cosworth high rpm misfire

[stephenh500]

just finished my escort cosworth build, from new shell... motor is on 250 miles, so want to start using a few more revs. the car runs perfect up to 4250 rpm, where it then starts to misfire, does it in any gear with or without boost(21psi) but only does it when under load (not stationary) the spec is p8 with MSD chip for greens, bd10s, 500 intercooler, low comp and sports cat. a group A coil is fitted with a long set of ford motorsport leads as its small turbo converted to t34. the dizzy is new and timed perfectly, with the crank sensor gapped at .7mm. i have checked the ecu fault codes and its clear of faults. it has new o71 plugs gapped at .65mm... any ideas, or had simular????

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[t4 and greys]

Originally Posted by stephenh500

just finished my escort cosworth build, from new shell... motor is on 250 miles, so want to start using a few more revs.

the car runs perfect up to 4250 rpm, where it then starts to misfire, does it in any gear with or without boost(21psi) but only does it when under load (not stationary)

the spec is p8 with MSD chip for greens, bd10s, 500 intercooler, low comp and sports cat.

a group A coil is fitted with a long set of ford motorsport leads as its small turbo converted to t34.

the dizzy is new and timed perfectly, with the crank sensor gapped at .7mm.

i have checked the ecu fault codes and its clear of faults.

it has new o71 plugs gapped at .65mm...

any ideas, or had simular????

no mention of the fuel pressure you have it set to ???
maybe worth checking ??
also check to see what voltage you are seeing at the pump too as the std wiring if being used deterirates over time ,sometimes resulting in only 10v at pump instead of a good 12v it should be

[LHD220Turbo]

take the gaps down to .6 to see if that improves, if it does then i suspect dodgy ht leads, cap or rotar arm

if it does not improve then it could be phase or crank sensor issue

i doubt this is the problem, but worth ruling out - do you know what the voltage is at the fuel pump? ideally it needs to be checked on boost.

Matt

[stephenh500]

Originally Posted by LHD220Turbo

take the gaps down to .6 to see if that improves, if it does then i suspect dodgy ht leads, cap or rotar arm

if it does not improve then it could be phase or crank sensor issue

i doubt this is the problem, but worth ruling out - do you know what the voltage is at the fuel pump? ideally it needs to be checked on boost.

Matt

i will check it, the plugs were changed yesterday and made no difference, but from the colour of the tips it was running normal, expected to see glazed. so was not thinking fuel

it has a group A pump in the tank and the regulator is tamperproof, but ill check it out


have ordered a new crank sensor and will regap asap, as ive seen small gaps cause top end misfires, but it usually throws up a CAS/ Phase sensor mismatch fault??

cheers guys........

[24vcossiemat]

fuel starvation i'd say mate

[stephenh500]

checked fuel pump voltage tonight @ 12.4v

but did not check pressure, as no fittings for guage.... sort tomorrow

removed group a coil and leads and replaced with new shorter direct leads and std coil...still the same, runs great up to 4250 and then holds back and misfires,if i ease off the throttle it picks up again.

checked throttle pot out and ok .5v at rest and 4.6 full throttle.

had a strange thing with the map sensor though. 5v supply 0v comm and 5v in signal return with map disconnected???? when connected ecu gets 1.5v in??? getting voltage out of the input?? will have to look deeper

still doing me head in!

[tabetha]

How old is the fuel filter, mileage doesn't matter but age does ?
tabetha

[stephenh500]

fuel filters new. hope to have a pressure test on tonight, still feels like a rev limiter effect though

[stephenh500]

before i go diving in, can someone confirm that a small turbo fuel regulator is any different than a large turbo regulator as ive retained the small turbo rail and reg

[stephenh500]

think ive found it, i have 5bar fuel pressure at tickover and 4.5 with the regulator disconnected, is it common for a sealed regulator to fail high???

i believe it should be 3.5 and 3 respectivly

[stephenh500]

found the pressure relief valve to be marked 4.0bar part number 0 280 160 575 964

what have i got?

[LHD220Turbo]

Originally Posted by stephenh500

think ive found it, i have 5bar fuel pressure at tickover and 4.5 with the regulator disconnected, is it common for a sealed regulator to fail high???

i believe it should be 3.5 and 3 respectivly

3.0 bar with the vacuum pipe on, 3.5 with the pipe off atmospheric at idle should be fuel pressure.

do you have a 2wd inlet with 2wd FPR and fuel rail?

Matt

[stephenh500]

i have a small turbo plenum with a built in regulator.

[kevinodowd]

rev limiter acting up

[BIG WULL]

Originally Posted by kevinodowd

rev limiter acting up

I had this problem, turned out to be the usual sierra fuel pump wiring fault so defently sounds a fuel issue

[stephenh500]

ive got too much fuel pressure, and yep its the other way round to what i said earlier, the reg has a guaze filter in it and looked a bit dirty. 4 bar regulator must not be contributing lol

[JTECH James]

from where you are now, all the base settigs need checking/adjusting,

the fuel pressure will cause issues for sure,

then i would personnally hook it up to some fuelling gear, and a IAW datalogger and drive it up the road,

any ecu issues will be seen live, and the fuelling can be checked out under load.

its very difficult to asume what the issue is withouit actually having the car in

[stephenh500]

ordered a new reg from MSD so prob be here monday now, when the reg is on ill road test it, but it is booked in for a full set up on the 19th Aug (wishing my life away) with yourselfs

[stephenh500]

well the fuel pressure is back to normal and ive changed the dissy cap and rotor arm,

still misfires but further up the rev range and starts at 5500rpm

went for a run with a calibrated boost guage on and its 21psi dropping to 18, so that needs a tweak. (least of my worries)

and tapped into the pump supply 12.5v constant through out the rev range.

[stephenh500]

fixed at last, massive overfueling and wrong spec chip for car, so ditched the greens and went siemens 55lb with chip...

big thanks to stu, james, kenny for fitting tweaking and sorting.

enjoyed the drive home, fook its responsive now!!!!

[JTECH James]

goes well eh!

glad your happy pal.

stunning car btw

[stephenh500]

"goes well", if i nail it in second, it nearly wheelies lol.. coil overs are about to go on at the weekend, should stop it scraping its ass on the floor.

ye its not bad for an "old nail" porn star gold wheels getting painted next lol