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Dyno Testing & Downshift

removing PCM loom bracket

The PCM loom bracket protects the wire bundle and prevents it from vibrating.

Unfortunately, it will be in the way of the supercharger intake manifold.

Removing it will give me easy access to the ignition coilpack trigger wire for cylinder pair #1 & #5. First I disconnected the ground terminal from the battery post. Then I removed the bracket mounting nut (11 mm) from the stud in the firewall and disconnected the PCM connector mounting bolt (10 mm).

Then I removed the ground lug mounting stud/bolt (11 mm) and carefully unwrapped the electrical tape that holds the bracket to the wiring bundle.

The bracket is shown laying on the upper intake manifold. When I looked thru my wiring diagrams I was disappointed that none of the three paired cylinder trigger wires are identified by cylinder number on the V6 but are identifed on the V8 drawings. When I looked at the SOHC V6 PCM pinout the circuit function was only "Ignition Coil". However, when I looked at the OHV V6 PCM pinout the circuit function of pin 26 was "Ignition Coil #1" and it was the same PCM pin number and circuit function as the V8. The V8 wiring diagram shows pin 26 as being the trigger for paired cylinders #1 & #6 so I assume pin 26 is the trigger for paired cylinders #1 & #5. It's associated wire is tan with a white stripe. I confirmed with a light that there is a TN/WH wire going to the coilpack connector so I found it in the PCM wiring bundle and tagged it with a small cable tie. Then I connected the ground lug to the firewall with the stud/bolt and the PCM connector to the PCM.

And finally I reconnected the ground terminal to the battery post. I think I'm now ready to return to the dyno to get some good pulls.

naturally aspirated baseline

I returned to the dyno shop this afternoon for another attempt. First I tried clipping the primary probe to the loom at the camshaft position sensor (CPS). I thought there was a possibility it might work since my CPS is a hall effect sensor. The loom was too large for the probe to enclose and the Dynojet did not register anything. When I installed the probe on the trigger wire I had isolated in the PCM wiring bundle there was a stable tachometer reading on the Dynojet but it was twice what my instrument panel tachometer read. Todd adjusted the Dynojet from 720 degrees between sparks to 360 degrees and everything then looked good for a run.

We did three pulls within about 15 minutes. The SAE corrected results:
Run 1 max torque = 206.28@3550 max power = 170.2@4936
Run 2 max torque = 206.21@3524 max power = 169.45@4824
Run 3 max torque = 204.04@3590 max power = 167.04@4850

During Run 1 the IAT increased from 104 to 114 deg F
During Run 2 the IAT increased from 116 to 140 deg F
I failed to datalog Run 3 but I assume that the IAT continued to increase.

There was a blower for the radiator to keep it cool but it did not prevent the engine compartment temperature from climbing. I think the decrease in torque and power for each successive run is due to the climbing IAT. Below are plots of Run 2 which I think was the most stable.


You may notice that the plots do not cross at 5252 rpm even though 4th speed (1:1) was selected. I noticed that the crossover shifted left (lower rpm) when the SAE correction was applied to the STD run. STD was the standard until 1990 when the dyno industry switched to SAE. STD max power is typically several percent greater than SAE max power. If the power is corrected but not the torque where the curve is fairly flat a few percent makes a significant shift in the crossover. I suspect that is the explanation.

Todd mentioned that my tires were starting to noticeably distort as the max speed reached 140 mph. I was surprised because last time my datalog showed a max of 127.5 mph so I began checking. According to the Dynojet the speed was 140 mph when the engine speed limiter activated at 6250 rpm. Using an axle ratio of 3.73:1 and a tire diameter of 28.86 inches (according to BF Goodrich) yields 143 mph at 6250 rpm. Apparently even though my tune no longer limits vehicle speed the PCM maximum output is 127.5 mph as shown in the Run 2 datalog below.

Bold Green > mph
Blue > rpm
In the above plot the speed hits 127.5 mph at 24 seconds and 5780 rpm. I was busy recording lambda on the air/fuel ratio meter display and didn't notice what the instrument panel speedometer did. I'm beginning to question the validity of drivers who claim to have driven their Explorer over 130 mph.

Anyway, I'm declaring my naturally aspirated baseline max torque to be 206 rwtq and max power to be 170 rwhp. That's an improvement of 20 rwhp compared to my stock configuration after major changes to the intake and exhaust systems.

Below is the Run 2 datalog showing uncorrected for E10 A/F ratio.

Lambda displayed on the air/fuel ratio meter gradually increased from 0.77 @ 3,000 to 0.85 @ 6,000.
Below is the Run 2 datalog showing spark advance.

max vehicle speed

I asked James Henson about the max vehicle speed in the datalog. He said the 127.5 mph is a PCM bit segment limitation. To me that means that when the vehicle speed exceeds 127.5 mph the PCM should detect a mismatch between the vehicle and transmission speed versus the engine speed. I'm surprised a DTC did not get set. The speedometer/odometer is driven by the four wheel anti-lock brake system so it may not have the same limitation. As I recall the speed indicator was all the way to the theft light area which would be more than 127.5 mph.

AFR Dyno testing

I decided to perform high flow AFR testing on a dyno for several reasons:
1. Controlled environment
2. No risk of tickets or accidents
3. The dyno is about a 10 minute drive from my house and there is a towing service within 15 minutes.

The main objective today was to datalog STFT (commanded lambda) vs actual lambda at high airflows to make MAF transfer function corrections. But I was also curious about performance improvements with the M90 installed even though fuel and spark are not yet optimized. Below is a graph of torque in 3rd speed.

The max is 262 @ 3500 rpm compared to the baseline NA value of 207 @ 3500 rpm (+55). I started the pull at 2000 rpm but for some reason the Dynojet plot starts at 2700 rpm. The engine was pulling strong at 2000 rpm.

Below is a graph of rwhp in 3rd speed.

The max is 227 @ 5300 rpm compared to the baseline NA value of 170 @ 4800 rpm (+57).

The plot below shows how the max rwhp for FI has shifted to the right compared to NA even though there are no engine internal modifications.

I am very pleased with the results but anticipate increased performance as fuel and spark are optimized.