Hello all. Having a problem with my gap 4 bar map sensor reading approx 1.4 times higher in boost then my mechanical gauge. At 12ish gauge psi, the sled is showing 17 psi on the hourmeter. I have been talking with gap mfg and they believe the sensor is reading properly. (They have been answering to me today on thr weekend so shout out to them for excellent support assistance)!!.
Thr next step would be to measure the map voltage with voltmeter and with a boost gauge hooked up and compare with sleds gap dashboard reading real-time. I will use a 2nd mechanica boost gauge to eliminate mechanical boost gauge error.
I was just wondering if anyone else has ran into this before or could point me in the right direction to troubleshoot and solve. The screenshots I posted show the boost gauge and sled discrepancies. (I pulled screenshots from a video I took).
(The sled is a TD tuned gap large turbo with stage 6 cams and all supporting mods as per TD). I have also closed the factory internal gate and installed a tial mvs 38 external gate in the header. as I was told min boost was 26 psi with the high flow cams and couldn’t run pump fuel. The gate was installed to lower boost so pump fuel could be run). I have a 11.5 lb spring installed and the sled hits 12ish psi on the mechanical gauge. I can hold this at wOT for 5-10 seconds and boost is ROCKSOLID at 12 psi. Yet my sled gauge is slowing 17psi psi. I’ve already tried 2 4 bar map sensors from TD and it’s the same result.
This is more an issue as boost is increased. The gauge will show 17-20 psi yet the sled is already recording 30-32 psi and boost cut is hitting.
I’ve done a boost leak check and it’s fine. You would think the only way the boost gauge would be reading lower than the front map sensor would be a massive boost leak. However I really feel this sled isn’t as it is spooling up instantly and at Barely a 1/4 throttle the boost hits 30psi. (Indicated ). Also the sled isn’t knocking so if it really was hitting 30 psi the knock would be lighting up like a Xmas tree.
Thoughts ?
Thr next step would be to measure the map voltage with voltmeter and with a boost gauge hooked up and compare with sleds gap dashboard reading real-time. I will use a 2nd mechanica boost gauge to eliminate mechanical boost gauge error.
I was just wondering if anyone else has ran into this before or could point me in the right direction to troubleshoot and solve. The screenshots I posted show the boost gauge and sled discrepancies. (I pulled screenshots from a video I took).
(The sled is a TD tuned gap large turbo with stage 6 cams and all supporting mods as per TD). I have also closed the factory internal gate and installed a tial mvs 38 external gate in the header. as I was told min boost was 26 psi with the high flow cams and couldn’t run pump fuel. The gate was installed to lower boost so pump fuel could be run). I have a 11.5 lb spring installed and the sled hits 12ish psi on the mechanical gauge. I can hold this at wOT for 5-10 seconds and boost is ROCKSOLID at 12 psi. Yet my sled gauge is slowing 17psi psi. I’ve already tried 2 4 bar map sensors from TD and it’s the same result.
This is more an issue as boost is increased. The gauge will show 17-20 psi yet the sled is already recording 30-32 psi and boost cut is hitting.
I’ve done a boost leak check and it’s fine. You would think the only way the boost gauge would be reading lower than the front map sensor would be a massive boost leak. However I really feel this sled isn’t as it is spooling up instantly and at Barely a 1/4 throttle the boost hits 30psi. (Indicated ). Also the sled isn’t knocking so if it really was hitting 30 psi the knock would be lighting up like a Xmas tree.
Thoughts ?
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I will also add that when driving the sled around without any crazy acelleration, the sled boost psi will show 3 psi already yet the mechanica gauge is still showing 0vac.
sledding rocks
Expert
did u confirm with ben the tunes u got are for a 4 bar map ?
Yes. I can see it says 4 bar enabled in the flasher. Also if it were set to read a 2 or 3 bar, amd a 4 bar were installed then the ecu indicated boost would be lower than the gauge, not higher.
Example :
If my tune is set to a 2 bar where 5v is 14 psi then now my 4 bar is installed, then at 14 psi the 4 bar would indicate approx half the voltage, not 1.4 times too much…
Example :
If my tune is set to a 2 bar where 5v is 14 psi then now my 4 bar is installed, then at 14 psi the 4 bar would indicate approx half the voltage, not 1.4 times too much…
NYTurbo
TY 4 Stroke God
Where is your gauge pulling boost from ?
Mechanical gauge is hooked to a vac line behind the tb. Same as the bov and the fuel pressure regulator.
The map sensor is connected to the intake manifold ahead of the TB.
I could move the mechanical gauge directly beside into the manifold but I’m not sure that will show anything. ? I can try this if you’d like ?
The map sensor is connected to the intake manifold ahead of the TB.
I could move the mechanical gauge directly beside into the manifold but I’m not sure that will show anything. ? I can try this if you’d like ?
NYTurbo
TY 4 Stroke God
Comparing apples to apples is always best.
kennyspec
Expert
Why not tee in the stock map sensor, boost gauge and the 4 bar into a length of rubber line. Pressurize it and compare readings. Should have your answer pretty easily.
NYTurbo
TY 4 Stroke God
Careful doing that some times it will set a code that is hard to clear
If the Boost gauge happens to read the same as the TB map sensor, yet the gap map sensor is reading high… then where could the problem lie? What could be then causing it to read wrong ? The two grounds on the engine and chassis are connected.
NYTurbo
TY 4 Stroke God
What is your map sensor reading on the Throttle body side ?
KnappAttack
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One thing I found with liquid filled gauges is they have to have the vent plug removed to read accurately. This includes the liquid filled fuel pressure gauge. I found inaccurate readings on liquid filled gauges no mater where they are used. I actually remove the oil on them and leave the vent open to the atmospheric pressure so they read accurately. If they are not vented, temperature and air pressure swings greatly affect them, one way to find out is put the hairdryer on them to warm them up with a constant pressure on them, you will see the fluctuations when you heat up the gauge housing and when it cools.
I learned this the hard way back when we were turbo charging RX-1's and Apex's on the liquid filled gauges. Gauges work on the pressure differential between the line and the atmosphere, put it in a sealed case and pug the vent like they are and it just can't and will never red accurately. I didn't even know why anyone even makes them liquid filled anymore. They are inaccurate UNLESS you pull the plug on the case and let them breathe to the atmosphere, and at that point might as well pull the oil out because they will leak it out anyway...
I learned this the hard way back when we were turbo charging RX-1's and Apex's on the liquid filled gauges. Gauges work on the pressure differential between the line and the atmosphere, put it in a sealed case and pug the vent like they are and it just can't and will never red accurately. I didn't even know why anyone even makes them liquid filled anymore. They are inaccurate UNLESS you pull the plug on the case and let them breathe to the atmosphere, and at that point might as well pull the oil out because they will leak it out anyway...
While you are Probsbly correct about having the gauge vented and the liquid drained (I will drain and vent it next ) ,
I have a hard time believing that the liquid filled boost gauge is incorrect by a factor of 1.4 when it matches the wastegate spring pressure to within 1 psi and holds it there rock solid. I can clearly hear the external gate starting to open at around 8psi and becomes fully open by 12. I have another autometer 0-20 psi boost gauge (non liquid filled) I can swap and try but I’m going to say it will also match the external wastegate spring pressure at 12 psi.
KnappAttack
24X ISR World Drag Racing Champion
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I see what you are doing now. I don't think however using a Tial wastegate is going to work with the sleds electronic ECU controlled setup as it was designed. The tuner designed it to operate with the controls on their wastegate & their controlled equipment. How is the ECU now supposed to bleed off the Tial wastegate and close it down to control boost?
I think what you have is going to need re-engineering. This 998 is designed to control boost thru the ECU obviously and use the map sensor from GAP to control the boost, you just over rode all that by installing a different wastegate entirely. I don't see this working properly ever myself. Gone are the days of mechanical operations of easy turbo systems with the ECU controlling the boost parameters. You can only cheat it so far and you are now in unknown territory and will need a custom setup to operate and control it. What does TD say about what you have done with the external gate?
I could be wrong but IMO the external gate is not going to operate properly for controlling boost as it certainly wasn't designed for it with the current system. You'll need to go back to the designed system it was designed around or it will never operate properly and control the boost. Electronics have taken over...
I think what you have is going to need re-engineering. This 998 is designed to control boost thru the ECU obviously and use the map sensor from GAP to control the boost, you just over rode all that by installing a different wastegate entirely. I don't see this working properly ever myself. Gone are the days of mechanical operations of easy turbo systems with the ECU controlling the boost parameters. You can only cheat it so far and you are now in unknown territory and will need a custom setup to operate and control it. What does TD say about what you have done with the external gate?
I could be wrong but IMO the external gate is not going to operate properly for controlling boost as it certainly wasn't designed for it with the current system. You'll need to go back to the designed system it was designed around or it will never operate properly and control the boost. Electronics have taken over...
kennyspec
Expert
Internal or external gate shouldn’t make a difference at all. They both have a line to the top and bottom of the gate to control boost. Assuming they have the same crack pressure point it’s going to make no difference.
The external gate was actually much better at controlling boost as TD said the min boost pressure on this kit was 26 psi due to the cams causing a increase of airflow. In reality the limits of the internal gate have been reached and it can’t bleed enough to keep the boost down. Since the external gate was installed this kit can now run at 5psi with a weak spring in the external gate.
Internal gate or external shouldn’t have an effect on the map sensor readings. Put them both in a piece of tubing with a mechanical gauge, pressureize it and with a volt meter see what they read.
No way this sled is making 30 psi at 1/4 throttle.
The external gate was actually much better at controlling boost as TD said the min boost pressure on this kit was 26 psi due to the cams causing a increase of airflow. In reality the limits of the internal gate have been reached and it can’t bleed enough to keep the boost down. Since the external gate was installed this kit can now run at 5psi with a weak spring in the external gate.
Internal gate or external shouldn’t have an effect on the map sensor readings. Put them both in a piece of tubing with a mechanical gauge, pressureize it and with a volt meter see what they read.
No way this sled is making 30 psi at 1/4 throttle.
