Benedunn

Now before you all go nuts and say 'the rebuild hasnt worked' it has ... ill explain how i know in due corse ;-)

anyway i dont really know what im asking you all to do for me i guess i just need some ideas realy

About 3 months ago i bought an 8 with a dud engine ... the plan being itd be run alongside my own car since i have a low power and this is a high power.

the car had died of complete front stationary gear bearing failure, the mug i bought the car off had litterally just bought it and was driving it home anyway he said he wound up parked on the hard shoulder and there were flames coming out of the exhaust . so anyway i gets the car home an quikly whips the engine out ready to pop an new 1 back in (ready built) but i used all the cars old anxillaries, gave everything a good clean and once over before doing so of course

so in goes the new engine, which starts first time but wait theres a problem it ran like a bag of spanners, a major fueling issue! if you feathered the throttle no problem shes rev cleanly through to about 4.5 k then bounce off what would seem like rev limiter - trying to give it any more gas and itd rev up and down irraticcaly - plant your foot an revs stoop at about 3k and struggle to stay there. this 1st time i didnt really get any further than disconecting the cat (thought it might be a blocked cat) which didnt help, cleaned the maf, different set of leads coils and plugs, and a few ecu resets

then another car came in ... so i decided i didnt have time to mess about ill get the engine back out and try it in the new car (blue car for referance)and so i did, i whipped the engine out of the black car (for referance) stripped all the anxillaries off it, fit the blue cars engine anxillaries and popped her in the blue car - starts and runs perfectly ... 2 and half months later the blue car is 2000 miles in and is still wizzing about the place quite happily!

then i got cought up with life and the black car has sat for a couple of months then monday i decided it was time i got my act together and made a start on the black car again, built another engine, fit it with new flow tested primary injectors, different wiring loom, gave the intake another good clean and fit a another front lamda sensor, popped it all in the black car annnnnnnnnd no joy - its just the same as last time

at 1st i was pretty disheartend and was very close to pulling the engine and sending the dam car to the scrappy! i wouldnt actually loose that much money but she's only done 52000 miles and is actually in really really good condition so itd be a shame to say the least

i had a sleep on it and calmed down and now im going to set it right i think .... the trouble is i thought id just about changed everything that i thought might have cause the problem when i stuck the engine in! so im a little stuck for ideas!

what i can tell you right now (because ive only aimlessly been trying things) is that i have a STUPIDLY high short term fuel trim! it ranges from about 15 - 30 % (i didnt even know they could read past 25% ) i dread to think how much fuel wash that must be causing!! LTFT are a pretty steady 5-7% - i think its safe to say that if we can get to the bottom of the STFT's being so high we will have the car right as rain

but i know little about that side of things if someone posted up saying they were having problems with there fuel trims 1st thing id say would be try a different lambda sensor right? thing is tho i have, and ive seen dying/ dead lambdas before and they never cause quite so much chaos and generally throw up a CEL right?


i dont know ... thats why im asking you guys ... i dont want shooting down but any helpfull sugestions would be fantastic to say the least ... cheers for reading everyone!!

rx8driver23

although i don't work on rx-8's besides my own, i do work on enough new engines to give you an idea where to look, first thing the short term fuel trims can get really hi, thats just the adjustment the PCM is making at that exact point in time, in your situation its adding a large amount of fuel because it feels that its getting alot more air than it should be, most of the time in my line of work this is caused by a vacuum leak, in your case i'd say that's most likely not the case as you have put the engine in yourself and most likely you wouldn't have made the same mistake twice, what i would suggest is either check for a REALLY big vacuum leak in the intake, possibly due to when the first engine blew, but more likely it would be in a sensor like the MAF, if that's reading out of range it could think that less air is coming in than really is and then the O2 sensor could be adjusting it after the fact causing it to run the way it is, a really easy way to check this is usually disconnect the MAF and see if it gets better, its been a while since i've looked at an rx8 manual and being i'm from the US i don't know if there's any differences between the two, but atleast its a place to start

dannobre

iTrader: (3)

Check the fuel pressure...if the pump is crap...you will have less fuel than you should have....then the ECU will add fuel ( high + fuel trim) to compensate. It will idle likely and run at lower fuel demand...but crap out higher

Benedunn

cheers for the suggestions chaps

after id calmed down and pulled my head outta my **** i started taking a more straight forward approach to the fault finding ... for future refence everyone it was the dam MAF sensor, no idea how the hell that happened!?!?! i know coincidences happen but really MAF sensor and bearing all in 1 go

so there you have it ... as everyone knows if your running in a lean state you have either a dodgy fuel pump, maf sensor vacuum leak or front lambda sensor ... dont ignore your instincts when fault finding no matter how unliklely you think it is

Benedunn

oh there we go at least 1 of us was switched on