4.0 Tuning exercise: phase 1

[mmag1982]

Flow daddy header, BBK 62mm throttle body and 24 lb/hr hesco injectors installed and PCM memory reset.

- there's now a HUGE improvement in low RPM torque, violent off the line acceleration, spins tyres in 2nd gear on dry pavement.
The way it sounds now is really exotic, a mix between american v8 and bmw inline 6 whine, I notice young people turning heads to look where the noise is coming from

- when i fired it up for the 1st time i noticed the pcm hunting for correct values, obvious from the way the afr guage fluctuated, got more smoother and steady each drive. It actually seemed to learn the new setup.

- Big improvement in engine smoothness across the RPM range, butter smooth idle.Engine revs freely to 5000rpm. Throttle response from mid range to full throttle is much sharper.


- pinging has VANISHED, no detonation whatsoever at all loads, at all RPMs even with 91 octane fuel, which used to make it ping like hell.

- AFR now runs a 12 to 13 at mid throttle, that's where i get most acceleration response, below that its usually locked in closed loop as before ( 14s and 15s ), at full throttle stays in the 12s till beyond 4000rpm dips to 10.2 near the redline. I noticed that the car is running now more often around the 13 figure at mid throttle, which may explain the improvement in mid throttle response

- No effect on MPG , it did not get worse as i expected from the 24 lb injectors.


The only PROBLEM is

The car doesn't start up as it used to, it takes significant cranking to fire it up even if hot, not just cold starts, however, if I turn it off then start it again right away or within 5 to 10 min, it fires up normally. The more it stays off, the harder it is to start.

The odd thing is that when it starts up , it has a with a beautiful smooth idle, battery voltage is ok, what has wrong here? the injectors? something related to fuel pressure dropping?

appreciate your thoughts

any ideas?

 

[Talyn]

I bet that 12-13 AFR at mid throttle will go away at when the PCM learns the new values. On the cranking issue check your fuel pressure at first key on. I still think the 24lb injectors are too large for a stock 4.0L.

 

[evowheeler]

their is a fuel psi hold valve on top of the fuel pump . may be bad . check to see how long the system holds psi after shut down . my 99 does the same thing . couple of key cycles and I bet your long crank time shortens . mine do

 

[gradon]

Try the turn ignition on/off 2-3xs before starting it and see if it's easier. If so, it is the valve. Also, being in the 10's at WOT is too rich, thus shows that those injectors are too big, even though they are nice. A solution to this is to make an adjustable MAP. I'd measure the supply voltage going into MAP while the engine was running to get a reference voltage. Install the adjustable MAP and then turn the voltage down from the reference voltage in small increments, then check out the WOT AFRs. You want 12.5-.8:1 for best power. Also, the pcm will learn and turn all areas light-mid throttle to 14.7:1.

 

[mmag1982]

@ Talyn and Gradon: you were absolutely right.
I decided to put back the stock injectors to see whats going on , I took some time as well to heat shield the intake with DEI reflect-a-gold thermal barrier. I hope this offsets some of the heat soak the intake has to endure by being just above the header. here's the effect:

- cranking problem gone. it firesup now within just a second of the starter motor.cant explain hows that related to the injectors though.
- even better throttle pickup from midrange to full throttle, no hesitation , very smooth. Before with the 24lb,I could actually see the PCM hunting for proper AFR values before as i floored it the afr gauge fluctuated wildly..

- wide open throttle at 12.8 to 12.2 up tp 4500 rpm, I can only see 11 just before the redline.

- I can actually feel a slight improvement in performance, specially in lower rpm ranges.

do you think its worth getting those 4 hole bosh injectors that are the same size as the stock?

 

[gradon]

It depends on how much they cost, but the 4-small holes spray better than 1 bigger hole. Your computer will compensate +/-30% in closed loop to accommodate your upgrades/changes. It's at WOT where you'll see if you should add an adjustable MAP, or bigger/smaller injectors to get those AFRs(where you now have them).