scottyMIz Posted August 10, 2001 Share Posted August 10, 2001 Here's the deal guys i took off the exhaust to see if my boost problem would go away.My problem was it would hit 15psi at first then slowly back down on pressure when the rpms went up.Anyway i took it off and it ran like crap it boosted the same too but i didn't want to take the rpms up too high cuz i didn't want to mess anything up.It also sounded funny after so high of rpm the turbo wasn't audiable anymore just the exhaust making a weird sound.Anyone know the problem?Or is this normal? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted August 10, 2001 Share Posted August 10, 2001 Is the turbo sized to small? I mean if the RPM's come up and it drops off boost, has the compressor shot its wad already so to speak at a lower RPM? Regards, Lone Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 It's the stock turbo for the 81zxt.It runs much better with the exhaust on than off. Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 10, 2001 Share Posted August 10, 2001 Scotty - Have you ever checked your air/fuel mixture under boost? Sounds like you could be running lean and misfiring. Actually, could also sound wierd if you were really rich, but I kind of doubt that is your problem. Were you still running a downpipe, and disconnected the rest of the exhaust from it? Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 Hey tim i've never checked the fuel/air mixture yet.I did turn up the fuel pressure up to 55psi and it will do it under boost.I did unhook the exhaust from the down pipe and it ran like crap i just wanted to see if it would run better. Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 10, 2001 Share Posted August 10, 2001 So, your fuel pressure with the reference hose to the FPR removed is 55psi, right? What does it go to when you are under boost? (should be 70psi at 15psi of boost) Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 Under boost it's 55psi when it's idling it's 45psi.I cruched the stock one and i leaned the AFM so it would idle right.The it seemed slower but i'm not for sure.I really need an A/F mixture meter.I think tomorrow i'll read the voltage on the o2 sensor. Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 10, 2001 Share Posted August 10, 2001 quote: Originally posted by scottyMiz: Under boost it's 55psi when it's idling it's 45psi. Also (this is important) are you saying that your idle fuel pressure is 45psi with the reference hose hooked up to the FPR? Your fuel pressure at 15psi of boost should be 15 psi higher than the fuel pressure with the reference hose disconnected, not the fuel pressure at idle with the hose hooked up. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 you lost me tim.At idle it was about 30psi or so i just crushed it and took it up to 55psi when the FPR is hooked up it's running 45psi at idle and 55psi at 15psi of boost.Should it be 60 psi at full boost?Won't it be the same at idle as under full boost with the referance hose disconnected? Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 10, 2001 Share Posted August 10, 2001 No. The FPR's job is to keep the difference in pressure between the fuel rail and the intake manifold constant. The base pressure is the pressure that the fuel rail has when there is zero vacuum at the FPR's reference port. You can easily check this pressure by disconnecting the reference hose to the FPR and checking the fuel pressure (just to be clear the reference hose is the vacuum line that goes from the manifold to the FPR). When your engine is idling, it has a vacuum in the intake manifold, meaning that the pressure in the intake is lower than atmospheric pressure. In this case, in order to keep the pressure difference across the injector constant, the FPR will drop the fuel rail pressure. For instance, let's say your base pressure was 52psi, and your idle vacuum was 15in. 15 inches of vacuum is roughly equivalent to -7psi, so your fuel rail pressure at idle would be 52 - 7 = 45psi. Conversely, when you have boost, your manifold pressure is higher than atmospheric, so the fuel rail pressure has to be increased to keep the pressure across the injector constant. If you have a base pressure of 52psi and 15psi of boost, the fuel rail pressure would have to be 52 + 15 = 67psi. If you hadn't noticed, I picked my numbers there for a reason . From what you are telling me, it sounds like your base pressure is somewhere around 52psi. It also sounds like your pump isn't keeping up. Many OEM pumps, including the stock pump for the Z, have an internal pressure relief that keeps them from running too high a pressure in the event of a failed FPR or clogged return line. If the pump is not designed for a turbo application, this pressure relief is usually set somewhere around 55psi. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 Ok i set the psi at 55 when i crushed it on the FRP i used a tank of air and crushed it little at a time and checked to point that the pressure was released.I'll check the fuel pressure with the referance hose off. Thanks tim for being patient. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 10, 2001 Share Posted August 10, 2001 Scotty, I really hope you do not take this post the wrong way, but I would like to see you slow down and understand and heed the advice being given. I just do not want to see you destroy your engine. Here is some advice that was given when you first queried about crushing the FPR. quote: Yes, I have done it and it is a fairly common no-buck mod in the DSM world. HOWEVER, there are lots of caveats: - Do you know how much of an increase you want and what it will get you? - If you go too far, there is no going back - Do you have an accurate fuel pressure gauge? Do not attempt to do it w/o one - If you are running the stock pump, make sure you do not exceed its capacity. I forgot what it is but TimZ posted the number recently so do a search - Do it in small increments. You might have to de-install/install the FPR a couple of times until you get it where you want it - If you go too far there is no going back. In case you do not know the formula for calculating the flow rate, here it is: Divide the new pressure by the old pressure, take the square root of that number and multiply it by the inj flow. Of course you must know the inj flow rate and what pressure it was rated at. E.g., I believe (could be wrong) that the stock turbo inj is rated at 260cc @ 36#. If you raised the fuel pressure to 42#, the injs are then capable of flowing 280+cc. Make sure you set the fuel pressure at idle with the vacuum line off. Go find TimZ's post and make sure the new pressure + max boost does not exceed the number he specified. REMEMBER, IF YOU ARE RUNNING STOCK INJS, THEY COULD BE AS MUCH AS 20 YRS OLD. Good luck. Anyone who has asked me for advice about tuning an EFI/Turbo setup for more power will tell you that my advice is probably somewhat annoying because of my emphasis on understanding the basic principles and being very, very patient. The HP is there and it will eventually come but one wrong step could be fatal. Good Luck. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 10, 2001 Author Share Posted August 10, 2001 Scottie i didn't take it the wrong way i'm new at this so it will take some getting use to.I'm happy you guys take the time to help.The FPR i'm not worried about i have a couple of them so if this one is junk cuz of my ignorance then i'll get another and try again.Eventually i will get an adjustable one but for right now the prie is right for crushing one.Tim is helping a whole lot he explained alot over the phone today when i can do it hands on i learn alot more.The math thing gets me i'm not good at it you know square root and all that never thought i'd be using it in real life i should of payed more attention in school.Gonna have to ask the woman for a lesson she's a wiz at math.The reason i ask you guys is cuz you know so much and the info is priceless to me.When are you gonna break the 10's mark?I can't wait til i can get enough money to start getting into it for real none of this stock ecu crap all after market and done right.I have so many bills but i love my z so i keep working on it trying to get it as far as i can.Getting a raise soon and all the extra money is going tword the zt.Hell i'm only 23 and i have five cars all run in great shape and i'm paying for one i don't have it got repoed from my ex and i have to pay for it.I also have a house and alot of toys that i should get rid of too.Enough about my junk,I just need you guys to continue helping me with the whole turbo thing.Like i said before Thanks for helping so far. Quote Link to comment Share on other sites More sharing options...
Sean 83ZXT Posted August 11, 2001 Share Posted August 11, 2001 Just to let ya know, I run my car with only a downpipe and it runs like a raped ape! a lil on the loud side though Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted August 11, 2001 Author Share Posted August 11, 2001 Hey sean what are you running for boost and quarter times?Just curious Quote Link to comment Share on other sites More sharing options...
260DET Posted August 20, 2001 Share Posted August 20, 2001 A suitable aftermarket ECU (EMS) for running 15psi boost would have a manifold pressure sensor capable of sensing up to 15psi. That sensor would tell the ECU to alter fuel injector and ignition timing requirements to suit the current boost pressure. Unless your present set up can do that (I'm not familiar with your cars particular ECU) you are never going to be able to set it up to run properly. And that can result in expensive engine damage. Quote Link to comment Share on other sites More sharing options...
Sean 83ZXT Posted August 20, 2001 Share Posted August 20, 2001 Hey sorry I just saw this but my best is a 15.1 @ 96mph I believe. Mods= just a 3" DP Blitz SS Blow off Turbo XS High Perf. Boost Controller @ stock 7psi More mods in the closet waiting Quote Link to comment Share on other sites More sharing options...
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