Technical 04 1.2 8v Punto - problem with RPM sensor?

[a1ant]

Hi mate,

Fuel issue shouldn't trigger the crank sensor error. And the fact that your LP pump is priming rules out the fuel cut off switch.

Does your LP prime and then stop? or continue to run?

Also ive just read back through this thread to see if we are missing anything... you say the code was P0355... are you sure this is correct? and it wasnt P0335

Did you check the continuity of the wiring for the crank sensor?

Alan

 

[Devondan]

Hi Alan

That's what I thought, the pump primes then stops.

I also have coil pulse which is why I don't think its continuity between the crank sensor and ECU. Plus the fact that it fires consistently randomly, which it did with the old sensor but stops when you disconnect it. If there was no continuity there would be no spark and if it was intermittent the firing would be more irregular?

I haven't had time to do much more investigation but I'm still thinking ECU and am considering sending it to the ECU doctor to be tested? (£35)

Dan

 

[a1ant]

Hi mate,

Don't know what diagnostics software your using, but have you got a scope function? to be able to look at the crank sensors output in more detail.

As you say, the fact it fires sometimes but then not at all if you disconnect the crank sensor suggests its getting some sort of reading from it, but to rule it out all together its best to look at it on a scope.

I cant remember if you did the ECU test as described in the guides to check the ECU is sending the correct signals to the coils? And then tested the coils?

It does look like heading towards ECU failure as potentially an option.

Alan

 

[Devondan]

Hi Alan

Yes I got the bulb flashing regularly at the coils and the AA man used a plug in bulb on the injectors and they regularly flashed too. So either I'm not getting fuel from the pump to the injectors or the crank sensor is sending a signal to the ECU which is triggering the fuel and coil pulse but for some reason the ECU is misbehaving and not sparking at the right time?

I havent got any diagnostics (yet anyway!) I'm relying on the AA man's box of tricks which gave the codes and also showed the RPMs the sensor was detecting which was 0 with an occasional spike to about 300 which is prob when it fired.

I suppose its possible that the sensor has an identical fault to the original one, but I think thats unlikely?

If I buy the leads is the software free to look at the sensor?

 

[a1ant]

Hi mate,

I agree that it's unlikely to have 2 faulty sensors.

I think the next steps would be to
A) check your getting fuel at the injectors
B) check the timing as it may have slipped.

Even though you can hear the LP pump priming, as you say it doesn't mean it's actually pumping fuel. So it's DEFINATELY worth checking!

Most people on here use a program called Multi ECU scan. If you google it, the site will tell you all the details of what cables you need and what features come for free, and which ones you have to pay for. I don't use it myself so hopefully someone else will be able to advise on if it has a scope function etc.

Alan

 

[Devondan]

Will try A, not sure B is necessary, it is firing on random cylinders and there is no damage to the cam belt. Plus the fact that you have to take off the pulley to see the sodding marks!

Dan

 

[Ziggy122]

you can check the timing by removed the phlonic wheel and top cam cover

its half hour tops todo

ziggy

 

[Devondan]

Me again! I took a gamble and the lazy option and sent the ECU off to be tested and rebuilt, the good (ish) news is that the ECU is fine. Which leaves me back at square 1! If it doesn't rain I'll check the markings (assuming it has any) but given that the punto runs with the timing out a few teeth and there's no obvious sign of belt damage I have my doubts, which brings me back to an electrical fault - continuity between the RPM sensor and the ECU or something else? What happens if the cam sensor fails?

 

[Devondan]

1/2 hour? sadly not ! one of the three bolts holding the engine mounting to the block will not shift, Ive tried heat (only have a blow torch), no joy, so have sprayed it with wd40 and will leave it for a bit, I'm in danger of rounding the nut off.

 

[s and b]

just reading a james dillon article about similar problem on a 3 pot vw and another tec mentioned he had similar problems with puntos fitted with wrong plugs,ive mentioned this a few times on this forum you must fit correct plugs and is why i only recommeng ngk,maybe this is your issue? i once blew a fiesta engine management system because i had fitted non resistive plugs

 

[fingers99]

What happens if the cam sensor fails?

Starting issues. Running issues. Generally when the TDC sensor fails tha ECU thinks the engine isn't turning and so stops firing the injectors and plugs. But they can fail permanently or intermittently. If the sheilding breaks down you can get interference related issues, including a hard rev cut.

Always use R plugs (never use copper ignition leads). The use of anything else on any car fitted with EFI will cause any amount of trouble. I prefer NGK, but Denso, Champion, and even Bosch make decent plugs.

 

[Devondan]

Interesting but I doubt its anything to do with my problem. As a recap - the engine suddenly lost nearly all power (felt like it was running on 1). When I tried to re-start it it fired occasionally but will not run (and remains the same now). The ECU fault said RPM sensor, I replaced the sensor which made no difference. I've had the ECU tested and its fine, so unlikely to be damage caused by a plug problem. My tests so far have established that I have fuel to the injectors, an injector pulse and a spark.

My next check was cam belt until I'd got stuck by a seized engine mounting bolt. and am still thinking about how to get it out.

 

[fingers99]

Interesting but I doubt its anything to do with my problem.

Yep, but you did ask!

It's rare indeed to get RPM sensor as a fault code. If the error is still there, I'd suspect the wiring. It's shielded and pernickity. If the code is still there after clearing I'd suspect a wiring fault upstream of the connector.

 

[Devondan]

Really I thought it was a common Punto fault? I cant test the ECU because I dont have the leads or software and am reluctant to throw too much money at it.

Any suggestions as to how to test the wiring?

Dan

 

[fingers99]

A good hard look is a fine start look for beaks in insulation, chaffing, soldered joints coming undone. Connectors need to be clean, the TDC sensor lead must be earthed at one end (and only one end) -- the shielding.

Most of the time you're just testing for continuity. Wiring diagram is your best buddy.

There are places that will test the ECU for £30 or so.

 

[Devondan]

I've tested the sodding ECU!!! What I cant do is read it - Wiring looks fine, connections are good. It has two wires which connect into the sensor and then disappear into the loom.

BUT ..... if I remove the sensor I get no firing, if I reconnect it I get an intermittent fire on one cylinder only. So something is happening, I am also getting fuel and spark pulses which I wouldn't if it wasn't working. How is a wiring diagram going to help unless it shows which pin in the ECU plug it is connected to? Shielding looks fine but is unlikely to cause my symptoms

 

[fingers99]

I've tested the sodding ECU!!! What I cant do is read it - Wiring looks fine, connections are good. It has two wires which connect into the sensor and then disappear into the loom.

I cant test the ECU

Well, I can only go on what you write. How did you test the ECU, BTW?

BUT ..... if I remove the sensor I get no firing, if I reconnect it I get an intermittent fire on one cylinder only.

No engine will ever fire with the TDC sensor disconnected. You've stablished nothing, nada, zilch.

I am also getting fuel and spark pulses which I wouldn't if it wasn't working.

If it wasn't working at all, sure.

How is a wiring diagram going to help unless it shows which pin in the ECU plug it is connected to? Shielding looks fine but is unlikely to cause my symptoms

Well, if you've tested the ECU, and if the ECU is fine, and if you're getting a code which says that the TDC sensor is faulty, then that's the logical place to look, isn't it? If you've changed the TDC sensor and you're still getting the code and etc. you'd naturally search upstream of the TDC connector.

This might involve unpeeling the harness and using a wiring diagram to give you ideas of where to test for continuity, to tell where the earth for the TDC shield is and, yes, reveal the ECU pinout. A visual inspection is generally quicker than testing, but it really is only a first step.

Ah well, your ignorance (and we are all ignorant in the sense that we don't know it all) is outweighed by your arrogance. Maybe someone else will help. I'm out of here.

 

[Devondan]

Amazing isnt it, how easily people mis read posts (or how easy it is to cause offence accidentally)!! I intended no offence and apologise if I did, I was trying to relay a sense of frustration at this car! I'm grateful for help but its also frustrating when people who try to help don't read the whole thread, and yes I expect I'm guilty of the same sin!!

The ECU was tested by the ECU Doctor, the ECU error readings were given to me by the AA who did the initial diagnostic, As I explained I don't have a the cables or software to read any new error codes, but the symptoms are the same.

I have visually inspected the wiring and the connections, (I have taken apart the plugs) which are good, but I have not stripped open the wiring loom.

My question about the wiring diagram was a genuine one, the diagrams in the haynes manual are not helpful. If there is one that shows the relevant pin numbers it would be really helpful and easy to do a continuity test with a multimeter. Is one available on line?

I'm still interested to know what happens if the cam sensor fails, is that a different error code and what impact does it have on the engine?

I should also add that I'm not a complete dingbat when it comes to engines, I race twinshock motorcycles and rebuild my own engines however modern electricery has me beaten on this so far.

I am also trying to check the cam timing as the belt is a bit looser than I'd like, but am frustrated by a seized bold at the moment.

Regards
Dan

 

[a1ant]

Hi mate, me again unfortunately!

If the cam sensor failed it should produce a different code such as P0340. A failed cam sensor can potentially cause difficulty starting etc similar to that you are experiencing as Its used to determine cylinder 1 postion on startup. Like any sensor, it may be failed but not necessarily enough to bring on EML.

Having re-read the thread, can we confirm if the AA mans fault code was P0355 or actually P0335? P0335 would point to crankshaft sensor, P0355 wouldn't.

I still have a feeling it could be a timing related issue, as you say the belt is loose, and if the crankshaft and camshaft sensors are seeing their marks at different points, it could explain why it thinks one (crankshaft sensor) is faulty.

Anyway,

Looking at the engine bay, the ECU connector on the RIGHT hand side is connector A....
starting at the bottom left of the connector (with the clip on the right as you look at it)....
Pin1 bottom left. Pin 10 bottom right
It then goes up from there, ie next row up is pin 11 on the far left, pin 19 far right... etc.

Cam sensor.....
Pin 25 (red)
Pin 35 (white)
Pin 34 (black)

Crank sensor...
Pin 32 (black and green)
Pin 24 (green)
Pin 20 (white)

Hopefully i' ve explained that all ok

Where abouts are you located?

Alan

 

[Devondan]

Thanks Alan, that is helpful, I'm pretty sure the error was P0335 but will check. The nice man from the AA wrote it down! Plus the second man from the AA also said RPM sensor.

The only thing that bothers me is that I think the RPM sensor only has two leads coming from it - I'll go and check! PS I'm near Honiton.

Got to into town for a new 15mm socket and a can of plus gas!

Dan