Too HOT Hot Hot!!!

[SilverXJ]

IIRC on Dino's build he suggests using a MAP adjuster. If you are running nothing for the adding fuel (piggy back, larger injectors, map adjuster), then it will run lean in open loop. How far away are you from installing the AFR meter?

[Dirtweazle]

That's next. What is the MAP adjuster? did not know about this one. thought stock ODB2 comp was adaptable enough for this.

[SilverXJ]

The OBD II system will most likely adapt in closed loop, but it doesn't do much for open loop. The MAP sensor adjusted adjusts the value from the MAP sensor that the PCM sees, which makes the computer adjust the fuel trim.. but it is over the whole RPM range not just at specific spots like an Apexi or PSC1 will do.

[Dirtweazle]

Googled it.. Got it from Dino's.. Its the first listing.. Will go from here.. Once I get the cooling situation worked out I may run each of these and document everything and post results. AF meter install baseline. 24lb injectors then this MAP adjuster.

[Dirtweazle]

Now im reading the Map adjuster only works for a few seconds then the O2 snifs out whats really going on and adjusts back. Does the comp already see a lean condition, add the 24lbs gets it closer if not over to whats tolerable and use the MAP adjuster to fine tune, but not so much the O2 overides? Trying to get this all under my hat.

[Mgardiner1]

IIRC anything over 80% throttle is considered "open loop" (at normal running temp). In open loop, basically wide open throttle, the O2 sensor readings are ignored, and the ECU uses a lookup table, along with data received from a few sensors (MAP, MAT, CTS, TPS), to determing how much fuel to inject. Of course this table is based on the air flow required for a 4.0 liter engine. So if 1.2 milliseconds of injector pulse is what is required for 100% throttle, 195 degrees coolant, and -0.2 bar pressure, on a 4.0 liter engine..... Then possibly 1.4 milliseconds of injector pulse would be required under the same conditions, BUT with a larger displacement engine. Therefor the lookup table in the ECU could potentially starve the engine for fuel. The idea of the adjustable MAP, is it tricks the ECU into thinking the air pressure is higher then it really is (it thinks a more dense charge of air is available to each cylinder) and fools the ECU into thinking it should inject more fuel then normal. HOWEVER, in closed loop (normal temp, below 80% throttle), the ECU will adjust the fuel mix as close to 14.7:1 air:fuel ratio BASED on feedback from the O2 sensor (yielding the adjustable map mostly useless in normal closed loop mode).

[SilverXJ]

What 24lb injectors are you planning on going with? Five-o had a set that worked out to like 27lbs, which was way too much when I put them in my 2000. I now have a set of ones that work out to 23.5lbs or so but I have yet to run them to see if they work any better.

[dwg86]

I think I have the same injectors. All the injector calculators I look at say those injectors should be fine(at max 80% duty cycle). Those injectors should flow good at less than 80% duty cycle and 49 fuel psi.

This computer controlled fuel injection thing is new to me. Am I looking at something wrong? Any input would be greatly appreciated.

[Heck]

I haven't kept up with my tech. Is the fi control strategy that jeep uses the same as what gm used to call "speed density"?

[SilverXJ]

I don't think you are looking at anything wrong, and yes the system on the Jeeps is similar to the speed density system.