Hard boost momentary misfire - Pain in the R's

[Flatout Phil]

Help if you please
Now here is a curiosity. Following on from a previous post about a random misfire that I thought was caused by a fill of Tesco 99 fuel on holiday when no VP was available, I have been running Vpower and it happened again. Both times (but not always - annoyingly) at motorway speeds under heaviest acceleration, get to about 5000 rpm and the whole thing just cuts for a fraction of a second, instantly returns to normal, and if pushed again cuts for a quarter of a second, recovers - by which time I have backed off. All settles down as boost drops and on one occasion, running was a bit uneven for a second or two.
Prior to all this, I have recently replaced the old hard and disintegrating hoses round the air flow sensor, with Volvo "cut your own" hose. WOndered if there is a periodic collapsing hose issue - since the pipes replaced were of the formed variety, rather than the bend it yourself type. The coil is Bosch and less than 2 years old, the plugs have been changed since the first occurence, It doesn't usually happen.
I am wondering if the BOV (Forge) is causing an intermittent pressure bypass? It has only been on a couple of months (and I have come across this issue on this forum before). Living in suburbia, it is a pain in the 'arris because I can't test the thing without driving quite a few miles out. May remove the BOV for a bit and see if it improves. It did not start happening until several weeks after I had changed the hoses either.
The RIP remains unfitted, and I can't fit it until I have sussed this one - otherwise it will add to the possibilities.

COuld go down the replace the ignition gear route - it does feel like a momentary electrical cut out, it isn't a persistent misfire on one or a couple of cylinders, the power just cuts and returns. Not an ignition barrel issue either.

It is absolutely related to boost levels (only have an ordinary gauge) but happens when the needle is across to the end of the white line (but only sometimes).

Frustrating.

[Rnash2002]

Could be the same as what i had,got to 5k rpm and all the boost went and engine just hung there.
Turned out to be the spark plugs,well could have been the gaps aswell but replaced them anyway with volvo ones and never had the same issue.
Could also be fuel cut,too much boost,with you replacing vac pipes it might have given you a few more psi,are you running a map?

[p fandango]

that sounds like your boost/MAF limit which is normally becuase your boost is too high, how you controlling the boost (ie you got a MBC or anything?)

[WOODY T5]

yeah check spark plugs ad this on t5 new plugs sorted.

[Flatout Phil]

Could be the same as what i had,got to 5k rpm and all the boost went and engine just hung there.
Turned out to be the spark plugs,well could have been the gaps aswell but replaced them anyway with volvo ones and never had the same issue.
Could also be fuel cut,too much boost,with you replacing vac pipes it might have given you a few more psi,are you running a map?

Interesting point that re replacing the pipes. Oddly I had done about 1000 miles after doing the pipes before prob cropped up. It has a RIca 304, K&N panel, Jetex 2.5 cat back, obviously being a manual also has a 16T, and until recently always been perfect - and as JelT5 will testify, it is a rapid car.
Don't have an MBC.

[Flatout Phil]

that sounds like your boost/MAF limit which is normally becuase your boost is too high, how you controlling the boost (ie you got a MBC or anything?)

I'm beginning to think I may need an MBC on this!

[Flatout Phil]

I have always thought MBC were a bit of a dodgy way of managing things - risk of burned valves, holed pistons etc.

[MC_Bob]

Only when theyre set up wrong imo. Theyre sold as a quick fix, when in reality, set it up properly with the right tools and its a good fix..

Like, turning it up till it points off the gauge, why not set it up with a proper gauge etc.

You may well be hitting boost cut.

[Dangerous Dave]

It does sound like the boost cut. I get it on mine with my mbc, under very hard acceleration at around 5k rpm.

It could be there is a very slight vac leak in the control system which is letting the boost go above the set limit.

[Flatout Phil]

I am still wondering if there is a pipe collapsing somewhere - the new stuff is that not very inspiring slightly soft hosing, whereas what came out was much stiffer. A case of boosters droop?

[Flatout Phil]

Only when theyre set up wrong imo. Theyre sold as a quick fix, when in reality, set it up properly with the right tools and its a good fix..

Like, turning it up till it points off the gauge, why not set it up with a proper gauge etc.

You may well be hitting boost cut.

Are there any gauges that come with good recommendation? And how do they fit?

[brett craig]

i thought with a 304 remap it would have the boost / maf limit removed ?

[Flatout Phil]

i thought with a 304 remap it would have the boost / maf limit removed ?

Not a clue on that one - all I do know is that the guage on this one goes to the end of the white line, sometimes even a bit further and off the end - and on the T5 it went half way up the white line.

[MC_Bob]

Are there any gauges that come with good recommendation? And how do they fit?

Usually just connected to the vaccum tree, but with the stock guage, im not sure if you could just tee from that. Most gauges serve well and are accurate, ive heard claims that certains ones arent as good as others, but when Ive bench tested them together, theyve all read that same, just dont get cheap cheap cheap tat! =]

[The Flying Moose]

I bought a boost gauage from Halfords for £25 as I needed one quick and it apprears to be accurate. Easiest thing I ever fitted. You just need to remove throttle cover and fit the pipe onto one of the spare connections on the vac tree and then route the cable into the cabin and connect it to the other end of the guage.

If you refer to pfandagos posts in this thread http://www.vpcuk.org/forums/showthre...ht=boost+guage it explains it fully.

If you need any pictures just ask I only fitted mine a month ago.

[Flatout Phil]

Took it for a few runs this afternoon and evening - up to 6000+ rpm and not a missed beat, pulling strongly and smoothly. One of thos annoying intermittent faults that will bite me at some inconvenient moment.

[The Flying Moose]

Took it for a few runs this afternoon and evening - up to 6000+ rpm and not a missed beat, pulling strongly and smoothly. One of thos annoying intermittent faults that will bite me at some inconvenient moment.

I have been reading this thread quite carefully as its something I think mine also suffered and I ended up replacing the pipe going to the wastegate actuator. Like with yours it didnt do it every time I drove the car. Ill try describe it to the best of my ability. It was also at around 5-6k rpm and happened only in 2nd,3rd or 4th and it was complete boost cut off I think. The car would suddenly feel like a car had just rammed the back of me as the boost just "fell off". Sound familiar? It wasnt the replacement hose that sorted it in the end it was the MBC I got off smithness after turning down the boost. I can only assume that as previously mensioned in this thread the ECU adjusted the boost according to the leaks from the old hoses and was overboosting.

[doug kyle]

I'd still have a look at the spark plugs buddy, i had the same sort of thing with my tuned S70 R it would not happen all the time out on the road, but mainly only under heavy load when it would blow the spark out.
I was running the standard Volvo spark plug, i upgraded them to HKS iridium spark plugs & fitted a msd race coil pack to the car, problem solved.

[RT MECHANICS]

Hi Phil

It sounds like a plug or possibly a lead take the leads out and look closely at the colour of them they should be a nice clean grey colour if they look brown or dark at all change them with a set of plugs (OE Volvo) or Denso IKK22 have you had the injectors cleaned by John?????

Russ

[Flatout Phil]

I'd still have a look at the spark plugs buddy, i had the same sort of thing with my tuned S70 R it would not happen all the time out on the road, but mainly only under heavy load when it would blow the spark out.
I was running the standard Volvo spark plug, i upgraded them to HKS iridium spark plugs & fitted a msd race coil pack to the car, problem solved.

Thanks Doug. Will try this.

Hi Phil

It sounds like a plug or possibly a lead take the leads out and look closely at the colour of them they should be a nice clean grey colour if they look brown or dark at all change them with a set of plugs (OE Volvo) or Denso IKK22 have you had the injectors cleaned by John?????

Russ

Cheers Russ, As above, will be trying this.

Phil.