Diagnosing Hesitating/Misfiring X35i with No Codes

[ClutchKickChris]

Originally Posted by SB1120

Did you say you have aftermarket ignition coils? And what spark plugs?
If it’s worth it to you, I’d grab a set of OEM dealer coils

No, all OEM coils and plugs, recently replaced as well.

[andrewwynn]

Re reading the initial post, I think there might be a sensor messing with you.

My understanding is the ECT sensor has two outputs. If one isn't reading correctly it could be both the reason the water pump kicks in and if it's used for determining closed loop or air fuel mix.

[ClutchKickChris]

Originally Posted by andrewwynn

Re reading the initial post, I think there might be a sensor messing with you.

My understanding is the ECT sensor has two outputs. If one isn't reading correctly it could be both the reason the water pump kicks in and if it's used for determining closed loop or air fuel mix.

Since replacing the waterpump again many months ago (thanks FCP warranty), the running waterpump issue has been resolved.

Still, I will check what the sensor is reporting via my scanner, thansk for the suggestion.

[andrewwynn]

Some engines have two in one sensor but I've only ever seen one reading in my scanners.

I would nevertheless monitor coolant temp real-time. Use a graph of possible to watch for abrubt changes that can't happen in reality.

The other thought that comes to mind is something to do with turbo pressure control.

Monitor the boost pressure during the hesitation. There was a problem that I helped with recently with a problem in the turbo pressure feedback. Sadly I can't remember exactly what that issue was but I found a web page that covered the symptom and it was a specific part in the turbo control that ended up being the cause.

[SB1120]

Originally Posted by andrewwynn

Some engines have two in one sensor but I've only ever seen one reading in my scanners.

I would nevertheless monitor coolant temp real-time. Use a graph of possible to watch for abrubt changes that can't happen in reality.

The other thought that comes to mind is something to do with turbo pressure control.

Monitor the boost pressure during the hesitation. There was a problem that I helped with recently with a problem in the turbo pressure feedback. Sadly I can't remember exactly what that issue was but I found a web page that covered the symptom and it was a specific part in the turbo control that ended up being the cause.

I remember something similar. I think it was the electronic bypass valve on the compressor. It might be worth removing to inspect..? I’ll attach a pic of one in a Passat I had. No code but I read it was common, removed it and sure enough the diaphragm was blown. Not sure if they use this same design on our Borgs.

If you can hear boost bypass after a part-throttle mid-range pull, its probably ok?

Ever replaced the valve cover? And also related to that, the short pcv pipe between the turbo inlet pipe and valve cover if cracked could be an air leak. In terms of air leaks: charge pipe to inter cooler seals, crack in charge pipe(s) after intercooler, and there’s a seal between the intake manifold and DME. That one is less likely but if oil vapor has attacked it, it could be shot.

[ClutchKickChris]

Originally Posted by SB1120

I remember something similar. I think it was the electronic bypass valve on the compressor. It might be worth removing to inspect..? I’ll attach a pic of one in a Passat I had. No code but I read it was common, removed it and sure enough the diaphragm was blown. Not sure if they use this same design on our Borgs.

If you can hear boost bypass after a part-throttle mid-range pull, its probably ok?

Ever replaced the valve cover? And also related to that, the short pcv pipe between the turbo inlet pipe and valve cover if cracked could be an air leak. In terms of air leaks: charge pipe to inter cooler seals, crack in charge pipe(s) after intercooler, and there’s a seal between the intake manifold and DME. That one is less likely but if oil vapor has attacked it, it could be shot.

Yes for sure I can hear bypass when letting off throttle at heavy load.

I did recently replace the valve cover AND short PCV pipe with OEM, VC was slightly leaking oil, was hoping maybe it'd fix any air leaks too if they existed.

As for the turbo diverter valve, the feeling of this stutter/hesitation is very sharp, like a misfire feeling. I think turbo pressure issues would be more gradual, like a sine wave sweep vs a sawtooth (what I feel).

[SB1120]

Originally Posted by ClutchKickChris

Yes for sure I can hear bypass when letting off throttle at heavy load.

I did recently replace the valve cover AND short PCV pipe with OEM, VC was slightly leaking oil, was hoping maybe it'd fix any air leaks too if they existed.

As for the turbo diverter valve, the feeling of this stutter/hesitation is very sharp, like a misfire feeling. I think turbo pressure issues would be more gradual, like a sine wave sweep vs a sawtooth (what I feel).

How does your high pressure fuel reading look during these events?

[ClutchKickChris]

Hey Guys,

So today I drained the ZF fluid and refilled with Redline D4 ATF twice and all of the slipping/hesitation issues have gone away completely.

It went from slipping in every single gear after 5 minutes of driving, to never slipping in any gear over an hour.

I will monitor if it gets any worse again, also going to order 2 more gallons of redline D4 ATF and drain/fill it again so I get as much of the ZF fluid out as possible. Also another new trans pan filter.

Pretty crazy that OE fluid can ruin a trans around 2 months later huh?

[SB1120]

Hope it’s resolved for good.

[ard]

Originally Posted by ClutchKickChris

Hey Guys,


Pretty crazy that OE fluid can ruin a trans around 2 months later huh?

Yes.