Crank No Start

[Schimpfy]

Need some help troubleshooting a crank no start issue. I tried a search, but didn't find what I was looking for so if this has been asked before please let me know.

Anyway...

99 K1500 5.7 is cranking, but not starting. The steps I've taken so far are:
1) Tested fuel pressure - 55psi.
2) Tested for spark at all the cylinders - nothing.
3) Tested for spark from the coil to the cap - nothing.
4) Tested voltage to coil and ICM - good at 12V.
5) Checked signal from ICM to coil - good continuity.
6) Swapped coils with known good one, twice - nothing.
7) Swapped ICM with known good one - nothing.
8) Checked switching signal from PCM to ICM - on with key in off position.

So, I stopped there because based on what I understand the switching signal is only suppose to be on when the engine is rotating. Why would it be on if the key is off?

 

[someotherguy]

Dunno about #8; above my pay grade.

You probably already did it but since you didn't include it in your post, did you check continuity and resistance on the coil-to-cap wire? Have you replaced the cap?

I would hope your '99 has the MFI actual real injector setup but really don't know. If it's got the original poppet valve setup, 55 psi isn't enough fuel pressure for a small block Vortec to start reliably. That wouldn't explain the lack of spark, though!

Richard

 

[Schimpfy]

I did check the high tension wire for continuity and resistance. It was good to go. I've also upgraded to the MPFI. I always thought that between 55-60psi was sufficient.

 

[Schurkey]

Crank sensor, crank sensor wiring harness?

No crank sensor, no start.

 

[Schimpfy]

The crank sensor is relatively new, but I'll check that next.

Any idea why I'm getting a switching signal to the ICM with the key off, though?

 

[deadbeat]

My dads truck did this, wouldn't even throw a crank sensor code. Changed it, that was a year ago, it has been fine since. My truck did something odd with the crank sensor, it would start and run fine, but if you were crawling in the woods, it would die. Once it cooled back off it would start and run. Those sensors seem to be troublesome on the vortecs. On dads truck I got the lower pressure on the gauge so I replaced the spider with MPFI, filter, new pump, everything fuel injected. Turns out the gauge I rented from Orielly's just didn't read correct, still showed 52 or so with everything AC Delco new. Crank sensor and it ran fine, even with only about 52 on that guage.

 

[stutaeng]

Obviously, the no-spark is the first problem to attack, and you are on the right track.

The ICM signal should blink with a test light while cranking. You said it was blinking with key "on" before cranking? I think this signal is from the crankshaft position sensor or computer. Need to look at a wiring diagram. What does the test light do when cranking?

 

[Schimpfy]

I haven't checked the test light while cranking yet because the fact it was on with the key off threw me. I'll try to check and see if it's on while cranking when I get home this evening.

 

[stutaeng]

I haven't checked the test light while cranking yet because the fact it was on with the key off threw me. I'll try to check and see if it's on while cranking when I get home this evening.

Yes, with key on (no cranking) you should have gotten a steady light indicator. You just had to crank to see if light was blinking! Keep us posted.

I believe on the later models S-10s/Blazers, there is a common issue with the ignition switch, but I don't think it's common on the GMT-400s. But that's another thing to check.

I'm not sure if you have seen these articles, but they show you how to quickly check for 12V, ground and reference signal on most of the sensors on the Vortec engines:

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-crank-sensor-1

 

[someotherguy]

I did check the high tension wire for continuity and resistance. It was good to go. I've also upgraded to the MPFI. I always thought that between 55-60psi was sufficient.

Correct, with the injector upgrade that you have. Most seem to report running 52+ psi and no issues. It's with the original poppet valve setup that the pressure must be in the high 50's for it to reliably start and run.

Vortec small block spec is 60-66 (with the original poppet valve setup); where the problems crop up varies from truck to truck but general rule of thumb is once it gets down to the mid 50's they are unreliable.

Richard