Ferrari 412. Extreme Exhaust Temperature Difference Between Left and Right Bank

Hello,

after a full top-end and injection system (metering heads, fuel pump, etc.) rebuild, I have been trying to dial in the air/fuel mixture via the CO/air-by pass/throttle plate.

I noticed that the right side bank exhaust is MUCH hotter (my placing my hand by the exhaust tip pipes) and louder than the left bank.

There are no misfires, I revs up to 5000/6000 without issue, starts right up, no black smoke, etc.

The car has no catalytic converter and is Euro spec (no frequency valve/o2 sensors).

Any idea what could be causing this?

 

Either the second k-jet is totally out of place or the ignition is wrong in the "cold" side (i would check that one first).

 

The ignition on the 412 is controlled electronically, no adjustment is possible - advance/retard is done by the ECU.

I will go over the K-jet again and start with the "baseline" setting - 1/2 turn "CCW" when fuel starts to rise at the port as per the Ferrari/Bosch manual and go from there.

 

Can the engine run on only 1 bank? If I completely close one side of the air bypass, the engine shuts off.

 

I do not know the 412 well, but you do have two ignition modules, so one of these modules could be setup wrongly.

I had a similar problem when reassembling my single ignition 400i . The car was basically running only on 6 cylinders. My mechanic spotted there was an issue as he noticed the difference of temperature. Took us quite a bit of search in this forum to identify the underlying reason: we had forgotten that the firing order was not like the distributor order (as the two fingers in the distributor are 180° apart).

You should check that the magnetic pickups are properly installed and I then check each bank with a timing light (I think there are marks for each bank in the 412 flywheel).

 

There is only one large ECU, that fires the ignition coils.

Both banks are running, exhaust coming out both sides, and both banks getting hot - but there is a significant difference in temperature and sound.

It is also running smooth now that I have re-adjusted the throttle plates.

 

You do still have two coils & two distributors, so one bank can go wrong while the other keeps going. Just check both banks with a timing lamp: if memory serves me well, cylinder 1 & 7 should be -30° apart, so if you do not have the proper marks on the flywheel, you can offset a "smart timing" lamp by that amount and connect its clamp to the ignition wire of cylinder 7.

 

If you have two distributors I’d check the timing on both banks just to see how it looks. Another possibility is cam shaft timing. Has there always been a temp difference? How is the tension on the timing chain? Just a few things to think about.

 

The ignition timing is set by the 2 magnetic pickups on the flywheel, and the distributors are fixed - nothing to adjust.

I replaced my timing chain and all the bearings, the marks on the camshafts and flywheel line up perfectly.

 

UPDATE: I removed one of the injector lines, kept the pump running and could not get any fuel ro rise from the injector port (by adjusting the CO screw).

Conclusion: it is running VERY lean, barely any combustion, hence lack of temp and sound.

I then connected the injector and moved the metering air flow plate, and a very weak spray came out the injector.

There is good fuel flow coming from the pump, but it seems I am getting very low pressure to the injectors.

Next stop: measure pump pressure and system pressure.



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360, you asked, "Can the engine run on only 1 bank? If I completely close one side of the air bypass, the engine shuts off."

In my early days with my 400i, I would lose one fuel pump due to the poor stock wiring (now revised). Motor would just barely idle on one bank and I was able to drive at 20-40 mph to get to a good stopping point. One exhaust completely cold so it was clear which pump was not working.
Ken

 

Thank you Ken. As stated in my previous post, it seems I have found the reason. Now I need to figure out as to why.

 

Ok, so I want to first measure "system" pressure - as that the is pressure that is fed to the injectors.

From the manual, the system pressure is measured in the same place as the "control" pressure, but with the valve going to the WUR closed off?

The "system" pressure should be the one from pump into the center of the metering head, which then goes past the slits...

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It's the pressure as defined by the pressure regulator that's inside the fuel distributor. You adjust the pressure with shims. Excess pressure from the pump returns directly to the tank, so it's one of the horizontal "bolt" between fuel input a' return line

 

Thanks - the question is where/how to measure the system pressure.

I also noticed that the two spline connector at the fuel pump (in the trunk) was much hotter than the one that is working correctly, so it seems that pump is drawing too much current.

 

You measure between the distributor and the WUR. The wur is a "second stage" of pressure regulation that converts the system pressure" (injector pressure) down to the control pressure (which allows to keep the metering plate at a given position given a certain amount lf airflow).

So pressure that gets out of the metering head is decreased from system pressure down to control pressure thanks to the wur that lets escape some pressure (to the return line that goes back to the tank).

If you block the wur, control pressure = system pressure. Hence the need for a valve which allows to shut down the wur. When valve is open you can see "control pressure" when it's closed you can see "system pressure"

I hope this is clear

 

So this means that the top of the metering head (marked in yellow) receives "system" pressure from the main supply, and then is bled out (red arrow) depending on the WUR parameters (temperature, vacuum).

So I should first measure:

1. The supply (850ccm3 per 30 sec) at the return port
2. Measure the pressure coming directly from the pump
3. Measure system pressure on the metering head (control plunger)

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No need to check the pump pressure: if you do have 850cc at the return line, it means, the pump was able to push through the pressure regulator and even send a 850cc excess.

So you only measure system and control pressure on the wur inlet.

Did you clean the tanks? Maybe you have some crap that found its way to the WUR inlet and blocked it (=blocked inlet = higher control pressure = way to lean).

 

Great, thank you. Yes, thanks were fully disassembled and all the rubber parts inside replaced.

The control pressure should not affect the plunger movement at idle (as the position of the plunger is set by the CO screw).

What I find very strange is the no matter how much I turn the CO screw (with the engine off, and the pump running), no fuel moves up the port - unlike the other bank that is running correctly.

Also, the air flow plate of the metering head feels "soft"/normal, if the control pressure is very high I would feel a lot of resistance.

 

So if I am getting very low pressure at idle, it is either the pump/fuel supply or the primary pressure regulator.

But the hot wires at the pump are suspect - will measure flow and pressure.

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Check the pressure first. (even if you are correct about resistance with high control pressure).

If the pressure looks appropriate, you can use a the 3mm key that you use for CO adjustment, and instead of adjusting the CO, you just use it to pull the CO screw so as to lift the metering plate. To make myself perfectly clear you do not turn the CO screw, but you apply a gentle lateral pressure so as to get enough grip to move the metering plate.

I know it does not sound obvious but it is actually easy to pull the metering plate this way, and test the flow without disassembling everything.

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(Allen key is in orange)

If you manage to pull the key by 1cm, you should hear the injector "hissing".

Do not forget to remove the spark plugs in order not to hydrolock your engine.

 

I think the hot connections on the pump are telling you that you have the very common problem of low voltage to that pump and it is running slow or unable to generate pressure. I would take some alligator clips and long wire and run a direct line from battery to that pump and see if you have a difference.
Ken

 

Great suggestion, thank you. Will try and post results.

 

Did you measure the flow on the return line (i.e after the pressure regulator inside the metering head)? If you measured the flow on the input line (before the metering head) this gives you no information on the condition of the pump and/or electrical circuit.

If you do have flow before the metering head, but not on the return line, I would assume Ken is right.

 

Will do that today. Watch this space