the thermostat (even though its been replaced). It will be fine like this just for testing purposes.
3. Modulation was way too advanced (5-10%) at 95c - this has now been adjusted and sits at around the 50% mark at 95c. (couldn't adjust it before with the low temperature) - I made sure to make the final adjustment towards the block to remove any mechanical slack in the chain.

Now - Present day - I set the modulation using @Datatek method with the steel ruler (Great method, I got it pretty much bang on 50% after only one adjustment!)
Unfortunately it still does not fix my problem.

The engine runs good, starts instantly after a single cycle of the glow plugs and runs nice and smooth (if you don’t touch it)

The actual problem is an inconsistent idle and a lumpy/bumpy return to idle while being driven - I will attach a video in a minute as it makes it easier to explain

I'm currently running the engine just after adjusting the modulation so the intake has been removed and its just running on open ports (This should bypass any other weird problems with leaking intake hoses etc as there are no hoses at present!)

I believe my issue lies in the fueling, on the Nanocom, the "Fuel Quantity Current" value at idle is only 0.25 mg/s - If I'm reading the correct value, this should be around 5-6mg/s at idle. It remains at 0.25 no matter what temperature, once its at idle its steady.

Also, my SWG Set point and SWG actual values appear to be wrong - they should be below 1500mv after 20 seconds but mine stay around 2500mv.

Im hoping that overall my injection pump has just been super badly timed by a previous owner, getting the modulation right was the first step.

Do you guys have any suggestions as to what I should do next?

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Datatek said:

Personally, I doubt fiddling with the top of the FIP will make a difference, but no harm in trying.
My first step would be a compression test.

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MikeFl4 said:

OK, I just stopped being a wuss and did it, i adjusted the mid section of the pump towards the front of the car. Fuelling now up at around 5mg/s instead of 0.25mg/s. Idle is super smooth and after a quick rev it returns to idle quickly and smoothly with no lumpyness or missing.

I do all this work on my own so I sometimes just need a bit of encouragement to actually get out there and try stuff. I was always afraid of causing the engine to run away or for the pump to move too far out of adjustment so that it no longer runs etc.

So, just currently on the first test drive. All seems good, maybe a little down on power but I can hear a pronounced turbo whistle so probably just a loose pipe. Other than that it’s no longer got any slow down shutter like before.

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