So the Monza runs! Uh...kinda sorta.....

[Fastmax32168]

I got my 3500 powered OBD1 controlled chevy Monza running on a stock tune for a 91 Z24 3.1 but it does not run well at all.
It fires right up, and at rest it idles fine, however when you give it throttle it pops out the exhaust. I tried to drive it, it has really no power at all , bogs terribly, and also pops out the exhaust when giving it throttle on the road. If you give it throttle slowly when in neutral it sounds pretty good. Turning up the fuel pressure seems to help a little, but not much.
All of the sensors seem to respond normally and when I monitor them there are no codes stored. I dont believe it is a mechanical issue as it is very inconsistent in its popping, idles fine, and sounds pretty good if I go into the throttle slowly. Is it possible the stock 3.1 tune is so far off, so lean, that it is causing this behavior?
Thanks
Roy

[Superdave]

what injectors are in it?

[Fastmax32168]

Dave,
The 3500 injectors are in it. I was hoping it would run well enough on the 3.1 tune that I could at least do some datalogging and have a starting point. I have never tried to tune one from scratch before, I have always started with something reasonably close to good and went from there. I definitely cant drive and datalog this mess.
Roy

[unchained01]

I could be wrong but I think the 3100 tune is for 21# injectors and the 3500 is running 24# I do some checking on the injector size

[Fastmax32168]

I am aware of that, I was sort of hoping the 14% larger injectors would offset the 13% larger motor and it would still run OK for a starting point.
Roy

[Superdave]

the 3.1 tune is set up for 16 lb/hr injectors, by running the 24's with that setup and unknown fuel pressure you are totally flooding it out.

If you want it to run good for a starting point you need to do a few things to the tune,

1. Drop the 0% BPC value to about 150
2. Disable the stock idle mode by un-checking "Idle BPW as a function of airflow"
3. Disable the charcoal canister purge by maxing out the enable temp
4. Disable the EGR by maxing out the EGR enable min coolant temp


After that it should start up and run much better, you are going to have to tune the idle table first but it shouldn't need much tweaking.

Be careful taking it above 4K RPM as the 3.1 tables will make it run extremely lean, above 5500 and you can kiss it goodbye.. lol

[Fastmax32168]

Dave, Should I also change the injector size to 24s when I do these things?
I do have a fuel pressure gauge so it isnt unknown. I had it set to 48 lbs at idle with the vacum line hooked up to the regulator.
Roy

[Superdave]

You can but in $A1 that value doesn't effect anything. I'd put the pressure up to 55PSI with no vacuum.

got any new pictures or videos? I'd love to see this thing.

[Mars]

got any new pictures or videos? I'd love to see this thing.

X2

[Fastmax32168]

Thanks guys, I will take some pics and put them up.

I used tunercat to read the old chip using the equipment moates sold me.
According to them I needed the $88 ecm definition file for this app.
However when trying to open the stock tune it is telling me I need the $86 definition file for this which I cant really find any info for.
I noticed my ECM is marked rebuilt when I opened it up.
Can somebody help clear this up?
Thanks
Roy

[Superdave]

91 Z24 5 speeds used the ARUR bin file which is $A1, I'd suggest starting off with BFUZ which is refined a bit more but still $A1. If it's an auto trans the a 91 would have ARUT (going off memory on that one), BATZ is one of the 92-94 $A1 auto bins.

[Fastmax32168]

I cannot figure out how to do this in tunercat:
"Disable the stock idle mode by un-checking "Idle BPW as a function of airflow"
Where should I be looking for this?
Thanks
Roy

[Superdave]

don't use Tunercat.


Tunerpro all the way.. I've tried tunercat but it's not even close to the other in function and i hate having to pay for definition files.

[Fastmax32168]

Do I have to change the pinout to change from $88 to $A1? I cannot get the computer to connect with my tunerpro.
EDIT: OK I may have found my problem. When I look in the help section of tunerpro it says I am supposed to have a choice/default setting under the preferences tab of connecting through a standard serial port which is what I am trying to do. However the only choices I have there are emulator or plug in. How do I set it to standard serial?
Thanks
Roy