More misfire woes
11-30-2008, 12:25 PM
#1
On The Tree
Thread Starter
iTrader: (1)
Join Date: Jan 2007
Posts: 178
Likes: 0
Received 0 Likes
on
0 Posts
More misfire woes Just cant seem to get rid of this misfire so heres a quick summary of whats been done, 3 months ago replaced the opti with a partsladi opti fixed the misfire. 2 weeks ago misfire came back on cylinder #7 bad plug, so i replaced the plug and wire and that fixed the misfire for the time being, a couple days later the misfire was back!!! but only sometimes, and sometimes it ran perfect and it did not seem to be based on if the engine was cold or warm, it just ran good when it wanted to. so of course it is throwing more codes now its cylinder 8 mis, i check the wire seems ok then erase the code to see if it comes back....now its saying i have a p0300 code and so it switches between the two codes p0300 and p0308 but never both at the same time....getting really frustrated.. 
any ideas??? BTW o2 sensors have been replaced recentley.
any ideas??? BTW o2 sensors have been replaced recentley. 
11-30-2008, 09:11 PM
#4
On The Tree
Join Date: Nov 2008
Location: Houston, TX
Posts: 162
Likes: 0
Received 0 Likes
on
0 Posts
same problem here Hey man i feel your pain just bought my 97 t/a and i took it to autozone and the p0300 code came out twice??? Hey quick question im new to v8s how did you find out the plugs that were bad??
11-30-2008, 09:20 PM
#5
On The Tree
Thread Starter
iTrader: (1)
Join Date: Jan 2007
Posts: 178
Likes: 0
Received 0 Likes
on
0 Posts
my car threw specific cylinder codes p0307 and p0308 so i just checked those plugs....if you just got your car i would just start off by replacing your OPTI they are notrious for going out on these cars, after you do that and the misfire is still there its a whole lot easier to track it down.
Trending Topics
12-01-2008, 04:54 PM
#11
TECH Fanatic
iTrader: (4)
Join Date: Feb 2008
Location: S.W. Missouri
Posts: 1,291
Likes: 0
Received 0 Likes
on
0 Posts
I would run a compression test, you may have a sticky valve/valves, if compression is good, take a good look at those 2 plugs, see if they are fouling for any reason, double check the ohm resistance on those wires too, wiggle them around & make sure the needle doesn't drop or flucuate.
12-01-2008, 05:02 PM
#12
On The Tree
Thread Starter
iTrader: (1)
Join Date: Jan 2007
Posts: 178
Likes: 0
Received 0 Likes
on
0 Posts
I would run a compression test, you may have a sticky valve/valves, if compression is good, take a good look at those 2 plugs, see if they are fouling for any reason, double check the ohm resistance on those wires too, wiggle them around & make sure the needle doesn't drop or flucuate.
compression test ....good idea thanks
12-09-2008, 08:54 AM
#14
It could be an arching wire. I had that happen on my car when the wire was too close to the header and burnt through slightly. I still connected when it was cold but would arch and cause misfiring similar to your description. I would check all the plug wires inch by inch before replacing the opti. The opti gets blamed for everything but many times it is something else.
12-09-2008, 11:37 AM
#15
Registered User
Join Date: Nov 2008
Posts: 15
Likes: 0
Received 0 Likes
on
0 Posts
It's unlikely a fuel pump problem. To check that, leave your door open and turn the key on, engine off and listen for a low buzz. If you hear it, the pump is active. To check pressure, there is a schrader valve near the fuel regulator. You should see about 43PSI at the port.
Based on what you've posted, I must ask, do you have roller rockers? If you do, check to be sure they are properly tightened. I had many of the same problems you describe, hard start/random or multiple cylinder misfires, etc. Found out I tightened the rockers down too tight and lost some compression on some of the cylinders. It ran horribly when it ran at all.
Also check your ignition coil ground. The loop on mine was almost broken off and was not grounding properly. Only replace the opti as a last resort. There are a lot of things that could be causing your problems besides the opti. If it's hard to start, it's unlikely the front O2's are causing the problems. They are not active at startup. MJD
Based on what you've posted, I must ask, do you have roller rockers? If you do, check to be sure they are properly tightened. I had many of the same problems you describe, hard start/random or multiple cylinder misfires, etc. Found out I tightened the rockers down too tight and lost some compression on some of the cylinders. It ran horribly when it ran at all.
Also check your ignition coil ground. The loop on mine was almost broken off and was not grounding properly. Only replace the opti as a last resort. There are a lot of things that could be causing your problems besides the opti. If it's hard to start, it's unlikely the front O2's are causing the problems. They are not active at startup. MJD
