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I got this email from a nice 75 year old man that has just bought his first Mx5, a 2002 NB8B, , I think it is a fuel pump, but if anyone else can share their thoughts it would be great.

The Mazda is a delight to drive and I am pleased I have it….BUT there is a dangerous problem which must be sorted ASAP. It was hot yesterday when I collected the car from Raj, after about forty five minutes driving towards home I started off from the lights in Midland and the engine suddenly lost power, then revved-up and lost power again (I had a Road Train right behind me) I managed to swing into a bus stop lane. The engine started but revved and died again. (It is unfortunate that the engine failure did not occur during Nick’s test drive.)

The fuel gauge indicated half full but I though it may be faulty. I took the petrol tank cap off and air rushed into the filler neck. I walked back to a service station for a can of fuel. After that the car started, I doubled back to the service station and filled the tank, the fuel gauge then indicated full, so I assumed I had not run out of fuel and probably had a fuel vapour-lock in the system. I drove the car home OK and then drove to Kalamunda, when almost in Kalamunda the same problem caused the engine to stop again, I waited twenty minutes and the engine started and ran as normal. I was in Kalamunda for an hour and drove home to Darlington without further trouble.

I have found lots of info on the net regarding engine failure, many owners have experienced similar problems. Some advocate fitting a new fuel pump, others suggest fitting a new fuel pump relay, but most mention replacing the camshaft position sensor, whatever that is.

Thanks
Terry

The symptoms sound like low fuel, be that from a pump not pumping properly, or blocked line etc.


Air rushing out of the cap is pretty standard, mine does it all the time.


I would be swapping the fuel filter (unless it's fairly recent) it may have a blockage and be causing the fuel to flow slowly.

After that i'd look at the fuel pump, they can often start to become very intermittent before stopping completely.
Apparently this is usually as they get warm adn stop, a full tank of fuel keeps the entire pump submerged and supposedly helps it stay cooler proloning the time between it stopping.
Of course, that's not a cure for the problem, since it will still slowly get worse until it stops all together.



My money would be on a fuel pump over things like the crank sensor etc.
Budget about $100 for the pump, and maybe a bit over an hour to fit it (the job isnt hard, but you need to remove interior carpet and some trims)

Make sure to check with the supplier that the pump is a direct plugin, my Denso pump had enough differences from the original one that I had to do a fair few modifications to parts to get it fitted.

actually, being a 2002 model the car may have the ODB2 plug, in which case you can just plug in a code reader and see if the car is throwing up any error codes to lead you in the right direction.

Same symptoms on mine were fuel pump relay. It's under the black cover in the engine bay on the driver's side. Subsequent OEM replacements also failed. It now has some rewiring done to a different block connector in order to allow fitment of a larger and uprated relay. The car does have an uprated fuel pump which might have contributed to the relay failing. I seem to remember seeing something somewhere about wiring to the headlights contributing to the problem. Mine did indeed have some of the wiring insulation near the headlights missing. Fixed that too, of course, although no idea whether it was related.

Can also be a partly clogged fuel filter...

As others have mentioned, could be:
contaminated fuel (unlikely)
fuel pump itself (likely)
fuel relay (likely)
fuel filter (maybe)
clogged fuel lines (unlikely)

I'd suggest changing fuel filter (probably hasn't been done and is cheap), replacing fuel relay and then pump... see if that solves the issue.

It could also be ignition related too. He notes that it occurred in the heat which could mean something is overheating... The NB8B's run individual CoPs though don't they?

Standard EFI relay defo does have a tendency to get too hot to touch.

madjak wrote:e.

It could also be ignition related too. He notes that it occurred in the heat which could mean something is overheating... The NB8B's run individual CoPs though don't they?

Kind of.

The coils sit on top of two plugs, with leads running to the other two.

So kind of COP-and-a-half


As opposed to the earlier version with the coils mounted to the back of the head and 4 wires leading to the plugs.

Then initial symptom of dying ignition coils is usually usually major loss of power/missing when they get hot. It doesn't matter if they're coil over plug or remote coilpacks, the symptoms are the same. Most often happens when the engine is generating a bit of extra heat and/or there's less airfow over the top of the engine, e.g. on hot days or lugging up long hills.

All NA and NB MX5s use waste spark ignition, meaning each coil fires 2 cylinders. When a coil stops working then 2 of the 4 cylinders stop firing and you get a pretty significant miss.

The revving up of the engine seems to be fuel starvation more than ign issues, I will get him to check those few things and will go from there, thanks for the feedback.

Was the fuel pump replaced recently (before purchase), if so was the sock installed correctly?

spikey wrote:The revving up of the engine seems to be fuel starvation more than ign issues, I will get him to check those few things and will go from there, thanks for the feedback.

Failing MAIN or FUEL INJ relays can cause fuel starvation. Basically there's irregular power supply to the fuel injectors and the car gets a seriously lean mixture which feels like fuel supply starvation. It's probably more common than fuel pump and filter blockage issues.

This is the reply i got from him today, thank you all for your feedback.

My Auto Electrician has reset the code record, nothing recorded applied to the engine failure problem. The plan is to run the car until it stops and then check any recorded code number. We did prove that one of the ignition

keys is faulty, the engine starts but shuts down almost immediately. By using the other key the car starts as per normal. We road tested the car for two hours this morning without any problem, the engine ran perfectly. Once we eliminate the

possibility of an electrical fault, I will have the pump changed for a new one.

The key that doesn't work is for the boot, it does not have the chip in it. You/he may already know this. Any locksmith can duplicate the chipped key.

spikey wrote:Some advocate fitting a new fuel pump, others suggest fitting a new fuel pump relay, but most mention replacing the camshaft position sensor, whatever that is.

The camshaft position sensor & the crankshaft position sensor are both fairly consumable on the NB8B, but not necessarily the culprit in this case, although should be on the list, just further down.
Also, as Davekmoore has mentioned, it's usually the green EGI relay (aka EFI or black Fuel Inj in NAs) in the engine bay fuse box, as opposed to the fuel pump relay that causes issues, if indeed that's the problem.
Only thing I'd add to the list, again further down, would be ECU as a result of moisture getting into the pside footwell at some stage.