110 TDi hesitation / misfire - help please

ASV is the TDI 110 engine, the best of the non-PD engines and generally very reliable.

One possibility for your hesitation is the MAF, the Mass Air Flow sensor that is just after the air filter. It may be starting to fail or the connector may be going intermittent.

However the battery warning light suggests something electrical. I would check the battery connections and the earth straps, both for the battery and those between the engine and the car body. The engine is isolated on rubber mounts, and has to have hefty electrical earth connections to pass the starter motor current and to keep the engine block at 0 volts.

The battery is earthed underneath the battery tray. The engine is earthed by a thick cable that's attached to the gearbox and also connects to the earth point under the battery tray.

Also worth checking the fuses on top of the battery to see if there is any corrosion there, and the alternator connections.

You replaced the alternator recently. It might be worth checking those connections, in case anything has worked loose, having been disturbed more recently than the rest of the electrics? Battery-top fuses are also worth checking, the leftmost one of them takes the full output from the alternator.

The slow deterioration of the MAF doesn't usually throw up a fault code. The sensor is quite delicate and cleaning is not always successful - isopropyl alcohol or electrical contact cleaner is best for this task.

The problem I had on my ASV engined leon was that at a constant load (60mph) the car had a feeling like it was holding back and then surging, gently. It also cut out abruptly very suddenly and then went again whilst the engine was aproaching full boost point. Felt like face against the windsrceen then wiplash all rolled together. It turned out to be faulty turbo pressure sensor. It was diagnosed using the force and replacement of the sensor to confirm assessment. I don't mean to be stepping on anybodies toes, just thought my experience with a asv engined car may confirm or eleminate a potential suspect.

PuV, your experience trumps my guesswork as you've had a similar problem and found a cure. Do you know if there were any fault codes set - were you able to do a VAG-com reading or get a dealer to do a diagnostics check?

Starbiscuit, if no fault codes are set then we've only got guesswork to go on. The loose MAF connector bothers me - others have found benefits from packing the MAF connector with silicone grease, so the area is a sensitive one.

Has the connector been broken? Can you tell if it is a standard MAF - they are made by Bosch. Aftermarket replacement MAF's have been known to cause trouble, according to many people who've posted here.

EGR is another possibility - it is active in the conditions you're experiencing difficulty in. One possible way to test that is to just unplug the N18 valve's electrical connector. That will stop all EGR operation, leaving it closed all the time, but will also bring up the CEL. However if disabling the EGR cures your problem then at least you've found out where to attack.

It might be worth taking the boost hose off the EGR valve housing and looking down the inlet with a torch.

EGR in our diesels puts hot sooty exhaust gas into the oily inlet charge (oily from the crankcase vapours) which results in a build-up of carbonised sludge in the inlet manifold downstream of the EGR opening. You should be able to see it. If the car has done a lot of relatively slow miles, town traffic or stop-start commuting, then the inlet could be quite choked up.

Here's an article from the TDIclub site showing how bad it can get and what can be done to clean it.

The TDIclub has a lot of good advice including a large FAQ section. Here's the maintenance section, which talks about the EGR amongst other things. And here's another.

When I had EGR problems in my old Mk.2 Ibiza it resulted in limp mode when overtaking at motorway speeds - not the best time for a fault to raise it's head. That was with the TDI 90 engine, which has a wastegate turbo, so I could rule out sticky turbo vanes.

One long-term fix to the EGR problem is to turn down the amount of gas recirculated using VCDS. You need registered VCDS-Lite or full VCDS to do this.

"Relay 109" is often used here to describe the "Terminal 30 voltage supply relay", because it is a type 109 relay, and usually the only type 109 on the relay panel.

The Terminal 30 supply voltage relay supplies power to the ECU and attached sensors when the car is powered up by turning the ignition switch. They've been reported on the forum before now as sometimes going flaky, either causing momentary misfires or failing completely and stopping the engine from running.

The relay plate is above the pedals behind the lower dash panels. There's a picture of one in this thread.

No codes, sorry. My MAF was fairly new so had a look at the three bar map sensor and was fortunate enough to get it first time.

Elsaweb page showing MAP sensor testing

http://elsaweb.spaghetticoder.org/doc/S.en-GB.1M-MG-MGAQM/21059497/2

With my old TDI 110 I found that disconnecting the N18 connector resulted in improved pickup from low speeds. Making huge assumptions I guess that the lack of exhaust gas means extra oxygen in the inlet charge and better combustion. EGR is known to be a nasty kludge in any case - generating more smoke just to reduce the NOx, which is blamed (with very dubious justification) by Californians for smog so the whole world has to suffer for it.

Even though you reckon the inlet doesn't look too bad, the EGR could be sticking, but your symptoms suggest that the N18 valve may be misbehaving, overdoing the EGR occasionally and choking the engine.

I really detest EGR - it's a horrible idea and a bad compromise for NOx reduction. The theory is that the exhaust gas is inert, and injecting it into the inlet manifold reduces the oxygen content, making the combustion inefficient (creating smoke) and reducing the peak temperatures in the cylinder - which reduces the NOx production. NOx is produced by the nitrogen in the air burning - being oxidised - which only happens at high temperatures.

Thermodynamic efficiency improves with increasing cylinder temperatures, so this is reducing the motor's efficiency and creating more nasty particulates to satisfy a dubious environmental requirement imposed by America.

A far better answer would be water injection - a spray of water into the inlet manifold to reduce the charge temperature. This would increase efficiency (the inlet charge would be denser and contain more oxygen) but would need a water tank that has to be refilled. Californians can't be trusted to do that, it seems.

Glad things are looking up

Ur in good hands on here with ppl like Muttley who knows there stuff & the advice is priceless

EGR, or rather NOx, is not tested at MOT, the only emissions test on diesels is a smoke test. Reducing or disabling the EGR will reduce the tendency to smoke.

I have used VCDS to turn the EGR volume down to minimum on my current car, which has the advantage that the CEL isn't activated, because the ECU is doing what it's been told to do.

Elsaweb should have a page or two on the EGR system.

http://elsaweb.spaghetticoder.org/doc/S.en-GB.1M-MM-MMAQM/21060179/2
http://elsaweb.spaghetticoder.org/doc/S.en-GB.1M-MM-MMAQM/21060180/2
http://elsaweb.spaghetticoder.org/doc/S.en-GB.1M-MM-MMAQM/21060177/2

Does the EGR vale look like a 3 inch across disc shaped thing with a vacumm lobe input and sits to the rear left of the engine as your looking in at the engine?

This picture of a TDI 110 engine bay indicates the EGR valve as no. 18.



I think that matches your description? The disc contains the diaphragm that moves the EGR valve itself.