3.2 starts fine but doesn't like pulling away cold...

[dickster]

It started when I sent it in for gearbox rebuild. On delivery to the garage the idle was getting rough (I thought nothing of it). Then on completion the guy installed the engine/box back in the car only to find black smoke coming from the exhaust on startup. He immediately changed the CHT sensor but instead of putting in the proper place, he opted to attach it to a rocker stud near a spark plug (to save time).

This sort of cured the problem. On starting from cold the engine revs would go up and down (alot) and would continue until the engine was warm. fine if you're driving around but not if you're stationery and everyone is staring at you! Otherwise the car drove fine.

I decided it must be the position of the sensor and so I moved it to the correct location. Now the car starts fine and idles nicely (sort of slight miss) when cold, but will not pull away, it hesitates and stutters until warmed slightly. Once warm its ok but the idle is a little lumpy.

I've tested the old CHT sensor cold and its reading 2,500 ohms (and now I get 485 hot) - which seems ok? The new one reads only 1,800 when cold and within only a couple of minutes idling reads as low as 170 - this range seems wrong to me? And to drop so low so quickly?

The speed/reference sensors do not read too bad - the speed one read 1,096 (a little high) when warm and down to 1,060 (within spec) cold.

My thoughts are with the new CHT sensor at the moment? I also wonder whether its an OE part.

Appreciate your thoughts.

Cheers

[dickster]

*bump*

comments on these numbers welcome!

"The new one reads only 1,800 when cold and within only a couple of minutes idling reads as low as 170 - this range seems wrong to me? And to drop so low so quickly?"

[ischmitz]

Originally Posted by dickster

...... but instead of putting in the proper place, he opted to attach it to a rocker stud near a spark plug (to save time)......

I wonder what else your mechanic does to save time (or costs). Maybe it's time for a new mechanic?

Honestly, there is a reason for the CHT to be installed where it is installed and by cutting corners you might not get the desired results. Aluminm is a very good heat sink and the temperature at the rocker housing is not the same as in the head. Moreover, these CHT sensors are not generic items. So is is really hard to tell from afar what is going on with yours.

The WSM has test values for the CHT - if these match your readings all is fine, if not I would get the propper part, mount it in the propper place and re-test.

Regards,
Ingo

[dickster]

Thanks Ingo, I am starting to realise what a headache that corner cutting has caused (the budget had been well blown for the job already so I understand why he did it). I have ordered some resistors (270 and 2,500) to test cold and warm - hopefully that will help eliminate the guess work.

Cheers

[ischmitz]

Rich,

here is the page from the WSM dealing with the CHT testing. As you can see your values are not so bad. But still, your mixture could be off because someone has messed with it compensating for a bad sensor before.



I would try and get an exhaust gas tester to read the mixture and also make sure there are no vacuum leaks, etc. Also, test the fuel pressure and make sure the microswitch for the idle engages when you release the throttle while you are at it.

Cheers,
Ingo

[Zeke]

Originally Posted by dickster

(the budget had been well blown for the job already so I understand why he did it).

You may understand why a kludge might do that, but I don't. How much more time does it take to slip it into the proper place?

[dickster]

Originally Posted by ischmitz

Rich,

here is the page from the WSM dealing with the CHT testing. As you can see your values are not so bad. But still, your mixture could be off because someone has messed with it compensating for a bad sensor before.

You could have hit the nail on the head, I spoke to wrench last night and he adjusted the mixture for the new sensor... Going to see him today to get it rectified.

Cheers

[stlrj]

Since your plugs are now properly fouled from the previous abuse of rich running, it might be time for a fresh set. Once fouled, I find it virtually impossible to unfoul a plug that is missing with the Italian Tuneup Technique.


Cheers,

Joe