Why won't my mx5 accelerate? AFM? Coolant sensor?

[meta]

Hi everyone,

I've only recently come into this drama and its really starting to get at my nerves,

My mx5 won't accelerate, up until say 3500 rpm, the car has no go what so ever, even with my foot on full throttle, it moves as fast as a granny crossing a road with a trolley, its terrible to drive at the moment and feels so unpredictable.

At the moment, i feel it could be either the Afm as the car will happily accelerate after 3500 rpm all the way, not perfectly, but it does, or the coolant temp switch as i recent broke it...however soldered it back into place lol

The symptoms of the car is at start up, it turns over however, stalls at times, you can hear it sucking in air, however, it just doesn't go, then when it does start up, it slaves at times, personally the car feels like you're trying to suck a whole bottle of coke through a straw really quickly, that's the angst i'm feeling right now with my car

If anyone has any ideas as to what my problem could be, please feel free to post, as i'm completely stumped at the moment as to what could be the problem!

[93_Clubman]

Not sure which coolant temp sensor you're referring to as there's effectively 3 on the NA6. One at front on thermostat housing to activate the cooling fans, & two on the back of the head. One for temp gauge & the other for the ECU for cold starting. A sensor breaking & resoldering back into place probably isn't ideal, especially depending on which sensor & the type of break. Take a look at this thread as it sounds fairly similar to your NA6's problems:
viewtopic.php?f=29&t=37822

[Juffa]

Wot he said ^^^^^

Have you changed anything in/on the car recently?

Spark plug leads are know weak link on the MX-5. How long since these were replaced?

I'd suggest starting with the free stuff first.

1. Check that there are no leaks in the intake system, i.e. all the pipes/hoses between the AFM and the intake manifold are good and tight.

2. Remove and check each spark plug. Check that the gap is correct and the end of the plug is a light grey colour. All the plugs should be the same colour. If not then that might indicate a problem with the spark plug leads or the spark plug its self. You can new plugs at most car parts hops (Super Cheap, Autobarn, Bursons....)

3. Check the engine timing

4. With the engine running disconnect one spark plug lead at a time. If the engine starts to stutter/cough then that lead/plug is working. If there is no change then that lead/plug are faulty.

5. Have you used a different fuel/service station recently...you may have a bad batch of fuel?

6. I hate to say it, but do you have an early model MX-5 from around 1989-1990? If so you may have the dreaded Short Nose Crank issue. Have a look at look at the pulley attached to the engine crank with the engine running and see if it has a major wobble. If the engine timing is wrong this can also indicate a problem with the crank.

J.

[93_Clubman]

As J says it could potentially be one or more of a number things in the absence of more info or a baseline on your car.

Btw, just saw your post in Kazjim's thread about you trying to get the same sensor as him, i.e. the front one.

[meta]

hi everyone,


A

Wot he said ^^^^^

Have you changed anything in/on the car recently?

Spark plug leads are know weak link on the MX-5. How long since these were replaced?

I'd suggest starting with the free stuff first.

1. Check that there are no leaks in the intake system, i.e. all the pipes/hoses between the AFM and the intake manifold are good and tight.

2. Remove and check each spark plug. Check that the gap is correct and the end of the plug is a light grey colour. All the plugs should be the same colour. If not then that might indicate a problem with the spark plug leads or the spark plug its self. You can new plugs at most car parts hops (Super Cheap, Autobarn, Bursons....)

3. Check the engine timing

4. With the engine running disconnect one spark plug lead at a time. If the engine starts to stutter/cough then that lead/plug is working. If there is no change then that lead/plug are faulty.

5. Have you used a different fuel/service station recently...you may have a bad batch of fuel?

6. I hate to say it, but do you have an early model MX-5 from around 1989-1990? If so you may have the dreaded Short Nose Crank issue. Have a look at look at the pulley attached to the engine crank with the engine running and see if it has a major wobble. If the engine timing is wrong this can also indicate a problem with the crank.

J.

Thanks for the reply Juffa, i've recently replaced all the the spark plugs, basically a basic service, my mechanic has double checked everything and gone over the possible problems, as for fuel, i've been running bp ultimate, it's possible that it could be a bad batch, however, i've been going to different petrol stations each time i fill up, so i'm quite unsure, i haven't checked the leads, however, i may give that a try now, as for the short nose crank issue, unfortunately i do have a 1990 model and yes, it does wobble .....i've also bumped up the cam timing to 14btc, however, would this short crank issue effect the way my car starts up? and delivers power?

As for the intake system, i've just ordered a replacement AFM, which could be the problem, as i've been running a mx5 mania style intake for the past year, so things could of sucked into the intake, other than that, i've recently had replaced the drive belt and timing belt done, so i'm alittle unsure as to what it could be...damn!

Not sure which coolant temp sensor you're referring to as there's effectively 3 on the NA6. One at front on thermostat housing to activate the cooling fans, & two on the back of the head. One for temp gauge & the other for the ECU for cold starting. A sensor breaking & resoldering back into place probably isn't ideal, especially depending on which sensor & the type of break. Take a look at this thread as it sounds fairly similar to your NA6's problems:
viewtopic.php?f=29&t=37822

Yeah, its the one above the thermo housing, however, seeing as it controls the radiator fan, i'm unsure on whether this would have a profound effect on my cars acceleration?

Thanks again everyone for the replies and support!

[meta]

Also, i just checked the leads, it does splutter alittle, however, not really that dramatically, it just kinda of hums with a little rougher, how much of difference am i expecting with the leads?

[93_Clubman]

As you say front sensor unlikely to be causing the problems your car's experiencing. In the thread above gobsmax found it was one of the rear sensors that was causing his problem. He took it out, cleaned it all up, reinstalled & it fixed the problem.

The hum you mention in your last post is worrying though - that's how my old '89 NA6 sounded just before the short nose crank problem stopped it from running. Immediately prior to stopping it was doing some of the things yours is doing but mine happened on a drive between Sydney & Canberra, so speed & revs were up nearly all of the time until it kicked right in & the car wouldn't run. Fortunately no damage & all was fixable fairly easily in my case.

If you've got some spluttering, hesitation, missing or rough idle due to plug leads then that should go completely with good leads.

[meta]

As you say front sensor unlikely to be causing the problems your car's experiencing. In the thread above gobsmax found it was one of the rear sensors that was causing his problem. He took it out, cleaned it all up, reinstalled & it fixed the problem.

The hum you mention in your last post is worrying though - that's how my old '89 NA6 sounded just before the short nose crank problem stopped it from running. Immediately prior to stopping it was doing some of the things yours is doing but mine happened on a drive between Sydney & Canberra, so speed & revs were up nearly all of the time until it kicked right in & the car wouldn't run. Fortunately no damage & all was fixable fairly easily in my case.

If you've got some spluttering, hesitation, missing or rough idle due to plug leads then that should go completely with good leads.

hhhmmm...sounds like i've found the culprit then lol ...that's pretty much how my engine is running right now, its a pain

That being the case, i might as well just get a new engine, do you know by any chance if the long nose version is a straight bolt in? or does it need minor mods to fit in place?

Thanks for the reply clubman, its greatly appreciated

[Dweezle]

Long nose just bolts straight in.

But before you do anything drastic.
Definetly confirm if you actually have the short nose crank issue.

I have had this problem twice with my old na6 and most said it was probably SNC failure.
First time it was the green temp sensor on the rear of the block.
Second time it was the Oxygen sensor.

Hopefully yours is something as simple.

Sent from my iPhone using Tapatalk

[93_Clubman]

Got a agree with Dweezle - first confirm it's the SNC problem. In gobsmax case, which was simliar to yours, it wasn't:

FIXED!!!

Removed the coilpack (three 12mm screws), the third screw on the bottom was a PITA to remove but got it out eventually, removed the engine temp sensor (19mm) and polish the tip with wet and dry, cleaned out the contacts and connectors with carby cleaner, reassembled and she been working fine since.

Even if it's the SNC problem, it doesn't automatically mean you need to replace the engine. Mine was fixed easily without changing the engine or crank, & ran for another 90k kms without a problem until I finally sold the car with over 180k kms.

[meta]

Got a agree with Dweezle - first confirm it's the SNC problem. In gobsmax case, which was simliar to yours, it wasn't:

FIXED!!!

Removed the coilpack (three 12mm screws), the third screw on the bottom was a PITA to remove but got it out eventually, removed the engine temp sensor (19mm) and polish the tip with wet and dry, cleaned out the contacts and connectors with carby cleaner, reassembled and she been working fine since.

Even if it's the SNC problem, it doesn't automatically mean you need to replace the engine. Mine was fixed easily without changing the engine or crank, & ran for another 90k kms without a problem until I finally sold the car with over 180k kms.[/quote


No i don't disagree with you guys, i've checked every possible issue, my mechanic today had a look at the temp switch at the back and its still running the same, the engine is at 233000km+ now, so i'm at a loss to keep repairing, i'm just going to bite the bullet and swap it out before things become worst as i'm already at a nerves end trying to sort out my issues with this car

thanks very much guys for your replies, its defiantly helped me out, i appreciate it very much

Meta

[93_Clubman]

No problem & fair enough given you've ruled out the sensor & it's done a few kms.

Mine went relatively quickly. Left ACT one morning for Sydney & noticed a very faint hum or vibration just after start-up. Needed to get to a meeting, so had to head off & thought I'd check it later. OK driving the 300 kms up, & ok until just passed Campbelltown on the way back, but then it went & car was undriveable.