TDI hot start issues
 

Hi guys. I'm wondering if someone could plug their 4.0 or 4.2 TDI in and tell what the RPM of the engine is while cranking. When the 3.0tdi A4 is cranknig it spins over very fast in comparison. (keep forgetting to plug in and see what speed it turns)

My hot starting problem is getting worse and worse and worse. The other day, after having sat on the drive over the weekend it wouldn't even start from cold. The engine sounds slow and gets slower.

Tonight after trying to start it I plugged my wee code reader in. On its own battery it started off turning at c150RPM and by the time it decided it wasnt going to start it was only doing c120RPM. With the jump leads on the A4 it started turning over at c170 RPM slowing to the mid 160's.

It isnt even starting with a jump until it has sat and cooled for 3-4 hours. Also, I used to be able to start from cold at work, then stop at the supermarket on the way home, by which time the engine had heated up to around 70 degrees and was still able to start it after doing the weeks shopping. Now it takes several attempts and usually needs the booster battery to start.

Ive bought a new starter motor for it. I'm not one for blindly throwing replacement parts at a probelm in the hope of fixing a problem but it was really very cheap so i thought i moight as well take a punt. Taking it to the "experts" to have it scanned on dealer level VCDS software gave me no information and the crank sensor did nothing to help so if this doesnt work I'm seriously considering scrapping the thing.

gill

If it cranks faster using another car as a booster, then your battery must be bad.

Try charging it fully, either by a long drive (3-4 hours) or put a charger on at least over night. If the problem doesn't go away, you need a new battery :)

But as you have thought of yourself, a worn out starter motor will crank considerably slower than a new one.

When fitting the new starter, it would be worth replacing the earth strap/cabling as a precaution also, they should'nt be too expensive.

Your symptoms sound exactly like crankshaft position sensor failing which happened on my D3. Only started well when cold and it flattens the battery everyone you crank it without starting. In the end it packed up altogether and the car wouldn't start until it was changed.

It's had a new one mate and a battery. See i've been paying attention to the other threads. :D Wasn't clear if the battery had been coded to the car tho.

It's actually had two new crank sensors. An intermotor one which I thought might have been a fake (cheapo off ebay) and a genuine bosch one straight from the bosch factory.

Its had three new batteries in the last two years as well. The current one was brand new in I think October.

I'm beginning to suspect something to do with fuel pressure but without VCDS I cant check. I'm hoping to get it in to my local garage for a scan next week sometime.

Cranking speed is definitely low though I think. I'm not going to bother with changing the starter until Ive had the fuel pressure checked.

gilll

Sorry I was dipping in to this over the mobile while out driving all day yesterday :o I'd be suspecting fuel next like you as well then - has the fuel filter been changed, its not blocked is it?

I would have thought that the engine would run a but iffy all the time if the fuel filter were blocked. It's due a service anyway, so I shall be changing the filter in the next week or so along with all the other service items. Even with my old man's very sizeable discount it still comes to around £100 for all the air filters, oil filter, oil and fuel filter. Im used to doing a full service for nearer £30 haha.

The only thing with the fuel pressure theory is that you would expect the pressure to still be high if you switch the engine off then immediately restart. So when it just cranks over during an immediate restart.When I get it scanned next week I will get a read out of the fuel temperature as well. Its also possible that the fuel temp sensor is reading high and holding the injection off. So many possibilities!

Another thing it does when its hot, now that I think about it, is that it makes a nose that kind of sounds like a viscous fan. Sounds like its coming from the back of the engine/torque converter sort of area. cant really hear it the same outside the car but its definitely noticeable in the car.

I got the old D2 back on the road today. It had been sitting for a few weeks after I got the D3 and someone was coming to hopefully buy it. So I moved it to make sure everything was ok and the rear passenger side spring burst and came out through the wheel, bursting a the cv boot and the brake hose. It has sat in my workshop ever since until today. I forgot that you need to drop the subframe to fit the rear springs. I managed without doing it, but by god it was difficult! Needless to say the front brakes are seized now so going to have to do a little more work before I can advertise it again. As much as i oved that car, going back to it from the D3 is an experience. The D3 is just in a whole different universe!

If the fuel filter was blocked it would let fuel through at lower rate and mostly affect high load situations not so much starting. I think It may well be combination of problems. It could be weak battery combined with poor electrical connection to starter and weak starter itself. The fact that it turns faster and starts when jumping from another car means that battery is weak. 3 new batteries in 2 years does not say much, it could be duff batteries or a fault with a car draining/damaging batteries. Check the battery if you can find a place that does it properly. Portable testers like many Halfords use will only put 100-200A load on battery and is not sufficient for a large battery like in A8. You would need at least 400A load, even better if you can do 800A; which means a lot of heat released which I am not sure if can be achieved in portable unit. Battery testing benches have large resistors and large fans to cool them down to allow high drain for longer period. Conductance testers like this https://www.aliexpress.com/item/Orig...0-2990ba944727 can give you general picture but are not very accurae when it comes to larger batteries. In my expierence anything less than 100% health indicated mean battery is on it's way out.

Where are you located? Some of the forum members might assist with VCDS if you are not prepared to buy your own genuine unit yourself just yet. I don't necessarily condone pirated things but for testing purposes you could buy and temporarily use Chinese copy of VCDS for ~£30 to evaluate and see if you would like to buy genuine kit. Or possibly try some alternatives like OBDeleven which receives good feedback but I have not used it myself so cannot give any feed back on that.

I would really like to get hold of VCDS. When I checked the rosstech website though I was just confused. The shareware version would appear to do nothing of any great use and the VCDS lite version as far as I could tell, doesn't let you do most of the output tests that I wold like to be able to do. Where it comes to the full versions, the cheaper one only lets you use it on three cars. Seeing as i have currently got 4 audis (sold another one last week) thats not of much use, plus i tend to change cars fairly often as well as doing a lot of work on other peoples' cars. So I'd have to get the professional version to be of any use. I was really quite disappointed with the info on the rosstech site. You basically have to buy it to know what you can and cant do with each version. Add to that the description for VCDS lite basically translated as "you're too poor to buy the full version so you don't deserve to get anything useful", which found more than a little insulting.

If you have a link to one of the chinese versions mentioned above then feel free to PM me the link. I have also read about the OBDeleven but wasn't sure what the capabilities actually are for it. for instance, can you even read fuel pressure or change suspension heights etc?

I think you could well be right about a combination of things being the problem. I will try a drain test on th ebattery and see what the actaul drain is. I'm not sure how much use this will be though as the battery management module runs various things for various lengths of time so I reckon I would need to have some sort of thing that would read and record the battery drain with everything connected up.

There are quite a lot of threads in various forums on the net with the same issue, but I have only seen one so far that has been resolved. In his case it was a dodgy battery but as the PO of my car changed the battery to try and sort the problem I am 99% sure its not the problem wth my car. (the PO told me it only happened once every few weeks with him. I believe he only used it for commuting though, so didnt really have occasion to hot start it very often. If I'd known it was every hot start I probably wouldnt have bought the car, or would have at least tried to knock the price down a bit more)