6.0L LQ4 random misfire

[Mater]

wouldn't that make noise? or have issues at lower rpm as well? and be a result of over revving it? i'll be honest LS sort of not my thing i mostly worked on 3.8 GM v6 engines using lq4 springs as upgrades to handle 7,000rpm and valve control with more aggressive cams with high lift. the lq4 cam is tiny in comparison. but again ls engines sort of new to me

this truck lived at idle as i was wrong it;s not 1800 idle hours it's 3800 idle hours (think the exact is 3894.6)

[Russell]

My 6.0 has a little tick. Seems to drive fine is this normal? I have not tried to track it down. I figured it's old truck noise mine has over 220k almost sounds like an exhaust leak to me.

[Mater]

a manifold bolt is probably broken. mine the driver manifold had 1 bolt holding it on. passenger side fell right off. all bolts broken inside the head LOL


i had a shop deal with that one

[Mater]

riddle me this batman

new pump ACdelco form the dealer after they put my vin number into the computer has 2 connectors the original crap that i just took out has a single




the balls man?

any one have any idea if i can use the new one or do i have to try and take it back now that it;s out of the box and get the "wrong" pump for my truck and listen to the parts people bitch at me


(sorry today has not been fun)

[Barry Donovan]

I would be interested in that answer..
even the 1996 (first year 55psi) has an update so huge the engine does not even sound like a 1996 after a new pump.

I know filters changed, the micronic designs...right at the pump. and the fuel sender is not an igniter for 23 gallons of bomb anymore.
other than that, it must be the pumps themselves.

have fun.

there is a trick after verifying it was fuel all along..
if you can somehow floor it while chugging at 1000 rpm.. just for some seconds..
you'll fill that half deadness. That helps with the sputters.
my own smelled like an old ignition coil, and a wires that cross fired for a long time...
and disappeared.


that chore is easier with a manual tranny.

..and 100mph quarters or close to it.
that is 20 years of 55psi. Easy test.

[Mater]

well called the dealer it appears GM only offers one style of assembly now and all i have to do is leave the tank pressure sensor in there to keep debris out and other then that ignore it as the pump it; self is all that matters and the numbers match that for a 6.0/8.1 (4.3,4.8, and 5.3 use different pump)

ill hook it up and see what happens but the part number cross references to this one. i just do not have a real EVAP system sense my truck is over 8,000 GVR (it's rated at 13,000GVRW) it just has a charcoal canister and hoses. no valves or solenoids

[Dan Barlow]

I have been watch this but have kept quite as I have nothing to add but hope to get smarter . Fingers crossed .

[Mater]

yeah so far it;s been multiple issues.

coil 5 was completely dead

plug one blew out of the head as some one over torqued it

filter was junk and clogged

regulator was leaking out of the vac line

and now i am chanign the pump as the ful pressure was 10PSI too low even after the regulator brought it up from 40PSI to 50psi (truck needs minimum 55 according to the service manual)


the pump needed to be changed as it was cracked where the supply line connects at and was leaking gas on the top of the tank just so small it never left a puddle

[chevybuytroy]

It sounds like you found your problems. Just to put my 2 cents in cause mine was doing this last year. I found it was sucking extra air in through the air filter tube and bypasing the sensor causing mine to miss. A small plastic tube was suppose to be in the place but fell out. Plugged it back in and havent had a miss again.

[Mater]

i'll look to make sure the tube is connected correctly it;s an aftermarket unit and some of those do not have the best fit

[anotheridiot]

I always start with the temperature sensor, since GM uses them to control fuel pressure, by adding or removing fuel when the temperature gets close to optimum, instead of just turning on the damn fans. Otherwise you have to check your primary wires to the coils. This happened on our 03 Monte carlo, but there are not individual coils, they are three coils that handle two cylinders and the circuit board beneath them is what causes the misfire. If yours are up on the valve covers it wont apply and must be a cross in the insulation somewhere controlling the packs.

[Mater]

the trucks are different as i have a clutch fan. and also only the early L67 supercharged cars had the variable rate pumps they went away in 2001 with the single speed pumps in both the N/A and supercharged w-bodies


that is a good point though. does the LS engines use a ICM? or are they just controlled via the PCM?

[Runner1972]

wouldn't that make noise? or have issues at lower rpm as well? and be a result of over revving it? i'll be honest LS sort of not my thing i mostly worked on 3.8 GM v6 engines using lq4 springs as upgrades to handle 7,000rpm and valve control with more aggressive cams with high lift. the lq4 cam is tiny in comparison. but again ls engines sort of new to me

this truck lived at idle as i was wrong it;s not 1800 idle hours it's 3800 idle hours (think the exact is 3894.6)

It didn't. With it idling that long, I'd pop a valve cover to see what's going on.

[Mater]

ill look into after i get it running again


waiting on a gas tank strap. one of mine crumbled when i went to remove it

[Mater]

hit a delay do to breaking the tank trying to get the lock ring off.


the lock ring is still rust welded on to the tank.



but "new" tank 31 out the door at the local salvage yard. even has a supply line i just got done buying at the dealer..... for way to much money..... sigh




change the fuel pump i said.

it would be easy i said.