3.2 911 engine: bit odd stating?

[911hillclimber]

Good call. Easy to run around the earths.
Still can't understand why changing a battery does all this.

James, yes, everything tight.

[Nine One One]

You have better voltage now so likely it has shown up a few short comings in the wiring. Have you checked the main wires to the starter as well, and also the earth from the gearbox?

[andytat]

Hi Graham.
Are you using the original 3.2 Carrera engine harness?
If so have you checked the DME relay which should be adjacent to the ECU?
These were always a known failure point.
Cheers.
Andy.

[911hillclimber]

Yes, some others are saying earths, but will clean them all surgically tomorrow and hope..
Yes, the engine has its standard loom and dome and relay.
Tried another relay a few days back, no difference.
Removed the huge connector plug and back on to clean the contacts, first time since 1995!

This engine has been 100% reliable since 1995 then this lot when I change a battery!!

[911hillclimber]

It's getting worse.

Tried to start it lunchtime today, so cold engine. Absolutely no fire just cranking over.

I've cleaned all the earth points etc, but nothing.
I've removed the motorsport isolator and all the contacts are good, high current and 12 volts.

Took a plug out to check for a spark (as I've done before) and nothing while cranking the engine over. After several long churns it showed a spark at the plug and fired! It's done this before.

Switched it off, and waited a few minutes, tried to start it again and it fired.

Repeated this a few more times, fired every time.

Not too much of a surprise it re-starts as the engine is all fueled etc ready to go.



I have 2 questions:

Should the fuel pump run when the ignition is switched on, BUT not cranking the engine over?

Or:

Does the pump get 12V only when the engine is cranked over?



When the engine is running the pump is exceptionally quiet, a like a distant bumble bee!

With the ignition on the pump is silent/not running.

Secondly, what would cause the spark not to be there and then spark after several long cranking of the engine?

I'll add that when it does start the engine runs really well.

And I'm going mad about this...

[andytat]

The fuel pump only runs when the engine is cranking, it won't run with just the ignition on.
Have you checked the ignition coil? another culprit could be the crank pick up.
I don't remember off hand where the ignition coil gets it's power from, direct from
the ignition switch or possibly from the DME relay. The trigger side of the coil is direct
to the ECU, there is no separate ignition module on a 3.2 Carrera system. It could be
a problem with the ECU maybe.
Good luck with your investigations you will find the solution Graham, you always do -_-

[911hillclimber]

Thanks about the pump.
Can check that tomorrow.
The fact that when it starts it runs perfectly means the pump runs!
I’m in fear it is ignition which points to the dme heaven help me.
However by the same thought, when it fires it runs perfectly.

If the sensors are the fault then surely it would not run so well?
Feeling very depressed by it all.
All I did was change a battery.

[jwhillracer]

All I did was change a battery.

Have you tried changing it back?

JW

[911hillclimber]

Yes, that was yesterday and still in the car now today.
Thus the battery 'pack' is exactly as before replacing the battery, one is 2 years old and he other about 8 years and the one i felt was not charging.

Just ordered another DME relay. Cheap and worth the try though I've tried my spare a few days back.
If this fails to cure this issue I will change the two crank sensors which is a pain to do.

Several stories about that these will cause probs if failing. Another £150.

Still cannot work out how changing a battery and charging the car can cause all this.

[911hillclimber]

Just might have found the issue.

With the aid of YouTube and 9-1-1 on here (always my tech advisor!) 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.
Will order one from Design911 and hope.

[Nige]

Start with your DME relay (always handy to have a spare anyway), you can bypass it to test the pump. I think this will be unlikely.
https://forums.pelicanparts.com/porsche ... rting.html

After that start looking at the 2 flywheel sensors, if you have no history of replacing them then do so, they swell over time and then intermittently fail, so testing them isn't always 100% proof. Changing them isn't that bad, just be careful not to damage the bracket they sit it, best to drill the old ones out.

If that doesn't work then it's time to look at the ECU, hair line cracks, dry solder joints, etc. Mine had this issue 15 years ago after going through the above options. Random no starts, which then turned into random stalls and then would only start again after multiple attempts, would ultimately then only run for about 10-20 seconds. Replaced the ECU and had the original repaired, I have a spare you could test with if required.

Regarding the pump, you usually hear it momentarily as it primes the system as the ignition key is turned. Once the engine if running, you should be able to hear it constantly.

There are actually 3 flywheel sensors, you don't need to change the TDC that isn't actually connected to anything (plug underneath the IVC) and sits at 12 o'clock on the flywheel. You only need to change the speed and reference that sit next to each other.

[911hillclimber]

Thank you for these details, and especially the offer to borrow the DME.
Really hope i don't have to ask!

Having owned this car so long and the engine going in back in 1995 it is tricky to remember all I've done, but i do recall changing one (maybe both) sensors way back, must be far more than 10 years.
However, I do not recall having a starting problem!
I'll try to find the bill in my massive history file.

Very busy week coming as I will be a grandfather on thursday, so time will not be my own...

[911hillclimber]

I think you can call that a bitch of a job, and I'm not finished yet after nearly 2 hours.
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.

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.

[Nige]

I can't remember it being that bad but it was +15 years ago and I was more flexible back then. Seem to recall it was more a feel around job as eyeballing the bracket was impossible.

I may have even removed the rear engine mounts and lowered it an inch or two. i.e. Partial-partial engine drop.

Hopefully, from the sound of it, you've found the culprit.

[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: