Reluctant cold starting

[GravelBen]

My '89 Eunos seems to be getting increasingly reluctant at cold starting lately - well it'll start up fine initially (though at times idling quite high for a start) and then bog down and stall if I don't give it some gas to keep the revs up(or sometimes even if I do), then takes a lot of winding over before it will restart.

Not ideal conking out when the revs drop as I stop at an intersection, then I sit there holding up traffic while I try to start it again. Especially as I'm currently trying to sell the thing.

It is winter here so its breathing pretty cold air at times (frosty mornings often -5° and colder), I guess its related to that but it seems to be getting worse.


Any bright ideas or experience of similar problems?

[miniman]

Sounds like airflow meter to me.

[MX-5 Lazza]

Could be a number of things: Water temp sensor, O2 sensor, AFM, HT leads, coils.....

[GravelBen]

Well was a bit warmer last night and this morning than it has been lately, so I've been able to verify that its related to air temperature as it seems ok at the moment.

As soon as I can get to an electrickery bits shop I'll pick up a resistor and LED to ask the ECU whats wrong.

http://www.mx5club.org.nz/maintenance/engine_diagn...

[franv8]

Another possibility - lazy idle speed control valve.

[GravelBen]

Well I checked the ECU for error codes last night and...

Nothing. So apparently its not a nice simple sensor fault, or if it is the computer doesn't realise.

Also took off the air bypass valve (the one beside the PCV, not sure if thats its proper name) to clean up and check if it was working, seems to be ok.

Checked the idle screw, also seems to be set about right.

So I guess tonight I try and find more things to pull off and tinker with.

Edited by GravelBen on Tuesday 8th July 22:36

[MX-5 Lazza]

Have you tried HT leads & plugs?

[GravelBen]

MX-5 Lazza said:

Have you tried HT leads & plugs?

Not yet, wouldn't that be noticable all the time rather than just when cold-starting? So far I've been focussing on things that are free to fix.

Another possibility could be as simple as a tired battery - checked it at 12.4-12.9V at the battery engine off and 14.49 engine on, what do they normally give?

Edited by GravelBen on Thursday 10th July 22:23

[MX-5 Lazza]

Try borrowing some leads off another '5.
Unlikely that plugs would be a problem but if leads have been bad for a while it could cause problems for the plugs & coils too.

[franv8]

Yes - and beware that plug leads can look fine, and even test fine for resistance within spec but still be cream crackered.

[GravelBen]

Cleaned out the idle control valve and throttle body then readjusted the idle screw, hasn't fixed the problem but it has sharpened up throttle response considerably so was worth doing that either way. Will hopelly get some decent diagnostic gear onto it at some stage soon to try and figure things out.

Do MX5s generally give ECU fault codes if the airflow meter (or its intake temp sensor) are starting to give up the ghost, or only if they let go completely?

[OnlyMX5ives]

Personally I'd change the plugs first.

Then as no fault codes I'd check idle speed - remembering to use the jumper and then check timing.

I presume your car has the 4 slot front pully ?

This can be the first indicator of crank nose failure.

Edited by OnlyMX5ives on Monday 28th July 11:32

[Munter]

OnlyMX5ives said:

Personally I'd change the plugs first.

Then as no fault codes I'd check idle speed - remembering to use the jumper and then check timing.

What year is your car as this can be the first indicator of crank nose failure ?

His 1st post says '89..... gulp. Got to be worth a look...

[GravelBen]

Munter said:

OnlyMX5ives said:

Personally I'd change the plugs first.

Then as no fault codes I'd check idle speed - remembering to use the jumper and then check timing.

What year is your car as this can be the first indicator of crank nose failure ?

His 1st post says '89..... gulp. Got to be worth a look...

That thought had occurred to me but it seems too dependent on air temperature for that?

Have adjusted idle speed and its fine most of the time except when stone cold.

Hopefully will get an engine builder mates diagnostic gear onto it soon to check things out a bit more.

[GravelBen]

Well I never did track down what was actually causing it, even with mates diagnostic oscilloscope etc on it. But bumped the timing to 14° and that seems to have fixed things as well as giving a bit more mid-range torque. Not to mention the days are getting warmer here now anyway so cold-starting isn't such an issue.

Managed to knock a hole in the exhaust on saturday so de-cat is the next thing to be done...

[hcanning]

franv8 said:

Yes - and beware that plug leads can look fine, and even test fine for resistance within spec but still be cream crackered.

Agreed. When I bought mine it had a bit of a misfire under load at low revs when cold. I didn't let it put me off buying it as I thought "Meh, this'll be a simple fix". Sure enough some new plugs and leads (don't know which of the two caused it, but sod it, they're service items ) cured it