[Scottmk1mx5]

Hi all, I’m still having issues with my 1996 mk1 1.8. Car struggles to start but does after a few attempts and then dies after 6/7 seconds of running but will die instantly if the accelerator is pressed. Managed to get two fault codes using the mx5tech tool but I am unsure as to wether these will cause this problem. I’ve checked for spark and fuel delivery up to the pressure regulator and I’ve had the fuel pump constantly running using the GND AND FNP but no difference. Any help appreciated thanks.

 

[Martin Y]

Assuming your car is stock, it doesn't have a manifold pressure sensor.

I'm not familiar with the tool you're using but I believe it's trying to read OBD1 fault codes but your 1996 car has the later 16-bit ECU which uses OBDII codes.

<having Googled the MX5 Tech website> Have you tried telling the tester you have a Mk.2? I think that might be the answer.

 

[Scottmk1mx5]

Yup car is stock, how would I go about trying to read OBDII codes? I have the LED diagnostic tool somewhere would that show OBDII codes? Thanks

 

[Martin Y]

The tester instructions say it can read Mk.1 and Mk.2 codes, and Mk.2 are OBDII codes. But late model Mk.1 cars are OBDII too. But I'm surprised the instructions don't say this, so I'm not sure what to think about that. I do suspect if you just switch it to read Mk.2/NB codes it'll start to make more sense.

 

[Martin Y]

PS If you wanted to try reading codes with a diagnostic LED tool, the format for the later OBDII models is;

Start with an extra-long flash, then there are four rounds of a long flash followed by 0 to 9 short flashes. Count the short flashes and that gives you a 4-digit number. If there's a second fault code stored then it'll do the next four digits the same way. Eventually it'll start again with the extra long flash and the whole sequence will repeat.

If you take your 4-digit number "xxxx" and Google "Mazda fault code Pxxxx" you should find a description. (Most codes are universal but I think some are proprietary to each brand so it's worth Googling for Mazda codes specifically.)

Hope that helps

 

[Scottmk1mx5]

Thank you, I tried switching it to read mk2 codes with the mx5 tech tool but no luck. I will try again with the LED tool and see if this sheds any more light on the problem. Much appreciated

 

[guitaristanime]

and Mk.2 are OBDII codes.

Are all Mk2 OBDII despite not having OBDII diagnostic ports?

 

[Martin Y]

Are all Mk2 OBDII despite not having OBDII diagnostic ports?

Yes, as far as I know. Right from when the later Mk.1 cars moved to 16-bit (3-plug?) ECUs around 1996 or so I think they used OBDII codes rather than OBDI but they still only had the usual Diagnostics port to read them from with an LED. North American market Miatas got an OBDII port fitted right from the start of NB/Mk.2 production but the rest of the world only got the port later, I think with the Mk2.5 facelift.

(My memory's not what it was but I think that's how it went.)

 

[Scottmk1mx5]

Hi all, still having problems as I aren’t able to get to the car much at the minute. Just a thought. Would turning the exhaust cam without timing belt fitted adjust the ignition timing as nothing else moved apart from the exhaust cam? When tightening the cam gear I turned the cam accidentally as I took the locking mechanism off (stupidly) when doing this. I lined the cams up for the main timing so they look correct but I’m wondering if this will throw ignition timing as the CAS is on the exhaust cam? Thanks

 

[guitaristanime]

Hi all, still having problems as I aren’t able to get to the car much at the minute. Just a thought. Would turning the exhaust cam without timing belt fitted adjust the ignition timing as nothing else moved apart from the exhaust cam? When tightening the cam gear I turned the cam accidentally as I took the locking mechanism off (stupidly) when doing this. I lined the cams up for the main timing so they look correct but I’m wondering if this will throw ignition timing as the CAS is on the exhaust cam? Thanks

I think if I've read this correctly you are saying that during changing the belt, your exhaust cam wasn't set to BTDC but then you did set it correctly before replacing the belt.

If so, yes that's OK, if the number of teeth between the cams top is correct, and they were both correctly set then you would be fine. Freely rotating them without the belt on will make no difference provided they end up where they need to be at the end of the process.

However your message is a little ambiguous to me, wondering if its worth fully checking your timing, to make sure your crank isn't out (I believe it can be one rotation out compared to the cams)

 

[Scottmk1mx5]

I think if I've read this correctly you are saying that during changing the belt, your exhaust cam wasn't set to BTDC but then you did set it correctly before replacing the belt.

If so, yes that's OK, if the number of teeth between the cams top is correct, and they were both correctly set then you would be fine. Freely rotating them without the belt on will make no difference provided they end up where they need to be at the end of the process.

However your message is a little ambiguous to me, wondering if its worth fully checking your timing, to make sure your crank isn't out (I believe it can be one rotation out compared to the cams)

Okay, yes basically I freely rotated the exhaust cam without the belt on but then lined them back up to do the timing. (Believe i set it to 19 teeth between the two gears) with piston 1 at TDC.

 

[Scottmk1mx5]

Just wondered if freely rotating the exhaust cam would throw the ignition timing out on the CAS. Trying to narrow every possibility down as I’m at a loose end with it. I can keep the car idling by blipping the accelerator but it is very broken up (sounds like misfire) and won’t rev past 3k but it will die if I don’t do this.

 

[guitaristanime]

Okay, yes basically I freely rotated the exhaust cam without the belt on but then lined them back up to do the timing. (Believe i set it to 19 teeth between the two gears) with piston 1 at TDC.

Sorry I just read back up, thought this was a mk2

I think you might be on to something with your thought process regarding the cam sensor, yes.

@Martin Y will definitely know.

 

[Scottmk1mx5]

No mk1 1.8. I’ve changed coil pack, ignition leads, plugs. Checked all sensors are connected etc and everything is as normal. CAM sensor is my last idea really.

 

[Martin Y]

Looking back, I'm reminded that the original report from your code reader mentioned manifold pressure sensor and barometric pressure sensor. It reminds me that in early 1.8 cars the ECU has a built-in barometric air pressure sensor. At least, I'm told UK models do. Japanese Roadsters like mine don't have it fitted. (Maybe they reckon Japan hasn't any mountain roads high enough to cause a problem with change in altitude.)

So I wonder if yours has a barometric sensor like that and it's actually an ECU problem rather than an engine sensor problem. That's all outside of my experience but I guess the place I'd go looking for others with similar problems is miata.net forum. Although you need to watch out for Miata vs MX-5 vs Roadster model differences, it's just a much bigger resource than here, and "barometric" seems like a useful search term.

 

[Scottmk1mx5]

Hi martin, my car is a 96’ eunos. I’ll try the miata forum see if I can shed some light on this! Thanks

 

[Martin Y]

Curiously, I just took a first look there and found a '96 Miata and attention is focussed on a sensor which measures manifold and atmospheric air pressure, seemingly for the EGR system. That opens another can of worms. I know earlier 1.8 Roadsters do not have EGR fitted, but I don't know about later cars like yours. Sorry if my (over)confident assertion your car doesn't have a manifold pressure sensor turns out to be bad info.

Thread here: 1996 Relay Identification Question - MX-5 Miata Forum

 

[Scottmk1mx5]

No problem thanks for your help! I’ll try do some more digging