mx5cartalk.com

Hi all
I have in the last two days just purchased a 1999 MX 1.8L when I picked it up it seemed to run fine drove it on a cool day back to my home from melbourne and it took about 2 hours with no problem .. once home drove it around some more but when I was driving home from work today in about 28 deg heat I started to get a problem. I was driving at H'way speeds for about 45 mins and then reduced speed to say 30 km to go through a roundabout and the engine started to run really rough and stalled I tried to restart it and at first it wouldn't fire ..
I then pushed it to the side of the road and waited 5 mins and tried again it fired an ran perfectly for about 1 min or 2 then the problem came back. I managed to get the car home by pulling up for 5 mins then driving for like 2 before having to pull up again.
Once home I let it cool down completely and then latter in the night took it for a spin in the cool of the night and the problem didn't resurface. it seems strange to me that the care can be running really well one min and so badly the next so anyway I thought I might put it to the forum folks here and see if you guys have run across this before.
Cheers
Bops

Hi Bops,

I think you work with my sister, if your co-workers made you a barbie poster ... well, they're nice people!

Were you lucky enough to get a service history with the car? If not there's a couple of lists to do a baseline service so you know what you've got. -> -> HERE <- <-
If you did get a service history, check the dates on it - my car had been dutifully serviced every 5000k's by the previous owner, only it took them about 3 years to do 5000kms so things would have been rolling over-due in time, but not in kms.

Back to your actual question: I had a poke around the internet, check your coil packs - they like to get hot and stop entirely when they're on the blink. If you know someone with a '99 too, you can swap with them and see if it helps. Coil Packs seem to be about $500ish new, looks to be cheaper to "upgrade" to Coil-on-Plugs, so swapping for a known good coil pack is definitely the way to go for troubleshooting purposes! These engines use a wasted spark method so they fire two cylinders at the same time (4+1 & 2+3), pop the plugs out after it plays up and either the two end ones or the two middle ones will be wet if it's the coil pack not firing.

There are some smart cookies here, but I'm not one of them, standing by for someone to tell me I'm wrong

- Cus

The cam angle sensor (CAS) on top of cam cover towards the rear and on the inlet cam side on the NB8B tends to break down under those conditions as they get older.
Your description sounds typical. Take a spray bottle with water in it with you and give the sensor a spray if it quits again. If the car starts up straight away after a quick spray to cool the sensor then it will have proved your problem
It is easy to replace the and is held in by one bolt as I recall.

@ Cus yep thats me and yep got the barbie poster waiting for me when I arrived at work!!
Thanks for the heads on the coil I will give it a look and also thanks JBT for mention of the CAS I am going to take Friday off as it will be a warm day and hope to replicate the problem
Also @ JBT is it possible that the CAS is on the front left hand top of the motor if view from standing at the front of the car .. have a haynes manual here and it seems to cover 1997 and earlier and then 99 to 2000+ mine is a 98 dont really know whats with that but anyway if you have any idea let me know
also the part at the front looks like the CAS part ..

Cheers

Heres a pic similar to what mine looks like hope that makes sense


Cheers

Yep, CAS on NB is at the front plastic cover as you have found

Similarly, coilpack can be checked by cooling with some water.

Only know what's on for the NB8B


Crank Position Sensor (CPS), although some call it Crank Angle Sensor - at the front near the crank pulley


Cam Angle Sensor (CAS) - top left of the motor


EGI Main Relay (Light Green)

bebop71 wrote:Heres a pic similar to what mine looks like hope that makes sense

OK, I'm not much good as a clairvoyant and didn't know you had an SE which has a different arrangement to the garden variety NB8B.
See pic - SE on the left and garden variety on the right. Blue circle shows location.

Fwiw the original post was not for an 8B ,as some would say ,so there may be some differences. As stated before if you buy parts from Mazda they always ask for the VIN which defines the model and break points for changes.

Who knows what it is Mr M.
His/her profile shows NB8B (as does yours) even though he/she talks about a 1999 car...and then shows a photo of an SE engine. As stated, clairvoyance is not my strong suit.

Well, I was under the impression all NB engines replaced the old Hall Effect dual Cam Angle Sensor unit mounted at the back of the exhaust cam with two separate Hall Effect units at the front - one on the intake cam gear and one mounted on the oil pump, to the side of the crankshaft pulley.

Hey Guys sorry for the confusion its a 1998 model not sure if its an SE ?? or not it has the sensor in the same position as the red motor but has a standard looking silver colour .. if that helps to ID it I don't know
In any case had a chat to a guy named Dick at MXfactor awesome dude as I live out in the coutry he is going to send me a second hand coil to try and see if it fixes the problem if not I will send it back and try the CAS ... really amazing service from this guy can see me getting my spares from him in future

Also thanks again to everyone that's offered help and advice here as well

oh and I am a He not a She .. just saying

gslender wrote:Well, I was under the impression all NB engines replaced the old Hall Effect dual Cam Angle Sensor unit mounted at the back of the exhaust cam with two separate Hall Effect units at the front - one on the intake cam gear and one mounted on the oil pump, to the side of the crankshaft pulley.

Yeah, the VVT engines had the Cam position/angle sensor mounted at the rear and it's prone to failure at high temps. Comes good again after a rest.
I guess the same can happen with the others mounted at the front.
The other sensor at the front down near the crank pulley is the Crank angle sensor. I've never seen one of those quit but they can get knocked out of adjustment.

bebop71 wrote:oh and I am a He not a She .. just saying

Sorry, I was being a bit naughty.

Ok guys Still having problems with this .. I have put in a new second hand coil a brand new crank and cam sensors and the problem still exisist I tested it today drove it for like an 50 mins on a 30 deg day and yep the problem is persisting ..
One think I did notice I when I was pulling the leads off (from the spark plug ) while it was running rough to see how it effected it was that when I removed one of the leads sparks fired from the top of the lead where it meets the coil unto the side of the coil .. could it be the lead failing ??

At this stage really hope someone can help with this

Cheers
Bops