If changing only injectors to larger size, is retune necessarry

[Vettezuki]

Well, a problem injector decided to really let go today and it sucked. So, I'm going to have them rebuilt and modified for slightly larger size. Mine are stock 26lbs and have always been on high duty cycle at WOT because my motor is a H&C. After talking to John at Injectors Plus, we decided on 32lbs. My question is, if I just swap out the current stock for these slightly larger would I need to retune or is it within a range the computer will relearn and adjust fuel trim using O2 data?

[jedhead]

I know on a SHO motor, going from 24lbs injectors to 36lbs injectors you need to retune or the engine will run too rich and eventually damage the cats. You have 2 more cylinder and lot more displacement. Can you hook up monitoring software running on a laptop to see how the engine is running then determine if you need a tune?

Bob

[94cobra69ss396]

You have to retune. The MAF is calibrated for the size of the injector so you have to retune when ever you change them.

[Vettezuki]

Just some information from my original tuner on this subject.

Well... There are many opinions on how to go about tuning! Not all ways are right and not all are wrong. However my opinion is the MAF is usually the last thing to change in the calibration. The MAF just like an injector on any GM Is a calibrated instrument. So, if you change the injectors you would need to re cal for the new part. Chances are the car might not seem to run bad because the computer is compensating for idle and close loop fuel. However the fuel trims can only go so far. At WOT is were you would physically experience any potential issues. A 6 psi Change in injector is pretty darn big but and such a small flow rate. There are more factors than just a injector #. there in inj.v; min pw; small pulse width adjust ext.. Its not that its hard to do just needs someone who can deal with checking and correctly calibrating for the new injectors. I think retuning the injector cal is a must, but tuning it via the MAF is defiantly not my first choose. It's not like it a ford mustang where the vehicles fuel comes from one source the MAF. If you just installed new the injectors I would predict -15 to -20 fuel trims over their current position. WOT could be off by at as much as - 1.5 AFR. Point. Richer than target. For who ever is trying to read the computer, make sure if they can connect , then have them try to read it on a slow rate some softwares piss off the computers and can't read in a high speed mode even when reading out the cal.

[Damian]

It will throw off your fuel trims. The ECU will do its best to compensate due to the O2 sensors. Not sure about your car, but my Eclipse ran like crap when I went from 220cc to 275cc injectors without changing the scaling and latencies.