Guest the_dj Posted May 15, 2002 Share Posted May 15, 2002 I have the Holley Commander 950 ECU and I'm having some difficulties tuning it for WOT. It runs a little bit lean, and I can't seem to get it to richen up. No matter how much fuel I program into the curve at WOT, the O2 sensor reads .75 (almost rich enough) volts at 2000 RPM and starts dropping to .71 (slightly lean) by 3000 RPM and keeps dropping past that. Also, the car doesn't seem to have ANY power left in it past 4000RPM. I know that the TPI limits the high end, but should I be seeing a shift point as low as 4000-4400 RPM? The TPI has the SLP runners on it, and I've heard that those help keep air moving to past 5000RPM, but I'm not seeing that at all. The car has monstrous amounts of torque below 3000 RPM, and it's really a bummer having it fall flat on its face past that. All in all, the car FEELS quick until you try to race it, then it starts to feel sluggish from low low shift points and lack of torque past 3500 rpm. Could there be a problem with my fuel system keeping enough fuel from getting to the system? The injectors are new 24# injectors. Thanks for the suggestions guys. Sam Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 16, 2002 Share Posted May 16, 2002 Firstly a TPI can decide to call it a day by 4800 rpm's, it was not designed for top end power, even with the siamesed aftermarket runners the length of them was tuned for Torque not total HP. In fact, from what I've read in a rather interesting article (by a TBI supporter) the TPI was designed for the 305 to approximate the torque of the TBI 350, thats why the 350/305 TPI intakes are the same, just difference between injector sizes. Chevy just went into the parts bin for the 350 TPI, put in bigger injectors, different map and called it a day. Thats what I was reading anyway. I'd hazard a guess that your fuel pump is not keeping up with the demand of the system. What fuel pump are you running, and how much pressure is it putting to the lines, what size fuel lines are you using. I'm guessing the computer is telling the injectors "Ok, wide open pulse boys" and the injectors are going "Umm, like dude, like where is the fuel we need for this?". That would be my guess, also look at the TPS for correct adjustment just to make sure its really telling the computer its wide open. Just some thoughts and some things to check. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Mike C Posted May 16, 2002 Share Posted May 16, 2002 Yep, like Lone says, it's either your pump or the duty cycle on your injectors. Doesn't the 950 have data logging that will tell you fuel press and duty cycle? Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted May 16, 2002 Share Posted May 16, 2002 The 950 can't log fuel pressure, I know that for sure. I haven't been able to fully test the system pressure, but I did a little bit. When the injectors are open, but not all the way open (60% duty perhaps), the pressure reads 50 psi at WOT to 2500 rpm, then drops to 45 psi by the upper 3000's. Lone: 4800rpm is FAR in the dead zone of my engine. It's quits by 4000 at the latest, is that normal? Thanks I'll reply again tomorrow with fuel line sizes and the type of fuel pump I have. I'll get the system checked again when I open them to 80 or 90% duty cycle and see what it reads. Thanks for the help so far, I'll get this eventually. Sam Quote Link to comment Share on other sites More sharing options...
fl327 Posted May 16, 2002 Share Posted May 16, 2002 i think its the fuel pump, check to see if its the stock 280z pump, i know tpi hits redline early, but man my 305 tpi motor doesnt fall on its face until 4500. Quote Link to comment Share on other sites More sharing options...
Mike C Posted May 16, 2002 Share Posted May 16, 2002 What displacement is your engine and what is the camshaft? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 16, 2002 Share Posted May 16, 2002 4000 is definitely on the low side like FL327 said. The drop of 5 pounds sounds like a definite problem to me, you want it consistent for sure and for sure it shouldn't drop as the RPM's raise. Is there a rev limiter gone awry possibly? Is there any codes the computer is throwing out BTW? More thoughts, good luck, Lone Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted May 16, 2002 Share Posted May 16, 2002 You have a fuel problem. If your pump, lines, and regulator check out, maybe the 24# injectors are too small. I'm running 30# in my 327, but it's not a TPI it's an Edelbrock Pro Flow. Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted May 16, 2002 Share Posted May 16, 2002 I think 3/8 should be fine. What do you mean by damper. Do you mean regulator? Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted May 16, 2002 Share Posted May 16, 2002 There is a fixed pressure regulator on the fuel rails of the TPI. The "fuel damper", as the factory service manual calls it, is what looks just like an adjustable pressure regulator that comes right after the fuel pump on the send line. Could I have 2 pressure regulators on the fuel send line? It confused me too... Sam Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted May 17, 2002 Share Posted May 17, 2002 Don't limit your troubleshooting to the fuel system. If it is a Goodwrench 350 crate motor then it could well be done putting out power by 4K. They are only rated at 250 hp to begin with. If it is one of the performance series, and if the valve springs are old and weak, you could be going into valve float. If it looks like the fuel system is good and functioning, which it looks like it is, then move on to the next likely cause. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 17, 2002 Share Posted May 17, 2002 Possibly, my 250 hp crate signs off closer to 4800-5000 rpms, but its carburated. Its cam is super mild at like just barely 200 deg at .050 duration. Its pretty much done by 4800 just like a TPI though (can't wait to change cams and heads that's worth plenty, another 1000 revs would be great). If this 'Dampener' is adjustable, I'd certainly research what it is, what it does, and how can you mess with it. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted May 17, 2002 Share Posted May 17, 2002 OK, I just got out from under the car and here's what I know: Fuel pump and damper are stock. The lines are much bigger than stock and very nice braided steel. The engine is a GM crate 350 with TPI added. The cam is stock, so the motor shouldn't make too much power for the 24# injectors to keep up. Is there something I can do to fix the issue without spending a bunch for a new pump? What is the fuel damper that's connected to the pump and what should I do with it? Thanks, Sam Quote Link to comment Share on other sites More sharing options...
Tim240z Posted May 17, 2002 Share Posted May 17, 2002 Maybe the fuel lines are to big? The larger ID lines may be creating a pressure drop...what is the ID of the lines? Tim Quote Link to comment Share on other sites More sharing options...
Guest the_dj Posted May 17, 2002 Share Posted May 17, 2002 The ID of the lines looks to be 3/8". Sam Quote Link to comment Share on other sites More sharing options...
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