Fluctuating Idle RPM -Diesel P38

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Went through VW forums searching for 'Hammer Mod'.
Since, I have no other option, decided to do it.
Started car & got it to normal temp.
With Nanocom, set idle RPM to 128.
With the 'injection quantity current' on screen, asked wife to keep an eye on it.
Got my boy to at the driving seat with instructions to kill the engine if things go wrong.
Loosened 4 bolts holding the mid section, about 1/4 turn.
Then slowly tapped towards the front, till the reading said 6 mg/str. :p:p:pVoila, RPM fluctuations vanished
and the engine note improved.
Then tightened the bolts back.
Glad that I could escape this easily, though it was expensive replacing few bits.

Reading the faults, though the CEL is not on, the previous fault 'injection timing out of range'
appears randomly. The timing modulation too out at 94 . Wonder why?

I am confident now I can put her back on the road but to be on the safe side, adjusted RPM to 130.

Thanks everyone for continuous support specially Wammers, N2O & Grrrr.:cool:
 
kapilamuni said:
Went through VW forums searching for 'Hammer Mod'.
Since, I have no other option, decided to do it.
Started car & got it to normal temp.
With Nanocom, set idle RPM to 128.
With the 'injection quantity current' on screen, asked wife to keep an eye on it.
Got my boy to at the driving seat with instructions to kill the engine if things go wrong.
Loosened 4 bolts holding the mid section, about 1/4 turn.
Then slowly tapped towards the front, till the reading said 6 mg/str. :p:p:pVoila, RPM fluctuations vanished
and the engine note improved.
Then tightened the bolts back.
Glad that I could escape this easily, though it was expensive replacing few bits.

Reading the faults, though the CEL is not on, the previous fault 'injection timing out of range'
appears randomly. The timing modulation too out at 94 . Wonder why?

I am confident now I can put her back on the road but to be on the safe side, adjusted RPM to 130.

Thanks everyone for continuous support specially Wammers, N2O & Grrrr.:cool:
Click to expand...

And you were so sure you had replaced the mid section exactly where it should go. 94% because static timing is wrong, it is retarded. For sake of ease. Mark flange of pump and engine case. Slightly slacken retaining nuts and rear bolt on injection pump. Put a piece of wood on it, tap wood with an hammer towards engine until you have a couple of mm movement on marks. Tighten two pump nuts and run engine, noting modulation. It should have dropped. Continue to do this until modulation is as near as possible to 50%.Tighten rear bolt.
 
I read somewhere that the FIP needs a certain amount of pressure from the lift pump to work properly. So, purely as a theory, what if the lift pump isn't 100% or there is some dirt or something restricting flow TO the FIP, or the FIP is tired and not giving full pressure. The needle in #4 might not respond quite as quick as expected giving the impression of being retarded. Once it goes past 100% modulation it is off the map, throws an error and stalls.
 
Grrrrrr said:
I read somewhere that the FIP needs a certain amount of pressure from the lift pump to work properly. So, purely as a theory, what if the lift pump isn't 100% or there is some dirt or something restricting flow TO the FIP, or the FIP is tired and not giving full pressure. The needle in #4 might not respond quite as quick as expected giving the impression of being retarded. Once it goes past 100% modulation it is off the map, throws an error and stalls.
Click to expand...

Do ya think? :D:D
 
Hey Wamms, why did you let him visit VW forums?
He'll be loading a Passat estate with his Golf clubs and Polo sticks now:oops:;)
 
Last edited:
myfirstl322 said:
Hey Wamms, why did you let him visit VW forums?:confused:;)
Click to expand...

He can visit where he wants to. Confusing part is that he has always claimed that he removed and replaced mid section long before he had this problem, he said car ran well after it was done, ran for a long period without problems. It is only after he did chains that this started to happen. He has been asked about what he did many times and always come back with the same answer that the car ran well after pump was done. Confusion reigns if the proper story is not being related. Some things it is better not to play with if you don't know what you are doing.
 
I'm teasing of course, This sort of reminds me of one man and his dog, if you catch my drift.....you being the ever patient shepherd:)

I also must respect Kapilamuni for striving for a cure.
 
myfirstl322 said:
I'm teasing of course, This sort of reminds me of one man and his dog, if you catch my drift.....you being the ever patient shepherd:)

I also must respect Kapilamuni for striving for a cure.
Click to expand...

He still has the 94% modulation to sort out. Which means the static is retarded. When he gets that down to around 50% he can call the job done.
 
Grrrrrr said:
No idea but weird stuff happens so I like to have as many options open as possible before I start sorting them to the bottom of the list. If something can happen it usually does somewhere, eventually.
Click to expand...

If the engine is running sufficient fuel is being injected. If fuel is being injected to cause combustion needle sensor must be being lifted The internal pump pressure is generated by the internal high pressure pump. No timing adjustment is possible unless there is high internal pressure between 3.5 and 4.5 bar. The lift pump cannot supply such pressure. On his car, on a hot start without glow plugs there is no lift pump until the engine starts and no internal pressure at all if the car has been stood for a while, until the rotating injection pump generates it. With no internal pressure the timing always returns to the static advanced position to aid startup. With the modulation at 94% with engine running the timing must be well retarded at static and will cause hot start problems because fuel is being injected as the piston leaves TDC and not just before it gets to TDC.
 
Last edited:
wammers said:
He can visit where he wants to. Confusing part is that he has always claimed that he removed and replaced mid section long before he had this problem, he said car ran well after it was done, ran for a long period without problems. It is only after he did chains that this started to happen. He has been asked about what he did many times and always come back with the same answer that the car ran well after pump was done. Confusion reigns if the proper story is not being related. Some things it is better not to play with if you don't know what you are doing.
Click to expand...

I still stand by what I said. The car ran perfectly without a hiccup up to the point where I changed the T/chains., h/gasket etc.
The only problem was/is 'hot start'. I have no idea how inj pump mid section shifted or whether change of timing chains made it so.

'Some things it is better not to play with if you don't know what you are doing"
Here again I played with mid section n without knowing what's going to happen. I took a chance as I had no other simple alternative.
But it solved my immediate issue.
Now the car is back to the position before the t/chain change. I got to reset the static timing n see.
 
our own learning curves a side, at least you have some good news and some faith restored.
just the last hurdle and your done.;)
wammers said:
And you were so sure you had replaced the mid section exactly where it should go. 94% because static timing is wrong, it is retarded. For sake of ease. Mark flange of pump and engine case. Slightly slacken retaining nuts and rear bolt on injection pump. Put a piece of wood on it, tap wood with an hammer towards engine until you have a couple of mm movement on marks. Tighten two pump nuts and run engine, noting modulation. It should have dropped. Continue to do this until modulation is as near as possible to 50%.Tighten rear bolt.
Click to expand...
 
kapilamuni said:
I still stand by what I said. The car ran perfectly without a hiccup up to the point where I changed the T/chains., h/gasket etc.
The only problem was/is 'hot start'. I have no idea how inj pump mid section shifted or whether change of timing chains made it so.

'Some things it is better not to play with if you don't know what you are doing"
Here again I played with mid section n without knowing what's going to happen. I took a chance as I had no other simple alternative.
But it solved my immediate issue.
Now the car is back to the position before the t/chain change. I got to reset the static timing n see.
Click to expand...

Whatever you did is now of no importance. You have learned a lot. Just get the modulation right and you have also achieved a lot. Good luck.
 
:)Well done for keeping at it, a lot would have given up and got rid of, many a p38 has been scraped as some just cant be bothered:(
 
Dynamic injection timing is controlled by a spring loaded piston into which the cam plate arm engages. With the engine not running and no internal fuel pressure, engine locked at TDC number one firing, static timing should be set at 0.95 mm lift on cam with new chains and 0.90 mm lift on cam with old chains. This is static advance needed for starting. When engine starts number four injector tells the ECU the actual point of injection. The ECU then compares that to the CPS readings for TDC by measuring the difference between two timing pips on the flywheel set 40 degrees before TDC and 20 degrees after TDC. It then modulates the timing solenoid to restrict or increase internal fuel pressure on the timing device piston. Which acts against the spring and rotates the cam to retard or advance injection, to set the point of injection around 1 or 2 degrees before TDC. 50% modulation is the null position of the timing device and cam plate, if static is spot on, the cam plate then has equal movement in either direction to compensate for advanced static or retarded static subject to engine speed and internal fuel pressure. Less than 50% modulation means the cam position is being retarded (more fuel pressure on the piston) to compensate for over advanced static and modulation over 50% mean the cam plate is being advanced (less pressure against the piston) to compensate for retarded static. At 94% modulation at idle there is almost no internal pressure on the piston to achieve correct point of injection of 1 or 2 degrees BTDC. And little or no movement of the cam left in the advance direction or modulation available to advance point of injection as engine revs increase and internal fuel pressure rises. Hope you can get your heads round that lot. ;);)
 
wammers said:
Dynamic injection timing is controlled by a spring loaded piston into which the cam plate arm engages. With the engine not running and no internal fuel pressure, engine locked at TDC number one firing, static timing should be set at 0.95 mm lift on cam with new chains and 0.90 mm lift on cam with old chains. This is static advance needed for starting. When engine starts number four injector tells the ECU the point of injection. The ECU then compares that to the CPS readings for TDC by measuring the difference between two timing pips on the flywheel set 40 degrees before TDC and 20 degrees after TDC. It then modulates the timing solenoid to restrict or increase internal fuel pressure on the timing device piston. Which acts against the spring and rotates the cam to retard or advance injection, to set the point of injection around 1 or 2 degrees before TDC. 50% modulation is the null position of the timing device and cam plate, if static is spot on, the cam plate then has equal movement in either direction to compensate for advanced static or retarded static subject to engine speed and internal fuel pressure. Less than 50% modulation means the cam position is being retarded (more fuel pressure on the piston) to compensate for over advanced static and modulation over 50% mean the cam plate is being advanced (less pressure against the piston) to compensate for retarded static. At 94% modulation at idle there is almost no internal pressure on the piston to achieve correct point of injection of 1 or 2 degrees BTDC. And little or no movement of the cam left in the advance direction or modulation available to advance point of injection as engine revs increase and internal fuel pressure rises. Hope you can get your heads round that lot. ;);)
Click to expand...
bloody hell wammers... Lz GOD of the year! Did you help design the pump? :eek::p
 
wammers said:
Dynamic injection timing is controlled by a spring loaded piston into which the cam plate arm engages. With the engine not running and no internal fuel pressure, engine locked at TDC number one firing, static timing should be set at 0.95 mm lift on cam with new chains and 0.90 mm lift on cam with old chains. This is static advance needed for starting. When engine starts number four injector tells the ECU the actual point of injection. The ECU then compares that to the CPS readings for TDC by measuring the difference between two timing pips on the flywheel set 40 degrees before TDC and 20 degrees after TDC. It then modulates the timing solenoid to restrict or increase internal fuel pressure on the timing device piston. Which acts against the spring and rotates the cam to retard or advance injection, to set the point of injection around 1 or 2 degrees before TDC. 50% modulation is the null position of the timing device and cam plate, if static is spot on, the cam plate then has equal movement in either direction to compensate for advanced static or retarded static subject to engine speed and internal fuel pressure. Less than 50% modulation means the cam position is being retarded (more fuel pressure on the piston) to compensate for over advanced static and modulation over 50% mean the cam plate is being advanced (less pressure against the piston) to compensate for retarded static. At 94% modulation at idle there is almost no internal pressure on the piston to achieve correct point of injection of 1 or 2 degrees BTDC. And little or no movement of the cam left in the advance direction or modulation available to advance point of injection as engine revs increase and internal fuel pressure rises. Hope you can get your heads round that lot. ;);)
Click to expand...

So if internal pressure is lower than it should be down to internal wear it may not push the piston as far as it thinks and it would show as high modulation?
 
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