Tuning a GMPP 383

[eagle mark]

Well, I don't remember where I read the 90lbs but I think it was on thirdgen.

If I go with 80 lbs and the excel injector sizing spread sheet then 13 psi isn't enough pressure as it says it will only support upto 320 hp.

Is the BSFC rate on these TBIs .45 or .50? I just read where this is based off of engine and heads? I'm guessing my GMPP vortec 383 is a .45 motor.

Using that spread sheet, BSFC .45 - 80lb inj - 15 psi will support 348hp with a recommended BPW or 107. (wish I would have found this spread sheet sooner)

I did some logging last night with no more then 50% TPS. The log is very bright green in a bunch of cells over 60 kpa. Some of the BLMs are in the 150 range.

I ordered a Jet adjustable regulator so I'll get that installed and set the pressure to 15 psi and go from there.

I have always liked using 15PSI on built motors with proper injector, dave said the same thing ealier.

BSFC: Brake Specific Fuel Consumed should be .45 to .50 for naturally aspirated engines, .55 TO .60 for supercharged engines, and .60 to .65 for turbocharged engines.

Usually when BPW is close to being correct the data log will show some cells lean and some cell rich. Ideally it is best to begin tuning with steady smooth driving, with a slow rate of accelerate and slow rate of decelerate.

I usually do city driving logs first, then highway, then WOT last.

The adjustable FPR will help find the best setting for BPW vs Fuel Pressure. Ideally the VE Table will have number ranging between 45 - 95. If need be, it's better to keep the low VE numers above 40 with the high VE numbers no higher than 98.

dave w

That is still a general rule and I agree, but at higher pressures (15PSI) I have gotten away with half of the 40VE for idle no issues, not sure it would work at 13, never tried.

Now if you go by industry standards injector duty cycle is 80%.
Most injectors will max out at 80% duty cycle and this is the accepted industry standard.

But even in a stock GM 1227747 ECM BCC ASDU if you add upper and lower VE tables together at 3200 RPM and others, you get 101.56

So I have proven you can go below 40 VE and GM has proven you can go above 95 VE ?

Lot's of varibles so 40 to 90 are guidlines, not set in stone failure points.

 

[cuervo]

I got the new pressure regulator install and set to a perfect 15 PSI. I didn't know you could not adjust them while installed so I had to pull the pod cover off 3 times to get it just right.

Burned a new 108 BPW chip and will install that in the tomorrow morning and get back to logging. I'll be doing the less then 70% stuff first. I'm kind of excited to see how this next round goes.

 

[eagle mark]

TIP: For getting pressure set is hook up the pod to fuel lines off throttle body, turn key on, only get 2 seconds, set pressure or jump wire on fuel pump relay, set pressure. When correct remove fuel lines and install pod on throttle body...

 

[cuervo]

Well, I'm making adjustments in the VE table now. Am I trying to keep the average BLM in the cell as close to 128 but between 125 and 131 is what I read. Is this correct?

 

[dave w]

Well, I'm making adjustments in the VE table now. Am I trying to keep the average BLM in the cell as close to 128 but between 125 and 131 is what I read. Is this correct?

I try, but it's not always possible to get the BLM's between 126 ~ 130. If needed BLM averages between 124 ~ 132 are acceptable.

dave w

 

[cuervo]

Well guys, I'm still plugging away on this.

Something new has started. Once the engine gets to temperature I start to get a backfire through the exhaust and some loss of power.

Thoughts? Is there a coolant timing table?

 

[dave w]

Well guys, I'm still plugging away on this.

Something new has started. Once the engine gets to temperature I start to get a backfire through the exhaust and some loss of power.

Thoughts? Is there a coolant timing table?

I'd try adding 10% to all the AE Table values. Sounds like maybe a lean mixture. The AE table is like a carburetor pump shot. The AE table adds extra fuel for the map sensor time lag. The map sensor needs a few 100 milli seconds to stablize during acceleration.

dave w

 

[cuervo]

I'd try adding 10% to all the AE Table values. Sounds like maybe a lean mixture. The AE table is like a carburetor pump shot. The AE table adds extra fuel for the map sensor time lag. The map sensor needs a few 100 milli seconds to stablize during acceleration.

dave w

Hey Dave,

Thanks for the feedback.

As far as tables go, I don't seem to have an AE table, but I do have a "pump shot Vs differential TPS" and a "pump shot Vs differential MAP".

The only other thing I see regarding pump shot is a scalar "accel 'pump shot' for IAC at idle.



One last question, in general how long should I leave the battery disconnected or the ECM unplugged when changing out the MEMCAL?

 

[eagle mark]

Well guys, I'm still plugging away on this.

Something new has started. Once the engine gets to temperature I start to get a backfire through the exhaust and some loss of power.

Thoughts? Is there a coolant timing table?

$85 is a rare animal! Those terms are closer to carb talk than EFI.

I don't think its the pump shot at idle, I don't even know why you would have a pump shot at idle? Maybe it's the first squirt off idle? Unless you've messed with timing beyond reasonable I don't think the backfire is timing.

Follow along with Dave, the backfire through exhaust with loss of power is probably a lean condition during acceleration, may be able to see it on a wideband if you turrned the sample times down to try and catch cylinders.

AE is pump shot so "pump shot Vs differential TPS" and a "pump shot Vs differential MAP".Add some to one table, test, if stll there add to next table, if gone remove from first table, rinse repeat!

You have always been rich right? Lean causes way hot, exhaust valves never get cooled by cool incoming air and fuel, they just get heated by outgoing exhaust.... when one starts to leak you get a backfire in exhaust...

 

[cuervo]

$85 is a rare animal! Those terms are closer to carb talk than EFI.

I don't think its the pump shot at idle, I don't even know why you would have a pump shot at idle? Maybe it's the first squirt off idle? Unless you've messed with timing beyond reasonable I don't think the backfire is timing.

Follow along with Dave, the backfire through exhaust with loss of power is probably a lean condition during acceleration, may be able to see it on a wideband if you turrned the sample times down to try and catch cylinders.

AE is pump shot so "pump shot Vs differential TPS" and a "pump shot Vs differential MAP".Add some to one table, test, if stll there add to next table, if gone remove from first table, rinse repeat!

You have always been rich right? Lean causes way hot, exhaust valves never get cooled by cool incoming air and fuel, they just get heated by outgoing exhaust.... when one starts to leak you get a backfire in exhaust...

That would suck if I burned a valve after coming this far and never running it very lean for for very long.

I raised the BPW up to 107 from 106 and added 10% to the pump shot differential to TPS.

 

[cuervo]

Adding 10% to either of the differential values didn't change anything.

Guess I run a compression check. It's gonna suck if it is a burned valve. The motor wasn't ran in a very lean condition for more then 10 minutes.

 

[eagle mark]

From your logs I would guess no! So don't sweat it yet. Unless you did a WOT run for miles at a time?

Is it a big bang backfire? Or popping when accelerated?

If the exhaust valve has any leakage, it will push out air, fuel, ignitied AF into exhaust system, can ignite what's in there... backfire...

Other causes could be a very rich mixture being ignited in exhaust. At this point I am realtively sure there are no spark plug wires crossed. But that gives you something else to look at. Spark plug wire cross fire? Distributor cap car cross fire, even a loose spark plug wire can cause spark to go elsewhere...

Can you remember when this started? What did you do just before that? Bunch of work under hood? Where? Look there...

 

[cuervo]

No WOT for longer then 8 or 10 seconds and non after I lowered the fuel pressure.

The part that has me puzzled is it doesn't happen until closed loop and warmed up engine. If it were plugs or wires or even a burned valve it seems it would happen all the time.

 

[eagle mark]

Not necceseraly.

Closed loop usually means a leaner harder to burn mixture, warmer engine can mean many things change, like less blow by and increased combustion chamber pressures because the rings seal better. Look at compression tests! Supposed to be done on warm engine... pressures raise between cold and warm...

Hope I'm wrong... may be a good time to pull all plugs and see if any are differant, could point to one cylinder...

 

[cuervo]

It has to be something in the tune!

I put my old "Extremely rich" Harris Chip in and the back fire is gone.

Since I know the timing in the Harris chips is not stock I'm wondering if by trying to lean out the tune the timing is just to advanced for that??

 

[eagle mark]

Sometimes you just have to go back to a known good tune and start again... could be you changed something using the $85 MASK that is not right? All that the MASK does is change hex...

Have you ever compared the harris chip to a stock chip to see how much of what is changed?

Glad it's not a valve issue...

 

[cuervo]

That was one of the first things I did was compare the two chips. There's a tone of changes.

If I recall correctly it always seem to happen on the second or third round of VE changes. I'll pay more attention this time around.

 

[dave w]

That was one of the first things I did was compare the two chips. There's a tone of changes.

If I recall correctly it always seem to happen on the second or third round of VE changes. I'll pay more attention this time around.

I think I would try correcting the rich mixture of the Harris Chip. First I'd start with BPW then VE changes. I try to make as few changes as possible on each chip, to better understand the effect the changes have. I usually start with low RPM VE cells then the mid RPM cells and finally the high RPM cells.

dave w

 

[cuervo]

I think I would try correcting the rich mixture of the Harris Chip. First I'd start with BPW then VE changes. I try to make as few changes as possible on each chip, to better understand the effect the changes have. I usually start with low RPM VE cells then the mid RPM cells and finally the high RPM cells.

dave w

I always started with the Harris chip, it's what I pulled down to get started.

I was doing what you guys were suggesting, but I was changing all the VE cells with each log.

I'll start over with Harris chip since I had changed the fuel pressure along the way and only work on a small range of cells with each log.

 

[cuervo]

It's getting crazy over here now.

It seem to run fine with the Harris chip in so I downloaded the bin from that chip and changed BPW to 112 to start. As soon as it went closed loop the loss of power and surging and jerking were back. I pulled over and put the Harris chip back in and now even the Harris chip is doing it.

grrrrr