alexx933 Posted August 28, 2013 Share Posted August 28, 2013 Today, I decided to play around with my engine a little bit. Check the oil, coolant, vacuum lines and such. While the motor was on, I was checking the vacuum line to the stock FPR. I unplugged the hose from the intake side. All of the sudden, my idle surges slightly higher. It actually sounded better. I plugged the vacuum leak and the idle went down to where it was to start with. I tried this a couple times with different vacuum sources and the FPR to the same result. What does this mean? I have no working tach at the moment so I'm not sure if either way results in a more stable/healthy idle. Thanks in advance, Alex Quote Link to comment Share on other sites More sharing options...
KyleG Posted August 28, 2013 Share Posted August 28, 2013 The fpr sets fuel pressure to 36psi above the pressure in the intake manifold. When you are idling, there is a vacuum in the manifold, reducing your fuel pressure (to 36 psi - intake vacuum). By unplugging this line, you are increasing your fuel pressure and making your car run richer and idle a bit higher. If you just want to increase your idle to a more stable level, turn the big screw by the throttle body. If theres an issue with your car running lean, you could find out by looking at your plugs. All this theory is covered in the EFI bible. Its a great read if you're new to the parts of the fuel injection system. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 28, 2013 Share Posted August 28, 2013 Think about what the throttle does, and the effect of opening up a vacuum port to the outside atmosphere. http://dictionary.reference.com/browse/throttle?s=t Quote Link to comment Share on other sites More sharing options...
alexx933 Posted August 29, 2013 Author Share Posted August 29, 2013 My car already runs pig rich. I get about 10 MPG. Currently in the process of switching over to MSnS. I didn't offer any information as to the year because I thought it was irrelevant. I have an 81 turbo in my 77. There is no idle adjustment screw on my TB as idle is controlled by the ECCS. I looked through the FSM quickly and may have missed that unplugging this would increase my fuel pressure. I was thinking that by drawing air in through the vacuum leak, it was actually running more lean as opposed to more rich. Quote Link to comment Share on other sites More sharing options...
Domzs Posted August 29, 2013 Share Posted August 29, 2013 10 mpg ? Damn ! Are you running O2 sensor ? Quote Link to comment Share on other sites More sharing options...
alexx933 Posted August 29, 2013 Author Share Posted August 29, 2013 Yup! It's a brand new O2 sensor at that! haha Accidentally shorted the blue/red wire from the ECCS that powers the fuel pump relay and so I had to wire it in separately. I'm pretty sure that with a combination of somebody having messed with my AFM is causing the ECCS to give it more fuel. I just thought this was weird how the idle seemed healthier with that vacuum leak. Quote Link to comment Share on other sites More sharing options...
cgsheen Posted August 29, 2013 Share Posted August 29, 2013 The L28ET doesn't really use the O2 sensor to the same extent a more modern engine does. It runs off of it's "base map" more than you would think and really only polls the O2 sensor when you're cruising. It only uses it for "closed loop" operation and there are very specific "requirements" - they're listed in the FSM. It's never using the O2 sensor when you're idling (anything under 1500RPM), or under load (acceleration), or over 3500 RPM, it won't even start polling the O2 sensor until the CHTS is over a certain temp... I'm pretty sure you're correct about the AFM though. Folks just can't leave them alone - for some reason... Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 29, 2013 Share Posted August 29, 2013 idle is controlled by the ECCS. Except in the case of conditions described in your first post. You might be so far off with CHTS, fuel pressure, and/or some other variable that the ECCS can't do its idle control. Probably be worth your time to check all of the basics, like timing, fuel pressure, vacuum leaks, etc. followed by whatever you can figure out from the FSM. Even without the O2 feedback, 10 mpg is terrible. You'll need to do the same with MSnS anyway. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 29, 2013 Share Posted August 29, 2013 176f...it starts looking. Actually the 1500 rpms it somewhat incorrect. It SAYS that in the FSM, but it is more a function of the ECCS / EFI module seeing a switching signal and really the TPS switch state. If you are up to temperature, and have a switching signal, closed-loop stays enabled! Take a heated three-wire sensor from a Z-31, and WATCH what happens to the lights on your ECCS.... the thing gets into closed loop and STAYS there because the O2 sensor doesn't "cool off" and stop switching. As long as the WOT indication is not on... The mileage on any turbo car can be enhanced in-town putting a heated sensor in, you get into closed loop and stay there in stop-n-go traffic whereas normally you stay n the programmed loop instead. Quote Link to comment Share on other sites More sharing options...
alexx933 Posted August 29, 2013 Author Share Posted August 29, 2013 The original one wire O2 sensor will be kept until after the MSnS conversion just because I'd rather put the money into a wideband. As far as closed loop goes, I don't know as much as you guys, but the best mileage I've ever gotten was during a 100 mile trip at a staggering 12.5 mpg. After passing about 5 cars in that one hour and forty minutes. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 29, 2013 Share Posted August 29, 2013 Depends on your speed....but with a five speed doing a steady 75 I got easily double that, and then some! You got problems! Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 29, 2013 Share Posted August 29, 2013 My 260 didn't break into the teens on the highway until I crossed the century mark on I80 Eastbound... And then only 19.5! The FI '76 got a steady 22 towing an 800# HF Mini-Trailer at a steady 80-85! Quote Link to comment Share on other sites More sharing options...
alexx933 Posted August 30, 2013 Author Share Posted August 30, 2013 Oh god, that sounds nice! haha I have been waiting to sell my CRX until the conversion to MSnS so I'm not always paying for my crappy mileage. $35 just to go 80 miles is ridiculous as opposed to $20 to go 160 miles. If I got about 25 mpg, I'd be perfectly content minus the fact that this will be scary to drive in the winter haha Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.