hello all. 02 blazer w/ 4.3, auto. had a nasty misfire at higher rpms, and threw a p0335 code. so i stopped into a advanced auto and bought a sensor. drive it half way home and it dies. so i crawl under it and change it in a parking lot. nothing. no spark (verified). i installed one shim, to see if that would help, nothing. i walked back and swapped the sensor out for a bwd (10$ more), and walked back. installed it, both with and without a shim, nothing.
i am pushing it home (AHHH!), but i need insight. i have power to the sensor, 11.0v, and i verified continuity from each pin to as far back as i can find wires to probe (about 4 inches). id like to check continuity from the plug to the PCM, but i cant find a pinout for a 02, just up to 96, which appears different. i verified twice i have no spark. plugs and wires are new, truck ran ok last week.
i found mention of a relearn procedure, but the steps involve starting the truck and letting it warm up, which i cant do.
what am i missing?
TL;DR - i need a pinout for a 2002 4.3 blazer, and i need to know what i should see voltage wise at each of the three wires going to the crank sensor.
-JON
Damaged CKP sensor connector Damaged reluctor ring (missing teeth or not turning due to sheared-off keyway) Sensor output open Sensor output shorted to ground Sensor output shorted to voltage Failed crank sensor Broken timing belt Failed PCM
Using a scan tool, check if, when engine is running or cranking, that there is an RPM signal. If there is no RPM reading, then visually inspect the crank sensor and connector for any damage and repair as necessary. If there is no visible damage, and you have access to a scope, you could check the CKP 5 Volt square wave pattern. If you do not, then, obtain a resistance reading of your crank sensor from a repair manual. (There are so many different types of crank sensors that there's no way to put here which resistance reading is correct). Then check the resistance of the CKP sensor by disconnecting the sensor and measuring resistance of the sensor. (It is best to check resistance readings from the PCM connector. This rules out any wiring problems from the start. But it does require some mechanical skill and shouldn't be performed if you\'re not familiar with automobile electrical systems). Is the sensor within resistance specs? If not, replace the CKP sensor. If so, recheck resistance reading from the PCM connector. Is the reading still okay? If not, repair open or short in the wiring to the crank sensor and re-check. If the reading is okay, the problem is intermittent or the PCM may be at fault. Try reconnecting and checking for RPM signal again. If there is now an RPM signal, wiggle test the wiring harness to try and induce the fault.
Read more at: http://www.obd-codes.com/p0335
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Can you verify the sensor was really bad?
I mean can you be sure the reluctor isn't bad?
Is there power to coil?
power to the coil i will check.
i will also check the reluctor. thanks.
-J0N
i cant actually test the old one, it got pitched at some point by SWMBO.
-J0n
GM connectors can be pretty fragile. I've seen a lot of "bad sensors" that were really just bad terminals in the connector. Swapping out parts just makes the connectors worse.
In a pinch you can TRY to tighten the pins up, but you might also be making things worse if that isn't it.
ok, i have 12v to the power feed, and verified continuity back to the pcm, pin #12. what is the third wire for?
i have power to the coil. reluctor ring is intact and spinning. i did notice a slight witness mark from rubbing, so i added the second shim, and tried it, no start.
? ahh!
-J0N
11.0 volts? That sounds very wrong. I'd think a crank sensor would be taking 5 volts, if not that, then full battery voltage. Maybe you smoked a regulator in the ECU? I'd be verifying what voltage that should be seeing and checking bus voltages at the ECU.
it is full battery voltage, just the battery is weak cause we've been cranking it. i thought it should be 5v too...
the other wire is signal return, and the middle one is pcm ground, which i have verified.
i have once again heard about a relearn procedure. is there anywhere i can find such info?
truck is home. we have verified that all 3 wires are making connection, and other than having 12v instead of the 5v i would expect, everything looks ok.
-J0N
http://my.cardone.com/techdocs/PT%2070-77-0003.pdf
http://www.fullsizechevy.com/forum/general-discussion/performance/port-injection-96-obd-ii/164702-gm-computer-relearn-procedure-including-crankshaft-relearn.html
ok, i found a faulty connector, and twisted the pins on the crank sensor a bit. now i have rpms in live data while cranking. but it still wont start. i cant hear the fuel pump running, and i have no pressure at the rail.
did i screw something up when i disconnected the PCM to probe wires? im certain the plugs are back on correctly and seated.
-J0N
WTH!!!! i have spark now, no codes in the pcm, but no fire. i cant hear pump running. jumping out fuel relay did nothing.
ih8gm!
-J0N
Just to put a cap on something: The crank relearn is only so the computer can learn the crankwheel for purposes of misfire detection. It involves bouncing the engine off the rev limiter once and letting off quickly, after yout put the computer into the testing mode.
So, a lot of the forklifts that I work on use GM vortec 4.3 engines. Only the most recent models use cam and crank sensors, but many of the old and new style engines have ignition system issues.
What I do when I find no spark, but good power supply and continuity is to replace the coil and ignition control module. In fact, I usually replace the ICM as part of the tune up on machines with questionable Maintenance history. They are cheap as Forklift parts, so they must be cheaper as auto parts. I've also seen a lot of distributor caps with burnt out center buttons, so check that carefully.
FWIW, the 4.3 is one of my least favorite engines.
Really interested in the cure here...
ok, so funny story. the crank sensor likely wasn't bad. neither was replacement #1. #2 is certainly good. i finally found that the connector was boogered. the connector inserts were attached to the wires, and i had continuity back to the ECM, but it wasn't making contact with the pins on the sensor. i could see the little flap that holds pressure on the sensor pins was either stuck or bent back on the 12v+ terminal. so i twisted the pins about 30*, and shoved the connector on, and that's when i got spark, and the code disappeared.
but it still wouldn't start. i verified spark at the #1 wire, good blue flame. checked for the code 3x, gone.
WHAT THE HELL!!!
i noticed after about 20 minutes of messing with it (and kicking it and cussing a bit), that i could no longer hear the pump prime...
the fuggin pump died. DURING the diag of no spark, i lost fuel pressure. i smacked the bottom of the fuel tank with a hammer, and she fired right up. i drove it to my dads shop where we put a pump in it today.
runs great now, and i hate chevys just a little bit more...at least whe my fords pumps die, it runs like crap for three weeks, and i know its going. it doesn't just fail and leave me off stringtown road and I-70. (Bitch).
so thats my GM story.
-J0N
the only fuel pump i've ever had die was in a 97 Cavalier that had 270,000 miles on it, and i was able to drive almost 30 miles home after i figured out that it had low fuel pressure. it ran like crap from time to time and put me on the side of the road twice, but it made it home somehow. well, i didn't quite make it home: i made it to within a half a block of my house before the pump finally wheezed it's final breath..
'94 Ford Bronco and a first gen Tiburon both died one me gave me plenty of warning.
Hyundai was infinitely easier to replace.
The fuel pump in the Malibu went bad and I whacked the tank to get it going. I then had the bright idea that since it was running I'd take it 100 miles to my friends shop so I wouldn't have to drop the tank in my gravel driveway. It died exactly half way there to teach me not to get greedy.
Wally,
funny you say that, the one in my 93 bronco died, and i did the EXACT same thing. whacked the tank to make it run, and tried to drive 62 miles home. i got 31 miles. exactly. AAA finished my trip. at least it got me under the maximum 50 mile free tow i had with AAA, so that was good.
-J0N
novaderrik wrote:
the only fuel pump i've ever had die was in a 97 Cavalier that had 270,000 miles on it, and i was able to drive almost 30 miles home after i figured out that it had low fuel pressure.
GM CFI systems (anything with the "spider") are very, very finicky about fuel pressure. 5psi off and they won't fire.
Fought an Astro for two friggin' days (not just me) checking spark and compression and timing and scoping the crank trigger to make sure it didn't shift somehow and a bunch of other things, and the problem was that it had only 58psi fuel pressure, which we THOUGHT was enough.
One of those times where learning something makes you feel dumber, you know?
yeah. we had about 62 before the pump swap, and it ran, but crappy. no power up top, no torque. we had 65 after the swap, and it seemed to run like new.
-J0N
gm pumps can die slowly too.
i had a 3.1 TBI lumina dustbuster van run on 2psi of fuel pressure.
4.3 TBI engines are one of my favorite unkillable machines, 4.3 vortec engines are one of my least favorites.
