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Discussion Starter #1
I have a 2001 S/C Frontier with 65K miles on it and here is my issue.... When the truck is cold, it's a beast, runs awesome, instant acceleration, I can spin the tires, it performs great. When it warms up, it loses power from a stand still in drive, off the line. It's a dog, no power until it gets up to speed. I also have noticed a very mild skip in the engine, at a stop in drive.

Here is what I have done so far (all have been present before the knock sensor relocation, I have no codes at all, no SEL also):

new fuel filter
cleaned the throttle body
new rotor and cap
cleaned the MAFS
new PCV
cleaned the throttle body
pulled a plug, it looks great, plugs are 1 year old 10K miles on them
tried two different fuel injection cleaners, two full tanks of fuel
checked for vacuum leaks, (I sprayed carb cleaner) lines look good cleaned my air filter (K&N)
battery pull
Wires look great

I noticed the following....If I'm driving and the truck is acting like a dog (powerless) from a dead stop and I pull over to the side of the road, shut the truck off, restart it, my first launch from a dead stop after shutting the truck off is where the truck should be, power and performance is there. As soon as I pull up to the next stop sign, come to a complete stop, she's a dog again. I did this 5 times and all five times the truck acted exactly the same: complete stop, shut it off, power, at the next next stop no power.

I've changed the knock sensor. The fuel tank was changed about 3 years ago due to extensive corrosion caused by the Nissan fuel pump recall campaign.

So to recap, truck runs awesome, COLD, as soon as she heats up, no performance launching from a dead stop.
When the truck is warm, and I pull over, shut it off, re-start it and launch, runs great for that first launch, consistently, then back to being a dog. On the highway it performs well, and under aggressive acceleration she doesn't sputter or bog down.
Any more help would be greatly appreciated

What am I missing?:pullout:
 

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I'll be the first to admit that I have very little experience working with engines, but two things came to mind. Based on what you've tried so far, I'm guessing you know more about powertrains than I do, but can't hurt to throw out ideas, so here it goes:

First thing that came to mind was wondering if you had done anything with your ECU? Any re-programing or anything like that? If so, might not hurt to try resetting to stock and see what happens.

Second thing that came to mind was some kind of exhaust issue. ie maybe your cats are bogging down, but that doesn't really fit with strong performance at highway speeds after warming up. But it does work with why the first launch after you shut it off is fine (ie time for the cats to dump their back pressure).
 

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Did you just recently change the KS? It may be bad again if you did not just change it recently. Also, you may want to install a boost gauge. It sounds as if you are not getting boost. This could be a couple of things but the gauge is your first thing you should do. Without it, you won't know for sure if you have boost or not.
 

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Could be a couple of things. Did you properly torque the knock sensor when you installed it, if not replace it again and properly torque it. Also what are your engine temps? Just because the gauge reads good doesn't mean it is there is a slight amount of deviation aloud by the ecu so that the gauge doesn't constantly flutter... you could be at the top end of it's allowance and the ecu pulls ignition timing and creats a loss in power. Also check your base timing with a light and make sure it's dead on. Also check the wastegate actuator and make sure it isn't sticking and that it's vacuume supply is good and therese no kinks.
 

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Sounds like you're experiencing 'boost-drop'. When the ECU detects detonation, it deactivates the boost soleniod to bleed off boost and cuts timing to keep damage from occuring to your engine. The only way to reset it is to shut off the engine and restart. I would check the codes to see if your getting a knock sensor code.

My 03 does the same thing in hot weather. It's like a different truck when it is cool outside. I am going to do the knock sensor relocation to see if it helps with mine.
 

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Discussion Starter #6
Sounds like you're experiencing 'boost-drop'. When the ECU detects detonation, it deactivates the boost soleniod to bleed off boost and cuts timing to keep damage from occuring to your engine. The only way to reset it is to shut off the engine and restart. I would check the codes to see if your getting a knock sensor code.

My 03 does the same thing in hot weather. It's like a different truck when it is cool outside. I am going to do the knock sensor relocation to see if it helps with mine.
I did the knock sensor relocation, I posted a supercharged relocation on this forum, and my truck did have a knock sensor code present when the ECM is read. I have scanned my ECM on three separate occasions, using three separate scanners, and it reads no codes.
I checked all the vacuum lines running to the BVA on the supercharger, all seems good. When at idle, the BVA keeps the bypass valve open, if I hit the throttle, the bypass valve closes, so I don't think it's a BVA issue. I'm stumped, I'm gonna change the wires this weekend. Do you think that the boost senenoid is causing this?
 

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I'd say you've got a leaky BVA. Put a vacuum pump on it and see if it holds vacuum.
I eliminated my BVA and installed a manual cable in it's place. Boost trigger on the shifter. My best mod.
Bump the base timing up a degree or 2.
Get a boost/vacuum guage.
 

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Discussion Starter #8 (Edited)
I'd say you've got a leaky BVA. Put a vacuum pump on it and see if it holds vacuum.
I eliminated my BVA and installed a manual cable in it's place. Boost trigger on the shifter. My best mod.
Bump the base timing up a degree or 2.
Get a boost/vacuum guage.
How did you know your BVA was bad? Was your truck performing similar to mine? Did you have a vacuum issue? The valve is only $46 to replace.

I HAVE FOUND THE PROBELM!!!!!!!!!!!!!!!!!!!!!!
Apparently for some reason, AFTER the knock sensor relocation, and everything I have done to rectify it, with the truck throwing NO CODES, it's running in "fail safe mode"!
Every time the ignition is shut off, the solenoid which controls the S/C BAV, is reset. For this reason, the truck has balls when it's cold, and every time I stopped, shut the truck off, and restarted it. For whatever reason, when the truck warms up, the ECM puts the S/C into bypass mode, controlling the BAV solenoid. If your BAV is located in the 12 O'clock position, the S/C is creating boost and everything is working correctly. When the BAV is in the 9 O'clock position, your S/C is in fail safe mode. To prove this theory, I removed the vacuum line which pulls the BAV to the 9 O/clock position and plugged by inserting a wire nut. With the truck warmed up, and the mode fail safe bypassed, THE TRUCK HAS HUGE BALLZZZZZ, it's like driving a different truck. Now my question is......what is throwing my truck into fail safe mode, bypassing the S/C after all of the following that I've done:

new fuel filter
cleaned throttle body
new rotor and cap
cleaned the MAFS
new PCV
cleaned the throttle body
pulled a plug, it looks great, plugs are 1 year old 10K miles on them
tried two different fuel injection cleaners, two full tanks of fuel
checked for vacuum leaks, none found
cleaned my air filter (K&N)
battery pull
Wires look great

I know I'm not the only one with this problem, and I will be dammed if I'm gonna let someone else go through what I have with this truck!
 

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How did you know your BVA was bad? Was your truck performing similar to mine? Did you have a vacuum issue? The valve is only $46 to replace.

I HAVE FOUND THE PROBELM!!!!!!!!!!!!!!!!!!!!!!
Apparently for some reason, AFTER the knock sensor relocation, and everything I have done to rectify it, with the truck throwing NO CODES, it's running in "fail safe mode"!
Every time the ignition is shut off, the solenoid which controls the S/C BAV, is reset. For this reason, the truck has balls when it's cold, and every time I stopped, shut the truck off, and restarted it. For whatever reason, when the truck warms up, the ECM puts the S/C into bypass mode, controlling the BAV solenoid. If your BAV is located in the 12 O'clock position, the S/C is creating boost and everything is working correctly. When the BAV is in the 9 O'clock position, your S/C is in fail safe mode. To prove this theory, I removed the vacuum line which pulls the BAV to the 9 O/clock position and plugged by inserting a wire nut. With the truck warmed up, and the mode fail safe bypassed, THE TRUCK HAS HUGE BALLZZZZZ, it's like driving a different truck. Now my question is......what is throwing my truck into fail safe mode, bypassing the S/C after all of the following that I've done:

new fuel filter
cleaned throttle body
new rotor and cap
cleaned the MAFS
new PCV
cleaned the throttle body
pulled a plug, it looks great, plugs are 1 year old 10K miles on them
tried two different fuel injection cleaners, two full tanks of fuel
checked for vacuum leaks, none found
cleaned my air filter (K&N)
battery pull
Wires look great

I know I'm not the only one with this problem, and I will be dammed if I'm gonna let someone else go through what I have with this truck!
I had the same symptoms. Boost when cold, nothing when it warmed up. When I lost my boost I noticed a small loss of vacuum. I could see this on my boost/vacuum guage.
When I pulled my blower to get at the gooseneck (long story, do a search of my posts) I stuck a vacuum pump on the BAV. Found that it wouldn't hold pressure. $10 manual cable took the BAV and the computer out of the loop.
I'm still setting 0328 (some years now) and one day I'll get around to checking advance curve. But for now I'm keeping up w/traffic and pulling strong in 3rd and 4th, so I'm not too worried about it. Worst it could do is keep my timing back, so I'm sure not going to have spark knock, but as long as it runs good, who cares.
 

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Did you pull the battery or have the codes reset? Cause the override will stay in there till the ECM is cleared (I think)
 

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Discussion Starter #13
I don't think that's a true failsafe mode. You're just losing boost after warmup. Pretty sure it's a leaky BAV.
Bill, here is what I'm leaning towards, after several of your posts. It is definitly a boost issue. I checked out the vacuum lines and narrowed it down to two things I could visualize: first the BAV, second the supercharger bypass valve control solenoid valve, this valve is located on the driver's side engine bay, just in front of the ABS solenoid, and is the bottom of the two solenoids mounted there. I can't find a part number or price for the SCBVCSV on the Courtesy Nissan site, they do have a boost sensor (part # 22365 on their site), it looks like a MAP sensor but I'm not sure, but the BVA is $47ish. I'm going to order the BVA and take it from there.
 

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You could just test it with a vacuum pump. If it holds vacuum your good if not then it needs to be replaced. My only thing is why would it be the bav? If it's bad it would be bad all the time since it's a mechanical part... either diaphram inside is bad or it's not. I could see maybe, big maybe, if it was a hot problem but you said you can restart it and it has balls for one pull, the rip in the diaphram (if it were to have one isn't reset) Also the boost solenoid valve that controls it probably isn't bad either. Why would it just stop when it's warm but everytime you restart (while it's warm) it magically works one time. The ecm is taking away boost because it doesn't like the data that it sees for full boost, and then it resets itself everytime you cycle the ignition. It has to be one of the engine sensors that is causing this since that is what is sending the data to the ecm. You need someone with a scanner that can look at live data during the first pull after ignition cycle and see which parameters are being exceded and then start from there, either that or your just going to blow money on parts you might not need. I saw the map sensor was mentioned somewhere in here that could be a problem or your maf or tps sensor or or or..... You really need to get someone with the scanner either nissans (i recommend but is really expensive) or someone with a good snap-on scanner like the modis. Seeing live data is the key b/c then they can compare it to a chart or allowable ranges for each parameter to determine which sensor is sending incorrect data or why that sensor may be sending incorrect data. good luck.
 

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Discussion Starter #15
You could just test it with a vacuum pump. If it holds vacuum your good if not then it needs to be replaced. My only thing is why would it be the bav? If it's bad it would be bad all the time since it's a mechanical part... either diaphram inside is bad or it's not. I could see maybe, big maybe, if it was a hot problem but you said you can restart it and it has balls for one pull, the rip in the diaphram (if it were to have one isn't reset) Also the boost solenoid valve that controls it probably isn't bad either. Why would it just stop when it's warm but everytime you restart (while it's warm) it magically works one time. The ecm is taking away boost because it doesn't like the data that it sees for full boost, and then it resets itself everytime you cycle the ignition. It has to be one of the engine sensors that is causing this since that is what is sending the data to the ecm. You need someone with a scanner that can look at live data during the first pull after ignition cycle and see which parameters are being exceded and then start from there, either that or your just going to blow money on parts you might not need. I saw the map sensor was mentioned somewhere in here that could be a problem or your maf or tps sensor or or or..... You really need to get someone with the scanner either nissans (i recommend but is really expensive) or someone with a good snap-on scanner like the modis. Seeing live data is the key b/c then they can compare it to a chart or allowable ranges for each parameter to determine which sensor is sending incorrect data or why that sensor may be sending incorrect data. good luck.
Agreed! The ECM is cutting the power to the S/C for some reason, this is the reason I need to find. The only thing I can think of is that I added Royal Purple, Purple Ice radiator additive to the truck about 3 months ago, which may be telling the ECM that the coolant temp is to low...? I reset the TPS, using the turn ignition on off, pull the wires for no more than 5 sec with the truck running, method. And cleaned the MAF sensor with a special aerosol spray, I even cleaned the throttle body just for GPs. I am truly LOST! BUT I do know one thing for sure, I'm not throwing codes!?!?!?!
 

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bringing a thread back from the dead. My truck was going into fail safe mod all the time until saturday when i replaced my MAF sensor. Seemed to do the trick. Some of you might want to look at getting one from the wreckers.
 
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