I've started tuning my new engine. Its a 11:1 383, Comp Cams 236/242, AFR 195's, Miniram (stock throttle body). I've got the VE tables close, but I have the dreaded tip-in stumble. It doesn't happen at all when in open loop, but when it goes to closed loop, the car will hardly move from a stand still. Once the RPM's finally get around 2000 it takes off. I searched and found a little info on the "pump shot" (acceleration enrichment?). My question is, how much should I change these values? I don't want to make huge changes and mess something up. Do i change the whole table or parts of it? Any chance of me messing something up by changing the table too much? With the stock TB, I had to really crank the screw out when setting the min. air. Could this be opening the TB too far and causing the stumble? When i had the Miniram on a 9.5:1 350 with ported stock heads and TPIS ZZ9-X cam, I never even had to adjust the min. air, it idled fine from the get-go. The acceleration tables are factory AUJP . Any hints in the direction to go are much appreciated. Thanks

 

If it were me and my expanding but what i still consider limited prom burning knowledge, i would head to the AE delta tps multiplier vs delta TPS and work from there...........

Increasing values adds fuel decreasing value subtracts fuel, from what i've seen with my own hotcammed 350 you will almost in all lilelihood have to increase those values.. U might even end up make some very large changes in their due to the increased air volume entering the engine from larger displacement, camshaft, etc.

make a chip with fairly large differences in fuel addition and make one with some somewhat noticeable fuel subtraction and hook up whatever u sue for scanning/datalogging and see what happens as u lay into it............I'll bet more than likely going lean with throttle opening

Let us know how it works out
later
Jeremy
PS see my post about hesitation under load dircetly off the torque converter, dont always overlook the obvious

 

Thanks 3.8 TransAM. I changed the values in the AE delta tps multiplier vs delta TPS table. It didn't seem to help at all. I made small changes, large changes, changes to part of the table, changes to the whole table, nothing helps. I burnt 13 or 14 chips today. I use Datamaster, and when i give it throttle, it goes lean (200-300 milivolts). Even when i maxed the table (the max is 2) i get the same thing. If this table went higher that 2, maybe that would help? When i first run the car and it is in open loop it drives from a dead stop great. As soon as it goes into closed loop i get the stumble so bad it almost kills the car. What parameters does the car use when running in open loop? What does it do for Accel Enrich in open loop? I thought that it ran off of the VE table (BLM locked at 128 by the ECM). When it runs in closed loop, my BLM's at and around idle are 115-120 (slightly rich). Should i max the AE delta tps multiplier vs delta TPS table and start changing some of these other tables to try to get more fuel?

Accel enrich Delta TPS PW factor Vs Async Pulse
Accel enrich Delta TPS PW factor Vs Coolant Temp
Accel enrich Delta MAP PW Mulitplier Vs Delta MAP
Accel enrich Delta MAP PW Mulitplier Vs Coolant Temp
Accel enrich Delta MAP PW Decay Factor Vs Coolant
Accel enrich Delta MAP Factor Mulitplier Vs TPS
Accel enrich Delta MAP Enable Threshold Vs TPS

Any idea what these do? My help file from Tunercat has no calibration help for these items.

I plan to go to a 58mm TB soon. Will this improve this situation, or will i have the same tip in problem?
Hasn't anyone out there run a stock 48mm TB on a Miniram and found a solution to this problem? Should i just buy the 58mm and hope that it helps clear this up? Any help to point me in the right dirrection greatly appreciated.

 

When reguardless of what you do with the fuel nothing changes, work on timing.

You have to have fuel and the timing right.


If your having troubles now, increasing the TB size will only complicate getting things correct.

One change
Rebaseline.

Try and just make one change at a time, and then get back to a known good tune.

 

Grumpy,

Should the max value of 2 in the AE delta tps multiplier vs delta TPS table be enough FUEL to take care of the tip-in, and now i need to go to SPARK to try to get rid of the stumble? Or should i also look at the other listed tables, and modify those values before going to the SPARK tables? Am i correct in that engines tend to need more timing as they start to accelerate? Thanks

 

92 Z,

Ok, I had the same problem with my MRIII on my 383 as well. However, I have MAF and not MAP, so I can only throw some ideas out there for you as I have very little experience with tuning MAP cars. Ok, your cam has a little more duration than mine, mine is 224/236, I am running 24 lb/hr svo injectors. What size are your injectors? Check for vacuum leaks.......check around the intake gasket, I had a leak like this once which caused the tip-in bog. Spray some carb cleaner around the intake runner/gasket/head surface and see what happens. Check your fuel pressure, I have mine set to 40 psi (set with the vacuum line off). I have my timing set to 8 deg BTDC.

As for your stock TB, IMO you should be able to get good driveability out of the car with the 48mm, not necessarily all out performance though. When you think about it, you are letting x amount of air in when the throttle blades open, and the TPS, MAP sensor work to match that volume of air (manifold pressure) with the correct amount of fuel, and of course the O2 sensor comes into play as well. If in fact you are leaning out when you touch the gas in open loop, switching to a 58mm IMO won't rectify your problem it might make it worse.

What is your injector constant set to? As 3.8 TA said, make large additions to fuel. Try setting the injector constant lower to fake out the computer into thinking you have a smaller injector which, in reality will deliver more fuel.

Let us know what happens and good luck, you will figure it out just be persistant.

 

Going by recommendations made by Grumpy, GlennL98 and other experienced folk here, Ive tuned 2 TPI's this way(spark tables at least)..

Start with a stock timing table..........basically drop 3 degrees from the entire table (i do some 3 degree areas some 3 degree areas from datalogging) and then once u find your knock and can start working it out and have aroughed in table. Then u want to ramp the timing down as quickly as possible from low to high load areas without incurring any type of bogging.... do a few searches and find a couple of posted .bins or timing tables from the regulars here and u will see what i am talking about.......

Then from there u can add timing back in usually around peak torque(some like it before/at/after, depends on the car).
And go from there..........there have been a couple decent examples posted of exactly what i am describing, believe it was a "final answer timing" post and another one i forget the name of

Later
Jeremy

 

I'm actually very surprised that you can't get enough AE. I didn't have to raise my values very much in order to get good tip-in response with my MiniRam - maybe 25% - 35% (and this was with a 58mm TB). You have 33 more ci but that should have been easily covered using the HUGE amount of AE TPS you used. Furthermore - I can guarantee you that I am running A LOT more timing than you are in the part throttle where you have normal tip-in problems.

Another idea is to decrease the decay rate for which AE is being removed.

Do you have an automatic or a manual? If automatic then what stall?

Tim

 

Traxion,

Auto with 2600 stall. I have noticed that the stumble goes away around 2400 rpm (just put that one together today). The car really picks up after that. My MAP at idle (850 rpm) is around 75-80 (it pulls about 10-12 inches of vacuum). The spark is 20-23 in that area (stock AUJP timing table). Do i need to add or subtract timing before the converter kicks in? The car drives great except for this stumble down low. I'm kind of a noobie to prom burning, so i greatly appreciate everyone's input and patience. Thanks

p.s. In the Accel enrich Delta TPS Multipiler Vs Delta Tps table, does RAISING the value INCREASE enrichment or DECREASE enrichment?. In funstick's "little something i put together on $8d ae tuning" it says that the tables are inversed. I believe that i read somewhere in one of your post that it is not. Once again, Thanks for the replies everyone.

 

O.k., i started back from the beginning. Stock AUJP chip with cyl vol. set at 784, inj constant at 36, and egr %TPS enable and %TPS disable at 98.9 (for the Miniram). There is still a small stumble, but at least i can drive the car. With the AUJP VE tables, i'm running BLM's of 108 everywhere. It seems that when i leaned the VE table to get BLM's of 128 it caused this horrible stumble. An engineer i talked to said that with a cam this size (236/242) the engine may need to be around 13-14 a/f at idle instead of the ECM targeted 14.7. I'm going to put my wideband on it this weekend and see what the a/f is at idle with the AUJP VE tables. Maybe i need to lean it to 13-14 (verified with the wideband) at idle and just let the computer run BLM"s of 108 at idle? Do this sound right? I just don't want to wash the cyl walls with fuel when the car is at idle. Any suggestions? What are some of you running for a/f at idle? Thanks again.

 

If I remember I'll post some of my tables later tonight.

Tim

 

My VE tables yield 126-128 BLMs. With BLMs in that range I have only modified 2 of the AE tables thusfar to produce great driveability (delta TPS mult vs delta TPS, and delta MAP PW vs delta MAP). The values I am using are shown below.

Do you KNOW that your O2 is functioning properly? Do you have long tubes or shorties? Are you using a heated O2 or a normal O2?

Tim

 

Trax,

I'm running SLP 1 3/4 shorties. I'm also using a Bosch single wire O2 sensor. I believe that the sensor is good , but may change it to rule that out. I'm going to run it tomorrow with the wideband and see where the a/f is. I don't get much time during the week to tune, as my 5 month old son consumes most of my time after work. I'll try to tune this weekend, and post as soon as i can. Thanks for the replies, it's great that everyone here is willing to help out. When i decided to build this engine, i knew that it would take some help from this board to get it running right. Once again, thanks.

 

An AC delco O2 sensor is the best choice. With a ratty cam the overlap at idle dumps a lot of the intake charge out the exhaust. This will confuse not only the sensor but the tuner. It looks lean but it isn't.

Again with the ratty cam a lot of exhaust gets pumped back up into the intake. Self EGR. Need more timing and less fuel (see first para) in order to get the idle proper. If staying with a closed loop idle you may need to lower the idle O2 window values.

RBob.

 

Sweet Trax.....

I been playing with my AE a ton lately and was going to bring my mult. values over 1.+ and see what happened then(still have small tip in prob from a stop). Guess it wont hurt anything at all to try now, just need to catch up again, lost the fuel pump in the fomrie fri after work :-( got it running today and 5 min later my reg diaphragm blew out lol oh well least its running

delta map Pw vs delta map: This would be most appropriately used for at cruise tip in correct? Having a lean spot at say 45-50 range with the TC locked up when tipping into the gas slowly?

Later
Jeremy

 

Changed to a Delco O2 sensor and its running decent. Seems the Bosch sensor took a dump. I always thought that the sensors read lean when bad, causing the computer to add fuel. Mine always read rich. Maybe it got contaminated from sitting around? Anyways, i'm running the stock AE tables and there is just a little stumble, but not much. Going to try to tune more this weekend. The temps here in K.C. are around 105 with heat indexes about 115, so most people don't even want to leave the house. Thanks again for everyones help, its much appreciated.


Note to self: Changing the O2 sensor when building an engine may prevent headaches!

 

The Bosch sensors have had problems for years with the internal grounds being flakey. Searching on DIY-EFi about 3-4 years ago will go further into things, as I recall.

Delco, period.

Some time ago, years actually, I went thru 3 new Boschs in a row, and all of them puked at 12 PIS of boost, the outputs would just slowly drop to 0, during a run.

 

or if a big load change occure example large steep hill. wihtout moving the Throttle the load goes up and kpa goes up. so yes it will lean out a bit. thats where the delta map comes into play. or for a shift when your at WOT.

 

thanks funstick

If the car wasnt being such a turd right now i would be playing with that table, least it was the plan, till the fuel pump went bye bye and then 5 minutes afer fixing it the regulator shot the pressure to 100psi when it blew out grrrrrrrrrrrrrrrrrrrrrr..

ran great for 2 days and on the way home today its on full rich................blm at 108 and int at 108-112 ...........everything checked so far comes out ok(its never something dumb with me i swear)

And as always its the week of when i want to have the car the worst, so i can go to the TA NAts and having some tuning fun as well............

Aint running by t'row im calling off thurs i already ahve fri off i will be there in the Formie!!!!!!!!!1 I must
thanks
Jeremy