2000 Blazer No Spark

Started truck to warm up ran for a while than died. When you cycle the key you can hear fuel pump running. Checked and don’t have spark at coil. Plugged in known good ignition module still no spark.
Plugged in good coil still no spark. Hooked up computer reader and cranked engine no codes or tack reading while cranking. Replaced crank position sensor and still no start. Replaced cam sensor still no start. Checked the power feed to coil, ing module, crank position sensor and cam position sensor all good. Checked all fuses to ignition and computer all good. Unplugged computer isolated EST pin and sent signal to ignition module and it sparked at coil. Checked for power with LED test light at computer pins from crank and cam sensor. Replaced Computer and still no spark. So now I am stumped 20 ½ inches of snow over the weekend and my 4 wheel drive is down. If you have any suggestions it may be a few days before I shovel any more snow to check it out.

Here is something you might want to think about.
Truck was towed in there was no spark. When cranking there wasnt any RPM signal.I checked power at the ignition fuse and I noticed it losing power as it was cranking. I then tried to start vehicle by not turning the key all the way and it would start.I replaced the ignition switch and it started right up with no more problems

I had a '95 blazer act similar- only it would try to start when I let off the ignition switch -that is it would not fire in "start" position- but it would hit once or twice when I released the switch to "run" position-- so did you check power at coil in "start" position??? -- mine was only hot in "run" position-- so to double check my diagnosis- I jumpered 12v battery hot to the coil hot inout lead-- and it started right up-- the ignition switch would not supply 12v to the coil in "start" only in "run"-- thus the need for a new ignition switch-- But since this was a job for a favor- I opted to install a relay which activates upon start commaned- and jumperes battery hot to the ignition pink wire under the dash- exactly the same thing the ignition switch does-- and the truck starts every time-- so now all I have done is to guaranttee the ignition is hot through a parallel relay circuit- without installing a new ignition switch- the choice was easy a $10 relay or a $100 plus ignition switch- plus the aggravation of installing it....Sounds like you have replaced just about everything in this truck- I feel bad for you- been there done that--

Put a test light from the coil battery terminal to ground on while in start position and while cranking and got power. Put a jump wire from fuse inj1 & ecm1 to battery this should bypass the ignition switch completely still no start.

Is your security light flashing? does it go off after ignition is on for a few seconds?

Security light doesn't flash and goes out after a few secounds. Owned it for 6 years and never had a remote assumed that it didn't have a security system.

How about crank sensor wires- connector- and continuity back to the vehicle control module?? .... also I had one that was blowing me away once- it was a Ford- I had checked with a meter- every fuse in the car- while the fuse was seated- they all worked-- but what I soon found out, was that some bast**d had pulled a fuse- so that the fuse was NOT there, that I needed to run the car-- so check every fuse slot as well-- I lost about 4 hours on that one......

The pink wire at ignition coil should show battery voltage when the ignition switch is in the RUN and START positions. The white with black stripe wire at the ignition coil is from the ignition module and should pulse while cranking. The black with white stripe wire at the ignition module should show less than 5 ohms to ground. The white wire at the ignition module is from the VCM. The VCM tells the ignition module when to fire the ignition coil. If those check OK, the crank sensor, the VCM, the ignition module, and all of their associated wiring is ok. The camshaft position sensor has nothing to do with wheather it has spark or not. Post your results.

Just checked continuity for both signal wires from the crank position sensor to the ecm ok. The truck was running than died kind of ruled out a fuse missing. Also the fuel pump is running, the security system shuts the fuel pump down.

Checked the pink wires going to the coil & ignition module and have power. Sent a signal to the ignition module from the ecm (white wire pin # 9 white connector) coil fires with big blue spark.

Disconnect the ignition coil harness connector.
Probe the ignition coil connector terminal C with a test lamp connected to B+.
Crank the engine. Is the test lamp flashing while cranking the engine?

....Sent a signal to the ignition module from the ecm (white wire pin # 9 white connector) coil fires with big blue spark.

explain...you manually sent a signal or the VCM sent a signal while cranking?

If a test light was flashing while cranking wouldn't the coil spark? I did do that though no flashing....... No ignition on not cranking to test the coil and ignition module...I am starting to think that the new crank sensor is bad

Inspect the plug to the crank sensor real good may be a connection problem and take a good look at the tone ring that passes by the crank sensor,back probe the connector at the crank sensor and see if you get a pulse while cranking.
. Using a lab scope check for a square wave signal at the Powertrain Control Module (PCM) connector C1 pin 31 Yellow wire.

2. Check for Battery Voltage (B+) at the crank sensor pin A Pink wire cranking.

3. Check for a good ground at the crank sensor pin B Purple wire while cranking.

If a test light was flashing while cranking wouldn't the coil spark? I did do that though no flashing....... No ignition on not cranking to test the coil and ignition module...I am starting to think that the new crank sensor is bad


The crankshaft position sensor is an input to the VCM and is constantly monitored by the VCM. If there is no signal from the crankshaft position sensor at the VCM while cranking, (or running), DTC P0336 will be set and the SES light will come on. If P0336 is not present, the crankshaft position sensor, and it's circuits to the VCM are ok.

The VCM applies a pulsing ground signal to the ignition module while cranking, (and while the engine is running). The ignition module in turn sends a pulsing ground signal to the ignition coil. To test for pulse at the module and/or the coil, the alligator clip of the test light must be connected to battery positive, and the test light probe connected to the white with a black stripe and to the black with a white stripe wires. You should have pulse to both while cranking. This checks the VCM output for ignition. If there is no pulse from the VCM at the ignition module, the circuit from the VCM to the ignition module needs to be checked for continuity. Ignition output from the VCM to the ignition module is a VCM output and is not monitored by the VCM, so no codes can or will be set if there is a problem.

next step

Turn OFF the ignition.
Probe the ignition coil harness connector terminal C with a test lamp connected to B+. Is the test lamp ON?
if yes, repair short to ground between coil and module.
If no, make sure you have 12 volts at the pink wire terminal A at coil, which I think you said you did. then check for poor connection/terminal tension. if ok then its the coil thats bad

Installed a hub on a 98 Bravada while I had it I swapped the crank sensor the Bravada ran fine but the Blazer now starts but dies right away can hear the fuel pump running for about a second after it dies swapped the sensors back and will still start but die I think it is possessed

So it runs while the starter is engaged?

It will continue to run after returning key to run position but just a secound or less. Ran out of daylight last night plan on hooking up fuel gage next.

Fuel pressure was about 60 than 50 than 55 than back to 60 jumping around. Unhooked gage from hose to pump a little into a gas can to check for water, wife said she just filled up. Than the pump stopped running, beat on the tank got it running but still not enough pressure to run. Pumping the tank now,Why do they always die when the tank is full?

Replaced the fuel pump and my 60 lb fuel gage pegs when I start it drops to 55 runs for about a second than dies. If I put some gas in the throttle body it will run longer. The security light goes out in about two seconds when I turn the key on

Did the Passlock auto learn procedure and it is running for now no clue about the spark

Hey Oldsdoc? I'm on this same problem all ready waisted $$ on a ign coil and Crnk sensor. I have not went thru the fuel pressure check, (as I tried starting fluid right off) then realized no spark. Your last comment is confusing to me, how did you do the relearn when there was no security light to watch?
Also as far as fuel pressure goes, I have not found any clear info on whether or not low pressure would cause no spark, do you know the answer to that? Any help would be greatly appreciated, just spent 4k on this still have 30 day tags and it cut out a few times on my way home. Died pulling in driveway and no start since!!??

I replaced the computer which on a 2000 has to be flashed for the VIN number. After install the security system will let it start but kill it after about 2 seconds.Verify no spark by cranking with a sparp plug hooked to a grounded old plug. Let me know how that comes out.

What did you spend $4K on?

The SECURITY system will not prevent spark.....it will prevent the injectors from firing.....

You have the coil on plug setup on a 4.2? Or a distributor on a 4.3?

Low fuel pressure will not cause no spark.....you need to see what the pressure actually is, when there is no spark....if no fuel pressure AND no spark, I would be concentrating on the crank signal......

If you have good fuel pressure, and you have replaced the coil(so I guess this is a 4.3), and there is no spark out of the coil, this has to be addressed first....checking the distributor cap/rotor comes later.....

This has an ignition module.........the question is, is that module controlling the coil....it can only do this if it is receiving a signal from the PCM...the PCM create the signal for the ignition module, only if it is receiving a signal from the crank sensor....I know you installed a new crank sensor, but the question is, is the PCM receiving it? This is where a scan tool is invaluable.....

So, if the crank sensor is ok, and the wiring between it and the PCM is ok, if the PCM is ok, and the wiring between the PCM and the ignition module is ok, then I would assume it's the ignition module.....

All coils work the same way......the primary coil is grounded by the ignition module...but that doesn't create the spark....what it does is create a slowly building magnetic field around the secondary winding.....when the grou nd is removed by the module, that magnetic field QUICKLY collapses, and high voltage is created in the secondary coil.....so either the ignition module is either not receiving a control signal from the PCM, or the module is bad....

Okay I think I found what I was looking for, getting ready to go try this today. See I have followed all the test in the tree for troubleshooting ignition system.
My results kept leading me to no pulse signal coming directly from the CPS itself. Here is a link to another problem found for the no spark condition;
http://blazerforum.com/forum/engine-transmission-35/2000-blazer-cranks-but-no-start-68126/

It only makes since to me at this point that this has to be where my problem is. I know for sure I have no spark, and I have no signal at CPS but voltage to CPS and thru Cps ground test good. Oh and key point I am working with a new sensor after the first failed this test (and yes I know the new sensor could possibly be bad).

I will post results after I do what camaroman and 1 other person list as the fix. Oh and the vehicle is the LT model 4.3 and its what I paid $3.950 for has 105k actual miles and in great condition. (the LT model in case you don't know has all the bells and whistles including all leather int).

Also Doc if your still having an issue you might want to try this as well! :smile:

The post is 4 years old the Blazer and is long gone a guy posted on cregs list that he wanted a 4 door suv I called him and put him in it.

Okay so far not getting any change, but I also didn't mention that when I start the test for the crank signal wire ign on and before I start manual turning of crank. I am starting off everytime (old sensor and new) with .5 -.6 volts and I can here clicking and buzzing (fuel pump/injectors) as soon as I touch ground??

Does that sound right, could I have a hot short somewhere on the signal wire to pcm?

And sorry about the age of this post guess I should have just posted a new one just thought you might have figured something more out. And congrats on the good riddens of your Blazer doc!

Just letting you know I won't be trying any thing. Also I can't look at my truck to see how things are laid out. I do have wiring diagrams though. I need to be sure that there is no spark so I don't tell you to check the wrong things. First thing is to check for 12 volt + at the coil's pink wire when the Ing is on. Depending on that I Can tell you other things to check.