Misfires

Well after replacing the engine (98 blazer VIN W) and many other components under the hood I developed another issue last week on my way home from work. When I went to pass a truck on the interstate...I accelerated and went to about 3100 RPM....I noticed the check engine light flashing and while not stumbling...the power seemed topped out. Backed off the accelerator and the engine light went on solid....remained that way for the rest of the trip. Pulled the code and found a P0300.

Next day I ran into work (about 30 minutes on InterState) with EFILive logging data and found I could reproduce the SES light by hard acceleration (Throttle position at 75 %) to 3000 RPM....The data logged showed that the misfire was occuring primarily on cylinder 1 (In fact that time the code was P0301) approx. 1500 misfires in 45 seconds. I also noticed the STFT jumps instatly to +20 % only on Bank 1...and the Advance was only about 19 - 20 degrees.

I've reproduced this about 10 times logging data and have the exact same results...9 out of 10 times it's a P0301...although I do see a small number of misfires on other cylinders.

Yesterday, after some research I changed the Coil, MAP sensor, fuel filter and cleaned the EGR...I then reset the Leared fuel mode. A Test drive now shows approx 1000 misfires on Cyl 2 on hard accerleration (3000 RPM) for approx 15 seconds. I reproduced this 5 times in a row...again with the STFT jumping to 20 % and back down to 0 when you let off the pedal, Advance was 20.5 degress when the MF occured. I'm not seeing misfires on any other Cylinders now.

The truck idles dead smooth and accelates smoothly with lots of power. I record no misfires as long as I don't hit 3000 RPMs

Here's what I've done

Yesterday

MAP sensor
Fuel Filter
Coil

500 miles ago

Reman GM engine
Radiator
Waterpump
O2 sensors
Wires
Plugs (Delco Plats)
Cleaned MAF
Cleaned Injectors and Intake (While off engine)
New GM distributor

9000 miles ago

Reman GM transmission
Fuel Pump
Starter


Anyone have any suggestions ? I could send some EFILive data if you tell me what attributes you want sampled.


Thanks
Mike

Check sparrk plug. Switch plugs and or wires with missing one and see if missfire changes?
Are you using the AC delco plugs the good book calls for?
What is the cam retard offset reading?
MT

Spark plugs are Delco and less than 500 miles...Wires were changed after this problem started to Carquest premium (ouch 60 bucks). The misfire cylinder does seem to change (although almost always Cyl 1 or 2)

The CAM offset is sitting at a near perfect 0. (I was the guy who had to file the distributor clamp to get it there. Approximately 1.5 teeth).


Run 1 misfires
In 14 seconds
Cyl 1 - 392 MF
Cyl 2 - 308 MF

Run 2
In 42 seconds
Cyl 1 - 7109 MF
Cyl 2 - 885 MF

Changed MAP, Coil, Fuel Filter

Run 3

In 18 seconds
Cyl 1 - 78 MF
Cyl 2 - 1906 MF

Run 3 At first misfire the state was :

RPM = 3154
MAF = 14.4 lb/min
VSS = 72.1 mph
MAP = 13.8 psi
Fuel Injector BW Pulse Bank 1 = 18.1 ms
Fuel Injector BW Pulse Bank 2 = 17.6 ms

ST Fuel Trim Bank 1 = 17.2 (Went up from -0.78)
ST Fuel Trim Bank 2 = 0.78
LT Fuel Trim Bank 1 = 6.25
LT Fuel Trim Bank 1 = 1.56
Advance = 20.5 degrees BTDC
Throttle postion = 82 %
Intake Air Temp = 78.8 F
Engine Coolant = 205 F
Ignition control Voltage = 13.7 v

Mike

Try checking your distributor cap. It could have a hairline crack between no 1 and no 2 cylinder trace. I had a similar problem on mine between 4 & 5, not detectable by eye, but I replaced it and it works fine now.

Spark plugs are Delco and less than 500 miles...Wires were changed after this problem started to Carquest premium (ouch 60 bucks). The misfire cylinder does seem to change (although almost always Cyl 1 or 2)

The CAM offset is sitting at a near perfect 0. (I was the guy who had to file the distributor clamp to get it there. Approximately 1.5 teeth).


Run 1 misfires
In 14 seconds
Cyl 1 - 392 MF
Cyl 2 - 308 MF

Run 2
In 42 seconds
Cyl 1 - 7109 MF
Cyl 2 - 885 MF

Changed MAP, Coil, Fuel Filter

Run 3

In 18 seconds
Cyl 1 - 78 MF
Cyl 2 - 1906 MF

Run 3 At first misfire the state was :

RPM = 3154
MAF = 14.4 lb/min
VSS = 72.1 mph
MAP = 13.8 psi
Fuel Injector BW Pulse Bank 1 = 18.1 ms
Fuel Injector BW Pulse Bank 2 = 17.6 ms

ST Fuel Trim Bank 1 = 17.2 (Went up from -0.78)
ST Fuel Trim Bank 2 = 0.78
LT Fuel Trim Bank 1 = 6.25
LT Fuel Trim Bank 1 = 1.56
Advance = 20.5 degrees BTDC
Throttle postion = 82 %
Intake Air Temp = 78.8 F
Engine Coolant = 205 F
Ignition control Voltage = 13.7 v

Mike

Go over the basics first.
Run a good fuel pressure check also tape gauge to windshield or mirrow and run it on the road.
Most scanners have a injector balance test that will show a weak or clogged injector. Also some strong injector cleaner like sea foam may help if it is a dirty injector.
Run a compression check and switch spark plugs and or plug wires from another cylinder. Check good hot blue spark to missing cylinder. Even new plugs can go or be bad.
When it has the miss check the end of spark plug for being wet or gas on the end,
Check for good vacume with a vacume gauge and watch for fluncation or lose at 2500 rpm. A good vacume gauge test can pick up a plugged cat.

Fuel trims way off point to fuel pressure, map sensor or bad 02 sensors
Does your baro reading match your allitude?
MT

MT....I don't have a fuel pressure guage or Vaccum guage so I'll try and borrow one this week. My scanner doesn't have an injector balance test but I did scan for injector faults and the reading was 112. Compression test came out good as follows

Cyl 1 161
Cyl 2 158
Cyl 3 160
Cyl 4 162
Cyl 5 157
Cyl 6 160

As far as the pressure goes the BARO is half the MAP and Atmosphere

Atmosphere = 14.74 psi (101.6 Kpa) today from NOAA
MAP (Engine off) = 14.1 psi (97.22 Kpa)
BARO (Scanner) = 6.9 psi (46.9 Kpa)

Where is the BARO reading coming from ?


Switched plugs and wire on Cyl 2 and 4 and ran seafoam through the vac line and gas tank. Took the truck for a spirited run and was able to accel past 3 thousand 3 times....on the way back I made it to 3900 and the SES light went off...scanned it and saw Cyl 2 - 787 MF, Cylinder 1 - 26 MF...code was P0302....better but not great.


Thanks
Mike

MT....I don't have a fuel pressure guage or Vaccum guage so I'll try and borrow one this week. My scanner doesn't have an injector balance test but I did scan for injector faults and the reading was 112. Compression test came out good as follows

Cyl 1 161
Cyl 2 158
Cyl 3 160
Cyl 4 162
Cyl 5 157
Cyl 6 160

As far as the pressure goes the BARO is half the MAP and Atmosphere

Atmosphere = 14.74 psi (101.6 Kpa) today from NOAA
MAP (Engine off) = 14.1 psi (97.22 Kpa)
BARO (Scanner) = 6.9 psi (46.9 Kpa)

Where is the BARO reading coming from ?


Switched plugs and wire on Cyl 2 and 4 and ran seafoam through the vac line and gas tank. Took the truck for a spirited run and was able to accel past 3 thousand 3 times....on the way back I made it to 3900 and the SES light went off...scanned it and saw Cyl 2 - 787 MF, Cylinder 1 - 26 MF...code was P0302....better but not great.


Thanks
Mike

The baro readings come from the maf sensor.
Looks like you may be on top of mt everest or way up in the air from your readings. :grinyes: :lol:
That could be your problem on missfire.
e mail me at [email protected] and i will send you a pdf on Baro readings and some info on it.
Also try a disconnect on MAF sensor and drive it and see what it does.
MT

Mt...Thanks for the PDF...I ended up putting in a new MAF. Today the symptoms seemed to get alot worse...drive home Cyl 1 started misfiring at 2200 RPM, followed shortly after by Cyl 2...all other cylinders reported 0 misfires.....as per usual the bank 1 STFT went up all the way to 32 % while the issue was happening....this time it would misfire on both cylinders constantly until I pulled over (60-70 misfires per second)...soon as the RPM's drop below 1500, I can resume acceleration and as long as I accelerate gently it won't misfire.

Finally got a FP gauge on it yesterday and it consistently reads 59 to 62 psi throught the range. Even ran more Injector cleaning fluid through.

What do Cyl 1 and Cyl 2 have in common....and why only those cylinders ? Could this have anything to do with slotting the Dist hold down and rotating it ? The engine idles and does low RPM acceleration smoother than when I picked the truck up new.

From what I understand the sudden increase in STFT to the +15-32 % means that for some reason B1 is running lean on hard acceleration.
I love a challenge but this one has me baffled.

Mike

Mt...Thanks for the PDF...I ended up putting in a new MAF. Today the symptoms seemed to get alot worse...drive home Cyl 1 started misfiring at 2200 RPM, followed shortly after by Cyl 2...all other cylinders reported 0 misfires.....as per usual the bank 1 STFT went up all the way to 32 % while the issue was happening....this time it would misfire on both cylinders constantly until I pulled over (60-70 misfires per second)...soon as the RPM's drop below 1500, I can resume acceleration and as long as I accelerate gently it won't misfire.

Finally got a FP gauge on it yesterday and it consistently reads 59 to 62 psi throught the range. Even ran more Injector cleaning fluid through.

What do Cyl 1 and Cyl 2 have in common....and why only those cylinders ? Could this have anything to do with slotting the Dist hold down and rotating it ? The engine idles and does low RPM acceleration smoother than when I picked the truck up new.

From what I understand the sudden increase in STFT to the +15-32 % means that for some reason B1 is running lean on hard acceleration.
I love a challenge but this one has me baffled.

Mike

You are welcome and I hope it helped.
Did you get your reading to match your allitude level with old ornew sensor?
If it made it worse you may have had a bad sensor and also another problem is showing up more.

On 1-2 cylinders in common they are right next to each other in the firing order.
Or run next to each other in the bottom of dist cap.
Check dist cap real close and always use AC-delco cap.
Also check cam retard setting on a good engine capable scanner.
Cam retard is what sets the rotor to fire dead center to plug wire terminal in the dist cap.
But a red flag is that fuel pressure reading.
Specs are 60/66 lbs of pressure. So make sure your gauge is accurate.
Hood up a good gauge and tape it to windshield or mirrow and road test it with gauge hooked up.
Full load/pull on road you should see 65-66 lbs of fuel pressure.
Also at cold cranking. Idle or crusing you should see 62-64 lbs of pressure.
Here is a guide line on fuel pressure.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

Well MT.....Driving home last night was terrible...I had to stop every 10 minutes to get the SES light to stop flashing....anything above 2100 RPM this time. I ended up taking it to a Chevy dealer near where I work to pay them the 90 backs for 1 hour diagnostics. He ended up calling me and telling me they couldn't find a problem through their diagnostics and belived it is an internal engine issue. The service manager approved shop time to pull the cover and ended up conclusing this is a GM engine warranty issue. They think the CAM shaft is off.....it should be fixed tommorrow with either a new engine or CAM under warranty. In the mean time thanks for all your help on this, I really appreciate your time to share your knowledge and experience with us fledgling mechanics.

In the meantime I'm driving a loaner purple lumina with red interior.

How is it realistic GM QA could ship a crate engine with a bad CAM shaft ??? At least it would explain why I had to slot the distributor clamp.


Thanks
Mike

One other thing...My equss FP guage is going back...Gm tested the pressure and said it's actually running 65/66. Fuel delivery is good.


mike

Well MT.....Driving home last night was terrible...I had to stop every 10 minutes to get the SES light to stop flashing....anything above 2100 RPM this time. I ended up taking it to a Chevy dealer near where I work to pay them the 90 backs for 1 hour diagnostics. He ended up calling me and telling me they couldn't find a problem through their diagnostics and belived it is an internal engine issue. The service manager approved shop time to pull the cover and ended up conclusing this is a GM engine warranty issue. They think the CAM shaft is off.....it should be fixed tommorrow with either a new engine or CAM under warranty. In the mean time thanks for all your help on this, I really appreciate your time to share your knowledge and experience with us fledgling mechanics.

In the meantime I'm driving a loaner purple lumina with red interior.

How is it realistic GM QA could ship a crate engine with a bad CAM shaft ??? At least it would explain why I had to slot the distributor clamp.


Thanks
Mike

You are welcome and glad I could help
Thank for letting us know how it is going.
Sounds like the dealer done a good job of checking it out and is helping you get it fixed.
And 10-4 on the fuel pressure gauge you need one right on the money for sure.
On the gm cam and crate engine it is kinda a bummer but strange things happen.
Was it a rebuilt or new GM engine?
Good luck and Let us know how it goes.
MT

What about the cap and rotor?

Lots of people have asked you about it yet you haven't stated whether or not it is new?

LT...the Cap and rotor were replaced when the new GM distributor was installed. Actually a new distributor is the first thing this dealer tried.

MT...It was a remanufactured Goodwrench job.


Mike

If they didn't align the distributor properly that would cause a misfire for sure.

This is an interesting problem. While it could very well be an engine problem, has anybody checked the injectors? Could be intermitent injector problems - its well known that the injector pack on these engines have had reliability issues.

Truck is still at the dealership. The service manager told me they have checked both the ignition and fuel systems. Apparently the engine is out of the truck and they were waiting Friday afternoon for GM to determine whether they will try to "fix" the engine or replace it.

The Dealership also confirmed that they could not get the distributor to line up without having to slot the hold down clamp.

One other piece of noteworthy info...When the technician was running diagnostics he told me that the misfire first appears at 2925 RPM on Cylinder 1 and at 3400 RPM stops on Cyl 1 and starts misfiring on Cyl 2. Backing off the acceleration causes the reverse (ie stops misfiring on Clylinder 2) and starts back on Cylinder 1.

One other piece of noteworthy info...When the technician was running diagnostics he told me that the misfire first appears at 2925 RPM on Cylinder 1 and at 3400 RPM stops on Cyl 1 and starts misfiring on Cyl 2. Backing off the acceleration causes the reverse (ie stops misfiring on Clylinder 2) and starts back on Cylinder 1.

Mdrush
That is interesting info on it.
No 1 and no 2 fires right next to each other.
What ever it is must be feeding back to the other cylinder.
A good old vacume gauge test on the engine may show something.
But it sounds like the dealer tech is really working up and beyond the call of duty on the problem.
Can you feel the missfire in engine running when it missfires?
Good luck and let us know how it goes.
MT

Got my truck back from GM beginning of last week and she runs great. They replaced they ended up replacing the CAM shaft, CAM gear, Timing chain, CKP reluctor wheel, CKP sensor and sent the heads out. That fixed the high speed miss but it deveoped a miss at idle on Cylinder 1...replaced the main injector and ran the GM cleaner through the fuel rail and poppets and the miss went away.

After a couple hundred miles of scanning and my scantool is pulling no misfires. I'm obviously glad it's fixed but I would've like to have know the root cause. I've got an appointment on Tuesday to change the tranny fluid and filter...and hoping that my CAT is not damaged by all the misfiring.

BTW...when I got it back I had the classic "partially engaged" 4WD, right front axle...loud whining and vibration at high speed that goes away when you hit the 4WD selector....replaced the vaccum switch on the transfer case (did the axle one as well) and problem solved. Upon inspection, both swutches have the ball stuck in the "In" position.


Thanks
Mike

Got my truck back from GM beginning of last week and she runs great. They replaced they ended up replacing the CAM shaft, CAM gear, Timing chain, CKP reluctor wheel, CKP sensor and sent the heads out. That fixed the high speed miss but it deveoped a miss at idle on Cylinder 1...replaced the main injector and ran the GM cleaner through the fuel rail and poppets and the miss went away.

After a couple hundred miles of scanning and my scantool is pulling no misfires. I'm obviously glad it's fixed but I would've like to have know the root cause. I've got an appointment on Tuesday to change the tranny fluid and filter...and hoping that my CAT is not damaged by all the misfiring.

BTW...when I got it back I had the classic "partially engaged" 4WD, right front axle...loud whining and vibration at high speed that goes away when you hit the 4WD selector....replaced the vaccum switch on the transfer case (did the axle one as well) and problem solved. Upon inspection, both swutches have the ball stuck in the "In" position.


Thanks
Mike


Thanks for posting back and letting us all know how it went.
Glad they got it fixed and give them credit for taking care of you.
Not all dealers would have do that good of a job.
But I am like you sure would be nice to have known the main problem.
Good luck with it.
MT