Engine Running Issues - ADVICE NEEDED

[carlos77]

Dear fellow 912ers and DDKers, I turn to your wealth of knowledge and experience in a great hour of need.

A few weeks back my 912 started to develop an issue where it felt as if there was slight misfire or fuel feed issue, mostly evident in lower end revs in 2nd and 3rd gear under slight acceleration. The condition would normally appear after 10-20 minutes of driving, so not always immediately obvious.
I checked the usual suspects from dizzy carp, rotor arm, timing, cleaned jets, fuel filter, etc. at the time but with no remedy.

On my way to my local mechanic after I'd quickly reached my technical limits, the car got much worse, almost undriveable at many points of the 15 mile journey, with heavy juddering, and sensation of not firing on all cylinders, eventually the engine cutting out and leaving me stranded at the roadside (first time in 11 years, so not too annoying to be honest). The car would not start, I could smell petrol but was not firing.

I got the car to the garage from the help of a very fortunate chance encounter with a former 912 owner and old friend who towed my the final few miles!

The car will start and run for around 15-20 mins before developing a 'stumble' and eventually dying, and won't restart. When left for sometime, it restarts but repeats the same issues time and time again. Nearly every obvious items has been swapped to find a remedy but nothing has sorted it.

3 weeks at the workshop and the cause is still not diagnosed!!! And now I'm at a complete loss as to the next place to look.

Work done so far:

Ignition
Leads Changed
New Dizzy Cap
New Rotor Arm
Electronic Ignition changed
Donor Distributor (050) used (Thanks Danny )
New Plugs
Donor coil
Bypass test direct from battery to coil

Fuel
Jets cleaned
Fuel filter
Bypass furl lines directly from fuel can to pump
Electric pump
Float levels checked
Carb Gaskets changed
Fuel is getting jetted into the throttle body
...

So, if any one has experienced anything remotely similar or has some ideas about what this could be then please please let me know.

Thanking you.

Carl

[SeanP]

Carl

Sound a lot like fuel starvation issues to me. Have you checked the fuel filter in the tank? and the fuel lines from the tank? I know you have tried to bypass the tank with a remote supply but you could have pulled some dirt into the mesh filters in the carb inlet, (trying to remember if you have solex or Webber carbs).

Is the fuel supply from the pump regulated?
Does the fuel pump get hot just before the car cuts out?

[carlos77]

Hi Sean,

Running Webers, and someone else has suggested this issue might be related to contamination from the fuel tank.
Fuel supply is not regulated, as far as I know. I'm just running an inline fuel filter and standard mechanical pump.

Will ask the mechanic to take a closer look through all the fuel line components.

Thanks

[SeanP]

Ah electric fuel pump into the mechanical fuel pump?

[Mike Smith]

unning Webers, and someone else has suggested this issue might be related to contamination from the fuel tank.
Fuel supply is not regulated, as far as I know. I'm just running an inline fuel filter and standard mechanical pump.

Will ask the mechanic to take a closer look through all the fuel line components.

The Normal Porsche set up is :-

A Fuel Filter on the Pick-up tube that projects into the Tank
A Fuel Filter inside the Fuel Cock
A Filter Screen inside the Fuel Pump

You may also have possibly have Fuel screens on the Banjo Bolts to the Carb. connections
You say that you are also running an In-line Fuel (I assume) near the Pump - (Never ceases to amaze me how many filters people think they need)

Some Fuel Caps do not Vent - Have you changed the cap
Is the Tank Vent clear - Blow through it
The Pump has Non-return valves in it (small flat fibre pieces) ---it is essential that these seal

Trying an Electric fuel pump is a good idea - just jury rig it for a trial

The golden rule with any Pump in Any situation whether it be Car, Garden or Sewerage is ---- Short Suction, Long Delivery so stick it under the tank or under the passenger floor board if it becomes a permanent fix

[carlos77]

Hi Mike, thanks for the advice.
We've been through all the things you've highlighted including an electric pump to no avail I'm afraid.
The problem is still there, including running from an external fuel can into the pump.
The compression test has shown some signs of ring wear on cylinders 3&4 but from my inadequate knowledge this shouldn't be enough to consistently kill the engine?
The search for a cure continues...

[neilbardsley]

Hi Mike, thanks for the advice.
We've been through all the things you've highlighted including an electric pump to no avail I'm afraid.
The problem is still there, including running from an external fuel can into the pump.
The compression test has shown some signs of ring wear on cylinders 3&4 but from my inadequate knowledge this shouldn't be enough to consistently kill the engine?
The search for a cure continues...

Seeing that you are close perhaps I could come over and do a weber/distributor swap for the afternoon?

I don't think that lower compression on 2 cylinders will make an engine stop.

A few years ago I had an issue like this in my 6v 356. It turned out to be a bad connect in the ignition switch. However, I believe that 912 are wired differently so that they volts to the coil doesn't go through the ignition switch? However, if not a fuel issue maybe a electric bit that is warming up, expanding and not working?? I'm guessing.

[Timo]

Might be worth checking the block off plugs in the carb bodies, a friend of mine recently had a very similar issue and it turned out to be one of the block off plugs had worked loose and dropped out causing a big air leak.

[carlos77]

Thanks for the offer Neil, but I've already swapped out the dizzy with Danny to run a test with no luck, and also used another set of carbs, albeit larger bore, but had exactly the same result.
Could be electrical as you say, with the heat build up, but nothing has shown up so far. There's a spark when the car dies too.

Timo, I'll check the block off plugs as you say. Every little detail needs to be considered.

Cheers fellas!

[Timo]

Have you checked the inside of the fuel tank for corrosion? My car had a similar fault just after I purchased it, turned out to be flakes of rust being pulled up against the tank screen, essentially blocking the supply. It’s worth popping the fuel sender out and shining a torch down inside to see if anything is causing an issue there, failing that stick an extendable magnetic stalk down there and see what comes out on the end once removed.

[mycar]

You've got a real whodunnit on your hands, very frustrating. It seems you've been very thorough with the detective work... when you eventually find the culprit that car will run like a dream

My thoughts, considering the fault may be showing itself only as the engine heats up, are failing condenser, there are many reports of newer condensers being badly manufactured. But then you changed the dizzy !

How about the valves ? When was the last lime you checked your valve gaps ?

Fuel supply problem ? I had a situation that sounds similar which was eventually diagnosed as blocked fuel galleries in the carbs. A symptom, besides a progressive stumble after a few miles, was that turning an idle mixture screw in and out would have no effect on the engine note as no fuel was getting through to that cylinder/ cylinders.

Grasping at straws here.

[takeflight]

I had all sorts of issues with my 911t and there’s not a cat in hell chance I or I suspect a lot of indies could have sorted.

However the man that did was Chris and his men at Fenn Lane Motorsport Nuneaton.
Can’t thank them enough.
Roy

[SeanP]

You've got a real whodunnit on your hands, very frustrating. It seems you've been very thorough with the detective work... when you eventually find the culprit that car will run like a dream

My thoughts, considering the fault may be showing itself only as the engine heats up, are failing condenser, there are many reports of newer condensers being badly manufactured. But then you changed the dizzy !

How about the valves ? When was the last lime you checked your valve gaps ?

Fuel supply problem ? I had a situation that sounds similar which was eventually diagnosed as blocked fuel galleries in the carbs. A symptom, besides a progressive stumble after a few miles, was that turning an idle mixture screw in and out would have no effect on the engine note as no fuel was getting through to that cylinder/ cylinders

Grasping at straws here.

All good points raised. Electronic ignition does ot use a condenser, (discussing with Jonny Hart today installing a CDI+ box on a 912 as an experiment to increase performance and mimic the distributor curve. Thinking that we may be able to use a 009 distributor locked and use the software to set the advance curve, watch this space). Valve clearances should show as a constant issue hot or cold engine. Fuel supply is my favoured diagnosis starting at the fuel tank filter.

[Timo]

Thinking that we may be able to use a 009 distributor locked and use the software to set the advance curve, watch this space).

Have you thought about a crank fire setup Sean? I had a conversation years ago with Tim (impmad) about the possibility of this set up in a 912.

[SeanP]

Tim. At the moment we are trying to asses if the cdi will add any meaningful power as an upgrade to a standard setup on the 616 engine. The box fires the sparkplug twice on each firing so we are hopingit is a setup mimicking a twin plug setup giving better combustion and a controllable curve. Once we have established this the world they say is our lobster