Running rough

I have a 98 ford explorer just changed the alternator and now its running rough also it sounds louder than normal from the muffler. im clueless anyone got any advice what the problem can be?

If you replaced the alternator it means the battery had to have been disconnected.

When you disconnect the battery it erases the adaptive memory in the computer. This means the computer has to re-learn all the operating parameters all over again. This is done by driving the vehicle in a normal manner.


after tons of reading i found the same solution. so i took the negative cable off for about 10 or 15 minutes then put it back on,but was no change in the way its running…but also just read some forums and some comments was that it might take longer for it to reset…so ill take your advice and drive it for a while…thanks for the imput from what i have read your rite on the money.

Assuming you’ve already tested the new alternator that it is functioning properly. Sometimes the new ones right out of the box can be bad too. Yes, give it a week to re-learn before deciding there’s another problem. I assume you took the battery negative connection off when the engine and car was turned off. You probably know to never remove either battery connection when the engine is running; that can damage the car’s electronics and the alternator itself. Besides the good comments above, it’s hard to see how replacing the alternator could cause these symptoms. Cross your fingers, it’s probably just the ECM needs to go through its relearning process. If not that, probably you accidentally removed or broke some electrical connection in the engine compartment in the process of replacing the alternator.

One more thing. Did you remove the battery neg connection during the alternator replacement? If not, you may have caused an electrical glitch. Unlikely, but good to consider if the problem continues. There may be some other circuit that got damaged.

Odd… Really?

I have a thread going on diagnosing my missing engine. Scan says 1 and 6 are misfiring.

I just bought this car. It has brand new alternator according to seller and it appears new.



I would say there’s a chance it’s related

When replacing the alternator, the battery was most likely disconnected. When disconnecting the battery, all codes (and the check engine light) are cleared

However, the pcm is constantly checking itself. And when the conditions have been met, that check engine light and the codes will reappear

While I’m not sure this is what happened, it’s possible the seller knowingly sold his problem child to you, BEFORE the check engine light reappeared. It’s somewhat unscrupulous, but it does happen, from time to time.

Did you buy this car from an individual, or from a dealer?

Here in California, the seller is technically responsible for getting the car smogged.

If the car has a check engine light on and is clearly misfiring, it will fail the smog inspection.

If the car has too many incomplete monitors (as is the case when disconnecting a battery), it is not ready to be smogged. This is not a failure, just a “not ready rejection”

Since you “just bought” the vehicle, I would think about contacting the seller

You’ve got absolutely nothing to lose

Nah they are off the hook. They said it could be anything and they thought the block was cracked. I bought it for very cheap given they thought it was bad condition.

Given my familiarity Im sure the block isnt cracked so I got a good deal. I just have to figure out the firing out problem.

So how do you fix this codes issue? Will disconnecting the battery again make it reset and possibly fire correctly?

Most consistent misfire Ive ever encountered. Usually occasionally even rarely but at least a few times you get a sputter and the cylinder fires.

This consistently and evenly misses.

It takes about 10 seconds of battery disconnection to reset the computer, sometimes less depending on parasitic drain.
What’s the error code (Pxxxx)? One particular cylinder missing or random misfires?
I would do a compression test.