installed 440cc injectors, now car runs terrible

[ceracer33]

i have a 91 mr2 with the 5sfe motor. i plan on putting a turbo on it so i bought some 440cc injectors and installed them today. but now the car is running like crap. from idle-3,000rpm it runs fine but from 3,000 to 4500 it misses a little but at 4500rpm it starts missing so bad that it will not go any higher. i can put the car in neutral and put it to the floor and it will not rev any higher than 4500rpm's. does anyone have any ideas on what my problem could be? this car is my daily driver so if anyone knows anything that could help let me know i need this car fixed quickly. thanks

[MRQtwinturbo]

take the 440s back out...n wait til u turbo the car to run them....ur stock injectors should be fine for now...what are u using to control/tune fuel??....

[91RED3S]

Have you tried a fuel pressure regulator?

Are ther fuel injectors for your specefic application? If they arent and they don't fit just perfectly right they might be leaking or not holding correct pressure and that would cause the problems you describe.

[ceracer33]

after i ran the car for a little while i noticed some gas leaking from one of the injectors so i think thats the problem. im gonna tear it back down tomorrow and see what i can do to fix that. i know my stock injectors work fine but i wanted to get as much done at a time so that when i get everything on i wont have to be a couple of days without a car since it is my daily driver. everything in the car is stock as far as fuel control and all that. thanks for the help guys.

[Culture]

The problem is that your ECU doesn't understand that you just put in 440cc injectors. It's telling the injectors to open for a specific time period, calculated based on a lower flow rate. It will NEVER get it right unless you use either an AFC or a newly programmed ECU. I wouldn't recommend the AFC if you're going to turbo your motor either, because when you're done leaning out the fuel - you've also advanced your timing too much = BANG.

What are you planning to do once you get the turbo, for control, that is..?

[ceracer33]

im new to all this turbo stuff so i really dont have a clue. i was gonna put one on it and someone told me i needed to buy those injectors from a supra so that the car wouldnt run to lean. i need some major help b/c i am totally clueless and have no car right now. i have resorted to driving my old chevy truck thats all banged up until i get this thing back on the road. i just assumed that the o2 sensor would see that the car was being flooded and adjust it accordingly but i guess not. also the car isnt smoking or anything so i would guess that its not flooding out. it seems like maybe i dont have enough gas pumping up to the injectors for them to work properly. i dunno but if someone could tell me how to get this thing working relatively cheaply i would appreciate it. i dont wanna have to put the stock ones back in b/c i know i will need these when the turbo goes on which should be soon. thanks guys

[Culture]

Ok - a few things.

1) 440cc injectors are from a MR2 turbo (maybe a Supra N/A - not sure about that. Supra turbos use 550cc injectors, which also drop right into an MR2)

2) You might not be flooding the engine with fuel - due to the O2 sensor feedback that you figured - BUT the ignition timing is now totall ruined, because it thinks it's putting in such little fuel (see my AFC comment from before).

3) All the injectors of the same application (i.e. cars, for example) will be designed to run at the same fuel pressure - so that's not your problem. However - you WILL have to get a fuel pressure regulator that is able to increase fuel pressure by 1 pound for every pound of boost. Most decent FPR's can do this (via a vacuum/boost hose attached to the intake manifold) If you don't have this - your fuel pressure will effectively decrease when your boost comes up.

4) With all due respect - don't plan on turbo-charging an n/a car real quick or real cheap without expecting problems like this. I'd highly recommend you go over to the MR2 Message Boards, and find the guys who have already turbo'd the 5sfe motor - that way, you won't be doing this totally by trial-and-error.

[Culture]

http://www.mr2oc.com/

[Ratko]

Yeah, youre running way too rich. Without an air/fuel controller to tune it, its doing more harm than good.

[MR-Jew]

How does leaning your mixture out with an AFC have any effect on advancing your timing? Does less fuel mean less knock sensitivity so the AFC or ECU (not really sure which you were talking about) advance the timing for more performance?

[Culture]

Originally posted by MR-Jew
How does leaning your mixture out with an AFC have any effect on advancing your timing? Does less fuel mean less knock sensitivity so the AFC or ECU (not really sure which you were talking about) advance the timing for more performance?

In order to trim the fuel, what the AFC is actually doing is telling the ECU that less air is entering the engine. This is equivalent to putting less load on the motor - at which point, the ECU knows it's ok to advance the timing to increase torque. In reality, the same amount of air is entering the engine (i.e. no drop in load) and therefore you will eventually get to a point - and this has been seen in action - where the ECU unknowingly advances the timing TOO much - resulting in knocks, not more power. It's a symptom of "tricking" the ECU, rather than programming it for the environment it's actually working within.

My belief is that the point at which a fully programmable ECU is worthwhile is WAAAAAAAAAAAAAAY earlier than most people think it is...