J4J1 Tuning

desmo01 · Post by **desmo01** » Mon Oct 13, 2008 8:19 pm

Gents,

Going to be tuning a friend's Cobra kit car with a J4J1 ecu.

What is the best process for tuning?

...as in what tables/variables to chase first...

Post by **dex** » Tue Oct 14, 2008 12:09 am

What modifications are there to the engine?

desmo01 · Post by **desmo01** » Tue Oct 14, 2008 6:54 pm

-75mm mass air
-75mm throttle body
-36 lb/hr injectors (FMS, so should have slopes)
-331 CID
-Edelbrock Performer RPM II
-Edelbrock Performer heads
-11:1 CR
-Factory Five headers

Again, I know some of the basics (injector slopes, mass air cal, etc.), but not sure on what tables to pursue first.

Wasn't there a published Ford doc regarding the GUFB strategy? I'd think the J4J1 (CBAZA from memory?) strategy would be similar... Anyone know where that GUFB doc is?

Post by **dex** » Wed Oct 15, 2008 2:35 am

Concentrate on getting the tune right with regard to the hardware changes first unless you have real problems with spark and/or fuelling. From the list you give these are the following areas to look at initially;

Injectors (e.g. slopes, min pw, breakpoint, offset, cranking fuel)
CID
MAF (e.g. transfer, upper and lower limits)
Throttle (e.g. throttle body airflow)
HEGO (e.g. delay)

And specific parameters;

'WOT Aircharge Correction Factor' (aka ARCWOTCOR) - raise to avoid aircharge clips.
'Peak Load at Sea Level vs RPM' (aka FN035)

The document can be found on the Tweecer website.

desmo01 · Post by **desmo01** » Wed Oct 15, 2008 7:09 pm

Most of that stuff I kind of know about, didn't the Mustang Cobra's do something different with the injector slopes, as in use a different way to rate them?

My buddy is going to flow the mass air and experimentally determine the curve...

I'll check the other stuff too, thanks!

Any other advice?

Post by **dex** » Wed Oct 15, 2008 10:21 pm

Yes, the J4J1 has the injector slopes set equal, when this is done the injector offset is extremely important in getting the fuelling calculations right.

If you still have the original MAF and can put it back on this will speed up getting the injector related parameters correct by eliminating one unknown. It also helps to fit a throttle stop to avoid pegging the smaller MAF if you find this occurring.