Exhaust lambda value too high

OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
Exhaust leak would be a cause. A Lambda of 1.7 means your running lean, assuming the exhaust isn't leaking. 1.7 is pretty darn high though, any chance that was 1.07? If not, it;s gotta be an exhaust leak because you'd have other signs of a lean running engine.
I did a test today at another workshop. It is indeed 1.7 lambda, not 1.07. All other gas component results are normal.
But engine is running well and rather smoothly.
Exhaust leak?
 

TRS666

New Member
Joined
Nov 11, 2021
Messages
71
Reaction score
66
Location
Gothenburg Sweden
I did a test today at another workshop. It is indeed 1.7 lambda, not 1.07. All other gas component results are normal.
But engine is running well and rather smoothly.
Exhaust leak?
On last inspection here in Sweden my lambda was also 1.7 and of course it did not pass. Car ran OK. 2 days after the engine just quit running, no fuel pressure. So the fuel pump was bad and it just did not get enough fuel, hence running lean -> high lambda value. I have a 2001 4.6 so not same but check fuel pressure. Not on Mustang but as they measure with a probe from tailpipe even a small exhaust leak can give high lambda values, on my sons 380hp Volvo S60 we had to glue all axhaust connections to get it pass inspection. The test probe must also sit as deep as possible in the tailpape so it does not drav outside air.
 

Mustang5L5

Active Member
Joined
Aug 1, 2023
Messages
734
Reaction score
782
1.7 still seems VERY high, and not triggering any sort of codes for a rich condition, however that makes sense a little with EEC-IV.

Do they check both tailpipes, or just 1? I'd check for exhaust leak. Cold start the engine and jam two socks into the tailpipes and listen carefully for a "tick tick tick" sound due to the increase in exhaust pressure on a suspected leak point.
 

TRS666

New Member
Joined
Nov 11, 2021
Messages
71
Reaction score
66
Location
Gothenburg Sweden
1.7 still seems VERY high, and not triggering any sort of codes for a rich condition, however that makes sense a little with EEC-IV.

Do they check both tailpipes, or just 1? I'd check for exhaust leak. Cold start the engine and jam two socks into the tailpipes and listen carefully for a "tick tick tick" sound due to the increase in exhaust pressure on a suspected leak point.
Lambda over 1.03 here in Sweden anyhow means lean, it is a calculated value on HC, CO2 and CO. I got no check engine lamp on mine. Here they take only one random tailpipe.
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
1.7 still seems VERY high, and not triggering any sort of codes for a rich condition, however that makes sense a little with EEC-IV.

Do they check both tailpipes, or just 1? I'd check for exhaust leak. Cold start the engine and jam two socks into the tailpipes and listen carefully for a "tick tick tick" sound due to the increase in exhaust pressure on a suspected leak point.
They checked both tailpipes, same result. Since no codes and same result both pipes, I guess (hope) it will be an exhaust leak betwenn the o2 sensor and the H-pipe. On Friday I will check the exhaust on a lift. Tonight I will check the fuel pressure.
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
Lambda over 1.03 here in Sweden anyhow means lean, it is a calculated value on HC, CO2 and CO. I got no check engine lamp on mine. Here they take only one random tailpipe.
Same here in Austria, 1,03 is the upper limit. Probably an EU regulation.
 

shovel

Active Member
Joined
Jan 4, 2023
Messages
309
Reaction score
266
have you inspected your EGR tube for cracks? it's stainless steel and brittle.
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
Did a fuel pressure test today.
33 psi with key on engine off
31 psi with cold engine idling
Little bit of revving did not move the needle much, stayed around 30 psi
40 psi with fuel pressure regulator vacuum off
Turning engine off, after 5 minutes it bled down to 28 psi.

What do you think? According to Haynes it should be between 30-40 idling and 40-50 without regulator.
20240529_223240.jpg
 

shovel

Active Member
Joined
Jan 4, 2023
Messages
309
Reaction score
266
remember that the fuel pressure regulator's job is to maintain fuel pressure across the injector not relative to atmospheric. if the pressure inside the intake manifold is 0.3bar that's about 4psi absolute which means fuel pressure relative to atmosphere would be about 30psi but fuel pressure across the injector is 40psi.

Fuel delivery rate changes very little with just <5psi in either direction, without looking it up I believe fuel pressure at sea level with the vac. hose disconnected should be 43psi which is 3bar. If that amount is correct then the amount with the vac hose will vary with vacuum and measuring it is of little use, except if you end up with much less psi under load/WOT (clogged filter or failing pump or damaged fuel hose limiting delivery rate) because manifold vacuum should be minimum at WOT.
 

TRS666

New Member
Joined
Nov 11, 2021
Messages
71
Reaction score
66
Location
Gothenburg Sweden
Did a fuel pressure test today.
33 psi with key on engine off
31 psi with cold engine idling
Little bit of revving did not move the needle much, stayed around 30 psi
40 psi with fuel pressure regulator vacuum off
Turning engine off, after 5 minutes it bled down to 28 psi.

What do you think? According to Haynes it should be between 30-40 idling and 40-50 without regulator.
View attachment 35431
Pressures a little low but as they measure in standstill at idle and 2500RPM here anyhow the the fuel flow is not that big. I would change fuel filter if not done lately and then concentrate on air leaks in exhaust and EGR system.
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
remember that the fuel pressure regulator's job is to maintain fuel pressure across the injector not relative to atmospheric. if the pressure inside the intake manifold is 0.3bar that's about 4psi absolute which means fuel pressure relative to atmosphere would be about 30psi but fuel pressure across the injector is 40psi
I'm a little lost in this explanation. Does it mean 30 psi as measured by me was to be expected?
KOEO 39-41
KOER 35 PLUSS
Is that your car's fuel pressure, or is that an ideal target value?
I would change fuel filter if not done lately and then concentrate on air leaks in exhaust and EGR system.
Fuel filter was done last year. I will replace it again, just to be sure. Car was barely used in the past few years before I got it last year. Might be it accumulated some dirt in the tank which was caught by the new filter.
EGR has some leak leak by the pintle, but it was suggested it is not something that would cause lean condition like this.
 

shovel

Active Member
Joined
Jan 4, 2023
Messages
309
Reaction score
266
I'm a little lost in this explanation. Does it mean 30 psi as measured by me was to be expected?

Fuel pressure should be about 3 bar, which is about 43psi. There is very little real difference in fuel delivery between 40 and 45 psi so it does not need to be precise and never will be.

Inside your intake manifold is a partial vacuum while the engine is running - not like outer space but less than ambient. The business end of the fuel injector is in the same air volume as the intake manifold so when your manifold has vacuum the tip of the injector also has vacuum.

At sea level absolute pressure from the atmosphere is about 14.7 psi, so your fuel pressure with the engine stopped is about ~40psi above that or about 55psi above outer space.

With the engine running at idle with the throttle closed you might have about 20in hg vacuum which equates to about a 10psi difference (air is pushing on the outside of the manifold with about 10psi, the air inside the manifold is about 4-5psi above outer space)

Since the fuel pressure regulator's job is to maintain about a 40ish psi difference across the injector that means you would measure 40psi compared to atmosphere with the engine off, or about 30psi compared to atmosphere at idle with the regulator connected to manifold vacuum. Either way the fuel inside the rail has about a 3 bar difference to the tip of the injector where it shoots out.

With the throttle open the engine will speed up and demand more fuel but also there will be less vacuum in the intake manifold, in a perfect NA engine it would be no vacuum but that is impossible. More often you might have 1in hg which is about 0.5psi of difference between the atmosphere outside and the inside of the manifold. So at WOT under load ideally you would be back up to 40psi roughly. Of course that is not really something you can test while parked unless the car is on a dyno to supply a load to the engine.

If fuel pressure drops at WOT it is likely you have a fuel delivery problem like plugged filter or failing pump, or I know this does not apply to you but if someone has built a very powerful engine and not upgraded their fuel pump and electrical wiring it might just not be able to supply the volume needed.
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
Fuel pressure should be about 3 bar, which is about 43psi. There is very little real difference in fuel delivery between 40 and 45 psi so it does not need to be precise and never will be...
Thanks for the explanation!
 
OP
OP
GTamas

GTamas

Active Member
Joined
Apr 17, 2023
Messages
490
Reaction score
526
Location
Austria
Well I am seriously getting confused. I was at the exhaust shop and no leaks were found.
I will check the codes tonight again.

If nothing found, I will have to bring the car to a workshop as it seems I am missing something or doing something wrong. :(
 

Mustang5L5

Active Member
Joined
Aug 1, 2023
Messages
734
Reaction score
782
1.7 would indicate lean. Need to focus on thing that would cause a lean condition like vacuum leaks, poor MAF reading, fuel injectors not firing, etc.
 

RAU03MACH

Legend
Joined
Apr 23, 2019
Messages
7,212
Reaction score
7,253
Location
NEW MEXICO
I'm a little lost in this explanation. Does it mean 30 psi as measured by me was to be expected?

Is that your car's fuel pressure, or is that an ideal target value?

Fuel filter was done last year. I will replace it again, just to be sure. Car was barely used in the past few years before I got it last year. Might be it accumulated some dirt in the tank which was caught by the new filter.
EGR has some leak leak by the pintle, but it was suggested it is not something that would cause lean condition like this.
that would be the target
 

Mustang5L5

Active Member
Joined
Aug 1, 2023
Messages
734
Reaction score
782
How do they run the test anyway?

Tested at idle? Tested at 3000RPM? Under load on rollers? Or just holding RPM in nuetral?

Is the reading reflective of a result obtained exactly at that particular set of conditions?
 

Latest posts

Forum statistics

Threads
77,727
Messages
1,508,974
Members
15,152
Latest member
chriso

Members online

Top