SureShot

What else can cause a fuel cut besides TPS<1.2v or boost >8.5PSI?

I'm getting a consistant fuel cut at 5PSI when I hit 6K RPM.
The fuel stays off until I lift the throttle.
Then when I resume light throttle the fuel comes back on.

No check light.

I also get the cut on high boost at 10PSI & 4KRPM.
Then when I resume light throttle the fuel comes back on.

I checked the FCD output to the ECU & it clamps at ~7PSI.
TPS sweep is nice & smooth - no bumps or drops.

Just for grins, I cleaned & re-seated the ECU connectors.

SureShot

Still no check light, but just for fun I pulled the codes. 30,33,42, all unplugged, and have been for over a year.

So what is making it cut fuel???

SureShot

I need some suggestions here.
It's now cutting off at 5PSI & 5K.
The trend is not good.

The cut off is a complete engine shut down until I completely lift to closed throttle.
Then it runs completely normal again.

This may be related.
Just before this happened, I got a solid check light with codes 08 10 13 18 30 33 42.
Re-seating the ECU connectors cleared the codes & the check light never came back on.

Of course I’m still getting the 30 33 42 with no check light.

RETed

Let's isolate the fuel-cut itself...

Unplug the electrical connector from the boost sensor and take it for a spin.
Does it still do it?
If not, it was overboost fuel-cut.
The boost sensor is the only sensor that triggers overboost fuel-cut.

You might want to check the TPS at WOT.
If the resistance is over 5.5k-ohms, it'll hesistate like crazy to high RPM's.


-Ted

SureShot

I can do that by switching the S-AFC back to using the TPS for the THR signal.

I have an inverse pattern: the higher I allow the boost the lower the revs where the shut off happens.

SureShot

Disconnected the pressure sensor - no change.
I watched the AFM and it showed no lean-out before the motor quits.
The engine just shuts off at about 2/3 power.
Then stays quiet until I close the throttle.
Then it refires & drives normal.

I rechecked the TPS - nice smooth sweep up to 4.5 volts.
It's an easy test with the S-AFC in graph mode.
I also rechecked the S-AFC settings - flap/up/6in/6out

So far, I'm baffled.

slpin

iTrader: (9)

maybe your AFM shows something that is out of range and it goes... wtfmate and then your ecu was like... wtfusayingson ?

SureShot

Further observation.
It felt like a fuel cut, but it is not.
I'm going into cripple (limp) mode.
The drop in power from 11 PSI @ 4K to cripple mode is pretty drastic.
It stays crippled as long as I hold open the throttle. Then it resets.
At least now it makes sense.

Now I can go after the check codes.

SureShot

The FSM says it could be:
AFM (checked)
TPS (checked)
Mileage sensor (disabled)
Knock sensor (not likely, but I will test it)
Neutral switch (not likely, but I will test it)
Clutch switch (not likely, but I will test it)
Power steering pressure switch (>interesting<)
Water thermosensor (not likely, but I will test it)
Heat hazard sensor (not likely, but I will test it)
Reverse/5th switch (not likely, but I will test it)
ECU plug (checked)

It looks like I'm turning this into a troubleshooting blog.

HAILERS

So? Why wouldn't you think it's OMP related?? Seems more likely than the fifth switch, neutarl sw etc.

SureShot

No code 12 20 26 27 or 37 , so the ECU thinks it's OK.

I am getting 30 33 42 (split air solenoid, port air solenoid, boost control solenoid), but they have been gone for over a year.
I will put ballast resistors in them, just to rule them out.

I currently suspect the FCD calibration.
The PRS input to the S-AFC is after the FCD, and it shows .37Kgf/cm2 max.
I converted it this morning for the first time .37/.0702 = 5.27 PSI (oops- way low)
I need to get out the mity-vac & test gauge, and tweak it up to 8.5 PSI

HAILERS

I set the clamping voltage on my home built one at 3.65vdc and even the RB one that I store bought I had to raise the clamping voltage up. It was set too low, too conservative for me. To be replaced on March 01 with a RTEK 2.0 and a Palm M515.

Actually It'd be more fun going for a drive with a meter connected to the input pin of the ECU and see just when it's clamping, and getting out and making a pot adjustment on the go so to speak.

SureShot

FCD reset to 8.5 - Still no change.
Ballast resistors in the port air & boost solenoid sockets - reboot the ECU - still no change.
I still need one more resistor for the split air socket.

I will disconnect the knock sensor, to test for that this weekend.
I may end swapping in a spare.

It drives fine if I stay out of boost, but what fun is that?

(Hi, My name is Bill, and I'm a boostaholic)

HAILERS

If you think it's a knock sensor..............disconnect the knock sensor and try again.

SureShot

Disconnected the knock sensor - get a check 05.
The car starts & drives great until I hit 5 PSI & 5KRPM, then I get the same fuel cut.
I'm one resistor short, so I'm still showing code 30 with no check light.

Checked the plugs. They looked OK (medium tan with hardly a tinge of black), but changed them anyway, just in case.

Took a 130 mile test drive. Got 19.6 MPG. (The only up side to this problem)

For now I'll assume the water thermo switch is good or my mileage would be worse.
The heat hazard sensor dash light comes on only with POST.
That leaves the clutch, steering, neutral, & 5th/reverse switches to still be checked.

I'm still missing something here..

HAILERS

You have not been messing around with the spring tension in the afm, have you? That'll play havoc with full throttle.

SureShot

It's an S5.
I experimented with a 929 AFM last week.
It worked well at the low end, but maxed out at WOT & 5K.
The S-AFC was at its limit to tune the extra low end flow.

I've been back on the stock AFM since Monday and this problem popped up Wed night when I checked the plugs..

Bottom line: I check the plugs & suddenly high end is limited. It's a WTF moment..

The AFM comment got me thinking. I'm going to bench check the AFM tomorrow.
Thanks
-Bill

RETed

I still think it's the TPS.
I don't think the S-AFC can display actually resistance, so it makes me suspect.

Can you disconnect the TPS and take the car for a drive?
I forget if the S4 or S5 cannot drive without the TPS connected.

If possible, disconnect the TPS and measure the resistance of the green and black wires - it should be under 5.5k-ohms.


-Ted

HAILERS

Checked the plugs and things went awry? PUt the wires on wrong on the plugs??? NAAAAAAAAAAAAAAAAAAAAAh, you wouldn't do that. But, then again, that's why they call them Mistakes.

SureShot

BINGO - it's the AFM!

Checking pins Vc to Vs & slowly pushing the vane in:
Closed = 135 Ohms
up to 3/4 stroke = bumpy steps up to 550 Ohms
above 3/4 stroke = a sharp drop to 270 Ohms. This SOB is definitely non-linear.

I drilled a tiny hole & sprayed in some contact cleaner - no change.
Then I drilled a 1/2" inspection hole. The slide contacts were perfect, almost no visible wear.
The potentiometer is a row of discrete surface mount resistors, each with it's own contact under the slider.
The top 3 resistors seem to be partially shorted??

So, I installed & retuned for the 929 AFM for now.
The BOH switch now works! (BOH = Bat Outta Hell)

Anyone want to sell me a good S5 AFM?

(edit)
BTW - Hailers: I did cross the plug wires once about 2 years ago.
The new yellow wires are much easier to trace.

HAILERS

CAUTION, CAUTION, CAUTION!

Sorry, but I KNOW on a S4, if you just check resistance with a meter, while slowly opening the vane, you get the same results you seem to have. The resistance will go up, then drop off, then go up, then drop down. This is from memory, the up/down. It could have been the other way. I'll check later.

It SEEMS to me the only valid check is to turn the key on and check the vane/cone while slowly opening the vane/cone.

Sorry to burst your balloon. But that's why I'm here, to burst balloons. humor

EDIT: ooopS! I only read the first couple of sentences and JUMPED to conclusions. I see the afm change did fix the problem. My bad. It's just that on S4 if you try to ohm out the pot while slowly opening the vane, you get a up/down/up/down resistance reading and I ***-U-ME d(*** out of you and me) you had made a mistake. My bad.

SureShot

Sorry about that. My posts can be like a mystery, with a surprise at the end.

I also checked the 929 AFM and it also fell off some at the end of the stroke, but not as much.
It measured 150, then up to 600, then droppped back to 450 at WOT.
It's possible these things are supposed to be non linear, but I have no idea why.

Like "slpin" said, my stock AFM went out of range, but not enough for the ECU to throw a check.
If anyone knows what the AFM's Ohms values should show. give a post.

So - a quick test ride.
The G-tech showed a net HP of 233 in 2nd gear, with the header dump closed.
Factoring back drive train, and aero loss, I'm happy.
The nearest back road that's OK for testing is 10 miles West of here.
I hope to get out there soon for some open header testing.

Terrh

iTrader: (7)

sounds like its time for an EMS and speed-density fuel calculation

if S5 n/a AFM's are the same then I have one I'll sell you cheap... if not - then I don't.

SureShot

The turbo AFM is built for a higher flow range (at the expense of more pressure drop).

Here's a webcam clip of the bad AFM test> link to short AVI file

HAILERS

A little off topic......you mentioned how you reached 100 percent around five grand or so and you determined this by looking at your SAFC airflow percent. Just FYI, on a S4 with the vane afm, my car does the same. It's not unusual. Car keeps truk'in to seven plus grand.