So, I did commentt on this issue several months back on my newly acquired 88 V12, 5spd 150k km. The car had not been driven much in the month or two before I bought it. For the first few trips it ran fine.
Then out of the blue..........pulling away from standstill you applied the gas and the revs cycled up and down even though my foot was stationary on the gas pedal. Needed to increase revs to 3000rpm and do a 'racing start' to be able to pull away from standstill.
At the same time on the highway if you backed off the gas and then ever so gently reapplied gas (in same gear) the transmission would 'slam' with a big jolt...... quite unerving!
Was like this for maybe a couple of short trips and then cleared itself.

Flash forward 7 months and the car has been sitting inside at my mechanics garage getting various items of work done as and when he had time to do it (car off the road for the winter, so no rush). Cam cover gaskets have been replaced (leaking), new heater core etc.
He called me today to say that the symptoms above have returned, along with a 'clacking noise' which seems to move around. It is also running ever so slightly 'rough' at idle (was fine before). He diagnosed a dodgy injector on the right bank, so first step will be to put in a known good injector to see if that cures it. FYI my mechanic is super knowledgeable about Jags and the V12 and has been awesome to work with. Just thought I would post on here too, as more minds the merrier!

Wondering if the above symptoms strike a chord with anyone? I am in Toronto, Canada and it seems no local shops that will rebuild injectors. I see that rebuilt injectors are available in US for ~$200........ is that the only recours for a replacement injector?

Any and all thoughts appreciated!

Quentin

 

Try Rockauto. I believe they have Canadian warehouses also. Rebuilt injectors are less than $50 US.

 

Can’t say if the manual transmission changes the normal explanation but…. Hunting is usually a vacuum leak, misadjusted throttle rods (plates), and broken throttle shaft bushings. The throttle shaft bushing will suddenly crumble. The throttle rods will often unwind or wind themselves up unless there’s a dab of lock tight but thats usually a gradual process. Vac leaks are pretty sudden too… rubber gets hard, falls off. Id’ start with these basics before doing anything expensive like checking injectors.

 

Thanks for your thoughts!
it seems one injector is playing up based on stethoscope diagnosis. I wonder if a sticky injector can be intermitent? Will pass on your thoughts. Much appreciated.
Quentin

 

Forgot to mention. He did a precautionary oil change (new oil last Fall) and noted slight gas smell in oil (rich running?)

 

leaking injector (s). Or more likely, shorting out injector loom. This is an item that should be replaced and is probably the most important thing to do.

 

Greg,
Thanks for your thoughts. A short in the loom could also explain why it appears to be intermittant? My mechanic did tidy up the loom routing while he was in there so that could be why the issue has reappeared. Replacing the injector loom was PM I was pondering. I read up on it re. Making one yourself or buying one off the shelf. Off the shelf would be quicker. Will do some more research re. Potential suppliers. Is there any source you would recommend?
Quentin

 

Quote:

At the same time on the highway if you backed off the gas and then ever so gently reapplied gas (in same gear) the transmission would 'slam' with a big jolt...... quite unerving!

I'm wondering if the ECU was recalibrated as part of the manual transmission conversion?

The system is designed with a closed throttle fuel cut-off; the injectors stop injecting. When the throttle is subsequently opened, the injectors are commanded back into operation. Depending on load, RPM, and road speed this could cause quite a jolt.

The inherent slippage of an automatic transmission torque converter absorbs this. But, with a manual transmission, there's no slippage or cushioning effect.

Just a thought.

Cheers
DD

 

Hhhmmm interesting thought.
The 5spd conversion was done in 2015 and it had been running fine. Agreed, the jolt was like a big dumping of gas into the engine. How does one go about recalibration an ECU I wonder?

 

So I spoke to my mechanic this morning. The guy tidying the ignition loom is an elec engineer and did check for bad wiring. Not definitive that the wiring is not at fault, but provides some comfort.
Plan at present is to check for vacuum leaks and then replace the 'bad' injector.

 

The part number is DAC3718. SNG Barratt have them and the part they have is very good quality. Some US places may have good second hand ones.

 

Thank you Sir!