HI all,

Hoping someone can shed some light as I'm desperately out of my depth. My car is a 2004 Skoda Octavia 1.9 TDi 110 81kw asv 1u5.

After a head gasket replacement and timing belt change, I'm trying to set the timing using the graph in VCDS. No matter what I do with the pump, the graph will only show 38 and on the bottom it says "timing within spec: slightly retarded. Nothing I do changes that.

I have adjusted the pump to retarded where it won't start and advanced where it clatters. I've tried in between those points but can't change that graph from 38.

The car drives well enough but has some slight hesitation under 2000rpm but fine after that. Idle is a horrible, feels like the engine wants to shake itself out.

I believe my G81 fuel temp sensor is lazy so I'll be changing that when the triangle bolt tool arrives.

I had the injectors refurbed. I've tested the needle lift wire and get a resistance reading of 117 so that's fine from what I've read.

I have a very low injection quantity reading which bounces from 0 to under 2. I tried changing the adaptation number but that didn't make much difference. When I first looked it was set to 32668. I've read the iq number should be between 3 & 5 and the "hammer mod" may be required?

I've wondered if I'm a tooth out on the timing, but AI says the car wouldn't run if it was a tooth out.

Any ideas on where to look and what to check would be massively appreciated.

Cheers

On the 1.9tdi BXE the camshaft pulley has three bolts in oval holes. When I did mine I had to loosen and adjust slightly. First I used locking tool kit and fitted belt then removed kit and rotated engine by hand but after a full rotation I had to adjust bolts slightlyt to get timing locking tools in again. Wasnt much probably 1mm but it may be enough to affect timing. Think they will run if only one tooth out but would be very noticeable. If its just slightly out by 1mm it may explain your problem.

Alasdair

Hello mate,

There no adjustment on the camshaft on mine, you lock it from the end where the vacuum pump sits.

So being is screwing with my fuel and I don't know what

Not familiar with that engine. All mine were 1.9bxe but had a quick look online and if the G81 sensor fails or the needle lift sensor (yours reads within limits) the car reverts to default 38. If its not the G81 then may be wiring damage somewhere to either.

Dont really trust AI but it came up with this to check G81

1. Check Group 007 in VCDS (The Live Data Test)

Before buying parts, let VCDS tell you exactly what the G81 is seeing.

• Connect VCDS, turn the ignition on (engine off or idling).

• Go to Engine (01) -> Measuring Blocks (08) -> Group 007.

• Look at the field labeled Fuel Temp.

• The Verdict: If it reads an impossible number like -40.0°C or 130°C+, or if it doesn't closely match the ambient temperature of a cold engine, the sensor or its wiring is dead. The ECU is using a hardcoded fallback value, which locks your timing calculations.

At this point its getting above my comfort zone.

Alasdair

I'll be changing the fuel temp sensor hopefully Monday.

I hope it's not worrying, 5 minutes totems into 5 hours.....

Hope it cures it. Cant be as bad as my sons Fabia mk1 console bolts. Thought an hour a side maybe two turned into a day and a half a side!! but managed it with a lot of patience and releasol.

As said hope it helps and cured prob

Alasdair

sadly the fuel temp sensor didn't make much difference. I'm totally stuck with AI sending me round in circles

I very vaguely remember my Mk1 Octavia timing belt change, ASV engine, also using VCDS, about 18 years ago. I also remember the graph not working for me, but that I could read injection timing in measuring blocks somewhere and set the value using the 3 bolts as per Skoda spec ( I think small amount ATDC), readout was changing when the gear was moved within the 3 bolt slots. Login 12233 might be needed.

If after adjustment the timing is within spec and the engine still stutters / smokes etc, you're off by one tooth, loosen the belt and retime crankshaft, pump and camshaft again. HTH

funny enough I was just reading with AI to use measuring blocks on VCDS instead of the graph.

I don't know, but AI says IU can't be a tooth out as I've gone through the pump range of not starting (too retarded) to bad clattering (too advanced).

Found this on AI not sure if it helps plus above my expertise.

1. Check for a Swapped Connector (Common Mistake)

The plug for the G80 Needle Lift Sensor (Injector #3) and the plug for the N108 Timing Valve (located underneath the injection pump) use identical 2-pin connectors.

• The Issue: It is incredibly easy to accidentally swap these two plugs during a timing belt job or head rebuild. If swapped, the ECU tries to read the timing signal from the actuator solenoid and vice versa.

• The Fix: Trace the wiring. Ensure the plug coming down from Injector #3 is connected to its true engine harness partner, not the N108 solenoid loom.

2. Verify VCDS is in "Basic Settings" Mode

If you are observing the value 38 while inside standard Measuring Blocks (08), the ECU is actively using the N108 solenoid to electronically correct and fight your physical movements. This can mask your adjustments on screen while causing the engine to clatter or stall.

• The Fix: You must click [Switch to Basic Settings] inside Group 000. When you do this, the glow plug light on your dashboard should start flashing. If the glow plug light is not flashing, you are not in Basic Settings, and the timing number will not reflect your adjustments.

3. Check Group 004 Data (The "Blindness" Test)

To verify if the ECU can actually see the timing, exit the graph and go to [Meas. Blocks - 08] -> Group 004 while the engine is idling:

• Field 2 (Specified Start of Injection): Look for what the ECU wants (usually around 0.5° to 2.0° BTDC at idle).

• Field 3 (Actual Start of Injection): Look at what the engine is doing. If this field stays locked at 0.0° or 0.5° BTDC and never shifts when you rev the engine or move the pump, the ECU is not receiving the signal from Injector #3, despite the injector's resistance being good. This points to a broken wire further up the loom toward the ECU bulkhead.

• Field 4 (Cold Start Valve Duty Cycle): If this is stuck at a flat 3.0% or 96.8%, the ECU has given up trying to control the timing loop.

4. Check the Pump Hub Mechanical Offset

If the mechanical timing belt installation is off by an entire tooth on the injection pump sprocket, you can experience a clatter-to-stall sweep while the internal windows of the pump hub remain physically outside the window of what the ECU's internal algorithm can map.

• The Fix: Pin the engine to absolute TDC. If you cannot drop the factory locking pin straight into the injection pump hub cleanly, the belt needs to be loosened and the pump repositioned by one tooth.

Alasdair