156 JTS miss firing fix ( blowing smoke ) - Alfa Romeo Forum
You are currently unregistered, register for more features.    
Thread Tools Search this Thread
(Post Link) post #1 of 1 Old 04-04-13 Thread Starter
Status: -
Join Date: Dec 2011
Location: Australia
County: New South Wales
Posts: 9

Member car:


Well Happy 156 JTS miss firing fix ( blowing smoke )

Alfa 156 JTS Missing fault.


To analyse the effects of voltage drops to the head and therefore the resulting attached electronic servo and or control systems associated with the engine management systems. In this document a specific electrical reason will be presented to outline a range of faults that are and can be caused by a significant reduction of the available current to the aforementioned components.

In the case of this particular engine there has been significant and systematic failures relating to the firing system and fuel control system in the form of transient and by result persistent inconsistencies in the frequency / duty cycle of the components.
One of the key indicators is the fact that the miss firing when the AC clutch is engaged, at first this seems to be a function of the load placed on the engine however it does introduce a significant current load to engage that type of solenoid. My best guess for that would be somewhere in the order of 5- 8 amps.
The second key indicator is the engine running very rough and the missing gets worse as more fuel is applied to the cylinder
Thirdly there is the production of copious amounts of smoke from the exhaust system.

Functionality of the components.
Bosch has in effect produced a system that is reliant on a given voltage to allow optimum performance and comes in the form of embedded electronic components, such as the coil pack. This unit has 4 wires feeding it

Positive supply =~12V
Signal -
Signal +
*** citation needed **

The latter forming a differential pair to eliminate commonly induced currents though means of a high common mode rejection ratio.
This is achieved through only responding to the difference in voltage between the differential pair. With the main output voltage being formed from the back EMF in the falling edge of the input pulse.

Fuel injector is in fact operated by the fuel pressure with the resulting impulses being used to close off the fuel supply.

Each component as explained previously requires a specific voltage and the resulting current to achieve optimum performance however in this case they have not been able to operate within these parameters and the reason falls squarely back on Ohms Law.

In the circuit there are around 10 current consuming components requiring what is in effect a zero voltage drop to ground however if these are floating there are a huge range on problems that will occur when requiring ~10 amps to operate.
In this case we will look at the mathematics and the attached electronics to present a practical reasoning for the ultimate failures.

there is a 0.25 ohm resistance in the ground it will present a voltage drop of:

E= IxR
as we know the current to be around 10 Amps, this equates to a voltage drop of

E= 10 x 0.25
E= 2.5 Volts
If we then subtract that from the supply voltage

E final = 9.5 Volts available to the injectors and coils to operate, which is in fact below the nominal operating point.

Secondly the total current needed to run the system increases at any specific point proportionally to the voltage drop, thus you have a system that has insufficient electrical charge to function.

Similarly the Fuel delivery system is heavily effected in the same way as it requires large inrush currents to close off the flow of petrol entering the cylinder.
In the case of the JTS system it provides fuel pressures at very high levels and thus needs a high powered solenoid system to seal it.
As the fuel cannot be shut off the system continues to flood the cylinder well after the end of the duty cycle, consequently it effects the stoichiometric mixing rations as well as diluting the Oil lining on the cylinder wall. One can easily imagine the result of the latter; Large amounts of blue and black smoke coming from the tail pipe.
Finally this will also cause the sensors to drift wildly, in particular the O2 and Temp.


DO NOT rely on Alfa Romeo to supply a good ground plane, the have never been able to deliver this in the past, so why should they start now.

Connect a ground wire DIRECTLY from the ground point of the coil packs, located on the lower left cam housing to the -VE of the battery and your JTS will magically start running like a Swiss watch and stop bellowing vast amounts of smoke

Gwyllym Suter
M.A. Sci... Blah Blah Blah

One hopes this will solve a Lot of JTS problems, it sure made my care come back from certain death

The same text is attached as a pdf for those who want to keep it in their files.
Happy Alfaring
gsuter is offline  

Go Back   Alfa Romeo Forum > Supported Alfa Romeo Models > Technical & Vehicle Assistance > Alfa 147, 156 & GT

156 , blowing , firing , fix , jts , miss , smoke

Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

For the best viewing experience please update your browser to Google Chrome