MAF (mass air flow) sensor is measured in hertz. A scan tool that can read data shows the frequency of the sensor. MAF codes can set due to other problems with the vehicle. What I like to do is to disconnect the MAF sensor wire and run the vehicle with the sensor unplugged. The computer will use other sensor to make the calbrations needed. If problem goes away the MAF is the problem, if problem still there. look else where. check the air tubes between the MAF and the throttle Body any leaks will cause code to set.
Low fuel pressure can cause MAF codes, Make sure you have good fuel pressure.
Make sure the distributor cap is tighten down all the way. A loose or even a cheep distributor cap can cause misfires. If problem still there try to see which cylinders are misfiring. here is a flow chart on MAF Diagnosis.
Circuit Description The Mass Air Flow (MAF) sensor measures the amount of air entering the engine during a given time. The Vehicle Control Module (VCM) uses the mass air flow information for fuel delivery calculations. A large quantity of air entering the engine indicates an acceleration or high load situation. A small quantity of air indicates deceleration or idle.The MAF sensor produces a frequency signal which can be monitored using a scan tool. The frequency varies within a range of around 5 to 7 g/s at idle to near 125 g/s at maximum engine load. This DTC sets if the signal from the MAF sensor does not match a predicted value based on the barometric pressure, the throttle position and the engine speed. This DTC is a type A DTC.Conditions For Setting The DTC The Following Conditions will set the DTC:
Action Taken When The DTC Sets
Conditions For Clearing The MIL/DTC
Diagnostic Aids Check for the following conditions:
Test Description The numbers below refer to the step numbers on the diagnostic table.
Thanks for the info I have checked all the sensors and am satisfied they are all working
fine. Checked fuel pressure and it stays between 50 and 55 .
Checked all the cyls and it seem the intermittion miss is on cyls 1 and 5. they are runnig
4to 6 KV with a 0 every 4 or 5 sec. The rest are running 20 to 23 KV. This tell me I am
running very rich on 1 and 5 maybe a leaking injector. but I am not sure how to chk this
type of injector I work on boats and these cars are different. If you can give me any suggestions that I may be missing. I run soapy water over anywhere that might leak.
One last thing I pulled the vac line apart at the T Before it goes into the vac cannistor and I can figure out where the other line is so I caped one side of the T.any sugestions
would help then I will pay what I owe. Thanks for the help. This miss is driving me crazy
now the only code is P0300.
Hi XXXXXXXX. Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way, it would help us to know:you said the fuel pressure is 50-55 is that with vehicle running ?
should be 60-66psi when turn key on for about 2 secondsThank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.
No I only have a code reader . I have a fluke scope . I have checked the wire many times
and I am sure they are not crossed.
I just wanted to say one more thing. When this first started and I had to Spray starting
fluid in the the throttle body in the mornings.Every few days I would see a code saying
number one cyl was misfireing after I replaced the fuel pump was when I started getting
a 300 code saying random misfiring and I see that it is 1 and 5 it seem like somthing
is happening on that bank. thanks again
Ok That info helps a little more. That style of injectors had trouble with the poppet valves at the end of injectors sticking either open or closed. Sounds kinda like what my be going on. I will include a bulletin to help explain it. they developed a new style of injectors to fix the problem. But first make sure you got a good distributor cap and the distributor cap and rotor tight.
I'm not sure what your asking about the vacuum lines.The only vacuum lines there are hooked up below where the pcv valve hose goes in the intake manifold. Ofcourse you have a brake booster vacuum line. that is another thing to checkmake sure your not getting fluid from the transfer-case into the vacuum lines. that could cause a miss also. but verry random.
#00-06-04-003B: 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) - (Jan 30, 2003)
This bulletin is being revised to update the Correction and Warranty Information. Please discard Corporate Bulletin Number 00-06-04-003A (Section 06 -- Engine).
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® 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.
Cleaning Procedures
This procedure should be performed before any attempt to convert the fuel system to MFI.
S/T and C/K Truck
Tighten Tighten the nuts to 3 N·m (27 lb in).
Tighten Tighten the fuel pipe bolt to 6 N·m (53 lb in).
M/L, G Van and P Truck
Tighten Tighten the fuel line nuts to 30 N·m (22 lb ft).
Central SFI to MFI Conversion Instructions
This procedure outlines the steps required to replace the existing Central SFI Fuel System with a new MFI (Multiport Flexible Injection) Fuel System. Be sure to use the appropriate year and model Service Manual for proper disassembly and re-assembly procedure(s).
Important: 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 a MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.
V6 Engines
Notice: Use caution when inserting injectors into lower intake manifold to be sure the correct injector is being placed into the correct hole.
Important: The Injector holes are numbered on the Lower Intake Manifold. The injectors are numbered on the side of the Fuel Meter Body.
Important: When installing fuel tubes, it is important that the tubes are oriented properly to provide minimal interference when installing the upper intake manifold plenum. Intake holes for cylinders 2, 4, 5, and 7 are closer to the fuel meter body. It is necessary to cross tube 5 over tube 7 and tube 4 over tube 2 as shown in Figure 4.
Notice: Lack of lubrication will make installation of the Upper Intake Manifold plenum difficult and may cause damage to the O-ring.
Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them in the of the Fuel Meter Body.
Parts Information
Cleaning Procedure Parts
Part Number
Description
12345382
Threadlock
XXXXXXX
Top Engine Cleaner (U.S.)
992872
Top Engine Cleaner (Canada)
12345104
Port Fuel Injector Cleaner (U.S.)
10953467
Port Fuel Injector Cleaner (Canada)
CSFI to MFI Conversion Parts
12568332
V-6 MFI Assembly
88894355
V-6 Bracket
17113215
V-6 Seal Kit
93441235
V-8 MFI Assembly
17113206
V-8 Seal Kit
93442096
V-8 Bracket
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:
Labor Operation
Labor Time
J5645
Injector, Fuel - Clean
C/K, S/T
1.3 hrs
M/L, P
1.0 hr
G Van
1.5 hrs
J5496
Meter Assembly and/or Gasket, Throttle Body Fuel -- Replace
C/K, S/T Trucks, G Vans, P Chassis
1.4 hrs
M/L Vans
1.6 hrs
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION
Notice: The number 3 Fuel Tube must be positioned behind the number 1 Fuel Tube to eliminate interference with the Upper Intake Manifold plenum when installed. See Figure 2.
Important: Lubricate the Fuel Inlet and Return Lines with clean engine oil before inserting them into the Fuel Meter Body.
V8 Engines
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