Problems With Start When Engine Is Warm

[stingray]

Meaby somebody knows. Have a 93' Audi 100 Quattro (4x4). Runs excellent, start up perfectly when cold. After driving, i stop engine. after 30 Minutes (engine still warm), it's very hard to start the car, almost impossible. It wan't fire up. Startermotor turns perfectly, ignition coil, distrubutor and spark works, it must be a fuel problem. Changed almost every sensor (even the coolant sensor) on the the engine, changed the fuel pump, the fuel pump, the K- jet tronic fuel distrubutor, the injection valves, etc. A mistery right now. Still fooling around with the car, Maybe someone knows a trick.

To mention: i bought this car fro ma Thai Navi guy who use it on LPG, wich i removed (for safety reason) It had troubles already on the beginnin (when i bought it), to drive on fuel. So after replacing the fuelpump car runs fine, except it start up very hard when warm.

[warwick7735]

Hello

Have you replaced the COLD START SENSOR, it could be faulty and is thinking the car is still cold and so its been over fuelled and hence flooding it. Try starting it keeping your throttle fully open, see if it starts easier.

I had an intermiitent fault with a 93 audi coupe which I traced to the fuel pump relay, something else you could try.

Hope that helps

[Tywais]

I had the same kind of problem with a Porsche I had. Cold fine but after turning the engine off after it was warmed it just wouldn't start again. I found when I removed the fuel cap from the gas tank I could hear pressure release and then it would start. The fuel tank gas vent was plugged up so too much pressure build up in the fuel lines.

[stingray]

I had the same kind of problem with a Porsche I had. Cold fine but after turning the engine off after it was warmed it just wouldn't start again. I found when I removed the fuel cap from the gas tank I could hear pressure release and then it would start. The fuel tank gas vent was plugged up so too much pressure build up in the fuel lines.

Thanks for the two posts. I disconnected the cold start relais, just to see if it would start. It's the same. I din't tought about the fuel tank gas vent. I'll check this today.

[Farma]

I’ve got no experience with Audi’s and have no idea of their fuel systems.

Years ago I had a car with fuel vaporization caused by fuel lines passing too close to the engine. The symptoms were very similar to the one you’re encountering with the Audi. The car would start fine but after driving it wouldn't start again until it had cooled down. The solution was to insulate the fuel lines.

It’s possible the fuel lines in the Audi were adjusted during the LPG conversion bringing them too close to hot areas.

[edd]

Your problem is usually with the injectors they will be leaking.

On a cold start the extra fuel will not make any difference to the starting but when it is warm the dribbled fuel will be vaporized on the piston crown then it back fills through the inlet manifold into the air filter.

When the warm engine is cranked the fuel vapor is drawn back through into the engine and will be mixed with the newly injected fuel, this gives you a wrong mixture that will not ignite.

The way to get it to start is,

Full throttle and crank without stopping for OVER 40 seconds.

The vehicles computer has a timer for a cold starts conditions this lasts for 20 seconds before it cuts off, (fuel injectors stop firing assuming over fueling because of none start condition) if you stop cranking at this point the timer re sets and you are back to the start point again.

So you need to carry on cranking with out stopping for at least another 20 seconds.

This problem used to be called ``The paper shop syndrome`` start from cold run for 10 minutes, stop at the paper shop then it will not start.

I hope this helps until you can get it repaired

Edd ( AA patrol for 32 years)

[stacychen0001]

The way to get it to start is,

Full throttle and crank without stopping for OVER 40 seconds.

[GayGordon]

I had one of these in the uk ( 2.2 5 cylinder ) when i went to spain i had the same problem, i was told they generate a lot of heat and the fuel vaporises ,if you keep it cranking it eventually fires ?. nothing to do with the cold start ( 6th injector ) .a friend of mine fitted a device that gave more pressure and seemed to cure it,. of course you may have a different problem altogether, but sounds familiar,.

[stingray]

I had one of these in the uk ( 2.2 5 cylinder ) when i went to spain i had the same problem, i was told they generate a lot of heat and the fuel vaporises ,if you keep it cranking it eventually fires ?. nothing to do with the cold start ( 6th injector ) .a friend of mine fitted a device that gave more pressure and seemed to cure it,. of course you may have a different problem altogether, but sounds familiar,.

Thanks for all the advise. The injectors are allready replaced, (useded ones). At least my mecanic say soo. But i have to make sure if he really done. Luckely he had another Audy A6 with the five cylinder engine in his workshop. So he swapped parts arround to see if he can find the fault. The cold start valve he disconnected. Today i'll check the fuel lines again. If car is worm can stop. If start right away again it will run. But if stop for a half hour, than is't very hard to start.

[warwick7735]

Hello again

We are all thinking its a fuel problem, have you checked the electrical side, are you getting a spark when the engine is hot. It might be a faulty coil breaking down when its hot.

Just another thought

[stingray]

Hello again

We are all thinking its a fuel problem, have you checked the electrical side, are you getting a spark when the engine is hot. It might be a faulty coil breaking down when its hot.

Just another thought

Yes it's defenitifely a fuel problem. If i keep the trottle fully open during the starting process it will start, but very hardly.

[hulahula85]

Just a thought, when you replaced the fuel pump, did you prime the pump BEFORE starting the car? You can destroy a brand new pump if you don't prime it by turning the ignition on and off a few times before initial startup.

Also, since the fuel tank wasn't being used during the LPG conversion, are you sure there is no rust or water sediment in the tank?

I went through 5 fuel pumps on an old Mercedes, from not priming the pumps, and from rust flaking off inside the tank and clogging up the pump pickup.

[stingray]

Just a thought, when you replaced the fuel pump, did you prime the pump BEFORE starting the car? You can destroy a brand new pump if you don't prime it by turning the ignition on and off a few times before initial startup.

Also, since the fuel tank wasn't being used during the LPG conversion, are you sure there is no rust or water sediment in the tank?

I went through 5 fuel pumps on an old Mercedes, from not priming the pumps, and from rust flaking off inside the tank and clogging up the pump pickup.

Thanks for your advice. I think it isn't the fuel pump, i quite shure, because the car runs fine when it started up, plenty of power and can drive for hours without any troubles. Cold start no problem at all. Warm start ok unless you stop the engine for at least 15 to 20 minutes and try to start again. Then the problem comes

[hulahula85]

Just a thought, when you replaced the fuel pump, did you prime the pump BEFORE starting the car? You can destroy a brand new pump if you don't prime it by turning the ignition on and off a few times before initial startup.

Also, since the fuel tank wasn't being used during the LPG conversion, are you sure there is no rust or water sediment in the tank?

I went through 5 fuel pumps on an old Mercedes, from not priming the pumps, and from rust flaking off inside the tank and clogging up the pump pickup.

Thanks for your advice. I think it isn't the fuel pump, i quite shure, because the car runs fine when it started up, plenty of power and can drive for hours without any troubles. Cold start no problem at all. Warm start ok unless you stop the engine for at least 15 to 20 minutes and try to start again. Then the problem comes

Yeah that's what i thought too. The car would run fine until it warmed up. Then it'd be hel_l to start, and if you could get it started it would buck and hesitate and eventually die.

Easy way to check is hook up a fuel pressure tester. Sometimes this doesn't even help though. If you're in bangkok i'll be around after this weekend and i'd be glad to help you with it.

[loubrockbank]

First thought is HT leads, either working there way loose after a drive or breaking down. Have you checked the earths from the engine to the body (and starter to chassis)? This might cause the intermittence. If not that, are you SURE you replaced ALL the sensors with the correct ones and correctly seated? Although I'm not sure why exactly you replaced them?

On Honda's there is a main relay for the ignition whihc a swift bang on the dashboard usually sorts, other than re-soldering the dry joint, but as you are getting (definately?) spark when it is warm, then I would say it is the K-Jetronic system. A common remedy is to retro-fit a mechanical fuel pump, have a look on VW/Audi/Porsche forums to double check as I am just going from memory. The system is so widely used but flawed.

Edited April 14, 2009 by loubrockbank

[BSJ]

It's a fuel vaporization problem, nothing to do with the electrics. Just possibly the mechanic that did the LPG conversion has tossed some of the heat shields that protect the fuel line around the engine.

[stingray]

It's a fuel vaporization problem, nothing to do with the electrics. Just possibly the mechanic that did the LPG conversion has tossed some of the heat shields that protect the fuel line around the engine.

Yes, i'll take all of your advises and will go see the mecanic after sonkran. Yes, we changed al the sensors, because another Audy A6 with a 5 cylinder engine was for other repairs in the workshop. Therefore my mecanic takes the chance and step by step he removed all the sensors (one by one) from the A6 to mine, to see what happen. No sucess.

[igme]

It's a fuel vaporization problem, nothing to do with the electrics. Just possibly the mechanic that did the LPG conversion has tossed some of the heat shields that protect the fuel line around the engine.

Yes, i'll take all of your advises and will go see the mecanic after sonkran. Yes, we changed al the sensors, because another Audy A6 with a 5 cylinder engine was for other repairs in the workshop. Therefore my mecanic takes the chance and step by step he removed all the sensors (one by one) from the A6 to mine, to see what happen. No sucess.

this maybe a long shot but how old is your battery? i had a problem similar to this before (but not on an audi) - even after checking alot of things, it turned out to be a simple battery problem. i know we would tend to think that it should have been more charged when you have just turned off the engine due to the alternator's activities, but it was the case with me. funny thing that time is the battery had enough charge left for lights and stuff, just not enough to start the engine.

another similar experience i had, not exactly as per your description but close - is that sometimes it starts and sometimes it won't - it eventually turned out that the starter needs some cleaning.

[hansgti]

Your problem is usually with the injectors they will be leaking.

On a cold start the extra fuel will not make any difference to the starting but when it is warm the dribbled fuel will be vaporized on the piston crown then it back fills through the inlet manifold into the air filter.

When the warm engine is cranked the fuel vapor is drawn back through into the engine and will be mixed with the newly injected fuel, this gives you a wrong mixture that will not ignite.

The way to get it to start is,

Full throttle and crank without stopping for OVER 40 seconds.

The vehicles computer has a timer for a cold starts conditions this lasts for 20 seconds before it cuts off, (fuel injectors stop firing assuming over fueling because of none start condition) if you stop cranking at this point the timer re sets and you are back to the start point again.

So you need to carry on cranking with out stopping for at least another 20 seconds.

This problem used to be called ``The paper shop syndrome`` start from cold run for 10 minutes, stop at the paper shop then it will not start.

I hope this helps until you can get it repaired

Edd ( AA patrol for 32 years)

I would tend to agree about the injectors, i had a similar problem on a golf gti using this injection system, try to assert if the used injectors are actually any good, IE why would they be available if there was nothing wrong with them?

[stingray]

My mecanic told me he changed the injectors already. But i'm not sure about this. Now after the big water war is finished in Pattaya (19. April), i'll get new injectors by my self. I guess this is the problem. All the fuel lines are ok. Battery ok as well. I understand what Igme mentioned, so even if i use 2 batteries in paralell (just for try, instead of one, same problem Spark leads and coil defenitifely ok.

Edited April 19, 2009 by stingray

[welo]

So what!?!

This thread keeps twisting like a detective story and in the end we don't get to know the murderer. dam_n it!

Did you fix it? What was the problem?

welo

Sorry to bring up the old thread, I love to rummage around the archives...

Edited July 18, 2009 by welo

[stingray]

So what!?!

This thread keeps twisting like a detective story and in the end we don't get to know the murderer. dam_n it!

Did you fix it? What was the problem?

welo

Sorry to bring up the old thread, I love to rummage around the archives...

Yes, it's fixed now. new fuelpump wasn't ok (possible f..kt up by mecanic), so replaced it again together with the fuel pressure valve. Mecanic changed ignition coil as well (used one). This new used coil was not ok and cutting out the engine ocasionally. There was nothing wrong with the originale coil. So after i saw the original coil laying in the trunk i changed it back and the problem of "cutting off" was gone. I replaced the battery and theyr connectors to make sure starter motor turn fast enought, and overhauled the alternator (charging was ok, but bearring had strong noise). Fitted a simple volt meter in the car, so can watch allways the voltage. Changed all engine belts, and manything else. Changed all the suspenson parts, like bushes, joints, etc. Car runs fine now. Drive it occasionally, maybe 2 or 3 times a week, sometime to Bangkok. Bought this car quite cheap from a Navi Officer 6 months ago. But finally i spent about 100'k to fix everything. Painted the whole car for additional 23'k in black metallic ( it was navyblue before). This is a typical story when depend on local mecanics and a car wich never was take in care of before. So now ist almost like a new car.

[Datsun240Z]

Stingray ; to avoid the work of changing the fuel pump, I advice you to make a measurment device, with different adapters, to measure the fuel pressure. This you can diagnose if the pump is defect or not. Most engines have a measurement point on the fuel rail for this. It's actually very simple to make from something like this:

[AnaisNin]

Fortunately I am not the owner of the A6 in the garage.

[Lopburi99]

The way to get it to start is,

Full throttle and crank without stopping for OVER 40 seconds.

I just read this interesting thread and had to make a comment on this advice. Sounds like a sure recipe to ruin the starter. Cranking for a long time overheats the starter and the internal solderings melt. NOT a good idea!

Also, some related experiences which may help others reading this thread in the future:

In a Jag XJ6 (1982) I had years ago, it had an intermittent starting problem where it cranked and cranked before starting. After many trips to the mechanic, he finally isolated it to a electric solenoid device which closes a fuel line to prevent fuel leakage back into the tank. Even though this now sounds like an obvious diagnosis, the XJs then had dual fuel tanks complete with fuel lines, seals, crossover valves, other various switches and valves everywhere. It was non-trivial exercise to do the isolation. Classic Jag owners: tuck this tidbit away.

And also in my then new 1985 Jag XJS V12, the beast had a nasty problem of completely crapping out occasionally while driving. After a couple of hours it would finally restart, like nothing happened. I assume vapor lock of some sort but the local Jaguar dealer in Detroit (Falvey Motors: anybody from Detroit will remember this notorious [to be charitable] dealership) was never able to remedy this condition.

Also brings to mind when my then wife worked for Jaguar Cars, Ltd as a model at various Auto Shows. Once when Sir Graham Whitehead (then the company president or chairman) came across the pond to the 1982 Chicago auto show and was red-faced when the shiny new signal red V12 XJS had problems starting so it could be driven off the auto show floor. Had to be pushed off. Mind boggling. Surely good old Lucas Electronics had something to do with that problem.

All good memories that I reflect on in my old age, nonetheless.

Edited July 19, 2009 by Lopburi99

[Lopburi99]

Fortunately I am not the owner of the A6 in the garage.

Annie, if that's really you in the photo , I am sure some well healed farang here will be happy to provide you with the car of your dreams , something far beyond an A6 ! He may be 50 years older, and 75kg heavier, but who cares about that in the LOS?

Sorry, not me..... I'm happily married.... but definitely not well-healed anyway... but thanks for considering!

Edited July 19, 2009 by Lopburi99

[jcon]

Stingray ; to avoid the work of changing the fuel pump, I advice you to make a measurment device, with different adapters, to measure the fuel pressure. This you can diagnose if the pump is defect or not. Most engines have a measurement point on the fuel rail for this. It's actually very simple to make from something like this:

7 bar fuel pressure?!?!?!?! can u imagine lol!!!

but yes, Datsun, an FPR with a gauge is always a good idea (or just the gauge itself placed as you mentioned).

stingray: how is the quattro system on that car? working fine? what happened to the front fenders are those 'cut-out' levres from a Range Rover????? or maybe a Merc???? poor Audi, it's a pretty car when left alone....

but anyway, good job on the diagnosis, and besides the fenders (which you probably didn't do, I'm guessing some Thai owner did it - or at least I hope it wasn't you), the car looks good. I will always have a soft-spot for Audis.... the German under-dog...

[stingray]

I tought already in the beginnin to buy a fuel pressure gauge. Had once a similar problem with a Hyundai Scoupe. so i bought a fuel pressure gauge in that time in Pattaya, where i living, in a Hardware Shop, opposite Foodland. Fitted the gauge right away in the Hyundais console, it even looked good and i could see immidently how much fuelpressurs is always on the system. But unfortunatly they not sale this fuelpressure gauge in Pattaya anymore. Proparly i'll get one next time i go to Woratchack in Bangkok. Thanks for all the advise. Yes the Quattro runs fine now. It makes a good pictures in my driveyard together with my Oldsmobile.

[ziiz996]

So what!?!

This thread keeps twisting like a detective story and in the end we don't get to know the murderer. dam_n it!

Did you fix it? What was the problem?

welo

Sorry to bring up the old thread, I love to rummage around the archives...

Yes, it's fixed now. new fuelpump wasn't ok (possible f..kt up by mecanic), so replaced it again together with the fuel pressure valve. Mecanic changed ignition coil as well (used one). This new used coil was not ok and cutting out the engine ocasionally. There was nothing wrong with the originale coil. So after i saw the original coil laying in the trunk i changed it back and the problem of "cutting off" was gone. I replaced the battery and theyr connectors to make sure starter motor turn fast enought, and overhauled the alternator (charging was ok, but bearring had strong noise). Fitted a simple volt meter in the car, so can watch allways the voltage. Changed all engine belts, and manything else. Changed all the suspenson parts, like bushes, joints, etc. Car runs fine now. Drive it occasionally, maybe 2 or 3 times a week, sometime to Bangkok. Bought this car quite cheap from a Navi Officer 6 months ago. But finally i spent about 100'k to fix everything. Painted the whole car for additional 23'k in black metallic ( it was navyblue before). This is a typical story when depend on local mecanics and a car wich never was take in care of before. So now ist almost like a new car.

Are You kidding me? Are you saying that it was the fuel pressure valve or the Fuel Pump?? Are you sure what the problem was???

[EvilDrSomkid]

Stingray, I am glad you finally found the problem and fixed it. That is quite a goodlooking 100Q C4 you have, and quite rare in Thailand. Especially, since its not an S4 or S6. I have an S6.

If you are looking for a mechanic who actually knows a lot about Audis and you are willing to go to BKK for this, let me know.

I know a place on Nawamin Rd where they know what they are doing. Do you speak Thai at all? The man does not speak English. He is honest, experienced and affordable.

Sign up on the Audiclubthailand site. These boys are very enthusiastic and can help if you need something.

Audi Quattro rules.

Edited July 21, 2009 by EvilDrSomkid