Overboost protection using Boost VE table

[ACCLR8N]

Someone once suggested increasing the Boost VE table (A0001) above expected MAP values as an overboost protection in the event of a wastegate failure. After some searching I haven't found any other suggestions of this. If my maximum ever recorded MAP value is 152 kPa, what is the danger of a steep increase in the 155 kPa cells?

Dropping the cells would create a devastating lean condition as the ECM interpolated from 145 to 155, but adding a bunch of fuel should induce a bog along with extra cooling. My injectors are operating below 60% duty so I have the fuel to support this.

2005 GTO Turbo LS2 6spd E40 with COS.

[johnv]

yes, and also use the boost timing tables to pull a heep of timing over 155 KPa.

[ACCLR8N]

Thanks for your input. E40 I don't get a MAP referenced timing table.

[ScarabEpic22]

I dont have an E40 COS file handy right now, but Id suggest going rich above 155kPa (or wherever above max boost). Like 10-20% rich, prevent damage by dumping fuel. I know Mercury Marine did that with their outboards, the rev limiter was literally a 100% IDC to flood the engine and keep it from revving higher. I wouldnt go crazy with it, but 10-20% higher than what the previous cell is would make sense and add a little security.

[ACCLR8N]

Eric, were you the one that originally suggested this to me? I added 20% to all the cells 165 kPa and up. As I understand this will start ramping in the extra fuel above 155 kPa. Anything below 155 will be unaffected. My expectation is I will feel the car fall on its face and instinctively let off the pedal. My boost gauge will indicate the error and I limp home with my stock block intact.

[ScarabEpic22]

Eric, were you the one that originally suggested this to me? I added 20% to all the cells 165 kPa and up. As I understand this will start ramping in the extra fuel above 155 kPa. Anything below 155 will be unaffected. My expectation is I will feel the car fall on its face and instinctively let off the pedal. My boost gauge will indicate the error and I limp home with my stock block intact.

I dont know/cant remember, I know a few people do it this way though. As long as you dont touch the 155kPa cell, all fueling up to that point (in SD) will stay the same. Above 155kPa, the ECM will interpolate the 155kPa to 165kPa cells so it will progressively get richer.

It should be noticeable, if not then add a little more fuel. Dont want to have it go super rich, but 20% should serve this purpose well.

[ACCLR8N]

Didn't work. I really don't understand how this ECM calculates air per cylinder. It must be using the MAF as well even though it is limited to 3600 RPM. I did a test limited to 145 kPa and the car drove right through it. All it did was set a pending P0121 & P1101.

[ScarabEpic22]

Interesting, try disabling the the MAF and see if that does it. The E40 can be weird at times.

What are your MAF enable/disable tables set to? Factory form GM uses VE to 3600-4000 then goes MAF only above that. If these are the same or close to stock, it's still MAF only at that point. Try making the MAF curve richer and see what happens.

I wonder if the ECM is doing a rationality test between VE and MAF values.

[joecar]

Disable the MAF (make sure a MAF DTC triggers).

[ACCLR8N]

Interesting, try disabling the the MAF and see if that does it. The E40 can be weird at times.

What are your MAF enable/disable tables set to? Factory form GM uses VE to 3600-4000 then goes MAF only above that. If these are the same or close to stock, it's still MAF only at that point. Try making the MAF curve richer and see what happens.

I wonder if the ECM is doing a rationality test between VE and MAF values.

The only tables I am aware of are B2001 and B2002. The description states that it stops dynamic air calcs above this RPM. Mine is at the factory value of 3600. Does that mean MAF only above 3600?

If I disable the MAF, then this won't work for me anyway. Unfortunately, I am right at the limit for my MAF and do not have room in the chart to increase it above expected levels.

I am certain it is doing a rationality test as part of the electronic throttle safety. I have spent the last few weeks experimenting with those settings to optimize them for my boosted set-up. I did not want to just delete the safety checks.

[ScarabEpic22]

The only tables I am aware of are B2001 and B2002. The description states that it stops dynamic air calcs above this RPM. Mine is at the factory value of 3600. Does that mean MAF only above 3600?

If I disable the MAF, then this won't work for me anyway. Unfortunately, I am right at the limit for my MAF and do not have room in the chart to increase it above expected levels.

I am certain it is doing a rationality test as part of the electronic throttle safety. I have spent the last few weeks experimenting with those settings to optimize them for my boosted set-up. I did not want to just delete the safety checks.

Yes, that's exactly what it means. Above the value in the high/max table, the ECM will only use the MAF for fueling. Below that, it is a mix of MAF and VE depending on transient conditions.