Well I snuck out at lunch and put the meter on the lines - the variable line "at rest" was .30v at full throttle it was 4.62. Not the most accurate meter but it sort of looks like tps is sending out the signal. Should I break out the wiring diagram and start tracing back to the ECU?

Rodger Bywater indicated that the car should run - but be lifeless without the tps plugged in. Mine dies as it comes off idle...

Looking at the vacuum lines. Where is e best place to test the vacuum?

 

I thought most vacuum related frustration was poor idle and bad reaction under load (as if the distributor advance was unplugged). But I am here to learn from those who have come before me!

M.

 

What does the voltage do *just* as the throttle comes off idle?

Cheers
DD

 

It gradually climbs to 4.6v at full. I have just got thru playing with this and there does not seem to be any jumps - nor dead spots in the whole range. Tracing back to the ECU is not fun - wondering if it needs to be done (per AJ6 people unplugging the TPS will make the car run sluggish (lifeless I think they said). Can keep tracing if that makes sense.

Newbe

M.

 

Well, I am admittedly a "new-guy" when it comes to these engines but I like to think I am learning. Can I ask for how long the car will stay running at idle; indefinately until, you open the throttle? Or, will it eventually die if you let it sit and idle? Does the exhaust smell overly rich or look greyish?

If you see my post "Starts, runs, dies" this forum got me straightened out by replacement of the Coolant Temperature Sensor. My symptoms were slightly different but it is easy enough to check the CTS by disconnecting the plug and jumping the plug side with a small copper wire. Good luck.

 

doug and a few others had good luck with the msutang TPS, but i didnt have **** for luck with them.

i had to exchange mine 3 or 4 times to get one that was even remotely in the ballpark of the advertised resistance values and voltage values.

 

W, she will idle for ever (well, it never has died if I do not take it off idle).

M90, this is still oem. Per the test - it behaves the way I think Doug and AJ6 explained, smooth voltage change from 0 position at .32v (mine reads .30) up to full throttle pos 100 at 4.50 (mine shows 4.62). I can say the meter is not a fluke - so its accuracy could account for the slight varrience. Per Rodger, car should run w/o tps - I tried unplugging, but no change at all.

Keep the suggestions flowing! It is great weather to be driving a jaguar here!

M.

 

Just a bit of guessing here (haven't tinkered with the '85 spec) but sounds like it may be running courtecy of the idle switch enrichment. When you move the throttle switch the idle switch cuts out and down it goes. That indicates that some signal that should ensure enrichment (i.e. longer injector pulses) do not reach the injectors. Either the ECU is bad, or some sensor is not giving the right signal. On my '75 D-jetronic I ended up making a test connector connected in parallell with the engine harness, thus getting good an safe (as in not destroying the ECU) access to all the signals. The rest was a doddle. Another possiblility is that fuel pressure: The pump may be up to the job at idle but nothing beyond that. Alternatively a bad pressure regulator but a test gauge should detect that at idle.

 

You need to check fuel pressure.

 

Fuel pressure at 36 on the rail. Spliced a "t" on the long hose and feel pretty good about that. The injectors were just gone thru and new hoses put on.

I see two micro switches on the capstan. Are one of those what you are referring to Per?

 

Your fuel pressure is good. Did you check it when the bog/stall happens? If not, make sure that you watch to see if it drops when the throttle is opened. If the pressure stays steady then we can rule out fuel pressure.

Your description of the TPS voltage sounds like the TPS is fine. You do not need a Fluke for this. ANy meter will do just fine. We are looking for the voltage to drop or lump around as you very slowly open the throttle with the key on. If it is steady then you have ruled out the TPS. Also your closed throttle TPS voltage is spot on , which is important.

You can unplug the coolant temp sensor and see if your problem is still there. If it stalls when you unplug the sensor when warmed up that is normal as the mixture goes full rich. Then short the two terminals together when warm and see if it is better.

Are the throttle bushings worn or missing? If so you need to fix those as they can cause some issues with stalling, idling, etc.

Next let's move onto ignition. If you have the firing order wrong, as in crossed wires you will have this problem. These engines will run smooth even if misfiring so do not look at it and think it can't be misfiring because it is smooth. Check the firing order several times. Since you changed the plugs this is a good possibility.

You will fix this do not lose your focus. A systematic and thorough approach will always find the problem. With older FI vehicle a bunch of small problems can add up and make you think you have a huge issue. Fpr example, if you find wires that the insulation has come off. Repair the wires then move to the next step. Repair things as you find them.

You questioned the O2 sensors. They are only in closed loop after the vehicle is warmed up. So if your problem exists before the engine is warm then these are not the issue. You can unplug them to be certain.

My money is on firing order or timing.

 

Thanks Greg. The car is new to me in this non running state. I am trying to diagnose and fix whatever the PO "mechanic" did. When I replaced the plugs I found all were gapped between .043 and .045!!! The plugs I put in are gapped to .025 per the under hood label.

I have checked firing order when I replaced the plugs. It looks to get healthy blue white spark at each end of the wire with my test plug grounded to the engine...

Fuel pressure is constant - even as the engine dies.

I will try the coolant sensor test today.

M.

 

Throttle bushings look to be in great shape. Checked that when I measured throttle plate clearance (to make sure I was getting an accurate reading).

 

Yes: One is active at fully closed throttle (idle enrichment) and the other is the full throttle on (at 80%?).

 

The thick plottens. When you say it dies, is it instantenuous or within a couple of seconds? If sudden, have one plug cable/test plug to watch the spark. Does it continue to give good sparks while dying? Then as above, you somehow do not get the longer pulses at the injectors. The simplest way of checking would be with a laptop and USB oscilloscope on an injector.

 

I think some year/model/market specs are being confused here.

An '86 USA-spec V12HE has a kickdown switch on the throttle cable and an enrichment switch on the throttle turntable. There is no idle switch.

Not trying to bust *****. Just don't want someone wasting time looking for something that isn't there. :-)

Cheers
DD

 

No offence taken Doug

 

The one micro switch that has two green wires to it is activated right as the peddal moves. It has a roller right on the throttle cable from inside foot peddal. With a meter on that it does not change always in open state unless i move the peddal cable. I have tried to tie one leg to the other with a jumper (closing the loop) and it makes no difference...

I put an inline spark tester and it shows contue to spark when it comes off idle. I returned the borrowed noid light to see if the injectors were firing. I am looking for my stethoscope to listen to hear the injector open and close... I think the signal dropping to the injectors is the only thing is can be since I am still getting spark, engine is rotating...

Also need to find the coolant sensor plug to do the above test....

M.

 

Per,

It dies like you pulled the coil wire off. Pretty quick.

M.

 

That's the transmission kickdown switch

Cheers
DD