Need help tuning my supercharged 94 Z28!

Ok, so I picked this Z up about 6 weeks ago and am having trouble getting it to run properly. I am having problems when I put car into gear. Idle's around 900 but when in gear drops to 300-500. I've been told its related to my cam. Looking at my data log I noticed that my spark advance at idle is in the lower 20's but when I shift into gear it drops to 9-12. IAC count is maxed out at 160, shouldn't that be at WOT, not when rpms are low? TPS voltage is at .57, I read in another forum that at idle it should be closer to .67, is this correct? Finally, car battery voltage sits at 13.3v at idle but when in gear drops into the upper 11's like 11.5-11.9 volts. I was getting dtc 33 map sensor but have deleted that code since. I am good at turning a wrench but my knowledge of efi's is very limited. I've been reading, reading, reading but its all still foreign language to me. Any help would be greatly appreciated.

Forgot to mention I've been using Scan 94/95 for data logging and recently started using TunerPro RT.

Battery voltage going low is probably just from lack of RPM's to the alternator, should fix itself when you fix the idle problem. The timing is also directly related to RPM, ie it's not that it's pulling timing due to knock or too high of idle, just that when the engine is turning that slowly there is more time for the mixture to burn at any given advance. For example the time between 20 degrees BTDC and TDC at 900 rpm is roughly the same as the time between 10 degrees BTDC and TDC at 450 rpm.

I'm not particularly familiar with that setup but my guess is that you need to adjust the physical throttle stop (or start by cleaning the throttle body if it's dirty), that will allow a bit more airflow getting the IAC valve back into a range where it can be effective.

My guess is that the bigger cam is pulling less vacuum which means at the same IAC opening the car is getting less air and producing less torque due to lower VE because of increased overlap. If that's the case and opening the throttle a bit restores a proper idle rpm then the next thing you can expect to do is decrease the VE in the lower rpms ranges and increase it in the higher rpm ranges to better match the cam. Of course you'll want to do this based on your data logs.

Attached is my most current data log. It was just sitting in my driveway with no drive time. As you look through my log you will notice a few times where I rev the engine and then when the rpms drop is when I put car into gear.

Thanks for the reply. So if I adjust the throttle stop screw should I do the tps sensor adjustment by drilling out the 3 sensor screw holes and moving it accordingly?

I don't think you'll need to. I think the amount of adjustment needed is so small that closed throttle tps voltage will still be within the normal range. There are certainly people more knowledgeable/experienced than me who could provide more specifics about where you want your IAC counts to be, and i'm sure you can find some forum posts discussing that, but I know you don't want it maxed out during idle. I would start by adjusting the throttle stop until it can idle at the target rpm with IAC counts below 140 and see if you can find better information on where it should be. Basically you want it to have enough adjustment both ways to be able to handle temperature and barometric pressure changes, along with extra load from accessories such as A/C, power steering, etc. When I get some more time i'll take a look at the xdf in tunerpro because there are probably some setting where the code predicts how many IAC counts need added when shifting from P/N into gear, and that might also need some adjustment to get a smooth transition, but that's more fine tuning and can come after...

Just some thoughts...

Firstly i'd try cracking the throttle blades to see if idle improves and iac tries to close some. You then know you have some control.

I'd strip check clean iac passages and throttle body.
See where the throttle blades are.
The blades are generally better being as closed as possible on an LT1 as this supposedly stops split BLM's (I've not directly witnessed that but altering the timing does)

I drilled out the iac passage in the front of the throttle body which allows more air in through the iac and iac counts go lower.
I would suggest iac counts around 40ish (1/4 - 1/3 of the range to allow some control) It will open up quite a bit whilst starting off cold. and will increase as driving speed increases.
Switching heating fans on also increase the iac around 10 points which then will come down again.

If you motor needs a lot of air i've read that people drill hols in the throttle blades like they do on carbs rather than cracking the blades.
On carbs if the blades are cracked you move over the transfer slots affecting the mixture.
I don't there is anything like that on the LT1 throttle body though.


HTH some
Mitch

Ok so I cracked the throttle blades and adjusted tps sensor to .66v. IAC's went down into the 60's, so that helped. I did a data log using EEHack but when I try to attach to this post it says invalid file. How do I attach this file so I can have somebody look at my log?

Did you zip the file?

Nope, but I will, thanks.

Heres todays datalog using EEHack. If anybody can figure out what changes I need to make I will also add my bin file. Or just use the EEX.XDF file. Also should I use the Lock BLM patch and the Stoich AFR target under funtions?

Can anybody take a look at my data log and tell me if I should make any changes? Thanks

I would have looked sooner but I hadn't used EEHack before. The software is much nicer than I expected.

First of all the log looks like a major improvement!

One of the first things I noticed is how the left bank BLM goes all the way to 153 after it enters closed loop, while the right bank stays quite close to 128. I'm not sure if that can be a result of your setup or if it's indicating that you need your injectors cleaned.

Next I can see that the idle rpm still drops too low when you initially put it into drive, then it mostly recovers as IAC steps increase. I looked in the XDF to see if there is any kind of in gear adder and I don't see any. Maybe the operating system doesn't support that, or maybe it just hasn't been put into the xdf.

Your idle rpm seems a bit low also. I downloaded the stock 95 z28 bin and the target idle speed is 800 in gear or P/N with a warm engine. You might try to duplicate that and see if it gives you a more stable idle.

Do I keep making idle adjustments using my throttle stop screw or can I make changes to my tune via one of the tables listed?

Adjust the desired idle speed using the "* Idle Speed Target RPM" table under the "Idle Air Control (IAC)" category. Your throttle stop is probably okay if not a touch too open. The IAC counts got down around 30 which is a bit lower than Terminal_Crazy suggested. I think the only potential "problem" would be if you were at a lower elevation with dense cool air the IAC could theoretically "lose control" if the IAC counts hit 0. In reality though the ECU can still control the idle speed by adjusting the spark timing. Notice that when the idle speed is hovering around the Target RPM the computer is constantly adjusting timing without changing IAC counts. Only when the idle is too high or low for a longer period does it adjust the IAC valve. Since you seem to be close to sea level judging by the Baro showing 99kpa you probably won't have any problems with your current throttle stop setting.

I think that some stock calibrations for automatic transmissions have the P/N idle speed set a bit higher than the in gear idle speed. Doing that will likely help with a smooth transition when putting the trans in gear. Maybe try 800 P/N -> 700 in gear and play around with it until you like it.

eehack can test idle parameters in real-time. simply use eehack's 'control' section.

check idle 'override' and spark 'enable', then play with the idle speed and timing until it feels right. it will default to your existing target and timing.

you may want to do this in neutral too. and while warming up. experiment a bit at different temperatures.

you can get test a hotter idle by overriding both fans to 'off' while monitoring coolant temperature, so you don't have to wait until you are in traffic in the baking sun to figure out that your idle only works in your driveway.

if you check the 'steps' button, you can control the IAC motor directly (so the ecm isnt trying to hit an idle target), you can use this to experiment and see how it behaves in other cases.

there's a small clipboard button next to the idle and timing controls, if you click them, it'll copy those parameters to the 'notes' screen in eehack so you don't have to write them down. then use those settings as hints for new values to use in your bin.

edit: one more thing, the LT1 really likes its throttle plates nearly closed so it can use the idle passages. the passages are fed both by a bypass hole and the IAC valve. the passages run through the manifold and feed the rear and front of the plenum more uniformly than the throttle plates. every lt1 i've tuned tends to idle best if nearly all of the idle air comes through those passages. if you have to open your throttle plates to get good IAC counts, in my opinion it might be time to consider drilling out your throttle body's idle air bypass hole a bit.

i had a few more thoughts on your log, do you think you might have a boost/vacuum leak? the last supercharger car i helped tune made way more vacuum than yours at idle. perhaps the map sensor seal is leaky or something.

another thing i'd consider is lowering your idle speed timing corrections. it's modulating pretty heavily in neutral. with a cam that size you might want to go 2,2,2,2,2 all across the board, it could really stabilize things (or make them worse, but it's worth trying...)

I second what Steve posted. Close the throttle plates and don't drill holes in the butterflies. Close the butterflies and try to get the BLM counts to even out bank to bank. I'd only really worry about the actual hot IAC counts if you reach a point where the IAC can't open enough to cold start the engine.

The TPS should not require any adjustments. You should never have to drill out the screw holes so you can move it around.

Also make sure the timing table (I'd check VE table too) are relatively flat in the area where the engine idles. Irregularities tend to upset the idle.

Oddly enough, I've found the BLM counts on my engine tend to go a little unbalanced during a cold start if the engine is left idling, like a 15-20 split. But, after a short drive they are balanced within a few counts the next time it idles. I don't even recall my IAC counts at idle. I just closed the butterflies until the BLM at idle balanced better instead of trying to find a "good" idle IAC count.

Ok thanks for all the replys. I will close my butterflies and test some parameters in real time. Then make adjustments in my tables.

Ok, so I got my throttle blades closed to where they were, drilled out my bypass hole to 1/4 inch and my iac counts went to 38 at operating temp. I also made changes to my idle speed timing corrections table using 2's across the board. Also made changes to my idle speed target rpm table to help my idle while in gear. So now when I put car back into park, rpms shoot up to 1500 and then slowly come back down. I also have to push gas pedal in to get car to start. Ive included todays datalog and my current bin, if someone wants to look at it.

Maybe the others have better suggestions but I think you need to modify some IAC parameters that aren't defined in the EE xdf's that I've looked at. Unfortunately the disassemblies that I have looked at are not great so it's going to be a significant amount of work to add those parameters to the xdf.

In the $E6 xdf there are a ton of IAC settings. Specifically I think that "Added IAC Flow for P to D Shift", "Added IAC Flow for D to P Shift" (I'm guessing this one is actually mislabeled and it subtracts not adds), along with "Idle Proportional Term vs. RPM Error" (actually a bunch of tables depending on open/closed loop, drive/park, etc).

Steveo, do you have access to a better disassembly? I looked at the EEXTRA xdf which has a few more IAC parameters so I'm guessing more work has been done on the disassembly for that...

EDIT:

I see now that the IAC stuff is on the t-side and already somewhat commented, so maybe not as hard to figure out as I thought...

This is a XDF with more stuff added. I believe it contains everything that had any kind of call-out in the disassembly. I have no idea if it can help.

http://www.gearhead-efi.com/Fuel-Inj...E-xdf-(EEXTRA)