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1984 3.2 Carerra Big smokey overfuelling issue. Help needed please!


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I hoped the wealth of experience & knowledge on here, might point me towards a solution for a serious running issue with my 1984 3.2 Carrera.

First, a brief history.

I purchased it in February 2015. It was delivered new to the UK in April 1984. I am the 9th owner. It's covered 106,000 miles and came with a huge history file documenting every service and penny spent from new. All carried out by Porsche main dealers and specialists. Which is one of the reasons I chose this particular example.

Despite all this, I acquired it in a somewhat project state. So it came to me essentially as a rolling, running, driving shell.

It was trailered home and sat in the garage awaiting my attention. I would occasionally start it up for a couple of minutes. It always started with ease, with a flick of the key and a half turn of the starter and without even looking at the gas pedal. It ran and sounded very healthy, like a good one should.

Then, it sat for about three months without being looked at or started. The next time I tried, it really struggled to start. After about a minute of intermittent cranking, it did eventually cough into life, albeit with a bit of a misfire and LOTS of white smoke which smelled very strong of fuel. I initially thought it had flooded. So I tried revving it up, both with a light and then a more enthusiastic foot on the pedal. But it would not clear or run properly.

I tried this a couple of times over the next few days and weeks, but with no improvement. Sometimes it would backfire quite dramatically, I think out of the inlet. There is no air filter fitted at present.

I checked the plugs, which look new, but were wet and dark grey / black.

I began to research causes of over fuelling, via Google links to a couple of US based forums, I figured it might be the cylinder head temp sensor. It's the original single wire item. I get no ohms reading with a cold engine. However, when I unplug it with the engine idling at cold, the idle note changes, so I guess it's functioning... ? Wouldn't a faulty CHT sensor cause over fuelling when hot, whilst providing adequate when cold ?

Last week, after ignoring the car for some time whilst I work on other stuff, I fitted new leads, cap and rotor, as the current ones were looking their age. This made no difference to the way it starts and runs.

One the whole, I know my way around cars fairly well. However, I'm not too good at diagnosing electrical / ignition / engine management issues. I have a very friendly local independent Porsche specialist, but I'd rather not go down that route if I can help it. He did suggest that they can get choked up by being started but not driven. But the way this fault manifested itself makes me think there is a bigger issue. How could this develop simply from sitting idle for three months??
My feeling is that the ECU thinks the engine is at full throttle, so is delivering that amount of fuel.

My thoughts of possible faults are

Faulty CHT sensor.
Faulty inlet MAF.
Faulty throttle position sensor.

I'm feeling rather stressed over this. I'm reluctant to start it up now due to the massive plumes of smoke and fuel bellowing from the exhaust. It really is that bad, instantly filling up the garage + outside and hangs in the air for ages. I have to consider my neighbours, who live in close proximity.

Help please would be much appreciated !

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Letting it sit there idling won't be doing it any favours as they take an age to warm up and thus sit there running rich washing the oil away from the valve guides. You then switch it off and all that fuel rich oil settles in the cylinders ready to burn off and pump out a load of eye stinging smoke the next time you run it.

 

Personally I wouldn't start hunting for a problem until you can properly take it for a drive, get some fresh fuel in it and get some miles and heat through the engine, clear those injectors and loosen up sticky valves, etc.

 

Where are you in the East Midlands.


By the way most puff out some smoke on start up, this usually clears within a few seconds though. Mine really does kick it out if it's had a short journey.

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+1 What Nige says.

 

Plus you will also get a lot of oil in the cylinders on prolonged standing adding to the smoke, poor running and slow cranking.

 

Oil drains back from the tank through the oil pump, builds up in the crankcase and gets into the bottom of the bores. This will be a lot worse if the oil is diluted with petrol from repeated starting of the car without getting it fully warmed up (3.2s run very rich on cold starting), or if the oil tank is over filled. I hope you have not topped up the oil without the engine running and it being fully hot!

 

 

Mark

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Lots of white smoke - sounds much more like a massive over-fuelling issue - than oil.

 

My car had this problem - after it had been sat for many years. Huge amounts of white smoke - that did not clear. My brilliant mechanic (Dave Harris - Meriden) when hunting in all the usual places you mentioned in your mail. We had the ECU checked and did lots of other tests. It was eventually traced to one of the failed fuel pressure regulators - that then allowed neat fuel to go straight into the inlet manifold. Bingo. Changed the fuel regulator - and no white smoke at all. Car goes absolutely perfectly now.

 

I hope this might help you. Fingers crossed.

Gary

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Just to add, mine sits for 4-5 months over winter with just a battery conditioner. Starts first turn of the key in spring and has done every year for about the last 10 years. When I did my intake swap, I reused much of the 3.2 fuel system and I had one of the fuel pressure regs fail when I first tried to restart. It was obvious as it was pissing fuel all over the place IIRC. Seems like they don't last forever and may have different modes of failure.

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It was eventually traced to one of the failed fuel pressure regulators - that then allowed neat fuel to go straight into the inlet manifold.

Sorry Gary, but it can not just have been the fuel pressure regulator (there is only one and a damper). The regulator is before the fuel injectors and the fuel injectors determine the fuel flow into the manifold. What is more, overpressure in the fuel rails caused by a failed fuel pressure regulator mean the injectors stop working, which is exactly what we found when MarkJs regulator failed (there is a thread on here about it). Stuck injectors, or faulty signal to them, would cause over fueling. But, 3.2s "over fuel" on startup/warmup anyway

 

Lots of white smoke - sounds much more like a massive over-fuelling issue - than oil.

Lighting and subjective interpretation can influence the description over the internet of a fuel, oil and condensation mixture.

 

:twocents:

 

 

Mark

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Sorry Gary, but it can not just have been the fuel pressure regulator (there is only one and a damper). The regulator is before the fuel injectors and the fuel injectors determine the fuel flow into the manifold. What is more, overpressure in the fuel rails caused by a failed fuel pressure regulator mean the injectors stop working, which is exactly what we found when MarkJs regulator failed (there is a thread on here about it). Stuck injectors, or faulty signal to them, would cause over fueling. But, 3.2s "over fuel" on startup/warmup anyway

 

 

Lighting and subjective interpretation can influence the description over the internet of a fuel, oil and condensation mixture.

 

:twocents:

 

 

Mark

 

I think the failure mode Gary and Richard are referring to is when diaphragm in either the fuel pressure regulator or damper fails it can allow neat fuel to flow back up the vacuum hose and straight into the throttle body - bypassing the rest of the injection system.

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Letting it sit there idling won't be doing it any favours as they take an age to warm up and thus sit there running rich washing the oil away from the valve guides. You then switch it off and all that fuel rich oil settles in the cylinders ready to burn off and pump out a load of eye stinging smoke the next time you run it.

 

Personally I wouldn't start hunting for a problem until you can properly take it for a drive, get some fresh fuel in it and get some miles and heat through the engine, clear those injectors and loosen up sticky valves, etc.

 

Where are you in the East Midlands.

By the way most puff out some smoke on start up, this usually clears within a few seconds though. Mine really does kick it out if it's had a short journey.

 

I've always been mindful that regular starting & idling wouldn't be good for it Nige, so I did keep it to a minimum.

 

Unfortunately, it'll be a little while before I'm able to drive it. But I'm not convinced that it will cure itself. This issue didn't gradually arise. It literally went from running perfectly, to dog rough overnight. (Well a three months of standing quietly.)

 

I'm 10 mins from M1 J25.

+1 What Nige says.

 

Plus you will also get a lot of oil in the cylinders on prolonged standing adding to the smoke, poor running and slow cranking.

 

Oil drains back from the tank through the oil pump, builds up in the crankcase and gets into the bottom of the bores. This will be a lot worse if the oil is diluted with petrol from repeated starting of the car without getting it fully warmed up (3.2s run very rich on cold starting), or if the oil tank is over filled. I hope you have not topped up the oil without the engine running and it being fully hot!

 

 

Mark

 

Mark,

 

Yes, I've always been conscious of potential bore washing.

 

The oil level is fine. It was serviced by a Porsche specialist just prior to being laid up.

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Lots of white smoke - sounds much more like a massive over-fuelling issue - than oil.

 

My car had this problem - after it had been sat for many years. Huge amounts of white smoke - that did not clear. My brilliant mechanic (Dave Harris - Meriden) when hunting in all the usual places you mentioned in your mail. We had the ECU checked and did lots of other tests. It was eventually traced to one of the failed fuel pressure regulators - that then allowed neat fuel to go straight into the inlet manifold. Bingo. Changed the fuel regulator - and no white smoke at all. Car goes absolutely perfectly now.

 

I hope this might help you. Fingers crossed.

Gary

 

Thankyou Gary.

 

I do feel convinced that it's a massive over-fuelling issue.

 

The smoke doesn't look blue or smell of oil at all.

 

Interesting theory about the fuel pressure regulator. Maybe worth me trying that first. Whilst I'm gambling on what the cause might be, it's probably one of the less expensive things to replace.

Just to add, mine sits for 4-5 months over winter with just a battery conditioner. Starts first turn of the key in spring and has done every year for about the last 10 years. When I did my intake swap, I reused much of the 3.2 fuel system and I had one of the fuel pressure regs fail when I first tried to restart. It was obvious as it was pissing fuel all over the place IIRC. Seems like they don't last forever and may have different modes of failure.

 

Thanks Richard. :)

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I think the failure mode Gary and Richard are referring to is when diaphragm in either the fuel pressure regulator or damper fails it can allow neat fuel to flow back up the vacuum hose and straight into the throttle body - bypassing the rest of the injection system.

 

So if the vacuum hose was disconnected from the throttle body, would it allow just enough fuel through to the injectors to allow the engine to start & idle? Or does the pressure regulator close completely without vacuum? Although I guess if one of the diaphragms has failed, I wouldn't achieve anything by trying this method...

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I'd recommend disconnecting the vacuum hoses from the the fuel pressure regulator and damper and then seeing if you have fuel coming from either unit during cranking. The pressure regulator is located at the back of the left fuel rail and the damper at the back of the right fuel rail. The vacuum hoses from the two units are joined with a rubber Y-piece just before connecting onto the back of the throttle body.

 

If you find you've got fuel coming from either the damper or regulator vacuum connections the you need to replace the unit - you could prove its this at fault by disconnecting and plugging the vacuum line and then running the engine.

 

If its not above I'd also check the inlet air meter flap moves freely - it should open smoothly with no tight spots and then spring fully closed. You can access this by removing the air filter element.

 

If you've got a multi-meter I'd also check the CHT resistance is as per the values in the Bentley manual and also that the air meter resistance varies as per the Bentley manual specs when you open and close the flap.

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I'd recommend disconnecting the vacuum hoses from the the fuel pressure regulator and damper and then seeing if you have fuel coming from either unit during cranking. The pressure regulator is located at the back of the left fuel rail and the damper at the back of the right fuel rail. The vacuum hoses from the two units are joined with a rubber Y-piece just before connecting onto the back of the throttle body.

 

If you find you've got fuel coming from either the damper or regulator vacuum connections the you need to replace the unit - you could prove its this at fault by disconnecting and plugging the vacuum line and then running the engine.

 

If its not above I'd also check the inlet air meter flap moves freely - it should open smoothly with no tight spots and then spring fully closed. You can access this by removing the air filter element.

 

If you've got a multi-meter I'd also check the CHT resistance is as per the values in the Bentley manual and also that the air meter resistance varies as per the Bentley manual specs when you open and close the flap.

 

Wonderful, thanks ever so much for that MaxDiesel.

 

I did identify the regulator, damper & hoses earlier today.

 

I'll give all of those suggestions a try! :)

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I think the failure mode Gary and Richard are referring to is when diaphragm in either the fuel pressure regulator or damper fails it can allow neat fuel to flow back up the vacuum hose and straight into the throttle body - bypassing the rest of the injection system.

OK, thanks Max, I stand corrected.

 

That vacuum line does go right up by the throttle body and so would be a problem.

 

Easy way to check would be to pull the vacuum line off the regulator and see what comes out.

 

For Mike, it is located on the left hand side of the engine bay (as you look at it) just behind the upright of the manifold. The engine bay heater blower and pipe will be in the way, but you should just be able to get your hand to it. The following picture is taken from the rear (ignore the nonstandard braided line) with the manifold off the engine, but it should show you what you are feeling for. The red arrow points at the vacuum line.

 

Mark

post-1486-0-84152300-1460494367_thumb.jpg

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So if the vacuum hose was disconnected from the throttle body, would it allow just enough fuel through to the injectors to allow the engine to start & idle? Or does the pressure regulator close completely without vacuum? Although I guess if one of the diaphragms has failed, I wouldn't achieve anything by trying this method...

 

The fuel pressure regulator only varies the supply pressure a little when the vacuum hose is removed at idle so it wouldn't stop the engine running. These vacuum hoses after often perished, split (or not even connected) and not noticed during normal use.

 

The vacuum hose to the fuel pressure damper doesn't serve any purpose other than to make it fail-safe by sending any fuel leaking past the diaphragm into the inlet manifold.

 

 

Wonderful, thanks ever so much for that MaxDiesel.

 

I did identify the regulator, damper & hoses earlier today.

 

I'll give all of those suggestions a try! :)

 

No problem - good luck. I can look up the Bentley resistance values for the CHT and AFM if you haven't got a manual to hand.

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OK, thanks Max, I stand corrected.

 

That vacuum line does go right up by the throttle body and so would be a problem.

 

Yes - that's the hose and Y-piece. I know someone who had the fuel regulator fail on his VW bus and pass so much neat fuel through the engine that it collected in the exhaust... he didn't realise and tried giving it a thrash to clear the smoke - eventually the fuel in the exhaust ignited and blew the exhaust open like a paper bag... his ears were ringing for sometime after!

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Thanks for all your help so far guys and thanks Mark for the image.

 

I'm eager to get out to the car tomorrow to have a fettle.

 

And MaxDiesel, I have a copy of a link saved somewhere with the resistance values for the CHT. Although when I previously tested it with a cold engine, I didn't get a reading. Should the resistance increase with engine temperature?

Edited by mike32carrera
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Although when I previously tested it with a cold engine, I didn't get a reading. Should the resistance increase with engine temperature?

Resistance decreases with temperature, an open sensor (max resistance) gives a rich mixture and a shorted sensor (min resistance) gives a lean mixture.

 

CHT Sensor Resistance from Bentley

 

0C = 4.4 to 6.8 K Ohm

15C to 30C = 1.4 to 3.6 K Ohm

40C = 1.0 to 1.3 K Ohm

80C = 250 to 390 Ohm

100C = 160 to 210 Ohm

130C = 90 Ohm

 

Mark

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The CHT resistance drops a temperature increases:

  • 0 degC = 4.4 to 6.8 kilo-ohms
  • 15 to 30 degC = 1.4 to 3.6 kilo-ohms
  • 40 degC = 1.0 to 1.3 kilo-ohms
  • 80 degC = 250 to 390 ohms
  • 100 degC = 160 to 210 ohms
  • 130 degC = 90 ohms

There's also a note in the Bentley manual: "An open break in the temperature sensor will cause the DME system to run rich" so if you have got an open circuit then this would make sense. If you can get hold of a resistor that sits somewhere in the above range of values for a cold engine and put this in place of the CHT you'll know whether this is the cause.

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If you follow the resistor test route, one end of the resistor to the CHT connector within the engine bay, the other end to ground. The old CHT's are single wire as they ground via the cylinder wall - it is this connection that often causes them to "fail".

 

Good luck.

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Spent half an hour in the garage yesterday.

Firstly, I blocked off the fuel pressure regulator vac pipe at the central T junction. (I wasn't able to crank the engine whilst checking for leaks from said pipe, due to having no assistant) I also blocked the corresponding hose take-off from the throttle body.

I'm happy to say, she fired up in an instant. But as per usual the place soon filled with petrol laden smoke. She didn't start so easily on the second attempt and continued to smoke.

She was dripping moisture and rather wet just on the inside. Her tailpipes that is! This was just water/condensation and NOT neat petrol.

Again, I tested the CHT, with the engine stone cold. It helps immensely if one sets the correct parameters on the multimeter! I had a reading of 3.6 k-ohms. I guess this takes into account the outside ambient temperature of 15c.

I've had a thought and I'm no chemist. Assuming the exhaust is emitting mucho stored moisture/condensation in the form of steam. Would said excessive steam act as a vehicle to carry "normal, 3.2 non faulty very rich cold start fuel" and hold it in the air for 10 minutes? In which case and as has already been suggested, warming her up and giving her legs a good stretching might be all she needs?

 

Unfortunately, it'll be some time before I have such an opportunity. Although, when she goes in for paint in a few weeks, I could plumb the brakes and fit a seat and drive her up and down their small-ish yard...

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  • 3 months later...

Update time.

A little more research indicated that the contents of the oil tank can empty themselves into the crankcase when the car is stood idle for any length of time. Apparently, the oil seeps past the oil pump via the force of gravity, causing lots of smoke on start up.

So I undid the drain plug in the bottom of the crankcase and sure enough a heck of a lot of oil was drained out !

The following week, the car arrived on a trailer at the bodyshop, where I could tinker without potentially annoying my neighbours.

The car started fairly easily, albeit after approx. 5 to 7 seconds and a small coax from the gas pedal. It used to fire from cold with a flick of the key and no gas pedal.

Still unable to drive due to no seat or brakes, I ran it up on a light throttle @ circa 3k rpm with the odd gentle rise to 4.5k. I felt this should help clear her lungs.

After a while the smoke did clear, completely. So that should be most of the oil and fuel residue dispersed. However, she still sounds a bit rough, with some backfiring and appearing to run on 5 or 5.5 pots and an occasional 6 for the odd second or two. All leads and cap were replaced with new a few weeks ago.

With the throttle held at a constant position say 3k, the revs will hunt up and down, sound good, then not so, then good, and not so, etc etc

I ran her for around 10 mins until the temp gauge was just above the cold square mark. Then turned off. She then subsequently refused to start at all. After abandoning and swearing for 15 mins, she eventually coughed into life, sort of. Now running very rough, but still without the initial smoke issue. Now with very poor response to any throttle application, which just got worse. In the end, 1.5 - 2k rpm and no further response from the throttle. Then 1/2 then 3/4's throttle and NO rise in rpm, just a feeling of bogging and reluctance.

To recap she used to run and sound 100% strong and healthy. This issue has only manifested from standing unused for a while. My bodyshop man has now suggested it could be the fuel going off ?

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hi mike....i think you should get some reading material to learn a little bit about your 911...it will help you to understand.

Regarding the oil.

The car takes over 13 liters of oil .If you do an oil change you put is first 10 liters and then after warming the engine(not on idle!!) you top it to about 5mm before the top mark on the dip-stick(the 5mm i do, in case you overheat the engine the oil will not get into the intake).

The remaining oil i am talking about is in your oil lines to the front oil cooler.

When you drain the oil there is about 9 liters in the oil tank and 3 liters in the engine case.So it is normal when you remove the engine drain plug -oil will come out-gravity;-)

Make sure you never overfill the oil.

if you car smokes white oil on start up -most of the time is either some one overfill the oil or you have a bad valve guides.

For your starting problem -it is very possible that you reference sensor is acting up...

Also how old is you fuel filter?

Ivan

Edited by proporsche
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