nb with hesitation under load

[hamx5ter]

Nope. it ran perfectly once we put swapped out my old MAF for this (2nd hand) one. Since then i had dríven it on a couple of decent spirited runs, did a club day at Marulan and it was perfect.

It was basically fine until the battery died. On the push start it started with a lot of hesitation but ran just fine until i stopped (but engine was running) at the Broke turn-off. It was idling fine at that point.

When i put it in gear and started to move off, it lurched and chugged. Only stayed alive because the road was a slight grade down and i pumped the clutched until i revved it to perhaps 3500-4500... After that it was the disaster of heel-toe-throttle and left-foot braking and blipping the engine like mad whenever the car had to stop (at intersections or lights)

When the engine is revved, it revved cleanly without any bad sounds... all the drama is at low rpm.

I won't have time today, but Saturday i'll try and test the MAF on/off again and see if i can pull the ECU out and see if there's any electrical marks / burns... but i doubt it.

I should say again that the tank would have been COMPLETELY EMPTY by the time i got into the carport. So i wasn't surprised it wouldn't just start even with the fuel. Is it possible that the pump or injectors have become clogged? It would have surely run on vapor for the last few kms

[93_Clubman]

It was basically fine until the battery died. On the push start it started with a lot of hesitation but ran just fine until i stopped (but engine was running) at the Broke turn-off. It was idling fine at that point.

When i put it in gear and started to move off, it lurched and chugged.

When the engine is revved, it revved cleanly without any bad sounds... all the drama is at low rpm.

Is it possible that the pump or injectors have become clogged?

Couple of things:
-With the 8bit NA ECU when the battery dies completely or is disconnected faults stored in the ECU are cleared & the ECU does some relearning - believe this also applies to the 16bit NB ECU.
-As you say above the low rev issue started as you moved off immediately following the Broke turn-off pause - what was the fuel level at this point?
-Also as you say the issue is at low to medium revs, but not at higher revs which would seem to suggest it's getting fuel ok to feed the high revs.
-Certainly by the time you've got home it's possible that if there was any sediment in the fuel tank it could clog to some extent the filter on the end of the fuel pump. But often the inside of our tanks are quite good, although there are always exceptions. Then there's also the cannister fuel filter between the tank & the injectors, so between the two fuel filters not much should get through to block the injectors. But again, it revs fine at high revs which suggests it's getting fuel.

[93_Clubman]

Btw, it possible a failing fuel pump could cause the low-medium rev issue, but there's still something else going on re starting when MAF disconnected & not starting when MAF connected, which could be wiring or connector shorting or ECU affected by moisture etc.

[hamx5ter]

oh wow... that's super informative 93C!

The fuel level when the battery died would have been ~30%. maybe a bit more.

I had 'filled up' at Windsor. The tank already had about 65% and i wanted to top it up but the nozzle kept tripping at the 7-11. I assumed it was full since it already had more than 1/2 of fuel in it already. It was only when i got into the car and and I waited for the need to go to F that i realised that it was tripping for some other reason rather than the tank being full.

I think it was about 80% when we left. I wasn't too concerned because i was going to fill up at Broke perhaps and it was plenty of fuel for that. Of course, that changed when i couldn't stop anymore and of course it was being dríven on a higher rpm so i wouldn't lug the engine.

I'm leaning towards the MAF because the symptoms are very similar to what we had before with the faulty MAF; just much more extreme and i guess the battery / fuel issue might have really pissed off the ECU. With the faulty MAF before, it was hesitation at off-idle and low-rpm but would rev cleanly at high rpms.

I'm busy today but tomorrow morning i'll start it up and do the MAF on / off and report.

[StillIC]

Some generic statements regarding fault finding...

Sometimes it is easier to ignore what happened in the past and focus on the symptoms as they currently present themselves. In hindsight it might all make sense, or perhaps not.

I tried diagnosing a problem which ended up being a distributor cap fault. I had been swapping dizzys but keeping the brand new cap on each swap. I took the car to a mechanic who swapped the dizzy with another 2nd hand one and the car ran fine. Hazar! It was the brand new dizzy cap at fault. Obvious in hindsight, but I couldn't figure it out at the time.

Manufacturer repair manuals have excellent troubleshooting guides in them.

I remember struggling with my Celica years ago. I borrowed the genuine Toyota manual from the regional TAFE college and went through the troubleshooting process. I made it to the last step where it said "try another ECU". I thought "that can't be it" and lived with the intermittent problem for another few months. I eventually had the ECU tested and the report was "it works fine". Upon a worsening situation I went back and borrowed the Toyota manual again, again made it to "try another ECU", so bit the bullet and spent up! Car worked immediately, problem never recurred, and the new second hand ECU was still going well when chunks of rust were filling the boot and footwell when the car was sold for $300.

[hamx5ter]

well here you go....

Started the car up with the MAF. As expected, the engine dies immediately. Now it seems quite obvious that it's not that it's not firing or stalling. The ECU is just turning it off. With the MAF unplugged the car started and ran high at about 2500rpm for a minute. Plugged the MAF in and it turned off. Restarted it and it settled down pretty quickly to a pretty decent idle (800rpm).

Took it for a drive. Drove perfectly well. Throttle is as smooth as always. Tiny movements of the foot translate directly to rpm. No hesitation at all. The idle wandered a bit (from 800 >> 600) when i came to a stop at roundabouts / lights but didn't stall. Even when i blipped the throttle it still would return to 800 fairly smoothly.

Revs DID climb quicker than i thought was normal and it would sink slower. Normal hamx5ter rev is very sharp both up AND down. This one would rev up quickly (almost any throttle and revs will shoot up to 3000 but sink at a slower rate back to idle).

The exhaust is definitely cracked. When you go past another car / wall, it's properly loud and i can hear more pops than normal. It might just be a hairline crack though... Not fussed as it's easily sorted i think.

Parked the car, engine idling and plugged the MAF in, and the engine died... video

https://photos.app.goo.gl/rsQmxVEvMmnjFQdU8

I'll check and see if i can get a MAF (@GM) since i'm keen to try and get this thing running consistently soon. I'm quite depressed still by the running into of the wall thing and keen to put this sorry chapter behind me

[greenMachine]

I'm going to be a disappointment I'm afraid - no MAF/AFM to be found. The one I took apart was a gutted one I ran on the GM to keep it looking standard, but all the insides had been hacksawed out so it was never going to any help to anyone. But I was sure I has one or two around, however none can be found. I did find the Bear rear towhook though .

Have you had a CLOSE look at the plug on the MAF/AFM? It seems that there must be something going on in the wiring ...

[hamx5ter]

I'll check out the wiring.

All good about the MAF. I'll see if Mania or someone else has one.

Yes please for the tow hook! I'mm PM you

[hamx5ter]

I found a few posts online about the mx5s running rough and then running ok when the MAF is unplugged so it doesn't seem like the ECU will automatically cut fuel if it doesn't receive anything from the MAF. It just means it will run to a map which may or may not be too rich / too lean, maybe foul your spark plugs OR burn a hole in your piston

It could be just a dirty MAFa for which apparently i could try

Cleaning it with AFM cleaner
https://www.repco.com.au/en/oils-fluids ... p/A9340831

Testing the MAF sensor wiring with a multimeter
https://youtu.be/p0ocaDmcAIM

is this what i was talking about when i said the revs climb very quickly?
https://youtu.be/p0ocaDmcAIM?t=270

https://www.youcanic.com/mazda-mass-air ... ms-repair/

Checked the onlines... New ones range from $260 to $450 I can get AliExpress ones for $50 watamitodo????

[93_Clubman]

watamitodo????

NB MAF $35.79 free postage or pickup Sydney:
https://www.ebay.com.au/itm/26527341076 ... %3A2047675

[hamx5ter]

hahahaha... Thanks @93C... i actually purchased the very same item soon after i posted and THEN checked compatibility. It said no, so i cancelled the order. Seller was very prompt in cancelling and funds were transferred back onto my card in the next day or two. yayy!

So.... also by way of an update about the car.

Yes it was the MAF. Mechanic swapped it for another and it ran perfectly. Weird thing was it sounded quite rattly and there was a whooshing / whistling sound from the engine but with the replaced MAF, everything has turned back to normal again.

The header is cracked at the collector but it will be welded and all ready in the next day or two, so hopefully all good for Marulan on the 12th

[hamx5ter]

Clipboard01.jpg

[93_Clubman]

Great to hear it's sorted!
Re MAF compatibility, the table of compatible vehicles in the ebay ad includes 1998-2000 NB8A & 2000-2001 NB8B, but as you say the checker says no when you load specific details for any 1998-2001 MX5, so something clearly wrong with either the ad, which states MX5 in its heading, or the table, or the checker. I used the heading & the table to inform me.

[hamx5ter]

Yes i think i did the same too and only did the checker _after_ i placed the order. At least the vendor was kind enough to cancel and refund almost right away...

I had purchased a lens from a vendor in UKR in January and the ebay shipping info kept saying it had been shipped and offered tracking info even _after_ the vendor had cancelled the order. Then the cancellation stayed pending for 3 weeks and i guess the vendor couldn't be bothered replying to a cancelled order (or perhaps they had no power because RUS bombs). I finally found the convoluted path to escalate the issue and the refund was finally made after a week or so. I was about to write off that money (which would have sucked).

Will collect the car tomorrow quite likely. Hopefully all good... booked in for Marulan this w/e

[bruce]

Straight back into it!