Engine goes into limp mode

[Steve Fuller]

There seems to be a lot of discussion about this subject so heres my problem, my 2.5 tdi goes into limp mode when under load, the turbo seems to working OK but it sounds like boost is leaking out somewhere, I have checked/redone all the hoses etc. I do not think it is overboosting but maybe the air leak is allowing the airflow sensor to be fooled into allowing too much fuel as I do get black smoke under acceleration plus the sound of the air leaking out, strangely it also makes a sound like an organ note at certain revs. There is an oily patch at the bottom of the intercooler so I suspect it could have a leak but you cannot detect anything with the van stationary only when it is pulling. Any thoughts or experience would be helpful as I do not want to spend money in the wrong place. Thanks in advance. Steve

 

[WelshGas]

There seems to be a lot of discussion about this subject so heres my problem, my 2.5 tdi goes into limp mode when under load, the turbo seems to working OK but it sounds like boost is leaking out somewhere, I have checked/redone all the hoses etc. I do not think it is overboosting but maybe the air leak is allowing the airflow sensor to be fooled into allowing too much fuel as I do get black smoke under acceleration plus the sound of the air leaking out, strangely it also makes a sound like an organ note at certain revs. There is an oily patch at the bottom of the intercooler so I suspect it could have a leak but you cannot detect anything with the van stationary only when it is pulling. Any thoughts or experience would be helpful as I do not want to spend money in the wrong place. Thanks in advance. Steve

Something similar.
https://www.vwt4forum.co.uk/showthread.php?t=180097

I do think you should look at the Intercooler more closely.

 

[Volkywagen]

Could possibly be the oil seal in the turbo

 

[sidepod]

If you look at you tube videos of various VW engine jobs you’ll see people draining the intercooler of oil.

That’s the first place I’d check.

 

[Loz]

Could also be the variable vane turbo actuator sticking and causing an overboost. You might be able to remove the linkage and check it works freely.

Hopefully @Vw guru wiill see your post and have some more qualified advise to offer.

 

[VW Guru]

Hi @Steve Fuller the most common cause for this is a split intercooler the steel bands that hold the intercooler together corrode and then snap under boost pressure. Look through your bumper the bottom of the intercooler starts to look warped and there is a visible oil stain on the radiator behind. If you can get someone to rev the engine while you look through the front you will see the movement in the cooler. The black smoke is due to the air pressure loss and the fuel being increased by the ecu

 

[cbdubs]

Or it could be a split intercooler hose I think. One of my friends had this trouble with similar symptoms.

 

[Steve Fuller]

Hi @Steve Fuller the most common cause for this is a split intercooler the steel bands that hold the intercooler together corrode and then snap under boost pressure. Look through your bumper the bottom of the intercooler starts to look warped and there is a visible oil stain on the radiator behind. If you can get someone to rev the engine while you look through the front you will see the movement in the cooler. The black smoke is due to the air pressure loss and the fuel being increased by the ecu

Hello, thanks for your comments, the straps are intact but the is an oily area at the bottom of the intercooler and I know that there is generally a bit of oil about inside these particular systems, interestingly when I tried to clean the oil off with brake cleaner it made the engine run strangely as if it had sucked the brake cleaner in through a hole, I repeated this and it happened again, I am guessing that at idle there is low pressure inside rather than boost hence the fluid being drawn in, anyway, I have taken the plunge and ordered a new intercooler. I will let you know the outcome in due course. Steve.

 

[Steve Fuller]

Or it could be a split intercooler hose I think. One of my friends had this trouble with similar symptoms.

Thanks, I have removed, cleaned and refitted all hoses so no problems there. Steve

 

[Steve Fuller]

Could also be the variable vane turbo actuator sticking and causing an overboost. You might be able to remove the linkage and check it works freely.

Hopefully @Vw guru wiill see your post and have some more qualified advise to offer.

Thanks for your interest, the linkage all seems to be free and the fact that I get black smoke tells me that I have too much fuel for the air going into the engine which would indicate a lack of boost pressure, this would be the case if boost was leaking away as the air mass meter would not know that the air passing through was not reaching the engine. I hope that is the case as I have ordered a new intercooler. I will post the results in due course. Cheers, Steve

 

[sidepod]

If it’s sucking brake cleaner in then it can blow boost pressure out

How big is this hole and why/what is it?

 

[cbdubs]

Thanks, I have removed, cleaned and refitted all hoses so no problems there. Steve

It was split right the clip fitted so it couldn't be seen until we removed the hoses and flexed to reveal the split.

 

[Steve Fuller]

If it’s sucking brake cleaner in then it can blow boost pressure out

How big is this hole and why/what is it?

Hello, because taking the intercooler off is not a quick "pop" job I have not examined it closely as I only want to dismantle everything once, I think the split must open under load as i cannot hear a leak when revving whilst stationary, the oily patch at the bottom is symptomatic of a leak though so it's fingers crossed when the new intercooler comes.

 

[Steve Fuller]

Hi, got my new intercooler but it is way too hot and exposed to the sun where I will have to change it so it's got to waitfor the weather to break a bit. I got the part from, Carparts4Less, which is really just Eurocarparts in disguise but 30% cheaper plus, on the day I ordered it, there was a promotion code which discounted it even further so I paid about ninety quid for it.

 

[Steve Fuller]

Hi @Steve Fuller the most common cause for this is a split intercooler the steel bands that hold the intercooler together corrode and then snap under boost pressure. Look through your bumper the bottom of the intercooler starts to look warped and there is a visible oil stain on the radiator behind. If you can get someone to rev the engine while you look through the front you will see the movement in the cooler. The black smoke is due to the air pressure loss and the fuel being increased by the ecu[/QUOTE

Hi, got my new intercooler but it is way too hot and exposed to the sun where I will have to change it so it's got to waitfor the weather to break a bit. I got the part from, Carparts4Less, which is really just Eurocarparts in disguise but 30% cheaper plus, on the day I ordered it, there was a promotion code which discounted it even further so I paid about ninety quid for it.

Hello, I fitted my new intercooler, the old one was, indeed split, one of the bands was missing off the back where I could not see it, the split was a good four inches long! Any way she goes like a rocket now so very happy. Steve

 

[Steve Fuller]

Hello, the intercooler was indeed split, a strap was missing off the back where I could not see and there was a four inch split. The old girl goes like a rocket now, all issues have dissappeared so very pleased, whilst changing the intercooler, I noticed a split CV gaiter so onwards to the next job!

 

[VW Guru]

Glad she’s all fixed