Hi all.
A bit of an odd one and one that’s always been with the car ever since I got it. Worse when cold I get this momentarily loss of power. Pull up to a junction and as you go to pull away it happens only for a split second though. It’s as if the engine cuts for this split second then away we go. Never ever stalls. Any ideas ? Car runs fine otherwise.
Rob.

 

TPS? They go out of synch very quickly. Test and see if it shows 0.32 at throttles closed, ignition on.
Also check throttle buttterfly gaps are at 2 thou and that they open exactly simultaneously.
Also worth cleaning the injection system power reistor contacts.

 

Hi Greg.
Thanks for the replay. TPS when last checked was in spec and also the throttle discs. This was last year mind you. I will check her out on Saturday and report back my findings. Thanks for your advise.

Rob.

 

Robbo
A momentary power loss can be "throttles opening fuel not arriving". On a Lucas car it can be far too retarted timing (which mysteriously happened to a friend's car for no discernble reason) but I think you have a Marelli?
The cleaning of the resistor pack connectors both sides is most important, too. If that is iffy, no fuel or not enough.
https://www.jaguarforums.com/forum/x...sistor-134745/

If none of this helps, someone with Marelli knowledge can maybe explain if it is posssible to check the timing setup is exactly correct. Are both crank position sensors new, by the by?

 

Hi Greg.
Yep Marelli on my car. Both cps are new replaced only a few weeks ago. Resistor pack connectors were checked and cleaned last year. To be honest they were clean anyway with none of the green crap present. I said power loss but it’s more like a split second cut out or hesitation quite difficult to put into words. The car has always done it and it’s more noticeable when the engine is cold. It doesn’t really cause me any problems but you know how it is just want the car perfect.

Rob.

 

How much lost motion in the throttle opening system, capstan to butterflies?

 

Again, adding from Lucas moments.

Check the Vac hose TO the ECU and the Marelli box.
The one running under the car does get contaminated by oily fumes condensing, and Vac signal is dergraded.

Inside the 16CU is a small, short, Vac hose from the spigot TO the MAP sensor, they split, usually reeking havoc, but heh, who knows.

Relays, the Main and the Fuel Pump, replace them, they be tired, and maybe having a moment at the wrong time, rare again, but for the $ involved, why not?

 

TPS is a good guess.
With throttle closed the voltage output is around 0.3V which probably switches off a transistor in the ECU.
That tells the ECU to stop fuelling with the engine RPM above, say, 1500RPM because it thinks you are coasting.
If there is a small break in the TPS resistive track above the 0.3V point, and your RPM is above 1500, the ECU calculates you are coasting.
If the problem happens much below 1500RPM, or you have a Hall effect TPS, look for another reason.

 

More suggestions after yakking with Greg.

1) temporally earth the Orange wire from the Fuel Pump relay, thus taking ECU control; out of the mix.
2) Bridge the CTS plug, foollng the ECU into thinking its at operating temp. Remember, the CTS is the prime fueling signal, as in, Running V12, unplug the CTS = Dead V12.
3) CTS wiring down the B Bank to the TPS splice. The Lucas cars had real shoddy solder joints in that wiring.

 

Thanks for all the suggestions guys. Throttle rods set as per Grants instructions last year. Will do again on Saturday. No goo on the bodies checked the other day. Vac pipe to the ecu holds vacuum again checked a couple of weeks ago. TPS was set correctly last time I checked again last year but will check again on Saturday. I have been reading a few older posts and found one with Grants instructions on adjusting the blue and white valve which was interesting so I might have a **** around with that.

Rob.

 

On the LH throttle linkage is an off-idle switch for the Marelli ignition. This switch tells the Marelli ECU to use "Idle strategy" or "Load Strategy" for the ignition timing. The switch is closed when the throttle is closed. Make sure it is adjusted to open the instant there is throttle movement.

Cheers
DD

 

Nothing to do with the blue and white full throttle valve I think. But Doug's post above seems to me to be a VERY likely cause!
Every day I start my car I give thanks it is a Lucas, non cat and non ABS car!

 

Just had a look at the switch and I get a round 1-2mm of movement at the linkage stop screw before the switch disengages.
Rob.

 

Reduce it!

 

Ha ha. Yes sir will do and report back.

Rob.

 

Hi all.
Switch now adjusted so it disengages as soon as the throttle is moved. I just checked the TPS and it’s showing 0.31v at idle the moves smoothly up to 4.6v at full throttle. I know the range is 0.32-0.34v so will my 0.31 make any difference.

Rob.

 

No, 0.31 is within spec. All good.

 

Hi Greg.
Just so I know for the future. The TPS setting is only a problem when it’s over 0.34v and anything less within reason is ok.

Rob.

 

Spec is 0.32 +/- .02v

 

Cool beans. Cheer’s Greg.

Rob.