Very Rough Running when cold - Mechanic and Auto electrician can't diagnose

[jiffjiff78]

vt running rough cold

hi all i know im late with this answer, but ive only just had the problem myself, and i solved it, under the throttle body or air intake with the butterfly flap there is two hoses one that is short goes straight to the valley cover (i just touched it and it snapped) the other has a rubber elbow on it (on mine it wasnt even connected) and it goes to the back of the motor, i replaced both these hoses and now the car runs perfect. also the other hint was it sounded like it had a carby not fuel injected lol (even though i liked that haha) hope this can help someone out.

 

[NadieD]

Hey thanks slowandlow, yeah some good options there. The mechanic said he noticed a slight manifold gasket leak when the car was cold but he reckoned that would not be related. I wondered whether this leak may have been throwing some sensor of track?

Did you ever sort it out

 

[Skylarking]

Did you ever sort it out

From the previous page …

Hi Guys

Sorry about the long time gap since last post. It has taken a while and also needed a new auto-sparky on the job but the guys did find the solution. Actually many of you guys found the solution way back :-( It was (as some of you suggested) a faulty Crank Angle Sensor.

The real curve ball in this whole process is that it was a brand new sensor that was causing the issue. The mechanic and auto-electrician did some tests on it - but probably only while in-car etc.

There was a secondary issue of a blocked catalytic converter also. This became evident when they put the car under load on the dyno.

So a big thank you to you guys for the advice, and suggestions. The mechanics and auto sparky felt bad about the time it took to diagnose and fix and as such have only charged for parts at cost and virtually no labour. So other than having no car for three months it has worked out well.

Cheers Guys!

Reading the whole thread can help…

 

[VitalStatistic63]

I'm late to the game here but I've got some thoughts about this. I'm having a similar problem with my VY, also used to happen with my VS. Could always tell when they were coming up for a service, runs rough when cold, have the service done and it's ok for a while then problem returns months later. Well now it's only lasting a week or so.

First, to find leaks in the intake system try spraying some Start Ya Bastard or Brake Cleaner around the engine bay while it's running, it will get sucked into the leaks and change the engine note. Did this recently on my VY and found a cracked intake pipe, rubber perished, and also that little hose under the throttle body had come off. Its just a press fit, and has stayed on for 3 or 4 months now.

But back to the rough running when cold, I'm thinking maybe injector O Rings. If I wriggle or replug the injectors it works OK for a day or 2, thought it was loose connectors, but I sprayed them with contact cleaner last week and it failed again 2 days later.

I'm thinking the injectors are 23 years old now, and probably still got the original seals. There's a good chance they have perished or shrunk, you wiggle them and it reseals for a while, then starts to leak again, gradually gets worse with time. I just googled VY fuel injector seals and it looks like you can buy a set of 6 injectors for about 60 bucks, not sure of quality, or new O Rings for 99c each. New seals it is then. Repco here I come. I'll give it a shot this weekend.

 

[Immortality]

Try running some Nulon Lifter Free. If clean oil fixes the problem then it's probably not injector related.

If new spark plugs temporarily fixed the problem then try running some injector cleaner. Generally speaking, if you try and remove the injectors from a engine that has never had them out they are normally stuck good so I don't see the O rings causing the problem.

If you are going to do it, grab some engine degreaser first and do a really good clean up around the injectors before you lift them out to get rid off all the crap that has built up there over the last few decades. Don't forget some O ring lube when re-installing them to reduce the chance of pinching one of the new O rings.

I had issues on our old VS, in the end I put in some injectors from a VX V6 (777) and it was much happier. Consider taking yours to get cleaned properly whilst they are out.