Non Starting Mazda Eunos (MX5)

[Diesel Fionn]

Hi folks, I had a coolant outage from the wifes 1991 Eunos 1.6 and after replacing the 23 year old radiator the car wasn't running great. I suspected the plugs and leads were doused in coolant so when I went to pull out the lead from the first plug it pulled apart leaving about a third in the head. Yes this was repeated three more times!!
After picking, vacuuming and blowing bits of rubber and plastic out of the head and fitting a new set of leads the car ran reasonably well again and thankfully the head gasket appears to be fine as the new radiator is doing its job.
However today when I went out to check the plugs which had not been actually removed at this point, the car started when I reversed it out of the garage but now refused to start again. I checked the plugs at this point and all but one of them were loose in the head. This thus explained the lumpy running and the leads being melted in the plug holes. I cleaned each one in turn but they need replacing anyway and refitted them in the head but the car still refused to start. the battery needs a charge but i had a booster which still didn't help. Until the battery is charged I can't check for a spark when cranking, however I'm concerned this may have damaged the coil/distributor?
Any ideas, also is it a known thing for spark plugs to work loose in these cars. I fitted the last set of plugs myself and didn't overtighten them.

[Luxobarge]

That sounds like quite a common fault on certain ECU controlled engines, that don't like being run for very short periods and then switched off - i.e. before the Engine Management system has had time to go into open loop mode. This only happens when the oxygen (Lambda) sensor has warned up, usually 2 or 3 minutes, so if you stop the engine before this point the ECU can get very confused and will often end up flooding the engine.

I've had it several times, I've usually got it to start by putting the accelerator flat on the floor and mercilessly cranking it until it starts to fire - it will then usually reluctantly start with clouds of grey smoke but once warmed up everything will go back to normal. In severe cases you have to pull the fuel pump relay to stop any more fuel being injected, but I've never had to do this.

You have a situation which has conspired against you, as you have a poor battery so you can't sustain long periods of cranking. Try and get a known good strong battery on it and do the foot-on-the-floor-and-crank technique, there's a good chance it'll fire up eventually. You could take the plugs out and see it they're wet, but this isn't conclusive and anyway they've probably dried off by now.

I've heard various theories as to why this happens but I don't believe any of them. Such as "hydraulic tappet jacking" - which wouldn't explain why I've had this happen on cars that don't have hydraulic tappets, and "bore wash" - excess petrol washing the oil off the bores and reducing compression, which doesn't explain why the ECU would command such a large amount of fuel to be injected in the first place, and anyway most modern engines would still start even with poor compression. Personally I just think it's an "undocumented feature" in the ECU software.


Or I could be totally wrong and you've got a relay or sensor failure....

Cheers!

[kevin]

I have an early Mk1 as do a few mates, they are prone to developing faulty coil packs which may (OR MAY NOT) result in non starting.
for me, id change the leads for magnacor ones, then try again..if still not starting get yourself over to MX5nutz http://www.mx5nutz.com/ and ask for some specific advice, really friendly bunch.
you could get some replacement coil packs by placing a wanted ad or shouting out for a bloke called 'junk yard dog'

Kev

[Diesel Fionn]

Haven't gotten back to it yet but thanks for the information lads. I'll try cranking it and see if it eventually fires. I have a good source of used parts in dublin, so if I don't see a spark I'll see if he has a coil pack. I know he has a car identical to mine being broken. I'll keep ye posted.

[Pavel]

Before replacing fairly expensive electronic parts I would suggest you check out the Air Bypass Valve [not to be confused with the Idle Air Adjustment Screw]. It can be found on the induction manifold, and has 2 small pipes attached which allows radiator coolant to circulate; 2 larger pipes for air from the air cleaner to it and out to the inlet manifold, plus 2 wires that operate the Idle Speed Control Unit which is integral with the Bypass Valve. The internal workings of the Bypass Valve are similar to the waxstat thermostat in the coolant system -- except it works in reverse. When the engine is cold it's open and allows extra air to mix with the added fuel the ECU causes to be injected for a cold start. Without this extra air the injected fuel mixture is far too rich.
It's an expensive piece of kit, but it can be checked out without removing it from the manifold.
With the engine cold, remove the air pipes and blow into one end. Air should come out from the other pipe. If not it needs replacing.
My daughter has the same engine and had this problem and a second hand replacement was fitted which cured it.
As a postscript I should add that if the engine starts, but stops after it warms up, then suspect that the thermostat is jammed open allowing too weak a mixture.

Pavel

[Diesel Fionn]

Well after a break of about 48 hours I got back to it and it started but it's still missing like a cylinder is not firing or not firing properly. The new leads seem ok and all connections are good. I'm hoping its a duff spark plug as I haven't gotten the new ones yet. if after they are replaced the misfire is still there I do have my original leads so I'll go cylinder by cylinder till its fixed.

I will check the air feed pipes as well just to be sure it's ok.

[rich.]

coolant outage???? is that what we used to call a leak

have you got it running yet btw?

[Diesel Fionn]

The car is running a whole lot better, however it's not 100% yet. I'll check the air bypass valve this weekend. It's cutting out now and then at low idle.
Also it's very noisy on the overrun. Acceleration is still good though. Think I'll go through the engine and clean all connections also.
The gearbox oil needs changing which may explain why it's a tad noisy. I need to check the Diff as I want to change the oil but I don't know if it's LSD or not.