Frustrating cold hard starting/no-start issue on 456

Hi all, been chasing down the solution to this problem since last year. Car has 16000 kms, last major in late 2016.

In a nutshell, the car starts fine when hot or warm (within 4 hours of being shut off).

When cold, 80% of the time it will cause the following problems when starting:
1st try: it will crank, fire on what seems to be a couple of cylinders only (oil pressure and battery light stay on), stumble and cough for 2-3 seconds, and die (stall).
2nd try (immediately thereafter): no problems whatsoever, it starts and runs fine.

The remaining 20% of the time, it stumbles and catches, settles in a high idle. However, there is no power when pressing the accelerator in the first minute or so. It's 100% fine thereafter.

What I've done so far: Changed intake manifolds and gaskets, changed fuel filters, changed coolant temp sensor, changed fuel pump mounts with the PE ones, tried Techron, tried resetting ECU (10 min idle), changed cat ECUs.

Variables: tried turning key from pos 1,2 and back several times before attempting to start, different grades and sources of gas, cleaned TPS, MAFs and their connectors. Tried parking car on various inclines, tried rolling it in key pos 2 before starting (to eliminate CPS issues)

Fuel pressure is good. @tbakowsky thinks it might be DME related.


Any insights greatly appreciated.

 

@henryr : no codes, and I've let it sit for up to a week at a time with battery cut off, no change.

@tazandjan : that'll be the next step. Is there any way of testing for that?

 

I've a 1995, so 2.7. Looking into rebuilders locally. Terry, did yours have the seal kit in stock, or did they complain that it was impossible to find and had to be special ordered?

 

Agreed. Bigger problem is every company I've called uses an ANSU machine that can only do 8 at a time. Waiting to hear back from a couple of local ones.

 

While running.

 

I guess I forgot to add that I replaced both of them too.

 

Update, since I've only just driven the car thrice this year.

I had the injectors serviced, new o-rings too. Made no difference. It doesn't happen every time, but seems better when I leave the key in position 2 for 30seconds-1 min prior to starting. Still hunting...

It was at the shop last autumn for a couple of weeks, where it seemed to start more easily.

 

The car bogs and stalls. No increase in rpm.

@Prit Singh: I'll try bypassing them, see if it makes a difference.

 

Update to this: I've put up with the issue for 6 years now, but I'm getting a bit fed up.
I'm starting to think it's a fuel feed/pressure issue, I suspect the check valves (which are integral to the pumps) may have failed. Symptoms below.

1. When filling up, my gas cap is very hard to remove, and I get an inrush of air to the tank.
2. After a drive, there is a very, very faint smell of gas in the garage up to about an hour later. It's hardly noticeable, but it's there
3. I tested the pressure at the fuel rails. It takes about 10 seconds on cold start to build up to 45psi, by which point the idle stabilises. It bleeds down to 25psi after 2.5 hours, and 0 psi overnight.

I had the injectors cleaned and rebuilt in 2018, and there were no leaks found prior to the service. Both fuel pump mount rings replaced with PTFE ones in 2018 as well.
Driveability once the car has started is absolutely flawless, plenty of power, no misses, no CELs, etc. Hot starts are also great.


I'd be very appreciative of anyone that could do a bleeddown test at their fuel rails, and ideally post a video of pressure readings on cold start!