Went to the dyno, something's not right...

[jeffmn8]

So after going to the dyno this last sunday, we discovered there's something not quite right about how my engine is running in high rpms. As you can see from the plot below, at about 6k rpm it starts running super lean. So what could be the cause of the issue here? Some thoughts thrown around were the fuel pressure regulator, injectors, fuel pump. Seems obviously fuel related.

Specs on motor:
S50B30 US
-3.5" 540i MAF
-3.5" Intake boot
-stock 17.5 lb injectors
-OBD1 Fuel rail
-Custom 2.5" single exhaust
-Turner chip for all mods



I've already been planning on getting the 21.5 lb injectors and a retune, I just need to make it happen. And yes, I know the numbers are fairly low, but I don't care. I'm just glad this issue was discovered this way instead of a melted piston..

[SLEEPYDUB]

How much boost are you running? Have any logs you could post up?

It looks great up until then. Are you tuning without a map sensor?

Fuel pressure could be a culprit. What bar fpr are you running?

[jeffmn8]

How much boost are you running? Have any logs you could post up?

It looks great up until then. Are you tuning without a map sensor?

Should be running about 14.7 psi boost, no map sensor ;)

[SLEEPYDUB]

What fpr are you running and whats your base fuel pressure?

[jeffmn8]

Stock obd1 (s50) FPR/Rail. Not sure what the fuel pressure is..

You know it's not FI right? lol

[Exodus_2pt0]

Looks like it's only going to about 13.5:1 which is a great AFR for a NA setup.

Are you logging your knock retard? If it's not detonating, then it's fine with how it's running.

[Beej '86 325es]

Is your Vehicle Speed Sensor wired with your swap? You should have pin14 to pin14 at your harness adapter. I've read that this can cause the engine to lean out at the top end when it's not connected.

[nrubenstein]

How old is your CPS? It wouldn't shock me if it's losing sync at high RPMs.

I don't think that it's fuel related at all. Something is causing the car to cut fuel. If you were running out of fuel, things would gradually go lean. Running into a wall means that fuel is getting actively turned off. Unless, of course, the fuel pump died othe dyno, but I would discount that if it drove off.

[jeffmn8]

Looks like it's only going to about 13.5:1 which is a great AFR for a NA setup.

Are you logging your knock retard? If it's not detonating, then it's fine with how it's running.

How is running that lean up top fine???

Is your Vehicle Speed Sensor wired with your swap? You should have pin14 to pin14 at your harness adapter. I've read that this can cause the engine to lean out at the top end when it's not connected.

I'll double check this tomorrow. I just swapped a VDO cluster into the car the other week, that has a glitchy speedo, but that shouldn't make a difference right?

How old is your CPS? It wouldn't shock me if it's losing sync at high RPMs.

I don't think that it's fuel related at all. Something is causing the car to cut fuel. If you were running out of fuel, things would gradually go lean. Running into a wall means that fuel is getting actively turned off. Unless, of course, the fuel pump died othe dyno, but I would discount that if it drove off.

Not sure how old the CPS is. You can see how it started to lean out at about 5.5k rpm and then hit a wall a little after 6.

[ak-]

That's scary.

[NbAmTwE]

That's a pretty significant spike at 5150 rpm in HP. I would think CPS myself (I'm not an expert). The rest of the curve looks way to linear to just see that randomly there IMO. Perhaps that is where CPS is losing sync and that's where a possible fuel cut is being triggered to account?

[SLEEPYDUB]

Afr looks fine for NA till the cut..looks like its cutting fuel out immediatley as previously stated.

[328ijunkie]

lol. 17.5 injectors.

[justin_l_]

Max duty on injectors? I can't see the log from work so I'm just throwing it out there. More air without more fuel will cause a lean condition.

[328ijunkie]

Thus my comment. No tuner makes a chip for 17.5s