The interweb seems to think that the crank sensor signal may not fail completely. Obvious reasons like dodgy connectors through to heat damage. I hate doing diagnosis by part swap, but it's looking like throwing a tenner at it may be worth a punt if I'm going to be taking it out to give the plug and socket a clean.
Technical 1.28v very hard to start
- Thread starter boguing
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Technical 1.28v very hard to start
If the crank sensor is stopping the start
There would be no spark
No rpm on scantool
No injector pulses
Plugs dry
Are we sure it's petrol and not oil?
We have conflicting information
In one post the rev counter is moving, another it's not
You can not rely on the rev counter, but it is a guide
Crank sensor fail in two ways
Broken wire internally worse when hot generally
Loss of magnitsam starts but will not rev past a certain point
I thought we proved it was a fueling issue ?
Wouldn't start on petrol but will on easy start
Engine check light on is normal until the engine has fired
Did we change the MAP sensor ? If it reoccurring afterwards, it's one thing we know it isn't
There would be no spark
No rpm on scantool
No injector pulses
Plugs dry
Are we sure it's petrol and not oil?
We have conflicting information
In one post the rev counter is moving, another it's not
You can not rely on the rev counter, but it is a guide
Crank sensor fail in two ways
Broken wire internally worse when hot generally
Loss of magnitsam starts but will not rev past a certain point
I thought we proved it was a fueling issue ?
Wouldn't start on petrol but will on easy start
Engine check light on is normal until the engine has fired
Did we change the MAP sensor ? If it reoccurring afterwards, it's one thing we know it isn't
You're right, I was jumping ahead a bit.
Revcounter. I asked the daughter if it moved while trying to start. I saw today that it does, about 1mm when it sees power. It doesn't do anything else until it fires. Obviously I'd like to see what it does on a screen with a laptop connected, but didn't think of that at the time.
I didn't look at the plugs today. Last time I was up there sorting the relay problem they were damp/wet but not so bad that I felt the need to dry them, gaps were about 1.25mm, closed them down to 0.9 Pretty certain not oil. (Oil consumption still not measurable, (90k Miles).
I'm almost certain it's fuelling. Anything in the ignition system would give other symptoms, there are none. If the car had a cold start injector I'd be looking hard at that. Likewise a cold start valve. So it seems to me that whatever the ecu is supposed to do (longer, earlier squirts?) it's not getting the info it needs from something.
MAP sensor, no it hasn't been changed - do they fail in this way - no other symptoms, no fault logged? I must admit that I didn't check the pressure while connected. That will be for the next session.
Looking again at your earlier list. Air filter's good. I didn't check the ducting for obstruction though. Petrol vapour recovery system. That's worth looking at, any pointers to usual failures?
Going back to the damp plugs. I think that was just from multiple attempts to start (with just not enough fuel?) and that flooding isn't the problem. I'm also thinking that easy start wouldn't help a flooded engine?
It seems to me that it's fuelling that's the problem, and we have the revcounter not behaving. Got to be linked, surely?
Really appreciate this, and apologise for not working through your earlier list methodically - I did so like the temp mismatch theory that I must've skipped bits.
Revcounter. I asked the daughter if it moved while trying to start. I saw today that it does, about 1mm when it sees power. It doesn't do anything else until it fires. Obviously I'd like to see what it does on a screen with a laptop connected, but didn't think of that at the time.
I didn't look at the plugs today. Last time I was up there sorting the relay problem they were damp/wet but not so bad that I felt the need to dry them, gaps were about 1.25mm, closed them down to 0.9 Pretty certain not oil. (Oil consumption still not measurable, (90k Miles).
I'm almost certain it's fuelling. Anything in the ignition system would give other symptoms, there are none. If the car had a cold start injector I'd be looking hard at that. Likewise a cold start valve. So it seems to me that whatever the ecu is supposed to do (longer, earlier squirts?) it's not getting the info it needs from something.
MAP sensor, no it hasn't been changed - do they fail in this way - no other symptoms, no fault logged? I must admit that I didn't check the pressure while connected. That will be for the next session.
Looking again at your earlier list. Air filter's good. I didn't check the ducting for obstruction though. Petrol vapour recovery system. That's worth looking at, any pointers to usual failures?
Going back to the damp plugs. I think that was just from multiple attempts to start (with just not enough fuel?) and that flooding isn't the problem. I'm also thinking that easy start wouldn't help a flooded engine?
It seems to me that it's fuelling that's the problem, and we have the revcounter not behaving. Got to be linked, surely?
Really appreciate this, and apologise for not working through your earlier list methodically - I did so like the temp mismatch theory that I must've skipped bits.
The fuel rail schrader is a larger diameter, and not threaded externally. It is supposed to be a pop-on fitting for a pressure gauge, quite common, but not understood by the cheap gauge manufacturers. I found a set that would fit, but it contained nothing to depress the valve core. Would need the core removed, which defeats the purpose of finding the pressure after an overnight.
They should be 1.0mm. If the gap is too small, it will spark at a lower voltage, which can lead to misfires. Probably not the cause of the problem here, but need opening up again.
Both 0.8 and 1.25 are not the problem
Depending on which manufacturer or alternative has been fitted they are supplied with either 0.8 or 1mm
They start to fail at 1.8 on most engines, my 69hp is a little less 1.6-1.7 but it is leaking oil a bit
Depending on which manufacturer or alternative has been fitted they are supplied with either 0.8 or 1mm
They start to fail at 1.8 on most engines, my 69hp is a little less 1.6-1.7 but it is leaking oil a bit
Where (and how) were you measuring the voltage?
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Haynes doesn't give a gap, the majority of opinions on the web seem to be split between 0.8 and 0.9mm. It gets even more varied if you go to the sites selling different brands to suit this engine - some go up to 1.2mm
Engine ECU via scantool
You can't measure it with a multimeter
Before the starter start turning, it's almost a dead short
Fiats officially specs
Most are original fitted with
NGK 4983 DCPR7E-N-10
Which come pre gapped at 1mm
But there's quite a lot of leeway before there's any problems
NGK 4983 DCPR7E-N-10
Which come pre gapped at 1mm
But there's quite a lot of leeway before there's any problems
Thanks, that's what I guessed.
What I've learned from that post then is that without enough V 'somewhere' the tacho won't display but the engine will start. You mention that if the BCU sees low V it will reset the clock. Your car will start with no tacho display. You use Scan Tool (?). Will MES give m the same graph?
We have the tacho not moving, and on this occasion the clock has not reset. (Did previously, dying battery).
I can see from the wiring diagram that the ECU and BCU have different paths to the battery. I've never taken the positive battery terminal apart to clean it. That might be giving ok V to the BCU, less to the ECU.
All of that said though, your car starts with low V, ours doesn't.
My present feeling is that there's something not telling the ECU to give a richer cold start mixture.
It doesn't appear to be the two temp sensors. I have (twice over the last few years) noticed a water temp sensor error logged. I haven't had one since I gave the ecus and fuse panel (top and bottom) a really good cleaning. Both gave sensible readings on the cold engine, and when it was running.
MAP sensor. Has never given an error message. Does that rule it out?
On the one hand I'm thinking that with no errors showing this must be a good old-fashioned air leak or blockage. On the other we have the apparent low V on the tacho with the engine spinning as fast as it ever has.
I'll check that battery terminal, and take the intake system apart so that I can see through it all.
I've always worked on that basis! (Points gaps, critical, plugs not).
Yes the BSI fails first at around 6.5V
The ECU fails a little lower, but not much, maybe a volt or so, sensors need 5V
First job, is while it's failing measure the RPM and voltage at the ECU
If the clock not resetting, I would expect the counter to bounce up a bit, with the new information, it's not, I would highly suspect the CKP sensor
Yes you can do the same with multiECUscan and graph both voltage and RPM
CKP should be easy to diagnose via MES as long as it's tested while the Rev counter is not moving
The ECU fails a little lower, but not much, maybe a volt or so, sensors need 5V
First job, is while it's failing measure the RPM and voltage at the ECU
If the clock not resetting, I would expect the counter to bounce up a bit, with the new information, it's not, I would highly suspect the CKP sensor
Yes you can do the same with multiECUscan and graph both voltage and RPM
CKP should be easy to diagnose via MES as long as it's tested while the Rev counter is not moving
Thanks again. She's coming down here on Saturday (as long as she's bought her own brake cleaner). I'll have a sensor waiting if that test indicates it's at fault.
I'm trying to get my head around why a failing sensor would affect the starting. As we've established, the V gets pretty low while cranking and coupled to some sensor degradation there's only a marginal signal, and the ECU somehow interprets it late and now the timing's retarded? Anything will start with a whiff of brake cleaner though, retarded or not. Engine fires, lots of V, all is good?
I'm trying to get my head around why a failing sensor would affect the starting. As we've established, the V gets pretty low while cranking and coupled to some sensor degradation there's only a marginal signal, and the ECU somehow interprets it late and now the timing's retarded? Anything will start with a whiff of brake cleaner though, retarded or not. Engine fires, lots of V, all is good?
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Just a thought. I scrolled through the engine parameters when it was running last weekend, but only paid much attention to the sensor stuff.
Is it possible to see whether the engine ecu has decided to enrich the mixture for starting? That really would help if it did.
Is it possible to see whether the engine ecu has decided to enrich the mixture for starting? That really would help if it did.
I'd love to close this off, but I don't feel we're there yet.
Pretty sure that some of the problems were dirty contacts on top of and under the engine bay fuse box and the ECU plugs - no more indicated and spurious fuel relay and water temp sensor fault indications.
It's been starting fine, but that's probably because it knows that the daughter has a can of brake cleaner under her seat.
I gave it a new crank sensor yesterday and we now have a tacho reading when it's spinning with no 12V to the coils, so that's good. I gave it some plugs (and leads because one snapped) and guess we'll see how it goes. I'm afraid I didn't have time to plug into MES.
Pretty sure that some of the problems were dirty contacts on top of and under the engine bay fuse box and the ECU plugs - no more indicated and spurious fuel relay and water temp sensor fault indications.
It's been starting fine, but that's probably because it knows that the daughter has a can of brake cleaner under her seat.
I gave it a new crank sensor yesterday and we now have a tacho reading when it's spinning with no 12V to the coils, so that's good. I gave it some plugs (and leads because one snapped) and guess we'll see how it goes. I'm afraid I didn't have time to plug into MES.
