To my understanding the CKP sensor on a 98-01 uses the white wire up from the PCM to the ICM to send its signal, how would i go about testing during cranking to see if i have a consistent crank signal with a test light and without frying the PCM by putting power where it does not belong. this specific truck may have an 03+ PCM/Harness as i cannot ID the block or PCM model year but i know at minimum the block is not OE. I can get it to run but its super intermitted and the only new major controlling component is the crank sensor, cap was ohm'd at 1.7ohm's for all contacts and the rotor is spotless. all plug wires are new, she wants to run but i just cant pin this issue down. shimming the crank sensor causes it to do absolutely nothing. wont even sputter.

 

You really cannot use a test light to inspect the output from the crankshaft position sensor and gain anything meaningful from it. You would need an oscilloscope to actually inspect the waveform for the proper shape and tooth count (4 pulses per revolution). Typically, the CKP and CMP sensor traces are compared together at the same time against a known good waveform to determine if there is any mismatch in the timing between the two that could indicate a problem with the engine timing. Inspection is performed by back probing the connections at the sensor(s) and connecting the leads to the oscilloscope.

You don't happen to have a stored DTC of P0338 do you? I just happened to see a TSB about this that states that if this code is present, it could cause the PCM to command a 50 degree spark advance which could cause a hard/no-start condition as well as potential damage to the starter and/or ring gear due to increased cylinder pressures. The TSB suggests that the CKP sensor is faulty and in need of replacement and that this code would not trigger a CEL.

 

No codes atleast none triggering SES, will check tomorrow as its getting very late down here. and actually i think i've isolated the issue further, if i turn the key to RUN, then OFF, then directly to START from OFF it bumpstarts like nothing was ever wrong. i think the ignition switch is on its way (222,315 miles on its OE switch and a whole lotta key cycles as this was DD for all of those miles). at this point i've isolated every other issue from it. my usual procedure for starting any vehicle is to turn the key to RUN then START in about a one second step to give the pump time to prime to prevent hard starts, so that may be whats been ****ing with it so far. If you've any other ideas i would love to hear them because this has been an issue for months now.

edit - Got out there today, no stored codes, and its back to kinda no start, it comes up to about 500rpm then stalls off, and it will atleast do that consistently until the battery runs down to much. and its still not throwing codes. cant tell if its overfueling or lean stalling, lack of spark or lack of 12v reference via the switch which i had tested for a little while back (got 12v key RUN 10.3 key START off the ECM 1 fuse and at the ICM/Coil reference) trying it in flood clear mode doesnt yield any better results.

 

And heres a video of it, dash apart because the lights control box on the left side pushed straight in, trying to figure out how to fix that still.

 

Well, I told you how to test the ignition switch in at least one of your now many threads concerning your research into your no start issue didn't I...?

 

This would be thread #2 and this started as i was trying to isolate what part is causing the no-start, starting with the one that was obvious to me as its new - the Crank sensor, the truck will *run maybe if its cold and the stars align right, you had recommended backprobing the switch with it still on the column but that would involve tools i dont have and the procedure for testing is not listed anywhere obvious that i can see. which contacts should i be testing and what would be a "normal" amount of voltage during key run/start, and what would constitute an out of spec fluctuation or voltage drop.

 

Did you ever get a scan tool? If so, what did you get? Did you ever test fuel pump pressure with a gauge? What was it?

FYI please stop making new threads for the same basic issue (Blazer won't start and run). I can hardly follow them. I had to go through them all to see what you have done and I'm still a little unsure. Better when they are kept together in sequence.

 

There should only be 2, this one which is related to a test i wanted to perform (signal from PCM to ICM as my understanding of the CKP circuitry was inccorect) and then the long crank no run thread which got one reply, the rest were me just posting things i've tried and bits i've tested. There is the Ignition probe points thread which was about testng the ignition switch *without* backprobes.

I have put a scanner on it and pulled no codes when the motor *is* running. there is an SES light key on with the motor off but my scan tool will not read it (cheapo ELM327 wifi scanner with CarDocPro as the app)
its secondary issues only become apparent when warm, that being inability to get about 200rpm above idle without it sounding like its not running and slamming back to idle without any dramatic noise, shaking or any physical signs. I lack a few basic tools and the means to get them so a fuel pressure test needs to wait, though this is an MPFI system and to my understanding pressures are not as strict as with the CPFI systems. i cant narrow down what the issue is at all.

I've gone from basic ignition to fuel delivery a few times at this point because each time the issue flares up the symptoms change. when i have some time off work i'll do a compression test although it's had one done when the truck was shelved and it tested "fine" according to the guy who did it, but i dont quite know what his definition of fine is. And i've not noticed any blowback into the cooling system.

Shortlist of things that have been tested -

MAF, MAP (reading live data while cranking/running, unplugging either/or when the no-run issue crops up does nothing)
TPS(live data motor off depressing the pedal slowly untril 100%)
Coolant Temp Sender, reads within a fair few degrees of ambient temps.
Ignition circuit voltage drop key RUN/key START
Distributor cap is new and so is the rotor though i dont believe they are delco, they should work for atleast a little while right?
Plug wires as two of the wires had large gouges in them.
Pressure regulator replaced by previous owner with an unknown part.
I've replaced the upper intake gaskets as they were properly flattened due to being 20+ years old.
regapped all the plugs to 0.060 and noted that they were mismatched autolite/bosch plugs, they were not too packed with carbon considering what i believe their age to be.


Things i've yet to test -
Voltage at the fuel pump, i'd seen a thread about that being a sign of a failing ignition switch, and i lack the tools to test that either (backprobes)
Fuel Pressure and leakdown
Compression although that can somewhat be ruled out as it runs *period*

And thats pretty much where im at. Distributor timing was done with the timing cover off and i've given the gear a very good lookover and noticed no chattering or uneven wear.

 

Ordering the Ignition switch (and a host of other odds n ends) on tuesday. the switch was with this truck when it rolled off the dealer lot in '99 so im pretty damn sure that weird intermitted issues can be directly linked to it.