Odd starting on my 3.2

[911hillclimber]

Just ordered a new DME relay.
If that fails to fix this then will buy 2 new crank sensors for £150.
Bitch to make the change but stories abound that these can cause my kind of issues!

 

[Motorhead]

Looking online it does sound as though the DME relay could be the source of your problem Graham.that sorts it!

Trial and error unfortunately, but maybe you could return it for a refund if it doesn’t work?

Jeff

 

[911hillclimber]

Just might have found the issue Jeff.

With the aid of YouTube checked the DME relay.

The two I have (original @ 1985 and the one Bob Watson fitted in 1995) both check out perfectly.
Soon I will have a nice new one too, so can compare that to the two I have, but I suspect I will soon have 3 DME relays that pass!

Moved on to the two engine sensors fundamental to the DME system, the RPM sensor and the TDC Sensor.

The resistance of each should be 600 ohms to 1600 ohms.
Checked both and the RPM sensor is 860 ohms so good, BUT the TDC sensor is roaming around at 15.000 ohms +/- a house brick.

I think this is the culprit.
ordered one and hoping this will do the job.

Has been a long time since I spent £230 on this car!

 

[vitesse]

Have you considered checking the coil resistances -is maybe the coil starting to fail or have I missed this point being resolved back in your thread?

 

[911hillclimber]

Thought about that, but I don't know how to check the coil and what parameters are the specs to meet.
If you know, please advise.
When the engine did start it ran perfectly.

 

[vitesse]

Not information I keep in my head but I have figures somewhere for a 4 cylinder engine.I have a spare coil in the garage which I'll check with a multimeter-you just check primary coil resistance & secondary coil resistance -normally one of them breaks down when the engine gets very hot but can annoyingly resolve itself when cold.just a thought thats all

 

[911hillclimber]

Google came to the rescue this morning, so once all the system is back together I'll check both circuits on the coil, but thank you for your thoughts.
However:
I think you can call that a bitch of a job, and I'm not finished yet after nearly 2 hours replacing these engine sensors.
Rather than moan (too much) the old sensor is out and the new in followed by the one I changed some time ago that almost dropped out of the housing, the bad original 1985 sensor did not pop-out....
Access is NOT easy.

Just need to button all the damper/heater hose, DME relay and a run of battery isolation wires to, I hope, the new idolater motorsport type that's 'in the post'.

The condition of the original part was poor, the outer loom sleeve all broken and much of the wires going into the sensor.
The other one, maybe 15 years old looks new.

I think the design of the 3.2 engine and all these parts are when engineers in Production Engineering decided to make things easy to assemble in the factory, and to hell with serviceability, a movement still in full flight today.

Just might get to see if it will start tomorrow.

If not it must be the DME unit itself, heaven help me.

 

[Motorhead]

Goodness me Graham … what a trial! Aged wiring and components are always a cause for concern.

Hopefully now you’re on the last lap to resolving the problem.

Jeff

 

[911hillclimber]

Time will soon tell Jeff.
When these things happen to me they are never simple, bit like the sorting of white start-up smoke on my Boxster.

When all is done I'll do a resume of the things that have been done and the costs.
Good job I'm very very cheap.
(something my wife does not agree with!)

 

[911hillclimber]

Got it all done now.

New sensor in after a tussle under there, as you say, feel your way through.
Started first time, and the second and the 3rd...and the 1,000,000th time this morning.
All good and runs just like it used to.

So, from changing a duff battery (which I am doubting now is actually duff, the old one and the 2 year old one is still in the car and the speed of starting is still bright..
Problem:
time to fire went from 3 seconds to 5 seconds to 10 ish secs to never.

Changed the DME relay with my 1985 spare. No change, no start.
Changed the ignition switch, £100, no start. Looked inside the 1973 original and it was perfect inside. Lesson: be patient! Left new on in the car.
Took the motorsport isolator out and cleaned and checked it. Seemed good according to the meter, so bought a nice new one, £23, now in the car, no start.
Changed the one engine position sensor on the engine, £70 and all is well. Starts just like it used to.

In all this chaos the oil pressure gauge showed max pressure with ignition on or off.

Removed the lead and replaced.
Now working.

My beloved 911 ex hillclimb car now back to normal.

Just as well as I expect to be a Grandparent tomorrow, so very soon nothing will seem normal any more!

x 1,000,000

This is the 1985 duff sensor:


73T 911 Coupe, road/hillclimber 3.2L

 

[Motorhead]

Good job Graham!

Unfortunately nothing you can do about the other matter, but hope all goes well.

Jeff

 

[JohnCRS]

Forgive my unfamiliarity with your model, but aside from the starter motor, does it have an earth strap from the engine to the chassis. It sounds as if the circuit is not completing, so a thourogh clean of all earth wires would be one point to check.

 

[911hillclimber]

The early cars all share the same basic designs, and earth points are no different. There is the braded copper strap from box to chassis but years ago I added another stout earth from engine to rear chassis.
Early on in this game I polished every earth point I knew or could get at.

They were all clean but always worth doing, cost free and always a benefit.

 

[vitesse]

Sorry I didn't get back to but something cropped up(like they do)
Thankfully all sorted ,those sensors do have wiring that degrades & hardens with age I've done 2x 924S's now when the old grey wiggle test failed to work.
Figures I have for 6 cyl coil are Primary 0.5 -2.5 ohms-Secondary -8k-19k ohms but couldn't get sensible figures for my spare 4cyl coil-maybe thats why its a spare.

 

[911hillclimber]

No problem at all.
Started the car today.
Good cranking speed, 2 seconds later full start on 6 pots and ticked over at 800 rpm.
Pity the oil pressure sender has gone wrong again...

 

[911hillclimber]

Pressure gauge all working now.

The wire from the sender to the gauge was open circuit.
Threaded a very very long length of black wire through the car and just left the broken wire in the car. It is buried in the loom somewhere.

All working as it should.
The 911 is back to normal!

Drive It day for classic vehicles tomorrow, so off out for some light breakfast.

 

[Motorhead]

Great to hear that everything’s sorted Graham and that you can get back to using the car with confidence.

Jeff

 

[911hillclimber]

Thank you Jeff.
Need tomorrow's drive to get the confidence back mainly in my wife's mind!
I'll be surprised if it plays up.
Only let me down twice since 1988 when I bought it as a wreck.

Both times my stupid fault too...