Strange stumbling/stalling issue

[Disco]

Hi Guys,

Over the last couple of weeks my NA8 has been doing a strange occasional stumbling, threatening to stall (a couple of times has) typically under a light load accelerating, and sems to occur just before the engine is at normal operating temperature. Give it a few boots and it seems to clear it It's running a Motec and big fuel pump but my suspicion is it's more likely to be an electrical issue? I haven't bothered lifting the bonnet yet since so far it is nothing more than a minor irritation and gives a good excuse for a squirrely snake up the road but I think it might be getting a little more common.

Any thoughts?

Cheers,

Stu

[Disco]

Ok it really let me down yesterday. Seems to be as the engine is warming up and after a short stop (say traffic lights) it will mess me around. Took a few minutes to get going again and then all fine. I know it's really vague but I don't know what further info I can give... No-one got any thoughts?

[Disco]

It could well be, and I was thinking that this morning, which would also explain the fact it's happening only when cold(ish). In fact a few months ago I richened it up because I felt it was running a bit lean. Thanks.

Which brings me too... can running rich cause mild overheating...?

[Disco]

I had a theory on this this morning and was wondering if anyone could comment - if it was running too rich, could it then foul the plugs to the extent it doesn't burn enough fuel and hence runs effectively lean, causing mild overheating?

[Boags]

Not sure about your theory Disco Stu... Doesn't sound right to me.

Are you running a NB or WB O2 sensor? When NB sensors are failing they read lean, so your ECU will compensate for the low reading by adding fuel. The start to do this only when cold (and after sitting at lights) until they get to temp. Then they work fine once hot. WB sensors will read rich when failing, so they will lean out your mixture (which will make your car run hot).

Snaking down the road? What have you done to your car? FI? How much boost? Disco Stu needs to give more information.

Boags

[Steampunk]

badly fouled plugs will mean you just lose power, and shouldn't overheat. If a plug is fouled bad enough then the cylinder wont fire, and if a cylinder doesnt fire, then it doesnt get hot.
IF its too rich, then you would be running well below 12:1 AFR across the entire rev range of prolonged periods of time

Running lean can cause overheating issues, but it would have to be ridiculously lean, >16.5:1 AFR, plus the fact that it would be pininging/knocking.

Here's a list of what I think it may be:

- bad batch of fuel
- idle enrichment incorrect (Wolf EMS is notorious with this)
- idle bypass tube is blocked
- dirty injectors
- there may even be a loose connection in the MoTec unit that causes a short circuit once in a while

If I were you, I would replace all the easy, serviceable parts like plugs, plug leads, air fitler (or just clean it), check the cleanliness of the intake, and stick in a good quality injector cleaner at the next fill-up and/or spray some cleaner into the manifold. You will be surprised to see how much gunk and oil and crap that accumulates in there.
Do all the above and go for nice, hot, constant medium - high revving run up the mountain for at least 20 minutes.

If the above doesnt work, then it may well be a tuning issues within the MoTec unit.

[Disco]

Thanks for the advice guys, I'll give some of the suggestions a crack. Boags, the car came with the mods on it so I'm not too sure of things like what o2 sensor etc are in it. So much under the bonnet is Heinz 57 which makes diagnoses difficult.

Cheers.

[Benny]

Sounds to me like the changeover from cold to warm running is not set correctly.
When the engine is cold, the computer tells the injectors to richen the mixture, and when it's warm, it leans it out to where it should be.
If this point is not adjusted properly, it can lean out too early, or too late, and so the engine is not getting the right mixture and then stumbles.
This point can also change depending on engine tune, ambient temperature, the condition of your plugs, O2 sensor and many other things, so you will have to let it sit at a dyno place overnight, and let them play with it in the morning in order to get this right.

If you car is turboed, these symptoms can also be caused by the boost controller, and you may have to solder on a capacitor between two of the pins to smooth it out a little.

The first things you should do however, is exactly what 1Red5 says.
That's would be a very good start before you start spending $$$$$

[Rotary]

Sounds to me like the changeover from cold to warm running is not set correctly.

It sounds alot like that, and the severely cold weather could be throwing mixtures off,
It could be either direction depending on how close it was to lean or rich to begin with. (Air Temp Enrichment also plays a part)

You said you adjusted it before, did you do it yourself, if so it should be easy to check this, don't play with Air temp Enrich though as it may upset normal driving.

not sure how the motec displays its sensors but if possible, keep an eye on the water temp, then you will know which Temp range requires adjustment, and where its working fine, then adjust for only those areas

[Disco]

Thanks for all the advice guys. Put some injection cleaner in and a couple of little maintenance items but a trip to mania diagnosed a pretty wasted radiator and crap tune, incorrectly grounded ecu etc. Had them reinstate the supercharger and been shrieking around all day. Enjoying no anxiety mx5 motoring again. Disco Stu smiles again.