Shock and Awe - 3200 Throttle Issues.

[Roberts Aerospace]

I'm not sure how often I need to say this, but, it's not the throttle body! I have collected a whole load of data from this car with several different throttle bodies fitted including a nearly new unit that I use for reference. The data coming out of the ECU is always the same.

The problem is that for 12 seconds from a hot start, the ECU "MIN. TARGET REVOLUTIONS" parameter is about 2700RPM. For a cold start it is about 1300RPM - which is normal. Any other car has a hot start target of about 1100RPM. The engine is doing exactly what it is told to do by the ECU, which is to run at nearly 3000RPM for 12 seconds.

What needs to be found is why the ECU has decided to instruct the engine to run at higher than usual RPM, there's nothing in the data to suggest why, and I cannot think of any circumstances why someone writing the ECU software would require the engine to run at that speed at start up without triggering some sort of "out of acceptable range" error for one parameter or another.

Mike.

 

[davy83]

This is one of those weird problems where some other problem forces the ECU to do this to the engine. It must require a number of other things that the ECU senses to be present to make it do this in the first place? So the real question is under what conditions would this be the right thing to do? very cold start? could it be that it thinks the car is very cold, or perhaps its a comfort thing and it does it when it thinks the inside of the cabin is really hot, and it wants to kick on the AC with enthusiasm right at the start? it could be a work round for oil pressure, or maybe it detects a sticking butterfly and opens it up to stop it sticking, but then why 12 seconds? I wonder if there is a connection to vacuum in the plenum? perhaps it increases the revs to get a certain level of vacuum? The ECU does sense vacuum pressure i think? is it possible it think the battery is low and its trying to get a stronger voltage on the battery, i know my car starts and idles much better when the battery has been on the conditioner rather than a cold start outside? Its a weird one for sure.

 

[Contigo]

Yep over revving has to be related to air leak you would think, the project 3200 was idling a little erratic even with a contactless TB and we decided to investigare. Rubber seal from an injector and some loose screws in the Plenum caused it. It wasn't as high as 3000 but it was erratic and sometimes random.

 

[boomerang]

It is clear to me that the TB can be ruled out.
It is also clear, that if you would try to close the butterfly by hand, you would feel the TB " pushing back", simply because the Ecu tells it to.
Again, Mike made very clear, that the ecu is ASKING for that higher rpm; air leacks would ALWAYS cause "highish" rpm, not only in these very special cicumstances.
There are two possibilities i think:
1) Someting in the periferie of the engine, a wrong treshold regarding voltage / temperature?, or something related to the automatic gearbox/ AC system must make the ecu decide to command a higher idle rpm.
2) Some weird Ecu problem.
Not that uncommon, stumbeled into a reconditioned ecu more than once.

As a next step, i would exchange the Ecu/immobilizer set first, just for testing.
Or just the ecu, using the emergency starting procedure when the code card of that ecu is available.

Very intriguing problem.

 

[allandwf]

How about a chaff, or short in loom somewhere. Possibly where they are bundled at the rear of each bank. You could try pulling at them while starting the car and try and replicate the fault.

 

[Almichie]

How about a chaff, or short in loom somewhere. Possibly where they are bundled at the rear of each bank. You could try pulling at them while starting the car and try and replicate the fault.

This situation might bring intermittent problems but this looks like a problem that is repeatable every time. As mentioned previously it can only be a faulty ECU or something that it is seeing (an input) elsewhere causing it.

Without knowing the way it was/is programmed it is impossible to comment. The only really way to diagnose this to to review the wiring diagram to see what the ECU looks at then link out that input (if a digital input) or bypass/replace the sensor (analogue input, eg temperature or pressure) until the fault no longer exists.

I'm happy to review a wiring diagram if anyone has one?

 

[urquattrogus]

Yes that confirms my thoughts. ECU issue, wiring issue, or one of the ECU inputs reading erratically.

Mike assures me that he has ruled all of these out.

 

[Contigo]

The only other thing which feeds the input to the ECU dictating rpm is the Pedal pot. I've seen two other cars with pedal pot issues doing exactly the same thing as your car which as I said Emblem fixed by plugging in at the pedal end.

 

[urquattrogus]

Well, I did about 1500 miles to Scotland and back.

I have continued issues, will probably send the car to Emblem or someone else to have a look at it, but it's a good few hours away.

I have the continued occasional high revs on hot startup (the original problem), but now some additional throttle issues.

All of these issues are inter-mittant, but have tended to occur after a good few miles on the motorway etc

The throttle sticks on lightly and causes the car to accelerate gently itself. A throttle reset helps this temporarily.

Interestingly, pulling the pedal up from below forcibly with your shoe often stops the car accelerating itself ( I haven't yet looked at the spring/pedal)

I have a CEL light and error codes P1665 and P1226 logged (read by ODB reader)

It has also gone into limp mode twice, with revs limited to about 3000 rpm and only part throttle allowed.

The car has had it's brake pedal switch and brake diode changed.

So - a string of things that people have hinted at - hard to see the wood from the trees.

Before my trip I spent an hour reading the workshop manual and made a list of all input's to the ECU, seeing if some could be ruled out.

At the time there were no error codes logged and I wondered if it was possible a sensor was giving bad readings, but some that were still in the range of plausibility (eg a temp sender shorts or resistance spikes at a certain temperature and gives a false reading. The air temp sender resistance was out of the recommended range, so I fitted a new genuine Magnetti Marelli one - made no difference, clutching at straws a bit with that one.

Anyway, the most obvious one is the pedal pot and sticking my foot under it helps (but doesn't cure that hot start revs problem I don't think)

Contigo pointed to another thread with the same problem - it this an SD2 pedal pot reset thing, or just likely to be a mechanical spring/tight spot in the pedal linkage?

My patience is wearing a bit thin now!

Otherwise my trip was a dream and the car was great on those twisty Scottish highland roads.

 

[Contigo]

Well, I did about 1500 miles to Scotland and back.

I have continued issues, will probably send the car to Emblem or someone else to have a look at it, but it's a good few hours away.

I have the continued occasional high revs on hot startup (the original problem), but now some additional throttle issues.

All of these issues are inter-mittant, but have tended to occur after a good few miles on the motorway etc

The throttle sticks on lightly and causes the car to accelerate gently itself. A throttle reset helps this temporarily.

Interestingly, pulling the pedal up from below forcibly with your shoe often stops the car accelerating itself ( I haven't yet looked at the spring/pedal)

I have a CEL light and error codes P1665 and P1226 logged (read by ODB reader)

It has also gone into limp mode twice, with revs limited to about 3000 rpm and only part throttle allowed.

The car has had it's brake pedal switch and brake diode changed.

So - a string of things that people have hinted at - hard to see the wood from the trees.

Before my trip I spent an hour reading the workshop manual and made a list of all input's to the ECU, seeing if some could be ruled out.

At the time there were no error codes logged and I wondered if it was possible a sensor was giving bad readings, but some that were still in the range of plausibility (eg a temp sender shorts or resistance spikes at a certain temperature and gives a false reading. The air temp sender resistance was out of the recommended range, so I fitted a new genuine Magnetti Marelli one - made no difference, clutching at straws a bit with that one.

Anyway, the most obvious one is the pedal pot and sticking my foot under it helps (but doesn't cure that hot start revs problem I don't think)

Contigo pointed to another thread with the same problem - it this an SD2 pedal pot reset thing, or just likely to be a mechanical spring/tight spot in the pedal linkage?

My patience is wearing a bit thin now!

Otherwise my trip was a dream and the car was great on those twisty Scottish highland roads.

Yep I had a year of it mate! I feel your pain, believe me Myles at Emblem will sort it out for you.

 

[urquattrogus]

Thanks, car booked into Emblem for Mid September - they are in demand!

Gives me plenty of time to go through and double check for silly issues before hand.

 

[Contigo]

Check the throttle pedal end stop for rest position, check there is no carpet fouling the rest point and also check the voltage at the pedal during idle. It should be between 350-700mv, anything more and it will result in high idle. I'd put £20 on this is a pedal pot issue caused by miscalibration or the pedal rest position itself.

 

[urquattrogus]

Well I'm pretty shocked and dissapointed to find that the wiring to the pedal pot has been altered.



It wasn't like this before, there was certainly no scotch lock on the pedal pot cable ( I know this as I fitted a Davy pedal pot)

The scotch lock joins the yello and white wires together.

It looks like the grey wires have been removed and another two wires have been run independantly.

Bodge.

 

[CatmanV2]

Who did that, then?

C

 

[urquattrogus]

I don't like to point fingers, but Maserati Shed. Must be. They had it for a month, and it came back like this.

It was at Grimaldi about a month prior, but that was for other work mostly, but they did try a different pedal pot, I looked in the area to check what they had done then and did not see any scotch locks.

Even if it went to maserati shed with this (which I'm 95 percent sure it didnt) then surely they would have noticed/found this?)

I suppose you can argue that running the two grey wires seperately was a chance to try and isolate things from the main loom - they are put in there correctly.

 

[Contigo]

The two grey wires are like that on all cars don't worry about that. The scotch block has been put in to take an average of both circuits, it is usually done when a pedal pot is on its way out but should by no means be left in and on an auto car is a no no.

 

[urquattrogus]

So the two grey wires are correct? Why are there two spare ones that were taped up/ look as if they should be in the connector?

The two that are connected at the moment go to earth, but the other two spares don't when tested.

Not pleased there is a scotch lock to stop the safety feature of the other potentiometer. (There are two within the pot assembly yes?) I have heard about these being connected etc

 

[Contigo]

The two grey ones that are taped up are the ones you don't need to worry about. What other two are you referring to in your picture? This is what mine looked like when I got it obviously this is not at the pedal connection but the one which feeds the ECU.

 

[urquattrogus]

Mine appear to be the reverse of your photo.

The stray pair are wrapped from the factory with the others that go from the connector.

The two that go into my connector at the moment are the two on the rhs of the footwell that run seperately.

 

[Contigo]

Let me check tomorrow on the auto car which is completely standard mate and then try to understand this mess. The main thing to do now is buzz out the voltages which will be harder now that there is an average voltage being taken.

If it were me I would disconnect the Blue scotch block and put it back to standard then measure the white cable at rest then the yellow cable. Do the same for both at full throttle.

Remember that there were two circuits for a fail safe reason and at the moment you don't have that which means your car could go into WOT at any time!