Vacuum leak smoke test

[george_edge]

Hi all,

I have a shed of 2010 Caddy Maxi 1.9 BLS that has an issue. It struggles to get past 50mph, I'm getting fault code P0299. After clearing fault codes the first push it goes well but then suddenly slows down.

First question, is this likely to be a vacuum leak? Having a look on youtube, some vacuum leaks seem tiny like small pinholes - would this really make that much of a difference to the power?

Second question, my dad's work have a smoke test kit but have never used it. Has anyone done a smoke test on a 1.9 BLS? If so, any tips of what to do and where to connect? I'm not particularly mechanically minded, just trying to save as much money on my incredibly cheap Caddy as possible so Layman's terms if possible would be greatly appreciated.

Thanks in advance!
George

[STP]

Ideally you would make a connection to the intake tube after the filter and pump smoke in there to check the intake tract and inlet manifold etc, and then next you can find any vacuum line, connect there and pump smoke in to try and find a vacuum leak.

Though you may be thwarted by a non return valve as the system is designed to suck at the vacuum pump end and not allow air to get back in, except to an actuator when it is released from the position the vacuum had pulled it to, by letting air into the actuator vacuum port from the other side but again not letting air into the main system or all vacuum would be lost when that happened.

To be fair on a diesel, it doesn't care about vacuum to run, only petrol engines need that. Diesel engines basically run with no throttle plate (they rev from injecting fuel only and air being pulled in, is as a result of that) so generate no vacuum internally, hence they need a vacuum pump to operate things like power brake assistance and turbo actuators.

Petrols on the other hand, rev from allowing air to get in past the throttle plate. Fuel is then injected as a result of that, in the correct ratio (roughly 14:1 air to fuel depending on conditions like air and engine temps)

A vacuum leak could be dropping off your turbo boost for example and that's what you are experiencing. Did you get a proper description for that code? Its a power train code of course, so engine related but I don't know what that one means.

The best way to test a vacuum system for a leak is introduce pressurised air with a pump or foot pump and listen for hissing. On a petrol you can spray bradex easy start (Ether based compound) and it will rev up slightly or stutter when the vacuum leak is sprayed (you can also use a water mist from a spray bottle, it will definitely stutter when water is sucked into the leak area) but a diesel will not even notice you doing either of those at a vacuum leak point. You could fit a vacuum gauge in the main line from the vac pump, and run the engine for a minute or two, observe the vacuum and then stop the engine, the vacuum should hold. If it drops off slowly, you would see this on the gauge and possibly hear it pulling air back in.

[george_edge]

Thanks for the response! I also read somewhere to use a plastic bag after the MAF sensor to prevent backflow into the air box, is this right?

The full code is '00665 boost pressure regulation control range not reached p0299'.

Initially I took it to a friend of a friend who is a mechanic, he changed the MAF and MAP sensors which didn't work, and he thought it was likely electrical. I then contacted an auto electrician who was pretty confident it wasn't and suggested a smoke test. I have to say I'm inclined to agree, to me it seems more likely there's a leak somewhere.

For an extra bit of context, the previous owner said they did an engine swap earlier this year including a new turbo.

Again, thanks for your help!

[STP]

Ok, then as I said before it could be a boost issue, so that sounds like it is then from the fault code. It's saying it can't reach the specified boost level requested.

I'd look around the boost solenoid and actuator for the turbo to see if you have any split hoses or a failed boost control solenoid. On the 1.9 TDI it used to be called the N75 valve for VNT turbos, I have a 1.6 TDI and I don't know what the system is here but I expect it's similar. It controls the boost level of the turbo by controlling the vane pitch, and that is by using vacuum to drive a rod to alter the turbine vane angle. You can get a hand held vacuum pump (trigger operated thing) from eBay and hook it up using a tee piece and see if the actuator moves all the way out when vacuum is applied, from memory it should drop to the full boost position with no vaccum, and when the system decides maximum torque is reached and has flattened out) it trims the vanes back by sucking on the actuator and pulling the vanes back to create less boost so it doesn't shoot over the required value. The solenoid is electrical but controls the vacuum passed across to the vane control rod.

Check around that area.

[Jase14]

Thanks for the info and explanation on how it works, I also have the same issue P0299 error under boost.
Cheers Jase