3.0 cold start misfire. What can it be?

[Shagy30]

Hey guys I am new to this forum but not new to Audi's. I recently bought a 2005 A4 3.0 USP 6 speed. I really love the car but it has been giving my some grief.

It is misfiring on cold start. It misfires for a few seconds then evens out. It does not misfire after the initial cold when the car is shut off and restarted. If the car sits for over night it will misfire the next morning. It has good power and runs smooth. Only misfires on cold start.

What i have done to diagnose the problem is replaced all 6 coil packs and spark plugs, replaced the MAF checked the wire harnesses for the coil packs and checked for vacuum leaks and replaced vacuum hoses as needed.

I thought it might be a head gasket issue but it is affecting all of the cylinders and the spark plugs are not contaminated. They all look good. It will occasionally throw a random misfire code and misfire codes for all 6 cylinders. Otherwise there are no other codes.

Can it be fuel related? Maybe fuel pump or FPR? Don't know what to do next. Has anyone else had this issue? Any insight is greatly appreciated.

I have done a search and couldn't find anyone with the same problem as me.

[cschuster]

Sounds like one or more few small things. Could be a clogged fuel filter - although that would be an issue when motor is hot too. You mentioned that you replaced the vacuum lines, but what about the PCV and breather hoses? That would cause misfires as well. A bad coolant temp sensor can also cause cold start issues (engine doesn't know if its cold or hot and mixes fuel/air incorrectly).

That should get you started. Don't give up!

[Shagy30]

Thanks for the reply. I havent checked the PCV yet. I guess that is my next step along with a new fuel filter. Is there an easy way to check if the coolant temp sensor is bad? Or is it a cheap easy fix?

[deyrag]

Cheap, yes. Easy,not so much.

[ChevSoAmazin]

iJust recently bought a 3.0 & iThink I'm having the same issues. iUploaded a video so that u can let me know if this is the same way yours sounds. I'm taking her back to the dealer on a few days. http://youtu.be/LkwAMgDBICs

[cschuster]

Is there an easy way to check if the coolant temp sensor is bad? Or is it a cheap easy fix?

If you have a code reader with a live monitoring function, you could see if the coolant temp is bouncing around or obviously wrong. You should get CEL if it is out of range. May as well replace it anyways just to rule it out. Cheap, yes. It's not difficult, more of a PITA.

http://www.audizine.com/forum/showth...erature-sensor

[SJorge3442]

If you have a code reader with a live monitoring function, you could see if the coolant temp is bouncing around or obviously wrong. You should get CEL if it is out of range. May as well replace it anyways just to rule it out. Cheap, yes. It's not difficult, more of a PITA.

http://www.audizine.com/forum/showth...erature-sensor

Also, the CTS tends to make the temperature gauge read irradically.

I would check your PCV system out. I would bet that you probably have a cracked hose causing the cold misfires. That caused some cold misfires for me.

[Furly]

pull your spark plugs out, all of them, and look inside the cylinders with a flashlight.

if some of the pistons look like they've been steam cleaned, you have a head gasket issue.

the symptoms are exactly how a 1.8T with head issues behaves. so i'd start there. it may be similar on 3.0

[Gf Jon]

I had similar problem with my 3.0 but with very slight irregular mis at idle when warm almost unnoticeable but could hear it from the tailpipes. Wasn't enough to throw a fault code.
I checked my variable intake flap and actuator. It had jammed and the flap was damaged. So temp I have removed the flap as I don't want any plastic bits going in my engine and just replaced the actuator to seal the manifold.
The upshot is even running without it the miss has completely gone ! The car is idling perfectly now from hot or cold. I am in the process of trying to find a decent but used complete inlet manifold to replace asap.
Might be worth checking this on your car ??

[imnuts]

I would guess that it's fueling related. Does it do the same thing if you turn the key to ON for a few seconds before starting?

Sent from my Moto X

[Shagy30]

So I took a look at the PCV and breather hoses today. All look good. No vacuum leaks and no lean codes.
I took out the spark plugs earlier when I thought it might be the head gasket. All of the pistons look like they have black on them.
Also my temp sensor looks brand new and the gauge works the way it should. I think it was replaced by the previous owner.

[Shagy30]

I had similar problem with my 3.0 but with very slight irregular mis at idle when warm almost unnoticeable but could hear it from the tailpipes. Wasn't enough to throw a fault code.
I checked my variable intake flap and actuator. It had jammed and the flap was damaged. So temp I have removed the flap as I don't want any plastic bits going in my engine and just replaced the actuator to seal the manifold.
The upshot is even running without it the miss has completely gone ! The car is idling perfectly now from hot or cold. I am in the process of trying to find a decent but used complete inlet manifold to replace asap.
Might be worth checking this on your car ??

Now that you mention it I think that my car has a slight irregularity at idle. I can hear it from the exhaust. How much do I need to take apart to check the intake runner?
Why are you looking for a used intake manifold? Is the plastic runner not sold separately?

[Shagy30]

I would guess that it's fueling related. Does it do the same thing if you turn the key to ON for a few seconds before starting?

Sent from my Moto X

It seemed to be better if i kept the key on longer for a little while but now it is misfiring no matter how long i have the key on.

[imnuts]

The runner can be purchased separately from the rest of the intake, but it's still a couple hundred dollars. If it were the issue though, I'd think that it would do it all the time, not just under a specific condition.

The temp sensor could still be bad despite a good cluster reading. The sensor has 2 thermocouples, one for the ECU, one for the cluster. The ECU thermocouple may be bad causing false high readings for the ECU until it warms up. You'll need an OBDII scanner to read the engine reported temp to verify though.

Sent from my Moto X

[WB650]

It's your head...calling it now...I have a 1.8T but I had exact symptoms last Sept and had to get head replaced last month due to it being cracked, the gasket didn't go. During the month of Dec I had to replace the coolant temp sensor, thermostat, water pump and coolant line from turbo, the final mechanic I took it to said he would have told me from the get go it was the head due to the back pressure from the system

[imnuts]

The 3.0 doesn't have the head cracking issues like the 1.8T. Also, given the carbon the OP mentioned on every piston and in the cylinders, I'd guess against it. There has only been one bad head on a 3.0 that was leaking, and the car overheated and needed a new gasket AFAIK.

Sent from my Moto X

[WB650]

LOL well then I retract my certainty and say maybe possibility...I'd have it pressure tested...though I guess if no clean cylinders then its out...crazy how exactly similar it is, misfire on cold start for like 10 secs then it smoothes out and drives fine

[Gf Jon]

Sometimes people sell them used seperatly but mostly as complete manifold. I am going the complete manifold route just incase the flap has worn or damaged the surfaces it runs on inside the manifold. It's only available from main dealer as complete manifold unit..., I've been informed around £1400!
Easy to check it ; remove/ pull off the black plastic cover over the drivenelt at front of engine. You will then see a twin vacuum actuator drive unit with vacuum hoses going to both sides. Be careful taking off vac hoses as connection nipples can go brittle and break. I took vac pipe off at T piece to save breaking any.
The twin vac unit is held in place by two torx screws into the manifold. Remove the two screws and carefully pull the drive unit away. You will then see a black disc which is the head of the cylindrical flap. I used a pair or long nose pliers just to grip centre to slide it out. The rad/ bonnet catch mechanism is in the way to get it right out as it is the same length as the inlet manifold but it's enough to inspect it.
I read that you have to remove the inlet manifold to pull it out fully but I managed to do it by removing the bonnet catch assembly.... 4 bolts ! Very tight and you have to take care but it did come out successfully.
It takes about ten mins to get drive unit off so easy to check.

[Shagy30]

thanks for all of the great info guys! this is why i love this forum.

I had some time to work on the car today. so a little update.
I went to start the carthis morning and it didnt want to start. i had to crank it over several times for it to start up.
It was sputtering but didnt start. As if there wasnt enough fuel or too much. It did start eventually. Same thing. Misfire for a few seconds then evened out and was fine.
I changed out the fuel filter even though i dont think i needed to. The fuel in the "old" filter was clean. Looked like some had already replaced it.
I pulled out the intake runner as far as I could in order to see if it was damaged and it looked good. A little dirty but i didnt see any signs of damage.
I pulled the spark plugs in order to check the head theory more thoroughly. All of the pistons have carbon on them. However cylinder #5 (driver side center) had the least amount of carbon.
Cylinder #6 (driver side next to fire wall) seemed to have the most carbon.

Not really sure what to do next. Thinking that I should do the CTS next but it looks like someone has already replaced it. Any help is very much appreciated.

[imnuts]

Shagy30, do you ever see white puffs of smoke coming out of the exhaust when it is hard to start, or are you loosing any coolant? While I don't think it's a head issue, if either of those are happening, it could well be, despite the carbon buildup.

As far as other things to inspect, when is the last time the plugs were changed, what type of plugs were put in, and what were they gapped to? What is the resting voltage of the battery after the car has sat for a little while?

[Shagy30]

Shagy30, do you ever see white puffs of smoke coming out of the exhaust when it is hard to start, or are you loosing any coolant? While I don't think it's a head issue, if either of those are happening, it could well be, despite the carbon buildup.

As far as other things to inspect, when is the last time the plugs were changed, what type of plugs were put in, and what were they gapped to? What is the resting voltage of the battery after the car has sat for a little while?

There is some smoke that comes out when it is on cold start But only for a second. It has NGK plugs. They are pre gapped.

Looks like all signs point to head issue. Opened the coolant reservoir and had my brother brother bring up the RPMs. There is a significant amount of bubbles in the reservoir.
The tail pipes get moist and after a while start to dip water. All of these things make me think that i either have a bad head gasket or cracked head. I dont know if the car was overheated. Previous owner didnt tell me anything about that. What do you guys think? Sound like a head issue?

[Shagy30]

Dont know why it is giving me a random misfire though and on all cylinders. Shouldnt it be only giving me misfires on the cylinders that are affected by the head issue?
Starting to go crazy here trying to figure this out. What is the best way to check if it is head related? Leak down test?

[imnuts]

Taking the cap off while running will likely cause bubbling as the system is meant to run pressurized. I'd get a coolant test kit and see if the system holds pressure. If it doesn't, start looking for leaks. If you don't see dripping anywhere, take the plugs out and look into the cylinders for liquid.

Sent from my Moto X

[Shagy30]

Taking the cap off while running will likely cause bubbling as the system is meant to run pressurized. I'd get a coolant test kit and see if the system holds pressure. If it doesn't, start looking for leaks. If you don't see dripping anywhere, take the plugs out and look into the cylinders for liquid.

Sent from my Moto X

The system holds pressure. If the car sits over night and cools down I can open the cap and it will release the pressure. I will have to get a camera or something to look in through the spark plug holes.

[Shagy30]

Just a little update on my misfire issue. My suspicion of blown head gaskets has been confirmed. Dont know if the head is cracked but the gaskets are leaking for sure. Looked into the cylinders and could see coolant entering cylinder #5 at a high rate. I have found a low mileage engine locally for a good price and will be swapping it in. Wish I could do the 2.7t swap but it is out of my budget right now and this car is a daily driver. I am thinking about parting out this engine but not sure if anyone would want parts from it. Maybe i can at least sell the intake manifold to some one that needs it.

[SJorge3442]

Just a little update on my misfire issue. My suspicion of blown head gaskets has been confirmed. Dont know if the head is cracked but the gaskets are leaking for sure. Looked into the cylinders and could see coolant entering cylinder #5 at a high rate. I have found a low mileage engine locally for a good price and will be swapping it in. Wish I could do the 2.7t swap but it is out of my budget right now and this car is a daily driver. I am thinking about parting out this engine but not sure if anyone would want parts from it. Maybe i can at least sell the intake manifold to some one that needs it.

What do you mean you find coolant leaking in? Using a camera can you actually see it dripping in?

[Shagy30]

What do you mean you find coolant leaking in? Using a camera can you actually see it dripping in?

yes exactly. Using a camera I could see coolant leaking into the cylinder after the engine has been warmed up. If it sits over night there is a "puddle" of coolant in the cylinder.

[SJorge3442]

yes exactly. Using a camera I could see coolant leaking into the cylinder after the engine has been warmed up. If it sits over night there is a "puddle" of coolant in the cylinder.

That's what I figured, but wanted to confirm. Why don't you just source a new head and slap it on? Replacing the whole engine seems crazy for a simple head gasket issue.

[Shagy30]

That's what I figured, but wanted to confirm. Why don't you just source a new head and slap it on? Replacing the whole engine seems crazy for a simple head gasket issue.

looked into doing that but havent found a head of a decent price. i think that this engine has been seriously over heated. the passenger side head gasket has signs of leaking as well but not as bad as the driver side. Which makes me think that both heads are either warped or cracked. Would have to pull both heads off to inspect. The motor I found has only 78k miles on it and its a pretty good price.

[Shagy30]

Btw thank you SJorge3442 for offering to lend me your cam lock tool. I will need it for when i do the timing belt on the new motor. I also wanted to see if you have the cam adjuster tool or know someone that does.

[SJorge3442]

Btw thank you SJorge3442 for offering to lend me your cam lock tool. I will need it for when i do the timing belt on the new motor. I also wanted to see if you have the cam adjuster tool or know someone that does.

The tool set I have contains the cam adjuster socket. The only thing you will need is a set of snap ring pliers so that you can properly aligned the eccentric idler. You need to adjust it so that the tool you're using is in line with the water pump pulley.