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Some recommended checking/cleaning throttle assembly when troubleshooting stumbling/hesitation. So, here I go.
First, found the following page/section in the green Jaguar repair manual:
But then when I tried looking from different angles -- I don't see the same connector as shown in the diagram. It seems like the connector should be fairly big and obvious (based on the diagram). Am I looking in a wrong place?
Is it on the other side of the round black thingy to which arrow is pointing?
The throttle switch in the pic from the manual is for a pre-HE engine. The green manuals used by most of us are edited and condensed versions of the shop manuals and are often not clear.
On your car the round black thingy on the underside of the throttle turntable is the TPS- Throttle Position Sensor. Different function than the Throttle Switch of the earlier engines. it should be adjusted to show .32 volts at idle position, checked with a voltmeter across the red and yellow wires.
On top of the throttle turntable you have the little enrichment switch. It is activated by the turntable itself and should be adjusted to ensure it closes when the 'bump' of the turntable presses against the actuator arm of the switch.
On your first photo, bottom left, look at the rectangular black wiring connector with the thin white wire. Might just be my eyes but it looks like the wire is about to break off. This looks like the much ballyhooed "dreaded shielded wire".
Do I take the whole thing off to get to TPS? (Four nuts around the corners of the plate) Do I have to also detach ignition coil first (which is attached to one side of the plate)?
Do I take the whole thing off to get to TPS? (Four nuts around the corners of the plate) Do I have to also detach ignition coil first (which is attached to one side of the plate)?
Before you get too deflated.
The TPS on the HE, as Doug has described soooooo well, is a sealed unit. Unless you want to drill the plastic rivets that hold it together, then glue it back, leave it alone.
Using an old style Analogue Ohm meter, do a swing test, and if that needle is swinging back and forth as you go from idle to WOT, the TPS is AWOL, and a new is needed. YES, we all bark at the price, but its 30+ years old, and done a LOT of work.
Most HE stumbles from idle are badly set TPS, cross rods set wrong, the Vac Fuel Enrichment switch is not "switching".
In all my years the TPS would be #1, and the rest are a fair gap down the list.
Using an old style Analogue Ohm meter, do a swing test, and if that needle is swinging back and forth as you go from idle to WOT, the TPS is AWOL, and a new is needed. YES, we all bark at the price, but its 30+ years old, and done a LOT of work.
Most HE stumbles from idle are badly set TPS, cross rods set wrong, the Vac Fuel Enrichment switch is not "switching".
In all my years the TPS would be #1, and the rest are a fair gap down the list.
Follow that BLACK tubing thingy, and you will come to a rubberish plug. About 6" from the TPS. There you will find a Red, Yellow, Green wire on the TPS side of that plug. Push the probes into the rubber, OR, partly detach that plug, about 2mm, and then probe via the gap. Fiddly, HELL YES, but you will see what I mean.
Last edited by Grant Francis; 05-07-2017 at 04:06 AM.
Reason: spelling still sucks
Follow that BLACK tubing thingy, and you will come to a rubberish plug. About 6" from the TPS. There you will find a Red, Yellow, Green wire on the TPS side of that plug. Push the probes into the rubber, OR, partly detach that pug, about 2mm, and then probe via the gap. Fiddly, HELL YES, but you will see what I mean.
Ahhh, I see. Yes, I saw that connector. In fact, I tried disconnecting and connecting it. Now I see what you mean by "fiddly". Yes, I think it will be fiddly. I will try tomorrow.
So, it was relatively easy to get to the point where I could test TPS voltage.
But before I started tinkering with it, I measured what I had been driving with: 0.49V. Quite a bit higher than recommended range.
After that I started tinkering... It is definitely fiddly. Even what appear to be minor movements changed the voltage from 0.1V-ish to 0.6V-ish, and occasionally higher. On couple of occasions I thought I got it: right in 0.32-0.36V range. But when I tightened the nuts and measured again, I saw that the voltage was out of range again So, looks like by tightening the nuts, TPS can be moved slightly, so you are never sure what you would get in the end. Kinda frustrating... And sorta random
So, I played with it for about an hour. At that point I decided to stop to take a break (for the day). I tightened TPS nuts and put everything back to how it was before.
Then I measured the voltage one last time (with everything connected, including wires and rods.) Surprise-surpsrise: DVM showed 0.351V! But, heck, I will take it!
We were discussing TPS voltages in another thread recently. I beginning to wonder how critical the .32-.36v spec really is. Mine is at something like .45v and if it's causing a problem, I can't feel it, hear it, or see it.
We were discussing TPS voltages in another thread recently. I beginning to wonder how critical the .32-.36v spec really is. Mine is at something like .45v and if it's causing a problem, I can't feel it, hear it, or see it.
Cheers
DD
Hmm... I guess I will have to test drive and see whether hesitation/stumbling from idle is less or more than before.
I was only able to drive the car around the block before shutting down for the weekend. (It was raining, almost snowing). I thought it felt better. But I have to take longer test drives to understand if hesitation-from-idle is gone
UPDATE: had a chance to drive the car more this weekend. I think the throttle is doing fine. I don't observe a hesitation from idle. And the range (swing) of throttle movement also appears good. (Both from the swing test using analogue voltmeter and by feel.)
I think I have something else. I call it mini-backfiring of the engine at low RPMs (around 1100 to 1500), most noticeable at slow speeds (and window open). Almost like barely audible coughing. Initially I confused it with the hesitation from idle. But after driving around more and listening, I think it is something else. Does not appear to be serious, because it either disappears completely when I gain speed/get above 2000rpm. Or it becomes completely unnoticeable. But eventually I would like to understand this mini-backfiring and fix it.
I think I have something else. I call it mini-backfiring of the engine at low RPMs (around 1100 to 1500), most noticeable at slow speeds (and window open). Almost like barely audible coughing. Initially I confused it with the hesitation from idle. But after driving around more and listening, I think it is something else. Does not appear to be serious, because it either disappears completely when I gain speed/get above 2000rpm. Or it becomes completely unnoticeable. But eventually I would like to understand this mini-backfiring and fix it.
Sometimes an old fashioned ignition misfire will give such a symptom/sensation.
In your case, though, I'm thinking more along the lines of a lack of fuel/lean mixture condition which can give a backfire into the intake manifolds. Not a "bang" backfire. More like a soft "pop'" or "woof".
A couple (or more) injectors not being up-to-snuff comes to mind but the 'could be' list might get long.
Do you hear/feel this only when accelerating? Only at steady throttle openings? Both? Any relationship to engine temperature?
Yes, Doug, exactly: not a bang backfire, but barely noticeable pops or woofs. Yeah
I was trying to isolate when this behavior is most prevalent. Typically, not when accelerating (or accelerating hard). I would say when I drive steady and slow, throttle engaged, engine at above 1000rpm, but below 2000. (Above 2000, I am usually driving at good speed, and I don't notice these misfires/pops.)
I would say it is more common when the engine is colder. If I drive for while, say coming home after driving around, I don't feel these pops. Or they may not be obvious
A cold/cold-ish engine requires a richer mixture to well. The coolant temp sensor signals the ECU to richen the mixture when cold....so a a faulty/lazy temp sensor is one thing to consider.
Here's an idea......
The enrichment switch on the throttle capstan, when closed, will fatten the mixture about 10%. Remove the wires from the switch and jump the wires together. Now drive the car. Is the backfiring reduced or eliminated? if so, it suggests we're on the right track in thinking the mixture is a bit lean
A cold/cold-ish engine requires a richer mixture to well. The coolant temp sensor signals the ECU to richen the mixture when cold....so a a faulty/lazy temp sensor is one thing to consider.
Here's an idea......
The enrichment switch on the throttle capstan, when closed, will fatten the mixture about 10%. Remove the wires from the switch and jump the wires together. Now drive the car. Is the backfiring reduced or eliminated? if so, it suggests we're on the right track in thinking the mixture is a bit lean
Cheers
DD
Thank you! Will do both these tests and report back. Will have to wait until next weekend, though, as I shut down the garage for today.
05-06-2017, 08:42 PM
Throttle Switch diagnostics
So, looks like by tightening the nuts, TPS can be moved slightly, so you are never sure what you would get in the end. Kinda frustrating... And sorta random