Just picked up a blazer and after buying it the Ses light came on. Misfire on cylinder #4 code. But the truck feels completely fine while driving. Fuel mileage is 15mpg ish. Checking with my autel scanner it’s showing missing on cylinder 4 and occasionally on cylinder 1. I noticed it’s only around 1500 to 2500 rpm. Idle and full or heavy throttle it doesn’t miss. Previous person said they did new distributor, plugs and wires,spider injection,cps, mass air and idle air sensor and valve and timing chain cover.
Side note at idle when warm and stopped in drive it runs about 15-20 psi. Is that normal ALL HELP APPE

 

Could be it never had a crank sensor relearn after installing the Jasper engine or a new crank sensor. This could cause a false misfire to be detected. You will never get to zero misfires on the scanner's counter. As long as the SES light stays off you are golden. Key here is do you feel a misfire?

Also what is your cam sensor retard value to check proper distributor installation? Should be zero +/- 2 degrees

15-20 psi at idle is normal oil pressure for 5W30 oil and a warm engine. Are you hearing noises?

15 mpg is normal combined mpg for a 4x4 Blazer in good weather.

Best Wishes

 

Thanks for the reply! Cam says -1 at idle goes to - 2 on throttle. Should I buy a new sensor and take it to a shop to have it relearned I don’t think my scanner can do it. I feel no miss at all. Also are jasper engines generally a good motor or are they prone to problems. I’ve never had one. Also hearing no noises. I had a 4.3 crew cab a few years ago but it’s warm idle was around 30-40

 

Cam sensor retard is great at 1-2 degrees. No need to buy new crank sensor - they are very simple and not prone to failure. I would bet the crank sensor relearn was not performed after previous repairs where the crank sensor was replaced or disturbed (like when installing Jasper engine or messing with timing cover.

How long after clearing codes does it take to set the misfire code again? Does the SES light flash? Because of the expense of crank sensor relearn, let's consider a few other things first.

Can you please display the 6 misfire counters and either screen record or video the rate of misfire accumulation at it's worst. Then do the same with the serpentine belt removed. I want to see the rate of accumulation and also rule out any vibrations induced by belt driven accessories.

We can go from there.

 

I’ll get a video here shortly. It only flashed on the interstate home for a 2 hour drive. Doesn’t flash around town. It takes about 30 minutes or more for the light to come back sometimes longer but always the same code. I’ll get my scanner and hook it up but under acceleration it shows cyl 4 missing the most and cyl 1 is occasional. The other cylinders show 0. But it “misses” enough for the computer to throw a code after a while