S14 hesitation at WOT

[Pavel]

Just a quick note - readjusted the ITB once again. I still only get about 10-12cmHg. Sprayed starter fluid around the intake blocks, with no impact. The O2 is set to read about 0.5-0.6V, via the spring and bypass screw. CTS is actually doing what is it supposed to now, after the different CAT.

The car drives perfectly fine with the AC off (taking off from a stop) That explains quite a bit, actually. I guess the hot Houston weather, and keeping the AC on screwed my troubleshooting earlier.

ethirtym the fuel filter is new, dampener looks good. I have a spare set of fuel pumps I could try, but I feel it's a different issue at this point.

[proctor750]

Just a quick note - readjusted the ITB once again. I still only get about 10-12cmHg. Sprayed starter fluid around the intake blocks, with no impact. The O2 is set to read about 0.5-0.6V, via the spring and bypass screw. CTS is actually doing what is it supposed to now, after the different CAT.

The car drives perfectly fine with the AC off (taking off from a stop) That explains quite a bit, actually. I guess the hot Houston weather, and keeping the AC on screwed my troubleshooting earlier.

ethirtym the fuel filter is new, dampener looks good. I have a spare set of fuel pumps I could try, but I feel it's a different issue at this point.

Any updates?

How does the car idle? Very smooth and no bumps or misses? You say full throttle is great now with new CAT and is also great from idle to WOT with AC off. Where does the problem area remain?

[Pavel]

proctor750 I just meant to post an update, today. Good reminder.

Short update - still no change.

The intake seal blocks are now replaced (ouch $), the little elbow from the ITB to brake booster is swapped too. I went ahead and tested a different ICV, no change. Replaced the transistors in the DME, still the same.

I just got a refurbished AFM from FIC.

Last night, while installing the AFM, i started noticing the following behavior (still no change to the way the engine runs). Reading voltage at pin 5 and 19 i would only get 10VDC. Still about 12-14cmHg. I have to back out the idle screw way out to get about 880RPM.

I went and checked the voltage battery, to only find out 11.3V while running. The battery is AGM, i need to look closer to the specs but that definitely was not a good sign. Swapped it with a battery from one of my cars, and now I have 13V running, and about 12VDC reading pin 5 and 19. I am looking for 50% duty cycle to detect proper closed loop condition.

In that test what I noticed was that when the blower is on, I get 0-12VDC oscillation at pin 5/19. When it is off I am at 12VDC, which means lean. When I turn the AC switch ON, I get 0VDC which means rich, but no idle ramp up as per status quo. This is the procedure I am following http://home.insightbb.com/~todd.kenyon/idle.htm

I have a ground strap upgrade kit on the way - oilpan to chassis, and alternator to starter. I looked into that originally, but with the clogged CAT had that idea slip away.

Few weeks back, I was measuring pin 29 on the DME. I was reading only about 10VDC. I am thinking of simulating 12VDC, to see if the ECU would idle up... any thoughts on that?

[Dave @nz]

Hi, might sound silly, worth checking first that you have the 3 air control leavers on the across to the r/h side to allow air to come out of the vents, there is a switch in behind the control levers which then allows the compressor to engage and idle up to happen. I got caught out with a/c not working last year got donkey deep in to diagrams before I figured out only one was across and the other two close position.


Confirming that the a/c clutch is engaged and turning would be the next step if it is engaging inspect the wiring at the temp switch on the thermostat housing make sure the three wires are intact. one goes to pin 29.

[Pavel]

Dave @nz Thanks for the tip. I will try that. The AC does blow very cold!

Installed the ground kit upgrade - Engine block to chassis, Alternator to block, Hood strap, Valve cover to battery tray (coolant expansion tank). Still the same.

[ethirtym]

FCP Euro's blog re fuel pump:

A weak pump may deliver enough pressure and flow for low-speed driving but “starve” the engine of fuel when engine speed and load increase, causing the engine to misfire, hesitate, or even stall.

Indicator 2: Your car hesitates or is rough on acceleration.

[Pavel]

ethirtym fair point. Worth a shot - i have a spare main and intank pump. Might as well try it at this point. I should probably do before (status quo) + gauge, and after with gauge.

[ethirtym]

Assuming it's a fuel pump it would be great to have a before and after video of the gauge showing how your fuel pressure reacts to throttle blips and revving - with A/C on.

[Pavel]

I just did compression test, last night. All in norm! Should have really done that a long time ago, but I am glad no surprises.

Also dropped off the injectors for clean-up. Earlier in the week tried a known good cap/rotor and wires, and a different set of injectors. Status is the same.

Currently going to try - fuel pumps, ref sensors and harness inspection.

[Pavel]

Injectors came back. 1 was failed, and the rest borderline. All cleaned up and restored. And still no change.

Fuel tank seems nice and clean, no residue. I ended up replacing the main fuel pump with a good known. No change. Also eliminated the dampner after the filter, as a test.

I am pending to do the intank pump, but I doubt any improvements.

I started pulling belts to see if they have any impact - seized water pump, or power steering. Same

Two new reference sensors are on order. They might come in today.

[ethirtym]

Injectors came back. 1 was failed, and the rest borderline. All cleaned up and restored. And still no change.

Fuel tank seems nice and clean, no residue. I ended up replacing the main fuel pump with a good known. No change. Also eliminated the dampner after the filter, as a test.

I am pending to do the intank pump, but I doubt any improvements.

I started pulling belts to see if they have any impact - seized water pump, or power steering. Same

Two new reference sensors are on order. They might come in today.

Maybe check that your fuel pump's flow rate is within spec, I don't imagine for instance that the new pump or new fuel filter would be bad but I'd want to definitively know I'm getting enough fuel. I don't recall but did you check/change spark plug wires?

[proctor750]

I just did compression test, last night. All in norm! Should have really done that a long time ago, but I am glad no surprises.

Also dropped off the injectors for clean-up. Earlier in the week tried a known good cap/rotor and wires, and a different set of injectors. Status is the same.

Currently going to try - fuel pumps, ref sensors and harness inspection.

What were the compression numbers?

Have you done a leakdown?

Is the injector wiring in good shape? I had to test mine to find it was bad and replaced with a kit from one of the bmw sites.

[basketcase]

This must be frustrating. Can I suggest, to try and tackle this in a direct and "scientific" way... If that makes sense. Throwing parts at the problem can be very time consuming and tiresome. Focus on the symptoms. When does it happen? What exactly does it feel like? What revs, load, speed, temp etc. Throttle position? Can it be easily replicated? I had a frustrating problem on my 2.5 build and found it by cintincont to go back to the area where I thought the problem was (TPS) until I finally found the wiring issue.
Think of what sensors and actuators are actually in play when the issue occurs. For example, the 02 sensor (on a stock engine) is only in use during idle and part throttle. So if the issue is at WOT, you know it can't be a problem with that sensor . Unless of course the TPS is sending an incorrect signal to the DME and the DME is thinking it's at part throttle when it should be at WOT. Unfortunately the e30 m3 DME is pre diagnostic capability so you canntc read out live data via the 20 pin diagnosis port. So testing is done old school with a multi-meter and wiring diagrams.
Your problem is eitere mechanical or electrical. Mechanical is fairly easy to determine. If everything checks out there then move onto electrical. Sorry if I am no help but stick at it and finally you will sort it. And it will run very nice once it's fixed.

[Pavel]

Maybe check that your fuel pump's flow rate is within spec, I don't imagine for instance that the new pump or new fuel filter would be bad but I'd want to definitively know I'm getting enough fuel. I don't recall but did you check/change spark plug wires?

Yes i did swap the wires along the cap and rotor, with a set from a working car.

proctor750 compression on cold engine, 4 turns was about 170psi all across the 4 cylinders. No, i need to do a leakdown.

basketcase - yes, I agree on the scientific method. I started with tackling this as a vacuum leak problem (smoke test), potentially AFM track, moved on with fuel delivery. Fixed all the vacuum hoses, seals etc. In the process I swapped parts from either my stash of good known, or other working M3s just to validate - TPS, ICV, ECU (new transistors), coil, rotor/cap, fuel pumps. It spiraled out of control.

The problem is very reproducible. I think WOT is not the right terminology anymore. It would act like that even at partial throttle, when the AC is ON. I originally had it as WOT because it would take that much for the car to take off from a stop. The vacuum in at the sync ports remains low, regardless of the load on the engine at idle. I need to install the ref sensors that arrived last week, and then get started with wiring loom checks. Almost take a step back and recheck all my work again - TPS, ICV, AFM voltage.

[proctor750]

Yes i did swap the wires along the cap and rotor, with a set from a working car.

proctor750 compression on cold engine, 4 turns was about 170psi all across the 4 cylinders. No, i need to do a leakdown.

basketcase - yes, I agree on the scientific method. I started with tackling this as a vacuum leak problem (smoke test), potentially AFM track, moved on with fuel delivery. Fixed all the vacuum hoses, seals etc. In the process I swapped parts from either my stash of good known, or other working M3s just to validate - TPS, ICV, ECU (new transistors), coil, rotor/cap, fuel pumps. It spiraled out of control.

The problem is very reproducible. I think WOT is not the right terminology anymore. It would act like that even at partial throttle, when the AC is ON. I originally had it as WOT because it would take that much for the car to take off from a stop. The vacuum in at the sync ports remains low, regardless of the load on the engine at idle. I need to install the ref sensors that arrived last week, and then get started with wiring loom checks. Almost take a step back and recheck all my work again - TPS, ICV, AFM voltage.

So just to clarify so we can continue to help - what are the exact symptoms as of today. You have done a lot of work so it sounds like the goal posts have moved a bit.