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Thanks for all the ideas and help. My problem was solved by takng the RPM signal for the MSS from ECU Pin #2. It's a blue wire with a black stripe and is the wire that feeds signal to the tachometer.
See my post at the end of this thread (Post #26) for details.
New VE install with DE MAF, VE injectors and JWT ECU. HS CAI, Fuji header, Greddy MSS, 2,5" VRS/Magnaflow exhaust.
Took her to the dyno and found that she is losing power above 6500 RPM. It's not real consistent -- sometimes it happens, sometime it doesn't. FWIW, I also have some minor idle issues -- hunting idle when not fully warmed up and too much idle increase associated with power steering inputs at rest. No biggie.
The first dyno session also showed dropping fuel pressure at high RPM. I replaced the fuel pump with a Walbro. Now the fuel pressure is rock steady throughout the RPM range, but the power loss persists. Here is a sample of some of my dyno runs where the power fell off:
After these runs, I added 3 psi fuel pressure and brought the A/F ration down to the low 13s -- but it did not help the pwoer loss issue. Since that time, I have tried 2 other DE MAFs, changed plugs, and removed and replaced the ECU to make sure it was properly plugged in. I'm running out of ideas -- would appreciate hearing yours.
One thing I'd like to do is eliminate the ECU as the source of the problem. I've got the OEM VE ECU -- how would the car run with this ECU and the DE MAF?
Thanks.
Bill
UPDATE March 13:
Here is some new information on what's going on.
1. I monitored the voltage in the solenoid activation circuits while driving on the street. Also, now that I'm sensitized to it, I can feel the loss of power at high RPM when it happens. I found that the voltage falls off when the power loss occurs. So it would go like this: I'm running up the RPMs in 3rd gear and at 6800, I feel the engine go soft and the rate of RPM increase decreases. At the same time, my passenger, watching the voltage in the cam solenoid circuit reports that it falls from 14.4 to 3 then 6, then as the power surges back on, the voltage returns to 14.4. I observed this repeatedly for both cam solenoids. Conclusion: the switching mechanism is intermittently shutting off the ground when the RPMs are in the "cam on" range, and the high cams are turning off. (Interesting side note: the solenoids pull about 1.1 amp -- measured with multimeter, confirming that the MSS should have ample capacity to control these solenoids). If the voltage drop is the cause of the power loss, the solenoids themselves and the JWT ECU are probably working properly. The question is what is causing this aberrant switching behavior?
2. When watching the screen on the Nissan DataScan, I observed a wildly fluctuating tach reading from time to time as I ran up the RPMs -- and this is often associated with the power loss. I'm wondering if the RPM input to the MSS is unreliable and this is causing the strange switching behavior.
I need to do some research on possible causes of the unreliable RPM inputs -- and I will try to log some data also. But it will be a few days before I can do anything as I must go out of town and won't have access to the car. Will report more when I have more information.
It would run like crap with that MAF and the VE ECU. Might as well run DE injectors also and use a DE ECU.
Could it be the knock sensor retarding the timing? What octane are you running? If you have anything loose that vibrates hard, it might sense that and retard the timing.
Could it be the knock sensor retarding the timing? What octane are you running?
I will take a look at the knock sensor tomorrow. Make sure that it's properly torqued and connected, look for loose stuff. I run 93 octane and the base timing is set at 15.
Edit for clarification: If the knock sensor is disconnected the ecu will pull timing accross the board. It will also throw a code, you should be able to see this with your consult software. If you aren't showing any codes, your problem is elsewhere. If your throwing no codes (i.e. fully functional knock sensor), the JWT ecu will not pull timing based on the knock sensor.
The stock ecu only uses the knock ecu at low revs. When it pulls timing due to the knock sensor you it will pull all the way across the rev range, not suddenly on the top end.
Are you datalogging these runs? If so post them up. Does Datascan do datalogging? I've never used it. If it doesn't download the latest version of CalumSult (see contrib ecu forum) and datalog a couple of runs (both windowed and normal, if your having tach problems at high rpm it will screw with the windowed runs).
Are you datalogging these runs? If so post them up. Does Datascan do datalogging? I've never used it. If it doesn't download the latest version of CalumSult (see contrib ecu forum) and datalog a couple of runs (both windowed and normal, if your having tach problems at high rpm it will screw with the windowed runs).
Calum: that's great info.
Bill is running the JWT ECU, IIRC. He hasn't mentioned any codes being pulled ( ie misfire or knock sensor ). The reason I'm interested is my car seem to go a little flat on top end too. Intermittently, no stored codes. Still stock ECU,so different story. Sorry Bill did not mean to hijack.. I will monitor this thread quietly .
Sorry Bill did not mean to hijack.. I will monitor this thread quietly .
Milburn
No worries there, Milburn. Thanks for the clarification on how the ECU uses the knock sensor, Calum. Just to confirm, I'm not pulling any codes, she's going soft at high RPM.
I think the new version of Datascan logs data but I've got some learning to do before I can make it do that.
If it doesn't download the latest version of CalumSult (see contrib ecu forum) and datalog a couple of runs (both windowed and normal, if your having tach problems at high rpm it will screw with the windowed runs).
Calum -- can you provide a link so that I make sure to get the latest version? Thanks.
Get your dyno complete info. Have it printed with and with out correction factors. Correction factors can really mess with the dyno curve in some situations.
1. I monitored the voltage in the solenoid activation circuits while driving on the street. Also, now that I'm sensitized to it, I can feel the loss of power at high RPM when it happens. I found that the voltage falls off when the power loss occurs. So it would go like this: I'm running up the RPMs in 3rd gear and at 6800, I feel the engine go soft and the rate of RPM increase decreases. At the same time, my passenger, watching the voltage in the cam solenoid circuit reports that it falls from 14.4 to 3 then 6, then as the power surges back on, the voltage returns to 14.4. I observed this repeatedly for both cam solenoids. Conclusion: the switching mechanism is intermittently shutting off the ground when the RPMs are in the "cam on" range, and the high cams are turning off. (Interesting side note: the solenoids pull about 1.1 amp -- measured with multimeter, confirming that the MSS should have ample capacity to control these solenoids). If the voltage drop is the cause of the power loss, the solenoids themselves and the JWT ECU are probably working properly. The question is what is causing this aberrant switching behavior?
2. When watching the screen on the Nissan DataScan, I observed a wildly fluctuating tach reading from time to time as I ran up the RPMs -- and this is often associated with the power loss. I'm wondering if the RPM input to the MSS is unreliable and this is causing the strange switching behavior.
I need to do some research on possible causes of the unreliable RPM inputs -- and I will try to log some data also. But it will be a few days before I can do anything as I must go out of town and won't have access to the car. Will report more when I have more information.
Try this, wire the solenoids with 12v all the time. This will turn the cams on without using the MSS. If the power doesn't drop off, then you found the problem, the MSS.
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Try this, wire the solenoids with 12v all the time. This will turn the cams on without using the MSS. If the power doesn't drop off, then you found the problem, the MSS.
Interesting thought. Wish I had had it! The car will run like crap with the high cams at low RPM, but it's a test worth doing. Maybe I can rig up a mechanical switch or something.
If the power does not drop off, then that would mean either there is a problem with the MSS or a problem with the RPM inputs to the MSS.
Interesting thought. Wish I had had it! The car will run like crap with the high cams at low RPM, but it's a test worth doing. Maybe I can rig up a mechanical switch or something.
If the power does not drop off, then that would mean either there is a problem with the MSS or a problem with the RPM inputs to the MSS.
Can't wait to try it.
Thanks.
Bill
It won't run that bad. Stock cams are a little bigger than S4s, so it will be like a SE with cams. It will idle a little funny though.
Interesting thought. Wish I had had it! The car will run like crap with the high cams at low RPM, but it's a test worth doing. Maybe I can rig up a mechanical switch or something.
If the power does not drop off, then that would mean either there is a problem with the MSS or a problem with the RPM inputs to the MSS.
Can't wait to try it.
Thanks.
Bill
Any switch, works, a lightswitch, toggle switch...whatever. My ecu freaks out and dies if the big cams come on at idle.
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Any switch, works, a lightswitch, toggle switch...whatever. My ecu freaks out and dies if the big cams come on at idle.
I wouldn't add a switch, that just adds to possible power problems. 12v directly on the solenoids at all times cuts out any other possible causes, except the harnesses coming loose.
Please see MSS screen when you have power loss on high rpm. Does it read 0 RPM sometimes, when you are revving up the engine?
My problem with power loss on high RPM with high cams was RPM signal for MSS. Reason was rpm input signal on MSS screen was reading 0 sometimes. I reconected MSS RPM wire to ECU, and now it is ok.
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