98 Chevy S-10 ODB error code P0304

[radger]

I left my chevy s-10 truck sittin over the christmas(23/24/25) and it was really cold outside and when i got back i started getting a P0304(Cylinder 4 Misfire). I replaced the sparkplugs and sparkplug wires. Anybody ever run across somethin that maybe the cold would cause this to happen? I think ive noticed the trucks fuels efficiency drop over the past month) Maybe the fuel injector(s)? Is the s-10 TBI or does it have fuel injectors for each cylinder? Im not a car guru so if i sound stupid i apologize


Thanks

[MT-2500]

Welcome to AF.
What engine and engine size and engine code?
Have you cleared the code and rechecked?
Can you feel a engine miss?
Has it got good hot blue spark to no 4 spark plug?

[radger]

Engine code= 4.3L V6 with Sequential Electronic Fuel Injection(SEFI)
Model code= 1998

I have cleared the code and the same P0304 shows up again.
I can feel the engine missing right when u first start it.
Also before all this I have this feeling like we're getting horrible gas mileage too. We just replaced the spark plugs and wires thinking that might be the problem but ill check to see if its getting a spark.

[radger]

Would this be what is going on? -->
1998 Chevy Truck S10/T10 P/U 2WD V6-262 4.3L VIN X SFI Copyright © 2003, ALLDATA 8.00 Page 1
Fuel Injector: All Technical Service Bulletins
Fuel System - MIL ON/Rough Idle on Start-Up
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 00-06-04-003B
Date: February, 2003
TECHNICAL
Subject:
Rough Idle After Start, And/Or A Service Engine Soon (SES) Light
(Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet
Valves or Convert to MFI)
Models:
1995-2002 Chevrolet and GMC S/T Models
1996-2002 Chevrolet and GMC C/K, M/L, G, P Models
1996-2001 Oldsmobile Bravada
1999-2000 Cadillac Escalade
with 4.3L, 5.0L or 5.7L Engine (VINS W, X, M, R - RPOs L35, LF6, L30, L31)
Except 2002 VIN X - RPO LU3 Models
This bulletin is being revised to update the Warranty Information. Please discard previous copies of Corporate Bulletin Number 00-06-04-003B with
warranty chart (Section 06 - Engine). This copy is for Dealers in the state of CALIFORNIA ONLY.
Condition
Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The
Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.
Cause
A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will
be mis-fueled, resulting in a cylinder mis-fire condition.
Correction
A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector
replacement should NOT be considered as a correction for this customer concern.
Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired
for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back
service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a
unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.
Notice:
Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to
retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine
damage could result.
Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return
for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of
which fix to pursue.
Important:
"GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.
The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to
provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the
means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2(R) to "energize" the injectors.
The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits
from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner
may have detrimental effects on the fuel pump.
1998 Chevy Truck S10/T10 P/U 2WD V6-262 4.3L VIN X SFI Copyright © 2003, ALLDATA 8.00 Page 2
Parts Information
Cleaning Procedure Parts
CSFI to MFI Conversion Parts
Parts are currently available from GMSPO.
Warranty Information
Important:
Some California vehicles may be covered by Special Policy 99066E if built with California Emissions RPO YF5. If the vehicle is covered by the
special policy, then that warranty information should be used.
For vehicles repaired under warranty, use information contained in Special Policy 99066E.

[MT-2500]

Yes and no.
Many things can cause missfire.
What is the mileage on engine?
Did you replace plugs with the AC delco plugs the AC book calls for?
Have you got good compression and good hot blue spark to all cylinders?
I would go over secendary ign real close and make sure it is up to par.
Check fuel pressure real good.
Get it on a good scanner and read out all sensors and engine running data.
Check dist cap and camshaft retard setting.
MT

[radger]

Originally Posted by MT-2500

Yes and no.
Many things can cause missfire.
What is the mileage on engine?
Did you replace plugs with the AC delco plugs the AC book calls for?
Have you got good compression and good hot blue spark to all cylinders?
I would go over secendary ign real close and make sure it is up to par.
Check fuel pressure real good.
Get it on a good scanner and read out all sensors and engine running data.
Check dist cap and camshaft retard setting.
MT

damn i knew i shouldve gotten AC Delco. i got the AutoLite(sp?)s.. i replaced the spark plugs after i started having the problem. U really think i should go replace them again with AC Delco?

[MT-2500]

Yes.

[radger]

Originally Posted by MT-2500

Yes.

Should i replace the AutoLite spark plug wires i got with it too?

[bobgrez]

I replaced the CSFI with an MFPI made by SMP for about $660 with labor and my P0304 cylinder 4 random misfire code and check engine light popped back on about 3 miles down the road. My mechanic will be troubleshooting this later this week. Already had new plugs, wires, and all replaced. Still not solved. This particular problem is a pain. Will let you know what he finds.