MX5 Crank No Start Challenge the Experts!

Technical Area Engine, Transmission, Exhaust etc
2

Hi All,

I have somewhat of a mystery non starter MX5 that has evaded a few people now in diagnosing the problem.

The vehicle spec is as per the description, its a 1999 Roadster 1.8 MK2 Automatic (anniversary model I believe).

The fault, cranks like a good un but show no sign of starting what-so-ever.

 

History:

The car is in excellent condition for its age with on 76k on the clock and has spent a great deal of its life garaged and only used in the summer months.

The previous owner had it for 8 years and it developed crank no start symptoms.

The previous owner had a local mechanic go over the car and they checked all the usual things like is fuel pump, fuel filter, relays, spark etc but this guy eventually gave up and arranged to deliver the car back to the owner when it suddenly started. The previous owner then claimed the car ran fine for the rest of the year before it was put to bed for winter. The following spring, the car re-developed its crank no start problem and its not ran ever since. They did get another mechanic out to their house who went all over the car again and also failed to diagnose the problem, his parting words were, “everything is right the car should be ready to go but it just won’t”.

I ended up buying the car with a suspected immobiliser problem and only discovered all of the above since.

 

Things I have discovered / tried below: (typed in no particular order other than how I remember them)

I traced all the CAT3 immobilisation wires and re-instated the original wiring essentially bypassing the CAT3 system. Absolutely no difference, so I suspect there was nothing wrong with the CAT3 system in the first place.

Checking the steering column, this model doesn’t appear to have the ring for a factory fitted immobiliser, so can probably rule out immobilisation I think.

Despite being advised the Crank sensor has already been changed, I have replaced with a new one but symptoms are exactly the same.

I observed CAM movement from the oil cap whilst cranking.

I bought a LED ECU code check kit to use on the Mazda diagnostic plug as this car is pre ODB II and no faults were reported, just one long flash.

I have checked all fuses and they all seem to be ok inside and in the engine compartment.

A basic check of the main relay (appears to click when inserted).

I can hear a noise when I link the fuel pump connector in the diagnostic plug, but I don’t hear or see the fans run when I try the same test on the fan connector! (may be relevant?). Another anomaly relating to the fans is they seem to fire up if I have the ignition on and I depress the accelerator pedal to the floor (may be relevant?).

I pretty sure the problem is no spark, I tried removing the spark plug and grounding it on the engine whilst cranking and observed no spark. The previous owner said they have a new coil pack and having removed it to check, I have no reason to doubt them because both packs on the mounting bracket look clean and I’m fairly confident both side would not be faulty at the same time and if I was a betting man I don’t believe the coil pack(s) are doing anything.

I haven’t had time to revisit the car yet but my next check is to see if theres power getting to the connectors of the coil pack(s).

The only other tidbit of information I have is the previous owner also purchased a second hand ECU with identical identification numbers to the original (he was advised they had to match exactly to be interchangeable)l. This ECU makes no difference what-so-ever to the symptoms so the original one is back in place. Also, I did check the power pins on the ECU which appear to have 12v.

 

Conclusion:

That’s where I’m at, I don’t think I’ve forgotten anything. You can probably tell from the list of things I’ve checked so far, I’ve done a lot of internet searching, forum reading and youtube watching, so far to no avail. 

I have about 20 tabs open on my browser all relating to these type of MX5 issues but I don’t think this car will ever run again 

 

3

You don’t mention grounds in your post have you checked all the grounding points?

We have recently rebuilt a NA into an Exocet and we had a similar issue when we refitted the loom and narrowed it down to a ground not connected at the back of the car.

Just a thought.

4

Thanks for the tip, no, I haven’t checked the grounds. are there any details on what points to check?

5

Wow - that is a rare car. Is the ecu a BP5A(same as manual)

My thoughts are stabs in the dark really. Have you tried another FP39 MAF sensor?

The MK1 auto has some sort of extra connection on the ignition block unique to the auto. Can’t remember what exactly it does but if there is something similar on the NB car, could possibly disable the engine. Perhaps a neutral indicator off the gearbox.

Other than that can only suggest wiring / earths. Bit drastic but maybe try another loom. 

6

My gut feeling is that this could be a loose connection, possibly an earth fault.

Have you checked the spark on all 4 plugs? No spark on 2 plugs indicates that plug’s coil pack.

No spark on all 4 plugs then firstly I would check the 12 volt supply to the coil packs and then check the coil pack earth on the engine, try running a wire from the coil pack earth straight to the battery negative.

After that you will need to check the output of the ECU to the coil packs and also the ECU earth.

1 Like
7

 

Thanks for the reply, Yes, the ECU is a BP5A.

I haven’t tried any other sensors yet other than replacing the CAS.

There is a weird black box connected to the loom of the clock cluster. Yes, I even had the cluster out thinking the check engine bulb had gone before I found out that the car wasn’t odb ii and didn’t have a check engine light 

 

8

Sorry, I dont know where the earths are on an NB, we were re-wiring completely into an open cockpit car so they were easy to spot in the loom, I guess there must be a wiring diagram available.   Someone else on here may know where the NB earths are to check.

9

 

Thanks for the response.

I haven’t checked all the plugs yet, I will do but my gut is there will be no spark on all of them, I could be talking out of my ■■■■ as I am a novice when it comes to car mechanics but when the car turns over it doesn’t sound like theres any firing at all.

I’ll test for voltage and try the ground trick to the coil pack when I next get a chance and I will keep this thread updated with progress and fingers crossed a conclusion one day because theres nothing worse than finding a thread with similar symptoms to your own only to find the OP never came back.

 

 

10

 

Thanks anyway, I do have some wiring PDF’s I’ve found during my research, I’ll see if they have the relevant information, sometimes I find its easier if someone just describes where to check as opposed to relying on schematic diagrams though, hence the question.

 

11

If there was a spark on even one cylinder I’d expect some kind of stuttering attempt to run. AS PR-Yorkshire said, if there is 12v getting to the coil packs and they are earthed correctly (just use a multimeter between the earth connection while still connected and the block to prove continuity) then the problem is probably with the firing signal. That takes you in to immobiliser/ECU territory with possibly added fun of wiring faults around that somewhere (for real frustration try the Renault Clio anti-tamper box chafing the loom gotcha). The suddenly and randomly coming to life again the first time sounds horribly like a tiny make/break in the loom somewhere.

Unfortunately, unlike old Italian motorcycles, a quick substitution test of each ignition component isn’t always an option on modern EFI. Doesn’t the ECU sometimes have to be matched to the security on the car? Even my Mk1 has a security ‘light’ that comes on briefly at every start.

Begin by confirming for sure there is no spark at all. Even try eliminating the plugs and caps by say hooking a strobe on to an HT lead and seeing if it flashes.

Best of luck.

1 Like
12

 

Thanks, Yes,regarding the spark on just 1 cylinder, thats what I thought, where-as it just sounds like its turning over with no attempt to fire at all.

Since my last post, I have only got as far as checking there is 12V on the first pin of the coil pack connectors (the pin on its own before the N/C and the next two pins). 

Its weird how your MK1 has security but in my manual for this MK2 it shows a picture identifying if the car has a factory immobiliser by the style of the ignition switch and mine doesn’t have the ring on it according to the book signalling no factory immobiliser!?

I think the next thing I need to check are the grounds on the car but I have yet to establish details on this. 

I mentioned earlier that there is a strange box attached to the loom on the back of the clock cluster. I have attached a picture below if anyone knows what this is?

 

Unfortunately, I am away at the Dorset Steam Fair for the next week, so I won’t be able to do any more checks until I get back.

 

13

Ok, I promised I would update this thread as there’s nothing worse than the OP not coming back and reporting on a problem when someone else stumbles on the same problem only to find no reported resolution.

The bad news is, I never found a solution but at least anyone stumbling on this thread in future will know that, as opposed to wondering if / how the problem was resolved.

I’ve had a mobile electrician out to help who has spent several hours trying to get the car running to no avail.

 

Update on where I got to:

We diagnosed the problem is definitely No Spark.

I had already changed the Crank Sensor.

We also changed the CAM Sensor. Ironically, no fault was reported with the old CAM sensor but the new CAM sensor now causes a 1345 error code which suggests a signal problem but the new Sensor measures out ok and a signal can be seen pulsing when cranked so thats just weird.

The mobile electrician checked the wiring signals back from the Crank and CAM sensors to the ECU.

The previous owner had already purchased a spare (matching) ECU and that operates in exactly the same way as the original, so doubt theres an ECU issue.

We are all out of idea’s and considering 3 other people before me also failed to find the problem, I think its now time to throw in the towel and scrap it.

Really frustrating and sad decision to make because its just a beautiful example of the 10 year anniversary model :frowning:

Thanks for all the help previously.

 

 

14

Has the cam jumped a lot of teeth and therefore the cam and crank sensor feeds are out of phase.

You need basically to look at a cambelt change article and check to see if the cams and the crank timing marks are matching up that would cause no spark.

You still have not advised what that box was for.

I still think it is electrical and got to do with the immobiliser but maybe not

15

HI Drumtochty,

Thanks for the reply.

The mobile diagnostic guy did wonder if it could be a timing issue but he didn’t have the means to check that for me before he had to leave.

I will check out the article and see if its something within my ability to check.

As for the mystery box, no-one knows what that could be, do you think it could be immobilisation on the back of the clock cluster loom?
It seems self contained because it literally gets power from the clock cluster and interrupts one of the lines, no wires go anywhere else, so I know its not part of the already eliminated LaserLine Alarm/Immobiliser.
Its possible it could be part of secondary 3rd party immobiliser but I have no way of knowing, the previous owners didn’t seem to know about any other immobilisation and they had the car 8 years.
I mentioned it to the diagnostic guy but without seeing it, he doubted it would be part of the immobiliser and speculated it might be something to do with the digital mileometer.

I must say, now you mention it, I do have a seed of doubt again about that box wired into the cluster loom, it seems a little un-orthodox to be fitted by Mazda!

16

It is getting a real pain. We will see if anyone on Menders has an idea, your post is now on there.

17

 

Mazdamenders.net forum and Facebook Mazdamenders Technical group.

 

Collective of experienced MX5 enthusiasts experienced in problem solving. 

18

Ok, another update:

I can’t believe this thing has been sat in my garage for over 5 months and I’m no further forward.

I tried MazdaMenders forum but other than identifying the black box behind the clock cluster, everyones hit a brick wall with this one.
I have been advised by the way that the black box is to convert KPHs to MPH.

I have also tried another Air flow Meter since my last post, unfortunate no difference other than my wallet being further drained :slight_smile:

So with all the suggestions from all the experts (which I am grateful for), other than checking if the CAM & CAS sensors are out of phase (which I don’t know how to do anyway), I think all idea’s have been tried.

Interestingly, I did find advert of another guy selling a MX5 in Weston-Super-Mare of similar age with the same problem who had also tried many things and given up.
I wish this stubborn fault was more common because then it might be easier to find the cure, I did message the guy and he was equally as frustrated as myself, hence selling it, perhaps its time for me also to admit defeat.

19

Not sure how much if any help these guys will be but after all you’ve been through perhaps an email to them might get you there - you never know !

 

CIM@mazdaeur.com

 

 

20

I have a 1.6 Mk1 Auto. When I purchased it the gear selector was loose and floppy because the bushes had gone. On occasions the car refused to start and only vigorous wiggling of the selector lever would coax it into life. Replacing the bushes instantly fixed the problem. The problem was that the gearbox selector was not registering the car was in Park. 

I can,t see anywhere in the above post where this may have been checked. However the only fly in the ointment with this suggestion is that I simply can’t remember if mine turned over or not. Â