Hey guys and girls, Had my car on the dyno again the other day and found its running extremely rich.. It was popping and farting under full load on the dyno. It won't do it on the road though.. I've recently upgraded my external fuel pump to a bosch 984 and also fitted a malpassi. the tuner seemed to think it was thanks to the standard computer, but i thought that would be causing it to run lean if anything? Any ideas?

what rising rate ratio is the malpassi, 1:1, or higher? if its a higher rate, that why it is running heaps rich. also if you didn't set the base pressure to correct spec it will also run rich. what pressure on idle are you running?

advance your timing when your on the dyno that will use the extra fuel

Quote: Originally Posted by RB30-POWER what rising rate ratio is the malpassi, 1:1, or higher? if its a higher rate, that why it is running heaps rich. also if you didn't set the base pressure to correct spec it will also run rich. what pressure on idle are you running? i honestly have no idea on the malpassi. got it secondhand. any way to tell the difference? the tuner set the fuel pressure. i think its about 30-35 on idle.

Not that i know of. Would have to check with a fuel pressure guage and make sure the fuel pressure is only rising 1psi for every 1psi of boost pressure. If its rising faster its a higher rate and the only way you will fix it, is to change the reg, or remap the ecu to suit the higher pressures.

i'll have to book her in for another roll on the dyno then.. my fuel pressure guage is attached to the malpassi, so i can't check it on the road. dammit. so, say the base pressure is 35psi, if i'm running 12psi of boost, it should be reading 47psi of fuel pressure under full load?

just checked fuel pressure at idle and its definitely 35psi.. now to find out on boost..

you could get some 1/4" hose and run it to your dash just temporarily mounting it there and clamp it with some EFI hose clamps to get a read if your desperate but the dyno sounds a better idea

Also, If you disconnect the vacuum hose to the regulator it will be exposed to the atmospheric pressure and should probally go to about 40psi. That is normal! Then after that pressure on boost, if its 1:1 ratio it should rise 1 psi for each psi of boost. So if you were running 10psi of boost on your engine the fuel pressure should be around 50psi. So for example if the fuel pressure was 80psi you would have to assume the regulator is a higher rate reg, raising pressure maybe (unsure what the malpassi ratio are offhand) the ratio would be like 8:1, which will never work with the stock ecu, unless you remap it to lean the fuel off. Is it the big black malpassi reg or all silver? (Fairly sure the big black ones are the rising rate ones that are higher then 1:1) The high rising rate ones are good if you were for example at the limit of the factory injectors (100% duty) and wanted to squeeze some more fuel through to richen it up. But when the injectors are less then maxed out on low boost, it will overfuel heaps. Giving heaps of flatspots, misfires etc. Your problem may not even be the reg, but i've seen it heaps before, people fit a high rate rising rate reg on the stock computer, then wonder why it runs rich as ****.

without the vacuum line it went to 40psi. its a silver one. i'll check it out on the dyno and let you know how i go. thanks heaps for the help.

i'm sure the black top is the rising rate. i would put the standard reg back on and see how it goes then. cos with the big pump flowing more than the standard one it will have a lot more pressure/flow anyway

i've still got the standard reg here so i might give that a go if its the 1:1 malpassi and still too rich

is it normal for the fuel pressure guage on the malpassi to be bouncing constantly between 30 and 40 on idle? i just figured average it out to 35psi.. just thought it might be worth asking..

your idle controls determines vacuum, and if your vacuum is stable it shoulded bounce like u say have u got a full tank of fuel almost sounds like its surging but highly unlikely at idle or do u have a rough idle in your car?

idles smooth. its just flickering between them really quickly, not like up and down..

bump is this normal?

how hot does it get when it warms up?

the engine? never see it go past half way on the guage..

any other things i can try before i book it in for another dyno run? or things to look for while on the dyno? whats involved in changing the fuel reg? thanks for the help guys, i really wanted it running 100% for powercruise... only 2 weeks away now...

It may be cheaper to get a standard fuel reg and put it on. Will take like 15mins to change if that. And if it still rich, you have a problem elsewhere. Do you actually need the rising rate reg? How much boost does it run?