4.6 conversion problems

I hope so mate cos that's what I have got!

Have you managed to view any live fuel trims yet Bill ?

Rich - int it about time to order the tilt tray and get back to cider country ? Your team are missing you,they need company - at least I think thats why they keep phoning me.......

Not yet mate - Braemar is too nice.

Actually, leaving in the morning. I dread to think how many traffic jams we will encounter on the way back to Somerset. Hope I won't be the cause either...

Just done these, although they show min/max and averages they are fairly typical! This is using ScanXL.



Cheers

Bill

There we go, not going over 0.35 as the garage said is the lambda sensor voltage.

That means it is picking up a lean mixture, which it is shifting the short term fuel trims as positive as possible, to try and get the mixture correct

So why isn't it managing?

Blocked injectors?
Low fuel pressure?
Knackered fuel pump?
knackered regulator on LPG?

or is it poor combustion?
Air leak? - check all pipes and gaskets.

You could have a problem on the inlet or exhaust side, where the "lean" mixture is due to air being sucked into the exhaust manifold before the lambda sensor.

On the topic of SAI, has someone removed a blanking plug?

Does the LPG regulator have a vacuum line to the manifold that has perished?
Is the brake servo vacuum line OK, or even the brake servo?

Does this scan hardware allow you to see the data changing as the engine is running? This is just a snapshot - Like hitting the pause button - but you need to check the Bank A and Bank B sensors are alternating.

Jon may see something in these numbers though. One bank looks different from the other, but either way, they all look like they are switching. My concern is the MAF readings don't look very good.

Bank 1 is lower than bank 2, which could mean that an air leak is nearer to that bank, or on the inlet manifold - head in the V for that bank.

Looking at the voltages, 0.3V is almost stoichiometric and 0.08V is about 20% lean.

If the fuel trims are having to adjust 20% - about the maximum possible, it looks like a lot of excess air is getting in somewhere.

As WSLR says about the MAF readings, an airleak will make the MAF readings lower than normal at each engine speed.

The voltages won't cycle if it's not going closed loop, it will be a monitoring output only.

This is because you need the ECU to change the fueling as the voltage changes, i.e. a feedback mechanism.

If this is an air leak, an exhaust gas analyser would show this, without relying on the lambda sensor data.

There are many ways to skin a cat.

On checking the brake servo, disconnect the pipe and blank it off, tape or rubber bung, but do the testing when stationary. I wouldn't want you to have an accident.

If you are really lean, you might start to get the odd misfire.

Is the idle control valve closed more than normal? Some engines have the valve half open to give some leeway to increase/decrease the engine speed. The duty cycle would be around 50% but it depends on the valve. If there is a large airleak, then the valve would probably be closed completely, instead of half-open.

Ignore the LPG, I am not running LPG at the moment and anyway the whole system has been overhauled with new new parts, by a specialist.

The 4.6 fitted is a non SAI engine so no need for blanking plugs and the SAI fault is a red herring LR have told me themselves that it has no effect on fuelling.

Given the fact it has plenty of "go" I doubt poor fuel supply but always worth investigating.

WSLR They are not a snapshot but high/low and average readings, but I take your point I have an 8 minute sequence saved, it shows hovering mostly around 0.035, occasionally dropping to 0 and occasionally rising to as high as .08, so yes they are switching but intermittently.

Do we know which bank is which?

Bank 1 = left hand side
Bank 2 = right hand side (drivers side in the UK)

This is looking at the front of the car as far as I know.

Cheers.

I take it back about the blanking plug for the SAI, I assume you are talking about the one in the plenum manifold area Microcat is not clear as to where it goes and if so I am not sure now!

There are different manifolds for the V8, so it depends on which one you have.

Ask the engine supplier / builder, they should know if it is an SAI one, if and how it was blanked off, and if any blanking was necessary.

If there is a constant sized hole, then the flow through it will be purely dependent on the manifold vacuum. When you get to higher revs, the size of the hole may be less significant, thus the engine would work well at high power, high revs, WOT. At high vacuum - about 2,000 rpm would be the worst rev range.

You might hear a hissing sound, but that would be dependent on where it is.

But as I said before, there could be other reasons for an air leak.

The plenum ect is from the old engine which had SAI. However having been out with a torch for a poke around (yes daft I know, but it's quite nice out), how about the throttle body assembly not tightened onto the the manifold being the problem, top two bolts were hand loose not checked the bottom ones yet!

Exactly as I thought,neither upstream sensor is switching,so its driving the fuel trims fully positive to try to get the to switch up to 0.8v - rich.Raving man is starting to make some sense now,why isnt it happening ? Remember its starting off closed loop and only going open loop when the ecu realises it cant get the oxy sensors to switch up rich to start cycling.
Bill can you please get me two readings form live data,first a maf reading at idle,hot engine ,all loads off.Second a maf reading at 3000rpm,hot engine running free,all loads off.It is looking like a low maf reading,so either the air leak or the maf itself.
A good trick to try with the live data running is to partially block off the inlet to the maf with it disconnected.With the engine idling use a piece of wood or similar to restrict the air going into the maf,this will speed up the air,fooling the maf.You should see the airflow go up and the oxy sensors starting to cycle.Be careful how you do it though.Its a worthwhile test to do as it proves then that the ecu and fuel system can properly go closed loop and fuel the engine correctly.
Now we are getting there.

Cheers will do so tonight when I get in.

Bill

eightinavee said:

Raving man is starting to make some sense now,why isnt it happening ?

......A good trick to try with the live data running is to partially block off the inlet to the maf with it disconnected.With the engine idling use a piece of wood or similar to restrict the air going into the maf,this will speed up the air,fooling the maf.You should see the airflow go up and the oxy sensors starting to cycle.Be careful how you do it though.Its a worthwhile test to do as it proves then that the ecu and fuel system can properly go closed loop and fuel the engine correctly.
Now we are getting there.

Click to expand...

Me not making sense?

This last test doesn't make any sense to me at all, but I accept I can be dim, a little slow, but please be patient.

Why not find the airleak? Loose throttle bodies and manifolds are an obvious culprit.

Let's open the throttle / idle control and restrict the flow before the MAF.
What happens? - MAF comes under vacuum - not normal, but air flow will increase because it is at a lower density (lower pressure), but what will happen to the cooling of the MAF (hot wire) or deflection of a vane type MAF.

The hot wire will not be cooled so well with the lower air density.
I can't say about the vane type MAF except the mass of air per second will not be any different. How much would the kinetic energy of the air change though?

What would happen to the temperature of the inducted air?

It's an interesting trick if eightinavee would actually explain the theory behind it.