Warm rough idle

[maxakarudy]

Howdy folks,

Just got hold of my first roadworthy 3.0SC, it starts from cold fine, but when it's warm, it gets lumpy on tick over & then cuts out, starts ok , but won't idle properly.
I don't want to start messin till I've asked the brotherhood watz up first, I'm guessing a vacuum leak somewhere.

Cheers
Martin

[KS]

Sounds like a cold start temp sensor of some kind has failed, tricking the fuel system into believing the engine is still cold, over fuelling it and making it run lumpily and stall - like leaving the choke on on a car with carburettors and a manual choke.

[Bootsy]

KS you describe exactly how my T25 is running at the moment

Apologies for thread hijack!

[DustyM]

The 3.0CS uses a Constant injection system (CIS) , one component of this is the WUR (warm up regulator) , this controls fuel pressure and therefore mixture as the engine warms. If you google it you will find there are tests to run to make sure it is operating as it should. You will however need to find someone who has the correct equipment. There are of course other reason why it may not be running properly, but fuel pressure tests are the place to start.

[Sam]

https://www.kmipetrolinjection.co.uk/Bo ... tronic.htm

Are the people for this sort of thing.

[maxakarudy]

Thanks for the responses, there is a lot to get your head around with these cars, lucky YouTube is a great resource.
I watched a very detailed refurb of a WUR, with benefit of making it externally adjustable too.
Yes I'm getting to know fuel pressure is really important, along with good vacuum.

Having a bit of mooch in the engine bay I found a blue square electrical connector, not connected to anything, its at the rear, possibly 3 pin, there seems to be a similar one plugged into the CIS, could this be the problem?

[DustyM]

There are two connectors on the rear, one is the cold start injector, and one is the safety switch (stops the fuel pump when the engine is not turning.) having either disconnected would not give the symptoms you describe

[maxakarudy]

There are two connectors on the rear, one is the cold start injector, and one is the safety switch (stops the fuel pump when the engine is not turning.) having either disconnected would not give the symptoms you describe

Thanks John,

My fuel pump does run with just the ignition on, so the disconnected plug is probably why.

[jjeffries]

Just about any CIS diagnosis requires a decent pressure test kit. As Dusty said, the WUR is pretty much the key variable in the system because it controls the fuel pressure, and fuel pressure is how the system varies mixture. There's also cold start functionality and other external devices to aid driveability, most of which can be tested with a DVOM.

Here in the US, I paid ca. $100-120 for a nice, simple gauge set; more generic, Chinese sets are available from the usual suspects for less. You'll be able to find copies online of the factory manual with graphs showing how the fuel pressure should measure at certain temps and after resting; this is what's needed to make intelligent diagnoses and take the mystery out of the system. If you'll be keeping the car or working on others, it's money well spent.

I have an 82 SC; the USA-spec 81-83 SC's have an added feature of an oxygen sensor, little black box/computer and frequency valve to further tweak mixture.

Best of luck, John