Boost Problem
11-11-2017, 05:35 PM
#1
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Thread Starter
Join Date: Jun 2016
Location: Huntsville Alabama
Posts: 15
Total Cats: 6
Boost Problem
Hi Folks,
I've finally gotten my car back together and I am having a problem with boost management. The car is a 2004 MazdaSpeed Miata with a full Begi intake setup, a flat top manifold, and Megasquirt DIDYPNP Pro. It has the stock turbo. I have an EBC plumbed in and wired up but its not activated in the ECU. I've done some checking to make sure its not coming on and doing anything.
The symptom is as follows. If I mat the gas at about 3500 rpm in second gear, boost builds from 2 PSI to about 9 PSI at about 4000 RPM. At that point suddenly jumps to about 18 PSI at which the fuel cut happens. All these numbers come from the data log so the boost numbers are what the MAP sensor is seeing inside the intake manifold. Based on my wastegate setup, 7 PSI or so should be the max. Since the boost jump happens so quickly in second gear, I don't think this is a boost creep situation.
I checked the wastegate with a pressure pump and it seems to work right. I have a spare turbo and checked that wastegate too and they both start opening at about 10 PSI pump pressure and are fully open at about 12 PSI or so. This seems to be normal. I used the hand pump to check the MAP sensor and it checks out OK too.
I hooked a boost gauge up between the EBC and the wastegate and went for a drive. The boost gauge indicated the boost would hit about 10 PSI and then drop to 7 PSI which is what I expected with my setup. So when the fuel cut happens, the boost gauge is seeing 7PSI and the MAP sensor is seeing 18PSI. I hooked the boost gauge up between the manifold and the ECU MAP sensor and went for a drive. I saw the same scenario on the boost gauge as I saw in the data log from earlier.
I have moved the MAP sensor line around to different ports on the manifold and the results are the same.
The plumbing is as follows
Wastegate is connected to the throttle body intake elbow
MAP connected after throttle body
Bypass valve connected after the throttle body
Any ideas?
I've finally gotten my car back together and I am having a problem with boost management. The car is a 2004 MazdaSpeed Miata with a full Begi intake setup, a flat top manifold, and Megasquirt DIDYPNP Pro. It has the stock turbo. I have an EBC plumbed in and wired up but its not activated in the ECU. I've done some checking to make sure its not coming on and doing anything.
The symptom is as follows. If I mat the gas at about 3500 rpm in second gear, boost builds from 2 PSI to about 9 PSI at about 4000 RPM. At that point suddenly jumps to about 18 PSI at which the fuel cut happens. All these numbers come from the data log so the boost numbers are what the MAP sensor is seeing inside the intake manifold. Based on my wastegate setup, 7 PSI or so should be the max. Since the boost jump happens so quickly in second gear, I don't think this is a boost creep situation.
I checked the wastegate with a pressure pump and it seems to work right. I have a spare turbo and checked that wastegate too and they both start opening at about 10 PSI pump pressure and are fully open at about 12 PSI or so. This seems to be normal. I used the hand pump to check the MAP sensor and it checks out OK too.
I hooked a boost gauge up between the EBC and the wastegate and went for a drive. The boost gauge indicated the boost would hit about 10 PSI and then drop to 7 PSI which is what I expected with my setup. So when the fuel cut happens, the boost gauge is seeing 7PSI and the MAP sensor is seeing 18PSI. I hooked the boost gauge up between the manifold and the ECU MAP sensor and went for a drive. I saw the same scenario on the boost gauge as I saw in the data log from earlier.
I have moved the MAP sensor line around to different ports on the manifold and the results are the same.
The plumbing is as follows
Wastegate is connected to the throttle body intake elbow
MAP connected after throttle body
Bypass valve connected after the throttle body
Any ideas?
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11-12-2017, 12:05 AM
#2
I would start by verifying the map sensor is giving you an accurate reading and then i would verify that the boost gauge is giving the proper reading. Its been a while since ive looked at it but there are some settings in megasquirt that will give you the wrong readings if it doesnt match the sensor output. If you post your tune i might be able to help more.
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11-12-2017, 01:54 PM
#3
Newb
Thread Starter
Join Date: Jun 2016
Location: Huntsville Alabama
Posts: 15
Total Cats: 6
I figured it out.
The EBC WAS doing something. It was being operated by the Megasquirt as if it were the stock Mazdaspeed valve. So at 4000 RPM the EBC was energized thereby closing the wastegate and creating the boost spike. I unplugged the wires to the valve and the problem is gone.
I checked the tune and thought boost control was off. I'll look again.
The EBC WAS doing something. It was being operated by the Megasquirt as if it were the stock Mazdaspeed valve. So at 4000 RPM the EBC was energized thereby closing the wastegate and creating the boost spike. I unplugged the wires to the valve and the problem is gone.
I checked the tune and thought boost control was off. I'll look again.
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