Took my black beauty out for the first time in weeks. Running so much better than the day I parked it. However, the milage dropped big time. Before I started having problems, one of the things I was amazed at was the milage I was getting. Since I travel a couple weekends a month, I would take the vette simply because it got better milage than anything else I own. Cruising on flat land at 60 -75 mph the display would read 30+ mpg. I was thrilled. If I was able to hit a stretch in town at 30mph, it would read around 40mpg. After installing the Bosch III's, I'm getting 20mpg on the road at 55mph and barely 24mpg in town. The only thing different are the injectors. What am I missing?

I'm glad the car is running better, but I miss the great milage. I just don't get the 30% drop.

 

Strange,you are the only one experiencing that .-

 

Did you reset the ECM when you installed them? You have to disconnect the battery, then turn on the headlights to drain the residual charge out of the system. Re-connect the battery, start the car, and DON'T TOUCH THE THROTTLE for ~15 minutes. Just let it idle until it enters closed loop. This lets the ECM learn the new injectors.

The first time I put Bosch III's in mine, I forgot to do this; it ran terribly and I lost major mpg. The computer still says I'm about 3mpg lower than I was before them, but I figure the ECM is still on it's learning curve, plus the computer might not work perfectly with the different injectors.

 

Did you verify the display manually?

 

I'm not the only one with this problem. I remember reading a thread about this very thing, but don't know if he ever resolved the problem. I had the battery disconnected over night with the headlights switch to on. On the initial start after the replacement, I did let the car sit and run about 15 minutes before turning it off. I then went on a short trip, about 30 min each way. I haven't yet filled the tank to verify the milage. My last trip took almost 1/2 tank on 55 miles.
What do you mean by "closed loop"? Maybe I need to go through the process again?

 

the guys that were having mileage problems via their e mails was the ECU not going into closed loop. This is where the computer takes over the modification of the injector pulse rate by information from the o2 sensor and a signal from the coolant temp sensor that the engine is at normal operating temp. If the ECU stays in open loop the injectors will pulse at a predetermined rate based on the cold start program . If the ECU does not go closed the gas mileage will be terrible. Injectors themselves do not control fuel mileage.
good combustion with a stoich air/ fuel ratio will pulse the amount of fuel needed to keep that ratio. Normally 14.7 to 1. However, in open loop on a hot engine the A/F ratio can be 12 to 1. Running rich all the time= poor mileage. A scan with datalogging will tell you by the BLM s how much the ECU is correcting the injectors.

 

Been searching through messages here about ECU and BLM and learned a few things, mostly over my head. Started thinking (dangerous thing) and had a thought. What if / does it matter after disconnecting the battery, light switch on process, I started the car while it was still at operating temp? Or does it have to be a cold start?

 

I dont know if this counts as hijacking or not but I am experiencing something similar. I replaced my stock injectors with 30lb ford racing injectors and got a tune. However I never drained the battery and let it run for 15 min. It runs strong and good, but my mileage is bad. I thought tuning the chip would make the computer recognize the new injectors. Am I wrong? Do I still need to "reset" the ECM?

 

Did you put 30# injectors in a stock engine?

 

Mostly. It has a ZZ4 cam, K&N intake and no mufflers.

 

the computer will not learn in closed loop. try it cold, also if you had two bad injectors before the swap. The ECU compensated by enriching the other 6 striving for stoich. It learned that pulse rate, now you put in new injectors and did not reset the ecu, I believe you will be too fat.

 

Anyone know if I have to reset the ECM after its been tuned for the bigger injectors?

 

????

 

don't know why. But after we put in the Bosch injectors, and reset the ECU cold, let it idle for 15 mins. they run better, I'm not a tuner, and don't want to be. And never will be. Now, if you can explain why that works I would really appreciate it. But, it does

 

How does one know when it changes from an open loop to closed loop? I let my car idle for 15 min and checked the dash gauges. It appeared to be operating temp. Maybe not? Should I have waited until the fan kicked on to make sure?

 

I'm not running bosch 3's, but I have similar problems with new accel injectors. it runs rich, and jumps in-out of closed loop. something with the newer style injectors. like the o2 sensor doesn't read correctly, and it's NEW. I'm considering putting in a heated o2 sensor.

If your cars are running in open loop, the o2 sensor is cold. plain and simple. my car runs rich, but the BLM's are way high. but it runs amazingly good. I'd never know if I didn't smell the rotten exhaust.

I thought the computer always learns. long term and short term fuel trims is a continual closed loop feed back system. The MAF cars are suppose to be pretty flexible.

I'm glad it's a bunch of us having these problems. we have to figure this out. mine is a MAF TPI motor with single wire o2 sensor.

I can reset the ECM 1 more time, but I don;t see that making a difference. it's something with the 02 sensor. maybe the 10% ethonal in the fuel is making the exhaust gases cooler???

 

I believe you go into closed loop around 130* coolant temp.

 

it's dependant on o2 sensor temperature, and some other things.. depending on model year.

 

The min pulse rate for the stock injectors is 1.59 ms, the new injectors will run linear down to 1.05 ms (Bosch type II and III). The ECM is compensating (in the loaded bin program) at lower injector ms for a non linear stock injector (leaner at lower ms), so when the new ones are installed they are linear to a lower ms. Ecm/Eprom is still adding more fuel at lower ms. Thats is why you are rich at idle and off idle.

 

I definately see something strange with new accel injectors in my 305 f-body, and I can't figure it out. there is definately a lineraity problem with the new injectors. or it's just plain different.
I tried 19's, car run great, except at WOT where it leans out too much, and stumbles.
then I tried 21's, and it's pig rich at idle, but BLM's way too high anyway (150+). but it runs great through out the RPM range.
either the o2 sensor is not reading correctly to compensate, or something. but the car is just not right with the stock PROM, and newer injectors. It feels great, but if you watch the BLM's, something is screwy.

my car is just dumping fuel at idle, cell 0, and the BLM's are 150+. exhaust stinks rich, and the computer is not compensating correctly. then it sometimes jumps back to open loop because I think the o2 cools off.

your the first person who has mentioned this. and I have been thinking about this. and all these people losing fuel mileage, but their car runs too good to notice. I only notice this because I have an auto xray, and drive around with it.