UKSaabs

Hi, can anyone help?

My 99 GL 5speed generally runs well and is quite reliable, but on longer runs the car will suddenly lose power and stop, then will turn over but not start again until the engine has cooled down. This to me sounds like a Vapor Lock problem!

Has anyone else had the same problem with either there carburettor 99 or 900? How did you solve it? Any ideas much appreciated..

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White 1983 2 door SAAB 99 GL 5 Speed, Inka Alloys, Turbo Front Spoiler.

CLASSIC SYMPTOMS OF POSSIBLE CARB.DIAPHRAGM SPLIT/FAILURE.

IF YOUR CAR STILL HAS THE 175CD FITTED,A LOCAL MOTOR FACTORS SHOULD BE ABLE TO SUPPLY ONE.


BIRDIE

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NEVER,SUFFER FROM INSANITY...............

ENJOY IT.

I never would have thought of that, Birdie. I always thought the classic sign of a split diaphragm was a flat-spot. The only cars I've had with diaphragm carbs have been my Chevette and my 90 and neither ever split so I've never had the chance to verify the symptoms. We have the diaphragms in stock if you need one, Rob. It's easy enough to pop the top off the carb. to have a look.

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Hi, thanks for the info,

Took the diaphragm out of the carb and had a good look. All looks in good order with no splits or damage? Put it back together again, topped it up with a little oil, the car starts fine?

The 99 runs really well with decent power and no flat spots.. It’s when the car gets quite hot after driving for a while, you get a sudden loss of power and it stops? Like you’ve run out of petrol? If you take the fuel line off the mechanical fuel pump and try starting the car, no fuel will come through until the car cools down then everything starts working again? Could I be getting an air lock in the fuel line? Or Vapor lock?

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White 1983 2 door SAAB 99 GL 5 Speed, Inka Alloys, Turbo Front Spoiler.

FOR THE COST OF A DIAPHRAGM,REPLACE AND SEE IF IT FIXES THE ISSUE.
I HAVE HAD THIS ISSUE WITH STROMBERGS ,MANY TIMES.IT ONLY NEED A PINHOLE,TO CREATE THE PROBLEM.

IF NOT,THEN I WOULD BE LOOKING AT POINTS,DISTRIBUTOR CAP,ROTOR ARM,COIL OR ON YOUR DESCRIPTION A FUEL PUMP ISSUE.

IT CERTAINLY LOOKS LIKE IT IS RELATED TO HEAT.
BIRDIE.

_________________
NEVER,SUFFER FROM INSANITY...............

ENJOY IT.

Vapour lock was starting to become a problem even back in the day when the last of the 99's were new.
Fuel was getting more volatile at around the same time that unleaded petrol was coming on the market.
Not a problem if the fuel is pressurised to around 45 PSI on an injection car.

To help combat this the later carb. 99's & 900's had a little plastic swirl pot and a return line to the fuel tank.
Fuel vapour would get seperated out in the swirl pot and sent back to the fuel tank.
Do you know if your car has got this?
If it has it might be worth checking it is all plumbed in correctly and does not have any blockages in the return line.
Saab used to market a retrofit kit to fit this system to earlier cars.

Try different brands and grades of fuel, I think I read a report somewhere that proved some fuel on the market is more volatile than others. Same report also suggested that additives used to be added in summer months to make the fuel less volatile in the hot weather. Unlikely I know but just thinking if you are still on a tank of 'winter' fuel? With all cars fuel injection now this might not even apply now.

Something else to consider is the fuel pump. I changed the fuel pump on my Sonett and the engine would just conk out in hot weather when stuck in traffic. Wasn't a problem before and wasn't a problem after I changed back to the original FoMoCo (Pierburg?) pump. I put it down to inferior valves in the new pump which just couldn't handle higher temps. Electric pump at the back is way forward for me here but not suggesting this is the best solution for your 99.

As Birdie suggested start off by just making sure what you've got is in good condition, just replacing all the fuel pipes and fitting new clips might help. Detereorating hoses can leak air into the fuel system on the suck side of the fuel pump or cause a loss of pressure on the carb side without actually showing signs of leaks.

Thanks both,

Diaphragm on order from Bill at Saabits.. All the other parts you mentioned Points etc Birdie have been changed... Thinking it may be the mechanical fuel pump I had already ordered a genuine Saab one from Bill this week so fingers crossed the combination of that and the diaphragm might rectify the problem. I think I’ll fit an inline fuel filter too, do you think that might help? Maybe bits in the fuel line!....

Pete, where exactly is this little plastic Swirl Pot located? My 99 is quite a late 1983 model so I would have thought it should have one?

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White 1983 2 door SAAB 99 GL 5 Speed, Inka Alloys, Turbo Front Spoiler.

YEP,IN LINE FUEL FILTER(CLEAR PLASTIC) IS ALWAYS A GOOD IDEA.THAT WAY YOU AN SEE WHAT'S HAPPENING,WITHOUT HAVING TO REMOVE THE FUEL LINE,ESPECIALLY WHEN IT'S HOT .

IF IT STILL DOES THIS,AFTER A NEW FUEL PUMP AND DIAPHRAGM?

CARRY HALF A GALLON OF FUEL AROUND(IN A PETROL CAN,WITH LONG NOZZLE) FOR WHEN THE CAR STOPS/BREAKS DOWN NEXT?
REMOVE THE BRAKE SERVO RUBBER PIPE FROM THE TOP OF THE INLET MANIFOLD,POUR HALF AN 'EGG CUP' OF FUEL INTO THE INLET MANIFOLD VIA RUBBER GROMMET IN THE TOP OF THE MANIFOLD(SMALL FUNNEL HELPS) REPLACE SERVO RUBBER PIPE,AND CRANK THE ENGINE.

IF IT STARTS IMMEDIATELY,THEN ITS DOWN TO FUEL/EVAPOURATION. IT MAY ONLY RUNS FOR 4-5 SECS,OR THIS MAY BE ENOUGH TO 'FOOL' IT,AND KEEP IT RUNNING.
OTHER ISSUES I HAVE EXPERIENCED,WHEN THE ENGINE IS HOT,CAN BE CAUSED BY CARBON/VARNISH BUILD UP ON THE OUTSIDE OF THE ALLOY PISTON,INSIDE THE CARB, MAKING IT STICK IN THE 'OPEN' POSITION. THE ENGINE THEN FLOODS,AND WILL NOT START.
THIS CAN BE CHECKED BY REMOVING THE PLASTIC INTAKE PIPE,AND FEELING INSIDE THE STROMBERG WITH A FINGER,OR SHINING A TORCH,WHEN THE ENGINE IS HOT.THE VARNISH CAN BE CLEANED OFF CAREFULLY WITH SOME P1500 WET AND DRY,USING WD40 TO LUBRICATE THE P1500,WHILST THE DIAPHRAGM IS BEING REPLACED.


INCIDENTALLY, FOR OUR READERS BENEFIT? AN 'ELUSIVE' ENGINE OIL LEAK,DOWN THE SIDE OF THE NEARSIDE FRONT ENGINE BLOCK,AROUND CYLINDER HEAD HEIGHT?
THIS IS USUALLY CAUSED BY THE(ORIGINAL) FUEL PUMP,WHICH HAS SMALL HOLES PUNCHED IN THE BACKPLATE ON 'H'SERIES(B201). WHEN THE PUMP BECOMES WORN,ENGINE OIL DRIPS DOWN,THE ENGINE BLOCK,FROM THESE HOLES.

AS '99 PETE' SAYS,THE LITTLE PLASTIC SWIRL POT KIT,WAS FITTED TO THE LATER STROMBERG EQUIPPED CARS,I THINK 84-85.
THERE IS ALSO A SMALL 'SOLENOID' VALVE FITTED,ON THE BOTTOM OF THE LATER STROMBERG WHICH SHOULD SHUT OFF THE FUEL SUPPLY,TO PREVENT 'RUNNING ON',WHEN THE ENGINE IS SWITCHED OFF. TRY PULLING OFF THE SINGLE WIRE TO IT,WHEN THE CAR WON'T START?


THE VERY LAST OF THE N/A 90/99/C900 HAD I THINK 'PIERBURG' CARBS,ALTHOUGH I SUSPECT THIS WAS TO MEET 'EMISSION' REGULATIONS? PICTURE HERE

YOU CAN ALSO SEE,THEY ALSO HAD AN 'INSULATING' BLOCK,FROM CARB TO INLET MANIFOLD,MAYBE 10MM THICK,WHICH DETORIATED/CRACKED OVER TIME.

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NEVER,SUFFER FROM INSANITY...............

ENJOY IT.

Thanks Birdie for the very useful info, I really appreciate it... It’s interesting that you talk about the oil leak from the fuel pump as I have that very leak Looks like I definitely have a worn fuel pump!

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White 1983 2 door SAAB 99 GL 5 Speed, Inka Alloys, Turbo Front Spoiler.

Hey Rob,

How did you get on with this in the end? I have a very similar problem with my 1984 99GL – but I also don't have the plastic swirl pot fitted to my carb.

I've replaced the carb diaphragm, the carb needle, the float, the float gasket, cleaned out the float bowl, and added an inline fuel filter. I've also replaced the dizzy cap, rotor arm and spark plugs and leads.

I usually find that on pressing the throttle pedal, nothing happens. I'd pull over and it would still idle, but not pull away (even though revving was possible in neutral).

A kind person from a good garage that I won't name (just in case anyone would pursue copyright) sent me the attached. It shows the vague fitting instructions for a vapour trap.

I fitted my fuel pump in late 2007. I realise that sounds like a long time ago, but it hasn't even done a thousand miles on it, I don't think. I have bought a replacement though, just in case.

Let me know if you find a vapour trap (and necessary fittings) for a CD175. I'm glad there's someone else experiencing this – I've not been able to drive it for a while, but I used to get horrible anxiety never knowing when it was going to cut out and if I'd be able to pull over etc.

Keep us updated!
Keith

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1984 Saab 99GL (Keeps stopping for some reason)
1986 Austin Mini City E (Needs lots of welding)

Hi Keith,

Sorry I’ve not replied sooner, I haven’t been on uksaabs for a while..

I’m still having this problem although not quite as bad now I’ve replace the old mechanical fuel pump. I’ve been told it’s down to the use of modern fuels. The document you’ve attached will hopefully be very useful. My 99 is due for its MOT this week so i’ll show it to my mechanic, see if there’s something he can do!

Meanwhile this is what I’ve found out online and I think is the problem:

Vapor Lock: The Cause, Prevention, and Cure

Vapor lock is often a problem with older carbureted cars, but not an issue with modern electronic fuel injected cars. A carburettor is a mechanical device that uses the engine’s natural vacuum to suck the required amounts of fuel into the combustion chambers.

Vapor lock causes a car to stop running when the fuel in the system overheats. It is most likely to happen when driving on hot days and in stop-and-go traffic. Constant acceleration and deceleration make your engine work harder, causing it to run hotter. Excess heat causes the fuel to vaporize. This keeps the fuel from reaching the engine.

The 99 has a fuel pumps next to the engine. The pump’s closeness to the engine, and the use of modem fuels, causes the fuel in the line to become very hot. When heated, fuel turns to a vapor, like water turns to steam when boiled. This process is hastened by the vacuum created in the line as the fuel is sucked into the engine.

When the fuel turns to vapor, the mechanical fuel pump can no longer move it through the system. As a result, the car runs roughly, keep loosing power or will suddenly stop and not restart until the car has cooled down.

The following are ideas that I think may help solve the problem:

Install a Low-pressure Electric Fuel Pump near the Fuel Tank. This will keep the fuel moving through the lines even if the engine compartment heats up. I think an electronic fuel pump can be used in place of or in conjunction with, the original pump. It then could be switched on and off, as needed/desired. They usually pump the fuel through the faulty pump which is not removed, thus preserving the original look.

Install an Electric Fan override switch. This Would let you put the radiator fan on sooner, cooling the engine, fuel pump and lines quicker.

Insulate the Fuel Lines in the engine bay may help.

Action to Take When Experiencing Vapor Lock.

Cool the System Down. With the ignition off, pour cold water over the fuel pump, carburetors, and fuel lines. This will quickly cool down the fuel pump and condense the fuel from vapor back to liquid, eliminating the vapor lock in the fuel system.

Any other ideas much appreciated.

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White 1983 2 door SAAB 99 GL 5 Speed, Inka Alloys, Turbo Front Spoiler.