For 8746 the table "EGR Injector Constant vs. Vac" is used to set up the BPC when the EGR is active. My question is what is the scaling for "Vac" for this table and what does the 176 limit represent????

I am using a BPC (egr off) of 77. Any advice on how to set this table???

 

I would scale the table by the same amount that you changed the BPC. You'll probably still have to modify it some from there but it shoudl get you in the ball park.

You said you have a BPC of 77? That seems awfull low, do you have some massive injectors in a mild combo? You could be getting your PW too small at idle unless you have it set up for Asynch idle.

 

Bsmonte

I figure the motor is good for 375+hp. The way I calculated I figured 110 lb/hr injectors required. I am running 90 lb/hr injectors at 16psi ( should be about 108 lb/hr) therefore the BPC of 77. I have lowered the async threshold so it only goes into async on decel, not at idle.

Thanks for the reply on the egr table.

 

BMmonteSS,

I just re-read my previous reply, Ah-oh I put your name as Bsmonte, sorry about that, nothing bad intented. Guess I better be more careful with names.

Any takers on the scaling of "vac" values in the egr injector constant vs vac table? I looked at the disassembly and it is not obvious what the math is doing with the map reading prior to seaching the lookup table. Just thought if someone has been here before it could save me some time figuring it out. I am wondering if I may need to offset my scaled values some to compensate for the fact that this engine idles at about 45kpa.

Anyway, I finished with the paint on the car this week and am trying to get at least the low speed stuff in order since I need to get the car through emissions testing next week before I can get it licienced. Kind of a catch22 can't drive it much until licienced and can't licience it without emissions which requires driving to get it tuned.

Any advice on getting this thing through emissions would be helpful. I have heard that maybe an engine with this amount of cam overlap does not need EGR. Any body have any comments on that? Should I just leave the EGR shutoff for the test?

Currently, the VE tables are in order at low speeds and idle. Spark tables have been set up and appear to be good for the limited driving I have done so far (26 degrees at idle, 28 degrees total advance). AE still seems to be a bit of a problem.

Al

 

Probably the best way to change that table would be to observe the BLMs while the egr is active and see how much correction you need as opposed to no egr at all. The exhaust gas displaces air in the intake, so the needed fuel will have to change. The table is bare bones and isnt the best at providing corrections as any exhaust or intake changes will effect the ammount of corrections needed, and the table will have to be altered. As for scaling it, just scale the entire table by the same percentage that the base BPW changed. IOW, if you decrease your BPW by 10%, decrease those by 10% as well.

As for the vacuum, the ECM uses vacuum as its based off of the manifold pressure and the barometric pressure outside, so it provides a pressure differential reference for estimating the EGR flow (some cars even have pressure sensors for the EGR, and other PCMs calculate the actual flow). I wouldnt get too hung up on what the actual code is doing. Basically its just formatting the vacuum to make it more table friendly and to preserve resolution. The "176" upper limit is just the highest vacuum value allowed for the lookup. If no upper limit was present, or set wrong, the ecm would go right off the end of the table and read in values from the adjacent constants/tables when doing a lookup.

 

Thanks for the replies.

As far as initial setup of the table, no problem, done deal.

However, if with monitoring I notice that say only at 50kpa the EGR being on is messing up my BLMs. How would I know which table value to change? This is why I was asking for the vacuum reference scaling associated with the table entries.

Al

 

To find out which row is in use: at key-on, engine-off read the MAP sensor KPa and write it down. This is barometric. Then when the EGR is active and the MAP is at 50 KPa, subtract the 50 KPa from the baro reading. The result is the vacuum.

So if baro is 92 Kpa, MAP is 50 KPa, Vac is: 92 - 50 = 42 KPa.

Don't forget to disable cannister purge (CCP) while tuning.

RBob.

 

Thanks RBob,

I understand your reference to how to determine "vacuum". So, if I got this correct the upper limit of 176 for this table represent a vacuum of 75kpa. and the 12 entries of the table are the BPC with egr active at vacuum reading of 20-75kpa in increments of 5kpa.

You also mentioned "Don't forget to disable cannister purge (CCP) while tuning." I had not heard of this before. Is this only for setting the egr table or for all BLM tuning? Is it sufficient to simply remove the connector from the top of the cannister?

 

My take on the table:

{edit: after double checking the code and verifying it on the test bench, I can say that these scale values are correct.}

WOT typically being 0 KPa vacuum. It may not be due to induction system restrictions prior to the manifold.

RBob.

 

RBob,

I think I see where you are coming from. I guess I assumed that since the vacuum value at L002E which is used for the table lookup appears to be in terms of s/d that the conversion to kpa would be the same as for s/d map.

KPa = (SdMap * 0.3125) + 20

So therefore I added the 20 offset and had the table range from 20-75 instead of 0-55.

Thanks
Al

 

RBob, Its been awhile, but I seem to remember the baro adjusted kPa values used for the lookups being scaled in a similar fashion as the scaled RPMs. Could be wrong. I have a hard time remembering my own name sometimes.

 

That jogged some gray matter, and I had to look. There is a routine that is called to scale the BArO and do table lookups.

With that I looked at the EGR vs VAC code a little better. Sure enough, there is some funny scaling going on. I ran some sweeps on the bench and saved the data. I'll crunch it today and update the VAC values for the EGR on BPC table lookups.

RBob.

 

Please note that I updated the EGR vs. VAC for BPC table. It is in a previous post up a couple.

RBob.

 

Thanks RBob for all your effort. This should help a lot.