42# injectors on stock computer?

[gt347mustang]

Does anybody run 42# injectors with their stock computer? with a matching Mass air of course. The reason im asking is because I have been told by C&l that it is possible to run 42# on the stock computer. But I was also told by Pro-m that you can only go up to 36's with the stock computer, and I would have to get an upgraded chip. If anybody is running 42's with the stock computer please reply. thanks.

 

[AznStanger3v]

chances are that if you need 42s, youll need a chip. i would listen to c&l though, they seem to know what they are talking about

 

[94TURBO5 O]

I run 42#'s with my S-Trim on stock computer no chip.
Stock block, cam , heads, and bottom. I have a Pro-M 75mm MAF.

 

[final5-0]

Many have done it using a tuning device or they got a chip burned.

Later
Grady

 

[Redsnk95]

On a stock EEC...some get away with it some don't. The main problem you will run into is hot start problems. You might be able to get away with flooring it to shut off the injectors on hot starts.

Troy

 

[VibrantRedGT]

I'm part of that group who couldn't get the car to idle with 42's and stock EEC. I could start the car and it would idle for a bit then bog out. With the chip it idled perfectly at 875rpm. Some can some can't.

 

[Don 95Vert]

Here's a MAJOR problem with running any larger injectors with a Pro-M calibrated for them without a chip. Pro-M calibrates a MAF by altering the circuit so the MAF sends the EEC less voltage, i.e, it fools the EEC. So, if stock you have 19# injectors and you switch to 42# injectors, the voltage at WOT that the EEC sees is about 45% of where it used to be. So for the same amopunt of air passing into the engine, it fires the injectors 45% less as opposed to stock. This same MAF data is also used by the EEC to calcuate load - and load is used by the engine (from '94 on up) to determine spark - it's also used to determine target A/F in the base fuel tables, even on earlier processors. When you look at the spark and fuel tables and see what the 45% load values are at 5000+ RPMs you'll see that rather than the timing being 25*, it is between 32 and 38* and in the fuel table the commanded A/F is about 14.1 rather than 12.2 (this is for a W4H0 EEC) - you can see, especially on a blown car, why this can be very bad.

 

[gt347mustang]

thanks for all the help guys

 

[95stangGT]

Here's a MAJOR problem with running any larger injectors with a Pro-M calibrated for them without a chip. Pro-M calibrates a MAF by altering the circuit so the MAF sends the EEC less voltage, i.e, it fools the EEC. So, if stock you have 19# injectors and you switch to 42# injectors, the voltage at WOT that the EEC sees is about 45% of where it used to be. So for the same amopunt of air passing into the engine, it fires the injectors 45% less as opposed to stock. This same MAF data is also used by the EEC to calcuate load - and load is used by the engine (from '94 on up) to determine spark - it's also used to determine target A/F in the base fuel tables, even on earlier processors. When you look at the spark and fuel tables and see what the 45% load values are at 5000+ RPMs you'll see that rather than the timing being 25*, it is between 32 and 38* and in the fuel table the commanded A/F is about 14.1 rather than 12.2 (this is for a W4H0 EEC) - you can see, especially on a blown car, why this can be very bad.

So is it better to go with a C&L then?

 

[Don 95Vert]

No it isn't, in fact IMHO, it's worse. I didn't mean to imply there is anything WRONG with Pro-M meters, they are terrific. It just that the common notion that as long as your meter is calibrated for the injectors, you are OK is false in most cases. Less problems with pre-94 EECs though.