Loss of power and sucking/hissing noise
Discussion
Hi all. Have not posted on here for a while as the car appeared to be sorted. Some of you may remember that I had all sorts of problems last summer, around SCH time with episodes of sudden power loss, missing etc. followed by over fuelling making the car run really poorly and mpg under 20.
My S is an S3c and the problem seems cat specific. Having plugged off the small solenoid that recirculates emissions through the carbon canister in the boot back to the plenum things seemed to return to normal again - once the ECU was reset. However, problem is back - exactly the same as before. Worst at cruising speeds, like a steady 3200-3400 revs although today it took 90 miles before it happened at all. Once it happens once, it just gets worse, but after leaving the car for a few hours it was fine again for the first 30-40 miles home, then problems again, then the last 20 miles all fine again! Just weird and very annoying!
I am now aware that every time the sudden loss of power strikes, it is accompanied by a hiss or sucking noise so I assume it is air/vacuum related. Cannot be anything to do with the route back to the carbon canister though it this is still blanked off. Where else (or whatvelse) could the fault be?
Also, is it necessary to keep all this recirculatory pipe work between the rocker cover, plenum, carbon canister, map sensor and so on - wouldn't life just be simpler without?!?!
Adam
My S is an S3c and the problem seems cat specific. Having plugged off the small solenoid that recirculates emissions through the carbon canister in the boot back to the plenum things seemed to return to normal again - once the ECU was reset. However, problem is back - exactly the same as before. Worst at cruising speeds, like a steady 3200-3400 revs although today it took 90 miles before it happened at all. Once it happens once, it just gets worse, but after leaving the car for a few hours it was fine again for the first 30-40 miles home, then problems again, then the last 20 miles all fine again! Just weird and very annoying!
I am now aware that every time the sudden loss of power strikes, it is accompanied by a hiss or sucking noise so I assume it is air/vacuum related. Cannot be anything to do with the route back to the carbon canister though it this is still blanked off. Where else (or whatvelse) could the fault be?
Also, is it necessary to keep all this recirculatory pipe work between the rocker cover, plenum, carbon canister, map sensor and so on - wouldn't life just be simpler without?!?!
Adam
Hi Adam
You'll remember that I was one of the people who looked at your car at SCH last year, and I came up with the carbon canister theory (just so that you can place me!)
I still think that this does all sound vacuum-related. You do need a MAP sensor connection as an input to the ECU, and you also obviously need a vacuum hose to the brake servo. You've blanked off the carbon canister, so that only leaves (I think - I can't look at my car at the moment) the connection to the rocker breather, which you don't need for the engine to work - you could put one of those little bling paper filters in the rocker cover hole instead of blanking it off, just to prevent any build-up.
There's a little plasic t-piece under the MAP sensor - it might be worth replacing that, and all of the smaller-bore vacuum hoses, just in case any of them are cracked or perished and letting air in, or are collapsing under suction and affecting the MAP signal or something. A couple of feet of rubber hose and a t-piece would at least eliminate that as a possibility.
Otherwise you could try spraying easy-start or something similar on to the vacuum hoses, around the plenum chamber and throttle bodies etc - if there's a leak, the engine will suck it in and burn it as fuel, and you'll hear the revs rise slightly - more little squirts might be required to narrow it down to a specific area (there's a joke in there somewhere, but I can't think what it is).
You'll remember that I was one of the people who looked at your car at SCH last year, and I came up with the carbon canister theory (just so that you can place me!)
I still think that this does all sound vacuum-related. You do need a MAP sensor connection as an input to the ECU, and you also obviously need a vacuum hose to the brake servo. You've blanked off the carbon canister, so that only leaves (I think - I can't look at my car at the moment) the connection to the rocker breather, which you don't need for the engine to work - you could put one of those little bling paper filters in the rocker cover hole instead of blanking it off, just to prevent any build-up.
There's a little plasic t-piece under the MAP sensor - it might be worth replacing that, and all of the smaller-bore vacuum hoses, just in case any of them are cracked or perished and letting air in, or are collapsing under suction and affecting the MAP signal or something. A couple of feet of rubber hose and a t-piece would at least eliminate that as a possibility.
Otherwise you could try spraying easy-start or something similar on to the vacuum hoses, around the plenum chamber and throttle bodies etc - if there's a leak, the engine will suck it in and burn it as fuel, and you'll hear the revs rise slightly - more little squirts might be required to narrow it down to a specific area (there's a joke in there somewhere, but I can't think what it is).
Gerald-TVR said:
Could it be an air leak into the servo, loud hiss (had it once with a duff servo seal where the pedal rod went into the servo) and poor running, under fueling with extra air sucked into plenum?
I was thinking about this later last night, because I have just finished an article about brake servos yesterday, and wondered the same thing. It could be the seal or diaphragm, or if it's rusty, it might be drawing air straight through the body of the servo.This could be a problem because as you and I coincidentally discovered on the same day last year Norman, Ford have discontinued those servos...
Adam's fault is very very intermittent though, so I don't think it can be that, but I might be wrong.
Thank you both - makes lots of sense. It must be something to do with pressure/vacuum building up and then suddenly escaping or sucking as a way of releasing this. It never happens on short trips, neither do I remember it happening if cruising above 3500 revs. Does this help?! I will check the servo though as well as probably replace / bin the hoses as appropriate. Talking of hoses, I do remember the larger hose between rocker cover and plenum looking squished (as if sucked at both ends) a few months back so perhaps it is dying. If I do go down the 'bling paper filter' route for the rocker cover, what do I do with this hose at the plenum end?
I really appreciate your help, so thanks again.
I really appreciate your help, so thanks again.
Viper1day said:
Sorry Barkychoc, our posts crossed there. When you say 'breather', where do you mean?
The offside rocker cover breather is connected to the plenum by a short hose. All you need to do is block that at the plenum endand preferable fit some kind of filter into the rocker cover.A couple of years ago, in the summer, I had an issue where I would drive the car approx 50 miles and then it would start running rough when cruising. If accelerated it was OK. If I was decelerating it was OK. But if I maintained a constant speed the car was a nightmare. Sounds very similar to your issue without the hiss.
The issue was intermittent and went away after a period of changing, plugs, leads, dizzy cap etc and a bit of random fiddling with the power boost valve. However, it reappeared a couple of months later - fortunately it happened on the way to Austec. They diagnosed corroded electrical connections to the air pressure sensors. After a quick clean the problem was resolved.
So...
Were there any error codes when your ecu was reset?
The issue was intermittent and went away after a period of changing, plugs, leads, dizzy cap etc and a bit of random fiddling with the power boost valve. However, it reappeared a couple of months later - fortunately it happened on the way to Austec. They diagnosed corroded electrical connections to the air pressure sensors. After a quick clean the problem was resolved.
So...
Were there any error codes when your ecu was reset?
Hi all,
Quick update to this saga. Following an epic trip to the Le Mans Classic recently it would seem that this problem, which has been giving me grief for the past 18 months, could have been down to an electrical short!!! The bundle of wires that run across the bulkhead at the back of the engine (just below the windscreen) had chaffed through and a couple of wires had shed their insulation! Following a running repair with a rubber glove and some cable ties, the car ran beautifully over the last 100 miles down to Le Mans. More importantly, having 'borrowed' some wire, the return journey was equally awesome (other than having no clutch fluid for the last 50 miles!). Yesterday the car flew through its MOT with no advisories so hopefully I can start to embrace the joys of the S once again. One very happy owner!!!
Quick update to this saga. Following an epic trip to the Le Mans Classic recently it would seem that this problem, which has been giving me grief for the past 18 months, could have been down to an electrical short!!! The bundle of wires that run across the bulkhead at the back of the engine (just below the windscreen) had chaffed through and a couple of wires had shed their insulation! Following a running repair with a rubber glove and some cable ties, the car ran beautifully over the last 100 miles down to Le Mans. More importantly, having 'borrowed' some wire, the return journey was equally awesome (other than having no clutch fluid for the last 50 miles!). Yesterday the car flew through its MOT with no advisories so hopefully I can start to embrace the joys of the S once again. One very happy owner!!!
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