3200 throttle issue driving me nuts

[rexpontius]

Hi Guys,

Hope you can help with the following:

My 3200 GT (1999) starts in limp-home mode with CEL on, everytime after sitting for a few hours.
Diagnosis with Unidiag throws a "P0221 - Throttle/Petal Position Sensor/Switch 'B' Circuit Range/Performance Problem"

All the obvious resets do not work (recalibration pedal pot with ignition on for 2 mins, connecting white and yellow wires in parallel, etc.)
Also I opened up the throttle body and checked the soldering joins of the Sacer sensor, which look fine and give plausible voltages (1.15 volts in default butterfly opening, going up to 4.8 with full open throttle)

I replaced the drive-by-wire relay, to no avail....

The only way to get it going is to let the car idle a few minutes (5-10 min or so), shut it off for a few mins, and then restart it again.
The car then drives without any issues at all, and no error codes in Unidiag.

Will try measuring voltages at the white and yellow pedal wires soon, but any other input is very much appreciated.

Cheers
rex

 

[Contigo]

1.15V is too high at idle. You need to measure the voltage on both circuits (white and yellow) at both idle and WOT (Wide open Throttle).

Idle should be 350-700mv
WOT should be 3.0V and over.

Don't join the two wires (white to yellow) as this is overriding the failsafe for WOT to occur. It's fine for testing/diagnosis but I wouldn't recommend it for everyday use.

 

[rexpontius]

Hi Contigo,

The voltage I am referring to is the voltage of the Sacer sensor at the throttle body.
It has 3 pins: ground, 5v+ and sensor voltage.

Have not measured the pedal pot yet, but will certainly do so shortly.

Cheers
rex

 

[Contigo]

I've never measured it at the sensor at the Throttle body end, if it is a Sacer sensor then it has been rebuilt to contactless at some point and there could well be a calibration issue with the TB. Measure the output voltages at the pedal first and take it from there.

 

[davy83]

i would recommend measuring the voltage on the yellow and white wires first off. if the idle voltage is over or under the limits (.35 to .65v) then yes it will fail every time you switch it on. Not sure why running it for a while would change it. also i would make sure after joining the white and yellow wires (and yes its not a great idea to leave it like this) you run the pedal sensor calibration again as this will change it and the change to the calibration will also make it fail at start up.
when running the sensor calibration make sure you leave the calibration conditions a little longer than the book says, and try it a couple of times it does not always work. in case you don't have it, put car in neutral, turn on ignition, do not start engine, and leave it not touching the pedal for at least 2 minutes, try 2 mins and 10 seconds. then ignition off, and again in neutral switch on the ignition and push the pedal to the floor, holding it very steady for at least 10 seconds, try 12 to 15 seconds. then ignition off. If you change the white and yellow wires you need to redo this calibration again as it wont like it.

 

[rexpontius]

Thanks Davy,

Will check the pedal voltages this weekend (after the car has sat for a few hours).
Took the car with me to work today, and drove it approx 80 miles, without a single problem.

So maybe the car will fix itself, after all the car is equipped with S.H.I.T (Self Healing Italian Technology) ;-)

Cheers
rex

 

[alfatwo]

Thanks Davy,

Will check the pedal voltages this weekend (after the car has sat for a few hours).
Took the car with me to work today, and drove it approx 80 miles, without a single problem.

So maybe the car will fix itself, after all the car is equipped with S.H.I.T (Self Healing Italian Technology) ;-)

Cheers
rex

Don't believe everything you read rex, there lots of questionable German made stuff in there too!

Dave

 

[rexpontius]

Haha, I was only joking ;-) I have two german cars as well, and they also have their quirks and niggles.

With regard to the limp-home/throttle issue, it still exists..... Fired it up this morning and voila CEL and barely any throttle response.
Very strange, drove the car whole day yesterday without any issues.

I am suspecting the rebuilt throttle body being out of calibration.
Does anyone have reference voltages for the sensor with closed, open and default positions of the butterfly?

Cheers
Rex

 

[allandwf]

Haha, I was only joking ;-) I have two german cars as well, and they also have their quirks and niggles.

With regard to the limp-home/throttle issue, it still exists..... Fired it up this morning and voila CEL and barely any throttle response.
Very strange, drove the car whole day yesterday without any issues.

I am suspecting the rebuilt throttle body being out of calibration.
Does anyone have reference voltages for the sensor with closed, open and default positions of the butterfly?

Cheers
Rex

Possibly the pedal pot that. Mine would do it if I inadvertently stood on it while I was waiting for all the lights to go out prior to starting.

 

[rexpontius]

OK guys, I think i am a little closer to finding the culprit...

Measured the voltage of both the pedal pots, and they were both 400 mV, so well within spec.
Then I checked again, if the car would work after warming up a few minutes, and after 10 minutes all was good again.

What I noticed during these checks, is that in the morning the throttle body makes no sound at all, whereas it produces a clearly audible 'click' and a light continuous humming sound when everything is warmed up.

So the question is now, is it supposed to always 'hum' with the ignition on, even after a few hours of sitting?
Would any of you guys be so kind to check if your throttly bodies 'hum' in the morning?

Procedure to check is really simple.
1. Let the car sit overnight.
2. Turn on ignition and NOT start the car
3. Pop the hood and listen for humming sound

Your help is much appreciated.

Cheers
rex

 

[boomerang]

Yes, it has to hum always.
I think you have the culprit, it's the TB.
Could be the internal electronic module, since I had some during the years that caused intermittent failures.

 

[rexpontius]

Many thank for the quick feedback Boomerang!

 

[rexpontius]

Well guys, the saga continues....

Today I bit the bullet and bought a new Throttlebody. It came from a 99 3200 GT, and had the Contact-less modification.
Bolted it on this evening and turned on ignition. Fortunately the TB clicked and made a nice humming sound.
Continued to start the car and voila, no CEL light.

Jumped in and wanted to drive away...... uh oh... no pedal response.
After pressing the pedal also the CEL popped back on.... ****!...

Tried the reset (both 2 min without touching the pedal, and the full throttle reset). No result....
Disconnected the battery for 15 mins, no result...

The car runs, and keeps running without CEL as long as I do not touch the accelerator. If I do, it kicks into limp-home and throws error P0221 which seems to be a generic error regarding anything TB related.

The old TB is on its way to Boomerang, hope he can fix it

Hope anyone here has any ideas on next steps....

 

[rexpontius]

Anyone ? Hope I do not have two fried ETMs.....

 

[Contigo]

How do you know that the TB you have sourced is OK? Too many unknowns really. Check all wiring and pedal return position plus clean the connections at both ends.

 

[rexpontius]

Wiring and pedal pot is double-checked, voltages measure OK too.

Cannot be 100% sure the 'new' TB is OK, but was converted to contactless and said to be coming from good running car.
Only difference I can tell between the old and new TB is, the year/month stamp. My existing one was dated 00/01 whereas the 'new' one is dated some month in 98.

Could it be that the 'new' TB has older software in it?

Cheers

 

[davy83]

could be old code in the TB not compatible with the ECU, one of the changes made in 2000/2001 was they tinkered with the driveability of the car and this would involve the TB and the ECU, i would guess. I am not sure how often we have seen people trying to swap an older TB into a newer car, i think Maserati shed and David Askew refurbish the customers unit, so don't disturb the firmware in the unit (if it has any?). also a new unit would be compatible with older cars you would expect, but older in a newer car, maybe not.

 

[rexpontius]

OK guys, I made a little progress this evening.

I compared the TB I bought with the one in the car, and indeed they are different. The shape and connectors are exactly the same, but for instance the partno's on the right Marelli caps are different (see pics).
This leads me to believe that the one I bought will probably never work with the ECU in my car......

Because the my original TB was broken anyhow, I decided to open it up before sending it to boomerang to see if I could find anything wrong with is.
The internal bits of the ECU actually look pretty impressive with very very thin silver connectors.
I also rigged up a small test set-up to be able to power the thing up without having to start the car.

What I noticed is that the original TB (the one I opened up) actually did produce the humming sound, it just does not 'click' (the click is actually the butterfly closing probably to set the 'zero' position).
When feeling the butterfly I could feel the motor trying to move the butterfly, but just very very weakly.

I suspect there is a faulty soldering join or connection inside the ECU, which also could explain why it does work when the car is warmed up (everything expands every so slightly).
Unfortunately my basic electronics skills end here.
Does anyone here have an idea which components to check on the circuit board?

 

[CatmanV2]

Surely the butterfly is driven by a stepper motor, so it's not just a power connector it needs. Are you sure there are just two connectors?

(Wiki indicates I may be smoking crack with this belief)

Does the butterfly move freely with the ignition off?

C

 

[rexpontius]

Nope, the butterfly motor is just a regular motor with two connections (they are behind the small oblong shaped cap)
Off course it moves freely.
Also checked with separate powersupply, no problems there.

It is really in the power supply from the ECU --> Motor