This is a discussion on Fpr within the TBI Tuning (87-95 / OBD I) ECM/PCM forums, part of the Performance category; I have a question regarding some work I just finished on my 5.7, and some work that is soon to ...
I have a question regarding some work I just finished on my 5.7, and some work that is soon to follow (over the weekend).
I have been hunting for an idle surge since I have owned the truck, and everything has checked out correctly. Last weekend I picked up a spare throttle body and injector pod minus all the sensors. Since then, I did a the TBI mods. I have a little work to do before the throttle body is ready to install(transmission linkage and swapping TPS connector to the later style.
I went ahead and made the FPR adjustable, and cranked a little extra into it, and installed it. I have a manifold on order to attach a gauge, but it isn't here yet, so I just winged it for now to see what would happen.
In any case, the initial results were disappointing to say the least. The idle was high, and would not drop below around 1100 RPM and was very slow to drop to that level when I blipped the throttle.. I figured a reset might help, so I went thru the IAC calibration, again to be disappointed. In any case, I had to run out for something, and didn't want to swap the old regulator back in, so I took the truck out as it was. In any case, long story short, the damn thing came alive. Throttle response was instantaneous, and the engine ran past 5000 RPM for the first time since I have owned it. When I pulled up to the first intersection, the idle was strong and steady, but a little bit low for my liking. At every stop, the results were the same. Rock solid idle at around 500-550. The tach is an old factory tach, so I'm sure it is off a little. Guess the initial results were so poor because the engine needed a little time to learn the new fueling curve.
The question is, what the hell is going on? I disassembled the original FPR, and while there was some corrosion, it appeared to be working perfectly. Was the stock setting so poor that it was running lean at idle? Everything points to that, but in open loop, the thing idled like a champ, and that is where I would have expected issues if the pressure was too low.
This is just the first of the mods I have planned for the truck, and I was hesitant to do any mods at all until I got the idle sorted out. Lucky for me, I can continue now.
The list is pretty basic, but it isn't intended to be a powerhouse. I am going to order the EBL this week, and start doing some experimenting, and see if i can drive the mileage up a few notches. One of the things I am going to try is running 4.3 injectors with higher pressure to see if it will improve atomization. Other than that, will look at opening up the exhaust some, and dialing in the timing.
One last question..... I think I know the answer, but want to be sure. Is the resistance of the later TPS the same as the older flat style? I can check with a meter, but my meter is in my company truck, and I loaned it out for awhile. I suppose it's a moot point, since I won't be able to set it till I get my meter back, but i just want to be sure before I wire it in.
Last edited by dahoyle; 07-19-2012 at 10:24 PM.