A friend of mine suggested that I back off the TPS sensor a little so that ECM doesnt go in WOT mode when the pedal is floored, therefore being able to compensate the A/F ratio by actually reading O2 sensor data.

With the mods I got, the engine leans out at WOT. The 02 is in the 800mV range. Does anybody know what the threshold is for the TPS ? Is it 96% or something like that when the ECM goes into open loop mode ?

[This message has been edited by Blade (edited September 15, 2000).]

 

Depending on the year, and my 92 factory manual, the ECM reads the TPS voltage and "sets" TPS voltage as "0" and uses the delta from "0" as reference voltage from idle to WOT. For example running with the stock TPS, setting idle voltage anywhere from .5-.7V doesn't make any initial changes in throttle response, because the ecm has set this as a reference "0" point. Conversley, while scanning my car to resolve some ecm problems, 3.9-4.1 volts @ WOT still had ecm saying throttle position was 100% wide open.

I know this doesn't directly answer your TPS threshhold question, but just letting you know your car may still think its WOT even by backing down the TPS voltage at WOT (like with a slotted TPS sensor, like the 88 vette one I'm using).

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KevinP92Z
92 Z28 383 SLP cam,SLP headers,SLP 2ontheLeft,Trick Flow TW heads & pistons,Edelbrock base,Accel SuperRam,52mmTB,Scat Crank & forged ConnRods,MSD 6AL,SLP convertor,Baer 13/12" Track,Moser axles,Hotchkis,Genuine GM 3.42s,SLP HD Torsen,17x9" chrome SS rims
96T/A w/SLP Ram Air,SLP 2ontheLeft, Bilsteins, Baer, Hotchkis, Genuine GM, Torsen
76 4X4 Blazer 400TPI project

[This message has been edited by KevinP92Z (edited September 15, 2000).]

 

Yeah and Diacom doesnt show anything. Even at WOT Diacom still shows Closed Loop Mode as "on". So it's kinda hard to watch and see when the ECM switches modes. Weird... I guess I just need a custom chip and get it over with.

 

one thing your forgetting is that the ecm adjusts the mixture to be 14.7:1 at part throttle, which is the most efficient mixture for cruising around


Way way way too lean for WOT

 

thats the whole point of having a TPS to tell the ecm you have WOT, so it can go into "Power Enrichment" mode where alot more fuel is added and more timing

 

The SD TPI cars use what was mentioned above...MAF TPI cars see WOT somewhere around 4.5 volts...I don't recall....but the point mde is what Pablo is referring to...your car won't run as well at WOT if the ECM does not read WOT.

If all you get is 800mvs and you're at WOT, then an adjustable fuel pressure regulator may be a good idea to bump up the pressure and get a little more fuel in there.

 

Well I have an AFPR set at 50 psi. If I increase the pressure performance drops. I'm thinking of dropping it down to 46 and go from there :/

 

Blade without any real background on your car it is hard to make suggestions. But I personally went through this until I slapped a fp gauge on the windshield and went for a drive. At approximately 4K rpms my fpr would drop 10 psi and then regain that when I shift into the next gear. Got a new 255 lph pump and that solved that. My afpr really didn't help me either. Car pulls alot stronger and I think I have managed to toast my first U-joint.

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1991 5.7L Z28 - gutted air boxes, K&Ns, airfoil, ported plenum, relocated MAT, accel TPI base, accel 300+ ignition, accel cap&rotor, homemade AFPR, derale fan switch, vette servo ,flowmaster exhaust, torque conv. lock-up switch, and fresh 255/50/16 Dunlop sp800s. More to come!

 

Well here's my car... Look at my sig. So far the car pulled a best of 14.6 at 93mph with a 2.0 60 foot. This was in Las Vegas, around 95 degrees temp and at 4000 feet altitude. This was also with my messed up engine running on almost 7 cylinders. A wrist pin walked, scratched my cylinder wall causing very high crankcase pressure sending oil up my intake. Anyway... here's my mods.


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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

The ecm goes into PE mode (WOT) at around 50% TPS opening in most apps. The 02 sensor cannot read AFR's beyond 14.7 accurately. This is why the ECm ignores the 02 at WOT. Look at Diacom, the closed loop reads On, but learn mode turns off when you go to WOT.

 

hehehe, i like this one...
Increasing the fuel pressure will make you run richer. If you run worse with more fuel, you're not lean.
The only way this would vaguely make sense is if your low end died with high fuel pressure, but you still lean out on the top due to a failing pump.
...ed

 

My 1988 GTA reads .50v at idle and 4.35v when the throttle is floored. The scan tool shows that the O2 sensor is still reading and adjusting the A/F ratio. In fact, when I activate the nitrous the fuel injector pulse width goes from 10ms to about 6ms, trying to lean out, due to the extra fuel added by the NOS wet system. Does this sound right? I am concerned my TPS is not indicating WOT.

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1988 GTA, 350; rebuilt, mostly stock; 700R4; rebuilt with Red Alto clutches and a Trans Go shift kit. Next mod ... Nitrous!

 

Blade: what size injectors are you running? With that cam, you definitely need the 22 lb size or larger. I mention this because some of the 19 lb injectors are known to be relatively weak, and can hesitate to open if the delivered fuel pressure is too high. Still, 50 psi shouldn't be too high.