Closed loop operation @ wot (1997 7.5 )
 

Going to try this post here first, here's the scoop, 1997 7.5, 5spd, s/d system. With my scanner hooked up driving @ wot the pcm goes into closed loop, you can actually feel the power loss. live data shows stft subtracting fuel and injector pulse dropping to 16.2 ms from 21ms.
From what I could understand is that it is some type of emissions strategy from the pcm, has any one else run into this and how do you over ride it.
(Thats the readers digest version any input would be greatly appreciated)
Thanks, Dom

I'm not sure what performance tuning is available for the early OBD-II systems. I don't know if Superchips or anyone like that has anything for your truck or not.

I put a post up in chips and tuning no response yet, I just can believe that all these 94 -97 big blocks run closed loop @ wot and nobody has come across this.
I tried an earlier pcm (1995) this after noon same out come, So all my engine modifications: headers, throttle body, cam exhaust, adjustable fuel pressure regulator, have no inpact @ wot because the pcm forces 14.7 -1 ratio:-arrgh
I can't be alone here, I'm just looking for pieces of the puzzle has any body else run across this?
thanks, Dom

The computer is supposed to go open loop at WOT. What is the a/f during normal part-throttle cruise and what are the fuel trims doing? Is it in closed loop at part-throttle cruise? To me, it sounds like the computer is correcting a general lean mixture in closed loop, then when it gets to WOT and goes open loop, the base fuel calculation is off, possibly because of some of the modifications to the engine.

What do you use to read the real-time data?

Domenico,
I would check your MAP sensor on your OBD-1 system.
I take it this is not a California truck.
Your Map sensor alone should send it to open loop at WOT.
What is your MAP sensor reading in your scan when the scan says O/T?
Or do you ever get a O/T?
As you know the throttle (TPS) has three positions, C/T, P/T & O/T.

I spoke to the head tech at "air care" (our emissions test center) about it, gave him some numbers he figures it has to do with heavy duty emission standards but beyond that had no words of wisdom. the scanner i'm using using is a snap on scanner, I have also had the lab scope monitoring the o2 signal on road trips, unlike most eec IV systems these vehicles have a sample type feed back.
As you cruise down the road it swings in and out of closed loop, taking random samples. I did a bunch of research on that and that is normal. Tried another pcm yesterday same result shifts to closed loop @ wot. I do have all the number on an spread sheet, if you monitor the tps you can follow 2nd to third gear pull and then 3rd to 4th

frame/ rpm/ 021 mv/ map hz/ tps v/ tp mode/ ect v/ ect c/ iat v/ 1at c/ iac %/ kph/ evp v/ evr 5/ inj pw /loop/ stft/ spk adv/ can prge/
0 1300 845 97 122 ct 0.66 86 1.18 66 42.2 19 0.49 0 2.91 clsd 3 31 off
1 1012 837 101 122 ct 0.65 86 1.17 66 42.2 18 0.49 0 4.45 open 11 31 off
2 964 788 102 122 pt 0.66 86 1.17 66 43.7 15 0.49 0 10.81 clsd 10 32 on
3 2012 901 139 196 pt 0.66 86 1.2 63 66.9 22 0.55 44.2 15.64 clsd 5 24 on
4 2300 869 155 288 pt 0.65 86 1.29 60 95.6 30 0.49 0 19.25 clsd -3 23 on
5 3128 807 156 4.65 wot 0.66 86 1.43 56 95.6 39 0.49 0 17.33 clsd -7 28 on
6 3896 50 156 4.66 wot 0.66 86 1.56 52 95.6 48 0.49 0 17.94 clsd 3 31 on
7 4532 280 155 4.66 wot 0.66 86 1.68 50 95.6 56 0.5 0 16.56 clsd 0 34 on
8 3824 20 96 1.21 ct 0.67 85 1.71 50 63 55 0.49 0 0 open 11 41 off
9 2796 858 157 4.66 wot 0.67 85 1.61 52 95.6 62 0.49 0 19.94 clsd -5 25 on
10 3156 786 157 4.66 wot 0.66 86 1.69 50 95.6 68 0.49 0 17.87 clsd -9 27 on
11 3300 82 156 4.66 wot 0.65 86 1.78 48 95.3 74 0.49 0 18.86 clsd 0 29 on
12 3644 95 156 4.66 wot 0.65 86 1.86 47 95 81 0.49 0 18.63 clsd 1 30 on
13 3788 170 156 4.66 wot 0.64 87 1.92 45 95.3 85 0.49 0 18.1 clsd -2 31 on
14 4060 665 156 4.65 wot 0.64 87 1.96 43 95 89 0.49 0 16.49 clsd -9 33 on
15 4268 101 155 4.66 wot 0.64 87 2.01 43 95.6 94 0.49 0 17.41 clsd -2 33 on
16 4464 301 155 4.66 wot 0.63 88 2.04 42 95.9 98 0.49 0 16.33 clsd -4 34 on
17 4356 906 104 1.21 ct 0.63 88 2.06 42 86.3 99 0.5 0 2.61 clsd -7 48 off
18 3208 877 92 1.21 ct 0.62 89 1.84 48 95.6 100 0.49 0 0 open 11 46 off
19 2640 12 96 1.21 ct 0.61 89 1.68 50 95.6 96 0.49 0 0 open 11 45 off
20 2724 4 96 1.21 ct 0.6 90 1.61 52 95.6 93 0.49 0 0 open 11 45 off
21 2584 2 96 1.21 ct 0.6 90 1.55 53 95.6 91 0.49 0 0 open 11 45 off
22 2516 2 97 1.21 ct 0.59 90 1.52 55 94.4 89 0.49 0 0 open 11 45 off
23 2440 2 97 1.21 ct 0.59 91 1.49 55 91 87 0.49 0 0 open 11 45 off
24 2376 2 97 1.21 ct 0.59 91 1.48 55 87.6 85 0.49 0 0 open 11 45 off
25 2340 2 97 1.21 ct 0.59 91 1.46 56 83.9 83 0.49 0 0 open 11 44 off
Sorry I can't get this to paste properly, little hard to under stand, the top row are the headings and below are the specs

The MAP sensor seems to be changing frequencies.
I re-did you data below.
This may be a little more readable:
http://i54.photobucket.com/albums/g9...M/Scan9775.jpg

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Thanks subford, I screwed with it for 20 min. and gave up.
To take the map sensor out of the equation I ran a vacuum solenoid off a throttle switch that would dump vacuum to the map sensor as a test, pcm didn't care if it saw 160hz or 155hz still closed loop.
Is it possible the pcm is looking @ the correlation between speed and rpm to allow closed loop? it's a long shot but maybe I'll try disconnecting the speed sensor and making a pass.
Any other thoughts?

deleted deleted


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Hi guys, didn't mean to leave you hanging, went out on a little camping trip and just got back.
Tried a little test, I wired a circuit with the use of a resistor and a switch into my o2 sensor signal, @ full throttle under major load (8000 lbs toy hauler) climbing a steep grade, I pulled my o2 sensor signal down to .300 mv, result: stft 33, injector pulse 25ms,(tons of fuel) no real change in performance.
Also i managed to take a snap shot with my scaner under unmodified condition, the pcm does seem to switch from open loop to closed loop and back @ wot (no major change in performance, so maybe I'm barking up the wrong tree and the pcm forcing closed loop operation @ full throttle is not my performance issue ?
I will try and post my snap shot when I get it on excel.
You can feel the vehicle hit 3900 rpm and just hang there under load but seems to over come the flat spot (3900-4200 rpm) empty.

rpm 021mv map hz tps v tp mode ect v ect c iat v 1at c iac % kph evp v evr % inj pw loop stft spk adv can prge
-9 3872 660 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 16.56 clsd 1 28 on
-8 3896 210 147 4.65 wto 0.4 220 2.14 104 100 81 0.49 0 17.48 clsd 6 29 on
-7 3888 240 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 17.48 clsd 7 29 on
-6 3868 307 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 17.25 clsd 5 29 on
-5 3988 333 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 17.56 clsd 5 28 on
-4 3928 149 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 18.17 clsd 11 29 on
-3 3920 593 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 18.02 clsd 9 28 on
-2 3948 652 147 4.65 wot 0.4 220 2.13 104 100 81 0.49 0 16.79 clsd 1 30 on
-1 3908 320 147 4.65 wot 0.4 220 2.13 104 100 81 0.49 0 17.41 clsd 5 28 on
0 3988 521 147 4.65 wot 0.4 220 2.14 104 100 81 0.49 0 17.48 clsd 5 28 on
1 3900 625 147 4.65 wot 0.4 220 0.14 104 100 81 0.49 0 19.25 open 16 29 pn
2 3960 775 147 4.65 wot 0.39 220 2.13 104 100 81 0.49 0 19.48 open 16 29 on
3 3900 767 147 4.65 wot 0.39 220 2.31 104 100 81 0.49 0 19.32 open 16 29 on
4 3921 775 147 4.65 wot 0.4 220 2.12 104 100 81 0.49 0 19.09 open 16 29 on
5 3916 783 147 4.65 wot 0.4 220 2.12 106 100 81 0.49 0 19.4 open 16 28 on
6 3860 778 147 4.65 wot 0.4 220 2.1 106 100 81 0.49 0 19.55 open 16 29 on
7 3921 775 147 4.65 wot 0.4 220 2.11 106 100 81 0.49 0 19.4 open 16 29 on
8 3927 778 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 19.48 open 16 28 on
9 3884 767 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 19.25 open 16 28 on
10 3988 770 147 4.65 wot 0.4 220 2.1 106 100 81 0.49 0 19.48 open 16 29 on
11 4008 759 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 19.32 open 16 29 on
12 3952 770 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 19.48 open 16 29 on
13 3964 770 147 4.65 wot 0.39 220 2.09 106 100 81 0.48 0 19.25 open 16 28 on
14 3980 754 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 17.71 clsd 7 30 on
15 3952 558 147 4.65 wot 0.39 220 2.1 106 100 81 0.49 0 16.72 clsd 0 28 on
16 3880 135 147 4.65 wot 0.4 220 2.09 106 100 81 0.49 0 17.33 clsd 5 28 on
17 3876 261 147 4.65 wot 0.4 220 2.09 106 100 81 0.49 0 17.71 clsd 7 29 on
18 3908 470 147 4.65 wot 0.4 220 2.09 106 100 81 0.48 0 17.56 clsd 6 28 on
19 3912 647 147 4.65 wot 0.4 220 2.1 106 100 81 0.49 0 17.41 clsd 4 28 on
20 3900 237 147 4.65 wot 0.4 220 2.1 106 100 81 0.49 0 19.32 clsd 14 28 on
Sorry I can't get this to post properly, if you follow map sensor 147hz ? and it's like I Hit a brick wall kph 81 not 1 kph faster?
You can watch it cycle in and out of closed loop but no change in performance, if you look at my previous post @ wot no load my map sensor hit 155/156hz any idea's guys?

Fuel Control

this is what they say i am looking at it Got a V10 RV
Fuel Control - Fuel tables are modified for either better economy or all out performance. Depending on your needs is how most tables are set up. Most RV’s that go into Open Loop use this fuel table for its fueling requirements. Most 2v V10’s will not step up into Open Loop (power enrichment) at WOT and from the factory are calibrated to operate in Closed Loop which restrains power levels. By correcting this power enrichment function alone can increase power and toque from your 2V V10.

If I am reading that right, your last run is saying the ECT is 220*C, and the IAT is 104*C? Unless for some reason this run was in *F.

147 Hz would indicate the manifold was under a very slight vacuum, which is odd when WOT. Is your airfilter clean?

As I said in your other thread, the closed loop question has the simplest answer, and that is that the software revision in the scanner you are using has the sense of the flag reversed. In fact you are already in Open Loop at WOT, and as would be expected, you are only in Closed loop at very low manifold pressure.

So this is NOT your problem. Your issues are best dealt with by attaching a Moates Quarterhorse to your ECU, getting a copy of Binary Editor, removing the band aids that you have like that ACT resistor, and retuning your air flow calibration for the mods you have done. Speed Density systems do not compensate automatically for mods like yours. When your ECU understands the correct amount of air going into your engine, it will then inject the correct amount of fuel.

Please post all the numbers from the label on your ECU, especially the "Catch Code", the short code in a font 3 times bigger than the other numbers.

Sorry I did switch to *F the last run, Haven't tried the run up the mountain pass without an air cleaner but did empty 0-90k 2,3,4 gear and still felt that dead spot @ 3900 rpm, so I think that rules that out?
That 147hz translates to roughly 5 inches of vacuum @ wot is possible i'm geting a ventury effect from the air speed passing the map vacuum port @ the back of the upper intake?
Mjp, I agree with you that it's not a open/closed loop issue after that last run, no deference in vehicle speed or rpm regardless of open loop / closed loop operation.
But if it's a lack fuel issue why no performance gains when adding 33% fuel trim at wot with o2 sensor signal dragged down to 200mv? and why the 147 hz map signal @ wot? (never heard of the moates quarterhorse, I'll do some research on that)
Thanks, Dom
(p.s going up the same mountain pass this weekend, good time to prove any theories by experimenting keep it coming)