Justice10

So, I'm keep having this issue for a month now of cylinder 6 keeps misfiring, catalyst system efficiency below threshold bank 1 & 2 and system to rich Bank 1. I've already replaced the spark plugs (3 months ago), distributor (3 months ago), both catalyst (4 months ago), 02 sensors (4 months ago) and fuel injectors (3 months ago). The fuel pressure and the fuel pump are good. There aren't any vacuum or head gasket leaks. There isn't any backfire or heavy engine rattle when in idle but with all of that. I searched on the web and found out that most misfire problem comes from the timing belt somehow slipped back messing up the firing order or something like that. Which also can cause more fuel to be put in, causes misfire and not all of it can be exorcist in the catalyst which let the o2 sensors go off and check engine light comes on. I just want some guidance on how I should deal with this, what other thing I should also be looking at and what should I also be looking for while I'm checking the timing belt.

Justice10

Update: I've checks the timing belt and its good. There was no damage, also each one of the gears was on point. While at it I also change my camshaft because i had a spare part in the car. But it still misfires on cylinder 6. At this point im just gonna go to a mechanic and let them deal with it.

mandyfig

You may have a bad ignition coil...good luck with your search.

Margate330

That is what I'm thinking too.
Can try moving to ignition coil to different cylinder and see if the misfire code follows to that cylinder

A misfire from bad coil will slightly raise fuel trims but not enough to throw a code.

Please hook up a scanner and show the fuel trims- need to see bank 1 & bank 2 for short term and long term fuel trims.

Car should be at idle and fully warmed up and all accessoried off for the numbers to be meaningful.

Battery voltage while at idle should be above 13.4V.

Justice10

Trust me I did that and its still giving problem. I change out all spark plugs, ignition coils, and fuel injectors. I'm thinking about its the fuel pressure.

I don't have a scanner that shows the fuel trims so that's why i would have to go to a mechanic to see if that's the problem. I went to them early this year because my car had problems to start with 1 crank. Maybe they did something like increase my fuel pressure for some reason.

Margate330

Hi friend, I always tell people like us that have older cars is they must have their own scanner that can read codes and live data.

Without it you are flying blind and replacing parts that don't need to be and chasing ones tail in circles.

First thing a mechanic will do is plug in a scanner and pull codes and watch live data.

And they charge for that even if it's hidden in the bill when parts are replaced. 😀

Justice10

No, its not that i do have a scanner it just the connection piece that connect to the car has been damaged. I lend it to my brother, and he give me back damaged. Now im just on hold waiting for another suitable one. For the time being I'm using this small FIXD scanner and it doesn't do much.

Margate330

I realize times are hard right now but these difficult and more complex troubleshooting jobs require a scanner with live data.

It's what a mechanic would do.

By comparing fuel trims from bank 1 to bank 2 it can quickly be determined if it's a problem that affects both banks for the fuel richness code.

The fuel pressure is regulated in the fuel pump assembly in the gas tank but this does not work with the other code for cylinder 6 misfire.

Good luck friend, plz keep us posted on your progress.

Justice10

OK Update. I haven't reached the mechanic shop yet because he closed for the week. So, I did some snooping around in the hood and one replacement and I think I found the problem. Cylinder 4 fuel injector might be the cause of making cylinder 6 back firing. It looks like it wasn't opening enough that the fuel pressure for 6 was higher that it should be. Now that's changed I haven't seen Cylinder 6 did a backfire. But now it looks like cylinder 6 fuel injector got damaged even though i replace it last week because im getting a P0172 code "System Too Rich bank 1". Either that or i have to change out that air sensor which i cleaned 2 days ago. Might as well do both to be on the save side. But now I'm just going to do some more research before acting.

Felix

Non of the cylinders are going to interfere w/ one another whether its fuel or igniton related...The different cylinders have their own injectors as well as coils/plugs.....Its not like you have a cheap set of plug wires that'd possibly arc over to a different cylinder, like 7&8 on a 289, wheres the '82 + later ones use the 351 firing order.....