#7 Cylinder Misfire

**Jessica C** · 01-03-2008, 09:14 AM

I'm looking for some help with my #7 cylinder misfiring. I've changed sparkplugs, sparkplug wire, and coils and the same message pops up on the computer tester saying the #7 cylinder is misfiring. I haven't dug any deeper yet from the coil to the computer to see if everything is working. All the plugs appear to be fine as in no corrosion or bent plug tines. I was wondering if anyone else has had the same problem or any suggestions. I'm pretty good at fixing and working on my own vehicles but I'm unfamiliar with the newer technology (i.e. wiring). I'm trying not to take it to a shop because I know they can be dishonest and charge out the ying yang because I'm unfamilier with the computers. Thanks!

**2001NBMZ28** · 01-03-2008, 10:06 AM

Haven't experienced it myself but P030X codes can be a pain to diagnose. There's a diagnostic flow chart for P0300 at www.gearchatter.com/viewtopic9365.php that might help, or at least let you know what you're up against. Sorry, not much help, maybe someone else will chime in.

**edcmat-l1** · 01-03-2008, 02:48 PM

It doesnt have to be ignition. Could be a bad injector, broken or bent pushrod, broken rocker arm, broken spring, burnt valve.
First check that it spark, then maybe listen to the injector with a stethoscope, although it can be working electrically, and be not flowing properly. So just cause its clicking doesnt necessarily mean its ok.
May wanna do a compression test, and pull the valve cover.

**Frost** · 01-03-2008, 05:24 PM

is the car boosted?

**Jessica C** · 01-03-2008, 05:44 PM

It isn't boosted. We did a compression check a little while back(about a month) on #7 and a few other cylinders and they all checked out around 170. The next thing I was going to do was check the injector and maybe change the fuel filter(it probably could use a new one anyways). As a side note the spark plug when I took it out was in good shape as far as wear and tear but it had a noticeably strong gas smell. This is the only reason why i don't think it's the injectors or fuel filter because it seems like it's getting gas, it's just not sparking. However it could be.?

Since the compression test came out all the same, does that help lean away from the internal parts(i.e. rods, valves)? I just don't want to pull the engine apart before I can afford to stroke it down the road.

**sunsetorangess** · 01-03-2008, 06:33 PM

Like said above check for spark and make sure it is, then your issue probly lies in the injector.
They can do some freaky stuff when there Bad. I had one that was stuck open, causing a misfire and a glowing manifold that would melt spark plug wires. Gas was igniting in the manifold.
J

**Jessica C** · 01-03-2008, 06:49 PM

thanks for the advice. we did check the spark plug for a spark and it was good so we'll check the injector. what's the best way to check an injector? is swapping a good injector from one cylinder to the bad one and see if the code follows it to the other cylinder?

**edcmat-l1** · 01-03-2008, 07:10 PM

Originally Posted by Jessica C

thanks for the advice. we did check the spark plug for a spark and it was good so we'll check the injector. what's the best way to check an injector? is swapping a good injector from one cylinder to the bad one and see if the code follows it to the other cylinder?

Without having some test equipment, thats probably your best bet.

**Jessica C** · 01-06-2008, 06:01 PM

Well we took a screwdriver to all the injectors using it as a stethescope and sure enough #7 was not sounding like the rest. So we took apart the fuel rail and popped out all the injectors and #7 was packed full of crap from the fuel tank. We took some carb and injector cleaner to all of the injectors and fuel rail and put it all back together and the car is running like a champ! No backfiring, no rough idle, no loss of power, just pure V8 music. Thanks for the help everyone and hope my thread helps out somebody else.

**0rion** · 01-06-2008, 09:47 PM

glad you got it figured out......just wish they all were that easy.

**Frost** · 01-07-2008, 01:29 PM

yeah congrats, all that garbage has a nifty way of making it to the end of the rail..

**Jessica C** · 01-07-2008, 08:28 PM

yeah it was pretty bad. the fix was easy but figuring it out wasn't. It took us at least 2 or 3 months to figure out what the problem was. We did everything from the spark plug, coil, wire, to even speculating the rings, rods, springs, and numerous other things. I'm just glad it was such an easy fix in the long run.

**BULLET_WS6** · 01-07-2008, 08:49 PM

Originally Posted by Jessica C

yeah it was pretty bad. the fix was easy but figuring it out wasn't. It took us at least 2 or 3 months to figure out what the problem was. We did everything from the spark plug, coil, wire, to even speculating the rings, rods, springs, and numerous other things. I'm just glad it was such an easy fix in the long run.

easy way to eliminate the other problems without spending money is how i did it... take 7 and 5 persay and swap the different components one at a time and if the problem moves cylinders you know its the last thing you swapped... thats how i trouble shoot my last misfiring...

**unospdklz** · 01-08-2008, 10:00 AM

yes....but you never siad the car ran rough or had a mis fire...when chasing the concern...when the compression checked out, that eliminated the internal engine components...thats when you start checking other areas...before replacing parts...swapping a coil or injector works but only if its running rough or missing...but its all good you got it fixed...

**shadowsnkx** · 08-13-2008, 08:45 PM

so I am having a similar issue. car runs fine at idle but is rough under speeds of 15+ mph. There is also a hum comming from the rear of the car.(fuel pump?) only code I see is p0307

**A RAIR 99** · 08-27-2008, 12:05 AM

Hmmm, Jessica C got lucky cuz I had a cyl. 7 misfire & it turned out I had not only bent, but broken a pushrod!!! It was a good thing cuz now I have an LS6 intake, cleaned-up/milled/painted heads, Comp Cams valvetrain upgrade kit (pr, spr, & ret.), P & P TB, cam, LT's/ORY, LS2 chain, & new oil pump, but after 14 months, I'll be able to drive it again tonight finally (God willing) & it only cost about $654987654646545 to fix it, too

Only another $550 for an FLP tune & I can break it again

**Sunset T/A** · 08-27-2008, 03:50 PM

Had this problem on my daughter's Saturn. Changed everything that you did. Finally took it to the dealer to check it out. Was an intake manifold gasket leak. I thought it was electrical, but a compression leak can cause a misfire too. Could be a head gasket leak also.