Pump Pulsations: Explanation and Troubleshooting

Hello everyone,

Since Bertil's vehicle apparently doesn't fall into the category of "rough running due to an overly aggressive fuel injection setting" (which would likely lead to regulation problems in the transition range from idle to low load), the most likely explanation, at least for now, is the well-known issue of a sticking actuator, which is often suggested by Bosch workshops.
It is immediately obvious that finely designed processes, such as those in the control system of the VP 37, can become imprecise and clumsy due to stiff or poorly functioning mechanisms.

However, what bothers me is that these kinds of jolting issues should ideally occur in a brand new car, but at least in my experience, I haven't encountered any such cases.
Because why should a mechanism constantly running in a lubricating fluid only become difficult to operate over time, if we exclude corrosion and deposits in the bearings (which I think is unlikely, except perhaps with poor-quality biodiesel)?
It seems more plausible that the wear and tear on the track switch shaft caused the play, as lubrication, as is well known, does not completely protect against abrasion.

In operation, the pulsed control voltage constantly causes slight movements in the control system. If this minimal vibration coincides with increased bearing play, and the entire pump is already constantly being shaken by motor vibrations, significant control errors can certainly occur.
Assuming that the top end of the wave, connected to the RWG short-circuit ring, is wobbling back and forth, while the control slide initially remains (almost) stationary. This unstable RWG signal causes the motor computer to generate correspondingly strong (and actually unnecessary!) correction impulses to the actuator, which escalates the regulation within the full range of play, and now the control slide itself can also move significantly back and forth. This results in noticeable jolting, which, of course, cannot be corrected by shifting the actuator.
The possible speed-dependent nature of the jerking could be explained by the fact that the instability in the system arises from the superposition of control pulses and speed-dependent vibrations of the entire pump, which can either amplify or largely cancel each other out at different speeds.

If this theory is correct, then the VP 37 would unfortunately be a wear item that, due to increasing mileage, will eventually lead to vibrations.
Attempts to diagnose the issue using tools like 1551 or VAGCOM are likely to be inconclusive, as they may only reveal the fluctuating voltage of the rotor winding generator (RWG), which is already experiencing instability. However, it will probably not be possible to definitively determine the root cause based on this information alone.

In both cases (difficulty starting and issues with the fuel tank), opening the fuel cap should provide clarity.
In this case, my relatively new fuel pump (34,000 km), which doesn't exhibit any jerking or misfiring issues when properly adjusted, could serve as a reference point for DIY testing.
The measurement short-circuit ring can be moved manually against a spring force with great sensitivity and without noticeable friction. Only in the area just before the maximum stop (where the pump is not operated anyway) does the movement become slightly "stiffer."
The rotor exhibits no perceptible play. Its estimated axial clearance of 0.3 mm appears to be insignificant, as long as the measuring ring does not come into contact with the magnetic laminations that it surrounds.

Discussions about this attempt at explanation are explicitly encouraged!

@Bertil: Could you please check your fuel pump (perhaps even the one you borrowed) as described and post the results? If your fuel distributor is difficult to operate, a can of diesel cleaner might help.

ulf wrote:

... "After all, why should a mechanism constantly running in a lubricating fluid only become difficult to operate over time, if we exclude corrosion and deposits in the bearings (which I think are unlikely, except perhaps with poor-quality biodiesel)?" It seems more plausible that the wear and tear on the switch machine shaft is causing the play, as lubrication, as is well known, does not completely protect against abrasion.

...after 150,000 kilometers, one can already talk about wear and tear or aging.

Quote:

... Assuming that the top end of the wave, connected to the RWG short-circuit ring, is wobbling back and forth, while the control slide initially remains (almost) stationary. This unstable RWG signal causes the motor computer to generate correspondingly strong (and actually unnecessary!) correction impulses to the actuator, which escalates the regulation within the full range of play, and now the control slide itself can also move significantly back and forth. This results in noticeable jolting, which, of course, cannot be corrected by shifting the actuator. The possible speed-dependent nature of the surging tendency could be explained by the fact that the instability in the system arises from the superposition of control pulses and speed-dependent vibrations of the entire pump, which can either amplify or largely cancel each other out at different speeds.

... that makes sense ...

Quote:

If this theory is correct, then the VP 37 is unfortunately a wear part that will eventually cause vibrations due to increasing mileage.

All VPs are wear parts.
Due to the design principle...
The HD injector operates within an aluminum housing and is only lubricated by diesel fuel (which is why I advise against using aggressive RME!!!). Consequently, some of the strokes after a cold start may sometimes be dry.

However, that has nothing to do with the issue of stuttering...

Quote:

Attempts to diagnose the issue using tools like 1551 or VAGCOM are likely to be inconclusive, as they may only reveal the fluctuating voltage of the rotary encoder (RWG), but it will probably not be possible to definitively determine the root cause. In both cases (difficulty starting and issues with the fuel tank), opening the fuel cap should provide clarity.

Hopefully!!

Quote:

@Bertil: Could you please check your fuel pump (perhaps even the borrowed one) as described and post the result? If your control panel is difficult to operate, a can of diesel cleaner might help. . .

I will do it.

However, I can only do it next weekend, as I will be busy installing the original pump tomorrow.
I am not allowed to open the borrowed one!!

Hi,

The old pump is back in place, and it's rumbling again...
I should be able to take measurements of the injection volume tonight (hopefully).

Hello,
With my Passat (1996, AFN engine, 136,000 km), this jerking has recently become more pronounced. However, it only occurs after a more demanding drive on the highway. You can already notice it in the idle, which is a bit more erratic, and recently there were misfires similar to those of a gasoline engine when you give it just a little bit of gas. However, it wasn't as bad after refueling.
"Does this never happen in city driving? How can that be explained (fuel quality, fuel tank filling, fuel temperature, etc.)? I also wonder if it's more likely due to wear and tear on the injectors, because he's already producing quite a bit of soot without any tuning and with a deactivated EGR system."

Best regards, Albrecht.

I've also been experiencing the jerking since around 130,000 kilometers, and now I have almost 185,000 kilometers.
I changed the timing belt, as I mentioned in another thread. The jerking was still present. Then, a few days later, I adjusted the injection timing, and since then, everything has been quiet. Coincidence? How is that explainable?

joergs wrote:

A few days later, I adjusted the start of the subsidy, and since then, everything has been quiet.

Is it a coincidence? How is it explainable?

Hi.

Hmm... when I experimented with different pump settings (rich/lean) and sometimes adjusted the injector voltage, it sometimes seemed like the programmed injection start was being influenced by the pump's flow rate setting – meaning the amount the engine control unit (ECU) believes needs to be injected at idle.

If these parameters in the EDC regulations actually influence each other (why: }), then a "jerk" mitigation measure via initial speed adjustment would at least be conceivable.

Who knows more about the internal rule functions of the EDC?

All VPs are wear parts...
Due to the design principle...
The HD injector operates within an aluminum housing and is only lubricated by diesel fuel (which is why I advise against using aggressive RME!!!). Consequently, some of the strokes after a cold start may sometimes be dry.


RME (Rapeseed Methyl Ester) should generally provide better lubrication than diesel fuel (especially better than desulfurized diesel).
'How and with what material is a VP37 actually sealed? I would expect to find a problem there.'

If the biodiesel has been degraded (e.g., due to the presence of acetic acid and water), then the situation looks different.

Hopefully, my 'wear part' will last a little longer (270,000 km, with 45,000 km using RME).

Regards,
Udo.

Hi Udo,

"Is RME supposed to provide better lubrication? Maybe, but RME is extremely aggressive to seals."
In addition, the viscosity of RME is worse than that of diesel (RME is more viscous), and this results in incomparably higher mechanical stress on the high-pressure part of the pump. Due to the poorer viscosity of RME, less fuel can also pass the high-pressure pump piston. However, this "leakage" is absolutely necessary for lubricating the high-pressure part of the pump!!!! Therefore, RME certainly lubricates the pump worse than diesel (at least the high-pressure part of the pump).

Hi Ulf and everyone else,

I got my Lappi back and want to post some pictures of the pump manufacturers here.
Idle speed.

P1 - 903 RPM P2 - 903 RPM

Injection volume.

P1 - 5.4 mg/H P2 - 5.5 mg/H

Voltage sensor, control slide position.

P1 - 1.5 V P2 - 1.5 V

Coolant.

P1 - 90°C P2 - 90°C


With the "P2" pump, it didn't jerk (I unfortunately had to return it ), but with the P1 pump, it does jerk, and it's getting worse.

Detasz wrote:

Idle speed. old - 903 RPM, new - 903 RPM. Injection volume. old - 2.6 mg/H, new - 6.2 mg/H. Voltage sensor, control slide position. old - 1.36 V, new - 1.60 V. Coolant. old - 88.2°C, new - 85.5°C

Bertil wrote:

P1 - 903 RPM P2 - 903 RPM Injection volume. P1 - 5.4 mg/H P2 - 5.5 mg/H Voltage sensor, control slide position. P1 - 1.5 V P2 - 1.5 V Coolant. P1 - 90°C P2 - 90°C With the "P2" pump, it didn't jerk (I unfortunately had to return it ), but with the P1 pump, it does jerk, and it's getting worse.

Hi Bertil.

The measurements prove that both pumps were practically set to the same values. Therefore, the uneven operation with one of the pumps cannot be attributed to a difference in their settings.

It would be interesting to remove the cover and check the switchgear shaft for excessive friction or play.
Then maybe you'll be able to see further.

'How and with what material is a VP37 actually sealed? I would expect to find a problem there.'


If you're referring to the pump piston, it's not sealed with anything at all. The only thing that provides the seal is the extremely small clearance and the length of the piston itself.
Externally, standard seals are used, which can easily be designed for use with RME.

I read a very interesting article about cavitation damage in fuel injection pumps, and I suspect that the gases dissolved in the rapeseed methyl ester (RME) could have particularly severe effects in this case.

CU Gremlin.

ulf wrote:

The measurements prove that both pumps were practically set to the same values. Therefore, the uneven operation with one of the pumps cannot be attributed to a difference in their settings. It would be interesting to remove the cover and check the switchgear shaft for excessive friction or play. Then maybe you can see further.

... neither too easy nor too difficult.

I got a fuel pump yesterday from a 110 horsepower Passat (the driveshaft was bent in an accident - it had 50,000 km on it), and compared to mine, the flow control mechanism is much stiffer !!

Bertil wrote:

... neither too easy nor too difficult. I got a fuel pump yesterday from a 110 horsepower Passat (the driveshaft was bent in an accident - it had 50,000 km on it), and compared to mine, the flow control valve is much more difficult to operate !!

.

Hi Bertil.

Oh, what a nuisance... the explanations would have been so helpful.

It's also possible that, over time, the linkage connecting the control slide to the signaling system could develop some slack, causing the slide to no longer precisely follow the movements of the signaling system.
The result would initially be a lack of regular oscillations, but if the slider is set into vibrations by the distributor piston moving back and forth, and the injection amount therefore "jitters," this might explain the tendency to produce jolts.

ulf wrote:

Oh, what a nuisance... the explanations would have been so helpful.

... But it could still be correct...

I just got back from a long test drive, and there's absolutely no more shaking/vibration!????
After the inspection, I repeatedly moved the lever of the signal box back and forth to check for any resistance, and I removed the (few) deposits that were present. I only observed deposits on the lever itself, but they were so minimal that I didn't consider them significant.
Let's wait and see if things get shaky again in the next few days.
I observed the flickering phenomenon more closely:
- Misfires occurring at 3rd gear, starting at 1000 RPM when accelerating, as experienced by some users.
- The engine runs at a constant 2000 RPM (~50 km/h ) under light load, but immediately increases in RPM when I accelerate.

Everything points to a regular oscillation, possibly even an overshoot.

ulf wrote:

It's also possible that, over time, the linkage connecting the control slide to the signaling system could develop some slack, causing the slide to no longer precisely follow the movements of the signaling system. The result would initially be a lack of regular oscillations, but if the slider is set into vibrations by the distributor piston moving back and forth, and the injection amount therefore "jitters," this might explain the tendency to produce jolts...

...that would also be a possibility.

Deleted upon request.

diesel.gustav wrote:

Good day, diesel specialists, The quantity control valve, the high-pressure fuel pump (HDK), the control slide, or the distributor piston are always primary potential causes. Other influencing factors include the pressure pipe connections (in older TDI engines with pressure relief valves) and, in conjunction with the pump, the fuel injection lines and the injector nozzles. Further components that could be relevant include the dual-mass flywheel (if present), the entire drivetrain, the motor mount, and even the tires. These are rarely identifiable as individual components, but they often have a significant impact on the overall system, encompassing both the motor and the chassis. A vehicle equipped with EDC exhibited some partial wheel slip after the summer tires were changed to winter tires. The problem disappeared after switching back to the summer tires. Regards, diesel.gustav

Hi Diesel.gustav,

Welcome to our group!

The following new parts were installed in my car (without success):
- three rims (were bent)
- Fuel injectors (one is leaking).
- New fuel line from the filter.
- Diesel filters
- Replaced the entire flywheel with a used one (initially suspecting it was a dual-mass flywheel, but it probably wasn't).
-all three engine mounts (one was definitely defective).
- Turbocharger boost control valve (was making a clicking noise).

Therefore, the most likely cause of the problem seems to be the fuel injection pump .
I also think it's more likely due to a lack of synergy between the components, but that's a pretty thin argument...

I don't have EDC or ABS, but I've heard multiple times about the problem of shaking with winter tires on vehicles that have EDC.