mx5cartalk.com

Hi,

I have a 93 NA8 Clubman and it is running MEGA RICH. It starts and runs fine but feels a little down on power but soots up the driveway and gets through 40l in just 260km of commuting. It is running the stock computer and has a full exhaust system as its only modification. I suspect that one of the following is wrong:

Engine coolant temp sensor
Intake air temperature portion of the MAF
Oxygen sensor
Leak in the extractors near the oxygen sensor
Fuel pressure regulator
Timing way out
The ECU is in some sort of limp-home mode (if there is one).

To test the possible electrical issues I need to know what the healthy range of voltages or resistances are for the various sensors. Does anyone have a workshop manual that gives these diagnostic values and which ECU terminals to check them at? Is there a way to see if the ECU is in a limp-home mode? I have used the search function to find manuals but with no success.

Anyone got any advice for an over-fuelling NA8??



Thanks,

M

Manual & Technical Data here:
viewtopic.php?f=76&t=43508
&
viewtopic.php?f=76&t=46376

If the above doesn't have the values, then some here that might help at Dann's 4th post:
viewtopic.php?f=55&t=48156&p=605204
Some more here at spikes' 1st post & Liam's last:
viewtopic.php?f=18&t=47933&p=602822
And some more here at Manga's final post:
viewtopic.php?f=29&t=39264&p=593114

Brilliant! Thanks.



M

ECU pinouts in case you need them:
viewtopic.php?f=76&t=38367

Sounds like O2 sensor - GL!

Ok ill call CTS


Dann

Mokesta wrote:Hi, I have a 93 NA8 Clubman

I thought you sold your clubman a few years ago? Or are you back in an MX5?

I still have the same MX5 that I've had for three or so years. It is now virtually stock with just the exhaust and alloy radiator and MX5Plus roll bar. All the other bits have been replaced with stock items and sold off. I was just about to sell the car when I got a parking space at the project office and started driving it daily. It will be for sale again when this project ends and I have to catch the train again. It is just about to clock over 112,000km and is still great fun to drive but I have the mortgage from hell and can't do track days anymore so I am chipping away at my other projects.

So tonight I got stuck in with the multi meter and found:

The CTS appears to work, at least it is correctly connected and reads the right resistance when cold. Will test hot tomorrow.
The TPS switch is fine
The TPS resistor is 0.452 kOhm at closed and 3.14 kOhm when at WOT << anyone know the correct range? It may need adjusting at idle.
The 4-Wire O2 sensor may be a problem. It started raining on me when I got up to that so I'll check again tomorrow.
What I think is the intake air temp portion of the MAF (red/black wire) had a resistance of 2.8 kOhm to the sensor earth when stopped & cold.
I haven't checked the timing, will ground the TEN point in the diagnostics and run the timing light over it tomorrow.
I haven't got the equipment to check fuel pressure.

I haven't got access to an MX5 94-95 1.8 workshop manual so I am trying to make do with a protege-1996 manual I downloaded but she's a bit different. I have found the right pin-outs and wiring diagram for my car but not any service numbers for items like the O2 and TPS.

Will update tomorrow.

M

it wont be o2 .

Dann

Dirty maf?

Mokesta wrote:...but not any service numbers for items like the O2 and TPS.

According to Rod's Mazda Miata 1.8 Litre Enthusiast's Shop Manual:

TPS:
Fully closed: 0.1 - 1.1 volts
Fully open: 3.0 - 4.6 volts
Continuity between terminals A & B [the two lower terminals], if not adjust TPS.

O2 sensor:
"Start engine & run at about 3k RPM until the meter reads about 0.55 volts. Suddenly open & close the throttle several times to check that when engine speed is rising a reading of 0.5 - 1.0 volts is shown. As engine speed falls the reading should drop to between 0.0 - 0.5 volts. At idle 1.0 volt or less should register. If readings are outside this range fit a new sensor."

"Measure the resistance between terminals C & D of O2 sensor (sensor end) connector. Correct resistance is 13 ohms at approx 20 degrees C (68F). Replace sensor if it fails this test."

Terminals C & D of connector are the two terminals on the right hand side of the connector when viewed end on with the mounting clip pointing toward you & the connector securing clip pointing away from you.

According to Haynes Repair Manual MX5 Miata 1990-1997 All models
TPS: with a 0.016 inch feeler between throttle stop screw & the stop lever, there should be no continuity between terminals C & D, i.e. the two lower terminals.

O2 sensor: on models with a heated O2 sensor, i.e. a 4 wire sensor, 11.0 - 17.0 ohms between the positive & negative terminals of the O2 connector (sensor end).

Thanks for all the help.

The timing was spot on, the CTS appears fine. The heater circuit on the O2 sensor appears fine and I assume the rest is ok. I can't really test it at night with a slightly loud exhaust and neighbours I don't want to piss off.

I may have found the smoking gun. When taking the connector off the TPS, it just slid off without me un-clipping it. Maybe it wan't on far enough and the harness wasn't conencted to the TPS?

I took lots apart to check resistances and put it all back together and the next day when I drove it the idle speed was noticeably lower. Maybe I'm dreaming it but it appears to run smoother. I have topped up the tank and will check fuel consumption over the next few weeks to see if it has improved. I am really hoping it is fixed.

Thanks again, especially 93_Clubman.

M