Random Cylinder Misfire...

[Dannk]

It has been getting progressively worse. I finally broke down and took it to a dealer to confirm my suspicions. They have diagnosed it as faulty injectors/poppets. At $91 a piece times 6, plus labor - they want $1200 to replace all injectors and poppets.

Has anyone else had this prognosis? Is there a "work around" - maybe some type of LETHAL fuel injector cleaner? The truck is only worth about $3000. I will do the work if neccessary and have already found a Delphi replacement injector assembly that elimates the poppets for about $300.

Please help - I need my winter vehicle!!!!

[BlazerLT]

Originally Posted by Dannk

It has been getting progressively worse. I finally broke down and took it to a dealer to confirm my suspicions. They have diagnosed it as faulty injectors/poppets. At $91 a piece times 6, plus labor - they want $1200 to replace all injectors and poppets.

Has anyone else had this prognosis? Is there a "work around" - maybe some type of LETHAL fuel injector cleaner? The truck is only worth about $3000. I will do the work if neccessary and have already found a Delphi replacement injector assembly that elimates the poppets for about $300.

Please help - I need my winter vehicle!!!!

If you pay them 1200 for this, it will be dumbest mistake of your life.

They don't have a clue what the problem is and they know it.

Have you even check the fuel pressure like I asked?

[Dannk]

Oh yeah,

I snaked my fuel pressure guage up to my windshield and drove around the neighborhood - with it running very poorly - while watching it closely (I almost took out a mailbox). It was right on the money at about 53-60 psi the whole time. There were no abrubpt changes, but it did vary about 5-7psi as RPM changed...

As a side note, I recently changed the fuel pump and filter about 6 months ago. The gas guage has not been the same since either. When I fill it up, it only goes to about 7/8 full. This repair did cure my slow start condition though.

[BlazerLT]

Check the fuel pressure with the ignition to the first on position and the truck not started again.

[Dannk]

Originally Posted by BlazerLT

Check the fuel pressure with the ignition to the first on position and the truck not started again.

I feel pretty confident I do not have a fuel pressure issue. I dumped 3 bottles of STP fuel injector cleaner into my tank and it's been running great since. I went and bought a $21 bottle of GM fuel system cleaner and put that in my tank when it was almost empty too. It has been running flawlessly since....Sounds like a fuel injector/poppet problem - right????? I am still open to ideas, because I know this problem will be back eventually.

[BlazerLT]

Originally Posted by Dannk

I feel pretty confident I do not have a fuel pressure issue. I dumped 3 bottles of STP fuel injector cleaner into my tank and it's been running great since. I went and bought a $21 bottle of GM fuel system cleaner and put that in my tank when it was almost empty too. It has been running flawlessly since....Sounds like a fuel injector/poppet problem - right????? I am still open to ideas, because I know this problem will be back eventually.

Could have been a poppet valve sticking.

It is not smart to run such a high concentration of fuel additives light that.

It will foul the plugs.

[Paraquat.]

I'm going to murder GM
I went through this whole ordeal. Just last night I got p0440 (which yahoo.com led me to this site.) after having swapped the plenum, and MAP.
http://www.mastrianni.net/stevespict...ges/repair.htm
check out my site. I havn't added p0440 to it yet.

--Steve

[Dannk]

OK. I am ready to give up on this. I am out of ideas. Here is what I have done so far - regarding my random cylinder misfire issue..

Replaced fuel filter (6 months ago) - seperate issue
Replaced fuel pump (5.5 months ago) - seperate issue
replaced plugs and wires (3 months ago)
replaced distributor cap and rotor (2.5 months ago)
replaced ignition coil pack (2 months ago)
replaced ENTIRE fuel injection system (2 weeks ago) ($350!!!) (not easy)

This last thing with the fuel injection system was supposed to fix my alleged sticking poppet valves. I paid $80 at a GM dealer for a "professional" diagnostic and that's what they came up with too (along with about 3 other people I had spoken with). Well, guess what - its runnin like crap again.

My symptoms are like this - Under normal acceleration I feel the engine intermittently losing power, mostly in first gear. If I am cruising at interstate speed, I feel a miss about every 1-3 seconds. This is most severe between 1500-2500 RPM. It does not feel like a single problematic cylinder. It feels like an evenly dispersed, random misfire. If I drive in first gear at about 2000 RPM for about 1/4 mile, the SES light will come on with a code of "Random cylinder misfire detected". (THANKS GM/OBDII FOR NARROWING IT DOWN).

I am about ready to set this "truck" on fire and watch it burn...burn...burn...Somebody, please help.

[Fireplug]

Wow the Dealer did not take your truck for a ride with the scan tool hooked up and take a cylinder reading while it is doing the problem??? I would go back to the Dealer that you paid money to and demand that someone good who knows how to check drivabilty problems take it for a test drive (at no charge to you because this is a come back problem)with you and have the Tech Tool 2 hooked up so he can get a true picture of what the heck is going on. I try to take every car owner on a test drive so they know that I really want to fix there problem and just talking to the owner about the problem helps most times to pin point when it does it so i can see it happen and then fix it.
I got every drivabilty problem that everyone else in the shope could not fix. And I blame a lot of no fix problems on the flat rate pay system. These Techs dont get paid if they are not turn a wrench

[Rick Norwood]

Originally Posted by Dannk

OK. I am ready to give up on this. I am out of ideas. Here is what I have done so far - regarding my random cylinder misfire issue..

Replaced fuel filter (6 months ago) - seperate issue
Replaced fuel pump (5.5 months ago) - seperate issue
replaced plugs and wires (3 months ago)
replaced distributor cap and rotor (2.5 months ago)
replaced ignition coil pack (2 months ago)
replaced ENTIRE fuel injection system (2 weeks ago) ($350!!!) (not easy)

This last thing with the fuel injection system was supposed to fix my alleged sticking poppet valves. I paid $80 at a GM dealer for a "professional" diagnostic and that's what they came up with too (along with about 3 other people I had spoken with). Well, guess what - its runnin like crap again.

My symptoms are like this - Under normal acceleration I feel the engine intermittently losing power, mostly in first gear. If I am cruising at interstate speed, I feel a miss about every 1-3 seconds. This is most severe between 1500-2500 RPM. It does not feel like a single problematic cylinder. It feels like an evenly dispersed, random misfire. If I drive in first gear at about 2000 RPM for about 1/4 mile, the SES light will come on with a code of "Random cylinder misfire detected". (THANKS GM/OBDII FOR NARROWING IT DOWN).

I am about ready to set this "truck" on fire and watch it burn...burn...burn...Somebody, please help.

I will make a few generic suggestions, forgive me if they don't seem applicable to your exact make/model. Some of these may be outdated.

Check for loose mounting screws that hold the distributor module to the base of the distributor, and that the wire connections are tight.

Check the little wires that attach to the module as the come through the distributor housing for bare spots etc.

Check to see if the Di-electric (White?) grease is all gone between the bottom of the distributor module and the distributor base. If it is all gone I'd re-apply more.

Check for any moisture under the distributor cap or in the distributor.

Check to see if there is excessive slop in the distributor shaft (where the rotor attaches). Don't ask me what excessive is, but it shouldn't be very much.

[TonyMazz]

This may help ... It is some insight to a P0300 Engine Misfire code...it's what the dealer would do...

Circuit Description

The Crankshaft Position (CKP) Sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the Control Module (PCM/VCM) will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or all cylinders randomly.

When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The Control Module determines which cylinder has misfired based upon the Camshaft Position CMP Sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, a this DTC will set.

Conditions for Running the DTC

Important: If start-up ECT is below -7°C (20°F), misfire detection is delayed until ECT is more than 21°C (70°F). If start-up ECT is more than -7°C (20°F), misfire detection begins after a 5 second delay.



No active VS sensor DTCs
No active TP sensor DTCs
No active MAF sensor DTCs
No active CKP sensor DTCs
No active CMP sensor DTCs
The fuel level is more than 10%.
The engine speed is between 450-5000 RPM.
The system voltage is between 11-16 volts.
The throttle position is steady within 2% for 100 ms.

Conditions for Setting the DTC

The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire.

Action Taken When the DTC Sets

If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the MIL after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.

Conditions for Clearing the MIL/DTC


The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.

A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature is more than 70°C (158°F) during the same ignition cycle).
Use the scan tool Clear Information function.

Diagnostic Aids

The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present.

Many different condition could cause an intermittent misfire.
Check for the following conditions:


Check the IC control circuit for a intermittent short to ground.
Check the spark plug wires and the coil wire for the following conditions:
Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
Check the wire routing in order to ensure that cross-firing is not occurring.
If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
Check for contaminated fuel or a low fuel level and the following conditions:
Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition.
If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and possible misfire condition. Check the fuel trim numbers in the freeze frame to determine if this has occurred. It would be likely if the short term fuel number was above + 20.
Check HO2S for abnormal voltage readings.
Check for a vacuum leak as a possible cause of the engine misfire.
Sticking intake or exhaust valves can cause a misfire when the engine is cold.
An intermittent may be caused by any of the following conditions:


A poor connection
Rubbed through wire insulation
A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. See: Diagnosis By Symptom

Test Description
The numbers below refer to the step numbers on the diagnostic table.


The misfire is considered random on all cylinders if, while viewing the misfire counters in the misfire data list, the misfire seems to move to different cylinders.
The misfire is considered consistent if the misfire is occurring on the same cylinder(s) consistently.
When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.

[Fireplug]

TonyMazz
where did you get that info in your post. It looks like its right out of the GM Manual? Did you find it on the net and if so do you have a link for it??

[TonyMazz]

Originally Posted by Fireplug

TonyMazz
where did you get that info in your post. It looks like its right out of the GM Manual? Did you find it on the net and if so do you have a link for it??

Actually it's through a paid subscription to AllData.com. It IS from the GM manual as AllData has the exact same service info that any manufacturer does...including service bulletines etc.

I pay 24.95 for the year and it's an ulimited use...great deal.

www.alldatadiy.com..

It is specific to a vehicle, and in my case it's a 99 blazer but you can use it with any vehicle....pretty cool tool...it pays for itself 100 times over when you fix something your self at a rate of $80/hour savings :-)

[Allbert]

TonyMazz, do you have similar detailed information for troubleshooting a P0440 evap system failure code?

[Dannk]

Originally Posted by Rick Norwood

I will make a few generic suggestions, forgive me if they don't seem applicable to your exact make/model. Some of these may be outdated.

Check for loose mounting screws that hold the distributor module to the base of the distributor, and that the wire connections are tight.

Check the little wires that attach to the module as the come through the distributor housing for bare spots etc.

Check to see if the Di-electric (White?) grease is all gone between the bottom of the distributor module and the distributor base. If it is all gone I'd re-apply more.

Check for any moisture under the distributor cap or in the distributor.

Check to see if there is excessive slop in the distributor shaft (where the rotor attaches). Don't ask me what excessive is, but it shouldn't be very much.

Thanks Rick Norwood for the good advice. As you mentioned the distributor area, I have had problems with the mounting screws that hold the distributor cap down...So I checked it again today by taking it apart (cap and rotor removal inspection). Everything looked great. No corrosion, some dirt particals but nothing big.

My mounting holes on my distributor base have both cracked and I have "rigged" a washer/bolt combination to hold it down - it has been like this for 3 months. I am in the process of locating a new distributor, BUT I did not see anything suspect.?

TonyMazz - I will re-post after making the dealer get me the misfire counters for each cylinder. I had no idea the computer logged this. Why did'nt they look at this before? It's one of the first things I would do for P0300!! That is GREAT info, thanks...

Again, I have a 1996 4.3 W vortec in a S-10 SS truck. When it runs good, it's somewhat peppy. Nothing like my 1997 Formula WS6 though.