Extreme Lean Condition / Power Loss at 5500

[flyingplatypus]

Can anyone help me diagnose this power loss issue I am having? From 5000 to 6000 rpms it really leans out and power dissapears. It is an 84 euro spec 3.2 with M&K bypass and 1 in 1 out muffler and steve wong chip. Any help would be greatly appreciated.

Thanks!

[stlrj]

If your fuel pump is original, it might not be putting out like it should.

[pors1968]

i would clean the injector and check the fuel pump .

[flyingplatypus]

The fuel pump recently blew out and was replaced. I feel like it runs rich most of the time and only leans out in that range.

[BGCarrera32]

Is the power loss something that started to happen slowly over time, or *bam* one day we got power loss? What has changed?

[flyingplatypus]

Originally Posted by BGCarrera32

Is the power loss something that started to happen slowly over time, or *bam* one day we got power loss? What has changed?

I'm not sure. I noticed it for the first time at a track day and I don't know if I had it for a long time before that or it was recent. I don't spend enough time over 5k i guess.

[Bob Kontak]

Originally Posted by flyingplatypus

I don't spend enough time over 5k i guess.

Seems you car sort of recovers at 5500 and fuel returns. Overall, appears you are still down on power but why would it start delivering fuel again at 5500?

I am stumped.

Check connections (condition of) at the fuel pump relay? Swap another in there?

Do a test on volume flow. I don't know how many liters a minute the pump should deliver but make sure it is at least to spec.

Going out on limb, what is overall ignition advance? I don't know what happens to AF ratio if you get close to detonation. Just talking here, not professin'.

[flyingplatypus]

Originally Posted by Bob Kontak

Seems you car sort of recovers at 5500 and fuel returns. Overall, appears you are still down on power but why would it start delivering fuel again at 5500?

I am stumped.

I'm with you. I can't understand why it would go down in such a short rpm range. Checked fuel pressure and it is fine.

[mnez]

Contact Steve Wong. He should be able to retune the chip for you. That assumes fuel flow and pressure and injectors are all normal.

[Josh D]

Do you have the original Euro spec chip? The Euro is rated @ 231 HP. If the SW chip is for a US car, maybe it's costing you HP?

If you have the stock chip, try it out and see if your problem still exists.

[Steve W]

It looks like one or more of the following scenarios may be occurring with your car:

1) air flow meter flap tension was tampered/tightened to lean out the mixture for emissions when the car was grey market imported into the USA. Look at the black plastic cover on it and see if it's been tampered with and resealed.

2) an aftermarket piggyback controller is tied into the DME system to implement an O2 sensor into the car for the grey market import certification

3) you are not getting full throttle and the full throttle switch is not activating

4) the fuel quality switch in the DME may have been tampered with to lean the mixture

5) possible low fuel pressure problem

[whiz05403]

Fuel filter semi clogged?

[ischmitz]

errr - doesn't the graph look too lean all over with an even nastier area from 5k - 6k region. How well do you trust the measurement of that Dynojet??

Next, what all others said - go back to the stock chip, make sure fuel supply isn't starving (even though that would not recover as it does in your case) and then check the AFM.

Your AFM could have a "flat spot" damage to the wiper trace that momentarily tells the DME to lean out at a particular air flow rate. A simple test with a 9V block battery and a DVM can tell if it is working properly. You have to take the AFM out but don't have to take the top off. See here: Air Flow Meter (AFM) Operation and Testing

[flyingplatypus]

Originally Posted by Steve W

It looks like one or more of the following scenarios may be occurring with your car:

1) air flow meter flap tension was tampered/tightened to lean out the mixture for emissions when the car was grey market imported into the USA. Look at the black plastic cover on it and see if it's been tampered with and resealed.

2) an aftermarket piggyback controller is tied into the DME system to implement an O2 sensor into the car for the grey market import certification

3) you are not getting full throttle and the full throttle switch is not activating

4) the fuel quality switch in the DME may have been tampered with to lean the mixture

5) possible low fuel pressure problem

1) The black cover on the bottom of it? It doesn't look like it has been tampered with.

2) The entire DME was replaced with a US dme when the original burnt out. Wiring harness was replaced too.

3) I checked at the switch and it is working. Would it be possible the signal is not getting to the DME?

4) It is set in the counter-clockwise position

5) Is there something that could affect fuel pressure under load but not during the regular test?

Thanks!

[flyingplatypus]

Originally Posted by ischmitz

errr - doesn't the graph look too lean all over with an even nastier area from 5k - 6k region. How well do you trust the measurement of that Dynojet??

Next, what all others said - go back to the stock chip, make sure fuel supply isn't starving (even though that would not recover as it does in your case) and then check the AFM.

Your AFM could have a "flat spot" damage to the wiper trace that momentarily tells the DME to lean out at a particular air flow rate. A simple test with a 9V block battery and a DVM can tell if it is working properly. You have to take the AFM out but don't have to take the top off. See here: Air Flow Meter (AFM) Operation and Testing

I will have to check this out. This seems like a likely suspect. The article indicates that there are 2 different versions of the AFM, could there be a possible mismatch between the AFM and the replacement DME that was installed?

Also, how do I remove the AFM?

Thanks!

[ischmitz]

No - the early AFM (log output, 12V input) only applies to early 944. All 911 AFM are the later 5V versions.

The engine has a fuel pressure regulator that looks at the intake pressure and adjusts fuel rail pressure so that the injectors always "see" the same pressure difference. This ensures the flow of fuel is tuely proportional to the electric pulse duration.

The AFM is bolted to the air box. First you need to get the air box out. Next there is a hose clamp that attaches the AFM to the throttle body.

Ingo

[flyingplatypus]

Originally Posted by ischmitz

No - the early AFM (log output, 12V input) only applies to early 944. All 911 AFM are the later 5V versions.

The engine has a fuel pressure regulator that looks at the intake pressure and adjusts fuel rail pressure so that the injectors always "see" the same pressure difference. This ensures the flow of fuel is tuely proportional to the electric pulse duration.

The AFM is bolted to the air box. First you need to get the air box out. Next there is a hose clamp that attaches the AFM to the throttle body.

Ingo

Alright, I'll check this out.

Is it possible that the WOT switch is being thrown, but not getting to the DME? Is there a way to check this too?

[ischmitz]

You can measure the WOT switch (Use Ohm meter on the 35-pin DME plug) just to make sure the signal is seen at the DME and there isn't anything wrong with the harness.

Next, there is a remote chance that the DME doesn't recognize the WOT switch and the only way to check that is putting the DME on a bench tester. I would call this a long-shot, not impossible but not one of the more comon failure modes I came across in my time repairing many of these boxes.

[Earlycar Fonzie]

My car was doing the same thing. Start with the little things. I changed the the wires and plugs..distributor cap and rotor..also put on a MSD coil. Started to run good for awhile but then would run lean above 4500-5500 rpms. I got some good advise but...The P/O had the wrong fuel filter on it...I put the correct fuel filter on and my car is running great. Good luck!

[Steve W]

1) the sealant on the AFM cover should have an original bead of clear sealant around the edge. If the tension is set too tight, it can create that extreme lean spot on top

2 & 3) How was the O2 sensor implemented into your car if any? The O2 sensor is only active at part throttle below 4800 rpm, and ignored at full throttle. Euro/ROW cars do not have DMEs and harness wiring for an O2 sensor. Your dyno shows your AFRs averaging at 14.7 from 2500 to 4800 rpm, indicating the car has the O2 active - which happens either if the full throttle switch is not activating, or full throttle is not being achieved. You need to have someone press down on the gas pedal fully, while verifying the WOT switch is activating, and you are achieving full opening at the throttle body.

Originally Posted by flyingplatypus

1) The black cover on the bottom of it? It doesn't look like it has been tampered with.

2) The entire DME was replaced with a US dme when the original burnt out. Wiring harness was replaced too.

3) I checked at the switch and it is working. Would it be possible the signal is not getting to the DME?

4) It is set in the counter-clockwise position

5) Is there something that could affect fuel pressure under load but not during the regular test?

Thanks!