mk3 abf no longer feels a bit unresponsive - now odd MPG!

You fit another crank pulley and all is back to standard again.

If you look in the various measurement functions of VAGCOM, there should be one in there that shows you how the TPS is reading. If you switch on the ignition without starting the car, you should be able to see how it's behaving. If it doesn't change smoothly and progressively with movement of the throttle pedal, then that's either duff wiring or a duff TPS. You could also take the unit off and check how resistance progresses when you turn it - again, it should be smooth and progressive. Then buzz test the wiring, checking for continuity and short circuits... or just strip off the sheathing and have a good look!

 

If the bolt is tight and the belt is still intact, then rarely does it 'snap' but it can shear off the key and start putting the cam to crank timing out of phase.

I have had a few 16v engines like these over the years and one did shear the key on the cam wheel to 'walk' and smack a few inlet valves on the pistons. This problem seems occur more frequently on ABF engines.
A case of the crank cog shearing locator, was seen in vw_singh vehicle, as reported here.

 

my belt kit came in today, and got it booked in to get it put on saturday. I bought a tensioner too as I wasn't sure how often you change them or when mine was last changed. I'm hoping this will make a good improvement.

 

You can use a KR one too. I think I only paid 20 for mine. Always worth changing the belt

 

Ouch.....I feel sorry for vw_singh poor engine.

So how much can you safely rev the abf engine before damage could occur? I see on your abf you can rev it over 7000, that's crazy but wicked lol

 

just a quick back on topic update, I replaced the vac lines with 3mm ID silicone hose today. I did the long one from ECU to intake, the shorter one from FPR to intake (managed to squueze a little oil into the FPR diaphragm as I read this could help) and also a tiny one from the plastic hard line from airbox to intake (connector - hardly worth it but it was dead!)

anyways, I took the car out just now and the hesitancy seems to be completely gone! I guess the ECU vac line must have been collapsing in the large vacuum change between idle and whatever pressure develops at moving away speeds. I'll get wifey to drive it later and just confirm this is the case as I only tend to get behind the wheel about once a week!

It still doesn't pull my face off at the top end, but I think that is more down to the fact that the TB is a single butterfly item, and I think from my mk2 days I'm expecting (psychologically at least!) to have a bit more kick after 4000, but I guess this is why it is so punchy low down. I also notice that the plenum is jetblack inside - is this bad? perhaps it has been running rich a lot or a mixture of rich running and also the oil breathers. Any speculation welcome!

I've got the cambelt booked in for 1:30pm tomorrow, so I'm hoping that will help too. I'll try to update tomorrow eve or sunday.

Cheers for all the help so far.

 

Did you do the one under the manifold? I did say from the start to change the lines?

 

this is true. I did the FPR one if that's what you mean? goes from cyl1 (by oil cap) underneath runner #1 to the fuel pressure reg.

I couldn't find any round the back of the head except the main ECU long hose from the intake manifold.

 

well the cambelt and other belts is done now along with auto tensioner. Fella said the timing was spot on so I wasn't expecting much in the way of a performance increase (for those wondering when I got the belt done on my mk2 it was night and day performance, but I knew that was off because i'd have to drop to 3rd just to get past 60mph on the motorway!)

I took it out after the belt was done and let the oil get to 80 before giving it a go. I hit 80 in 3rd and 100 in 4th on my secret runway so I don't think it's off pace by much. The rotor arm is a little corroded which makes me think that ignition parts will help it along.

He said he may have the kit to do the VAGCOM check so i'll run it by him, he only charged me 80 for 3 hours work as he does it on the side of his normal mechanics job so charges a bit less than normal. I'm now thinking i'll do the classic things like ignition parts and filters, try and get it scanned (don't have a laptop at home) and then do sensors after that.

It did 32mpg on our last tankful of 95RON but i was expecting more as my missus drives so slow she could convoy with the lorries!

 

another pictue based update! going on what tshirt said, I ran the car up to temperature (needle verticle so ~90deg) and oil on 70 through MFA and unplugged this:



and nothing changed. no flutter, no splutter.


Am i right in thinking that temperature sensor is goosed then? I remember changing the classic BTS on my mk2 and whenever I pulled the connector off that when engine was warm it would splutter and sound like it was going to stall.

If I can get this diagnosed tonight or tomorrow, I can pop out and buy a new sensor

 

Pm'd

 

Cheers dude. I will go pick one up tomorrow then I'm hoping all will be well for a little while!

 

Well I changed the coolant temp sensor today and went for a long hard run and the plugs went from this (before):



to this:



so I think the car is running a bit better now. I got the MFA to read 50mpg when cruising in 5th also but I know they can be about 10% or more out. I'll let the missus run the tank down this week and hopefully at next fill up we'll be looking at a better average than 32mpg.

Thanks for all the help, I'll keep this thread updated for further searchers.

 

Does it feel better?

 

tbh it doesn't feel massively faster than before, but i'm not sure what i'm expecting. It has a lot more urgency when you put your foot down which makes me think the bum dyno is working and the sandy spark plugs are a sanity check. it's more willing to pull from further down the rev range and leaving it in 3rd at 60 it definitely has more go than before.

It's still a wallowy old hector being bone stock so I don't chuck it about like I did the mk2, but after changing up to 5th at 100 and seeing it was still pulling I think it's a good sign that things are better. There's a slight miss at idle due to an old rotor arm I think, but with recommended BOSCH plugs being over 30 a set and the leads about 50 I want to be sure about the next thing I change. I may do the ignition system for the winter just for peace of mind.

 

Well, just another weekly update! The car has been running great this week. Seems the temp sensor was to blame after all. I took the plugs out yesterday and all nice and sandy (MUCH better than either of the pics above) but the car is still drinking and my slow-driving wife is still only averaging 32mpg on her commute of A43-M40-A34 and return. What am I missing or is 32mpg to be expected?

My thoughts:

Possibly fuel is physically leaking out - check all fuel lines filter and pumps.
Air filter is really dirty and full of leaves - would this make a big difference to mpg?
Lambda sensor is duff - but then surely the spark plugs would still be black?
Plugs work but are not burning efficiently - Top cylindrical face of plugs are still black even though electrode is sandy - replace with the Bosch B3DPO(?) and go from there.

Any other ideas gratefully welcomed!

Jon.

 

Think all that mentioned should help. The mk3 coils aren't the best. I had long standing problems with mine that were caused by a dodgy coil. Doubt fuel pump would be a problem.

I don't think 32mpg is too bad. Maybe the wife although slow may not necessarily be gentle enough in the throttle to affect average FE.

 

Thanks tshirt. I found this thread through google:

http://www.clubgti.com/showthread.php?166336-mk3-16v-fuel-consumption

seems a lot of people cleaned up their earths (which I did on the mk2 and forgot to on this!) - I found the front wing to bonnet earth on nearside was snapped but doesn't that just earth the body? I'll try to get out with some electrical contact cleaner and go over everything including the ECU.

32mpg on a full tank (12 gal?) is about 380 anyways so it's not THAT bad I guess. She does his traffic from time to time going into Ox in the morning and leaving in the evening.

 

Plugs should BKUR 6 ET-10 NGK or similar tripple electrode type.

 

Indeed, I made the mistake of wrapping the wiring around the back of the engine with plastic coil wire tidy and it melted. Fortunately it didnt stick to the wiring, so I then cut long strips of linen wrapped to insulate my wires then used electrical tape. All good now.