I decided to take the plunge today and throw in those 3L injectors that I had. They are the light-blue injectors that some people have reported were 24# injectors.
I threw them in, and reset the pcm. I started the engine and let everything stabilize.
I put a few miles on it and then I checked a few things.
The long term fuel trim is showing about -10% (actual range was -8% to -13%) for both left and right banks.
This means that the pcm is leaning out, and most likely is the result of bigger injectors.
I cannot confirm directly that these light blue injectors are 24#'ers, but I have enough indirect evidence that agrees with it.
First, with the SVT orange injectors, there was only a little positive fuel trim adjustments, abou 3-5% or so. With higher fuel pressure (65-68psi) the long term fuel trim was about the same. 65-68psi on the 19# injectors equates to about 24# per hour output. So the two separate conditions seem to agree with each other.
The bad news. It didn't change anything with the driveability. I did a little examination of O2 sensor values with the Palm III. The O2 sensor voltages are now much richer under acceleration. They are reading abou 0.94 Volts at WOT in any gear.
When I made good power before, I was running 0.86V at WOT. This translated to a rich mixture on the dyno. These 24# injectors may be making me run too rich. Also, if I let off the gas a little to cruise after accelerating, it takes longer for the O2 sensors to start swinging in open loop than it did before.
The stuttering is apparently a misfire, but only at low rpm. This misfire did not change at all between the injector swap.
So far, I still am thinking that the stock MAF is the culprit, but I am not sure.
I need some ideas.
Here are some other things I checked in addition to the above mentioned stuff.
I've qualitatively observed the coolant temp sensor, IAT sensor, TPS sensor, airflow values, and spark timing. They values are all close enough to what I would expect in normal operation.
By this I mean that there are no 'way-out' values.
This problem did not show up when I had the stock catback system on the vehicle. It seems to have shown up around the time I put the new more open exhaust system on. It also does not seem to vary with the different changes to the intake system (like with or without a filter, pipe diameter, etc).
Lastly: The engine runs with good power once the rpms get close to the IMRC opening point. It does not have any idle problems, and if I give it a small amount of throttle until I hit 3000 rpm then it will not show the stutter issue. Basically, the stuttering seems to go away around 3000 rpms and up. Having a load on the engine does not seem to affect the stuttering at all either. i.e. I can rev the engine at a stop and it still stutters/stumbles/misfires (whatever you want to call it) when the rpm is off-idle and below 3K rpm.
I think that is everything. I appologize about the length, but I want to make sure you all have the same information I do before you begin to ask questions, or offer advice.
Any ideas are appreciated. Thanks in Advance,
warmonger
"Tom"
