93Z28 W/Hot cam 1.6RRs C A intake, 3" corsa exhaust and PCM tuned. Is it necessary to re-flash or re-tune the chip when changing the injectors from 24 lb to 30 lb?

 

You just increased the fuel delivery for any given pulse width by 25%. The ECM is only capable of pulling 15% excess fuel using the long term fuel corrections.

YES - you need a tune.

PS: Stock 93's use 22 #/HR injectors. = 36% increase over stock when you run 30's. If those 30's are SVO, it gets even worse, because of the difference in fuel pressure.

 

That much extra fuel is capable of washing down the cylinder walls destroying them and the rings while it pollutes the oil with fuel and starts working on the bearings.

The 93 I believe also "forgets" fuel trims on shutdown so it will be full rich on every startup, at least a 94+car would "remember" how rich it was last time it was rubn and compensate the full 15% it is capable of on startup.

 

You may also need to adjust the pulse width and timing correction factors depending on the specifications of the injectors.

 

Yes yes yes yes yes yes yes. I ran my car for only 15 minutes with 30lb injectors after upgrading to 24lb before I had someone come over and recalibrate the tune for the 30lb injectors. I was told by a buddy that it wouldn't be that big of a difference. Not only did I wash the cylinders with gas, I didn't realize I was flooding it with too much gas and ended up having 2 quarts of gas in my oil and completely wiping out my bearings. I had to have my crank bored 20/20, my cylinders bored out 0.040. Get a tune... it's a lot cheaper than the $1200 in machine costs, labor, and new parts.

 

Thank everyone for the instructions! I switched to the 24Lb injectors before my previousl tune. I am using the stock fuel pressure specifications for the daily driving, the problem is that on a dyno the engine is running very lean at 5200 RPM. If I adjust the pressure higher it idles and runs very rich at low engine speeds. (below 2000 RPM).
I recently saw a Car Craft article where they used 24Lb injectors on a 383 LT1 , W/ aftermarket heads and 55 Lb fuel pressure. The article did not say how the car ran @ low speeds. Perhaps it was tuned for that.
Thanks again for all the help. Ted

 

The factory 24 #/HR injectors (24.9 #/HR program flow constant) will flow 28.0 #/HR at 55psi pressure. That injector will support 400 flywheel HP, with an 85% duty cycle limit. In theory, at 100% duty cycle, they could support as much as 500HP, but you don't want to run them at 100% DC.

You have to tune it for the injector flow rate (and offsets as well if you change the style of injectors). That's the key number the PM uses to calculate the pulse width.

If you raise the pressure, how long are you waiting for the engine to stabilize? It's going to take the PCM a few minutes to reach the required long term corrections. As you increase the pressure to 58psi, you have used up all the head room in the long term corrections (assuming no other operating conditions have force the long terms to pull fuel). You don't tune by changing the pressure. You adjust the pressure to reduce the duty cycle on the injectors, then program the PCM with the correct flow constant.

 

Thanks again, I will search for the tuner mentioned in that article. Lancaster, PA., i think, I'll let you know the succes /rest of the story.
Thanks, Ted

 

up load your stock tune bin file and and send it to me ..and i will set it for 30lb inj and send it back all for free ..

 

LT1srule, the '93 has a removable chip. i do not have the equiptment needed to send you that data, thank you for your help. What, exactly do I need to extract the data and send it to you?
Thank You, Ted