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Thread: Cosworth Enginge stuttering when the fast pedal is pressed hard

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    Cosworth Enginge stuttering when the fast pedal is pressed hard

    It worked great on the Dyno no issues
    All I have changed is the fuel pump because it was leaking.. Walbro to standard Bosch 044
    So Im not sure if I have a faulty pump or fuel regulator..?

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    could be anything at fault! first point of call is spark plugs

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    plugs are clean and brand spanking new... less than 100 mile

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    gaps? boosted cars often want small plug gaps

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    If you haven't touched anything else then I would blame the part you have changed first.
    And maybe even put the Walbro pump back in even if it is leaking. (a bit)
    Is it a used Bosch pump? Is it a proper Bosch pump or a Chinese copy?
    Have you cleaned it before fitting?

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Same size inlets and outlets on the Bosch pump? Nothing silly like an adapter that's been put in to the replacement pump that's dropping the size down or something like that?

    Definitely try the old pump back if you can - though be careful with the leaking fuel. The Bosch pump hasn't ingested some rubbish after swapping out the leaking one?

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Gaps all ok Graham, thanks for the reply..

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by MegatronUK View Post
    Same size inlets and outlets on the Bosch pump? Nothing silly like an adapter that's been put in to the replacement pump that's dropping the size down or something like that?

    Definitely try the old pump back if you can - though be careful with the leaking fuel. The Bosch pump hasn't ingested some rubbish after swapping out the leaking one?
    Process of elimination...It runs fine on tick over etc...

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by EVOGUY View Post
    It worked great on the Dyno no issues
    All I have changed is the fuel pump because it was leaking.. Walbro to standard Bosch 044
    So Im not sure if I have a faulty pump or fuel regulator..?
    From what Walbro to an 044 ? Walbro make loads of pumps.

    What is fuel pressure doing ? What are mixtures like ?

    You've said plug gaps are "ok" ? What exactly does ok mean ? And what do the plugs look like ?

    Presumably the pump was not leaking when it was dyno'd ?
    9.85 @ 145mph 202mph standing mile

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Stevie Not sur of the ID of the walbro it was spec'd for a cosworth and is 220 litre per hour
    Plugs are iridium .7mm gaps
    Fuel pressure seems to have dropped slighty but ive noticed that the pressure gauge on the fuel reg is leaking oil
    Car was set up by MSD less than 40 miles ago, and ran great the only thing I have changed is the pump to a Bosch 044
    Quote Originally Posted by stevieturbo View Post
    From what Walbro to an 044 ? Walbro make loads of pumps.

    What is fuel pressure doing ? What are mixtures like ?

    You've said plug gaps are "ok" ? What exactly does ok mean ? And what do the plugs look like ?

    Presumably the pump was not leaking when it was dyno'd ?

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    In general, an 044 will flow about 80100lph more than the pump numbers you're quoting for the Walbro ( depending on what pressures you're quoting for of course ). So it will have a huge effect on the system. Your regulator may or may not be able to cope or need re-adjusted because of this increase in flow.

    It would certainly make no sense for fuel pressure to have dropped moving to a pump that flows substantially more.
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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Other thing is pump inlet hose size - if the 044 is choked down to, say, 8mm bore it risks severe cavitation and loss of pressure and flow!
    Inlet bore from tank should be no less than pump inlet.

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by katana View Post
    Other thing is pump inlet hose size - if the 044 is choked down to, say, 8mm bore it risks severe cavitation and loss of pressure and flow!
    Inlet bore from tank should be no less than pump inlet.
    Some of the M18 fittings you can buy actually do restrict the inlet quite heavily.

    Although even a -8 ID of most fittings is pretty small too.. Although it probably isnt the problem here.
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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    does it stutter as it comes on boost then goes ok? 0.7mm plug gap could be your issue a lot of boosted engines will need a smaller gap .5 or .6
    Last edited by Graham; 04-04-2017 at 11:53.

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by Graham View Post
    does it stutter as it comes on boost then goes ok? 0.7mm plug gap could be your issue a lot of boosted engines will need a smaller gap .5 or .5
    Hey guys thanks for the advice, Ill check it out.. Graham point noted on the plug gap...It does appear to be under boost..

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    If it's under boost then plug gaps or fuel pressure would be my guess as well. Are you running the MSD wasted spark system?

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by MegatronUK View Post
    If it's under boost then plug gaps or fuel pressure would be my guess as well. Are you running the MSD wasted spark system?
    Yes Matey, MSD wasted spark

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    In that case, as long as the plugs are gapped reasonably, you're not really going to get any better in terms of the spark. The general wisdom is that with the wasted spark setup you don't have to run the tiny electrode gaps that the tuned Cossies had to run in the old days.

    It's an odd one. Have you got a way of trying the old pump again? If the pump is the only thing that has changed (and the problem followed the change) then it's got to be linked to that.

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Have you spoken to MSD about your problem? Have you got a fuel pressure gauge inside the car? if not fix one up in some sort of fashion, even if it;s taped temporarily onto the windscreen. I had a problem with an Escort Cosworth Rally car with a similar situation, it turned out to be fuel surge when the tank was less than half full. Whomever had built the car had the fuel pump sucking directly from the Bag tank instead of fed via a swirl pot. I elected to fit an inbuilt one into the tank with submerged pump.

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by MegatronUK View Post
    In that case, as long as the plugs are gapped reasonably, you're not really going to get any better in terms of the spark. The general wisdom is that with the wasted spark setup you don't have to run the tiny electrode gaps that the tuned Cossies had to run in the old days.

    It's an odd one. Have you got a way of trying the old pump again? If the pump is the only thing that has changed (and the problem followed the change) then it's got to be linked to that.
    Im collecting ideas at the moment, Ill be trying every suggestion when I get back to the UK..

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    Re: Cosworth Enginge stuttering when the fast pedal is pressed hard

    Quote Originally Posted by Forest_rallying View Post
    Have you spoken to MSD about your problem? Have you got a fuel pressure gauge inside the car? if not fix one up in some sort of fashion, even if it;s taped temporarily onto the windscreen. I had a problem with an Escort Cosworth Rally car with a similar situation, it turned out to be fuel surge when the tank was less than half full. Whomever had built the car had the fuel pump sucking directly from the Bag tank instead of fed via a swirl pot. I elected to fit an inbuilt one into the tank with submerged pump.
    Thanks for the reply, I definitely need to check the pressure the fuel tank has an internal swirl pot and is fed from there..

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