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1996 Suburban Misfire when cold P0307


1993Suburban
02-20-2009, 01:23 AM
When the vehicle has been sitting over night, I go to fire it up and find it running rough. Can barely make it up the street. The Service Engine Soon light blinks and the code is P0307. After 3 or 4 minutes, it will completely go away and the vehicle runs great. The ignition components are less than a year old, plugs, wires, cap, rotor and they are good AC-Delco parts. I have checked the connections to the plug and all connections are good and tight. It just started doing this a few days ago and can't figure out what the deal is. I live in Idaho so it's cold here, but its been colder this winter. I have found posts about misfires when warm but not too many when cold. Any ideas are appreciated. Thanks!

MT-2500
02-20-2009, 11:14 AM
What is the mileage on it?
Any coolant lose?
Intake gasket seeping?
If it barley runs you have more than one cylinder miss.
Things to check.
Check for good hot blue spark to all plugs.
After a cold start and when it is missing shut of engine and pull spark plug and see if the are wet on end and if coolant on them or in cylinder.
Check that fuel pressure on cold start for up to par and for fast leak downs.

Try if with mass air flow sensor unplugged and or coolant sensor unplugged.
If you have a scanner check all sensor readings.
Switch plugs and wires and see if miss fire changes.
Camshaft retard ever been checked.
Dist cap and rotor can go bad and still look good.

GMMerlin
02-21-2009, 06:38 AM
When the vehicle has been sitting over night, I go to fire it up and find it running rough. Can barely make it up the street. The Service Engine Soon light blinks and the code is P0307. After 3 or 4 minutes, it will completely go away and the vehicle runs great. The ignition components are less than a year old, plugs, wires, cap, rotor and they are good AC-Delco parts. I have checked the connections to the plug and all connections are good and tight. It just started doing this a few days ago and can't figure out what the deal is. I live in Idaho so it's cold here, but its been colder this winter. I have found posts about misfires when warm but not too many when cold. Any ideas are appreciated. Thanks!

This truck has a unique fuel injection system that most likely is the cause of the concern.
The injectors on this truck are a poppet style that over time will get clogged up due to hydrocarbon deposits from the engine and fuel deposits from the quality of fuel you use.
Unfortunate thing is, cleaning the injectors via pour in injector cleaners or pressurized fuel injection cleaners will not and I repeat WILL NOT fix the problem.
In this case, your dealer is the best option here. They have a tool that will unstick the injectors using high pressure nitrogen...I don't know of any aftermarket or independant shops that have this ( an A/C Delco backed shop may, so you can check there).
If you do not want to go this route, there is a retrofit kit that will update the injectors from a poppet style to a multec style injector...either way you go, this will fix the problem

j cAT
02-21-2009, 08:46 PM
When the vehicle has been sitting over night, I go to fire it up and find it running rough. Can barely make it up the street. The Service Engine Soon light blinks and the code is P0307. After 3 or 4 minutes, it will completely go away and the vehicle runs great. The ignition components are less than a year old, plugs, wires, cap, rotor and they are good AC-Delco parts. I have checked the connections to the plug and all connections are good and tight. It just started doing this a few days ago and can't figure out what the deal is. I live in Idaho so it's cold here, but its been colder this winter. I have found posts about misfires when warm but not too many when cold. Any ideas are appreciated. Thanks!

check fuel pressure,plug wire resistance,ect resistance when cold for the proper spec...40deg f should read 6-7,ooo ohms range.

check the engine ground points/fuel tank,fuel pump ground points.........

for some reason the engine apppears to be running lean when cold..testing will get to the problem....plugged injectors are possible..

TEST FIRST THEN OPEN THE WALLET...

1993Suburban
02-22-2009, 07:07 PM
Hey guys thanks for the responses. I went and reseated the plug connections and added a little die electric grease to the tips of the plugs. For the life of me, I can't get it to reproduce the problem so I don't know what the deal is. Merlin, I've read into the injectors and found the poppet style to cause problems. I bought the truck nearly 2 years ago and when I bought it, it supposedly had a new injector "spider" assembly installed. I say "supposedly" because I don't have any paper work on it, but I bought it from an individual whom I trust. Also at the time of the injector replacement, the cylinder heads were taken off and remachined, thus the intake gaskets are less than two years old. Of course these are prone to failure, but it's not loosing any coolant and the oil looks nice and clean. Only thing is I don't know if it was replaced with the updated style injector or if it is indeed the poppet style. Anyhow if it starts to act up again, I will definitely go over the things you guys have posted. Oh another thought, is it possible moisture could form in the gas tank, causing a misfire? I normally don't run it under half a tank, but it's sitting around half right now. I've heard warnings about when it's cold, to make sure you leave plenty of gas in the tank to keep moisture out. 161,000 miles on the clock and still runs like a champ. Thank goodness gas is down at the moment because I really enjoy driving this thing.

j cAT
02-23-2009, 12:00 PM
Hey guys thanks for the responses. I went and reseated the plug connections and added a little die electric grease to the tips of the plugs. For the life of me, I can't get it to reproduce the problem so I don't know what the deal is. Merlin, I've read into the injectors and found the poppet style to cause problems. I bought the truck nearly 2 years ago and when I bought it, it supposedly had a new injector "spider" assembly installed. I say "supposedly" because I don't have any paper work on it, but I bought it from an individual whom I trust. Also at the time of the injector replacement, the cylinder heads were taken off and remachined, thus the intake gaskets are less than two years old. Of course these are prone to failure, but it's not loosing any coolant and the oil looks nice and clean. Only thing is I don't know if it was replaced with the updated style injector or if it is indeed the poppet style. Anyhow if it starts to act up again, I will definitely go over the things you guys have posted. Oh another thought, is it possible moisture could form in the gas tank, causing a misfire? I normally don't run it under half a tank, but it's sitting around half right now. I've heard warnings about when it's cold, to make sure you leave plenty of gas in the tank to keep moisture out. 161,000 miles on the clock and still runs like a champ. Thank goodness gas is down at the moment because I really enjoy driving this thing.

if the problem is gone it can't be the injectors...this is more of an electrical problem...using the info I gave earlier when it acts up test before replacing parts....

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