When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am having an issue that I cannot sort out and would really appreciate some advise from the good folks here. My buddy and I dropped an LS1 in a 240sx and I have set this up for road course and street use. It's been running great for a few years now with plenty of driving around town and on about a dozen track days. I am facing an issue currently that I have not been able to figure out. When I am wide open throttle my RPMs won't go past 6000. The tuner has set the redline to be 6700. When the pedal is all the way down the low end is great and then it just hangs at 6000 and wont progress any further.
I have changed plugs/wires and fuel filter/regulator this weekend, issue still present.
I used a heat gun to test the headers at idle and they all seem to be around the same temperature when idling. I also verified all of the plugs and they seem fine (not burnt and not oily).
The engine is all new internals as of a few years ago and all of the sensors and accessories are new as well. The coils are original and I thought these could be the culprit but I am not sure how to properly test these as I am getting a spark to each cylinder. The idle is fine. The low end power is fine. Perhaps it's breaking up under the high RPM range?
Appreciate any ideas or any insight if anyone here as experienced something similar and found any resolution.
Thank you!
Sounds like it's electronically governed at 6000 instead of 6700.....
It has been working fine for the last 2-3 years. This issue just started recently. The tune is set to 6700 as the redline and it's been fine hitting that and even pinging off that on occasion (all internals are built). Not sure why it is no longer allowing anything past 6000 RPM. I was hoping it was something simple like a fouled plug or damaged wire but I changed all of that and it's still happening.
When I am WOT it will rise to 6000 RPM but then just stay there. It doesn't go higher or lower, just stays right at 6000 RPM.
Appreciate the read and the advise.
It has been working fine for the last 2-3 years. This issue just started recently. The tune is set to 6700 as the redline and it's been fine hitting that and even pinging off that on occasion (all internals are built). Not sure why it is no longer allowing anything past 6000 RPM. I was hoping it was something simple like a fouled plug or damaged wire but I changed all of that and it's still happening.
When I am WOT it will rise to 6000 RPM but then just stay there. It doesn't go higher or lower, just stays right at 6000 RPM.
Appreciate the read and the advise.
What does it do when it hits 6k RPM? does it misfire or just lay over and lose power? Will it rev past 6k in neutral?
Are you looking at a tachometer or have you verified RPM against a data channel from the ECU?
I would think that when engine speed consistently stops on a fine line then it is likely due to some kind of sophisticated controls like a rev limiter. If engine just wasn't running right then you would get more variability in results.
Previously it would run strong all of the way up to redline (6700) and act like a normal rev limiter as it is suppose to. Currently it will run strong in the lower RPMs but just kind of give up the ghost right around 6000 RPM. It's not hitting a rev limiter but rather just kind of stopping the charge forward and becoming flat.
I have a quick video of this happening in both 2nd gear & 3rd gear. It shows the tach climbing properly under WOT and then just stops around 6000 RPM and won't go any further with my foot on the floor. It is really odd behavior and not something I have dealt with in this build yet.
No misfires during this entire process (low, medium, high RPM). I presume the plugs, coils, are all firing as designed as that is the first area I have checked and tried a different, brand new, set of wires and that didn't help.
If I am just revving the motor and not moving I can rev past 6000RPM and hit the limiter without issue, the problem only occurs when I am moving, under load. It still revs strong and fast as it always has since we rebuilt this motor.
I don't have a way to verify ECU data as I only have a cheap ODB2 reader for pulling codes. There are no codes being thrown.
I don't think it's always happening precisely at 6000 RPM, it could be slightly above or below that, so it doesn't seem to be something wrong with the mapping or ECU settings. Also, not sure how the mapping could have changed.
I keep trying to consider other sensors that may failed (even though they are all new as of a couple years ago when we rebuilt the engine). Perhaps a temp sensor or MAP sensor that is giving a false reading that tells the ECU that it should limit fuel? Not sure, just trying to think of anything here.
Without knowing anything else about this, I would guess there's a glitch telling the ECM to cut power under load when approaching 6K.
I know zip about ECM's, just taking a common-sense approach to this.
Without knowing anything else about this, I would guess there's a glitch telling the ECM to cut power under load when approaching 6K.
I know zip about ECM's, just taking a common-sense approach to this.
I don't know anything about ECM's either but that sounds like a smart step to take to ensure the ECM is programmed correctly. I'll call the tuner tomorrow and see if he can hook it up and verify.
Have you checked fuel pressure under load? Dirty fuel filter? I've heard of Vette regulators causing some odd driveability when they start to fail.
I have not checked the fuel pressure under load. I read about this and thought it may be the issue so I changed out the fuel filter/regulator with a new one two days ago and the issue is still present. I am using the Corvette LS1 fuel filter/regulator. I could try running a gauge and tapping it to the windshield somewhere so I can see it while driving under load.
Having a few years as you do on a built road race engine skews me toward thinking valve float could be your issue. However, this is not much more than a shot in the dark guess at this point, and there are a lot of easier things to rule out first.
If there is no check engine light then that suggests it is something that the engine ECM cannot recognize as a problem. That narrows the field a lot.
Ignition related problems probably would be detected by misfire diagnostics and such. But the ECM could be blind to mechanical issues that restrict airflow.
do you have a copy of the tune file by chance? there are several rev limiters - rev limiters for cold engine, rev limiter with failed VSS, ETC rev limit, fuel cutoff. Would want to make sure the tuner changed them all.
although, i kind of agree with gametech on this one, if it's a load issue vs static it could definitely be mechanical rather than tune - maybe your intake tube is collapsing under suction and choking the engine? those rubber elbows, especially the cheap ones, are known to do that. you might be able to "guess" that that is the problem, by looking at the MAF readings as it approaches 6k.
Having a few years as you do on a built road race engine skews me toward thinking valve float could be your issue. However, this is not much more than a shot in the dark guess at this point, and there are a lot of easier things to rule out first.
I'll definitely keep this in the list of things to test out, thank you!
If there is no check engine light then that suggests it is something that the engine ECM cannot recognize as a problem. That narrows the field a lot.
Ignition related problems probably would be detected by misfire diagnostics and such. But the ECM could be blind to mechanical issues that restrict airflow.
This is great and yes, I do think this narrows the field considerably. If it was knock sensors, O2 sensors, coils, etc I would get a code thrown. I will look more at the hoses this weekend and ensure they are all opened properly with no tight bends.
I made my own PCV system, following the stock routing, just made with my own hoses and connectors. I may need to take that off and ensure those lines are clear. I did ensure that my catch can is empty and shut properly. I will double-check this again this weekend.
do you have a copy of the tune file by chance? there are several rev limiters - rev limiters for cold engine, rev limiter with failed VSS, ETC rev limit, fuel cutoff. Would want to make sure the tuner changed them all.
although, i kind of agree with gametech on this one, if it's a load issue vs static it could definitely be mechanical rather than tune - maybe your intake tube is collapsing under suction and choking the engine? those rubber elbows, especially the cheap ones, are known to do that. you might be able to "guess" that that is the problem, by looking at the MAF readings as it approaches 6k.
No, I don't have a copy of the tune. It's a stock ECM that has been tuned by a highly reputable local tuner that specializes on GM, LS, motors. I will message him and ask about the different rev limiters you mentioned. This has all been running fine for a couple of years. Is there any way for the tune to change without someone connecting to it and manually changing it?
The 90 degree intake is a cheap one and that may have become softened with the heat over the years. That would surely explain a lack of power if it cannot bring in the air needed. I'll look to get a replacement elbow for that and clean the intake filter properly. That's an easy and cheap step to take for sure.
Really appreciate all of the great advise and brainstorming together on this all. This is such a great community and forum here. Thank you all so much. I look into these things and be sure to post here what the resolution is so that anyone reading this later on can have an easier time with their issue.
No, I don't have a copy of the tune. It's a stock ECM that has been tuned by a highly reputable local tuner that specializes on GM, LS, motors. I will message him and ask about the different rev limiters you mentioned. This has all been running fine for a couple of years. Is there any way for the tune to change without someone connecting to it and manually changing it?
The 90 degree intake is a cheap one and that may have become softened with the heat over the years. That would surely explain a lack of power if it cannot bring in the air needed. I'll look to get a replacement elbow for that and clean the intake filter properly. That's an easy and cheap step to take for sure.
this would also explain why the engine appears to be running correctly - ie not misfiring or fouling plugs. the MAF is measuring the air, and its measuring correctly, so the engine is running at the proper a/f ratio and timing.
11-06-2023, 09:50 AM
Nissan with LS1 - won't go past 6000 RPM 
