Engine 850: B5234TR/2.3/20v/T5R: 85OR won't start - help/suggestions/reccomendations

[Antz]

Originally Posted by ASt85

Have you taken a spark plug out, then reconnected lead, grounded the thread on a convenient bit of the car's body and then checked for a visual spark?

If you have a spark, it is just possible that during the time for which it was off the road the oil seal in provided by the oil control piston rings has drained down.

This results in a lack of compression and a failure to start - it is a common problem found in larger/older engines, particularly older Jaguars & other high end higher mileage cars.
My own 850 was prone to this effect if I turned it off after less then two minutes running from cold. On one occasion I could only get the compression back by pouring about 50mls of engine oil into each pot via the spark plug holes...........I must admit it was a really smokey start-up, but it did start on the first if lengthy cranking after having repeatedly failed to start after being turned off after less than a minutes running.

First thing we checked was for spark and fuel. That's how we know we have no spark

[Baffler]

Originally Posted by Antz

First thing we checked was for spark and fuel. That's how we know we have no spark

Does it perhaps fire up for a second or so and then stop? If so you could try cleaning the contacts of the antenna ring with some contact cleaner and see if you can tighten the spade connectors in the harness plug a little. If you measure for resistance across both pins of the antenna ring you should see a stable value...any fluctuations in value would indicate a breakdown within the winding...hence the intermittent starting.

[KBB]

Can you explain how exactly you went about checking for spark?

[Antz]

Originally Posted by Baffler

Does it perhaps fire up for a second or so and then stop? If so you could try cleaning the contacts of the antenna ring with some contact cleaner and see if you can tighten the spade connectors in the harness plug a little. If you measure for resistance across both pins of the antenna ring you should see a stable value...any fluctuations in value would indicate a breakdown within the winding...hence the intermittent starting.

It either starts up and runs fine or it doesn't start at all. There is no cutting out. It's fine or it's not.

I'll check the antenna ring this weekend.

Originally Posted by KBB

Can you explain how exactly you went about checking for spark?

It's not my first barbecue, I know how to check for spark and we did it the same way you'd always check. You wet your fingers, grab the end of the plug and crank it over right?

Anyway..... Being serious.

We checked at the plug. Nothing.
We checked at the coil. Nothing.
The AA man checked at the plug. Nothing.
The AA man checked at the coil. Nothing.

There is no spark but the gearbox lights and p0120 code of a TPS fault confuses us. We have tried two TPS sensors and two throttle bodies.

[KBB]

Originally Posted by Antz

It either starts up and runs fine or it doesn't start at all. There is no cutting out. It's fine or it's not.

I'll check the antenna ring this weekend.



It's not my first barbecue, I know how to check for spark and we did it the same way you'd always check. You wet your fingers, grab the end of the plug and crank it over right?

Anyway..... Being serious.

We checked at the plug. Nothing.
We checked at the coil. Nothing.
The AA man checked at the plug. Nothing.
The AA man checked at the coil. Nothing.

There is no spark but the gearbox lights and p0120 code of a TPS fault confuses us. We have tried two TPS sensors and two throttle bodies.

This is where these threads can become confusing, I was posting for the originator of this thread SKATTRD but you came in at post 12, SKATTRD has a crank no start and you have a combination of a mixture of start and no start and when threads go like this they become cluttered when test procedures offered up are meant for the original poster. needless to say I will offer some test procedures for your specific case in a moment. Both these vehicles are running with the Bosch Motronic 4.3 system its a fairly simple system to diagnose and the main ECU is very reliable, test procedure to follow.

[KBB]

For both posters:
1. When key is at position 2 (key on engine off KOEO) dose the engine management light come on and go off?

2. Got to the ignition coil unit, KOEO locate RED wire terminating at the coil (Terminal 15 have you got system voltage? Crank engine what voltage do you have?

3. Go to the ignition coil unit, KOEO locate BLUE wire terminating at the coil (Terminal 1 have you got system voltage? Crank engine what voltage do you have?

4. At the coil connector there will be 3 wires the plastic housing the connector fits into is the coil power stage unit which switches the coil to ground to charge it. it receives a control signal from the main Motronic ECU in the form of a 5v square signal. When 5v is on the power stage transistor switches the coil to ground charging it, when the 5v is removed the coil fires. Options for testing is, ideally oscilloscope, LED test light (should pulse on/off when cranking) or volt meter that can display Duty Cycle or Dwell (will display a reading if the control signal is reaching power stage unit).

5. At coil connector disconnect and locate pin 1 Black wire. This is the ground circuit for switching the coil and needs to carry around 8 amps of current to sustain coil charging, you can make a test light with 2 55w headlamp bulbs connected to battery positive in parallel creating around 8 amps of load and connect to the black wire at pin 1. If ground is good then they will glow at full brightness.

6. Disconnect TPS sensor and check for a 5v reference voltage at pin 2 (white wire for manual transmission, yellow wire for an automatic).

If you could report back on those tests I will be able to advise next step.

[Antz]

Originally Posted by KBB

For both posters:
1. When key is at position 2 (key on engine off KOEO) dose the engine management light come on and go off?

2. Got to the ignition coil unit, KOEO locate RED wire terminating at the coil (Terminal 15 have you got system voltage? Crank engine what voltage do you have?

3. Go to the ignition coil unit, KOEO locate BLUE wire terminating at the coil (Terminal 1 have you got system voltage? Crank engine what voltage do you have?

4. At the coil connector there will be 3 wires the plastic housing the connector fits into is the coil power stage unit which switches the coil to ground to charge it. it receives a control signal from the main Motronic ECU in the form of a 5v square signal. When 5v is on the power stage transistor switches the coil to ground charging it, when the 5v is removed the coil fires. Options for testing is, ideally oscilloscope, LED test light (should pulse on/off when cranking) or volt meter that can display Duty Cycle or Dwell (will display a reading if the control signal is reaching power stage unit).

5. At coil connector disconnect and locate pin 1 Black wire. This is the ground circuit for switching the coil and needs to carry around 8 amps of current to sustain coil charging, you can make a test light with 2 55w headlamp bulbs connected to battery positive in parallel creating around 8 amps of load and connect to the black wire at pin 1. If ground is good then they will glow at full brightness.

6. Disconnect TPS sensor and check for a 5v reference voltage at pin 2 (white wire for manual transmission, yellow wire for an automatic).

If you could report back on those tests I will be able to advise next step.

Will check and report back when I can.

[Antz]

Garage solved it. Two broken wires somewhere along the front of the car.

[skattrd]

Originally Posted by KBB

For both posters:
1. When key is at position 2 (key on engine off KOEO) dose the engine management light come on and go off?

2. Got to the ignition coil unit, KOEO locate RED wire terminating at the coil (Terminal 15 have you got system voltage? Crank engine what voltage do you have?

3. Go to the ignition coil unit, KOEO locate BLUE wire terminating at the coil (Terminal 1 have you got system voltage? Crank engine what voltage do you have?

4. At the coil connector there will be 3 wires the plastic housing the connector fits into is the coil power stage unit which switches the coil to ground to charge it. it receives a control signal from the main Motronic ECU in the form of a 5v square signal. When 5v is on the power stage transistor switches the coil to ground charging it, when the 5v is removed the coil fires. Options for testing is, ideally oscilloscope, LED test light (should pulse on/off when cranking) or volt meter that can display Duty Cycle or Dwell (will display a reading if the control signal is reaching power stage unit).

5. At coil connector disconnect and locate pin 1 Black wire. This is the ground circuit for switching the coil and needs to carry around 8 amps of current to sustain coil charging, you can make a test light with 2 55w headlamp bulbs connected to battery positive in parallel creating around 8 amps of load and connect to the black wire at pin 1. If ground is good then they will glow at full brightness.

6. Disconnect TPS sensor and check for a 5v reference voltage at pin 2 (white wire for manual transmission, yellow wire for an automatic).

If you could report back on those tests I will be able to advise next step.

Cheers, I'll give that a try next time I'm at the garage.

[Paul240480]

Glad yours is sorted Antz.

What about the OP?

I, prompted by this thread have just updated on my one linked above by Baffler (I think).

I'm still not certain of exactly what sorted mine, but my last post may be of use, as it brings up something not yet mentioned on this one:

Here's a copy of that 'last post'.
Should have updated this a while back. After the two months away, the car did start up but the battery was weak. After a charge all was good. Tho' a few days later it was sluggish again. Volt meter at 11.4v.
So I got a new battery. Whilst I had the old battery out, I lifted the battery tray.
There are a couple of earth straps going into the inner wing below that tray.
These cables were really cruddy, to say the least.
I gave these a proper clean up and then fitted the new battery.
The car has started 1st turn EVERY time since.
No idea if the issue was the dirty earth straps all along, but it appears sorted & hopefully this thread will help others that suffer the same symptoms.
__________________
Its about a year since that battery change/terminal clean up now & it still fires on the button everytime.