After rebuilding the valve train I finally got around to more tuning.

I have a 84 Vette with a 383 and I am running dual 2 inch TBs with 90 lb injectors @ 20 lbs. I calced my BPC vs Vac and it came to 80. So I plugged it in all the cells in the table and lowerd my VE values considerably. When I start the motor it just surges wildly and my wb shows it is bouncing from 10:1 to 25:1. Needless to say I am perplexed. What am I missing.

 

Most likely the engine is leaning out which causes the surging. The BPC of 80 is OK, reducing the VE may or may not be OK. There are a couple of things that can be done to correct the issue.

I would start by getting the engine up to operating temperature. Feather or hold the throttle a little to keep the engine running (no romping on the pedal). Once up to temperature see how it idles. And start data logging.

Can now use the VE Learn function along with looking at the data log. There will most likely be lean areas. If the engine wants to die, or it starts surging again, feather the throttle to keep the engine running and out of surging. Gather some data at these points.

Then make corrections to the VE table. And run the engine along with data log again. If you have an emulator this is the one area where they really shine. You can plug in new VE numbers as the engine is running and get instant results. And, the vehicle is at a stand still, so it is safe.

After a few interations the idle should settle down. Once it does then see how the car drives over a short distance. This can be up & down the driveway, and if that is OK then around the block. Take it easy and data log. From the log do additional VE Learns. It doesn't take long to rough in the VE table.

RBob.

 

ELK: i was idleing synch at 20 lbs about 70% of time. now that i raised FP to 25 to cure a WOT at 13+/1 i see i am cycling synch-asynch-synch and the idle is surging slightly. this is OL. is it possible the fuel is being reduced in asynch and engine stalling and being caught by iac/tf routines? maybe up idle temporarily?

 

Jim,

I would have changed my BPC but leave my VE table alone. Datalog, then make the changes as required. By dropping?? the BPC AND the VE, you may have made everything too lean. The surging could then be invoking the stall saver. Believe me, I went through the idle surge thing for longer than I care to remember. Sometimes, the fan kicking on was enough to start the motor surging. It was that close to the edge. Give serious consideration to using the VAFPR. when you do, you'll kick yourself for not having tried it sooner.

 

you probably know this. idle A/F is OL for me. the idle A/F is a set of tables other than VE 1 or VE low. i am idling at about 13.0/1 OL when it happens to be in synch mode. then all is well with idle. i may fatten those tables up to keep in synch. but one change at a time or i get confused.

 

So do you think that the VAFPR helps with the surging? I have noticed that the higher I go with the FP the more surging becomes an issue. Before at a lower FP the idle was rock solid. And I still need to get the fuel pressure higher.

 

that is the benefit of VAFPR. allows low pressure at low loads to avoid "asynch" default at idle/light cruise. my experience is the transition from synch to asynch the fuel is momentarily cut off or greatly reduced. you can see PW dropping to zero then coming back. this is W/O any IAC as it is zero in count during event. VAFPR will allow you to fuel WOT. allows a fueling limited TBI system to function on a stronger motor. i believe VAFRR is used on TPI to cotrol fuel as well. i will go that route VAFPR only after i experiment a bit more with non VAFPR tune.

edit: my surge is minor. if i had IAC/TF involvement it might be much worse. i do see some additional fuel fed to motor when it recovers at lower rpm.

 

Open loop still uses the VE tables. The major difference between open & closed loop is the commanded AFR. In closed loop it is the stoich value. While in open loop it is the value from the 'Open Loop - AFR vs CTS & VAC' table. Closed loop will then also correct according to the O2 sensor feedback.

Elkabong, please see this thread for more info:

https://www.thirdgen.org/forums/diy-...dle-synch.html

It covers using sync mode only, and better injector bias offset values.

RBob.

 

RBob - I will give it a go. FWIW - I am running a Ostrich with a 8746 so changes are quick.

Dom - I have a Aeromotive FP regulator. I just cant find a good spot to mount the darn thing. I am thinking of removing the air solenoid because I wont need it for a couple of years until my next emissions test. FWIW - When I luckily passed emissions in Sept the air solenoid and egr was there to put on a good show and I passed without them functioning.

 

Jim,

I have my VAFPR on a very short bracket attached to a manifold top plate bolt. Here's a couple of pics.

 

Dominic sorry if I have asked this before but do you have a part number for that FPR?

Thanks.............DM

 

Thanks Dom.... I did not think of mounting mine that way... hmmmm....

DM - Its a Aeromotive #13301.

 

Thanks Jim

 

Aeromotive Universal Bypass Regulators: AEI-13301 - summitracing.com
Sorry for being redundant

 

That item is pretty pricy.....is it worth it to have the regulator out side of the TB? I don't remember how much the GM vacuum referenced unit is exactly but I thought it was about $60-70ish. Or will the GM unit not adjust as high?

Thanks.......DM

 

apples and oranges.

the GM VAFPR is not adjustable to best of my knowledge. it can be made such and i think that info is available here. it comes with one spring that is too strong so plan on using your stock spring or the one on topdownsolutions website which is a notch stronger.

the aeromotive is a high quality unit. machined aluminum. easily adjustable .50 lb increments. serves low pressure TBI as well as 20-60 lbs. has various to mount FPG as well as fuel lines.

 

DM,

I originally tried a less expensive Mallory. I found the Aeromotive to be better since it allowed for use of 2 different rate springs. I think the GM unit is rated for FP in the 40+psi range. I was looking for something that had a range between 10-25psi. So far the 13301 has performed flawlessly for the better part of 5 years. I'm using the 20lb+ spring on it right now, and the Vacuum Port takes FP down to 11.5 at idle.

 

Thanks....that sounds like the one to have then. I had noticed the second spring with the unit that would put the pressure in the sweet spot that several of us are shooting for. What is nice is that you and others are the Ginny pigs with the EBL and a VAFPR.....


Oh by the way........sorry to get this thread so far off subject......

 

Well here is the latest. I have set the BPC to 80 and I am roughing the VE table. The issue is some of the VE cells are at 100 and it is still running lean. What other items should I be looking at?

RBob - It was Ron who was interested in the Synch idle... But it is good info none the less.

 

I would raise the fuel pressure. Bump it to 24 psi and see if that is enough. Can leave the BPC at 80.

RBob.

 

Ok.... I have a GM VPFR that I am thinking of setting up before I replumb using the Aeromotive 1307. I also have the spreadsheet to calc the values for the BPC table. What value do I need to change to accomodate 90# injectors? I see a value of 80.5 is that it?

Thx

 

Jim,

I would agree with RBob on raising the FP. If your motor and mine are comparable at all, I'm using 20psi with 80# for WOT DC% of 75. So I would think you need more fuel than I do. However, the greater the FP, the smaller the PW at idle and decel. RBob may want to chime in, but I wonder if that won't make the surging worse. You have a larger displacement but your TBs are 2" while mine are 2.13s. Is it possible that may also contribute to lean condition at WOT?

 

Jim,

Yes. You'll need to change that to 90. Also the cyl volume since yours is a 383. The number there is for a 350.

 

[QUOTE=elkabong;3106796]Well here is the latest. I have set the BPC to 80 and I am roughing the VE table. The issue is some of the VE cells are at 100 and it is still running lean. What other items should I be looking at?

wow this is exactly what happened to me!

i printed my VE tables from tunercat and then put them into EBL VE1 and VE2. ran car day one and over 100 in WU. that was with 20 lbs FP. ended up increasing BPC 5 ticks at a time. then 10 at a time. started at 83 and ended up 140. that got VE2 at 2500-3000++ 40 map-60 map under 100. fixed WB02 and read WOT at 13.3. upped FP to 25(that dropped WOT to 12.6/1 last week) and started dropping BPC till i saw 90 or so in those cells that were 100+.

does not seem to adversely affect drivability by fudging the BPC. seems choke/AE/PE etc were OK.