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

found some good info of what to expect from fettling here on nick's problem thread:

http://www.clubgti.com/archive/index.php?t-187213.html

Emailed him today and said he never got to the root of the issue. I haven't actually had the plugs out yet to see if they're wet, so i'll do that tonight as it's easy. Vac lines also.

 

This evening in pictures:



Plugs look a little darker than I would have hoped. More hot chocolate than sandy/cappucino!




Recently replaced crankcase breather - has reduced the lurching when moving off quite dramatically (wondering if the clutch is next culprit)




Intake manifold vac line to ECU - looked ratty here so trimmed it back about 20mm and reconnected. Didn't seem to make much difference.




Bit musty under the scuttle panel.




No breakages through the bulkhead section due to little rubber gommet thingy.








Looks like these connectors have seen better days...

I was actually thinking tonight (after i had come in for the night!) that it might be the air filter - if the car can't breathe top end then it'll run rich and won't pull very well will it? I might pull the filter out tomorrow and send the missus out naked...and leave the filter out too.

 

Don't just trim back vac lines. Replace them with silicone. Although they look ok, they can still collapse under vacuum when they start to perish.

 

Ah thanks for the tip. I'll go order some.

Edit: any idea how many metres i'll need? Thought i still had some but looks like it went with the mk2.

 

I was going to suggest checking the vac lines, but someone already did. No harm in just replacing them, as they're probably a bit perished, even if you cant see under the sheathing. As the throttle doesn't seem to make as much difference as you'd expect, I also wondered whether the TPS was doing its job. You should be able to read TPS values in VAG COM, when you get round to scanning it.

I've seen some Mk3 ABFs with very crispy wiring round the back of the engine as well, which doesn't help the control systems to do their job!

Rally design will sell you 3m of Samco Vac hose for about a fiver + VAT, but it helps if you're buying something else to spread the carriage cost. I expect you could find some on ebay too.

 

Cheers Mike, appreciate your input! I did see some wiring go down under the brake servo and across the rear engine mount - I'm guessing lambda? was quite a large connector though, perhaps 6-8 wires. That got me thinking that a goosed lambda might make it run rich too. It's all guesswork until I can get the VAGCOM done and see what it says. The wiring to the TB also seems to be right over the exhaust manifold, despite it being shielded.

If VAGCOM doesn't come up trumps, i think i'll bite the bullet and just give it a full service of filters, ignition and belts. it's been sat for a number of months so I can't really expect it to just run perfectly when wifey is doing 200 miles a week in it. Although last night she said the old mk2 8v was quicker and it seems to be doing 120miles to half a tank (if the guage is right) which is quite concerning...!

 

That FE isn't right. Have you check CLT sensor? You can check resistance measurements. Or just replace anyway.

I find vagcom is almost useless when faultfinding on the mk3. The usual stuff that needs replacing is what I did to get mine running better. Vac lines were the main issue. Ecu relay also helped. My Tps wiring was also extra crispy with the conductors burnt through.

 

Yeah it looked a bit off! was expecting more like 120 miles to 1/4 tank.

if the TPS wiring is fooked, that would explain why the car lurches forward like it's on WOT when you just twitch your ankle. What's the fix here, replace all the wiring back to the main loom?

I don't actually know where the CLT sensor is on a mk3, don't even have a haynes yet!

 

Scan it for fault codes before you start buying bits, but it does sound like the TPS wiring needs replaced either way, and that's not expensive to DIY. Have a look in scrapyards and chop a bit of loom off an audi or something similar, or just replace the wires with new yourself.

 

CLT sensor is on the RH side of the head with the white plug. As i said previously, scanning a mk3 is is almost pointless as it won't tell you much. I scanned mine several times when it was running bad and nothing showed up.

 

Tshirt, how was yours running bad and what cured it? Was vagcom playing up or was it non-diagnosable issues?

 

Mike, do you know what should happen when tps is unplugged on an idling engine? I guess nothing until the throttle has moved away from the micro switch? When I was checking it the other day I unplugged the tps, black box on front of tb, and it didn't seem to make any difference to the idle.

 

Same sort of thing. Felt flat, also had troubes starting when cold. Coil replacement helped . Vacuum lines,. Ecu relay. Vagcom showed nothing. Previous owner also had troubles with it before me, by looking at reciepts. When i stripped down engine for turbo conversion i noticed my TPS wires were burnt. so this could have also been a problem , although it wasn't that obvious.

 

Ah cheers fella! useful to know what else to check.

So got a lift in this morning and the car's done 175 miles on a half-tank, not 120. So I felt a bit better.

 

I was thinking, on the abf 16V I have fitted into my MK2 and the problems jonlikescad has. Could it be possible to knock one tooth out on the intermediate shaft where the dizzy is driven off when doing a cam belt change as there is no way to lock the intermediate shaft. I know the crank and cam shafts have notches on for TDC, I always mark the shafts with a paint pen before taking cambelt off.

From memory the rota arm faces towards ignition number 1 under TDC?

I know the timing is controlled by the ECU, however could this be adjusted manually using a KR dizzy on a ABF engine as the abf dizzy is fixed. So in theory you could retard or advance the timing as required to get a little extra grunt.

 

I'm sure the cambelt itself could jump a few teeth if it's getting old - I know when I got the belt done on my mk2 8v it was like night and day difference when driving it after!

 

The dizzy on an ABF engine, is a cam phase sensor and cannot be used to alter global advance as in a KJET CIS application, such as a KR or 9A.
The holes on te dizzy remain fix for a reason.
If you were to remove the securing fasteners and spin the G145 sensor while the engine was running, you will cause it to be out of range and log a diagnostic fault.

 

No but the crank cog and or cam gear can break reference keys alter crank to cam phasing, meaning your OEM marks would be scrap.

 

That's not good! How do you re-time it after reference marks are scrap?

 

Are you refering to the crank pully key? I know if that snaps your timing will be out and probably damage the valves. I made sure my crank plully was tight and not going to undo under lots of stress.