Octavia Starting Problems: ESP Repair Not the Issue?

Hello fellow enthusiasts,

This time, I'm not having a problem with my own vehicle, but with my in-laws' car...

In this vehicle, the faulty ESP (due to the use of biodiesel ) was replaced by the BOSCH service in January 2015 and installed by an independent workshop. Therefore, there is still a warranty on the repair...

I'm back home again and wanted to test drive the car after the repairs. It doesn't smell like an old oil drum anymore, but it still starts very reluctantly!
You must crank the engine for at least 3 seconds, both in cold and warm conditions, before the glow plug can start to function. Even if the engine starts immediately after being turned off, you still need to crank it.

When it's running, everything seems fine. There's no noticeable stuttering or lack of power.

Since I'm on vacation here, I obviously don't have any other measuring or testing equipment with me. Just my laptop with VCDS - and that's perfectly fine.

First, I used the TDI Timing Checker to verify the injection timing. Everything is within the 'green zone,' meaning it's close to the blue line.

Oh yes: After a short period of inactivity, a small air bubble repeatedly appears in the transparent supply line of the ESP.

The error code 17656 (fuel injection start control) was stored in the fault memory. However, I don't know if this error is related to a previous repair or if it's a new issue.
I deleted it for that reason, and after trying to restart it ten times, it still hasn't reappeared.

Due to the current health situation requiring care, the vehicle is needed every day. Therefore, for the time being, it is not possible to have the vehicle brought to a workshop for inspection and repair.

The car:
Skoda Octavia 1.9 TDI, 90 horsepower.
MKB: AGR
(No translation needed, as it's an abbreviation.)
ESP: Completely overhauled by BOSCH service.

Do you have any advice for me?

Cash registers.

Hello,

Please check the coolant temperature value that the engine control unit (ECU) is reading in the corresponding measurement block, and verify that it is a plausible value.
Please check the fuel injection quantity of the engine when it's warmed up and idling, with only the lights on and without the rear window heater or similar accessories. It's possible that the fuel quantity setting is generally set too low after the fuel injection pump overhaul (ideally, it should be 4-5 mg/stroke; higher values can worsen starting and maximum performance).

Best regards, Rainer.

Hello Rainer,

Thank you for the quick response, as always!

The test drive revealed the following:
The coolant temperature sensor is functioning correctly. Depending on the duration of the trip, the instrument cluster (MID) displays temperatures ranging from 72°C to 84°C.
But: The injection volume (MWB 1-2) is between 3.2 and 3.4 mg/dose. According to your description, that is clearly too little!

With the coolant temperature sensor disconnected, the car starts immediately (and then, of course, briefly over-revs).

I then went to the workshop, where they replaced the pump, and that's how I came across this opportunity.
You have confirmed the poor starting behavior and want to contact the BOSCH service as soon as possible to discuss how and when this problem will be resolved.

Thank you again for your prompt support.

Best regards, Kassen.

oldewurtel wrote:

However: The injection volume (MWB 1-2) is between 3.2 and 3.4 mg/dose. According to your description, that is clearly too low!

You misunderstood Rainer. Low (displayed) values tend to lead to improved starting behavior and a slightly increased maximum performance.

The amount of fuel injected at idle is (actually) nearly constant with a warm engine and few consumers operating. Moving the pump head changes the displayed amount. If a smaller amount (than the actual amount) is displayed, then slightly more fuel is injected than displayed during startup, based on a predetermined amount. This results in better starting performance.

Values that are too low will at most cause pump jerks with the minimum injection amount (idle). As long as this doesn't occur, low values are beneficial.

Greetings.
Guste.

Hello guste100,

Thank you for the correction.

But what could be a possible cause for the poor starting...?

I thought that when the temperature sensor is disconnected, the starting fuel amount is increased, which is why the car started immediately.

Am I confusing the initial amount with the idle amount here?

By the way, the initial amount (MWB5-2) was 26.2 mg per dose.

Best regards, Kassen.

oldewurtel wrote:

But what could be a possible cause for the poor starting...? I thought that when the temperature sensor is disconnected, the starting amount is increased, and therefore the car started spontaneously.

In addition to a possible change in the starting fuel quantity, disconnecting the temperature sensor will also reduce the minimum engine speed at which fuel injection begins.

Check the RPM and fuel injection amount during the 3-second start-up phase. If possible, log the data and review it later, provided that it yields meaningful readings within that short timeframe.
Please also check if the Turbo mode is supported by the MSG and the interface.

Greetings.
Guste.

Quote:

With the coolant sensor disconnected, the car starts immediately (and then, of course, has a slight over-rev).

Don't waste time; just go to an auto parts store and get a new one. The replacement takes a maximum of 5 minutes.

Best regards, Rainer.

Quote:

With the coolant sensor disconnected, the car starts immediately (and then, of course, has a slight over-rev).

It makes sense; it's only being preheated to a maximum level (which isn't usually done when the temperature is above 5°C), and that's why it starts so easily. The over-fueling might be caused by the pump being set too rich.
It is certain that the preheating system is working and the pump is delivering fuel.
If we're going to do it, then all temperature sensors should be checked for plausibility. While this has been suggested before, the coolant temperature has only been checked when the engine is warm. However, a faulty coolant temperature sensor should have little impact on starting behavior when the engine is warm.
Was ist der ursprüngliche Einspritzzeitpunkt, eingestellt für einen warmen Motor, und wurde er für den korrekten Motorkennbuchstaben (MKB) überprüft? Ist die Nockenwellenposition (NW) korrekt eingestellt?
hg
Herbert.

Hello fellow enthusiasts,

I'm finally back home in Baden-Württemberg (and I left the Octavia in Northern Germany so that the workshop can take a look at it when they have time).

@ Herbert: I also read the coolant temperature with a cold engine (an outside temperature of 10°C). It corresponded to the outside temperature.

What I noticed before reassembling the engine cover (and after the visit to the workshop and after my post here) is that the oil return lines look 'damaged' and that a lot of air bubbles are being sucked in towards the ESP (Electronic Stability Program) system!

This type of whirlpool can only have a negative impact on the willingness to start .

A rather rhetorical question: Could leaking oil lines cause these air bubbles?

Unfortunately, I do not know why these 'cent' parts were not replaced at the same time as the ESP unit.

The revised nozzles from the admin for my A4 came with these hoses included in the package.

Best regards, Kassen.

Quote:

A rather rhetorical question: Can leaking oil lines cause these air bubbles?

Sure... let's replace those first. Maybe the problem will be solved then.

A 5-meter roll of cable from a general hardware store, plus a dozen Oetiker clamps in 9mm, costs a few euros. This allows you to replace all the control cables at the same time, so there's no more room for doubt!
Oetiker clamps are not needed for the oil return lines, as they are sealed by being clipped on.