First day out with new motor...

[SnakeyesTx]

Would an oxygen sensor really cause something like this?

I got my car out of the shop, start it, and I notice it idles kinda rough. There's a cocktail of seafoam and xymol I believe to help clean up my fuel system since the car had sat for 2 months. They think maybe its a sticky injector but suggested I drive on it for a day or two and bring it back if things don't get better.

Anyway, driving it today I noticed a few things.

* Idle is pretty poor. In drive it lopes to where the whole car moves a bit in gear.

* close to WOT once in a blue moon I'll get a backfire.

* Acceleration feels very lethargic, moreso than I remember pre-engine swap. I believe it could be described as feeling like you're towing something. This generally gets better after 60mph.

* At freeway speeds everything is smooth and normal feeling.

* It took a long time for the engine to warm up too. My trip to school and back is about 30 miles and the temperature never made it to the 1/2 way mark. Close, but not on it. It was 52*F this morning so I didn't want to draw any conclusions with this.

* The check engine light was on. Shop assumed it was the oxygen sensor since coolant eventually did get there. Didn't put one on to soften the blow of my bill in case their assumption was wrong. I did a stomp test today and got a 1221 error code, which came up as "Oxygen Sensor"

What do you guys think? Would that sensor really be the root of all the other issues, or is it possibly something else? Your thoughts?

[31Hertz]

I can't see the o2 sensor causing all of these symptoms by itself. Both of mine had cracks in them when I replaced them. It made a big difference in the performance of the car and the economy, but it was not "super-rough" before that by any means, and it always got up to temp. There has to be more to it; with everything you went through to get an engine in the car... Your o2 sensor should definitely be replaced though. It sounds like a timing issue to me. Was the head off for any reason? Terminal plugs switched around? Large vacuum leaks/hoses detached... Bizarre that it operates as normal at highway speeds...

[fujioko]

That really sounds like a vacuum leak to me. Dose this shop work on BMWs often? I’ll bet any qualified BMW mechanic would recognize the typical lumpy idle and O2 fault as a vacuum leak.

Anyway I could be wrong.

Typically a vacuum leak will cause the idle to hunt. That is to say the tach will jump up and down a few times after you rev the engine. The idle will then become lumpy. The leak will upset the air/fuel ratio and trip the check engine light. The O2 sensor will show a fault because un-metered air is being consumed by the engine.

Good luck, hopefully you’ll have it sorted out soon.

[bsell]

That really sounds like a vacuum leak to me. Dose this shop work on BMWs often? I’ll bet any qualified BMW mechanic would recognize the typical lumpy idle and O2 fault as a vacuum leak.

Anyway I could be wrong.

Typically a vacuum leak will cause the idle to hunt. That is to say the tach will jump up and down a few times after you rev the engine. The idle will then become lumpy. The leak will upset the air/fuel ratio and trip the check engine light. The O2 sensor will show a fault because un-metered air is being consumed by the engine.

Good luck, hopefully you’ll have it sorted out soon.

Vacuum leaks can be found using carb cleaner sprayed along the intake gasket and other suspect joints while the engine is idling. Take your time and be thorough but don't soak the engine as that stuff is very flammable!

What about the air mass meter? Could there be some crud on the wire or a loose/cracked boot? Older rubber doesn't like be pulled around like happens during engine R&R. The cleaner test should help find a cracked boot.

If you are confident you have no vacuum leaks and the O2 sensor is kinda long in the tooth, I would recommend opening the wallet for a new one. I have seen O2 sensors bite the bullet during engine R&Rs, even when they were left in the manifold and handled gently.

I hope the guys got your cams timed correctly and the crank sensor is in the correct place. Either condition could cause a lack of power. Or it may just be the engine being 'tight' still. I would worry about this after you get the idle/backfire issue fixed. But if the cams or ignition timing is off, they might be causing the idle/backfire problem. Time for the shop to make good on their work IMHO.

Brian

[bsell]

I can't see the o2 sensor causing all of these symptoms by itself. Both of mine had cracks in them when I replaced them. It made a big difference in the performance of the car and the economy, but it was not "super-rough" before that by any means, and it always got up to temp. There has to be more to it; with everything you went through to get an engine in the car... Your o2 sensor should definitely be replaced though. It sounds like a timing issue to me. Was the head off for any reason? Terminal plugs switched around? Large vacuum leaks/hoses detached... Bizarre that it operates as normal at highway speeds...

Elevated engine speeds can hide some serious mixture problems. A mildly rich and or mildly retarded ignition timing will smooth out a rough idle caused by other problems but the richness and retarded timing bring their own symptoms (poor mileage, smelly exhaust/low power respectively).

I am concerned about the engine not heating up properly. Retarded timing can push the heat event of the ignition cycle into the exhaust manifold versus making heat (and power!) in the combustion chamber, hence the backfiring during WOT and cooler than normal water temp.

I hope the OP takes the car back to the shop that did the rebuild so they can make this square.

Brian

[SnakeyesTx]

Update : Well, I *really* should have known this was the problem since I go through this so often with my Camaro. I'm almost a little embarassed to say it. Sluggish, backfires, towing sensation, crappy milage.... BAD COIL. It was clearly fried on both sides of the insulated box and sometimes it would fire, most of the time it would ground itself against the head.

Good news since I don't have to take it back to the shop. Better news that its something I can remedy in 10 minutes. Sure, I had to spend 70 bucks and order another one which won't be here till Monday leaving me grounded, but I'll also be going back to the shop and having them get all 6 of my coils from my old motor back so I'll have 6 spares as well. I'll try to update on how well it runs after I get it in there. :D

[winfred]

i was about to suggest a **** coil/boot but i see you figured it out at the top of the thread, id do a oil change after you run out whatever crap they put in the fuel, i generally avoid most gas treatments due to the fact that the solvents can and do break up **** in the fuel rail and lines after the fuel filter so every thing gets washed past the injectors, a couple months will not effect gas in a closed container (like the tank)

[Milkboot]

You steal my coil, and i will take a sledge hammer to your rims, and put a narrow grill on the front end of your car :P

[bigtisas]

How come the coil went bad after the car sat for two months? Just want to understand the cause of the problem.

[SnakeyesTx]

These aren't the same coils that came out of my old motor, they were the ones that came with the new one. I'll be getting all 6 of my good ones from the old motor on Tuesday or Wednesday for spares.