Crank Sensor?

[mchristyuk]

Chaps,

One for the engine gurus out there..

I've had an intermittent problem with my car where I get a flat spot that seems to last from 2k RPM up to 5k RPM when all of a sudden the engine comes alive again and pulls strongly.

If I put my foot down, once above 2k RPM I can play with the throttle pedal but it seems to have little effect on my rate of acceleration nor engine noise/effort/rpm. It's almost like it's not letting the throttle open fully until I hit 5k RPM.

In the past 12 months I've had replaced all the knock sensors, lambda sensors, 1 coil, plugs, filters, MAP sensors, turbo pipework and dump valves.

The car has no CEL's, no errors in the ECU at all and the engine runs faultlessly (no smoke, no misfire) apart form this annoying (massive) flat spot.

A colleague and I were staring in the engine bay at work today discussing what on earth it could possibly be (we've ruled out an air leak on the turbos as it's producing the right amount of boost (around 0.7bar peaking at 1.1bar)). He seemed convinced it's more of an electrical problem than a mechanical problem, and I'm starting to agree with him. He then suggested I double check the MAP sensors because if there is some kind of discrepancy there it could be causing all kind of issues with the electronic throttle and ignition.

Well I've put the multimeter across them and they're reading the right values within the tolerances given in the book of words. I then decided to start going around all the connectors trying to find anything amiss.

That's when I got to the crank position sensor.. the book says it should be 650ohm (which seems around normal for a lot of these sensors..approx 500ohm). However I got 1300ohm which seems way out to me.

Now I always thought a crank position sensor would cause a misfire, or failure to start, or a sporadic RPM dial.. none of which I have.. however it's clearly out of spec and could therefore be feeding the ECU duff information.

What do people think? Have I found my culprit?

Looking for a replacement (as it's clearly not right) Eurospares are out of stock (and I bet this will be another discontinued part!) but stumbled across this 1999 Fiat Punto 1.2 crank position sensor http://www.ebay.co.uk/itm/Engine-Crankshaft-Position-Sensor-Fiat-Punto-Panda-Doblo-Cargo-Bravo-Brava-Crank/331315598390?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3De57b709acf4b43309259ceaa627945ae%26pid%3D100338%26rk%3D12%26rkt%3D19%26sd%3D291239967479

At first glance it looks identical to whats mounted to my 3200; what do you think the chances are that this is exactly the same part but in a Fiat box??

Cheers

Mark

 

[allandwf]

I'm not convinced it's crank sensor, they usually work then fail, possibly TB, won't throw an error if both circuits agree.

 

[mchristyuk]

The TB butterfly tracks the pedal perfectly with the engine off and intakes disconnected... I would have thought if it was playing up that wouldn't be the case?

 

[allandwf]

The TB butterfly tracks the pedal perfectly with the engine off and intakes disconnected... I would have thought if it was playing up that wouldn't be the case?

Agreed.

 

[mchristyuk]

Though of course if there was a discrepancy between the crank and the cam sensors I'd expect the ECU to throw an error.. which it isn't... but surely 1300ohm for a sensor which should be 650ohm points to something not being right??

Mark

 

[Gazcw]

"I've had an intermittent problem with my car "

Should I expect Benny to be along shortly all surprised that it is only an intermittent problem?

I would think such a difference in resistance is indicating a potential problem at some point even if the sensor is not the cause of you flat spot.

Hope you can sort it.

 

[mchristyuk]

Haha.. yeah asking for it really

To be fair, every Italian car I've had has been a royal PITA... why do I keep coming back and doing this to myself?!

I've read a few BMW forums now where the sensor going South hasn't caused any CEL's but caused flat spots and reduced performance.. so there's a glimmer of hope here.

Shame it's such an @rse to get at.. does anybody have any tips for removing the dipstick tube???

Mark

 

[Rex B]

Hi

Give Mcgraths a call they would normally keep a stock of sensors.

You say you are getting the correct boost but at what RPM? is boost only prodeced at 5,000

Rex B

Rex B

 

[mchristyuk]

Hi Rex,

Good idea. I'll give them a bell Monday and see what they've got, also see if they think the crank sensor could cause some kind of misbehaving.

We didn't have the logger recording frequently enough to get a very accurate picture, but it seemed to have around 0.3bar at 2k RPM, 0.7bar at 4k RPM and overboost of 1.1bar at 5k RPM. I believe the 3200 is set for about 0.8bar?

My colleague had some issues with his Subaru relating to the crank sensor and in the end it was just contaminants on the end of it. So I'm going to give it a good clean tomorrow and see if that brings the resistance down to spec at all. Would be nice if once and a while an issue was that simple!

Mark

 

[jluis]

I dont think its the crank sensor but i have a used one you can have for 10 quid plus postage.
Mine has a hot start issue and i replaced it with a new one only to find out that the sensor was fine and the engine does the same with the new one.

Your problem seems to point to throttle body even if you see it moving.
I saw a similar behaviour altough more serious where the car would not even accelerate when the car is stationary and that was swarf on the tb magnet.

Try pushing the butterfly open with the engine off and key off all the way open.
You should feel a linear force from the spring.

If it feels sticking while opening, you may have a corroded magnet on the tb

 

[jluis]

Also, the logging frequency on this ecu is quite low (1 read per second) so you can only get a decent reading if sampling only 1 sensor at the time which is a bit useless

 

[mchristyuk]

I dont think its the crank sensor but i have a used one you can have for 10 quid plus postage.
Mine has a hot start issue and i replaced it with a new one only to find out that the sensor was fine and the engine does the same with the new one.

Your problem seems to point to throttle body even if you see it moving.
I saw a similar behaviour altough more serious where the car would not even accelerate when the car is stationary and that was swarf on the tb magnet.

Try pushing the butterfly open with the engine off and key off all the way open.
You should feel a linear force from the spring.

If it feels sticking while opening, you may have a corroded magnet on the tb

Hi Jorge,

I'll definitely take you up on your offer of the sensor. Mine is out of spec to it can only be a matter of time... PM me your bank details and I'll send the money over.

Regarding the TB it's perfectly smooth.. and seeing how hypersensitive they are to throwing CEL's I would have thought that as soon as the pedal pot didn't agree with the TB it would be throwing a CEL?

My gut feeling is telling me this is some kind of timining/ignition/fueling issue.. something somewhere isn't telling the ECU the truth.. just have to find what as nothing is throwing an error!... which is quite unheard of for a 3200, normally they like to throw errors when everythings fine!

Mark

 

[allandwf]

Mine bogged down sometimes, and didn't throw an error. It was the pedal pot in my case.

 

[mchristyuk]

Mine bogged down sometimes, and didn't throw an error. It was the pedal pot in my case.

Already replaced mine after the old one died.. checked the voltages on the new one and they're all spot on... grrr

Mark

 

[davy83]

i think timing, fuel or some thing in that area. i think the crank sensor could be a problem if it was reporting the wrong engine speed this would definitely cause some problem. also being inductive and proximity related they produce a bigger signal at higher revs, so its possible, it does not work at all up to 5000 rpm? i would change it out what about knock sensors? did you say you had changed these? if the ECU thought there was knock it would retard the ignition all the way back and leave the engine flat, sounds sort of like what you are reporting? These only throw up an error when they don't produce any signal (they get wet in the VEE there and they are not water proof doooh!) But if the knock sensors produced too much signal then this could also make it flat, its odd that its such a well defined rev range, which does point to something rpm related like the crank or CAM sensors, either of these might be the culprit. I would change em both if it was me. an ODB reader would tell you rpm, and if you had a strobe meter on the crank you could compare them and see if its right?

 

[mchristyuk]

Hi Davy,

I wouldn't say it doesn't work at all up to 5000rpm, I don't know how I would tell.. what I do know is the engine suddenly comes alive at the higher RPM's and has a massive flat spot below. When a turbo pipe came off it didn't even come alive after 5000rpm so I know what that feeling is like!

The knock sensors have been changed (CEL signalled one on the way out, so changed both).

I've just tried cleaning the cranks sensor which made no difference to the readings.

Measured the CAM sensor and that's reading 800ohm.. but the book of words doesn't appear (that I can find) to give any value ranges for it.

Has anybody measured these sensors with a multimeter and can give me an idea of what theirs are reading? They're dead easy to get to as the connectors just sit on top of the engine

Mark

 

[davy83]

i thought there was a page in the manual that gave the resistance of the sensors but i am not near my book, and i cant find it on the electronic version, if i do i will let you know. I asked the missus to look it up and that was ..... well ... not successful. They are only 34 pounds so not the end of the world if its a problem. not hard to fit if i remember right. The heat in the engine bay really shortens the life of these sensors.

 

[mchristyuk]

Hi Davy,

Each page that deals with where the sensor is gives an expected OHMS reading for the sensor.. except the cam sensor. Maybe there's another page with a list on.. I'll go for a flick through it again and see if I can locate anything.

Regarding the replacement of the two sensors..

1) I managed to get the crank sensor undone and loose, but couldn't get it out because it hits the dipstick tube. Considering how tight it is down there how do you get the dipstick tube loosened off to move it enough to get the sensor out? Is there any cunning tool that helps (I have a reasonable selection of hex tools)?

2) Similarly the cam sensor, it looked easy enough and I got 3 of the 4 bolts out from the cover, but the fourth is hidden under a metal pipe which then has the secondary metal air pipe running in front/above it.. and then another metal coolant pipe in front of that making access to it nearly impossible without removing a lot of pipework.. there has to be a simpler way?!

Cheers

Mark

 

[Rex B]

Mark,

The camshaft sensor is a semi-conductor and there are no measurements given in the manual for it.

The trick for quick removal of the the Crankshaft sensor is to put a small dent in the dipstick tube in line with the sensor which then enables the sensor to be removed without removal of the tube. You however do have to struggle to remove the tube to do this.

Rex B

 

[mchristyuk]

Mark,

The camshaft sensor is a semi-conductor and there are no measurements given in the manual for it.

The trick for quick removal of the the Crankshaft sensor is to put a small dent in the dipstick tube in line with the sensor which then enables the sensor to be removed without removal of the tube. You however do have to struggle to remove the tube to do this.

Rex B

Hi Rex,

Thanks for that.. however, is the removal dipstick tube just a case of struggling in the dark to free the 3 bolts retaining it? Does it then spew oil all over the floor in doing so? Is there anything I can remove to make life a little easier? (I did remove the oil separator box and the throttle body intake pipe).

Cheers

Mark