I'll try to make this as short as possible.

The car involved is the one under my user name.

It had a bad injector, so I went out to replace it....10 minute job...nope, not for me and THIS car! The lower section of the fuel injector cracked as I was tightening the screws.

Went to the local "Pull-a-Part" and aquired the entire injector housing(injectors and all) from a 4.2(?) V-8 Cadillac. It all bolted up like a champ.


Now, only when its' cold, I get a "rolling" idle. Once it warms up, it idles just fine....but then it throws a code 44. I've replaced the O2 sensor twice in the last 6 months....I've got a feeling my problem may be somewhere else.

Any ideas out there?

 

Cold = Open Loop Mode.

Warm = Closed Loop Mode.

Open Loop means the fuel delivery is based upon pre-programmed lookup tables designed for your engine, including the injector flow constants.

Closed Loop means those tables are less significant the the ECM relies on the oxygen sensor input for fuel calculations, and adjusts injector pulse rates accordingly.

If the injector(s) you installed have a lower mean fuel delivery rate (PPH) than the originals, the engine would be running lean in Open Loop mode. The injector pulse timings used in Open Loop would be programmed for a higher fuel rate, so they would tend to be too short to deliver adequate fuel based on the tables. Once the O² warms up and becomes active, the ECM would enter Closed Loop Mode and recognize the lean condition, then skew the pulse rates longer to compensate, giving the appearance of everything being normal.

The lean Open Loop condition would also tend to cause idle RPM wandering, since the RPMs would drop until more fuel/air mixture is applied to restore the target RPM.

If fuel pressure is correct, I'd suggest going back to the stock injector sizes to see if your problem is cured. Even if you compensated for the smaller injectors somehow, the system would still be lean at WOT, since that is also an Open Loop Mode function.

 

Thanks...that makes sense.

I'll "limp" it along 'till the weekend, then re-install the 305 injectors(this time without braking anything....I hope!) and see what happens.

Quick question, if you don't mind.....would there be any difference in the pressure regulators? If so, I still have the one from the 305(thats' not the part that broke)....should I change back to it when I swap the injectors?

 

I know the 305 TBI system operates at 11-13 PSIG, and am not sure what the Cadillac fuel pressure is supposed to be. To be safe, I'd swap it back if everything is O.K. with the old regulator.

 

Thanks, Vader. Yeah, the old regulator is fine...the bowl section was the part that broke. I've got to pull it to replace the injectors anyway, might as well go back to the stock one.

Your advice explains the code 44, as well. It only happens when it transitions into closed loop. I'd say that is the ECM overcompensating for the earlier lean condition.

One day I'll understand 'puter cars.....but most likely no time soon! I'm just tremedously grateful that this site is here to pull me through!

 

Vader.....just to let you know.

That was it. Swapped the injectors and regulator. All is right with the world!!!!


Once again, THANKS!:hail:

 

Cool! It's always good to hear the results, rather than just wonder.

Now you can go back to normal, or strange, or whatever is normal for you...