some background info:
I have an 04 with the gm eco s/c and a 3.0 pulley. aeromotive afpr, new oem fuel pump and filter, new 62# injectors
Problem:
My car's going lean under boost. I noticed it going lean one day, and then the next worse, and then maybe a little worse, but now it's been about the same for a week or two. I don't have a fuel pressure gauge in the car yet, but I do have one of those temporary ones that you can hook up to the schraeder valve. I hooked it up and when I revved the car up by hand (probably 3k rpm's or so since in park), I could see the pressure dropping on the gauge and then whenever it hit either the rev limiter for in park or i let off, the pressure would go back up. So, this is making me think maybe my suspicions that it could be a fuel pressure problem are right...but I'm not completey sure because I thought another day I didn't see the pressure drop, but maybe I just didn't test it enough.
So anyway, I'm wondering what all should I look at? I'm guessing some possibilities are the fuel pump or afpr. I'm also wondering about the injectors though since I had had problems with them misfiring before (but now I think I fixed the misfire at least). So anyway, I'm wondering if there's anything I'm missing and also how I should go about testing things best.
as ive told ya many times already , you gotta check the fuel pressure going down the road on it
sitting still isnt gonna tell you want you need to know
Right, im going to get a regular gauge soon, but just thought this might tell me something. For what its worth, i raised the fuel pressure a little bit and it didn't seem to go lean as easily today.
what is the fuel pressure set at? you have 62# injectors and your running a stock fuel pump?
Yes, wideband, and to reassure me the sensor wasnt messed up i checked the narrowband reading on hpt and same thing (i know its not reliable, but enough to show lean or rich in boost since it levels off). Also to double-check i saw knock and it felt kinda sluggish in general.
whiteboyz24 wrote:what is the fuel pressure set at? you have 62# injectors and your running a stock fuel pump?
Fuel pressure is around 48 now when idling. Recently it was about 46, so I just barely raised it last night. The injectors were rated at 62# @ 43 psi. I've played with raising the pressure some before (had this problem for a couple weeks or so) and it didn't seem to help too much, I'm wondering if any it does help is just a band-aid fix if the pressure is still dropping. I had had trouble with the injectors misfiring before but usually it was just one or maybe two at a time, so I think it had something to do with the installation, so I replaced the seats and their o-rings and it got rid of the misfire. I am using the stock fuel pump because I was told that it should be fine and that people have had problems with the aftermarket ones. I had someone else replace the pump, I'm wondering if maybe they got a generic one that wasn't strong enough or didn't install it right or something along those lines. BUT it goes lean fairly easily, even when in low boost or about half throttle situations, so I'm wondering if something else is going on. Im thinking about swapping back in the 42# injectors I had before and see what happens, but the thing is I dont think the problem started right when I swapped injectors (although it's hard to remember exactly because all around the same period of time I was trying to get rid of the misfire, and my fuel pump went bad and I was putting in the new injectors). I'm not sure if this helps clear things up any, but thought I'd throw it out there anyway...the reason I swapped in the 62's is because with the 42's it was getting a little lean in the upper rpms, which looked to be because the injector duty cycle was going too high (even over 100 at times) according to hpt.
i would swap in the other injectors to narrow the problem down. you're right about raising the pressure being a band aid. The fuel pressure shouldn't drop.
did you try raising the fuel pressure on the 46# injectors??
whiteboyz24 wrote:i would swap in the other injectors to narrow the problem down. you're right about raising the pressure being a band aid. The fuel pressure shouldn't drop.
did you try raising the fuel pressure on the 46# injectors??
Ok, I'll try swapping the injectors, i was kind of considering that anyway. The thing holding me back was I was trying to figure out how the bigger injectors would cause it to go lean, but not misfire. Any ideas? Also, if it works better with the 42#'s, does that necesserily mean the 62's were at fault...or could it mean something else isn't accomodating the 62's right? Hope that makes sense
Ok, so I finally got a pod fuel pressure gauge hooked up. The only thing is, I'm not completely sure what's normal...but I don't think it seems normal.. Anyway, here's what I've seen so far. Under idle the pressure is about 50-52. Cruising down the interstate probably about 48-50. But when I give it a little gas...not even that much it drops down to about 40-42 and holds there until I let off. The more I press the gas the lower the pressure gets. At about half throttle it goes down to like 36 or 37 and holds around there. Air/fuel ratio at half throttle usually is ok, but sometimes a little lean. At 2/3 throttle it goes down to about 32-34 and holds around there. Air/fuel ratio then is leaner, enough to cause some significant knock. I try to stay out of those conditions and definitely no more. Also it seems like the effects are worse when I give it gas at higher speeds/rpms than at lower ones.
Anyone have any ideas? I'm thinking maybe the afpr has something wrong or the fuel pump isn't keeping up or something along those lines. I have 62# injectors, a stock fuel pump, and an Aeromotive LT1 afpr. I took the afpr off the other day and reinstalled it, tightening all the screws, and trying to make sure everything was good and tight and installed right. It may have helped a little bit, but nothing big. I have some videos I took on my cell phone camera of the afr and fuel pressure gauges the other night under 1/2 to 2/3 throttle, I can try to put them up if it might be helpful, but might be a little blurry/bouncy. Thanks in advance for any help!
No idea, but is your tank full?? 3/4?? less than half??
-Seth
Does it at any fuel level. It may be worse at some levels than others but I don't know.
hmm, idk. It was just a hunch cause i know our cars don't like when the fuel gets lower.
-Seth
