I've had my '92 Z28 tuned 4 times. Each time it runs/idles great for awhile. After each successive time I start the car it will idle/run worse and worse. It gets so bad that the car won't even go above 25 mph without bucking really bad so I quit driving it. It will die at stop lights, at idle it surges and dies, and requires a heavy foot on the gas pedal just to get it moving. If I let it sit and idle in the driveway the idle will constantly surge and drop and then after a few minutes it will die.

So, my concern is:
A) My tuner isn't qualified to tune my car?
B) Instead of trying to keep burning a new chip I should get the Commander 950 system (or similar) to tune with instead?
C) My setup is all wrong and not ever going to run right?

My setup:
1992 Z28
Bored .030
Comp Cam: Advertised 280/288, 230/236 @ .050, .576 lift, 113 LSA
Heads: 64cc ported Performax aluminum
Holley Stealth Ram
Holley 58mm TB
Holley fuel rail kit w/adjustable FPR
Accell 30# injectors
Hooker LT's with true duals back to Dynomax X-Muffler
No smog pump/emissions hooked up.

Any ideas??

Here's a pic of the setup if you have any questions before responding:

 

does it seem to clear up and run right at WOT? then run like crap from idle to almost wot then like flipping a switch it cleans up and pulls right?


I had a stock one wire o2 sensor do that to me once when is slowly fouled out from being in my header. a 3 wire solved it.

 

I have been fighting my tune for 2 monthes now and the idle by far took the longest to get right, it now idles at 670rpm in park and 600 in drive all day long. However you are going to have a way harder time than I did due to cam size and TB size both which kill your vac. I would consider a vac pump or at least a resivoir, you also better get an emulator hitched up to the computer so you can adjust the lower VE table youself and the spark curves. I don't think your tuner will be able to get it without being able to see what its doing in real time. Hope this helps

 

Maybe this helps. It was dyno tuned and street tuned also. Each time it gets tuned the tuner unhooks his laptop, burns the chip, and sends me on my way and it runs fine. As time goes by it will run worse and worse until it needs to be tuned again.

On the dyno initially at WOT it will run strong until about 3500 RPMs then it will basically "cut out" and gradually recover up to 6000 RPMs. So the dyno chart shows a big dip and recovery. That for some reason can't get corrected. But on the street at WOT it doesn't do that.

I just can't believe it would be that difficult to get this thing tuned. The setup is not that radical.

 

Sounds like you are traversing the point where the cam wakes up. Using the same continuous settings from low RPM through the range where the real power comes in will be the difficult thing to deal with. Having a tight converter will make this even more difficult.
For fueling corrections,
If you can check your bin to see where the BLM boundaries are setup for on the RPM and MAP ranges and shift them so you have better range of the actual car's operation.
ie: stock is set Low, med, high to 900, 1500 & 2000 RPM boundary
Modified could be 1000, 1900, 2500 (as example only)
MAP Range is the same at 30, 50 & 70 Kpa where your car probably idles at 55 Kpa so allot of range is not being used.
Changing to 45, 65, & 80 (examples only, need to see where your combo operates at while driving)
Adjusting the ranges to provide an "idle" and coasting range, Part throttle range, and higher end (prior to PE) range "may" provide some relief to your issue.

Once you hit P.E. mode, they don't do anything but keep the "current" correction cell value active so keep the boundaries below the point where Power Enrichment would normally be invoked.
That point of activation is based on several factors and can't be explicitly stated in this context. You'll have to experiment and log data to see what those points are.
HTH

Edit: The cut out and resume could be the PE engagement points are also off from where they should be as well as the amounts of % change applied when PE comes on. You should see that on the WB of the dyno when that happens too.

 

JP86SS is right. Your car should run fine with a 113 LSA. Did your tuners allow the car to go in to closed loop?

 

Yes this is exactly what happened to me for a month (since I'm not Rrob), the car needs a learning curve for 20 minutes as you know. but the rpms must be varied not constant so tuning on the dyno for idle won't cut it. I also noticed that it sometimes it would take up to an hour of driving before the idle would stop changing. I'm running an lt4 hotcam (525 lift) a heavily ported tpi set up with a bone stock TB, this is on purpose because of the idle. the car still goes up fast to 6000rpm because I kept the air velocity up, air volume is good for high rpm but sucks for anything else(feel free to disagree with me). you have high air volume but no velocity down low. try starting with the park idle at about 900rpm or 950 once you have it solid there then start working it down. I had to take spark advance out of the bottom then take out 50% or more fuel out. do a search on rough idle you will start getting the picture what you are up against.

 

Thanks for the info. Before I tackle the actual tune itself I'm trying to determine if I should by the Commander 950 system and tune it or find another tuner?

Before I make that decision I need to understand (if possible) how an hour or two of working on a tune it would run ok one day and then the very next day start running worse? I'm not joking. Each day the car is started it runs worse than the previous day. It is as if it is "untuning" itself each day I start it up. How can it run fine all the way home from the tuner (50 miles), and then the very next day start acting up? Isn't a tune burned into a chip and that's that?

Any ideas? Is the tuner not doing something correct, or is there something I'm missing here?

I've had the car trailered to the tuner cold and started for the tune, and I've driven the car to the tuner and it's hot to be tuned. Both get me the same results - a car that runs crappier every day I start it.

 

Something is changing which causes the tune to change.

One thing to try is to reset the ECM by either disconnecting the battery for a moment, or pulling the ECM fuse for a moment (inline under the hood near the battery). Then see if the tune clears up for a while. Over time the ECM will save a few BLM cells to use the next time. This could be getting out of wack. Resetting the ECM resets the cells.

It may also be that the fuel pressure is slowly dropping off.

It may also be that the distributor clamp is loose and the timing is changing.

You need to ask the tuner what changes he/she is making to bring the tune back in line. Then look at what mechanical change would cause that.

Note that I'm moving this thread to the DFI & ECM board. It really isn't DIY related.

RBob.

 

I'm thinking all this points to me getting the Commander 950 system and getting the data up here on the board if I can't tune it myself.

Anyone recommendations other than the Commander 950 based on my mods?

 

What you already have is capable of running your setup.
Changing for the sake of changing will just cost $ IMO.
For a small amount you could get a cheap laptop, chip adapter and a chip burner, cable and start tweaking. www.Moates.net as a starting point for the stuff to do it.
Logging what is actually happening over different times will give you the info to get it running well.
Like RBob said, something is changing or you are never going into closed loop and enviornmental conditions are not being compensated for in the values programmed.
With any system you will need to understand its operation so you can judge what changes are needed when tuning.
Check out the sticky on the DIY-PROM board under the 730, $8D sections.
Other sections apply also in the scheme of things so read all you can to decipher your symptoms and generate a plan of attack.
Even if you do change to another system it will operate on similar principals.

 

Ahh ok. I was thinking that with the Holley Stealth Ram that perhaps I would be better off going with the Commander 950 system (or other) instead of using the stock computer to try and tune it.

I'm open for whatever makes the most sense, and appreciate everyone's input.

 

it's Your camshaft, Your tuner set-up idel when car is in WU and readings form MAP/MAF are low, then when engine warms up it consumes different amount of air and fuel and because of cam at higher temp your idle readings form MAP/MAF goes to different area of the table which is propably not tuned and this is why car dies. Is it possible for You to get tables of VE and SparkAdvance that You run now??
As for EFI i would choose any standalone like MegaSquirt, AEM or any other but standalone nod piggy-back.

best regards

 

Looks like I may have the piggyback you talk about. Is that where part of my problem is?

 

No thats normal, that is the moates G1 adapter, the part on top is the memcal, the half not plugged into anything is the factory PROM and the chip on top is the EPROM, it is where the tune is.

A piggie back system is a computer that takes the incoming sensor signal and changes it to make the factory computer think something else is happening than really is so it does different things, with the chip nothing is modding the signal, your changing the preset programming for how the computer reacts.