As the title suggests I have a strange problem.
Symptoms:
- Whole engine cuts out but almost instantly restarts
- Cutting has happened in all conditions (inc. tick over and high revs), but seems to be worse when cold and under load
- When the engine cuts out, the ‘security’ light briefly comes on on the dash. No other lights come on
- When the engine cuts out a clicking is heard which I have identified as the circuit opening relay under the dash
- The symptoms haven’t really changed and I have continued driving the car for the last week.
- It has NEVER actually stalled itself
Worthwhile extra info:
- Car was in storage for 6 months in a dry but cold garage
- Alternator seized over winter, replaced with eBay unit
- Car has had new HT leads (no difference)
- Car has had new coil pack (no difference)
- Tried swapping MAF sensor (no difference)
- Tried strapping closed the circuit opening relay (no difference)
- Tried adding redex (no difference)
- Checked and rechecked battery and main engine earth (no difference)
- Checked main EGI relay, can’t see any visual clues of an issue
My remaining suspicions: Imobiliser, key barrel ignition wiring, water in fuel.
So…any thoughts? I would really appreciate any help, I am stumped, and so is my local MX5 specialist!
hmm strange one…
I had a strange problem with my mx a few years ago, engine would just randomly cut out whenever it felt like it
had all the coils, leads plugs changed and still couldn’t work out what the problem was.
in the end it turned out to be a small split in the big hose going from air filer to inlet (was on the ribbed part so was very hard to see)
hose was expensive so i just used duct tape for a few months but that solved the issue.
might be nothing to do with what you have but its worth a look
this was on a '92 NA 1.6 btw
Sounds like a difficult one to diagnose as it’s effectively intermittent. My first thoughts would have been an electrical issue, but you’ve tackled the most likely causes other than perhaps ECU connection, fuel pump connection? Another possible issue - have you refreshed the fuel? 6+ month old petrol will be stale enough to potentially cause issues. Try topping up with some super.
Which model do you have?
Ben
Have you/your mx-5 specialist checked for diag codes?
I agree with Ben possibly dirty fuel,check the fuel filter or maybe the sender unit is dirty and needs a clean.
Wow, thanks for the quick responses. I’ll check those out over the next few days and let you know how I get on.
SOLVED! (well sort of)
The nature of the problem convinced me of two things.
-
It was electrical, the cut out and recovery were so instant, I couldn’t see fuel doing this
-
It was affecting all 4 cylinders simultaneously, but not affecting any other electrical systems, i.e. radio or headlights
Therefore I focussed on coils/primary ignition circuit.
But since I’d already changed the coil packs, it must the signal telling the coils to fire. Eventually I traced an earth connection spliced into the loom which bolted to the inlet manifold. I disconnected this, and it has been 100% fine since, not one misfire. Anyone seen this before?!
So, it’s fixed. BUT. I’ve disconnected something to do this, hence it cannot be the root cause. My thoughts are immobiliser/ECU are attempting to cut ignition by earthing the coils. By me taking away it’s earth point it can do what it likes but won’t be able to interfere. This is fine, but do I now have no immobiliser, or do I still have a fuel cut? And if I do have a fuel cut, what if this circuit fails next?!
It’s a 1998 mk1, with TEMIC immobiliser unit under the dash and a transponder built into the key.
One day I hope to supercharge, so should I bite the bullet and prepare for an aftermarket ECU? Does this affectively bypass the immobiliser?
Thanks for your help, it’s great to drive it properly again! James