torqls1

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So I've got a great stumper for you guys. First Id like to say I am a proud owner of a 02 ws6 lightly modified exhaust,lid,cutout with 38k miles. Ok let's begin, I get incredibly **** gas mileage let's say 42miles to a quarter of a tank shifting at 2k rpms with my m6 also I notice a slight missfire popping. So, I decided to change my plugs went with the ngk tr55s gapped them at .050. guess what still **** gas mileage and missfire popping. Now let me remind you that before I did the plug swap I hooked up to a slp tuner which read I was getting consistant random cylinder missfires 1-5-3-8-2-1 etc. Then decided to hook up to a hp tuner and it read nothing at all. Now with that all being said my car never threw any codes on the dash at any given time. I would like to believe my 02 sensor is bad because if so it wouldnt read a bad plug=no code and there goes my gas mileage, but if that was the case a code would throw for the bad 02 sensor..... Anyways I decided to buy lucas fuel injector cleaning $5 ehh why not. Also jumped under the car took a peek at the fuel filter and it looks to be in good shape.

Sneakyws6

I think that gap is a little on the large side, I thought the plugs in the LS1's were gapped in the .035 range. Might be time for new plug wires and all 4 of the O2's to be replaced.

How many miles are on this car?

mannyman84

iTrader: (2)

Wow that's bad. Try Tunning back to stock form and see how that goes, maybe I did something wrong somewhere and I think .050 might not be the correct gap either. Also check your fuel pressure and make sure u are holding pressure in the line, if u aren't then u will have bad injectors and will be running to rich and o2 will try to cut fuel, so that might be your poping u hear mixture isn't right. U can also check your o2's. I forgot how to test those.

torqls1

[QUOTE=mannyman84;13345289]Wow that's bad. Try Tunning back to stock form and see how that goes, maybe I did something wrong somewhere and I think .050 might not be the correct gap either. Also check your fuel pressure and make sure u are holding pressure in the line, if u aren't then u will have bad injectors and will be running to rich and o2 will try to cut fuel, so that might be your poping u hear mixture isn't right. U can also check your o2's. I forgot how to test those

Are you sure .050 is to large?..I've read alot on this forum about .50-.60 range is ideal. As for the fuel pressure how would I check this? And if im not mistaken bad o2's would throw a code

Paul Bell

iTrader: (9)

Unless your fuel filter is glass, you can't tell if it's "good".

How are your cats? Any loss of power?

Any chance the crank sensor is acting up? It controls the coils.

That's alot of misfires. How are the plug wires? Lots of dirt on the coils?

I don't think gauging from a quarter tank is very accurate. Fill er' up and do a nice hundred mile highway drive. Fill it again and get a real MPG number.

On highway runs, cruise control in use, minimal hard acceleration, I've hit 30 MPG. I'll say this is a bit high as I have crappy 2.73 gears.

Around town and sitting in traffic, occasional stepping on it good, I get about 12-16 MPG.

torqls1

Thanks for the good feedback. ur correct the fuel filter may very well be clogged any idea when they typically do go bad? as far as the cats go when i bought the car not even 10minutes of driving it home the ses light went off got a diagnostics done and it was a bad cat! called the dealer up immediately and they claim they put a new one on. If a cat was bad wouldn't it throw a code though? and crank sensor im not sure I even know what that is maybe you could point that out to me and ill check it out in the morning and toss u some feedback after work. The wires however looked fine, thanks again

mannyman84

iTrader: (2)

[QUOTE=torqls1;13345356]Yeah they would throw a code... Have u tryed scanning it either way. As for the fuel pressure I have to look into it because I haven't done it on a 4th gen. And what does the gap say in the engine compartment?

mannyman84

iTrader: (2)

Just really check that filter and let us know what's up. U can also check the fuel pressure when u take out the filter with a fuel pressure gauge

97ramsst

iTrader: (162)

You listed exhaust as a mod....do you have headers??? Could the plug wires ve touching them causing them to burn a hole in them enough to arch to them and mis-fire?

Paul Bell

iTrader: (9)

Ah right, headers. Headers cool the exhaust sooner in the system than cast manifolds do. The O2 sensors simply may not be getting hot enough. Installing Bosch 13111 O2 sensors may help as they have a higher wattage heater in them.

Before spending money, try to narrow down the problem so you don't throw time & money at other stuff.

torqls1

No sir, no headers, But the wires look perfectly fine and no burn holes . I've got this topic posted under the ls1 newbie help section and have moderators chimeing in, so check it out and let me know what you guys think!

My wallet is drying up from these fuel costs!!!!

Nopps

iTrader: (1)

If the plug wires are fine I'd vote for the crank sensor...But honestly you don't know if they are fine...You're best bet is to find a buddy with a Fluke who knows how to use it and start checking voltage drops. You're wallet is really going to dry up if you blindly start replacing s*** that doesn't need to be replaced. It could be anything really...

Z28/2002

iTrader: (27)

stock gap is .060"

Lucky 13

FWIW have you checked for a vacuum leak?

idformula

To check for vacuum leaks, take a can of brake cleaner and start spraying around places that would have vacuum, like the intake, hoses ect.

Mattn

i do a highway run at least once every week to clean her out and actually seems to help.

sjsingle1

iTrader: (1)

check your pcv to intake mani hose........it craps out famously...........and you never know til ya look.......major vacum leak

LS6427

iTrader: (2)

Just so you all know....

Failing 02 sensors DO NOT give you an SES light or a code until they totally fail OR the engine starts running so terribly bad that its about to fall apart and will hardly run. I never got SES lights or codes in the past 12 years when my 02 sensors needed to be replaced, the car ran terrible though.

Same thing with the Crank Shaft sensor, no SES light until they are totally failed. Its not that because all that does is make your car turn off randomly and makes them hard to start.

You need to check your PCM to engine block ground wire. Its in the harness that comes out of the PCM and connects in the back of the block somewhere. If that gets loose it will cause misfires in all cylinders....this happened to me 2 months ago. My loose ground wire also completely fried my PCM, had to get a new one.

Also, if one fuel injector is messed up because of an "electrical" issue (not a clogged injector)....it will take out that entire side and cause all 4 injectors to go nuts on that side.

Its happening on both sides of the engine, if its not the fuel filter, I'd look into PCM/ground wire problems.

But deifnitely change that fuel filter...that could be the simple fix.

.050 gap is the best gap for the normally aspirated LS1. Also, make sure that NONE of the spark plug wires are touching or able to bang up against any of the exhaust manifold piping....that causes misfires too.

.

zamora7

iTrader: (4)

If your wires, the o2's, fuel filter are good, and no vaccum leak, I'd say you have leaky injectors. They allow the fuel into your cylinder and burns tooe arly causing the popping sound. My best guess.