Misfire Problem (Very Puzzled - long)

[Adrian G.]

Here are the facts:

- Bought a 2000 M Roadster last fall with 48K miles, the car appears to be completely stock
- The car sat all winter and I started driving it this spring, shortly thereafter got the CEL light
- Bought the Peak tool and pulled three codes:
- 1)cylinder 2 misfire 2) Secondary air supply low cyl 1-3 3) Secondary air supply low cyl 4-6
- Reset all the codes and only the two codes for the air pump came back within a week or so.
- The secondary air pump was dead, replaced it and verified that it works upon startup and the codes associated with it (2 and 3) have not come back for a few weeks now
- The code for the cyl 2 misfire has not come back either, but the symptoms persist
- I replaced the original plugs(which looked perfect) and moved the coil and injector from cyl 2 to cyl 3 and 4 to see if the problem follows
- No oil in the spark plug holes, everything appears normal
- I don’t know how to test the coils, but I checked their resistance (ignition off) and the resistance is the same for all 6.
- The misfire code has not come back, but the symptoms persist

Symptoms:

- Every morning or only if the car sits for several hours and fully cools down, it runs very rough for about a minute or so.
- If I tap the gas, it seems like the car is chocking
- The idle however, stay nice and low and doesn't bounce or anything, during that minute, but it seems like for that one minute it is misfiring
- After about a minute it completely stops running rough and runs perfectly; the throttle response it normal
- Also after it warms up it run great

I don’t know what else to check or how to proceed. Any ideas?

[Ferris]

Ditch the PEAKE and buy and ODB-II cable and laptop software...

My initial thought is the coolant sensor but you'd more then the peake tool to see.

Also for shiets and giggles you can try to let the fuel system fully pressurize before starting and see if that fixes the problem. ie turn the car for a few seconds before starting.

[///MDex]

Symptoms:

- Every morning or only if the car sits for several hours and fully cools down, it runs very rough for about a minute or so.
- If I tap the gas, it seems like the car is chocking
- The idle however, stay nice and low and doesn't bounce or anything, during that minute, but it seems like for that one minute it is misfiring
- After about a minute it completely stops running rough and runs perfectly; the throttle response it normal
- Also after it warms up it run great

Cold / Rough Start issue. Totally normal. The whole backfiring thing you talk about first, I dunno.

[Adrian G.]

Ditch the PEAKE and buy and ODB-II cable and laptop software...

My initial thought is the coolant sensor but you'd more then the peake tool to see.

Also for shiets and giggles you can try to let the fuel system fully pressurize before starting and see if that fixes the problem. ie turn the car for a few seconds before starting.

Are you talking about the Coolant Temperature Sensor? Would that have it's own code if it was faulty? Do you know if it is easily accessible?

[Hugo]

Vaccuum leak.

Tighten down your intake manifold. Shoot brake cleaner where the manifold meets the head, see if it stops/revs higher as the manifold sucks the brake cleaner in.

[Adrian G.]

Vaccuum leak.

Tighten down your intake manifold. Shoot brake cleaner where the manifold meets the head, see if it stops/revs higher as the manifold sucks the brake cleaner in.

Wouldn't a vaccuum leak have an affect on the engine at all times and not just for a minute on cold start up?

[Ferris]

The coolant sensor reading a wrong but valid value wouldn't trigger a fault. The DME uses coolant temp to help determine a cold start vs warm start. Though as MDEX said there is a cold start TSB and it could very well be that.

Like I said it may help to hook up with someone with and ODB-II converter and a laptop to help eliminate that. Plus you could see if the idle smooths at the open loop closed loop switch. It's a lot more data to help narrow things down.

[JBgotM]

Cold / Rough Start issue. Totally normal. The whole backfiring thing you talk about first, I dunno.

yep, i have the same thing and even posted a video clip of it. The cars there, spits and spudders for aboutr 45 seconds then smooths out. If I try to drive it in the first 45 seconds or so it will try to choke and die. I always let it run its course then take off. I drive it gently for about 5 minutes then don't really get into it for about 10 minutes.

[Hugo]

Wouldn't a vaccuum leak have an affect on the engine at all times and not just for a minute on cold start up?

Possibly, unless the leak is caused by a veri small defect in a seal that expands when the engine heats up and the leak is then plugged.

[///MDex]

yep, i have the same thing and even posted a video clip of it.

Did Nick tune that out for you? Mine fires right up with a strong woof, and idles perfectly now. Hence my debut post: Fixed: Cold Start Issue

[Adrian G.]

Has anyone here replaced the coolant sensor? What were your symptoms?

[StouffvilleZ3]

Coolant temp sensor is very cheap and easy. It's located beside the overflow canister on the passenger side of the rad and it's actually threaded into the rad. You could try to replace it, can't hurt. You just have to drain the rad to do it which by the sounds of your post you're more than capable of. It would be wierd for this to be the issue though.

It will not be a vacuum leak. A vacuum leak (if big enough to affect the operation of the engine) will always be felt with seemingly poor throttle response. What actually happens it that it deosn't respond untile it gets fed the fuel it needs to burn the unmetered air leaking into the intake tract.

Plugs were all bown or black to the colour?
Throttle response and power are completely normal when warm?
No CEL's for a missfire since?

It could be just the cold start issue. The remedy for this is to install a blower!

(Just kinddin) Try a Shark injector that will richen up the mixture a little or just deal with it.

Just so you know, if you had noticed reduced power both warm and cold I might have suggested the cats might be clogged up. They have a habit of biting the dust right around 80K miles. Usually just after warranty!

[///MDex]

It could be just the cold start issue. The remedy for this is to install a blower! (Just kinddin)

-cringe- I hope I didn't sound shietty with my statement

[Adrian G.]

Thanks for replying.

Coolant temp sensor is very cheap and easy. It's located beside the overflow canister on the passenger side of the rad and it's actually threaded into the rad. You could try to replace it, can't hurt. You just have to drain the rad to do it which by the sounds of your post you're more than capable of. It would be wierd for this to be the issue though.

Why do you say it would be wierd for this to be the issue?

It will not be a vacuum leak. A vacuum leak (if big enough to affect the operation of the engine) will always be felt with seemingly poor throttle response. What actually happens it that it deosn't respond untile it gets fed the fuel it needs to burn the unmetered air leaking into the intake tract.

I didn't think it would be a vaccuum leak for the same reason.

Plugs were all bown or black to the colour?
Throttle response and power are completely normal when warm?
No CEL's for a missfire since?

Plugs looked good..not much color...somewhat tan
When the car is warm the throttle response is great and the car runs like a beast.
No CEL's for a misfire since March.

It could be just the cold start issue. The remedy for this is to install a blower!

I have been thinking of a way to convince the wife that I need one...She wants one for her car :-)

(Just kinddin) Try a Shark injector that will richen up the mixture a little or just deal with it.

Just so you know, if you had noticed reduced power both warm and cold I might have suggested the cats might be clogged up. They have a habit of biting the dust right around 80K miles. Usually just after warranty!

Full power when warm...is there a way to check if the DME has been reprogrammed?

[clintjg]

Did someone say coil packs? I see that you swapped them out but they have been know to do some funny things and cause some strange issues.

[JBgotM]

Did Nick tune that out for you? Mine fires right up with a strong woof, and idles perfectly now. Hence my debut post: Fixed: Cold Start Issue

nope, being in Florida and having warm weather, it never did it. As soon as I got back to Ohio it did it again.

[Adrian G.]

Did someone say coil packs? I see that you swapped them out but they have been know to do some funny things and cause some strange issues.

Anyone know how to test the ignition coils?

[JBgotM]

Anyone know how to test the ignition coils?

well, to me i would say if you aren't getting a consistant misfire then the coils are fine. if one cylinder isn't firing you would know.

[clintjg]

Agreed. Maybe not the coils themselves, maybe a loose/corroded connection?

[Adrian G.]

well, to me i would say if you aren't getting a consistant misfire then the coils are fine. if one cylinder isn't firing you would know.

My thinking is along those same lines as far as the coil and the injectors...so needless to say I am somewhat stumped...

[JBgotM]

roughness at cold start = par for the course

just don't drive it for the first 30 seconds or so