'94 T5
Replaced plugs - oem platinum, bougicord leads, distributor and rotor arm, coolant temp sensor and coolant since problem started maybe 4 months ago.

Problem is that sometimes the engine will not start when warm, journey can be 4 miles or 100, and is intermittent, maybe 1 in 20. No problem starting from cold.

Engine turns over on starter and tries to catch but fails. On occasion it will run for maybe 5 sec but is very lumpy before dying and fails to start after that.

Only part of ignition system left to replace is the coil. Then it will be fuel system, to investigate.

Any ideas on how to proceed diagnosing?

Check the cam phase sensor , mine had a bit of damage right where the wiring goes into the case . They are a common problem on these more so than the crank sensor

It should have a flash code box on the inner wing . Not many codes but should tell you something

[Edited on 10/3/15 by froggy]

Back to basics so went out today with a spark plug fitted on the end of a lead.
Drove to Tesco (15 min drive) and it started ok when I stopped and again after doing shopping.
Parked on drive to open garage door and then failed to start.

Lead in, turn over and healthy spark. Grrr.......

Reconnect the lead to the coil and it starts!
Now this is the third time this has happened - the disconnect/reconnect of king lead at the coil and starting, which made me think it was ignition lead fault. I know it can't be as I'm on second set of new leads.

Seems more than a coincidence but if there is a clue here, then I'm not seeing it.

Might be worth checking the fuel pressure? Injection system needs pressure at all times

try the old leads back in ......

Distributor cap ok ?

Double check that centre lead

After having eliminated most of common causes a leaking injector is next on the list .I f the engine has a Schrader valve on the fuel rail it easy to check but you need the right gauge just look for rapid pressure drop after the engine is shut off.

See http://performancefuelsystems.com/tech-leakdowntest.html

[Edited on 11/3/15 by britishtrident]

Yes, there is a shraeder valve on the fuel rail..... off to erbay to look for a gauge,

I take it the car can be driven with the gauge fitted?

[Edited on 11/3/15 by 02GF74]

The test is done without driving, fit the gauge, turn on the ignition to allow the pump to build up full pressure, then turn the ignition off and watch how quickly the pressure falls.
If the pressure falls quickly then an injector is dribbling fuel in to the manifold.

See eBay item http://www.ebay.co.uk/itm/Fuel-Injection-Pump-Pressure-Injector-Tester-Test-Pressure-Gauge-Set-w-Case-/331499781139?pt=LH_DefaultDomain_3&hash=ite m4d2eed3c13

Makes sense. Thanks. For some reason i got intk my head that the engine had to be running which is the problem.