Hi

Rainy day, around 15C.
Did 40 miles motorway and some slow driving. No problems
Returning 2 hours later. After the 40 miles highway the car struggles to accelerate slowly in city. Idle is a bit high, maybe 900 rpm. If I push the pedal further I get more power than the rear tyres can cope with on wet asphalt, so normal slow driving in city zone is not easy. Engine seems to run on a varying number of cylinders, causing the propulsion to be somewhat unpredictable...
When I reach home I try to rev the engine and gets sluggish reaction and a few backfires.
Ignition components are all new. Could this be caused by faulty fuel supply/pressure ? Pump and fuel pressure regulators condition is unknown...
Could it maybe be the resistor pack for injectors, that has become wet or just bad ? I have not yet checked the connections to this component...

 

I'd start by checking the TPS, throttle gaps, and the throttle rods adjustments.

 

Thanks JigJag. I will add that to my todo list...

After a nights sleep I've been thinking that several things could point towards low fuel pressure:
I believe the engine doesn't have O2-sensors. It does thereby not have any feedback if mixture gets weak.
Fuel consumption is fairly low, 18-20 mpg I total average. Not only with warm engine at 50 mph...
Temperature needle was in 'upeer N' region yesterday on the return drive.
It does need a little right foot action to start. When started it's ok, but when warm it's missing a bit on 1-2 cylinders at idle. This gets worse in warm weather. Yesterday was far from warm, but it missed quite much in idle.

Today I will check for fuel in FPR vacuum lines. Easy job...
I'm quite busy at the moment, so I will not dig in to too much right now, but I look forward to see it fixed ��

 

I wonder if the rain is getting into the ignition system somewhere and causing random shorts to ground?

Could also be a failing ignition module and/or coil.

 

Coil is new, but that is of course not always a guarantee for function.
But: It did something similar with the old coil as well, just not as bad.
Coil should have good working conditions at low throttle and low RPM though.

I checked for sparks in the dark, nothing. Also, it's not really random failure as an intermittent short would be.

It could easily be bad synchronizing of throttles causing one bank to get more air than the other and thereby run lean as suggested by JigJag.
Or low fuel pressure
Or bad TPS
Or...

No fuel in FPR vacuum lines by the way, I just checked.

 

leo
Have you renewed your amplifier (assuming Lucas engine) and checked all the connectors? This has got to be electrical.

 

Thanks Greg

The amplifier is old, most likely the original from '89 , and I have not checked any connectors.

What makes you so sure it's electrical ?

 

Remove that condenser/noise suppressor from inside the ignition amp. They leak to earth, and can be intermittent before killing the engine.

TPS going AWOL is high on the list.

Resistor pack plug R&R is almost #1.

CTS creeps into the top 5 for me, and at $20, fit a new one. NOT Jaguar specific, Many Euro cars have the same CTS. Bosch part # ends in 026 from memory.

Fuel pressure numbers are needed, but I doubt its fuel.

 

Thanks a lot, Grant.

I will take the car for a drive today to see if the problem is still there with cold engine. I think not, but we will see.

CTS must be coolant temperature sensor ?

 

Yes it is.

 

8 mile drive done with a few stops. Nothing special to report, but quick revving warm is still a bit hesitant. I guess that I have just adapted to that, but it was actually not far from how it acted yesterday after we came home and I made the video in first post. That was some 3-4 miles after it really acted up and was close to being non-driveable.

CTS measured 2875 ohm cold and 240 ohm warm. The air temp sensor measured 2890 ohm cold. Cold is 15C again today.

I will work my way through your lists this weekend. The good part is that I will have to do a lot of test drives...

Is there a how-to for check of TPS or is it just to check that resistance changes smoothly during the range of opening ?

 

Your CTS sounds about right. Yes, on the TPS you're looking for a clean change as you move it through the range, no dropouts.

 

Leo
Attached a note on how to test and set the TPS. Obviously you must test it. I still think your amp might be going home in the damp though! Good luck with the diagnosis

 

Throttle pot seems ok. Edit: display shows resistance, not voltage

Throttle disc adjustment: feeler gauge 0.05 mm is a loose fit, 0.10mm is tight
But: B bank throttle axle bushing is badly worn. A bank starts opening immediately, while B bank is delayed a lot. Or was, as I adjusted the rod to improve sync
I'm aware I need a new bush, but I will try this as a start.
No test driving today. Rain is pouring down...

Movement necessary to make B bank throttle start opening...

 

Your TPS is way out of adjustment. Adjust it to .32V closed.

That much throttle capstan rotation to just crack the B bank while the A bank opens immediately will not do. Brass door hinge bushes will suffice instead of the rubber linkage bushes and are readily available at parts stores. When they are both synchronized, set those butterfly gaps to .002"

 

Hi JigJag

The displayed value in the video is resistance, not voltage. That was not clear at all, so I have edited the post. I have not measured output in volts yet.

I do not think I will find a suitable brass bushing in a Danish hardware store, so I will just make one in the lathe at my job. For now I have adjusted the B-bank pushrod to compensate.

Next: Breakfast, then testdrive

 

Have you checked the voltage leo?

 

Now I have. 0.318V. Pretty amazing. I'm beginning to have respect for previous owner and/or his mechanic...
Thanks for the reminder.

 

15 miles done. Start as usual, needed a few taps on the accelerator pedal to wake up. Still caughs a bit when I revs it quickly.
Drove fine, slow and fast. Traffic prevented speed above 90 MPH, but it felt good. Slow driving was tested after motorway, no issues
it still hesitates when I turn the capstan quickly, but that is not really happening in traffic for me. Smooth driver...

I will look into the amp and get the resistor pack connectors cleaned. I think the issue was either moisture (electric) or a sudden breakdown of the B-back butterfly axle bush causing severe lack of sync at light load.
I have also ordered a fuel pressure tester. I still think pressure might be too low.

 

All good ideas Leo, and must be done of course.

Those capstan rod/arm synchronisation will be the rest of the issues you have.

Sort them both 100% and I reckon it will be almost as designed.