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Originally Posted by mdrush
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
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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.