I went for a test drive in a tidy but well used Audi 80 1.9 TDI Avant last night - I'm on the hunt for a tow car / load lugger / workhorse, and 50+ mpg is a big appeal. The car was reasonably ok, apart from the brakes felt pretty dead and ineffective. It's been laid up for a few months, so I wasn't all that surprised. The other issue was it was completely gutless - no power, especially below 3000 RPM. I know they're meant to only be 90 bhp, but it felt more like 50. My initial thought is that the turbo might be blown. It ran and idled nice and smoothly, no excess smoke or anything. What else could cause a gutless response, especially at the bottom end. I think these are essentially the same engine as the early 90s Passat TDI. What diagnosis and checks can be carried out. Like a damn fool, I forgot to take my laptop and VAGCOM lead. Would that show up low boost errors, or faulty control valves? Should I be able to hear a turbo whine or whistle in these? I couldn't hear any on the test drive.
Welcome to TDI fault code heaven. Numerous potential causes Mike. Best dig out the Vagcom lead and see what you come up with.
Four years in to this one, none the wiser! Drives like an n/a, all mid/top end. 1Z code, 90brake. Out of junctions, it's a totally different approach! Of course, it's never been 'booked in', so it could be still an issue undetected. 38 -43mpg, with the finest lead-ish driving shoes available. Highest seen: 54, average 39, sample size: 68. 50s generally jump out from nowhere, leaving me querying the maths. Avry mod helped mid range more, thought doesn't seem to be working of late Once drove a Mk3 TDI, M-reg ish - you may recall @ the Running Horse - but may have been a 110, and with a tuning box on it. Much perkier. I should probably ask the owner tbh.
Hmm... think I might leave it well alone then. I'm not expecting a performance car, but it definitely wasn't right. I'm looking for reliable transport rather than yet another project. I'll talk to the bloke round the corner who has one (he's a mechanic / classic Ford specialist, but uses it for commuting).
It seemed OK (relative to the gutless performance below 3000) at higher revs, but I was on back roads, so didn't get beyond 4th.
A guy on Audifans says he had a similar problem caused by a faulty MAF Not sure if you've checked that on yours, Chris?
MAF is probably the killer of power on that car Mike. A simple log in vag-com would tell you for certain though. To test the MAF do as described here in part 1. http://www.ross-tech.com/vag-com/cars/tdi. Part 2 will show you how well it's boosting or not too. Also clogged up fuel filters don't help either. But theres probably nothing terminal wrong with it and a good service and maybe a MAF will sort it out for not too much. Depends how cheap it is to start with though.....
I also forgot to add, a cheap way to get rid of the MAF is to bridge two wires with a diode. Makes the car a bit less smooth to drive but costs pence vs the pounds a new maf does. Plus replacing the boost hose from inlet manifold to the ecu and inside the ecu to the MAP sensor is well reccomended as most are perished and leaking by now.... This will also cause lack of power.
A MAF can be sussed quick, even on a road test: unplug, drive & check for difference. That is assuming MAFs are a binary on/off animal and don't decline. Engine bay fuel filter canister has been changed, so that's all fine. Made no difference when done. Before the day comes when I part with what is an ultra-reliable workhorse, barring a few quirks, I would actually like to feel I knew whether it was 100%, or a stealthy 75% all along.
Unfortunately these MAF's decline and don't just die usually. Unplugging it from experience doesn't show much difference if you have a declined one. Logging is the best way to check. Do you have a full version of vag-com? There are a few logs you can make that should show if your getting your 100%.
http://www.ross-tech.com/vag-com/cars/tdi.html Somehow missed the html. The maf on this car will only ever reach 847.9mg/str, there is a measuring block which will do actual and requested maf. Log this block and graph the two against rpm.
Here's the MAP the ecu uses which takes the MAF readings and rpm, and outputs to an injected quantity of diesel. Hence why if you have an underreading MAF you get a low powered car.
At the risk of asking the bleedin obvious, where's the diagnostic plug on an 80 TDI - the only car I've VAGCOM'd up to now was a '93 Corrado, which has the plug under the gear lever gaiter. Is it in the same place?
Hmmm apparently in the fuse box in the engine bay, http://www.s2forum.com/forum/showthread.php?t=45083 and needs a 2*2 adaptor. Like so http://cgi.ebay.co.uk/VAG-VW-AUDI-2...iagnostic_Tools_Equipment&hash=item2eb5890fb5
This is worth bearing in mind too, it seems if pre 95 it seems you need an expensive vagcom lead. http://www.ilexa.co.uk/forum/index.php?topic=4603.0
