ransomnotes Posted July 17, 2010 Share Posted July 17, 2010 (edited) I've been dealing with this for a few months now, and have not been able to narrow it down to an obvious answer. There is no rhyme or reason to it. Some times at WOT I get a strong and steady 10psi, while other times I'm getting a louder than usual "whoosh" of air sound on the drivers side as power drops off. Like I'm coasting, and just blowing air. It will still read 10psi on the boost gauge while boost drops off. Doesn't matter if it's at take off, or from a rolling start. Some times boost is there, some times it just drops off. Every time I think I have found the problem and the car runs really good, it starts happening again. I've pressure tested my intercooler and piping. Even taken off individual sections and tested. Each time with more than 10psi. Holding strong. Tried two different BOV's thinking that was the problem. Currently using a GReddy type S recirculated. I've removed my intercooler piping, and gone with stock J-pipe (with BOV). No change. Was running 10psi with manual boost controller. Removed that and ran stock boost. Still leaking. Tested the wastegate actuator, which opens fine under pressure. Disconnected the wastegate rod and made sure the arm swings freely. It does, and the rod is straight. I've also pulled and checked the ECU connections. They are clean and tight. I have no exhaust leaks. The car runs great except for WOT. Idles good at -21 vacuum. What else?.... Turbo has no shaft play, and spins freely. Wastegate and BOV get their signals from the intake. BOV is vented between AFM and turbo. Boost gauge is T'd with FPR signal. I don't know what else to check, so hopefully someone can point me in the right direction . I don't post problems often. I can usually figure it out with time, but my brain is starting to hurt. Edited July 17, 2010 by ransomnotes Quote Link to comment Share on other sites More sharing options...
hoov100 Posted July 17, 2010 Share Posted July 17, 2010 what gauge are you using? is your waste gate sticking? Quote Link to comment Share on other sites More sharing options...
S130Z Posted July 17, 2010 Share Posted July 17, 2010 What spark plugs are you running and what are they gapped to? Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 17, 2010 Author Share Posted July 17, 2010 what gauge are you using? is your waste gate sticking? Seems like it could be my wastegate sticking, but it moves back and forth by hand just fine. I haven't removed the downpipe to inspect it further. I'm using a new aftermarket gauge but I don't remember the brand name. Had to replace my old $30 one a couple months ago. Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 17, 2010 Author Share Posted July 17, 2010 What spark plugs are you running and what are they gapped to? NGK BPR6EY gapped at .040 Quote Link to comment Share on other sites More sharing options...
letitsnow Posted July 17, 2010 Share Posted July 17, 2010 Does it still have the stock pop off valve? Quote Link to comment Share on other sites More sharing options...
dhartig Posted July 17, 2010 Share Posted July 17, 2010 If it only happens at WOT it might be fuel starvation. It sounds like your boost pressure is holding steady and you have pressure checked all the components. I might start looking other places for the fall off in power. Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 17, 2010 Author Share Posted July 17, 2010 (edited) No POV. I have been wondering if this is fuel related, and maybe the problem is the old fuel pump. I have an extra one I could try. Fuel pressure is normal at idle, but I have no way to check it under boost. It has been taking longer to start up lately, where as it used to start quick every time. Injectors are only a couple months old, as well as the FPR, and fuel filter. I just picked up an Air/Fuel gauge, so I'll hook that up and see what I get. It's a narrow band, but better than nothing. Edited July 17, 2010 by ransomnotes Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 22, 2010 Author Share Posted July 22, 2010 I replaced my fuel pump and Fram filter by the tank yesterday, and my pressure at idle improved a little. Still having the same boost problem though, but now it's started happening almost every time I boost. Not just WOT anymore. It bucks like hell at WOT too. I pulled and checked all of my plugs. Gapped them a little bit tighter at .038. Double checked wiring, and vacuum lines AGAIN. The car was running awesome for a while, and this problem just popped up out of the blue. Frustrating me more and more. I have my Air/Fuel gauge installed now, so I'll be monitoring it on my way to work. Is there anyone around the Lawrence Kansas area who would be willing to help me out? Usually I enjoy having one of the very few Datsuns in town, but now I'm feeling lonely Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted July 22, 2010 Share Posted July 22, 2010 I replaced my fuel pump and Fram filter by the tank yesterday, and my pressure at idle improved a little. Still having the same boost problem though, but now it's started happening almost every time I boost. Not just WOT anymore. It bucks like hell at WOT too. Check your connections on your VCM, a guy with a L28ET swapped S130 had connection problems with his 'boost module' and it kind of felt like what you are describing. Quote Link to comment Share on other sites More sharing options...
S130Z Posted July 22, 2010 Share Posted July 22, 2010 I was helping my buddy with his FC because he was losing boost. It ended up being a tear in a coupler. It would seal itself when not under boost......talk about a PITA to diagnose. You could hear it under boost, but not any other time. Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 22, 2010 Author Share Posted July 22, 2010 Ok, according to the Air/Fuel gauge, I am running super lean under boost. That narrows some things down. Arrgh! Quote Link to comment Share on other sites More sharing options...
S130Z Posted July 22, 2010 Share Posted July 22, 2010 I have my plugs gapped at .028. Maybe you are blowing out the spark and the rich unburnt mixture is causing your O2 sensor to read lean. Gap your plugs down more and see what happens. Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 22, 2010 Author Share Posted July 22, 2010 Thanks, I'll try running a smaller gap and see what happens. I'm also gonna check my ECU connections again, even though they appear to be tight and clean. Then my next test will have to be hooking up an additional fuel pressure gauge that I can monitor while driving. Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted July 22, 2010 Share Posted July 22, 2010 I have my plugs gapped at .028. Maybe you are blowing out the spark and the rich unburnt mixture is causing your O2 sensor to read lean. Gap your plugs down more and see what happens. Wouldn't it be more likely he IS going lean and should check that stuff first? I'd check couplers and all the electrics thoroughly Quote Link to comment Share on other sites More sharing options...
Lazeum Posted July 22, 2010 Share Posted July 22, 2010 (edited)  I'm quite curious to follow this thread and see how it would be resolved If your narrow band is reading lean, it would mean you're above 14,7 AFR???? that would be super lean! Since narrow band are either rich or lean, there isn't much in between! How does the spark plugs look like? are they all white? That would confirm or not what you're seeing with the narrow band. Personally I don't believe you can run at WOT with boost and lean AFR above 14.7. I would start looking at ignition & timing for sure. having some missing might make your AFR looks lean. If you have an air leak, could the ecu be able to retard the timing to avoid knock? You should run a boost leak to check that. It has to be big because a small air leak will make your engine to run too rich; the MAF will see more air coming into the intake than what is really going into the engine, so fuel will be in excess. Good luck! Edited July 22, 2010 by Lazeum Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 22, 2010 Author Share Posted July 22, 2010 More weirdness. After gapping the plugs at .030, and resetting ECU connections, the air/fuel was now showing normal to slightly rich under boost. Still had the same symptoms as before though. Very little power during boost. So I parked and ran into work for a couple minutes. Took the car back out, and now boost is back, but still not as strong as it used to be. Definitely feels a lot better, but not great. Air/fuel still showing normal to slightly rich. Been running stock boost again until I get this figured out. I'm beginning to question my ECU since this is such an off and on thing. I really don't think I have a boost leak going on. I've checked piping, couplers, hoses, etc MULTIPLE times now. Quote Link to comment Share on other sites More sharing options...
zxtman Posted July 23, 2010 Share Posted July 23, 2010 I've been dealing with this for a few months now, and have not been able to narrow it down to an obvious answer. There is no rhyme or reason to it. Some times at WOT I get a strong and steady 10psi, while other times I'm getting a louder than usual "whoosh" of air sound on the drivers side as power drops off. Like I'm coasting, and just blowing air. It will still read 10psi on the boost gauge while boost drops off. Doesn't matter if it's at take off, or from a rolling start. Some times boost is there, some times it just drops off. Been running stock boost again until I get this figured out. I'm beginning to question my ECU since this is such an off and on thing. I really don't think I have a boost leak going on. I've checked piping, couplers, hoses, etc MULTIPLE times now. From the information you've provided, I'm assuming you do not have this problem when running stock boost (6 PSI?), but you do at 10 PSI. Could it be blow-by and time for a new set of rings? Have you you performed a compression test on the motor? ...it might be time to "freshen-up" the motor. Quote Link to comment Share on other sites More sharing options...
ransomnotes Posted July 23, 2010 Author Share Posted July 23, 2010 I have not done a compression test for almost a year now. I don't recall the exact numbers, but it was something like 135-140 down the line. You are right though. I should do another test. As far as boost goes, it happens regardless of how much I'm running. There were a couple times when I thought I fixed the problem, and the car started running good again, so I raised the boost back up. Otherwise, I try to keep it down anytime I'm trying to diagnose an issue. Quote Link to comment Share on other sites More sharing options...
S130Z Posted July 23, 2010 Share Posted July 23, 2010 When you say normal to slightly rich under boost, what numbers are you seeing? Quote Link to comment Share on other sites More sharing options...
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