Very lean on full throttle

[himizoli]

Hi

We have a 1978 930 turbo
We have checked the follows
- fuel delivery rate 1240CC/30sec
- System pressure 5.8bar
- cold control pressure 1.8Bar
- Warm control pressure 3.6Bar
- The Full throttle enrichment 2.9bar
- we have also checked intake for leakage, but nothing

We have installed a WBO instrument
When we drive the car everything ok AFR 13-14 if not full throttle.
On full throttle AFR goes high the instrument show until 16 and no power at all....
even on 2000RPM we floor it we have a problem

[smurfbus]

Could be big leak or bad misfire from overly rich. What happens if you slowly accelerate to higher rpms and them stomp on the pedal? Onboost is normal to be rich and after500 it usually gets lean.

[T77911S]

i don't know what this would do to the AFR's but check the rubber elbow that goes from the AFM to the turbo. if it is soft it will collapse killing the airflow to the turbo. it would also stop air from coming in which "MAY" make it appear lean.

[smurfbus]

Soft elbow brings the headbanger moment, cant be missed

[himizoli]

Checked the rubber until the turbo and the was a small leak.
Now if i press down the throttle the AFR around 14.5
The full theottle are 16-17 and rising....

can it be a spark problem? one of the spark plug is more dirty...more black

[T77911S]

can you squeeze it,
is it soft.
it should be pretty hard.

[himizoli]

Checked the rubber elbow and it is hard.
Now I think it is more like ignition problem on boost, I will change the spark plugs

[smurfbus]

Plug wires, rotor and distributor cap might be an issue too.

[himizoli]

Change the spark plugs, rotor, cap and the cables.
But nothing has changes.
IF I press slowly the throttle the AFR goes up 15-16 at 4000Rpm and after over 17...
IF I press quickly it has some bang like backfire and AFR over 17

I think the "Full throttle enrichment " does not work....
How can I test is when the car is running ?

Or any idea?

[RarlyL8]

Fuel delivery rate is off spec low. Verify pumps are getting 12V minimum, when the engine is running. If good change the fuel filter and see where you are.

[himizoli]

Checked the fuel delivery rate when the car is idling 1 liter/20sec which is good
Only the system pressure is low a bit 5.8bar I will adjust it to 6.5 bar tomorrow ( need some shim)

I have also found a broken ground cable in the ignition system.
Now I put everything together.
The good news is the when full throttle no bang at all
The bad new is the Afr is still +17
If I floor it 4th gear around 1500rpm the AFR is 14 until 3000 and then going to lean.

I will make a vacuum into the cabin so I can some emulate the "full throttle enrichment"

[T77911S]

you nee to check the fuel flow OUT of the FD. I think it is around 1500ml per 30 sec. don't hold me to it.

are you sure the WUR is dropping the CP when on boost.
does your timing retard under boost.

[himizoli]

I have rechecked the fuel delivery rare and it is 1550ml/sec
System pressure is adjusted to 6.5bar
Warm control pressure is 3.5bar
I have found a small leakage on the WUR house, The sandwich plate leaking,when the Full throttle is activated
I will fix it

[himizoli]

I have made a fuel line to the passenger side. So I made measurement when I drive the car. Warm control pressure is 3.6bar and the full throttle is also working 2.9Bar
Now I suspect the fuel delivery rate is low under pressure or the fuel injector valves....

any idea?

[T77911S]

I doubt it.
you have 1500ml per spec right.

has the FD been rebuilt or how is its condition.

what turbo are you running.

does the sensor plate have full movement

[himizoli]

Originally Posted by T77911S

I doubt it.
you have 1500ml per spec right.

has the FD been rebuilt or how is its condition.

what turbo are you running.

does the sensor plate have full movement

Yes I have 1520ml/30 sec fuel delivery

The FD has not rebuild yet... Just bought the car and rebuild the engine, it was sitting for some years.
It has K27 7200 and SC cam 1 bar spring now

How should I check the sensor plate have full movement? Should the pump running?

Thanks for helping!

[T77911S]

I would not run the pump when checking the sensor plate as that will dump a LOT of fuel into the engine.
just make sure it moves freely, no binding. it should be very lose with the pumps off.

I had issues with my euro FD even after being rebuilt twice. it would run lean at cruise speeds, like around 17 if I set the idle to 13 or so.

I would have to set my idle AFR to around 12.5 to get 15 at cruise,
my WOT was fine from what I remember. I spent all my time on the cruise being way too lean.

I put on a modified aluminum head that removed the FV and it ran perfect.

just something to think about

[RarlyL8]

Your '78 930 should have the Euro CIS -037 FD and -054 WUR if USA or -112 WUR if Euro model.
What you are describing sounds like fuel starvation, such as a weak fuel pump. Typically the engine will run on the rich side at idle cruise and quickly go lean when under load. The rich idle can be compensated for with the mixture adjustment screw, masking the issue. If you can measure fuel pressure and AFR while at cruise and then when the engine is under load but not boost this will expose the issue if it is fuel delivery.

[himizoli]

I have measured the system pressure and is 6.5Bar on I was cruising without boost.

I also made a test with the injectors on full throttle on the FD plate and the fuel rate is 175cc/min. Is this should be 220cc/min?
I have 009 injectors

The injector opening pressure is 2.7bar



I have managed to get a aluminium FD , I will exchange it andsee whats happens

[1979-930]

I had the same issue as Brian mentioned, except it would go so lean I would get a misfire. It ended up being the front pump going bad.
Raw suggested testing pressures with disabling each pump by pulling the relay. Try testing pressures that way and see if you have a big pressure drop between pumps.