Collapsing vacuum hoses under boost...what is best to use?

AllHailKingVolvo · Jan 23rd, 2020, 20:38

Hi all,
I have been experiencing some minor hesitation under heavy load in my 940, and have been chasing the issue since I bought the car earlier in the month. It drives very well other than this, and I've done a good stage zero service on it.

Speaking to a very experienced tech who runs a Volvo breakers near me to today, he said he suspected that my vacuum hoses may be collapsing slightly under boost, as they are commonly replaced with soft and inferior hoses.

My vac hoses ARE very soft and floppy. I think it might be prudent to replace them with better/stronger hoses, but I'm not sure what the best hoses are to use...can anyone advise if there are there any specific hose kits or materials that are best for use with turbo cars? It's a stock B230FK.

Ta!
Phil

aardvarkash10 · Jan 24th, 2020, 00:10

this or a similar local product

Laird Scooby · Jan 24th, 2020, 00:37

These people are usually a safe bet Phil :

http://www.autosiliconehoses.com/

As for collapsing vacuum hoses under boost - bit of an oxymoron!

My guess is it would be on the suction side between the turbo and MAF but only a wild guess.

TonyS9 · Jan 24th, 2020, 01:24

The induction side doesn't care about the breather system. Worst case the turbo won't dump, but that's a pretty much unheard of issue regards the vac pipe. Maybe you could have a collapsing fuel pressure pipe but it is quite rare in narrow section pipe. Is it collapsed at idle?

He might mean inlet hoses, but these are rarely replaced with silicone hoses because they are a custom shape.

Weak spark is common with the distributor on the end of the cam. Oil can cause hesitation.

AllHailKingVolvo · Jan 24th, 2020, 07:38

Thanks all!

I'm not altogether sure that the vac hoses on my car are intended for purpose at all-I have replaced vacuum hoses in the past and the stuff I used was much stiffer and more substantial than the material that is on my car. I think perhaps they were replaced by a well-meaning PO who just used whatever he had to hand. Many of them are secured at the nipples with cable ties (so to speak!) Which aren't what I would use for an airtight connection on soft pipe-I'd far rather use the correct gauge pipe and let the barb of the nipple do the job it's intended for.

I'll order some more and replace them to be on the safe side, as they're not exactly an expensive part. Can anybody advise on what size ID I need?

Laird Scooby · Jan 24th, 2020, 12:15

Quote:

Originally Posted by AllHailKingVolvo

I'll order some more and replace them to be on the safe side, as they're not exactly an expensive part. Can anybody advise on what size ID I need?

Easiest way Phil is to get your "very-near" gauge (Vernier) and measure the core diameter of the stub - not the diameter of the barbs on it. Get the size of hose closest to this but go down rather than up. For example, if the core diameter of the stub is 4.2mm, get 4mm bore hose, likewise if it's 4.8mm get 4mm hose.
If the stub is 5.0 or 5.1mm, use 5mm bore hose.

Chances are you'll need 4mm hose but i'd honestly say measure first to be on the safe side.

AllHailKingVolvo · Jan 24th, 2020, 16:00

Quote:

Originally Posted by Laird Scooby

Easiest way Phil is to get your "very-near" gauge (Vernier) and measure the core diameter of the stub - not the diameter of the barbs on it. Get the size of hose closest to this but go down rather than up. For example, if the core diameter of the stub is 4.2mm, get 4mm bore hose, likewise if it's 4.8mm get 4mm hose.
If the stub is 5.0 or 5.1mm, use 5mm bore hose.

Chances are you'll need 4mm hose but i'd honestly say measure first to be on the safe side.

Great advice, thanks Dave! I'll whip the Vernier out and do some sleuthery!

TonyS9 · Jan 25th, 2020, 00:51

The nipples are not barb'd, they are straight. They need a little stretch, sometimes a tie wrap helps a badly choosen pipe or using what you have. It's quite difficult to find the perfect size, and I'm quite anal on restoration.

Volvo use metal clips, although I don't think they are needed.

On the track none of the little pipes come off, but the large boost pipes do with high boost pressures and a bit of oil contamination on the surfaces.

Jan 23rd, 2020, 20:38	#1
AllHailKingVolvo Ye olde Volvii galore! Last Online: Dec 18th, 2023 11:23 Join Date: Oct 2017 Location: Sherborne	Collapsing vacuum hoses under boost...what is best to use? Hi all, I have been experiencing some minor hesitation under heavy load in my 940, and have been chasing the issue since I bought the car earlier in the month. It drives very well other than this, and I've done a good stage zero service on it. Speaking to a very experienced tech who runs a Volvo breakers near me to today, he said he suspected that my vacuum hoses may be collapsing slightly under boost, as they are commonly replaced with soft and inferior hoses. My vac hoses ARE very soft and floppy. I think it might be prudent to replace them with better/stronger hoses, but I'm not sure what the best hoses are to use...can anyone advise if there are there any specific hose kits or materials that are best for use with turbo cars? It's a stock B230FK. Ta! Phil __________________ Barges of Distinction: '96 945 SE LPT M90 '95 945 GLE D24TIC M90 ‘88 745 GL B200E M47

Jan 24th, 2020, 00:37	#3
Laird Scooby Premier Member Last Online: Today 20:02 Join Date: May 2012 Location: Lakenheath	These people are usually a safe bet Phil : http://www.autosiliconehoses.com/ As for collapsing vacuum hoses under boost - bit of an oxymoron! My guess is it would be on the suction side between the turbo and MAF but only a wild guess. __________________ Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........

Jan 24th, 2020, 07:38	#5
AllHailKingVolvo Ye olde Volvii galore! Last Online: Dec 18th, 2023 11:23 Join Date: Oct 2017 Location: Sherborne	Thanks all! I'm not altogether sure that the vac hoses on my car are intended for purpose at all-I have replaced vacuum hoses in the past and the stuff I used was much stiffer and more substantial than the material that is on my car. I think perhaps they were replaced by a well-meaning PO who just used whatever he had to hand. Many of them are secured at the nipples with cable ties (so to speak!) Which aren't what I would use for an airtight connection on soft pipe-I'd far rather use the correct gauge pipe and let the barb of the nipple do the job it's intended for. I'll order some more and replace them to be on the safe side, as they're not exactly an expensive part. Can anybody advise on what size ID I need? __________________ Barges of Distinction: '96 945 SE LPT M90 '95 945 GLE D24TIC M90 ‘88 745 GL B200E M47

Jan 24th, 2020, 00:10	#2
aardvarkash10 Master Member Last Online: Oct 8th, 2022 22:22 Join Date: Sep 2016 Location: Auckland	this or a similar local product

Jan 24th, 2020, 01:24	#4
TonyS9 Premier Member Last Online: Apr 9th, 2024 21:44 Join Date: Jul 2009 Location: Holywood	The induction side doesn't care about the breather system. Worst case the turbo won't dump, but that's a pretty much unheard of issue regards the vac pipe. Maybe you could have a collapsing fuel pressure pipe but it is quite rare in narrow section pipe. Is it collapsed at idle? He might mean inlet hoses, but these are rarely replaced with silicone hoses because they are a custom shape. Weak spark is common with the distributor on the end of the cam. Oil can cause hesitation.

Jan 25th, 2020, 00:51	#8
TonyS9 Premier Member Last Online: Apr 9th, 2024 21:44 Join Date: Jul 2009 Location: Holywood	The nipples are not barb'd, they are straight. They need a little stretch, sometimes a tie wrap helps a badly choosen pipe or using what you have. It's quite difficult to find the perfect size, and I'm quite anal on restoration. Volvo use metal clips, although I don't think they are needed. On the track none of the little pipes come off, but the large boost pipes do with high boost pressures and a bit of oil contamination on the surfaces.

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