PSA 2.0tdci Lumpy cold start

[kenJungUn]

Hi All

35k miles

The 5 or 6 turns followed by a cough persists after new battery and fuel filter.

Press Start/Stop button with clutch depressed. She waits for the heater coil light to go out, then fires. But with poor results. No smoke. It's annoying but don't think it will get worse.

I'm thinking air (as in fuel pressure) or heaters.

I'll tackle heaters first. And I have no idea how to do so tbh. I'll look for somewhere to measure current and see if there's any monitoring in the forscan. Taking the OS one out looks tricky. They're not old, so it's likely the case that there's no power to all of them rather than them failing. I would have thought the system would have identified any power issues such as dead fuse and given me a warning. I'll check the fuse and relay if no power. 

Will update.

Open to comments and hints 🙂

Thought: I could disconnect the heater power and see if poor starting behaviour persists. This isn't very scientific but gives me more info.

[kenJungUn]

Minus 2 degrees Celsius this morning. Expecting a tough start. Set up the forscan oscillator. She started perfectly. 

One difference is that I had the ignition on for a minute or so before I started her. 

Also, I had a long run yesterday after the new battery was installed last weekend. 

So, I'll try again later in the week. She's going to be sitting up for 5 days, so that will be a good test.

I'll set up the oscillator outside the car next time.

Does the forscan need to be connected to the car in order to set it up if I have the profile saved ?

Thanks.

[kenJungUn]

Update on this.

I've had mainly perfects starts (all very cold) but caught a poor start on forscan yesterday. I've compared the fuel pressure v RPM values for both.

With the poor start, there is a spike in fuel pressure at low revs. It jumps 10kPa in an instant to almost 40kPa while revs are under 500 but increasing (as they should be) while the commanded pressure is 35kPa. It quickly fell back to the required level and I suspect it's this spike that causes the cough. Or could a sticky injector cause the spike along with the cough ?....

Now, it seems normal for actual pressure to be higher than demanded but a perfect start sees the fuel pressure increase linearly until the required pressure and RPM meet at a sweet spot and she fires up.

But this massive jump so early in the start up cycle must be the problem and I have no idea what the problem might be.

Anyone have advice on where to look with FP spikes ?  She's driving fine otherwise.

Here's my excel chart of a GOOD rpm v fuel pressure (or at least good in my view). I enabled all of the PCM sensors in forscsan, so I found it easier to extract relevant ones and chart them myself. I will do same with the dodgy start to give a visual comparison.

Cheers,

Good Start

Poor Start

You can see the fuel pressure jump over 40kPa thn settle back. It coughed twice during this startup just before firing. I think its during that spike.