Hot Starting Problem

[davidbooker]

My 75 2.5 v6 has been starting and running very well since I fitted a new battery. I have had no problems until Sunday, when the car proved difficult to start when hot on two occasions. The motor spun rapidly, and finally caught after about four short bursts, with pauses in between. It normally starts instantly, both hot and cold. Cold starts seem to be OK at present.
This may just be a glitch, so I connected TOAF on my phone. Despite showing a green cloud and trident, TOAF refused to read the ecu's. Rather than connect my laptop, I then tried Torque, which showed no errors. Reading other posts, this fault is usually caused by a failing camshaft sensor. Would this register as an OBD fault? If not, what could it be?

Many thanks.

[Lincoln Green]

I don't know if it's the same on a 2.5 V6 but after having the same problem on a 2.0 cdti it was the cam sensor.

[SD1too]

Originally Posted by davidbooker

Reading other posts, this fault is usually caused by a failing camshaft sensor.

Hello David,

From personal experience and reports from other members, when the camshaft sensor fails it does so totally. The engine is impossible to start. As you did manage to start your engine with repeated attempts I would begin by separating the connector mounted on a bracket at the lower corner of the cam cover (below the oil filler cap) and checking it for cleanliness and good electrical contact.

Yes, I'm reasonably sure that you should expect P0340 or P0341 to be logged for camshaft sensor failure.

Simon

[vitesse]

My daughter’s 2.5 Tourer went through a funny spell, refusing to start typically after a short period of use. Toaf showed no errors but somehow, a replacement fuel pump relay managed to get it started, until next time. Got tired of towing her home and connected the T4 which is much more of a fuss than Toaf, however the T4 identified a bad cam sensor even though Toaf didn’t. Daughter then raided Dad's spares as is standard practice, and then all was good. Odd but it happened.

Good luck

[Costa Fortuna]

If no signal from crank sensor then the rev counter won't read.

[richw]

I had similar. When hot, a high chance it won't start. The emergency fix was to remove the camshaft position sensor and leave it in free air for a minute. Then re-fit and the car would start.

Proper solution was to replace the sensor with a new one.

[SD1too]

Originally Posted by Costa Fortuna

If no signal from crank sensor then the rev counter won't read.

You're correct Tim that if the crankshaft sensor failed the fuel pump would not run during cranking and so the engine wouldn't start. However, David has reported that his engine continues to start normally when cold, the problem only occurring when the engine is hot. This is indicative of a camshaft sensor fault so I think we can eliminate the crankshaft sensor.

Simon

[davidbooker]

Many thanks for all your helpful replies. I'll take a look at the camshaft sensor. As you say, a good clean may cure it, or it could be in its early death throes, and not yet throwing a fault code!

[Tracker]

Another vote by me for the cam sensor being faulty. I had exactly these symptoms on my KV6 (failing to start when hot - no problem when cold). After researches on here I replaced the cam sensor and the problem entirely disappeared. As has been said, it's not the only possibility but should be the first port of call when the problem is hot starting.