Engine hesitation above 5k

[SurlySurdi]

Chaps, got my Fuel Pressure Regulator changed today and the warm start problem has gone away, good stuff. What's not so good is that an issue which I thought was related has not gone away. This was the engine hesitating above 5000 rpm.

It started happening a couple of weeks ago on a high speed run, every time I got past 5000 rpm the engine would miss a beat, if I kept accelerating more beats would be missed.

Today after replacing the FPR i went for a drive and it's still happening, though this time it also happened going from 2000 to 3000 rpm.

I'd like to know what you think I should check. Should it be the rotor arm? The HT leads? The fuel injectors? The rotor arm is an easy check, for anything else I'd like to know how to check. I have a multimeter so if someone recommends using it some guidance would be most welcome, thank you all.

SS

[Chris_911]

Check your flywheel sensors.

[SurlySurdi]

Thanks Chris I think checking the resistance across the plug terminals as explained in Bentley is what I'll do. The speed sensor is my first suspect.

SS 

Edited September 6, 2023 by SurlySurdi

[PeterK]

I’m sure that you know this, but just in case …..The SC & 3.2 rotors are almost the same, except that the SC has the built in mechanical rev limiter.

Which do have installed ?

[Lesworth]

That's more of a sudden stop though than missing when it kicks in. It's a horrible sensation.

[SurlySurdi]

I have the 3.2 rotor AFAIK Peter.

Lesworth what do you mean by sudden stop? Is that what happens if the speed ref sensor is going bad because I thought the missing was a known symptom for that?

SS

[Chris T]

I think what Les means is that the engine cuts out until revs drop, for perhaps only a second but a shock if you are not expecting it. Even if your reference sensors measure good they can still be problematic. As they are magnetic they can gather metallic debris on them so worth a check, however If they have not been changed then I'd suggest you do so. Bosch make the exact same sensor for a similar era BMW at half the Porsche cost, so shop carefully. 

[Lesworth]

Yes, thats what I meant. When you are approaching max revs you;re going pretty fast with strong acceleration and then it feels like an anchor is thrown out the back unlike a more modern car with more progressively reduced power. Jonny's CDI box allows use of a rotor arm without the heath robinson spring based cut out and provides a nice progressive cut off at the chosen rpm limit. I know thats off topic for a 3.2 though but just trying to describe how the SC cutout feels when it kicks in in cased this is what you have.

[SurlySurdi]

OK thanks guys, no I'm not experiencing that symptom, it's as if it misses a beat going up past 5000 to 5500 rpm.

On another note I have tested the sensor terminal resistances and I'm now more confused.

Assuming my flywheel ref sensor is good (car starts on the key every time) then according to Bentley I should be getting 960 ohms plus or minus 96 ohms between terminals 1 and 2. I'm actually getting 990 ohms so I think that's good. In fact I get 990 ohms for both flywheel sensor and also speed reference sensor.

Now comes the interesting part. Bentley says I should be seeing greater than 100,000 ohms when testing across terminals 1 and 3, also should be getting greater than 100,000 ohms when testing across terminals 2 and 3.

Now, for BOTH sensors im not getting any reading at all. I've checked the setting on the multimeter, touched the contacts together and get 000.1 ohms when I do that so I know the probes are working so I can't work out why I'm not getting any readings?? 

Update: when I say I'm not getting any readings the meter actually shows 0L which I think means open circuit. 

SS

Edited September 6, 2023 by SurlySurdi

[SurlySurdi]

Came across this video on YouTube, applies to 944's and Carrera 3.2 engines:

I'll be testing the sensors tomorrow. The thing that really interests me is that there is a dynamic test you can do that involves cranking the engine (just cranking not starting).

SS

 

[Jonny Hart]

Open circuit (infinity ohms) is > 100k ohms.   I think that part of the test is just to check the shield wire isn't shorted to the signal wire.

Just because internal sensor/wire is good ( e.g. the 960 ohms ), doesn't mean that something else of the device isn't bad.  It could have ingrained dirt / metal fragments on the outside or the sensor might be loose inside its 'jacket'.

[TargaWayne]

You can also have problems with the sensors swelling and breaking the mounting. 

Haith had his mount crack and mine was the same.
 

 

[SurlySurdi]

Cheers guys. So taking what's been said into consideration I'll need to check the physical sensors. But before I do that should I unplug the ecu connector and perform the tests described in the video first? Can the tests pass and yet the sensors are still bad as described by Wayne and Jonny? Or should I dive straight into examining the sensors first?

SS

[Type911]

How old are the sensors? They can be fine when cold and break down when hot, checking the resistances doesnt really prove they are ok, If they havent been changed in your time with the car, change them

[SurlySurdi]

34 minutes ago, Type911 said:

How old are the sensors? They can be fine when cold and break down when hot, checking the resistances doesnt really prove they are ok, If they havent been changed in your time with the car, change them

Cheers Matt, so in summary, the resistance check can reveal they are toast but if not a physical check is in order? If they look ok and don't have any obvious damage and the bracket looks OK should I still change them?

It's just that I don't want to start down the road of changing things in the hope that it fixes the problem which can end up being quite spendy. 

SS

[sopor]

There's a BMW sensor that is siginificantly less than the Porsche sensor - Bosch part number 0 261 210 002

The sensor might be fine when cold and but not when the engine's hot and vibration can affect them as well.

IMHO remove them and check them physically. There is loads of ancedotal evidence here and elsewhere that they don't last forever. The last thing you want to to have the car die while on the road, no?

[Lesworth]

I guess it would be good if you could swap in a known good one to see before you commit?

[SurlySurdi]

2 hours ago, Lesworth said:

I guess it would be good if you could swap in a known good one to see before 

3 hours ago, sopor said:

There's a BMW sensor that is siginificantly less than the Porsche sensor - Bosch part number 0 261 210 002

The sensor might be fine when cold and but not when the engine's hot and vibration can affect them as well.

IMHO remove them and check them physically. There is loads of ancedotal evidence here and elsewhere that they don't last forever. The last thing you want to to have the car die while on the road, no?

 

Before I do inspect or replace I'm still need some help in deciding whether the tests that are performed on the ecu plug are worth doing guys?

[sopor]

The tests will cost you nothing but time. If both pass I would not rule out there still being an issue - this is based upon your symptoms and the likely age of the sensors. I personally would go straight to inspecting them.

Apologies in advance if this comes across as rude but assuming you're going to do the test or inspection yourself you're spending more time sitting on the fence and debating with yourself about how to proceed than the tests or inspection would take!

[SurlySurdi]

8 hours ago, sopor said:

The tests will cost you nothing but time. If both pass I would not rule out there still being an issue - this is based upon your symptoms and the likely age of the sensors. I personally would go straight to inspecting them.

Apologies in advance if this comes across as rude but assuming you're going to do the test or inspection yourself you're spending more time sitting on the fence and debating with yourself about how to proceed than the tests or inspection would take!

I disagree, I'm almost kind of sure 😅 I should maybe do something!

Seriously though, I'll check the sensors. Once I remove the nearside rear wheel are they easily accessible?

SS

[SurlySurdi]

This morning went for a drive to confirm symptoms. In every gear, between 5000 and 6000 rpm the car hesitates several times, very consistently. After the test drive, went to the shops, came out and could not restart the car. It would turn over, try and fire up and then die. Eventually it started after many attempts while pumping the accelerator but it was an effort.

I thought my warm start issue was down to a faulty fuel pressure regulator (it needed changing anyway as there was fuel leakage into the manifold from the regulator). So, there are still 2 issues, hesitation and now non-start issues. I just want to be fully sure the flywheel sensors need changing before I buy them. I still have no definitive test I can perform to verify their operation and I don't have or know how to use an oscilloscope as I've read that's the only way to know.

I'm not adverse to spending money but I'd like to know for sure my issues will be fixed, or am I being naïve and should start replacing bits?

SS 

[Type911]

Did someone say change the flywheel sensors yet?

Both of your symptoms are indicative of fecked sensors

[SurlySurdi]

Had an interesting chat with a porsche specialist, he categorically said it could not be the:

Coil

HT leads

Plugs

Flywheel sensor / Speed reference sensor

Dizzy / Rotor Arm

This is without seeing the car. I'm somewhat bemused by this. He said I should leave the car with him for a week to diagnose the issue. 

SS

Edited September 14, 2023 by SurlySurdi

[Type911]

Wow, he's good then..............................

[Roy M]

Is it still hesitating in the 2-3k range,? That was the exact symptom I had with a bad cht sensor. At the time I didn't rev much higher as I wasn't sure how serious it was so don't know if your other symptoms fit.