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Engine Cranks Over, But Does Not Fire...



Well, back to the same old problem I had with my car. Although this time, its not my car - I've tried everything I can think of (considering ive had this problem 10x over, and its worked fine since) - Just thought I would post up to see if anyone had any better ideas.

Its a Mk1 with a 172 Ph1 engine, the same as mine. The ECU is from a Ph1 also, and has been fitted with an emulator to disable the immobiliser completely - This is 100% confirmed as it starts my 172 Mk1 perfectly fine, every time.

Basically - Key In. Turn to position 2. Fuel pump primes. Then go to crank it and it cranks over for as long as you hold it, just never fires up. There is no fuel pump running when cranking (no fuel comes to the rail), nor is there any injectors, or any spark (tested with spare plug and lead).

Below are the things we've tried. Every one of the sensors are 100% known working from either my own car which as we know from above runs fine, or a 172 Ph2 which is faultless.

  • Crank Sensor
  • Knock Sensor
  • MAP Sensor
  • Coolant Temp Sensor
  • Throttle Position Sensor
  • Lambda Sensor
After swapping all those we still had no joy. So we decided to buy a new engine loom from a 172 Ph1. We modified it as per the guide I made for the Mk1 conversions (which Mine, Whiteleys, Mattehs and many more are the same as, 100% working). We then fitted it to the car, and the problem still remained - so the loom was out of the question.

  • Tested ECU was getting 12V on cranking - Which it is on both the Ingition Live and Permenant Live Connections
  • Checked the ECU earths for continuity, all spot on.
  • Cleaned all the earths (chassis and box), and replaced box-to-chassis earth lead.
  • Tried Replacement Key Barrel (In case of any issues with position 3).
  • Replaced all the black relays in the engine bay (Fuel Pump, ECU, Immob)
  • Checked and Replaced relevant fuses in the engine bay.
There are no other alarms/immobilisers on the car. So at this point we were thinking it may be interior loom related - to get around this we unplugged it all, and just ran the bare minimum to the engine loom for starting the engine.

Which consisted of - Fuel Pump Live (From ECU), Ignition live to engine loom and starter solenoid wire. Connected these up, the ECU primes the pump as it should, then touch the solenoid wire onto a battery and it just cranks exactly the same without starting - so that rules out the interior loom.

This leads me to think it is 100% engine bay related. I know the ECU earths one of the small black relays when it recieves all the correct signals from the sensors which in turn releases power to the Injectors/Lambda/Coil etc.

This relay earths fine when the ingition goes to stage 2, although it does not when cranking - Which says to me that the ECU isnt seeing something it needs to, hence not letting the engine start.

From that I had a think what might cause the ECU not to release this relay - only things I can think of which will stop it starting are the crank sensor signal and the ECU immobilser. Although, we have a known working crank sensor fitted, and a known working ECU plugged in! Which makes no sense.

I then thought what does the crank sensor actually read......the flywheel teeth. We turned the engine over by hand and inspected all the teeth via the inspection cutout to see if anything was stuck in them/damaged (which could provide a bad reading) - although they were all fine. The flywheel spins true when cranking also so its not like thats loose/wobbling etc.

From that I think its every option exhausted, and ive not really got any ideas of what to try. We're going to wire up an OBD port tommrow and read the codes from the ECU via a reader/or an RSTuner (which has worked fine on mine in the past). Im hoping this will reveal some codes, but if it does not - I have no idea whatsoever of what could be causing this.

I might have missed one or two bits out of the post as I was trying to think of everything we have tried - but any suggestions of things to try would be welcome!
 

TimR26

South Central- West Berks
ClioSport Area Rep
Have you tried replacing the crank sensor loom? My 172 would crank and not fire but a modified loom and sensor from Renault fixed it.
 
Noope, I know which one you mean though. The 'blue' sensor that comes with the new plug/partial two wire loom...

All we've tried crank sensor wise is a couple of known working sensors (that run another 172 and run mine), along with two different engine looms... so there isnt really any reason why they shouldnt work (as both work on other cars) :(
 
Last edited:
Indeed... Ive not touched mine since October lol. I think its just French in general......... hence why I went German!
 
Have you managed to plug into the OBD yet?

I've plugged Adam's old ECU into my car and got this
adam faults.JPG

I cleared the faults to get this
adam faults 4.JPG

The sensor values were:
adam faults 2.JPG

it won't start, and many of the actuators won't run - cam and fan, fuel pump seemed OK.

No idea what any of that means, so plugged mu ECU in to get a comparison
andy fault 3.JPG
andy fault.JPGandy fault 2.JPG
 
Very very interesting - the O2 sensor fault in the first picture will have been from when we went to the rolling road day. We had to unplug the lambda as if it was connected it would missfire under load, once it was unplugged it ran fine... which was weird. I wonder why those faults are stuck on too once cleared, maybe its completely f*cked?

We've not managed to plug it in yet as I've not got anything that will read a Clio ECU, don't have my own RSTuner any more... Its got my ECU on it at the moment too (which still starts my car fine). The only sensor we've not tried is air temp sensor, but I doubt that would stop it starting completely to be honest... New lambda is plugged in also. Don't think there is anything else to try apart from reading the codes, but got no way of doing that yet...
 
  Mk1 F4R
Really havent got a qlue now, so as jord said going to put an OBD port in and waiting for a friend to get back to me on lending his code reader
 
  Golf GTD Mk7
Honestly if you need me to pop down at the weekend, I can bring clip and tuner with me ;) Might rule a few things out. PM me if you need a hand.
 
  Megane dci 130
So the fuel pump relay is good as the pump primes when you turn the ignition on (which means you must get a 12v pulse at the ignition coil aswell as there wired together. But nothing whilst cranking?

The ECU controls the Earth to activate the fuel pump relay try putting your own to it see if it starts up (or at least see if the fuel pump runs)?

This would be why you have no spark aslo because the coil runs on the same circuit.


Then you have the injection locking relay. This also recieved an earth to activate the relay from the ecu.
This gives 12v to all of your injectors and other sensors on the engine. Do you have 12v with the ignition on at all of the injectors? If not, try giving this relay a manual earth signal too.

Let me know how you get on. ;)
 
Really havent got a qlue now, so as jord said going to put an OBD port in and waiting for a friend to get back to me on lending his code reader

Will be lucky if his picks anything up I think as its not like an RSTuner, the data lines are different on the plug-to-ecu..

Honestly if you need me to pop down at the weekend, I can bring clip and tuner with me ;) Might rule a few things out. PM me if you need a hand.

Would be ideal Jonny, although im not holding out too much hope to it shining any light on the matter, as the only thing it could come up with that we havent tried is air temp sensor..

So the fuel pump relay is good as the pump primes when you turn the ignition on (which means you must get a 12v pulse at the ignition coil aswell as there wired together. But nothing whilst cranking?

The ECU controls the Earth to activate the fuel pump relay try putting your own to it see if it starts up (or at least see if the fuel pump runs)?

This would be why you have no spark aslo because the coil runs on the same circuit.


Then you have the injection locking relay. This also recieved an earth to activate the relay from the ecu.
This gives 12v to all of your injectors and other sensors on the engine. Do you have 12v with the ignition on at all of the injectors? If not, try giving this relay a manual earth signal too.

Let me know how you get on. ;)

Injectors do get 12v on ignition stage two, but when you crank the ECU does not earth the relay (small green wire). We put our own wire in and earthed it constantly, although it made no difference.. Fuel pump runs fine when manually put to a 12v on that relay as expected, but the ECU does not seem to be doing its job 'activating' the relays on cranking!
 
  Megane dci 130
So if you earth both relays manually so your fuel pumps running, 12v to coil, 12v to all injectors and it still doesnt run?

Got fuel in it?! :p
 
So if you earth both relays manually so your fuel pumps running, 12v to coil, 12v to all injectors and it still doesnt run?

Got fuel in it?! :p

Yeah as said plenty in it..

And yeah, earthed, so everything gets power. Although if the ECU isnt earthing the pairs of coils or firing the injectors in time it wont run... which it does not seem to be doing!
 
Right, plugged into RSTuner and Renault Clip this evening thanks to Jonny, although its not given us much more insight. This is all done on my ECU.

The RSTuner connected fine, could view all sensor data fine, no faults apart from the ones expected (Purge) either. Booted the Clip up and checked for faults, pretty similar result...

1.jpg


So next, viewed live data whilst cranking on Clip. The one issue I noticed was there is no flywheel signal being recieved (even though we know the loom is good, and the sensor is good as it runs another car)...

2.jpg


Then flicked through and view the sensor data labelled 'Petrol Injection' functions test. It states the Immobiliser is active, although this cant be true as my car starts fine with this ECU. So we cranked it to see if the 'Fuel Pump Relay Command' became active, which it did not. The engine speed remained at zero also..

3.jpg


Lastly, we thought there may have been an issue with Clip seeing the data. So we put the RSTuner back on, then onto live data, and watched while we cranked. There was still no flywheel signal/rpm being recieved, stayed firmly at zero. As said, this crank sensor starts and runs another car fine...

So basically lost for ideas now, as both diagnostic tools have given us no insight whatsoever (apart from the RPM). Maybe there is something wrong with the flywheel and its not being read correctly?

Also here is an RSTuner log of some sensor data, showing the null flywheel signal also (started cranking at around 420s).
 
Got it here to try later/tomorrow, didn't end up going back round last night. Il be sure to post in here with the result of that though!
 
Tried two (known working off running cars) crank sensors on the old original engine loom... Then purchased a 172 Ph1 engine loom from a running car, wired it upto the Mk1 loom etc, then tried both crank sensors and still no different... Would have to be some serious co-incidence for it to be the sensor/loom having tried different ones of both surely?
 
£50ish IIRC, although I dont think its that.

One way to confirm would be to try the loom and ECU on another car.
 
Did you try the starter in the end mate?

Tried it tonight - no different, still just cranks :(

Also cut the crank sensor connector off my loom (which works fine) and soldered it to Adams loom. No different again, just cranks over. As BRUN said the revised one is out, but to be spending 40 quid (after buying spare sensors and looms already) is pointless if my working one does not work!

Engine is coming out tomorrow, had enough of pissing round now!
 
have you buzzed out the loom from the crank sensor to the ECU? Also checked for shorts? How sensor teeth on the flywheel look? Surely it has to be something to do with the ECU not seeing a crank signal.
 
Yeah both wires have continuity to the ECU connector. The teeth look OK when looking through the inspection cutout on the box and turning it over by hand, but its hard to tell properly...

I agree about the ECU, but its wierd how we know all the sensors we've tried are good, the piece of loom to the sensor is good (from my car) and my ECU is good. The only other thing that could be stopping it seeing the flywheel is a bad flywheel surely? We've even triple checked the earths, cleaned everything up multiple times, put new earth leads on etc with no joy. All we have to go on is the 0rpm reading from both diagnostic tools..

Pretty much lost for ideas now apart from taking the engine out to inspect the flywheel properly - we were going to fit my spare flywheel and spin it over on the starter out of the car with the loom plugged in to see if we get spark, we'l know its going to work then before re-fitting it...
 
  Golf GTD Mk7
Sh*t. That's annoying. Have you tried manually earthing everything with jump leads or similar? Could be a break in the wire somewhere? Seems unlikely that the fly wheel is damaged at the teeth?
 
Yeah very unlikely, but who knows, its pretty much the only thing left to try..

Earthed both gearbox and chassis together in various locations with jump leads previously to no avail..
 
  Mk1 F4R
The only other thing wh havent tried about 3 of is the ecu.... still need to get mine fixed or get a new one
anyway im starting to strip the engine down tonight so will see how it goes :S
 
Well - Andrew Cooke has confirmed Adams is knackered, so I'm guessing his old loom f*cked it up. Then plugging mine into the old loom must have knackered it too... since fitting the new 172 loom it made no difference meaning mine is probably knackered... especially seeing this other one we bought started it first time.

Not tried it on mine yet, probably going to try it later in the week. Fingers crossed.
 
Not when I'm getting rid of it at the end of summer lol!

We'l see, going to give it a try later this week and see if mine starts
 

wilky19

ClioSport Club Member
  Leon FR 184
if you still want mate i can still pop up and test the dud ecu's on mine and my working ecu on adams to confirm its the ecus
 


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