Trent13

Bought a new distributor cap and a mechanic put it on. Ran rough, so I took it back. He took it off, then put the old one back on and it ran great. But returned the cap and got a new one. My gramps took it back to get the new one put on and it still runs rough. Don't understand. Got new spark plugs as well, a new module. Check engine light comes on as well. But that's because of H02 sensor and EGO not switching. Anyone know why it would be running rough? It starts right up and runs but rough. Has cut off on me twice as well. Will take it to another mechanic but if it's something simple that I could do.. I would do it. Anyone know?

Urambo Tauro

Welcome!

The fact that it runs "great" with the old cap tells me that your new caps are either faulty, poor quality, or an incorrect part. Also, it's best to replace the cap and rotor at the same time, preferably with matching parts from the same manufacturer, just to help rule out any discrepancies between the two.

I started to suspect a problem with old spark wires having a bad connection, but that doesn't explain why it runs better with the old cap. You've pretty much narrowed it down already.

Is the car overdue for a tune-up? You've already started part of it; might as well finish the rest.

mjr46

stop shopping at auto zone and buying the valucrap craft parts

dawson1112

First thing I would do is take care of that check engine light. What code did it pop up? I think there is about 10 different 02 codes it can throw.

02 codes are not always an indication of a faulty 02 sensor, you could have a vacuum leak, dirty MAF, weak fuel pump, faulty fuel pressure regulator etc. Even a leak in the exhaust before the 02 sensor can give you a lean reading. Its just telling you that it has reached its adaptive fuel trim limits.

Trent13

88 orangepeel notch

If both banks show lean, I'd start looking for a broken, disconnected vacuum line. Maybe one was inadvertently pulled off or took a hit and cracked, allowing unmetered air in.

dawson1112

So your lean on both banks, look for vacuum leaks. Those lean codes mean that the ecm has reached its fuel trim thresh hold and can not add any more fuel. Now even though it indicates lean, that is just code for the computer to add fuel. But if the ecm has reached its maximum fuel trim thresh hold, that means it is dumping an excess amount of fuel trying to remedy what it sees as a lean problem. Indicative of unmetered air entering the combustion chamber, or exhaust leak.

While it could be faulty 02 sensors , and likely bank 1 sensor is bad because your seeing a switching problem, a quick search for the vacuum leak is where I would begin. A lot of times the vacuum hoses on the under side of the upper intake become cracked or rotted. A smoke test is the easiest way to find a vacuum leak, but you should visually inspect all the vacuum lines.

Failing to find a vacuum leak, I would next move on to the 02 harness and look for broken, melted, or frayed wires/ corrosion at the plugs even.