Having trouble with 3200GT throttle

[cmb]

I'm looking for a little help from the collective knowledge of all of you.

I am putting back together my 3200GT that has been off the road for about 3 years. The engine bay is mostly back together - the only things missing are most of the turbo / intercooler plumbing because I'm waiting on parts.

The glitch I have is that the throttle does very little. The car fires up fine, but when you put your foot on the accelerator, it only goes up to about 1500 RPM, but that's it. I measured the yellow and white wires and the voltages are in the expected range. I checked the throttle body and the butterfly opens and closes fine - so it doesn't appear to be stuck or anything. I've also checked the various fuses and relays - they all look fine.

Could it be just that the turbo boost control system isn't fully connected with the various hoses off the car? I should have the turbo outlet hoses in about a week and can put all the rest of the plumbing back on - so will then have all the various other hoses / sensors wired correctly.

Does anyone have any idea on what to look at next? Is there an easy way to bench test the throttle body or measure the inputs to it?

(Picture of engine that is starting to look nice, has lots of missing bits, and doesn't rev over 1500rpm attached)

And yes @Lozzer I should wait for the parts to arrive before firing it up, but I'm impatient

thanks guys

...cmb

 

[cmb]

Having just read the end of this thread: https://www.sportsmaserati.com/index.php?threads/throttle-playing-up.39089/ it looks like I'm having an identical problem to JimBlob

 

[davy83]

I presume you are getting an engine error light? It sounds like its in limp home mode, and this can be either the throttle body or the pedal position sensor. If you could read the error codes it might help, as these can indicate where the problem is. Especially if you have had it all apart as there may be more than one issue here. Have you tried the pedal sensor calibration to see if that helps?

 

[cmb]

Hey,

I'm getting no warning lights. Just no accellerator. I don't think it's limp home mode - because the accelerator does almost nothing. Max revs is about 1500. Yes - I did the pedal sensor calibration - no help.

 

[davy83]

its hard to determine exactly what is going on here. I am wondering why you are not seeing an error? does the engine go from idle to 1500 rpm when you press the pedal or does it just sit at 1500 rpm once started? Can you see visually if the flap is opening when you press the accelerator? Also can you check if the whistling noise the throttle body makes when its running stops as soon as you turn on the ignition? If the whistling stops immediately then it has failed its own power up test and its the throttle body thats the problem.

 

[cmb]

Hi Davy... thanks for the help.

I'll pull the hoses off the front of the throttle body and take a look at the butterfly in the morning and let you know. It starts fine, goes to about 1200 revs. when you hit the accelerator it goes to about 1500 but that's about it. As to the whistling - I'll listen for that tomorrow too and see what it tells me.

I think my new turbo outlet hoses are arriving tomorrow so I'll be able to put the rest of the parts back on (not sure how much it'll help)

 

[davy83]

When starting and idling the turbos are not doing much so unlikely reassembling the turbos will make much difference. Have you checked the pedal sensor outputs are within limits? If its got moved for some reason and its outside the limits no amount of calibrating will help?

 

[cmb]

yup - was exactly in the limits... about 400 on idle and a little over 3000 on full throttle

 

[davy83]

yup - was exactly in the limits... about 400 on idle and a little over 3000 on full throttle

Worth a try! also note this does not mean your pedal sensor is ok. The most common failure mode is the two outputs read a different value to each other. They need to be within 0.015 volts of each other at start up or it will throw up an error and be in limp home mode. The carbon tracks wear and the position of the sweeper arm moves a little and its dead.
Worth also checking if the throttle body flap moves and also if that wistling noise continues after power up.

 

[James3200GTA]

So you're turbo plumbing is not fully connected yet? Could be map sensors are fooled. The computer determines the TB response based on gaspedal input but also the pressure inside the manifold and near the air filters. Apparently the computer can calculate air mass flow from the pressure readings.

Im no expert, but if there is no vacuum in the manifold vs. outside airpressure then the car may get false inputs and not react or go into limp mode. If you have an OBD reader with live data tracking, look up the vacuum values. When you floor it, pressure in the manual should drop, at idle it's more or less the same as outside pressure if I remember correctly.

 

[boomerang]

Worth a try! also note this does not mean your pedal sensor is ok. The most common failure mode is the two outputs read a different value to each other. They need to be within 0.015 volts of each other at start up or it will throw up an error and be in limp home mode. The carbon tracks wear and the position of the sweeper arm moves a little and its dead.
Worth also checking if the throttle body flap moves and also if that wistling noise continues after power up.

But when they differ more then 0.015v, you would get limp mode and check engine light.

 

[cmb]

Hi @davy83 & @boomerang I tried connecting white and yellow - didn't make any difference so guessing it's not a delta between the two tracks issue. The throttle body doesn't make much more than a hum when on - no whistle at all. I let the car get warm and in neutral, pressing the accelerator increases revs to 2000rpm, but that's it - nothing higher. So somethign is getting some type of signal and doing something - just not as expected.

I've included a picture of the throttle body. Is this an aftermarket contactless mod? Would it make any difference to anything?

I'll try a throttle reset again - just incase I didn't get it right last time, but feels like that's not the issue.

 

[davy83]

The throttle body should wistle as soon as the ignition is switched on. @If that whistling stops as soon as you power it up then the throttle body has a problem and is failing its start up test. you can see the correct response here

. The fact you get some response to the accelerator pedal suggests this is not happening however. If the throttle body fails its start up test it will sit in a single position producing a little over idle rpm and will not respond to anything. The contactless position sensor on your throttle body means some one has worked on it. And depending on who that is could well be the source of your problem, it's not uncommon for these sensors to be swapped out and no attempt made to try and set it up properly (because this is quite tricky) and as a result it does not work
As well as joining the white and yellow wires did you check the voltage the pedal sensor was generating was inside the spec?

 

[boomerang]

Once I got a converted unit in, that had a serious problem.
Someone had made a connection between the two outputs of the sensor......
If you do that, check engine light could stay out, while a mechanical problem in the TB could be on hand.

 

[cmb]

Hey guys,

Before I pulled it apart to paint the car, everything was working, so I assume the contactless sensor was configured properly at some point.

I don't get anything sounding like whistling at any stage including prior to ignition or immediately after. I did check the yellow and white wires right at the pedal and they are perfectly in range - both about 400 to 3200.

I can confirm the white and yellow are most likely not connected to each other, because at idle they had a very minor difference in voltage.

Is there any test you can run on the throttle body? Is there any check I could do on the inputs to see it is getting power and/or a signal correctly?

I did check the fly by wire fuse / relay and both looked fine. I also checked the engine ecu and everything appears nicely connected, but that was the extent of it.

My guess (if I had to) is a gremlin in the wiring only because the pedal and throttle body didn't really get touched while the car was off the road.

I got a little busy last week, but should have time to try solve this in the coming days.

thanks again for the help.

 

[davy83]

ok the two outputs on the pedal sensor have to be within 0.015v of each other at idle or it will fail. So check that small difference it might be important. There are no easy tests on the throttle body, it is controlled directly from the ECU via CANBUS and so to do anything with it you need a CANBUS interrogator to talk to it. There are no meaningfull measurements on the interface wires really. The throttle body goes through two sets of start up tests, it first does a self test, and if this one fails it shuts off the power to the motor and the whistling stops. Secondly the ECU has an initialisation test where it checks angles and currents are within its internally stored limits, if this fails the engine light comes on and you are in limp home mode, but the throttle body still whistles! if it does nto whistle at all even briefly at power on perhaps the electronics have failed? It should very briefly apply power to the motor when switched on and if this does not happen then something is broken.
Most of the throttle bodies are starting to suffer from the internal rotor magnets failing which causes friction on the rotor which you can feel with your hands. This can often get a lot worse if the throttle body is left sitting for a while (just as you have done with the painting?). I have tried to capture this here

this might be worth checking too.

 

[boomerang]

Agree, but when the rotor can not rotate (enough), this would also make the check engine light pop up.

 

[boomerang]

If your car is an automatic, you could check if the butterfly is completely open at full throttle, with the help of someone who pushes the pedal, ignition on, engine NOT running.