1.4 TDi - unexpected Limp-home-mode on motorway

[Littlepixel]

Was driving der Kleiner-Panzer [53 plate; 91k miles] down to Calshot from London super-early this Sunday morning through the fog on the M3.

I'd just put the hammers down a wee bit to overtake something - pushing reasonably sedately from maybe 2500 revs to 3000+ when shortly after power fell away and the car carried on - seemingly limited to about 2500 revs.

My foot was on the floor and it wasn't doing more than about 65 mph - slowing to 55 or something on the hills. My mind instantly went to hushed mentions of 'limp-home-mode' as I took her into Fleet services where I'd planned to break the journey and get some breakfast. Maybe it was the fog? Moisture? Maybe it's just all brokeded?

I hadn't seen any warning lights so figured perhaps it was just some sort of glitch (I had a weird one about a year ago when it immobilised itself for a few minutes after I stupidly tried to drive with the handbrake semi-on.) I'm not too au-fait with problems in cars that are so comprehensively controlled via the ECU - my last cars were a 1970 Saab 99 and a 1982 VW T25 westy van - so I find the way the computer takes over a bit unnerving!

Anyway - after my break of about thirty mins and turning it over it seemed fine again though I did get a glitchy 'service 100 miles' message on the dash for like a millisecond even though it's not due for more like 3000 miles. Revs were free and happily going over 3000; power was fine. I finished the journey fine with no repeat of the glitch and my return trip the same day in the evening was fine too.

But I'm worried about it happening again on a busier day (This was at about 7am on a Sunday so it wasn't too bad - 6pm on a Friday might not be so much fun.

Wondered if anyone had any advice? - I'm guessing I should get it checked out - at least with a VAG com diagnostic, but I've read it might be problems with boost pipes perishing on the turbo or a chink in the intercooler.

Any sage thoughts appreciated!
(Thanks in advance for any help!)

 

[spike]

Hi and welcome to the A2OC

It sounds like a problem with the aftercooler radiator core or pipework. In the early stages, splits can open up due to the high turbo boost pressure while accelerating hard or going up steep inclines. This causes the engine to go into limp home mode. Switching the engine off resets the ECU and everything goes back to normal until the engine is working hard again.

Cheers Spike

 

[dan_b]

Hi and welcome!
As you already surmise, I'd put money on it being either a split intercooler, or a split boost control hose. However, just one thing to also check, do you have a 75 or a 90PS TDi? Does your car have rear disk brakes or drum brakes?

You can do a quick visual inspection of the intercooler to look for any evidence of oily residue at the bottom. The boost control hoses are a little bit more fiddly to say the least.

 

[Littlepixel]

Thanks Spike - I'm a Long time lurker - first time caller.
I'll get it checked out; Hoping it's not hard to diagnose.

Idle thinking out loud now - I've been procrastinating about getting the ubiquitous Stealth remap for a while anyway - if I took it there, would they be happy to deal with the fault first as well as the remap do people think?

Obviously I wouldn't want to increase power BEFORE fixing the issue—but it seems to me if they'll do both it'd save an extra trip to the garage and be with an A2 expert into the bargain.

 

[Littlepixel]

Hi and welcome!
As you already surmise, I'd put money on it being either a split intercooler, or a split boost control hose.

Thanks Dan. I try at least to do my homework

However, just one thing to also check, do you have a 75 or a 90PS TDi?

Meant to say in my post - it's a 75 with rear drums.

You can do a quick visual inspection of the intercooler to look for any evidence of oily residue at the bottom. The boost control hoses are a little bit more fiddly to say the least.

Thanks for that; I have to admit I've never yet had cause to have the bonnet panel off - Intercooler must be somewhere behind the bumper - under the fake access 'grille' maybe?

 

[a2sumo]

To answer your question about stealth racing fixing and re mapping - yes I'm sure vince and his helpers will have it sorted and you will be so pleased you had it mapped- you will wonder why not sooner!
If it requires a new inter cooler then they would have to source you one, but it maybe a pipe split. One other point to remember is that the trip was early and foggy --- both are great for engines. Cold air is more dense so more boost landing with moist air is a great combination.
Good luck I look forward to hearing about your re map v soon. Cheers mike

 

[Littlepixel]

...and you will be so pleased you had it mapped- you will wonder why not sooner!

One other point to remember is that the trip was early and foggy—both are great for engines. Cold air is more dense so more boost landing with moist air is a great combination.

Are you saying that it might just have been almost a 'freak' occurrence because of the cold + moisture at that time of day, and that in more normal driving (I don't often drive at 6 in the morning) it's pretty unlikely to happen again?

Thanks for everyone's quick and straightforward help btw. Great forum.

 

[andybaggies]

One other point to remember is that the trip was early and foggy --- both are great for engines. Cold air is more dense so more boost landing with moist air is a great combination.

I can whole heartily agree with this. Many years ago I used to run an old bevel drive Ducati with 40mm accelerator pump Dellortos and straight through Contis. The performance when driving back from my mothers through Stratford on Avon in the middle of a winter's night was always noticeably better with the exhaust having a much harder bark to it. And what a bark with those Contis!

Andy B

 

[dan_b]

Not as such, if you have a leak forming, it'll only get worse over time, but it's possible that the extra power afforded by the cooler, damper and therefore more dense air, plus colder temps making rubber less flexible, may have been enough to push it over the edge.

If you take the bonnet off, when you're standing peering into the engine bay, the intercooler is the smaller of the two radiators you can see behind the bumper (in front of the engine) and is the one on the left as you look down. Peer down into the murky depths and if the intercooler is healthy, it should be a nice dull aluminium colour all the way to the bottom. If it's stained with oil deposits at the bottom, it's blown...

Are you saying that it might just have been almost a 'freak' occurrence because of the cold + moisture at that time of day, and that in more normal driving (I don't often drive at 6 in the morning) it's pretty unlikely to happen again?

Thanks for everyone's quick and straightforward help btw. Great forum.