Turns over but slow to fire

[TomPaine]

Indeed, hot starting is fine which doesn't square with the usual CPS issue.

No CEL.

I've read that with the check valve problem, if you prime it two or three times rather than the once, and it then fires as normal, that's that an indicator.

[TomPaine]

Went out to see what it would do from a cold start last night, in particular whether the tacho flickered while it cranked (if not then CPS, if so maybe fuel check valve). For about a second I thought "it isn't flickering, aha, CPS" and then it started completely normally. And then ran fine. So I'm baffled but if it keeps behaving like that I'm happy to stay baffled.

[TomPaine]

OK well we have a verdict I think - on the day I have to get Heathrow it won't fire at all [aaaaaaaaaaaaaaaaaagh]. Multiple cranks, but won't start, and tacho not flickering. So CPS I assume, noting that the symptoms really weren't the standard ones.

[sgould]

If you have the means of checking the resistance.  Two of the pins should show a resistance across them.  It should be between 770 ohms and 950 ohms.  Usually fails on the high side.

[carrera]

Also:

Are you sure this isn't a different (perhaps new) problem.... like fuel pump failure

They can fail suddenly

[TomPaine]

I'm not sure of that no - but I thought that the tacho not moving was the sure sign of CPS? Wouldn't it flicker if the fuel pump was the culprit?

I'm afraid measuring the resistance is beyond me. A new CPS is in the post, though I'll need a mobile mechanic to fit it ...

[TomPaine]

Googling does disclose instances of people replacing the CPS cos the tacho wasn't flickering, only to find it was the fuel pump.

I've lost all confidence in my own diagnosis now so I have added HomeStart to my AA cover and will call them (when it's active). If they say it's the CPS, yay, I've got one; if it's something else at least I know and they can either fix it or tow me.

[carrera]

Take the DI cartridge off,

Let the engine it crank over for 5-10 seconds or so

Remove plug(s)

Wet / smelling of petrol, fuel pump is OK

Alternatively

Remove DI & plugs

Place DI upside down on the block, reconnect & place plugs in holder. Use jump leads to earth plugs to battery / good engine earth (a couple will be fine)

Get someone to crank the engine, watch / listen for a spark from the earthed plugs

[TomPaine]

Many thanks for your counsel carrera. That's beyond my confidence / competence, so I'll get the AA to determine that - and report back!

Extensively Googling I do note (at least) two things:

1] I thought that unmoving rev counter simply meant CPS - and of course it often does - but plenty of people have replaced a CPS on that basis only then to find that it was indeed the fuel pump, or a relay.

2] We all know about hot-start difficulties being a sign of CPS failure - and of course it often is - but plenty of people have had cold-start only difficulties too. The CPS is a bit of a maverick ...

More when I have it.

[TomPaine]

Well, if anyone's interested - and I'm pretty bored with this saga myself - it was indeed the CPS.

So I'd warn anyone thinking that hot starts are the red flag that for me it was purely cold starts. Before it failed it would only fire on the second or third attempt despite fast cranking. Warm re-starts were never a problem. Then when it failed it was a cold start, just cranking not firing. The rev counter not moving at all is the key.

[carrera]

Glad it's sorted, and hopefully you are a little more confident in your diagnostic abilities

[sgould]

Before I started to strip the 9-5 today, I went shopping.  The car refused to start after the first shop, only half a mile along the road.  It started eventually and the rev counter was moving a bit, so at a bit of a loss to diagnose.   It hasn't done the non-start since the Pyrenees over a year ago.  Starting hasn't been really sharp for all that time, and some time before that.

[TomPaine]

It was thanks to this forum that I had any clue really. I told the AA guy what I thought; he didn't do any diagnostics, just said "it sounds like you know what you're talking about [!], so if you've got a crank sensor let's change it and see", and it worked yay.

[sgould]

Seems like a fix!

As my 9-5 is off the road waiting for parts, I may change my CPS and see if it makes a difference to the starting.

[TomPaine]

I think mine is idling better now too. It could be a bit uneven but it seems a little happier and smoother at idle.