Thread: tps questions ?????? D1 V8 3.5

I do not pretend to know the exact intricacies of the 14CUX however AFAIK the prime determiner of ongoing mixture is the MAF at steady throttle, but it is reactive ie responds to increased air flow AFTER the event
The TPS is a predictive indicator to the ECU of mixture requirement . I have likened it to an accelerator pump only to be flamed . However I can say that if the TPS is faulty there always will be a stutter on resuming throttle after overrun. I have experienced this on a number of cars.

However the TPS controls a number of things sometimes in conjunction with other sensors.
In a 14CUX the TPS tells the ECU if under 0.49 volts that the foot is off the accelerator. This triggers overrun cutoff of the injectors at 1500RPM in conjuction with a signal from the VSS that the car is moving. I guess it also gives a signal to the ECU which causes the IAC to select a value for idle.Eg the ECU when stopped will aim for 700RPM and manipulate the IAC to target that while if a VSS signal is detected it will aim for 1100 or suchlike to smooth the Auto 2-1 gearchange on stopping.

If the voltage exceeds a set value (which I never been able to determine) the ECU will go into open loop if O2 sensors are fitted , and over a certain value which I think is about 4.2 volts the ECU will regard as full throttle and the mixture richened.

I personally have found no difference in performance of the engine in experiments where I increased the TPS values except when idle exceeded 0.49 volts , then it disabled the overrun cutoff.

However I guess there are arguments that if the idle voltage is very low , there is probably a slight delay as the voltage will take longer to get to 0.49 when the ECU knows it is no longer at idle.
I must admit that subjectively when the idle voltage is quite high, and mine is at 0.45 the car feels "snappier" as if I have adjusted the accelerator pump on a carby car.But the effect is small.
The workshop manual stipulates any voltage between AFAIR 0.12 and 0.49 as within spec.
Regards Philip A
BTW, My instincts tell me that many people who see improvement to engine running by changeing the TPS idle value are moving the TPS from a worn area to a less worn area and seeing an improvement when the real answer is a new TPS.

Originally Posted by scruffy

Hi to All Knowledgeable Persons, My querie is what effect does a lower or higher TPS reading have on 1. fuel economy, 2. running of the vehicle, eg, a lower reading of say 2.5 instead of 3.2 or a higher reading of 4.5. Remembering, that as the TPS is adjusted either way, it sends a certain signal to the computer to allow the computer to make adjustments to the fuel. My limited understanding is that if the TPS is set at, say, 2.8 instead of ideally 3.2, then the computer would not be injecting as much fuel because it would think that the throttle was not opened as far as it was. Would this cause a lean burn???
Similary, with the MAF, how would a lower/higher setting affect the running, performance and economy of the vehicle??? Waiting in anticipation for a reply from the mentally unchallanged and more knowledgeable than myself. Thanks all. Bob

Start with building a broadband O2 sensor reader (Jaycar?) and work out what your mixtures are. Then your adjustments may be checked as you go along. Working blind is a waste of time. Or adapt the ECU to read a LR O2 sensor, it can be done, others on the forum have done it.

Re the MAF.
Adjustement to the MAF bias voltage will affect the steady state mixture up until the TPS voltage says WOT, then the ECU will defult to an internal map.
The factory MAF setting of around 1.1volts is supposed to result in a CO reading of 0.5 % which is lean and designed to meet Australian emission standards of thetime. Have a look on the RH rocker cover AFAIR for the values. Also the timing is relatively retarded for the same purpose although in this case to reduce Nox.

So if you want a richer mixture at all steady state cruise points which probably uses more fuel you can richen the MAF bias. In my case the cruise mixture was always rich at about 13.8 so you may find neglible benefits

As Bee utey suggests you should use a wide band sensor to see what it is doing, or the very least a Jaycar mixture sensor on a narrow band sensor, although there is really no real way on a 14CUX to change performance parameters controllably without chipping it or fitting an interceptor to change the ECU inputs.
However having said all that, you will only get minor gains at best, as the majority of gains on a 14CUX are made from manipulating the advance curve of the Dizzy. An interceptor such as Haltech or Unichip takes over the vacuum advance function enabling much more part throttle advance and a little more full throttle advance.
To be crude you can tune the engine for the max advance it can take by adding marks up to 30degrees on the crank and running the engine up to 4000RPM and then adding advance until you are at 30 to 32degrees total advance( or maybe even 34 on a 3.5). You may then find you have pinging and so back off in 1degree increments. This usually equates to about 10-13 static advance.
DISCLAIMER_ seeing you ask these questions it suggests that you are not all that conversant with how injection works. perhaps you should study the subject by reading for example the Bosch Fuel Injection & Engine Management book ISBN0-8376-0300-5. It is quite old now but covers LE Jetronic which is what 14CUX is based on.
Also I take no responsibility for any damage you do by advancing the engine as suggested.
Regards Philip A