Rough running and P0307

[Daedalus]

Just got it back from the cam weld, after some starting problems that turned out to be the crank pos sensor wiring, I am dissapointed to find that my SHO runs very poorly. Ran OK before the weld, now it runs rough at idle and sometimes at speed. It throws a P0307, which I know is Cyl #7 Misfire, but I've replaced the coil with a known good one, and tried a new spark plug but no joy. After a code reset, it idles rough, I can drive it and it seems ok, but the first hill I climb or WOT takeoff the SES light starts flashing. Tremendous lack of power felt rather suddenly.

I need this car to get to work and back; can someone please help me out?

Thanks,

- Dan

 

[Daedalus]

Update, #7 is sparking, I pulled the coilpack and put the old sparkplug on it, grounded it, and it is definately sparking. A fuel problem perhaps?

 

[Mr Anonymous]

First, verify the spark intensity. You don't need a plug in there, just pull the coil with the engine running and hold it about 1/2" away from the valve cover and watch the spark jump from the coil to the valve cover. Do the same with another coil to compare intensity.

It's very common for a weak coil to generate a spark, but insufficient for proper combustion.

If that checks out OK, next thing to try is move coil #7 to cylinder # 5 and coil #8 to cylinder #6. It's also common for a weak/failing cylinder 7 or 8 coil to interfere with the MAF sensor signal and cause rough running and stalling.

If all that fails, try cleaning your MAF sensor.

Keep us posted.

 

[Daedalus]

Thanks for the advice, unfortunately it's too dark to do much work now so I put the appearance cover and hardware in the trunk.

When the cam weld was done, I had 8 brand new coils and spark plugs installed, so I had initially overlooked the possibility that one of my new coils was bad, but that would certainly simplify things. I have 8 known good (or at least "well, they worked last time I used 'em") coils so I certainly have spares if one of my new ones is bad. I'll try the 1/2" spark test and move the coils around like you suggested tomorrow morning, thanks.

Would you say that the car is "safe" to drive - "safe" meaning, will I do damage to the car just by driving it?

 

[ThatShoGuy]

Thanks for the advice, unfortunately it's too dark to do much work now so I put the appearance cover and hardware in the trunk.

When the cam weld was done, I had 8 brand new coils and spark plugs installed, so I had initially overlooked the possibility that one of my new coils was bad, but that would certainly simplify things. I have 8 known good (or at least "well, they worked last time I used 'em") coils so I certainly have spares if one of my new ones is bad. I'll try the 1/2" spark test and move the coils around like you suggested tomorrow morning, thanks.

Would you say that the car is "safe" to drive - "safe" meaning, will I do damage to the car just by driving it?

i wouldn't drive it if i was you. if its a spark problem you would be washing the cylinder walls down with fuel. which that aint good!

idk tho its your car but if it was mine i wouldn't drive it till it was right again!

 

[Daedalus]

Ok here's the latest update: I checked all 4 front coils, and they all threw a brilliant spark a distance of at least 1/2 inch. I swapped them around like Mr. Anonymous suggested, reset the SES light, and drove it a short distance - popped the SES light, P0307, misfire on Cyl 7. So other than the MAF cleaning which I will do shortly, what comes next in the troubleshooting cycle?

Thanks for all the help so far.

- Dan

 

[KickerBeast]

Well, if you switched the front and rear bank coils and still have a missfire on cyl 7 then I would start looking at wiring or injectors. You could have a broken wire to cyl 7 coil from having the valve cover off. I would start there. If it ran fine before, then I would go back and check everything. I'm not saying that anything got screwed up when the cams were welded, but things were disturbed and something could have gotten accidentally broken.

 

[venom]

Ok here's the latest update: I checked all 4 front coils, and they all threw a brilliant spark a distance of at least 1/2 inch. I swapped them around like Mr. Anonymous suggested, reset the SES light, and drove it a short distance - popped the SES light, P0307, misfire on Cyl 7. So other than the MAF cleaning which I will do shortly, what comes next in the troubleshooting cycle?

Thanks for all the help so far.

- Dan

Did you check the plug going to the injector for #7?

Also you could:

Remove the coil from #7 with the engine cold. Start the car for just 10 seconds or so. Quickly remove the plug and see if it is wet.

 

[Mr Anonymous]

Did you check the plug going to the injector for #7?

I think Beaker just hit the nail on the head. :sun:

Re-checking your sig in your first post I see you have a '99.

It's very common for the little clips that secure the connectors to the injectors on '99s to break off when being disconnected (such as most cam welders do to remove the lower intake to clean it).

Definitely check the injector connector for cyl 7 which will be located directly behind the intake runner for that cyliner. It may take a little meandering with one finger from each side to get in there.

 

[Daedalus]

You guys are amazing.

It was the injector plug, it was unplugged but in close enough proximity to the socket that I hadn't noticed it before. Plugged it in, reset the codes, and she runs better than I've ever seen her run before.

Thanks so much for your help. I think I'm one of the happiest SHO owners in Ventura County right now.

 

[venom]

I think Beaker just hit the nail on the head. :sun:

I need to figure out how to type and *sound* like beaker... Speaking of - I don't think you have been named..

Glad it worked out.

 

[Mr Anonymous]

I need to figure out how to type and *sound* like beaker... Speaking of - I don't think you have been named..

Glad it worked out.

Pretty much everyone just calls me A__hole.

I'm going to stop at the cane store this morning in hopes that everyone will just start calling me House.

 

[KickerBeast]

House is awesome!!! It's the way I feel inside everyday....