Pig to Start

[Fred Hindle]

Advice needed please.
My 924S (same 2.5 engine as 944) has become a pig to start when cold. When it eventually does catch then the engine is very erratic, coughing and sputtering. It needs to sit for a few minutes (with the throttle being played with) before setting off. If I do set off before the engine has settled down it will cut out under load. Being automatic I can't just dip the clutch. A couple of times it won't fire up again if it does die completely. I think that it is 'over-choking' itself. Does anyone have any suggestions as to what is causing the problem and how to rectify it? (Already had a new DME relay fitted).
Cheers,

 

[xenon]

The DME relay provides power to the fuel pump and the DME, so it will either be off or on, i.e. working or not, and needs to work properly whether the car is hot or cold. Could be the ICV?

 

[Fred Hindle]

Hello Ian,
I mentioned the DME as it is such a common cause for problems on Porsches. It was basically to stop people suggesting it as a possibility. Once the engine is warm it runs normally, so it is something to do with cold starting. It has definitely gotten worse over the last week. Before that I was confident that it would start at some point, now I'm making sacrifices to various gods in the hope that they get it to start![]
I'll get it in the garage at the weekend, too wet and horrible to start playing around with it at the moment.

Cheers,

 

[xenon]

I see - yep, the DME relay gets it in the neck everytime a starting problem is mentioned! [8D]

If you say it feels like it's "over-choked" it could be the idle valve, cold-start valve (if there is one(?)) or possibly an air-leak that gets better as the hoses warm and become flexible. Good luck, whichever.

 

[924nutter]

Fist have a look at all of the breather hoses and check for leaks and splits. Then check all the components that make up the inlet tract and do the same. Then check the plugs.(also the leads, cap and rotor arm) Most modern ignition systems give such a whopping spark that the the gap can get as large as 1mm, yes 0.040 inch and stil functuion, but quite suddenly the plugs will refuse to fire a rich, cold mixture and the symptoms are coughing and banging until the engine pick up speed and warms up. Failing all that I would have a look at the pot connections on the metering unit Fred. The dme gets all its air flow data from the flap device but corrosion and wear accumulate over the years making it hard for the dme to decide how much fuel to meter. When Bosch designed the dme system they did not anticipate the cultural change that occured in this country which results in the entire gnp of Siberia being deposited on our roads during the winter; salty air and aluminium bits do not cohabit well. Once a bit of heat gets into the metering body the mechanism frees up and generally works well. A tell-tale sign of something amiss is a hunting of rpm at idle.

 

[Fred Hindle]

Thanks for the info John.
Looks as if I maybe slightly busy this weekend. - Why can't cars wait until summer before they start breaking down?

Cheers,

 

[PJS917]

Fred, it's not very nice calling your 924S a pig, try treating it with respect and it might start a little
more happily[][][]

 

[rob.kellock]

Fred, my 944 had the symptoms you describe which were cured by replacing the fuel filter. Best of luck.

 

[Fred Hindle]

Peter,
Wasn't calling 'The Shed' a 'pig', just saying that it is being a pig to start.

Rob,
Another possibility, no idea when the fuel filter was last changed. It may have some German fingerprints on it. Will certainly bear it in mind if other things don't cure it.

Cheers,

 

[peanut]

this trouble shooting guide from Pelican might be helpful to anyone with ignition problems
http://www.pelicanparts.com/911/technical_specs/911_DME_troubleshoot.htm

sorry Fred this is the guide I meant to link to . Cold starting and running problems
http://www.clarks-garage.com/

Mmm can't seem to link directly to the page so I've copied it here. Hope I haven't transgressed any law or protocol

Introduction Troubleshooting starting and running problems can sometimes be quite difficult. This is especially true if you aren't aware if all the possible causes of a problem. This is a general guide which will list symptoms for 944 starting and running problems and common causes of those problems. It is intended to help you map out a troubleshooting plan. Running Problems

1. Rough Idle
   1. If the car starts when cold but, idles rough or does not want to stay running, this can indicate a problem with the engine temperature sensor. When the engine is started cold, the engine temperature sensor sends a signal to the DME control unit to provide a richer mixture. As the engine temperature sensor starts to fail, it sends a higher than actual temperature signal to the DME control unit. The DME control unit leans the fuel mixture thinking the engine is at normal operating temperature. This causes the engine to run rough. As the engine warms, it not longer needs the richer cold idle mixture and the engine runs smoother. If the car idles rough this can also be indicative of bad plug wires, distributor, or rotor. One way to check for bad plug wires is to inspect the plug wire runs with the car running in a very dark area. If the plug wires are bad you should see some arching to the cylinder head or fuel rail. If the car idles rough or cuts off at low RPM or idle, the cause could be a failing O2 sensor. The O2 sensor is out of the loop at full throttle and will not affect the way the car runs. A rough idle can also be caused by a problem with the air flow box. The damper for the air flow box can fail mechanically or the contacts inside the box can get dirty and send a errant signal to the DME control unit. This can sometimes be corrected by cleaning the electrical contacts inside the air box. This requires removing the cover on the air box which is held in place by caulk. You will need to cut through the caulk and gently pry the cover off. Once the cover is removed, clean the circuit board inside with a good contact cleaner. When you have finished cleaning the circuit board, reattach the cover using a non-corrosive caulk. If the car experiences a rough idle or idle fluctuates several hundred RPM, this can indicate a sticking idle stabilizer valve. Many people have removed and cleaned them but, this is normally a temporary fix and the valve should be replaced. A faulty O2 sensor can also cause RPM to fluctuate at idle. Unplug the O2 sensor and see if the idle still fluctuates.
2. Difficult Starting
   1. If the car is difficult to crank after sitting for more than several hours, the fuel return regulator or fuel pump check valve could be faulty. This will allow the fuel rail to depressurize and it takes some time for the fuel pump to increase fuel rail pressure sufficiently to fire the car. If the car is difficult to start when warm, again the fuel pump check valve, fuel return regulator, or individual fuel injectors could be leaking. The fuel pump check valve or the fuel return regulator leaking allows the fuel to drain back to the gas tank depressurizing the fuel rail. When the car is warm, the fuel remaining in the fuel rail can flash causing vapor lock. There are several ways to check this. One is to connect a fuel pressure gauge at the fuel rail. Start the car, let it run until fuel pressure is stable, then shut down the car and monitor the pressure at the fuel rail. With the car not running, the pressure at the fuel rail should not decrease to less than 15 psig. If it starts to decrease, clamp the rubber part of the line from the fuel return regulator to the gas tank and see if it stops the pressure decrease. If not, clamp the line at the discharge of the fuel pump and see if it stops the pressure decrease. An individual fuel injector leaking can depressurize the fuel rail and cause the same problem. If the car starts easily when cold, but is difficult to start when warm a failing DME relay could be causing the problem. As the DME relay starts to fail, it operates at a higher temperature. If the car is stopped, the higher temperature of the relay creates a high enough resistance to keep the relay from picking up when the car is started again. When the relay cools and the resistance decreases, the relay will again function normally. If the car is very hard to start or only fires part of the time and then dies it could be a problem with the distributor cap or rotor. 944 rotors are notorious for having the set screw back out of the rotor allowing it to spin on the end of the camshaft. When this happens the car will not fire at all or will fire momentarily when the rotor is in line with the correct cylinder to be fired. If the car is difficult to start when cold it could be a problem with the engine speed or reference sensors. One of the sensors sends a signal to the DME for TDC and the other an engine speed signal. The DME uses these signals to time the pulses to the ignition coil and the firing of the fuel injectors. If the sensors do not send the proper signal to the DME the normal result is a failure to get proper spark from the ignition coil. Sometimes their failure may be a result of debris building up on the ends of the sensors which reduces the gap between the sensor and the flywheel. If so, cleaning the ends of the sensor may get them working again. If the car is difficult to start or will not start at all regardless of operating temperature, there are a number of problems which could be causing this. Here is a list of possible causes:
      • DME Control Unit
      • DME Relay
      • Security System Control Unit
      • Fuel Pump
      • Fuel Pump Fuse
      • Distributor Cap, Rotor, Coil, or Primary Coil Wire
      • Engine Speed and/or Reference Sensors
      A fuel pressure gauge, spark tester, and voltmeter are extremely useful in narrowing down the possible causes of the problem.

Clark's Garage © 1998

 

[Fred Hindle]

Hello Nick,
Thanks for the Clarks Garage info. I couldn't get into the site but the info you have pasted here will hopefully guide me okay.
Haven't done anything yet as I can't get the car into the garage and the weather is not conducive for working outside. (Too old and fragile nowadays, like some creature comfort like a space heater!)

Cheers,

 

[Fred Hindle]

Think I may have cured the problem. Took the car for it's MOT yesterday, left it there overnight. Spoke to the lad who started it this morning.
Asked him 'How did it start?'
'First time on the key, no problem, ran lovely'

So what did I do to the car yesterday before taking it to the garage? Cleaned the dizzy cap and the rotor arm. Rotor arm was mucked up to hell.
Motto - look at the simple things first

Watch this space to see if it has actually cured it or just a hiccup.

Cheers,

 

[morris944s2john]

Yes, its a good idea to go back to basics. Check for spark first.

 

[924nutter]

See Fred, what did I tell you in the first two lines of my post? Checking for splits requires no tools, so is easiest to do then its back to basics as you discovered. It looks like someone will be changing all theirH T components in the no too distant future. Happy motoring.

 

[Fred Hindle]

John,
Spot on with the rotor arm check,
Just need to source a second hand one from somewhere.

Only kidding.

Cheers,

 

[Fred Hindle]

After I brought the car home yesterday morning I parked it up and left it.
I bit cold and windy overnight so a good test of its starting this morning.
First turn of the key and ticking over like as littl' good un.
So, looks as if it is cured. Thanks everyone for your input and suggestions, they will be noted for the next time.

Cheers,