Misfire Under sudden acceleration

[mewse]

Hey guys,
Im still very new to mechanics and automobiles so sorry for my terrible explanation and lack of knowledge. So ive just bought my second mx5 (89 aus na) after the first had a mishap with a tree, as far as i knew although the little white rocket looked a little rough the engine still ran fine but upon getting it all back together it starts and idles fine and if im very gentle it will rev through just fine but if i push the throttle suddenly it misfires and then splutters and starts to rev, it makes the car undriveable.
So far the list of things ive checked are plugs and leads, fuel filter, TPS, AFM and the timing is correct and im at a loss and any help will be greatly appriciated.

[project.r.racing]

see misfire thread 3 below this.

[93_Clubman]

just bought my second mx5 (89 aus na) as far as i knew although the little white rocket looked a little rough the engine still ran fine but upon getting it all back together it starts and idles fine and if im very gentle it will rev through just fine but if i push the throttle suddenly it misfires and then splutters and starts to rev, it makes the car undriveable. So far the list of things ive checked are plugs and leads, fuel filter, TPS, AFM and the timing is correct

Sounds like you've dismantled part/s of the car. How was it running prior to dismantling? Is it possible something you've done in dismantling & reassembling has caused this issue? When you say you've checked the spark plugs & spark plug leads, have you tried swapping in known good plugs & leads? On the NA6 it's usually plug leads &/ or coilpacks. Alternatively, does the issue persist once the engine has warmed up? The coolant temp sensor at the rear of the head for the ECU & cold starting is also a common issue. This causes poor cold running that clears up once warm.

[mewse]

The only things i has dismantled is the headers and exhaust as this car come without any, i put in working plugs leads and the coilpack from my old car today and still no change having the car at operating temp doesnt seem to make any difference either

[emily_mx5]

do you have an exhaust leak? if there is a really bad leak up near the headers/cat, it can mess with the O2 readings and cause your symptoms.

[mewse]

do you have an exhaust leak? if there is a really bad leak up near the headers/cat, it can mess with the O2 readings and cause your symptoms.

I think i may have a exhaust leak at the joint between the headers and the exhaust but the o2 sensor is before that so i didnt think that would matter, although my exhaust has a second o2 sensor in it but i couldnt find anywhere for it to plug in?

[emily_mx5]

yeah an exhaust leak anywhere can mess up a quite a few things, definitely get it checked out, maybe you need a new gasket or a hole welded up.

ummm 2 oxy sensors? thats not stock. Do you mean a little sensor that plugged into the original cat? if so that is a temp sensor. If its just hanging around under the car, unplug it.
this is my custom cat with the oem sensor port welded in.

[mewse]

im hoping its just a gasket as i half assed it and just reused the old one, and that looks exactly like the sensor i mentioned thanks for clearing it up and sorry for my ignorance haha

[mewse]

Fixed the exhaust leak today and still no change, any other suggestions of what might be causing my issues? Would it help if i uploaded a video of it?

[spikey]

Try unplugging the oxy sensor, if that fixes it then it is your sensor that is faulty.

[mewse]

Try unplugging the oxy sensor, if that fixes it then it is your sensor that is faulty.

Just tried that still no change ive also swapped injectors, fuel pressure reg, fuel pump with known working one and still nothing, im out of ideas.

[Steampunk]

Check all the pneumatic hoses, you may have a vacuum leak.
Did you clean the AFM connection?
What did you check re AFM? Does the flap move freely?
I doubt a leaky exhaust causes this kind of hesitation, unless the leak is really early on in the primaries and it'll have to be pretty darn close to the flange to affect anything.
The car should still drive ok with a faulty/non-existent O2 sensor, try unplugging it completely.

[93_Clubman]

it starts and idles fine and if im very gentle it will rev through just fine but if i push the throttle suddenly it misfires and then splutters and starts to rev, it makes the car undriveable.

Alternatively, does the issue persist once the engine has warmed up? The coolant temp sensor at the rear of the head for the ECU & cold starting is also a common issue. This causes poor cold running that clears up once warm.

[mewse]

Check all the pneumatic hoses, you may have a vacuum leak.
Did you clean the AFM connection?
What did you check re AFM? Does the flap move freely?
I doubt a leaky exhaust causes this kind of hesitation, unless the leak is really early on in the primaries and it'll have to be pretty darn close to the flange to affect anything.
The car should still drive ok with a faulty/non-existent O2 sensor, try unplugging it completely.

I've checked the hoses and could not find a vac leak but i will check again, i haven't cleaned the connector for the AFM but i did swap it out for my known working one off my old car. Also the car behaves exactly the same regardless if it is cold or at running temp

[93_Clubman]

Also the car behaves exactly the same regardless if it is cold or at running temp

ok - check ECU PCB for any discoloration or other obvious signs of an issue, also check earthing points.