Boost Leak?

[Christophski]

hey guys

So having got my car all back together and running ok for a few months now I think I have a boost leak but I just need some guidance on if it could be something else that springs to the minds of some of you more in the know.

The car is a homefried ABY with all Samco boost hoses and all of the vac hoses done in Poly too so none of these should be split anywhere (some of them only done last December) and it has the Mark H mod too.

Obviously I will check all the hoses for splits anyway and need to run a leak test, but i just want to know if it sounds like any other common issue? I will also just nip all the hose clamps up a bit in case its that simple

Basically if i floor it Sometimes I only reach 1 bar boost sometimes not even that but if I ease off slightly and floor it again in the same run as it were it will boost a bit higher and then fall a bit. Does this soudn like boost leak or something else I need to investigate. I dont get the big boost cut thing like its breaking all of a sudden. It runs and idles fine....

Also, I do have a leak test kit but the bung with the nipple on it is way to small for the MAF hose for some reason. Does anyone have one I could borrow to pressurise the system please?

Cheers in advance.

[Christophski]

Oh and a few months ago i fitted a new turbo (Standard) which doesnt smoke or anything. Can slightly loose bolts or a missing gasket between pipework cause a boost leak? I refitted the solid ribbed pipe in the correct direction with new gaskets but reused the other gaskets I had.

[Rusty]

If you had a boost leak, then the overboost protection would more than likely cut in, as it's quite easily triggered on the homefries.

The boost profile is not linear. Don't forget that there's also the time taken for the boost to build, which in the lower gears means you're much further up the rev range.

You need to be sub 2k RPM in 4th or higher to get the full 1.5 Bar and even then, if it's cold outside and you've got a decent IC, it'll only register 1.35 Bar or so. 1Bar ~ 14PSI

[Christophski]

Cheers Andy.... So des this mean I most likely have something else up rather than the boost leak??? I dont get the opportunity to do full boost run in 4th or higher lol so I dont know about that. I thought the ar should be hitting 1.2bar in first to third on a full run from low revs? I only have a standard intercooler too. It used to go to 1.2bar happily but these days doesnt. Lst time I had this issue it was a hole in the membrane of the wastegate which I replaced. I didnt get boost cut then either, it just wouldnt boost over 1bar.

[Rusty]

Don't have to hit 120+ Just give it WOT from 2k in 4th and back off at sensible speeds. If it doesn't hit 1.4-5 bar when the boost comes on by 2750, then you might have something wrong. It should hold that boost between 3k and 4k5.

This thing about gears and boost is a classic case of misinformation. The boost is lower in the lower gears because the time the turbo takes to spool up is pretty much constant but in the lower gears, the car has increased revs by a chunk more, so the ECU is further along the boost curve (above). If you were to leave it in second and bind the brakes or go up a steep hill, the boost would be higher because the rev increase would be less than going downhill

So, in conclusion. Put it in 4th at 1k5-2k RPM on a straight, clear piece of road or a quiet motorway and give it everything. If it doesn't hit 1.4-5 Bar or so, then sure, start to worry but if it does then you're just fine.

If you're not happy staring at a gauge, then get a passenger to video or similar.

[Christophski]

Hahaha, cheers Andy. Appreciate the info. Things I did not know. I will get my brother to watch the gauge tomorrow evening when we take the car out for a run to a pre 93 local car meet. Anyone near to Tring is welcome.

[Rusty]

Yeah, better than getting him to drive It's funny how mch faster these cars feel from the wrong seat. I got a mate to run mine through the gears and it's quite indecent, so God knows what another 100+bhp would feel like.

[Christophski]

Haha yeh. Friends and family always tell me its a fast feeling car from the wrong seat lol. Thing is I want to make sure this is right as next year im planning on colelcting and doing RS + spec to the car so its important its right first. Plus I know what my brother drives like after his gearbox and driveshaft exploded in a car he was gunning at the time. Needless to say hes rebuilding things at the mo lol.

[Christophski]

Right guys, I do have a loss of boost somewhere. two nights ago I took the car out and tried as Rusty suggested. I came onto a dual carriageway heading up a hill with nothing around in 4th gear and started from just under 1500rpm and planted my foot on the floor. The guage would only read upto just under 1 bar. I slowed down again and tried again only this time when I hit 1bar it stopped so I eased off for a split second and punched it again and the boost rose to 1.2bar, held for a few seconds then fell. (My brother was watching the guage) So I am going to do a leak test on it to see if I can find anything. Failing that whats the next step??? All of the breather system is new so I might check the jubilees are all tight on that and as I have said all the hoses arwe Samcos and all the vac lines have been replaced for blue poly lines so all should be good too... I also do not get any boost cut or kangarooing caused by the protection thing either.

[prj]

If some of you devoted 1/10th the time to maintaining your car as you devote to posting on forums problems would be solved much quicker
Just do the test, there is no need to play hamlet "to leak or not to leak".

If you never pressure tested your car 99% you will have leaks. Never seen one that didn't leak, but I sure saw a lot of bruised egos once the leak was pointed out.
You should do a boost leak test every oil change on these cars, I sure do.

[Error404]

[Rikki Kitto]

Who is doing boost leak tests then?

[Christophski]

Yeh cheers for that PRJ nice to know that all the non maintenance that I don't do on my car means it's so terrible lol. Shame it won't stay leak free for a whole year... As leak test was done in January along with a second oil change since the previous one that was done a month before hand lol. I am asking so that on e I have done the leak test I can move onto the next stage in the same day as I like to do as much as I can in one go rather than waiting another week or so to do the next item after I have found out about it. This wasn't a thread asking for do I or don't I leak test, this is a thread asking for the next step to check after doing a leak test. I do however appreciate your input as you are a valid I5 guru and know these engines really well. Besides I hate Shakespeare too lol

[Christophski]

Oh and rikki seems I'm doing my boost tests again for not the first time this year lol.

[prj]

Don't take it personally, I'm just taking the piss