2001 chevy blazer LT 4x4
p0304 cylinder 4 misfire
p0335 crankshaft position sensor

p0304 Freeze Frame Data

Fuel sys 1 CL
Fuel sys 2 CL
Calc Load (%) 4.3
ECT (`F) 185.0
STFT B1 (%) -4.7
LTFT B1 (%) 7.8
STFT B2 (%) -7.0
LTFT B2 (%) 5.5
MAP (inHg) 8.9
Eng RPM 1020
Veh Speed (mph) 7
MAF (LB/min 1.0
TPS(%) 0.0

Seems to idle pretty good. but once in gear seems to misfire about 2000 rpm. when it warms up to normal temp it seems to be a little worse. been fighting this for a while it was a p0300 random misfire but now its the p0304 cyc#4 and the p0335 crank sensor..
I have replaced lower and upper intake manifold gaskets, plugs,wires, cap, rotor, distributor, all vacuum lines, crank sensor, fuel filter, fuel pump, upgraded the fuel injector spider, cleaned all ground wires, tested fuel system pressure, cylinder compression test, cleaned throttle body, cleaned egr valve and replaced egr gasket with the screened one. replaced coil, been over everything 3 or 4 times. so tired of throwing money at this thing.
I did remove rear cat as thought it to be clogged. ordered new cat to replace. would like to get this resolved first before i do any further work or any more money to it. check engine light stays on and flashes when it in gear and is running about 2000 rpm or higher. I do know i need to get the crank sensor relearn done, but would like to resolve the misfires code before spending money to take to shop for relearn. Not really sure how to read the freeze frame data. I'm hoping some one knows how to read this and can help point me in the right direction.... Thank You so Much...

 

Here's one I have some experience with!!

FYI, freeze frame data says the PO304 code set at only 1020 RPM and 7 mph and you were off the throttle completely. That's about all I personally get from this particular freeze frame data.

Does it have a real felt misfire at 2000 RPM, or are you just basing the presence of a misfire on the SES light coming on/flashing and setting a code? It may or may not be a false misfire code. To me, your answer to this is key.

Worse at normal temp? Let me ask you about your oil pressure at idle in drive when fully hot and the presence of any knocks or ticking noises when fully hot..... If you don't have a real misfire, then your answer to this is also key to me.

Sounds an lot like my 2001 LT with a consistent P0304 (100% of time), but mine never had a real miss only the SES light and misfire counter going up all the time. Also was worse when hot.

Do you have a scanner that allows you to view the misfire counters in real time? If so I suggest inducing a miss in a different cylinder and seeing if the system can recognize an actual miss. (Mine could not). (Don't just pull a plug wire and let the spark jump). If it can't recognize a dead miss correctly, then the codes are probably false codes set by failure of the misfire detection system and we can go from there.

Added.....

Quote:

Originally Posted by blazerhelp01

just bought a 2001 chevy blazer had for few daysnow and noticed the oil gauge was pretty low. about 20-25 when on the gas. whenat a stop or just idle is like 5-10. runs good now oil light on seems to havelots of power still and not making any noise in motor. runs quite and smooth..is this a problem. changed oil and oil filter still the same. oil pressure runsnormal first 5 min of cold start up.

Quote:

Originally Posted by blazerhelp01

I have a 2001 Blazer LT. when itscold the oil gauge at idle is about 40 psi. while driving its about 45-50 psi.when engine warms up to normal operating temp the oil gauge drops to about 10psi at idle and about 25 psi when driving. I bought a oil check valve and wasgoing to replace this weekend. oil gauge seems to work pretty consistent wheneither cold or warmed up. does anybody know how hard these are to replace andany special tool i may need to remove it. I heard they can be a real pain. Iasked a couple different auto part stores any they had no idea... Please helpwant to get this oil gauge fixed it is stressing me out.. thank you

Quote:

Originally Posted by blazerhelp01

mechanic did say the compression was good onmotor. and has great throttle responce and you cant even really tell if thereis a miss. One thing i did notice is the tach gauge when you hit about 2000 itbounces up and back down a little bit. but seems to have no effect on motor revor shifting or way it runs... 2001 blazerLt 4x4

I see you pretty much already answered my questions in previous threads.

Check if system can recognize an induced misfire code as I described above on another cylinder. If it can, then go back and fix the miss on cylinder #4. If it cannot, the the crank relearn needs to be attempted. If the crank relearn cannot be successfully completed, the I expect excessive clearance in the crankshaft bearings are causing your problem and the extra clearance/knocking is whacking out the crank sensor signal and causing the misfire code. That will become much more apparent if bearings are bad and you try to do the RPMs required for the crank relearn several times. Did you replace the lower intake gaskets because they were leaking coolant into the oil? This is a common cause for bearing failure in a 4.3.

Les

 

Was there scuff marks on the old crank sensor?
P0335 can be from the wiring to the sensor or the sensor is hitting the reluctor ring and needs to be shimmed when installing a new one. Most likely the latter is the problem. Seems that this is a common problem with the 2001 year.

 

the oil pressure does drop when it warms up and is at idle. but goes right back up when i give it gas. there is no knocking or ticking that i can here and when removed valve covers seemed to get plenty of oil. never seemed to have coolant in oil. coolant seemed to leak externally. the miss does seem to get worse when motor worms up. yes you can feel the engine miss pretty good while driving not while in park idling or revving in park really. when i pulled old crank sensor out did seem to have damage to top of it like something was hitting it. but had a mechanic down road replace that while i was at work. when put new one in would crank but not start. tried shims and no shims. he said he did crank relearn but not really sure if he did. oil pressure is great when engine is cold. probably gonna take it some were to re do crank relearn just in case. any further help or ideas would be great

 

yes misfire seems worse at normal temp. and oil does drop at normal temp when idling about 10 lb. moves up to 30 when giving gas. also the tach seems to jump as it misfire pretty good. motor doesnt seem to tick or make any noise i can here. thanks for all the help. single dad of 3 and need to get this fixed without putting to much time or money into it. love the blazer. thsnk you so much in advance

 

If the reluctor was hitting the crank sensor then the new one needs to be shimmed or you will still have the problem of misfires even though you have a new sensor. Maximum of 2 shims are recommended. If 2 shims are not enough then the timing cover should be replaced due to possible warping.
Get the crank sensor checked again. If it runs bad, spits and sputters and the rpm is messed up then the crank sensor is hitting.

 

When replacing the new sensor the engine don't run just cranks... Tried shims no shims finally put old one back in starts right up. Won't run at all to do crank relearn.. Oil pressure still drops at idle after normal temp.. Not sure what to do with that. Oil pump seems to work fine.

 

Replaced oil lines, filter, running 10-30 with Lucas, also replaced oil by bypass valve and oil sensor. Any ideas on that. Don't think bearings or can are bad