Crank, no start - ECU not 'seeing' Crank Sensor

[steamdriven]

So after doing a few routine bits and pieces on my 1998 GT3 it decided not to fire-up for me.  Cranks but no spark, fuel pump heard to run ok so I've ruled out fuel problem for now..  Concerned that I had disturbed something, but I have visually gone over everything and can see nothing obvious.  The sudden failure may just be coincidental.

No Fault Codes on FreeScan but interestingly no RPM reading during crank so I suspected Crank Sensor.  However, after bench testing the sensor, and checking sensor wiring back to the Ignition Module, I can get c. 2 volts a/c at the ignition module, so it must be something between the Ignition Module and the ECM ?

When I exposed the ECM Module to see if anything obvious I found one of the mounting bolts to have dislodged itself, leaving the module loose, so wondering whether it has had some vibration damage going on ?

Any ideas anyone ?

 

[CarBuff]

Vibration damage?... 😶‍🌫️🤥

 

You may want to check/re-crimp those sensor wires going to the ECU.

 

IME Lotus' harnesses are famous for marginal connections at the crimps.

 

+++++++++++

 

When you mention .2VAC, is that what you really need?  I thought sensors provide a square-wave DC voltage pattern, and HIGH = ~5VDC, and LOW=  less than 0.5 VDC.

[steamdriven]

Thanks @CarBuff.

I've been doing bit more research and exploration this evening :- The Crank Sensor feeds to the Direct Ignition Module and , to quote from Service Notes "pulses are received by the ignition module (located with the ignition coils) which by noting the frequency of the pulses is able to determine engine rpm, and by comparing the time interval between individual pulses can recognise the positional 'sync' pulse. The ignition module uses this information to control ignition timing during engine cranking and also sends reference signals to the ECM.........These signals inform the ECM of engine speed and position,".

So from this I now suspect DIM rather than ECM but there could still be some sort of corrupted interaction between the two I guess.

I want to think its something simple so will be checking the relevant connectors as you suggest as my next steps.

Regards output from Crank Sensor, the service manual merely refers to "voltage pulse" and I was going off some general info I had picked up on-line:- you may well be correct about square wave DC but I dont have an oscilloscope unfortunately so had to rely on a very crude reading off my multimeter.  The meter is unlikely of course to be able to handle the pulsed input so I was happy to just get any sort of reading on my lowest a/c setting of the multimeter.  Perhaps I do need to look at these signals more closely.

I am thrashing around a bit here and by no means an expert so any advice is welcome.

 

[fjmuurling]

AFAIK the crank sensor is a VR type sensor and the signal coming out of it is an AC signal. The peak to peak voltage depends on the engine / flywheel rpm.

[Chillidoggy]

On 25/04/2024 at 22:18, steamdriven said:

So after doing a few routine bits and pieces on my 1998 GT3 it decided not to fire-up for me.  Cranks but no spark, fuel pump heard to run ok so I've ruled out fuel problem for now..  Concerned that I had disturbed something, but I have visually gone over everything and can see nothing obvious.  The sudden failure may just be coincidental.

No Fault Codes on FreeScan but interestingly no RPM reading during crank so I suspected Crank Sensor.  However, after bench testing the sensor, and checking sensor wiring back to the Ignition Module, I can get c. 2 volts a/c at the ignition module, so it must be something between the Ignition Module and the ECM ?

When I exposed the ECM Module to see if anything obvious I found one of the mounting bolts to have dislodged itself, leaving the module loose, so wondering whether it has had some vibration damage going on ?

Any ideas anyone ?

 

Have you got the Lotus Service Notes for your car? They contain numerous fault-finding flowcharts which may well assist you in pinning down your problem.

[Sparky]

Heres my tried and trusted logic path in situations like this...

The engine was running.  I screwed with it.  Now it doesn't run.  Ergo, must be something I did.  Retrace steps.

Normally gets me out of trouble before referring to service notes, signals, voltages etc.  I'm a simple man, and the answer is very often simple.

BTW is it does turn out to be DIM, be very careful what you buy.  Alternatives out there may look identical, but they'll throw a code.

[steamdriven]

I am of the same view @Sparky that it will inevitably be something very simple and due to something I did.

I started this thread because having retraced my steps and checked and checked so many times now I am getting a bit frustrated (think Basil Fawlty)

I only mention other (more esoteric) possibilities because my desperation is forcing me to those tangents, but I am not (yet) considering them as serious causes.

I will keep at it and no doubt eventually post back here and confess my stupidity !

[rongoldsmith]

hi guys thankyou for your help regarding no spark bad connection clean up now firing

[sailorbob]

Starting with the basics; when using Freescan under the 'Engine Data' tab are you seeing values of 0, 1 & 2 for the 'Crank Sensor' parameter when cranking the engine? If you aren't then that suggests an issue with one of the following:

1. The crank sensor

2. The wiring between the crank sensor and the ignition module

3. The ignition module

4. The wiring between the ignition module and the ECU

5. The ECU

[internets]

Also worth checking for a vacuum leak, the cheap elbows have a tendency to crack when you knock them while working on the engine and it’s easy not to notice! Follow the vacuum all the lines, and from my vague memory, the ones near the ECU.

Appreciate it’s not electrical but easy to end up down a rabbit hole on these things and I’m speaking from experience

[steamdriven]

Thanks @sailorbob and @internets your advice is appreciated, I hope to get back into my garage this weekend and will check out your suggestions and report back.

[steamdriven]

Ok, so I AM seeing Crank Sensor parameters on FreeScan under Crank.  (Thanks for the tip @sailorbob as I am not very experienced in using FreeScan, but learning fast !).

Car fires on 1st crank after standing for a while, but dies immediately and is simply 'dead' on subsequent cranking.

I think I read somewhere that the ECU will start picking up fault codes after 8 revolutions under crank, but my current battery is beginning to die away after so much cranking so I am going to try again tomorrow with a fresh battery.    (Any previously stored fault codes that may have been on the ECU when she was running ok will have been erased because I had disconnected the battery for a short time before I started getting this problem)

By the way, I've now actually removed all the wrappings from my engine bay harness in the course of thoroughly re-checking all wiring, sensors and connectors. Connectors are the 'weather-pack' type and all look clean and sound. Also checked all vac lines for damage and I had already replaced the elbow connectors a while back and all are sound.

Beginning to feel like a possible Ignition Module problem to me, but I would have thought I might have seen that coming earlier rather than a straight sudden failure.  I still want to believe its something more simple.

Any ideas on next steps ?

Edited Friday at 18:29 by steamdriven
typos

[Sparky]

Is it absolutely definitely spark?  Are you certain you're getting fuel delivery?

[Escape]

As above, an engine that starts but immediately dies often doesn't get (enough) fueling. If you take out a plug after trying to start, is it wet /soothy/smelling of fuel (indicating fuel but no spark) or dry (no fuel)?

[fjmuurling]

Fuel Pressure Test?

[steamdriven]

Update from the rabbit hole :-

GT3 '98

Indeed it is now looking like fuel problem (I had not been 'fiddling' anywhere near the fuel delivery components so did not initially suspect it as the cause and I had  therefore persisted down the rabbit hole of ignition, thinking I had disturbed an electrical connection somewhere).

Spark is confirmed and yes plugs 'dry' .  Crank Sensor and wiring ok (although the mystery still remains in my mind of why I get no RPM 'blip' on FreeScan when cranking, which is what initially encouraged me toward a possible  IM /ECU problem).

I've not yet done fuel pressure test (largely because I dont have equipment to hand) but I have confirmed 12v supply to in-tank fuel pump when ignition turned on, and relay/fuse intact and functional, and inertia sensor/ connections ok.  I do notice however that after an initial 'flash' of 12v to the fuel pump supply on turning the ignition key, the reading falls back to zero.  Is this usual (ie after energising does the pump turn off if sufficient fuel pressure is sensed , or should pump continue to get 12v )  ?

 

 

 

 

[LotuStuart]

Can you jump the fuel pump relay for a few seconds and see if that gets it running?

At your own risk of course-there may be a good reason why the car has shut the fuel off!

[steamdriven]

Hi @LotuStuart yes i've already done that.  In fact that is exactly what the service manual suggests and it also comments that you might need to remove tank filler cap to hear the pump running.  I thought I had heard the pump running early on in this saga (hence my concentration initially on ignition) but I am now beginning to doubt that it is in fact running- if it is running then it is v quiet !  I think the only place for me to go next is to get a guage on the fuel rail.

[sailorbob]

If you are seeing the crank pulses but not getting any RPM reading then that suggests a faulty ECU. The ECU will use the fuel pump to prime the fuel system at key-on (the time varies according to whether the engine is cold, warm or hot) but if it does not see any RPM then it shuts the fuel pump off for safety reasons.

[steamdriven]

Thanks @sailorbob that is also my understanding from the service manual, but I am still holding out some hope that its not an ECU fault.

I think I also need to dismiss the possibility of a faulty fuel pump by testing to ensure that I am indeed getting fuel system prime at key-on ?

[Escape]

If you jump the fuel pump relay with everything else off, you should hear a clear buzz coming from the tank. Cracking open one of the connections on the fuel filter is the easiest way to prove there is flow or not. If you take the output side, you have tested flow through the filter at the same time. 😉 

If there is flow with the jumper instead of the relay, try starting like that. If the engine still doesn't fire, I'd check if the injectors are being fired. You can do this by unplugging one (1 and 2 are easy to get to), first check for 12V at the orange/white wire and then have someone measure for voltage across both pins while cranking. A decent multimeter will see a voltage spike as the ECU applies ground to complete the circuit.