mx5cartalk.com

Hi Guys,

So here's the story... I'm new to MX5s, but not new to cars... here's what's happened...

Car ('98 MX-5 1.8, NB) overheated and needed to have the head redone. It started and ran, but over-pressurized the system. So I took the head off, had it refurbished and put it all back together. Now it cranks, but won't start. I've been chasing this problem for at least 2 weeks now (and am on the verge of a mental breakdown!)reading forums everywhere and still have no idea what is wrong. Well, here's what I do know: there's no spark. Up to this point I have done the following:

Cleaned the grounds. I found two of them. One a braided wire at the back of the engine and one that basically sits on the top of the intake. Is there another?

I've replaced the crank sensor and ensured proper distance. When I hand crank the engine I can hear the injectors pulse.
I've checked the cam sensor... it checks out fine.
I've confirmed that the ecu get's power to 1A and switched power to 1B
I've confirmed that the coil packs get power
I've confirmed that the crank sensor has power
I've confirmed that the cam sensor has power
I've confirmed that the maf has power
I've replaced the ecu with another identical ecu from a wrecked car

Now I do notice that the tach does not move when the car is cranking. Now, I know the next logical thing is to test the coils... but I just replaced the plugs, wires and coil about 4 or 5 months ago. So they should be fine. That said though, I did do a test on the primary coil and it checks out fine. I don't have a reader that will check the secondary coil.

WTF?! What am I missing here? I keep thinking it has to be a connection issue because the car started and ran before I took the head off. Now it doesn't. There's a guy down the street from me who has the identical car and he's let me poke around the engine bay to see if there's anything different... but everything looks the same.

Just for fun I pulled the fuel lines off tonight and made sure fuel was pumping, and yes it is.

Any help, heck, any idea would be greatly appreciated.

I would look at the maf also. This caused a massive headache with us one time. Unplug it, it should fire then promptly die. If it does this and stops doing anything once reattached this could be your culprit.

Thanks, but no good. Just tried it and no change.

Have you double checked base ignition and cam timing? If the plugs are firing, you should be able to run a timing light while cranking and point it at the pulley. If no light pulses from the timing light, then there could be a coil problem.

There's no spark at the plugs or at the end of the wires... that's the essential problem. As for the coil, I mean, I get why that could be a problem, but it just makes no sense. It's a coil that was new 4 months ago, and worked before the head came off. It also seems strange that both coils would die simultaneously while sitting on the garage floor for a week. But despite all of that, I'll probably take the coil to a mechanic tomorrow to have him test it... mostly because I have no other ideas.

Where are you located?

I'm in Hurstville, just south of the Sydney airport.

That explains it. Move to a more peaceful suburb and it'll work. Hurtsville my head just thinking about it.

On a serious note have you tried an ecu... I doubt it'd be the coils themselves. Maybe a wire got nicked in the process?

Is the battery in good condition?

Have you confirmed the injectors are working? If no spark and injectors working they should be wet. If no injectors Cam Angle Sensor. If injectors working but plug not wet fuel issue.

The crank angle sensor is the home, this lets the ECU know where the engine is in relation to TDC #1. The cam angle sensor (trigger) lets the ECU know when the engine is in compression or exhaust stroke. If you have not installed the timing belt or cams correctly you may have the engine too far out of sync to get a spark.

Anyway other suggestions...
Are the coils in the correct way and the correct lead to the correct plug?
Is there 12V at the coil pack when cranking?
Continuity test on both coil packs?
Timing belt moving when cranking?
Static compression test on all 4 cylinders?

Check the timing belt is all good.

A snapped or stripped one can mean that every sensor bench tests fine, coils etc all test fine, but without the cams actually turning the whole lot has no signal to trigger the ECU.

Ok, if you’ve got power to everything the next step is to check they are all triggering correctly.
First off is to make sure the cams are turning as you crank, have a peek down the oil cap hole and see if they spin.

Do you have spark? Coils may well be charging, but may not actually be firing. Remove the plugs and leads and see if you can spot a visual spark when you ground the plug and crank.

Injectors, I normally use the screwdriver method to listen for them ticking, alternatively crank the engine and remove a plug, see if you can smell fuel.


Regarding sensors, the NB8A has two sensors that let it know the position of the engine, one in the rocker cover to tell it where the intake cam is, and another down near the crank to tell it where the crank is.
The crank sensor is a single hall effect one off to the right of the harmonic balancer (looking from the front bumper)
It is triggered by a timing wheel sandwiched between the balancer and the pulleys. The timing wheel has 4 little pips on the outer edge.
Make sure this is there, and also that it is the correct way around (the pips aren’t symmetrical, and the wheel can easily be placed on backwards which completely stuffs the ignition timing)

I’d also be just trying the diagnostic mode with the LED in the diag box, it works much the same way as an NA, and I seem to remember someone posted the NB codes a while ago (some are different to the NA)
Usually I find the diag mode pretty useless, but it might help in pointing you in roughly the right direction.

Just for fun check the belt timing.

I know its all too crazy. yes I know you said you had no spark. Timing belt has nothing to do with spark. totally independent. But what the ƒü¢k. what have you got to loose?

Also check the timing plate that goes on behind the crank pulley. It's easy to put this on backwards and have the timing way off that it doesn't start.

StanTheMan wrote:Just for fun check the belt timing.

I know its all too crazy. yes I know you said you had no spark. Timing belt has nothing to do with spark. totally independent. But what the ƒü¢k. what have you got to loose?

Actually on the NB8A at least I'm pretty sure it does, in a roundabout way.

The cam sensor is what tells the ECU to trigger the coils to spark (and which coil)
If the timing belt is stripped/snapped there is no signal to the ECU and so it wont tell the coils to spark, they'll just sit there charging thinking "man, sure seems to be taking a while for the engine to turn today"

But yeah, as long as the timing belt is there you shoudl still get spark regardless of cam timing (just that the spark will be at the wrong time)

hks_kansei wrote:

StanTheMan wrote:Just for fun check the belt timing.

I know its all too crazy. yes I know you said you had no spark. Timing belt has nothing to do with spark. totally independent. But what the ƒü¢k. what have you got to loose?

Actually on the NB8A at least I'm pretty sure it does, in a roundabout way.

The cam sensor is what tells the ECU to trigger the coils to spark (and which coil)
If the timing belt is stripped/snapped there is no signal to the ECU and so it wont tell the coils to spark, they'll just sit there charging thinking "man, sure seems to be taking a while for the engine to turn today"

But yeah, as long as the timing belt is there you shoudl still get spark regardless of cam timing (just that the spark will be at the wrong time)

I'm just thinking basics. If allignment is out it just will not start. If everything works one day, you take the head off.Replace it all. Its just too suspicious. No harm in checking. All you need to do is take the cam cover off. check the alignment.count the teeth. 15 min? maybe more complicated with the NB's