Help with rough start (please!)

[treadstone]

Hi

My car is a 2002 1.8 Sport with 50,000 miles on the clock, and I've been trying to fix what I'd describe as a rough or slightly lumpy starting problem for the last few months.

It's an irregular problem which can happen whether the engine is hot or cold. Oddly though sometimes there's no sign of the starting problem at all. I'll describe it as best I can;

I put the key in the ignition, turn it, and the engine will crank a couple of times before firing up strongly, just like it should.

That is what happens when it's behaving itself. However when it's not behaving there's two consistent symptoms;

1. Turn the key, engine will crank for an unreasonably long time (5 seconds + ) before spluttering in to life.

2. The engine seems to momentarily dip and lose revs as it cranks and fires up, almost like it's going to stall out (though it never has) before quickly coming back up to normal rpm levels.

Sometimes it's one of the symptoms, sometimes it's both together, sometimes neither are present and the car fires up without a problem. There seems to be no consistency.

Things I have done so far to try and fix the problem without success;

Replaced cam shaft position sensor.
Replaced crank position sensor (and gapped it correctly).
New battery.

My car has the following mods;

Magnecor HT leads.
New NGK original spec plugs.
K&N flat panel filter.
IL Motorsports backbox.

Serviced 5000 miles ago (7th year service) with Shell Helix Plus 10w-40.

I'd say that it's happening frequently enough to be an annoyance, probably 50% of the time I try to start the car. Can be quite annoying/embarrassing in a car park when it's cranking over and over and spluttering in to life like some old heap.

I'm at a loose end with it and don't really know what else to try. If anyone would be kind enough to offer advice on what to try next I'd be very grateful.

Thanks

[maser_spyder]

Coil packs?

[Odie]

Fuel pump/fuel filter perhaps. (at 50k id suggest changin ghte fuel filter anyway)

Battery/alternator maybe

TBH with it being so intermittent its going to be hard to chase down the problem. And it could be anything fuel or spark related.

[Rhino]

Do you get a hestitation as you accelerate at all, say at about 3000rpm?

Have you checked if the front crank pully bolt is lose at all, or if there is any movement of the pulley relative to the crank?

[treadstone]

Thanks for the replies so far guys, much appreciated.

Coilpacks - I'll have to find a way of testing them to determine whether one or both are faulty.

Fuel Filter - As far as I know it's been a very long time since this car had a new fuel filter so I'll look in to that.

Hesitation - I've not been able to detect a hesitation around 3k rpm (or anywhere else). I checked the front crank pulley bolt and it seemed very tight, also checked the pulley for any play but again it seems to be tight.

Another thought... There's no record in the service history of this car having had a timing belt change. At 8 years old / 50,000 miles this is probably (over)due.

Could these symptoms be explained by an old/tired timing belt?

[MX-5 Lazza]

Find someone with an OBDII reader who will check your error codes. Most independent garages should do it for free in the hope that they will get some work out of it. Most dealers will charge regardless.
I have one myself but I'm down in Wokingham so not a lot of use to you up there in Cheshire.

p.s. Your timing belt is a year out of date but still in date on miles. It wouldn't explain anything even if it was 100k miles and 20 years old though.

Edited by MX-5 Lazza on Wednesday 2nd June 12:43

[treadstone]

Hi Lazza, I've got an OBDII reader and there's no DTC's pending.

I did get a "P0012 “A” Camshaft Position - Timing Over-Retarded (Bank 1)" code a while ago but that was long before these issues started and it never returned after I reset it.

[MX-5 Lazza]

How old are the leads?

[treadstone]

Bought the Magnecors about this time last year. I've tried using both the original HT leads and the Magencors but the problems remain unfortunately.

I do appreciate the help trying to trouble shoot this, it's doing my OCD no favours.

[MX-5 Lazza]

It'll probably be a dodgy sensor somewhere (water temp, O2, CAS) or a failing coil but as it's an intermittent fault it'll be more difficult to track down.