[Lemi]

I'm having trouble removing the rear exhaust manifold in my 156GTA.

I followed the 'Alfa_002's' post on ausalfa.com.au and took everything off, plenum, a/c pipes, heat shield, o2 sensor... like he did in his 147 GTA. But, I still cannot get the rear manifold out.

Could it be that the 156GTA has less space between the engine and firewall than 147GTA. Is there any other trick that I perhaps missed.

Might have to undo engine mounts and tilt the engine forward... I hope not.

No turing back now

Lemi

 

[edward]

Why you taking it off?

 

[gotcha]

A friend of mine has done it from the bottom on a 156 GTA by dropping the subframe and removing everything in the way. I have some pictures, but I haven't been present personally so I don't know exactly what was removed...

 

[newalfisti]

The biggest issue that you will have removing anything on a car is that it would have been subject to the crap weather conditions compared to lets say Australia.

 

[Lemi]

I am in Australia
I'm replacing the manifolds with euro 2 (pre-cat) ones.

Should the rear head cover come off?

 

[edward]

That all sounds very interesting - are they from a GTV?

 

[Dan Chan]

Lemi what is the rest of your system? I am thinking of going a similar route and would like to know if you think it worth while. Pros & Cons.

 

[Lemi]

I'm replacing the manifolds and front pipes only. The manifolds are front 164 24V and rear 156 v6. Front pipes are not equal length, when compared with each other, but when mated to manifolds they make the secondaries (which they are) equal length, if you know what I mean.

I will have a full write up when its all done.

Lemi

 

[silvervalver]

Very interested in the write up as I would be looking to go down this route in the summer

 

[Lemi]

Manifold is off. Had to unbolt the rear engine mount and tilt the engine forward. It took about 15 min max, and it came out pretty easy then.

Lemi

 

[silvervalver]

In terms of hours, for an experienced mechanic what would you say it would take to change the manifolds - assuming they are aware of all these little tricks?

 

[edward]

That's interesting as I have a pair of 164 24v manifolds sat on the shelf waiting for a warm day. Lemi can I ask which front pipes you used?

 

[Lemi]

Silvervalver, approx 4-5 hours max.


The front pipes are custom made!

 

[Lemi]

It all done now, but I'm not happy at all.

First of all, engine light came on as soon as I pressed the accelerator pedal. I tried resetting it but it came back again.

Secondly, there is a little bit of annoying sound coming from under the car. I guess where the new front pipes are.

Thirdly, I don't think I gained anything in terms of performance. On contrary, it feels as if I lost a little torque. Could this be due to the "Motor Control System Failure" ???

 

[GTAlfaromeo]

Did you put the lambda sensors in the new manifolds?

 

[MattyB]

ALFA001 has the same strange noise too - judging by a recent post he hasn't resolved it yet. Have a look here:

ausalfa.com • View topic - 147 GTA de-cat manifolds + full exhaust

 

[Alexandrus]

It all done now, but I'm not happy at all.

First of all, engine light came on as soon as I pressed the accelerator pedal. I tried resetting it but it came back again.

Secondly, there is a little bit of annoying sound coming from under the car. I guess where the new front pipes are.

Thirdly, I don't think I gained anything in terms of performance. On contrary, it feels as if I lost a little torque. Could this be due to the "Motor Control System Failure" ???

Yeap, MSCF can cause limp mode, which means lower performance. But why did the MSCF appear in the first place ? Lambdas all in order ?

 

[Lemi]

All O2 sensors are plugged in.

The rear ones are untouched. The front-rear one had to be extended, and the front-front one is from 147 GTA.
I think one of the sensors are faulty.

Lemi

 

[chris_155v6]

Got the awful noise in the 155 v6 after I fitted a custom exhaust and decat, fitted a more restrictive backbox and it went away, recovered some of the low end torque.
Backpressure is important, free flow may benefit performance on the higher end of the rpm range but that is at the expense of low end torque.

Here is a vid of the engine when the exhaust had the awful noise, listen when the revs drop:

YouTube - Alfa Romeo 155 v6 Noise free rev

Sound of the engine with more restrictive backbox:

YouTube - Alfa Romeo 155 v6 Test Run


Surely the engine light has something to do with the lambda sensors picking up a reading that the ecu reads as out of normal range. Measure the reading and compare it to the one on the workshop manuals, if there is more than a 10% difference then that's the problem.

3 ideas to solve it if that is the case:

1) Remap.
2) Fit some kind of resistor to alter the output signal and get the reading closer to the stock parameters.
3) Get a lambda probe that sends a different signal, closer to stock parameters.

Hope you get it sorted and if I can help you with anything just ask!

 

[Lemi]

Good News !

I instytalled the Alfadiag again, cleared the fault codes, and they are NOT back.

This is what Alfadiag found:

Fault Code: PO141

Failed Component Code: Lambda Sensor Heater Bank 1 (Post Cat)
Fault Symptom: No Signal
Warning Lamp Status: Warning Lamp Illuminated
Fault Test State: Test not complete for this Error.
Fault Code Storage State: Error Present at time of request
Event Count: 40 count
Environmental Condition One: Engine Speed: 1080 rpm
Environmental Condition Two: Relative Load: 39 %
Environmental Condition Three: Engine Coolant Temp: 28.5 °C
Environmental Condition Four: Air Temp: 32.25 °C
Environmental Condition Five: Throttle Valve Angle: 0 °
Environmental Condition Six: Battery Voltage: 11.28 volts


Fault Code: PO 136

Failed Component Code: Lambda Sensor Bank 1 (Post Cat)
Fault Symptom: No Signal
Warning Lamp Status: Warning Lamp Illuminated
Fault Test State: Test not complete for this Error.
Fault Code Storage State: Error Present at time of request
Event Count: 39 count
Environmental Condition One: Engine Speed: 720 rpm
Environmental Condition Two: Relative Load: 24 %
Environmental Condition Three: Engine Coolant Temp: 87.75 °C
Environmental Condition Four: Air Temp: 34.5 °C
Environmental Condition Five: Throttle Valve Angle: 0 °
Environmental Condition Six: Battery Voltage: 13.95 volts


It seems like it was related to the rear lambda sensors. Maybe they got dirty when I first took them out and the dirt/oil burned off now.... who knows...

The engine was defenetly retarded by those faults, it now runs much better than last night. It terms of performance, compared to before this project, I am yet to draw a conclusion. It is defenetly better, but how much I don't know. So far I'm not impressed but I'm not devestated either. I'll report back about this.

The noise I was talking about seems to an exhaust leak. I'll get it checked later.

So yeah, its been a good day so far.