Fiat 500 Crank-no-start got really, really complicated...

This one is driving me nuts so I thought I'd reach out for ideas before I set-it-on-fire!

Fiat 500 2009 1.2 8v Non-Stop-Start - UK RHD

Car refused to start
Recovery replaced broken engine-earth but car still crank-no-start.
Car scanned - no codes but no engine-speed when cranking so recovery replaced crank sensor.
STILL crank-no-start so car was brought to us.

We did a thorough scan/check over - everything seemed OK other than there's no engine speed when cranking...

Crank Sensor is a 2-wire VR sensor (Stop-Start cars get a 3-wire Hall)
Checked the sensor - resistance near-enough correct - signal looks OK on a scope (sensor NOT connected to car when testing)
Checked wiring - lights a test light easily
Checked ECU - neither signal nor ground pins have ANYTHING on them - absolutely nothing

At this point I called the ECU - I'm pretty sure the engine earth problem damaged it as we've seen this before with Fiats

Sourced a replacement (not a factory - they're more than the car is worth - a warranted 'virginised' ECU)
installed the 'new' ECU and - STILL crank-no-start!!!!!!!!!!!
Tested ECU (sensor disconnected) - now getting 2.1v on the ground and 1.2v on the signal which seems wrong but is better than 'nothing' before!?

The new ECU is clearly 'working' better than the original BUT still isn't seeing engine speed (and thus the car will not start)???

Ideas??

Well I've learned a lot in the last week - primarily that these ECUs don't report engine speed when cranking so we can rule that out as the problem.

Sadly I still have a crank-no-start Fiat and I'm absolutely 100% baffled and it's about to get kicked into the nearest scrapyard...

We have 2 ECUs - both have been tested on the ECU guy's "test" car and it starts and runs fine - I think that rules-out an ECU issue (and the odds of 2 ECUs having the same issue is too small anyway??)

I have cam and crank signals which look fine to me - both sensors have been swapped with known goods - no change.

I DON'T have spark but a 'Coil Test' from the diagnostic gets spark so the coil pack works, it's just not being triggered for some reason (and we tried a known-good coilpack just for laughs - no change)

I believe it's not firing injectors as there's no fuel on the plugs/smell of fuel in the exhaust - likely for the same reason it's not firing the coils??

It's clearly not a fuel issue but I've checked the fuel pump and it's working fine (and it's triggered by the crank sensor so that's more proof the ecu/crank sensor is working)

All that's left is that it's jumped-time but if the timing slipped we'd still have spark surely?? At the wrong time perhaps but we'd still have spark?

Note: I've been through all the keys/codes/immobilizer stuff, it's all OK and 'Starting is authorised' (it wouldn't crank otherwise anyway)

Back probe cam sensor and see what you get if that's ok unplug MAF sensor and try starting car. A shorted maf car reek havoc on any car line. Also did you test the asd relay?

Thanks for the reply - any help in a storm gratefully received!

No MAF on this car - it has a MAP which I've checked and I've tried starting with and without - I've even disconnected the Knock Sensor to rule that out

The ASD relay is good - the car can spark (when the diagnostic tells it to) - it's just not sparking when it cranks for starting (which is why I assumed this was an engine speed issue - I can't think of anything else which would stop spark but allow crank)

Other thing to check is fuel pressure and if there's fuel in tank. Have you tried using ether sprayed in throttle body?

There's fuel in it, pump works, pressure at rail

There's no fuel pressure sensor so it wouldn't know it had no fuel and should fire the coils anyway!?

I checked the timing belt today - it's in good condition, no missing teeth etc. - but even if it had slipped, we should still be getting coil triggers (at the wrong time perhaps but they should happen??)

It's not triggering the coil or the injectors but you can trigger those from a diagnostic tool so they're connected OK/grounded/working - just not being told to work

I went through EVERYTHING again today and we've given-up - I've put all the parts back on which it came with and the owner is (against our advice) taking it to the main dealer - a tech from them called today to check what was going on and I went through what we've done and their response was "if we find the same we'll be putting another ECU into it" which - erm - yeah...

Lol actually it could be the bcm not sending signal to asd relay to to allow injectors and coils to start

Hardtopdr2 wrote:

Lol actually it could be the bcm not sending signal to asd relay to to allow injectors and coils to start

Coils have power before/during/after cranking and Fiats don't QUITE work that way

The body computer authorizes starting (via CAN I'm assuming) - the underbonnet fusebox then feeds a bunch of fuses either directly or through the EC Relay (control of that relay is fed from the same megafuse and grounded by the ECM when authorised - e.g. that's the immobiliser circuit)

It's even running the Fuel Pump (triggered by the Crank Sensor) so it's doing everything it needs to do EXCEPT triggering the coils...

I'm 100% convinced we have a logic/signal problem and not a power/ground problem and I have no idea what else to check.

It even possible we have 2 dead ECUs - that would be really annoying but a common fault on Fiats are misfires caused by faulty ECUs - we may just have 2 ECUs which have given-up on firing coils entirely - or Crank/Cam signals which aren't quite in-range - or "something else" and I can't keep guessing forever - sadly...

I'm willing to bet we get a car with the same engine within a week of this leaving - and yes, I'll be testing that anyway

Hi There,

I feel your pain! I am currently looking at a 16 plate Fiat 500 with a ‘no fault code, crank but no start’ issue.
This one has stop/start, so has a hall crank sensor. We have spark and fuel spray with the injector rail pulled. It’s already had a crank sensor and the head repaired as it was low on compression on one cylinder caused by leaking valves. It’s believed the vehicle was poor running for a week or two before it stopped all together.
I can get it to run on easy-start so spark is happening at the right time, but I don’t know about the injector timing yet.

Unfortunately I can’t offer any advice to help with your issue, but am on the scrounge if you can help.
I don’t suppose there is any chance you have any cam/crank correlation scope images?

Many thanks
Rupert S

This is the only cam/crank I saved - obviously I've no idea if it's OK as my engine doesn't start and this is a 2009 1.2 8v which MIGHT not be the same?

I've attached a screenshot and the Snap-On LSM savefile (you can download ShopStream Connect for free to read that file if you need)

p.s. interestingly, the same pin on the ECU reads the VR Ino stop-start) and Hall (stop-start) Crank Senso and the ECUs only differ by a software revision code so I suspect the ECU simple reads pulses over a certain voltage rather than worrying about the wave/wavelength specifically...

Thank you for that.

The engine has been about for years and I believe the crank pulleys are the same on the inductive and hall sensor systems. It tells me the cam trigger hasn’t moved if the patterns are the same. I’ve just got to find a way of measuring both with works busted scope that doesn’t work properly.

I have a suspicion that an issue with the fuel that is playing a role in my issues so I will be taking the pump out and draining the tank.

Thanks again.

I have same issue, have compressions, sparks,fuel,sensor readings etc...won't start...spray easystart runs like a dream!!!!!
Did anyone get a conclusion

The 500 I was looking at was as I suspected and had contaminated fuel. I’m unsure if the fuel problem caused the burnt out valve on one cylinder or there were two separate issues. It turned out that the customer drove it for nearly two weeks with a misfire!!!

Mine did have a low compression, done headgasket etc now have good compressions,spark,fuel,sensor readings,runs on easy start....customer has since said put fuel in 2 days before breakdown and wasn't running brilliantly for a while!!! Will be draining fuel and putting fresh in....thanks