Starting Issues - all help appriciated

matt944S2 · 07-22-2009, 05:10 AM

Hi everyone.

Im having problems with my '91 S2.

The car, from cold, will refuse to start completely the majority of the time. Car cranks fine, but does not catch. After a few tries, or depressing the accelerator pedal, the car will catch but run very badly for a few seconds, then idle at around 600 rpm. If you give more gas, it will either stumble until it reaches 2000 rpm then rev normally, or be fine, but on both occassions when you release the pedal, the revs will dip to around 200 rpm, the car will almost stall and then the revs rise to 800 rpm and settle. On some occasions the car will stall.

This condition lasts for around 2-4 minutes, either at idle or driving, then will drive and idle completely normal. There is no loss of power, jerking, misfiring or anything else untowards apart from the described problem. Shutting the car down and restarting, it will catch and run first time, albiet with the stall issue. Hot starting is fine.

This is intermittant, but seems to be happening with increasing regularity. Car has been recently serviced including the fuel filter. I have tried unplugging the DME ECU temp sensor when this happens, it makes no difference.

I would appriciate any pointers, any help would be welcome!

Thanks

Matt

ColoradoSteve · ColoradoSteve's Garage

Check your fuel injectors, they may be sticking. I ran some seafoam through mine and it worked like a charm.

matt944S2 · 07-25-2009, 05:42 AM

Thanks for the tip - i have run injector cleaner through the car twice now.

This now happens every time from cold.

Yesterday morning, after sitting overnight, 4-5 attempts at starting, 10 second cranks. Car dosent so much 'catch', but does fire and after 1-2 seconds idles at around 800. For 1-2 minutes, a little throttle causes the car to try and stall. Strong fuel smell from the engine. 3minutes or so after starting, the car runs fine.

Parked up car at work yesterday, 4 hours later tried to restart. Caught and ran fine (no issues) after 4 seconds cranking. Shut car down.

5 hours later, same thing. Drove home, no issues at all while driving.

Today, 5 minutes ago, after sitting over night. As described above. Once started, you can shut down and it will restart every time.

Im currently in two minds here:

1) Fuel injector is leaking.
2) Ignition is not strong enough, until the plugs get some heat.

Anyone agree/disagree?

Icey1174 · 07-25-2009, 06:03 AM

I would investigate the strong fuel smell first. Right off the bat that is not right and is a HUGE fire waiting to happen.

Check your rubber fuel lines for cracks and leaks. There is a rubber fuel line that goes from your fuel damper to the fuel rail. This line sits on top of the cam housing which gets very hot. This hose was a safety recall from Porsche as the heat in the area caused the line to fail and many fires. I would advise taking it off to inspect it properly. I took mine off and found the bottom very dry rotted and cracked. The top side looked great, almost brand new. It was very deceiving and if I had not just happened to have this off a few years ago I am sure it would have leaked fuel by now potentially causing a fire with the hot cam housing.

Find the source of the fuel leak and work from there.

cvriv.charles · 07-25-2009, 06:44 AM

As icey said,.... it's probably a fuel problem. you probably have a small leak somewhere. The leak is letting out the fuel pressure which is needed for a quick cold start. By your cranking and cranking and then idling at 200 or so rpm's,... the pressure is slowly building up. once the pressure has built up enough,... the car will run as normal BUT you still have a leak which mean liquid fuel and gas can be spraying out somewhere which can catch fire.

Was you car doing this before the servicing? If not then atleast you have an idea as to wear to look. Check the fuel filter. It may not be on tight enough. Then check the fuel rail along with all the fuel lines.

Icey1174 · 07-25-2009, 08:22 AM

I see this is an S2. I am not sure if the S2 has the same fuel line issue as the 2.5L 944.

The fuel issue does need to be addressed right away. I think you might find your solution there. These fuel pumps put out a lot of pressure. Maybe it could be a bad fuel pressure regulator. My fuel filter is back by the fuel tank. I' am not sure where they are on the S2. I would guess they are in the back as well. If this is the case and it was leaking, you would smell the fuel much stronger in the back of the car then under the hood.

Was there any recent service to your car that may have caused this?

Correct the fuel leak first and go from there. You may be pleasantly surprised.

Grandad#3 · 07-25-2009, 08:36 AM

You may need to change out the fuel check valve as they can stick on you after a time. It is located on the out flow side of the fuel pump itself. Its main function is to keep fuel pressure in the line to the fuel pressure regulator.

Cheers,
Larry

matt944S2 · 07-27-2009, 12:36 PM

thank you for all the help,

Found that the fuel smell is NOT from the engine bay, as i first thought - its from the exhaust.

matt944S2 · 07-29-2009, 02:16 AM

Car wouldn't start at all from cold yesterday. Took out plugs after a few attempts and they were all very wet. Checked the coil, resistance seems ok, cleaned up plugs and went to get some spark checkers. With this all in the car caught, from cold, on the first turn. Taking out the checkers, the car would still start, a little more lazy. Didn't seen to be so bad on a little gas as usual.

So now im wondering if the ignition is not strong enough on a cold start. Plugs were a little fouled (probably from bad running on start up) cap and rotor were not too bad, but now im thinking of renewing the leads/dizzy/rotor and maybe even the coil.

One more thing - charged up the battery and took a reading, it was 25 volts? Thought it must be a multimeter error but it did the same on my other meter too?

cvriv.charles · 07-29-2009, 03:00 AM

Plugs were wet because the cylinders were flooded from all the cranking. Did you see your plugs sparking? Pull your plugs one at a time and stick it in the plug wire and get someone to crank the engine once or twisce. See what the spark looks like. if weak looking then maybe its ignition. Check all four.

When you say your plugs are fouled a bit,... how are they fouled? With oil or just wet?

You have a fuel pressure tester? If not get one. Test your fuel pressure. The two things you check first is fuel and spark. Check your spark and then check your fuel pressure. You might have a small fuel leak somewhere which to draining your fuel pressure which is keeping your car from starting on a cold start.

Fuel pressure tester.

cvriv.charles · 07-29-2009, 03:02 AM

I think we all are 100% that this is a fuel problem. your have a fuel leak.

matt944S2 · 07-29-2009, 03:22 AM

Thing is, im not discounting anything. Im trying to get hold of a fuel pressure tester.

My way of thinking, the plugs are fouled with carbon, and wet with fuel. That suggests to me, that when cranking, fuel is being injected but not ignited. if the fuel pressure was low, wouldn't that give a lean condition? Although it could be too much pressure, but i tried the clarks garage tip of disconnecting an injector and no joy.
Of course, i cant be totally sure until i get a pressure tester, which ill probably have to order.

Im only going on past experience, but i once owned a car that was bucking under boost. Was told by numerous shops it was either fuel related or a vacumn leak. Spent countless hours under the bonnet changing and checking fuel and vacumn lines. In desperation, i tock it to a good tuner in the area who took it for a quick run, and told me to change the plug leads. Bang, problem solved. The plug leads were all within spec of a resistance check and were fairly new.

Guys, i hope you dont think im trying to argue with you after all your help, im truly thankful for all of it. Whatevers causing it, im 100% better informed with your help.

Icey1174 · 07-29-2009, 04:01 AM

I don't think you are arguing. These is a problem that needs to be fixed, that's all.

I doubt there is a problem with power from the battery. If it has enough power to crank the starter then it has enough power for the ignition system.

25 volts sounds strange. Maybe 13 volts?

If the plugs are wet then they are getting fuel. That does not sound like the problem. Did you ever find the source of the fuel smell under the hood?

Check for spark from each wire while cranking. If each wire has spark then try a new set of plugs that are properly gapped.

matt944S2 · 07-29-2009, 06:07 AM

Thanks Icey, its hard sometimes to get meanings across on a forum.

The fuel smell wasn't coming from the engine area - it was coming from the exhaust - i hadn't vented the garage as much as i thought (a bit of a brain f*rt there) and because i smelt it while under the hood, i put 2 and 2 together and got 5. The last couple of times i had the hood up and the garage properly ventilated - nothing under the hood.

As for the 25 volts, i dont get it either. Happens on 2 different multimeters. A voltage tester i have that is not very accurate seemed to suggest it was slightly lower than 12v. Readings were taken at the battery and at the coil.

Makis · 07-29-2009, 07:47 AM

I'll suspect the coolant temperature sensor. It happened to me on my S2 and the symptoms where the same. Easy to check. Disconnect the wire harness take a voltmeter and start measuring the impedance between the to pins and then check to see if there is any impedance between the pins and the ground. If so then the sensor is damaged and you need a new one. Impedance between the two pins should be around 2K ohms when cold and around 200 ohms when hot.

matt944S2 · 07-30-2009, 04:04 AM

Thanks Makis, forgot to add i had already done this. However, just as a experiment, i tried again today.

I cannot get a resistance reading at the DME, however, the Clarks Garage connector pin diagram is not for an S2, so i have no idea if the same pin in used.

I rechecked the temp sensor, its within specs. I even took it out and placed it in boiled water to test it was working, seems fine.

I then placed a hot sensor in the cold engine, and it fired straight away. Let it get cold and tried the same again, very hesitant but did start.

The thing thats bugging me, is that ever since i got the car, i never had the DME warning lights in the dash (ie the idiot lights, oil level etc) at ignition on. Later on, they started to appear sporadicly. Made absolutley no difference to the car, so i assumed there was a bad wire to the dash, something to fix on a rainy day. After removing and refitting the connector today, on turning the ignition on the lights came on and stayed on until i fired the car. Shut down and restarted and they disappered again. Wondering if its connected.

Makis · 07-30-2009, 04:39 AM

Is important to do this when you measure the sensor.
Measure impedance between the sensor terminals and the ground with sensor plugged into the engine. There should be no impedance at all. My sensor failed as the terminal were not isolated from the ground and the DME was getting wrong reading as a result.

matt944S2 · 06:27 AM

There is no impedance between the bottom of the sensor and ground (ohm and continuity)

There is infinate between both terminals and ground.

I thought it was supposed to be this way?

Just tested again after an hour. Sensor out, into hot water, resistance about 50 ohms.

Car fires up from cold. Just as an afterthought, took a voltage reading at the temp sensor connector, 10.3 v. Is that correct, or shoul it be nearer 12v?

Makis · 07-30-2009, 06:27 AM

Quote:

Originally Posted by matt944S2

There is no impedance between the bottom of the sensor and ground (ohm and continuity)

There is infinate between both terminals and ground.

I thought it was supposed to be this way?

This is what is supposed to be. So the sensor is probably OK.
You can try to start the engine from cold with the sensor disconnected. If the engine starts easily then the sensor may still have something to do with this. However I think you may have to look elsewhere for the hard start. Is the engine compression OK when cold? Low compression can cause hard start. Also weak battery, slow running starter can contribute to poor starting.

matt944S2 · 07-30-2009, 06:38 AM

Yep, tried with the sensor unplugged, no change.

Although, by my way of thinking, the higher the resistance in the sensor, the colder the DME thinks the engine is, and adds more fuel. If you take off the sensor, the resistance is infinate, so the DME must think the car has moved to Siberia during a particulary cold winter, and fuels appropriately. Im sure my problem is the car is running too rich at startup.

With the sensor heated up in a cold engine, it fires up fine, idles on the button and has none of the earlier symptoms.

I just need to figure out why the car is trying to run so rich on start up, especially if the temp sensor is (or seems to be) fine. i need to figure out what the voltage should be to the sensor.