as the subject stated, my car feels like it lost power under 2500 rpms. my car stalled out on me yesterday, so i replaced the plugs and the car started back up. thing is... it sounds like it's misfireing now, and the car seems to have lost power off the hole. when im driving, the car seems to shake a little under 3k, and when i step on it from a stop or rolling slow at around 10mph or more, like i said before, it feels like ive lost power. i checked the timing and it was at 12*btdc, so i changed it to 8*btdc. i have a laptop and datamaster, so if anyone needs me to log the car, i'll do it and post the files on my server. im really upset because my car shouldnt be this slow. it feels pretty much the same after my rebuild, but the thing is, i had my heads ported, put headers on, and had a comp cam 502 cam installed. also had a custom prom put in, as well as 24# svo injectors.

atleast i should be running in the 13's since i was running 14.5 stock... but today, i barely beat an audi a6 2.7l biturbo... i don't know exactly what they run, but online i found a place that says they run 14.6, and a place that says they run 15.2... so i dunno. if anyone can help me figure out why my car is missing and why it feels like it lost power below 3k, you have no idea how much i would appriciate it. it sucks to have a mechanic you trust just to realize he isnt as good as you first thought =\

 

The same for my V6.

I think: 2 injectors are running rich (leakages), then ECM compensates the injectors rich with the other 4 running extremely lean. This condition would produce the shake a cruise speed and bad power at low RPMs (only 4 -5 cylinders works O.K.).

What do you think about this?. It's only my theory about this problem (I'm replacing injectors the next weekend).


Denis V.

 

TPI is batch fire so the ECM cannot compensate for individual injectors. If you have changed your cam you may have airflow characteristics that are not compensated for in the ECM. Is your car SD or MAF?

 

SD. i had one of the board members burn me a chip for my car, but im sure i need a lot more tuning on it before she's up to par with what she should be running. i'll wait to do the tuning when i put the HSR and a bigger cam on.... but i still dont think she should be running this bad =\

 

Hmmm, let me say again...:
I mean:
6 injectors are working as follows:

Injector # 1: A/F ratio = 14.7: 1
Injector # 2: A/F ratio = 14.7: 1
Injector # 3: A/F ratio = 14.7: 1
Injector # 4: A/F ratio = 14.7: 1
Injector # 5: A/F ratio = 14.7: 1
Injector # 6: A/F ratio = 8.0: 1

ECM reading a rich Average A/F Ratio @ O2 sensor = 13.58: 1

Then, ECM instruction will be: + 8.25% LEAN for the 6 injectors (batch).

Then, injectors # 1 to # 5 will works at 15.91: 1 AFR (extremely lean). Injector # 6 at 8.66: 1 AFR.
New average @ 2 sensor will be = 14.7:1 (15.91 x 5 + 8.66) and the car will shake at cruise speed. (It's only for a theoretical discussion).

 

how would i go about checking my fuel injectors?

 

Also be sure to check your fuel pressure regulator, the loss of power under sounds like the same problem I had when my fpr's diaphram went out. It's worth a shot at least.

 

now my car's starting to smell like gas, even though the fp is at 39psi (w/ vacuum disconnected). it also seems that when im running the car hard, the moment i let off the gas, i hear a nice little backfire. i dont know if that has to do with me having a nice hole in my y-pipe though. what would cause my car to backfire like that if i have my fp set at 39 and i have an msd box putting out maximum spark on brand new delco plugs?

 

Well I will comment on two things.

1. When I say batch fire theoretical or not, the ECM only has one injector driver. The driver is timed between two pins leaving the ECM for current purposes. If you look at the wiring going to the injectors you will notice that one side is green and blue and the other side is pink and blue. The car cannot compensate or trim individual fuel delivery from each injector. The DIY GM fuel injection site has some great schematics.

2. As far as the car not running correctly. From what you have stated (39PSI). That fuel pressure is way to low. Ideally it needs to be about 42 to 45 PSI. When you shut of the car does the pressure bleed off quickly or does it remain constant? You want it to remain constant. You also need to know the base timing that was burned into your chip. If you go beyond that the timing will be way off across the whole RPM range and the car will surge erratically at idle.

 

Interresting. My car is a pig below 2500-3k also, but I've been going on the assumption that it was just because of my heads (461 fuelies - not a good match for TPI). Adjusting the screw on the FPR doesn't ever seem to make a difference in my fuel pressure. Maybe it's time to throw a new diaphragm into the FPR.

Dave, what table or location in the chip has the base timing listed? I don't remember seeing that field anywhere when I burned my chips. I'm only running 8 or 10 degrees of base timing, and the timing on my chip isn't very aggressive (no knock counts), but I'd like to at least check that situation.

 

I do not know what program you are using to edit your chip, but I use WinBin and my own ECU file. In most ECU files in WinBin the initial timing is in the Values tab.

 

I use Tunercat. I'll give it a look tonight if I get time.

 

one word:

like i said, my car was missing, and it wasn't running good, so i went along and started to look at my plugs, even though they were only a week old. #1 was perfect... went to #2, and it broke off while i was trying to take it off. when i took it off, it looked perfect. went to #3, and, yet again, it looked perfect. went to #4 and i noticed the white part of the plug was a little loose... like it had broken, but not broken off. took off the plug and lord and behold! dirt black... no crusty crap on it... just black. smelled like gas... looked like it never fired. went to discount auto to replace it, reinstalled it, and listened to the car. doesnt seem to miss anymore, and the power seems to have come back. i would have NEVER guessed it was a malfunctioning spark plug... i think i need better quality plugs rather than the ac delcos i have now (2 broken plugs).

thanks for all your help guys... now all i need to do is find out if im running lean or rich. is there any program i can use to find out from my o2 sensor if i am running rich or lean? i really don't want to pay someone to do it for me if i can do it myself. not to mention, i'd like to find out how my fuel injectors are doing... is there any way to test the injectors out?