help, car stumbles at idle, injector ? too
03-19-2005, 06:48 PM
#1
help, car stumbles at idle, injector ? too well im in the process of tuning my car and i just put a new fuel pump and injectors in. i scaled the injectors for 58 psi and the rated 43.65 lb/hr and put it into an excel sheet i found on here. i had a pressure gauge hooked up to my rail and at idle and some gas (sitting still) the pressure was anywhere between 60-62. should i recalculate the tables for a higher pressure? or keep it at the 58? also, the car stumbles at idle and the fuel trims are all negative, about -10 or -8 or so, would this cause the stumbling? im just trying to figure out if i should adjust the VE table or rescale the injectors for the specific psi i am getting then relog, then scale the VE. any comments on this?
03-19-2005, 08:18 PM
#2
i was just wondering if i took the rail pressure for a certain kPa if i could stagger my fueling based on the pressure at the certain area, at idle pressure is 62, light gas its 60 and wot its about 58-59, then that should help fueling across the board right?
03-20-2005, 10:13 AM
#3
i find it hard to believe that noone on this board can help me out with this. the car will idle ok but once the trims start to change it is hunting around. could it just be the car needs to learn the new injectors and everything for a little bit of time??
comeon i know you guys can help me out so please help!
comeon i know you guys can help me out so please help!
03-20-2005, 11:03 AM
#5
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Need more info - did everthing run fine until you replaced just the injectors and FP? Because you did not specify, I assume that you replaced with stock injectors and stock fuel pump??? Are your fuel trims the same left to right? Because your trims are only correcting to -5 to -10%, I don't think it's an IFR problem, if it was the % would be greater and it would start to run better as it learned, O2s lieing to you? Some info is missing here because this is not adding up - more info please.
03-20-2005, 11:08 AM
#6
ok the fuel trims arent too bad i think the IFR table is ok. i was having cranking issues with after the fuel pump install, possible bad regulator or faulty pump. the stumbling the car sees now *i think* became and issue after the injectors were put on. they are 38# racetronix injecotrs and a racetronix fuel pump. im goin to do heads and cam in about a month, thats the reason for the upgrade. the fuel pressure at idle is about 62-63, with a little bit of gas it will jump to about 59-60 but when i open it up a whole lot and get the rpms really high, and this is at idle so its a fast stab, the pressure goes to about 52 psi. on a drive last night it seems the car acted ok and at low kpa the trims were negative but nothing too serious lowest was -10. need any more info?
03-20-2005, 12:08 PM
#7
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Here are some possibilities - air distribution, a vacuum leak such as lower injector O-ring(s) not sealing. Fuel distribution, uneven fuel injector flow. Either of these problems will not show with O2 trims because they just average A/F, however usually show with a left/right difference but not always. Air leak, headers or AIR system leaks confusing the O2s. I've had certain cam/mods combos really fight my tuning because the engine just refuses to idle or cruise at 14:7 A/F, but yours should because it's not that radical. Your FP deviation bothers me because it is actually working against your IFR table but again, if your O2s and trims are working properly, it looks like it is compensating with your low trim values. I'm not real good at guessing over the internet, good luck.
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03-20-2005, 12:21 PM
#8
the idle just got screwed up, from waht i can tell, after i did the injectors. this is the second damn thing i got from racetronix that has given me issues, first the fuel pump and then now my car isnt idling after the injectors. is there any way to check for leaks or not? the car will run ok for a litlte then stumble and then be ok. i have no way to check the fuel pressure at full load because this is a fuel gauge i got that is just a tester. i have logs from last night if that will help, from hp tuners
03-20-2005, 12:54 PM
#9
so i was looking at the air fuel gauge when the car was at idle its hooked up to the driver side header, and the damn thing wasnt moving like it normally does, im gonna check out the passenger side one, i wonder why at idle it wont osc right. it was before. they are brand new o2 sensors, and i figure this coudl be part of the problem? maybe
03-20-2005, 01:02 PM
#10
ok well i just logged idle and the o2 sensros were oscillating fine....ahhh this is so frustrating
is it possible that the car just needs to be driven and retuned? maybe it has to learn something? i just dont see why it would do this all of a sudden
is it possible that the car just needs to be driven and retuned? maybe it has to learn something? i just dont see why it would do this all of a sudden
03-20-2005, 01:05 PM
#11
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The best way to check for vacuum leaks is with the smoke test that many auto repair shops provide as a service. There are older less effective methods such as spraying carb cleaner in the suspected leak area and listening for an idle change or monitoring the O2 readings for changes. I'm going to bow out on this, too used to utilizing my own diagnostics tools and not guessing. Hopefully you can draw some new ideas from others in on this one. Usually by now someone always sits back, then jumps in and states how stupid the first responder's solutions sound, which could be true. Good luck.
03-20-2005, 01:57 PM
#12
well im gonna drop the tank and look for the initial problem, the car not starting right, maybe there is a loose line or something but we will see. ive run a fuel system cleaner that smokes in my car and i have no leaks until the ypipe meets the i pipe. ill post up if i find anything, thanks for the help so far
03-20-2005, 06:02 PM
#13
ok so my hose clamp was a LITTLE loose, from what i can tell that helped the stumbling problem and the car, as of now, seems to be fine, idle is smoother and so is the response, the fuel pressure is also better, before the thing would look like it was vibrating between 64-62 and now its constant 62 at idle and full load its at 60, so its a ton better than before. i still have start up issues which are prob the pumps check valve. thanks for all the help and the pointers i hope this fixes the poor idling problem
03-21-2005, 10:20 AM
#14
well incase someone else is tryin to help me out here, lookin at the log it seems like the idle always dips when the fuel trims are trying to recover themselves from a negative number. when the trims stay constant the rpms seem to be constant as well. we will see later today if tuning the trims will help out
