456 - Tach not working / Sluggish Throttle Response

The last few times the 456 got out, the tachometer is not working and the throttle response is very sluggish. Almost like a limp mode. No lights are present on the dash. After 4-5 miles, all of a sudden the tach springs into action and the car builds revs as normal.

Recent modifications include - Quicksilver cat bypass pipes, Braden center resonator bypass, BMC air filters.

Not sure what the issue is, but guessing it is something related to the recent changes. Any insights would be great!

 

Just recently did the Braden center resonator delete with straight pipes. I've had now issue like yours and can't see how those pipes would contribute to such. Nor with the air filters. You might wish to focus on the cat bypass and whether proper cold start data is making it to the ECU. Did that configuration change do anything to the O2 sensors? How about the cold start aux air pump?

 

Agreed, must be something to do with the cat bypass. Wondering if anyone here who has done a cat bypass has run into something similar. If the secondary air pump wasn't working properly, would my tach also not receive a signal?

 

If the tach is working intermittently, I would suspect one of the crank sensors or their wiring (Not sure about the 456, but the right bank (cylinders 1~6) crank sensor usually provides the signal for the tachometer). In the following diagram, the wiring seems to be relatively close to the cats.

The 1~6 crank sensor (18) is circled. The 7~12 crank sensor is (17)

Image Unavailable, Please Login

Being at the bottom of the engine, crank sensor connectors are often contaminated with oil from leaking seals, so it's possible that the problem is independent of the exhaust component change.

 

Just to clarify, the crank sensor for the 1~6 bank is found on the opposite side of the engine to the 1~6 bank. The 1~6 bank is on the right side of the car. The sensor is on the left side of the car.

 

Here's a message thread relating to a similar problem on a 550, but it turned out to be an engine ECU problem

https://www.ferrarichat.com/forum/threads/550-intermittent-limp-mode-asr-error-no-rpms.605253/#post-146762426

Hopefully, it's just a contiminated connector or faulty crank sensor, otherwise you're looking at big bucks.

 

Just noticed that on the Ferrari 355 with 2.7 Motronics ECUs, the tacho signal comes from the left bank. It may be the same on the 546. I don't have a wiring diagram for the 456 (non-M) car, so I can't confirm which crank sensor is used for the tachometer signal.

Do you know which ECUs you have on your car?

If you plan on replacing your own crank sensors, be sure to get the sensor gapping correct.

 

My car is a 95 so Motronic 2.7.

I read that 550 thread before posting, it was the only thread I could find that referenced no tach signal. Do you happen to know the part number for the LH crank sensor?

 

I keep forgetting the crank/rpm sensors are on the clutch housing on the V12 models...

https://www.ricambiamerica.com/car-diagrams/ferrari/v12/gt-group-2-2/456gt/clutch-controls-not-for-456-gta.html

If you believe the catalogue, there is only one sensor on the 2.7 car...

P/N 158729 or 164083
I don't know if it will be easy to find. Some sites may indicate they are in stock even if they aren't.

https://www.ferrariparts.co.uk/part/ferrari/164083?id=4509

If you can see a Bosch number on the sensor, I would do a Google search on it, and see if there is a replacement part.

If it is hard to find or parts suppliers want crazy prices, I would be doing basic checks on the sensor (check for damage/contamination, check the magnetism, see if you can get a voltage change by moving a piece of iron across the head, etc).

I'm not sure why it isn't throwing a Check Engine Light. Perhaps it's providing enough pulses to keep the ECU happy, but not to run the engine and tacho properly (???).

As mentioned in the other thread, you could try swapping the ECUs, but I don't know how hard that is on your car. (EDIT: seeing how hard it is to get to the sensor, it might be easier to swap the ECUs first).

Experts????

 

The parts suppliers indicate different part numbers for 2.7 / 5.2 cars, but also a supercession. Does anyone know if p/n 164083 will work on a 2.7 car? Image Unavailable, Please Login

 

Isn't that what the table is saying?

Ricambi shows something similar

https://www.ricambiamerica.com/164083-sensor.html

 

It was my understanding in the parts world that `superseded` generally means it is a direct, compatible replacement for the original. Otherwise, I don't see the point of adding the `Superseded by` note. The lack of information I'm finding regarding the sensor would lead me to believe they don't go bad often?

 

They often fail on F355's, but I haven't been on the 456/550 forum long enough to know how often they fail on the V12's.
They fail for a few reasons, including age. The permanent magnet in them simply loses its magnetism. Because they sometimes fail slowly, they can result in annoying intermittent problems. Because the F355 type sensors can be found on cheap Korean cars, it's one of the first things DIY-ers replace if they are having problems with no starts or other ignition problems. I have one on standby for my 355.

Unfortunately, you are getting no CELs and the problem is intermittent, so diagnosis is harder. Even if you had an oscilloscope, you might not be able to fault the sensor.

Your tachometer problem can be caused by
1) failed instrument internals
2) instrument power problems
3) wiring
4) engine ECU
5) crank sensor

It's unlikely that there is a power problem as power would affect other instrumentation.... unless there was something wrong with the power wire right at the back of the instrument.

If a 446/550 forum search is only showing the ECU as a cause, then perhaps you should try swapping those first.
If you took the car to a garage, they would probably change the sensor first as it would be the fastest/easiest/cheapest thing to change, but, of course, they can get under the car easily.

 

I can take it back to the shop who put the exhaust on. The problem at this point is finding p/n 158729 or the Bosch equivalent which I don't know the p/n for. The superseded part is available, but I don't know if that will work with Motronic 2.7. It would be nice to have a new sensor to bring to the shop to test.

 

Disregard the post above!

I thought that Eurospares page clarified the issue, but on further investigation, it shows both a left and right side sensor on the non-automatic non-M 456, so we are back to square one (not knowing if the left or right sensor provides tacho data)

https://www.eurospares.co.uk/parts/ferrari/456-gt-gta/transmission-pedals/clutch-controls-not-for-456-gta-31274

The sensor on the right side of the bellhousing (which feeds the left ECU) was part number 152262. It has now been replaced with 164082. This has Bosch part number 0261210152 and can probably be found more cheaply than the Ferrari part.

The sensor on the left side of the bellhousing (which feeds the right ECU) was part number 158729. It has now been replaced with 164083. Google shows no Bosch replacements for this sensor, so it must be uniquely Ferrari

 

Here is a cheaper source for the 164082 (right hand sensor)

https://www.summitracing.com/int/parts/bch-0261210152/applications?ibanner=SREPD2

 

oops... I meant disregard my message/s above, not Cory's.

 

This eBay listing would indicate the LH sensor (164083) Bosch # is 0232103006. But I still don't know if that works with Motronic 2.7.
Image Unavailable, Please Login

 

I had a similar problem on my 2.7 Motronic 456GT and it turned out to be a faulty connector to the ignition module mounted on the left hand air filter (which feeds the right bank, to add to the confusion). One of the wires didn't make full contact and the engine ran on 6 cylinders and tacho didn't work. Some fiddling with this connector solved it. But it took some time for me to find this.

 

Bizarre. Doesn't make sense at all. The ignition module wiring couldn't be further away from the crank sensors or exhaust system.

Assuming you mean the left hand filter in relation to the driver (looking forward), the ignition module mounted to the left hand filter would still power the left bank plugs. The crank sensor attached to the left hand ECU/ignition system would be on the right hand side of the bell housing. i.e. p/n 164082 according to Eurospares

https://www.eurospares.co.uk/search?partNumber=164082

Fortunately, that seems to be the easier/cheaper one to find

https://www.summitracing.com/int/parts/bch-0261210152/applications?ibanner=SREPD2

Looked like a good find until I saw this ad

https://www.ebay.com.au/p/249591412

It shows the sensor as being a cam sensor (Ferrari part 150866) with a short wiring harness. These are very easy to find with Google.

https://www.ebay.com/itm/BOSCH-Sensor-camshaft-position-0-232-103-006-/152697241045

I wouldn't trust that previous ad (showing two sensors, one of which looks like it has been repaired)

 

Some updates on this.

Ordered Bosch replacements for what I thought were the correct sensors based on the eBay listing I posted. The cam sensor obviously was wrong but the crank sensor with the Bosch # 0261210152 did seem to be correct.

Both of the crank sensors on the car looked original and a little worse for wear, likely just due to age. Also, both the left and right were the same Bosch p/n. The only different was one had a blue connector.

I had my shop use the better of the two looking original crank sensors and the one new one that fit (0261210152). The car started up great, tach worked and the car performed great.

I took it on a long drive, which was fantastic and parked it for a week or so while I ordered a second Bosch p/n 0261210152 to replace the original I still had in the car. I actually purchased the sensor from Gian Paolo here (https://www.affordablesupercar.com/post/using-cross-referenced-parts-ferrari-part-164083-l-h-side-angolar-speed-sensor) since I couldn't find any more Bosch parts readily available.

The sensor arrived in the mail and I drove the car to the shop today. No tach and sluggish performance again...

The shop swapped out the one original sensor that was still in the car for the new Bosch sensor and when they pulled it off the lift they said everything was great. When I got to the shop to drive her home, no tach and sluggish performance again!?!

I am now trying to figure out what could be causing this intermittent behavior. Sensors get plugged in, the car operates as normal and then a short while later (in this case a matter of hours) and at least one of the sensors is not working again??

 

My knowledge of these cars is one millionth of Ian’s experience, but I would be curious to know your operating voltage during warmup vs. when the tach drops. I am pretty sure my alternator/voltage regulator is going out and causing my system voltage to drop from 13.5v during warmup to a very low 11.2v in operation which has shown a number of very strange issues, including sluggish performance. I haven’t lost the tach since the ECU was repaired, so I am probably way off, but I am learning these cars do really weird things on low or dirty voltage.

 

Good to know. Thanks.

Ugh... that only leaves wiring and the ECU (for tacho problems). If you swap the ECUs, you might still get sluggish behaviour, but perhaps the tacho will work.

Of course, as niftyfivefifty says, low volts can also cause some bizarre problem. The ECUs should be able to operate with a relatively wide range of voltages, but who knows. Do you have a way of checking the voltage with the car on the move?

 

x2 on trying the ECU swap. And I used this OBDII bluetooth reader with an app on my phone to datalog voltage.