Engine missing under load

sheffmx5 · Engine missing under load

Hi
My 1.6 mk 2 is missing under load it started yesterday for some reason. Ive had the plugs out and all but no 4 look OK. No 4 is sooted up so I think it may be the leads. Just fitted new plus about 4 weeks ago. It ticks over fine and smooth but chugs and pops when under load.

Any Ideas

Thanks

nathmill85

airflow problem? clogged fuel system? HT leads broken up? sensor problem? cambelt jumped a tooth?

no idea overall but all previous problems that i remember...

roadsterbloke

speak to andy, theres a way of reading the computers fault codes with a bulb and wires,

sheffmx5

Think I am going with the HT leads first of all as its a cheapish fix and the ones that are on look like they were put on by Mazda when car was new. It starts fine and ticks over as if nothing was wrong until a bit of throttle is used then it miss fires . came on suddenly yesterday but seems to have been using a bit more fuel of late.

Thanks anyway

roadsterbloke

So, what’s up with your engine? Is your engine playing up? Want to know what’s wrong with it? Well now you can find out what’s wrong with your engine, or, at least what the Engine Control Unit (ECU) thinks is wrong with it, which should lead you a good way down the path to correct diagnosis...

The MX-5’s ECU continuously monitors many of the parameters related to engine performance such as fuel, spark, air, RPM, etc. It uses this information to get the most performance and fuel economy possible from the engine. A nice side effect is that it can detect many problems your engine may be experiencing and it even has a way to tell you about them. You may have read in Miata Magazine about reading off the error codes on the check engine light on the dash-board, but our MX-5’s and Eunos Roadsters don’t have this light. Due to a bit of detective work by Glenn Stephens in England, we can now report to you how to make an indicator so you can read these error codes yourself, without having to bother your friendly local Mazda technician with his expensive special service tools.

You will need a Light Emitting Diode (LED) and a resistor. These can be purchased at Dick Smith Electronics, Jaycar or any other similar electronic hobbyist supplier for spare change - less than $2. You’ll also need a separate short length of wire. (An unpainted paper clip will do) If you buy a red coloured LED, you will need a 2000 Ohm resistor, or any other colour will need a 500 Ohm resistor. (If you happen to already have a selection of resistors, any value within about +/ - 25% of these will do). Simply solder one lead of the resistor to one lead of the LED. It doesn’t matter which side of the diode you put the resistor on, but it will pay to take note of which is the longer of the two leads on the diode, as this will determine how you plug it into the car.

The finished product is shown in the picture - it's that simple! Now, locate the Diagnostic Connector in the engine bay. It’s a small black box about the size of a packet of matches, near the top of the passenger’s side (Right hand drive MX5s) shock absorber, also near the engine air inlet snorkel (and it has Diagnostic stamped on it!). After you unlatch the cover, there should be a label inside explaining what the different terminals are called. With the ignition off, use the short piece of wire (or paperclip) to connect the TEN terminal to one of the several GND terminals. Now, connect the indicator between terminals B+ and FEN, with whichever side of the diode had the long lead towards B+ (If you get it the wrong way around, no damage will be done, you’ll just get no light out of it)

Code Meaning
1 Ignition pulse
2 Ne signal
3 G signal
4 SGT signal (1.8L)
8 Airflow meter
9 Water thermistor
10 Intake air thermistor in airflow meter
12 Throttle position sensor
14 Atmospheric pressure sensor
15 Oxygen sensor (output too low)
16 EGR function sensor (1.8L)
17 Oxygen sensor (output not changing)
25 PRC solenoid valve (1.8L)
26 Solenoid valve (Evaporative canister purge)
27 EGR solenoid valve (vacuum)(1.8L)
28 EGR solenoid valve (vent)(1.8L)
34 34 Idle air control (1.8L)
36 Idle speed control valve

Now turn on the ignition, but don’t start the engine. The LED will light up for about five seconds (assuming you got it the right way round) before it starts flashing out the error codes (if there are any). This will give you a chance to get around to where you can see the indicator. Count the number of flashes to indicate the malfunction code. If the code is a two-digit number, the tens digit will be displayed first with a long flash, then after a 1.6-second dark pause, the ones digit will be displayed with shorter flashes. If there are multiple codes, they will each be separated by a four-second pause and may include two-digit codes, so pay attention. (For example, one long flash followed by three short flashes would be a code of 13) The codes will repeat after four seconds so don’t worry if you miss them the first time. Take as long as you need to record the codes and then refer to the Fault Codes chart shown.

Keep in mind that the indicated device may not be faulty itself, but may have a bad electrical connection, or some other fault may be making it have an abnormal signal. The fault codes are stored by the ECU indefinitely, so after you’ve done something to cure the problem, you need to clear the codes by disconnecting the car battery for a minute or so. This will wipe the computer of its error codes. Now you can drive the car again for a while, and re-check to make sure the error code hasn’t come back. (If you didn’t clear the ECU’s memory, it will still have the old codes.) Hopefully, as several others and I have been able to, you’ll be able to use this information to find the cause of whatever’s wrong with your car. However, I do know one car that runs poorly, but has no fault codes, so its not a complete solution, but it should help the home mechanic (or any mechanic without Mazda’s diagnostic gear) get a better idea what any fault may or may-not be. I hope you’ll only need to use this info to satisfy your curiosity rather than from necessity.

5Alive

Hmmmm . . . . . . . Yes

roadsterbloke

this is sommat similar to what your headlight does clive

Damo

I should get round to Dick Smith Electronics first thing in the morning mate!!

nathmill85

Its so simple in theory, and very clever considering the rigmorale you go through with my citroen on a pre OBD II connection... at least it doesnt flash 36 times for the final fault...

also doesnt work if a mechanic has set fire to the loom and rewired it funny so that when you connect the LED up the fans come on...

roadsterbloke

" Its so simple in theory "

this sentence alone is why the english language was invented

sheffmx5

O.M.G

Thanks for ALL YOUR HELP!!!!!!!!!!!!!!!!!!!!!!!!!

Glad to know it is something simple then HAHAHAHA

Im still non the wiser but I might have to take it in if the new leads dont cure it.

Any more suggestions, (short ones only please) lol

Cheers

5Alive

Yep you're thick !!

That short enough ?

BUT

ya in good company cos there's a few of us thicko's on here.

On a more sensible note !!

Why don't ya try n meet up with one of the not so thick or come to Nath's tech day. If it's a 5 min job i'm sure someone will be able to help you out.

sheffmx5

ME THICK !!!!!!!!!!!!!!!!!!!!!!!!!

Where is the tech day going to be held next sat?

I was hoping to get it sorted before then as its "THE WIFES" daily car so I need to get it done ASAP (last week if pos) lol

I could meet up but im on nights on Monday and Tuesday and afternoons rest of week.

I live in S20 near Crystal Peaks

MAZMEL

I had same problem...make sure plug leads are pushed down tight on coil and plugs...this is what my problem was

sheffmx5

Ive tried that as well. Plug 4 is very sooty so that indicates to me that its not burning the fuel/air so it might even be a poor plug but I havnt got a spare to try it with. This has only happened since I replaced them 4 weeks ago

5Alive

sheffmx5

Oh, creeping now are we mate? pmsl

I know you were (sob sob sob into my beer) hic , sob hahaha

I am infact, a very very very very very intelligent person and am made to feel very welcome here.

5Alive

sheffmx5

Im a mechancial engineer and work for Sheffield Forgemasters. Thats not nosy. Just cheeky. lol

maybe I should be able to sort this prob out but I know when I need help. HEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEELLLLLLLLLLLLLLLLLLLLLLLLPPPPPPPPPPPPPPPPPPPPPPPPPP

Is there any other sort of life? My life is pretty real all the time.

MAZMEL

IF YOU SUSPECT NO4 PLUG....SWAP IT WITH NO3 PLUG (clean plug first)THEN IF NO3 PLUG SOOTS UP YOU KNOW IT'S DEF THE PLUG THAT IS FAULTY.IF NO4 SOOTS UP AGAIN SUSPECT HT LEAD OR COIL

sheffmx5

Hi all
Thanks for all the help

I have just fitted a new set of NGK plugs and a new set of leads and the problem has gone!!!!!!!!!!!!!

Hopefully it was the leads

ill keep ypu informed

mxavo

maplins for the bits, next time i am in there i will buy some bits and make up a couple of said test diagnostic leads for future use..you could also download the software to your laptop !!!!!

nathmill85

Nice one matey easy fix for ya!

5Alive

excellent result !! lets hope alls well that ends well fingers crossed.

Sheffield Forgemasters ! thats about as real as you can get

sheffmx5

Oh yes mate Its just about as real as it gets. Anything up to 300tonne castings and the like and I LOVE IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!

nathmill85

just thank god you dont work for corus mate

sheffmx5

Too right. Ive been through this before and hopefully we will be ok this time. Things look ok for now but who knows? No point thinking about it as the world has not stopped yet and the press have a lot to answer for!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Been on a good run in 5 today and the fix with plugs and leads seem to have fixed the misfire. It feels like a different car. Im going to have to try it again tomoz. DAM. LOL

MX5 parts where I got the plugs from will refund the cost as the plugs were at fault if I send them back to them. Good service always gets my vote.