Z-Monster Posted May 7, 2006 Share Posted May 7, 2006 hi guys, i have a problem i experienced last night for the first time at an increased boost. i have been running my rb25det that is generally stock for the past yr and it has been boosting 0.4 bar standard. i increased the boost to 0.7 on monday last week and it has been great all till last night. The story goes like this. I was chasing a ferrari f360 modena and we were cruising at 180 kmh untill he decided that he didnt want my old 1980 280zx on his tail so he drop a gear as i did and floored it.... i droped from 5th to 4th gear and floored it.... no problems till my rev shot up between 5000 to 6000 rpm. my engine felt like it was misfiring or backfiring. it was either short on fuel or the tuning isnt right somewhere. (i obviously dont knwo where i went wrong). my exhaust temp shot up to 850 degrees celsius. thats where i felt that there must be a problem with my fuel deliver system. i do however have a fuel pressure regulator which i have set to 38 psi and that has worked for the past yr running 0.4 bar boost. so the question is, why is my engine bogging at high rpm at 0.7 bar boost when it had no problems at 0.4 bar boost before? what else do i have to tune to get my car running reliably and safely without blowing anything? Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted May 7, 2006 Share Posted May 7, 2006 well when your exhaust temp shot up like that im guessing that your engine leaned out. .7 bar is like what, 9-11 lbs? I dont think your injectors are maxing out. however, are you running a stock fuel pump? Quote Link to comment Share on other sites More sharing options...
Z-Monster Posted May 8, 2006 Author Share Posted May 8, 2006 i'm running on a jaguar 4.6L V8 Bosch fuel pump. the problem is that the fuel pump is a N/A engine pump and i have heard that there is a difference in n/a as well as turbo engine pumps.... i hav eahd no problems with it while running 0.4 bar of boost with my fuel press regualtor before... i would have though that this pump should suffice.... aside from the fuel pump being the root problem whatelse shold i look into?? Quote Link to comment Share on other sites More sharing options...
cheftrd Posted May 8, 2006 Share Posted May 8, 2006 If your tune is "on". there are only two major causes of a high boost/high rpm misfire (and a lot of little ones). Fuel and spark. Assuming your set-up is stock, your injectors are not running maxing out at .7 bar. Is the boost/vacuum line attached to the regulator? If so, you need to install a pressure gauge in the fuel line. Tape it to the windshield. Verify that the fuel pressure rises a proportionate amount to the boost. i.e. you are running 38psi, static, (vacuum line off), if the boost goes up to 10psi, fuel pressure should be 48psi. I would put my money here. That pump is probably not up to the task. You will see boost go up, and as the revs climb, fuel pressure will go down. Pumps lose a lot of capacity as the pressure is increased. Additionally, turbo engines have a higher BSFC than NA engines. As pressuere in the CC increases, it takes more and more spark power to jump the gap. While the stock Nissan ignition is certainly up to the task, what of the plugs? I've seen lots of high-dollar (yen) "race" plugs give up the fight pretty quick when run on a daily driver. They may run fine until you lean on them. Electricity takes the easy road; this may mean the gap until the going get's tough in the CC. Then they may leak-to-ground through cracks in the insulation, not firing the charge. El-cheapo, non platnium/iridium plugs also have a hard time playing the boost game without some back-up in the form of a CDI, etc. Be awaer that most in-cockpit EGT gauges are very slow resopnding. Open-junction sensors are the only ones you should believe. I've put HKS, Autometer, Defi, etc against my Omega hand-held. They are usually about 200 degrees behind on the climb. Once stabilized, they are the same, but in a gear where you pass through quickly, just be aware of what's going on if the gauge is climbing. A lean misfire will cause my Omega to show 1200 c, sometimes, where the aftermarket gauges will barely register a blip. The aftermarket stopped using open junction long ago because the sensors burn out pretty quick (reletive to an enclosed junction). Quote Link to comment Share on other sites More sharing options...
Z-Monster Posted May 8, 2006 Author Share Posted May 8, 2006 If your tune is "on". there are only two major causes of a high boost/high rpm misfire (and a lot of little ones). Fuel and spark. Assuming your set-up is stock' date=' your injectors are not running maxing out at .7 bar. Is the boost/vacuum line attached to the regulator? If so, you need to install a pressure gauge in the fuel line. Tape it to the windshield. Verify that the fuel pressure rises a proportionate amount to the boost. i.e. you are running 38psi, static, (vacuum line off), if the boost goes up to 10psi, fuel pressure should be 48psi. I would put my money here. That pump is probably not up to the task. You will see boost go up, and as the revs climb, fuel pressure will go down. Pumps lose a lot of capacity as the pressure is increased. Additionally, turbo engines have a higher BSFC than NA engines. As pressuere in the CC increases, it takes more and more spark power to jump the gap. While the stock Nissan ignition is certainly up to the task, what of the plugs? I've seen lots of high-dollar (yen) "race" plugs give up the fight pretty quick when run on a daily driver. They may run fine until you lean on them. Electricity takes the easy road; this may mean the gap until the going get's tough in the CC. Then they may leak-to-ground through cracks in the insulation, not firing the charge. El-cheapo, non platnium/iridium plugs also have a hard time playing the boost game without some back-up in the form of a CDI, etc. Be awaer that most in-cockpit EGT gauges are very slow resopnding. Open-junction sensors are the only ones you should believe. I've put HKS, Autometer, Defi, etc against my Omega hand-held. They are usually about 200 degrees behind on the climb. Once stabilized, they are the same, but in a gear where you pass through quickly, just be aware of what's going on if the gauge is climbing. A lean misfire will cause my Omega to show 1200 c, sometimes, where the aftermarket gauges will barely register a blip. The aftermarket stopped using open junction long ago because the sensors burn out pretty quick (relative to an enclosed junction).[/quote'] hey cheftrd, wow!!! sounds like you have encountered numerous cases similar to mine. i think you about covered everything i need to work on in my car... i have not checked my spark plugs for a yr now and it is possible that my NGK platinum plugs are not working too well already. i have been driving daily with a rich fuel supply of fuel to my engine even before i increased boost... so much so that i back fire alot when i heel and toe while down shifting. maybe there is lotsa carbon build up from riching out. my fuel press regulator is a sard unit which is progressive... i will go to 48psi and beyond if need be...my money is also on the fuel pump not being able to deliver the load. what is a good cheap alternative. for example can i get a bosch merc/bmw/toyota/etc unit??? i am currently as you know running on a jaguar 4.6l v8 pump which was good till i uped my boost. by the way whats the CC??? i'm also running a Sard ext. temp meter which i dont know if its an open or closed junction. i think its not a bad unit as i have seen how fast it picks up heat. ok hope you can carry on with the good stuff you have been providing me hope to hear from you again. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted May 8, 2006 Share Posted May 8, 2006 well how rich have you been running? maybe your fouled a flug/s. I just changed all six of my plugs from the cheapo autolites to ngk platinums, just under a hundred bucks.... outch Quote Link to comment Share on other sites More sharing options...
cheftrd Posted May 8, 2006 Share Posted May 8, 2006 CC is for combustion chamber. If the pump can't keep up with the flow/pressure demand, the pressure will drop, regardless of the pressure regulator; you will see a huge drop. Very obvious on a gauge. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted May 9, 2006 Share Posted May 9, 2006 Platinums, ouch. I have had nothing but trouble with platinum in turbo motors. L28, buick 3.8l GN, and RB. I really reccomend NGKs. Are you sure your base fuel pressure is right? Sounds a little low to me. 42 psi sounds more correct. This would account for your running out of fuel as well. Just something to check out. Evan Quote Link to comment Share on other sites More sharing options...
Z-Monster Posted May 9, 2006 Author Share Posted May 9, 2006 i have variable pressure depending on the RPM... at stand still if i rev my car to the limiter...7000 rpm the gauge on my fuel press meter shows a leap from 38psi to 43psi... i'm guessing there is a huge diffeenc when the car is on the road and driving. so it does go up to as high a psi the engines requires... the only week link i see is my fuel pump!!! i as you all already nkow am using a 4.6l N/A jaguar v8 pump. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted May 9, 2006 Share Posted May 9, 2006 i guess what im saying is that it sounds like your base fuel pressure is too low Evan Quote Link to comment Share on other sites More sharing options...
AK-Z Posted May 9, 2006 Share Posted May 9, 2006 Platinum is poor conductor. get different plugs. And don't get those multi point plugs either, the spark only jumps across one point. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted May 9, 2006 Share Posted May 9, 2006 Platinum is poor conductor. get different plugs. And don't get those multi point plugs either, the spark only jumps across one point. Well besides platinum the only thing I can think of is Denso's iridium plugs, which by the way I highly DO NOT recomend for Nissan engines. But, Since were on the topic of fuel pressure, May I ask what I should run my fuel pressure at? It's a stock RB25DE. I have a walbro 255LPH fuel pump and i had to back it down with a Nismo FPR because it was running to rich. A friend told me most n/a nissans ran at 36.5 ish PSI of fuel pressure. Runs fine, just wondering if that sounds right. Sorry For the steal on the thread! Quote Link to comment Share on other sites More sharing options...
Z-Monster Posted May 9, 2006 Author Share Posted May 9, 2006 Well besides platinum the only thing I can think of is Denso's iridium plugs' date=' which by the way I highly DO NOT recomend for Nissan engines. But, Since were on the topic of fuel pressure, May I ask what I should run my fuel pressure at? It's a stock RB25DE. I have a walbro 255LPH fuel pump and i had to back it down with a Nismo FPR because it was running to rich. A friend told me most n/a nissans ran at 36.5 ish PSI of fuel pressure. Runs fine, just wondering if that sounds right. Sorry For the steal on the thread![/quote'] hey EMWHYROHEN, dont appologise about stealing this thread.. i think you question is totally valid. this was a question that came to my mind as a friend of mine who is running a AE86 with a 1.6L 4age engine who is running 40psi!!!!!!! @#$%%^ what? and i'm only running on 38psi?!?!?!?!? so whats the standars fuel pressure for an rb25det and whats the right pressure for a rb25det thats not running standard boost??? i'm running 0.7bar when standard is actually 0.4 bar. i hope some one seriously knows... Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted May 9, 2006 Share Posted May 9, 2006 43 psi is stock base fuel pressure, with line off. I do not know for sure about the DE motor though. I got this information from a very reliable source who knew what it was from working on a few RBs. Evan Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted May 9, 2006 Share Posted May 9, 2006 hmm, good to know. I still think a DE would run a little less FP. I think maybe a Z32 NA would have the same FP. But now im just guessing... Quote Link to comment Share on other sites More sharing options...
Pyro Posted May 9, 2006 Share Posted May 9, 2006 You really need a fuel pressure gage in your car to see what is going on. I have an electronic fuel pressure gage mounted on the A-pillar which really helps me tune my car since I adjust fuel deliverly on boost with a FMU. I use two efi pumps in parallel with one pump connected to a pressure switch which turns it on at 6 psi of boost. Really helps out with the pumping capacity during high pressure/high volume runs. Quote Link to comment Share on other sites More sharing options...
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