Cossie engine severe misfire (fuel starvation????)
Discussion
Hello all
I've got a Dax rush with a stage 3 tuned cossie red top engine.
i've always had a problem with fuel starvation on corners when the tank gets below a 1/3. the result being a loud bang / backfiring sound and severe (but temporary) loss of power, i have just accepted this as normal and keep the tank topped up as much as i can.
The thing is that i am now experiencing the same symptoms but in a straight line and with a full tank. i am running 18psi boost and when i hit 4500rpm on full throttle or about 5000rpm on 3/4 throttle the problems start. thinking that it was fuel pressure related i have turned the boost down to 14 psi and that has reduced the severity of the misfire.
Trouble is, i want to run 18psi+ boost!!!!!
I am wondering if anyone has any ideas where to start looking for the source of the problem and how to test any bits and pieces that need looking at. i've got a trackday coming up on the 26th july and i need to get full power back by then or i'm gonna be pootleing about without a big grin on my face!!!
There is another symptom too, the car has become increasingly difficult to start when hot!! it has now got to the point where i expect to sit around until the thing cools down a bit.
Any ideas would be much appreciated
Tim.
I've got a Dax rush with a stage 3 tuned cossie red top engine.
i've always had a problem with fuel starvation on corners when the tank gets below a 1/3. the result being a loud bang / backfiring sound and severe (but temporary) loss of power, i have just accepted this as normal and keep the tank topped up as much as i can.
The thing is that i am now experiencing the same symptoms but in a straight line and with a full tank. i am running 18psi boost and when i hit 4500rpm on full throttle or about 5000rpm on 3/4 throttle the problems start. thinking that it was fuel pressure related i have turned the boost down to 14 psi and that has reduced the severity of the misfire.
Trouble is, i want to run 18psi+ boost!!!!!
I am wondering if anyone has any ideas where to start looking for the source of the problem and how to test any bits and pieces that need looking at. i've got a trackday coming up on the 26th july and i need to get full power back by then or i'm gonna be pootleing about without a big grin on my face!!!
There is another symptom too, the car has become increasingly difficult to start when hot!! it has now got to the point where i expect to sit around until the thing cools down a bit.
Any ideas would be much appreciated
Tim.
i have got a regulator 3.5bar and more than one in line fuel filter. i have been running 18psi for about a month now with no probs. its only last week that this problem arose.
i was after some ideas of components that could cause this type of problem through a failure and how to test for this.
The chip i have should run up to 23psi boost with standard fuel pressure and as i have been running 18psi for a while i think something may have gone wrong rather than require upgrading???
What you think???
P.s. sorry for x posting
i was after some ideas of components that could cause this type of problem through a failure and how to test for this.
The chip i have should run up to 23psi boost with standard fuel pressure and as i have been running 18psi for a while i think something may have gone wrong rather than require upgrading???
What you think???
P.s. sorry for x posting
ooops took too long writing the last one 
Thanks guys, i think i'll try and hook up a pressure gauge (better get on the blag) a guy i've been chatting to reckoned that it was fuel flow not pressure? but i thought that they go hand in hand (flow proportional to pressure & duration ???)
if low fuel pressure is found which bits do i change first?? cheap -> expensive -> extortionate or is there a better (more technical) approach
Cheers
Tim
Cheers
Thanks guys, i think i'll try and hook up a pressure gauge (better get on the blag) a guy i've been chatting to reckoned that it was fuel flow not pressure? but i thought that they go hand in hand (flow proportional to pressure & duration ???)
if low fuel pressure is found which bits do i change first?? cheap -> expensive -> extortionate or is there a better (more technical) approach
Cheers
Tim
Cheers
Thanks for all the responses,
I have traced the hot starting problem (with some help!!) to an incorrect gap between the phase sensor and whatever it senses??, after changing the coolant temp sensor had no effect.
This has cured the loud severe banging that felt like the cornering fuel starvation, but has not cured the car completely.
I now have a car that splutters from 4500 - 5000 rpm on boost when running more than 12psi boost. the effect is far less severe and noisy than the original problem but is just as annoying.
I have cleaned out the fuel pre filter (a super fine phosphor bronze element which was pretty dirty) changed the distributor cap and have fitted new platinum plugs.
The cossie specialist that i spoke to reckoned that my boost gauge was wrong and that i was running too much boost which was blowing out the spark!! i'm not sure that i agree with that diagnosis, they had a look at the car and concluded that fuel wasn't the problem by squirting fuel out of the rail inlet, not by plumbing in a fuel pressure gauge as i'd expected, the guy does run a cossie with >700bhp though so he should know what he's talking about, right??
Basically i'm not happy with having to turn down the boost to solve the problem. everybody else runs big boost so why shouldn't i
Any comments??
Tim
P.s. i think the last paragraph almost answers ultima andy's question
I have traced the hot starting problem (with some help!!) to an incorrect gap between the phase sensor and whatever it senses??, after changing the coolant temp sensor had no effect.
This has cured the loud severe banging that felt like the cornering fuel starvation, but has not cured the car completely.
I now have a car that splutters from 4500 - 5000 rpm on boost when running more than 12psi boost. the effect is far less severe and noisy than the original problem but is just as annoying.
I have cleaned out the fuel pre filter (a super fine phosphor bronze element which was pretty dirty) changed the distributor cap and have fitted new platinum plugs.
The cossie specialist that i spoke to reckoned that my boost gauge was wrong and that i was running too much boost which was blowing out the spark!! i'm not sure that i agree with that diagnosis, they had a look at the car and concluded that fuel wasn't the problem by squirting fuel out of the rail inlet, not by plumbing in a fuel pressure gauge as i'd expected, the guy does run a cossie with >700bhp though so he should know what he's talking about, right??
Basically i'm not happy with having to turn down the boost to solve the problem. everybody else runs big boost so why shouldn't i
Any comments??
Tim
P.s. i think the last paragraph almost answers ultima andy's question
andy,
if i thought the car would be 100% reliable at max boost 22-23psi, then that is where it would be set. but, not being a particularly competant mechanic and in view of the hammering that the car receives on a daily basis (i don't have another car!!), i don't think that regularly blowing head gaskets would be much fun.
18psi is plenty for the road really, that gives 300bhp and 300ft/lb, but everyone always want more though
Tim
if i thought the car would be 100% reliable at max boost 22-23psi, then that is where it would be set. but, not being a particularly competant mechanic and in view of the hammering that the car receives on a daily basis (i don't have another car!!), i don't think that regularly blowing head gaskets would be much fun.
18psi is plenty for the road really, that gives 300bhp and 300ft/lb, but everyone always want more though
Tim
Andy,
Silly question "Spark plug gap, do you buy plugs with a specific gap or do you bend the electrode yourself??"
I always run Optimax Fuel, and i've checked the system for air leaks.
I don't know what pinking (knocking??) feels like but to illustrate
"before we sorted the phase sensor you did nearly hit the windscreen and the one big bang that came out the exhaust was deafening. Now the result is a far gentler repeated stuttering accompanied by a much quieter more muffled popping ("Phut --- Phut") sound. you can actually drive through this stuttering where as before there was total loss of power."
Hope you can understand my child like descrption of the problem
Silly question "Spark plug gap, do you buy plugs with a specific gap or do you bend the electrode yourself??"
I always run Optimax Fuel, and i've checked the system for air leaks.
I don't know what pinking (knocking??) feels like but to illustrate
"before we sorted the phase sensor you did nearly hit the windscreen and the one big bang that came out the exhaust was deafening. Now the result is a far gentler repeated stuttering accompanied by a much quieter more muffled popping ("Phut --- Phut") sound. you can actually drive through this stuttering where as before there was total loss of power."
Hope you can understand my child like descrption of the problem
P.S. Sometimes i think i must be nuts, but it only takes a single dry day to remind me why i put up with it.
I reckon that 99% of people would consider us mad, but hey, who cares its them that end up spitting teeth when their posh porker or prancing horse gets eaten for breakfast on a nice sunny day
(p.p.s. nothing against porkers or horses I just cant afford one to sit beside the dax in the garage. the dax will only go when i can afford to replace it with an Ultima!!)
I reckon that 99% of people would consider us mad, but hey, who cares its them that end up spitting teeth when their posh porker or prancing horse gets eaten for breakfast on a nice sunny day
(p.p.s. nothing against porkers or horses I just cant afford one to sit beside the dax in the garage. the dax will only go when i can afford to replace it with an Ultima!!)
andy,
I gapped the plugs to 0.025" (approx 0.6mm ?) last night and that seems to have sorted the problem. i took the car for a blast this morning running 20psi approx.
The car has a single stutter as boost peaks at around 22psi but is fine on constant boost of 19-20psi. very pleased at the moment as i will back of the boost tonight to peak at around 20psi (with no stutter hopefully).
The car runs a std 2wd intercooler at the moment, this sits just under the top of the nose cone at the front of the engine bay (std installation). i am currently looking into fitting a bigger cooler, the rad lies back at an angle in the front of the car and i am thinking of fitting a cooler directly against the front of it (i.e. //) and directing the air onto the pair of them with some sort of scoop.
the air filter also sits directly behind the rad in the rush so i need to look at getting a fresh air supply to that (another owner has sorted this one already!).
I think i'm gonna fit an oil cooler in the gap left by the old intercooler.
No cash at the moment so these are all just plans for the future, i'll get round to them eventually.
I've got no pics with me at the moment but i'll have a look around and try and find some, if not i'll scan some of mine in tonight.
Thanks to all for all of your help, now the car's running well i've got my insane grin back at work this morning
I gapped the plugs to 0.025" (approx 0.6mm ?) last night and that seems to have sorted the problem. i took the car for a blast this morning running 20psi approx.
The car has a single stutter as boost peaks at around 22psi but is fine on constant boost of 19-20psi. very pleased at the moment as i will back of the boost tonight to peak at around 20psi (with no stutter hopefully).
The car runs a std 2wd intercooler at the moment, this sits just under the top of the nose cone at the front of the engine bay (std installation). i am currently looking into fitting a bigger cooler, the rad lies back at an angle in the front of the car and i am thinking of fitting a cooler directly against the front of it (i.e. //) and directing the air onto the pair of them with some sort of scoop.
the air filter also sits directly behind the rad in the rush so i need to look at getting a fresh air supply to that (another owner has sorted this one already!).
I think i'm gonna fit an oil cooler in the gap left by the old intercooler.
No cash at the moment so these are all just plans for the future, i'll get round to them eventually.
I've got no pics with me at the moment but i'll have a look around and try and find some, if not i'll scan some of mine in tonight.
Thanks to all for all of your help, now the car's running well i've got my insane grin back at work this morning
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