Low reference does not "receive anything". Think of it as a ground comparison for the PCM.
Low reference does not "receive anything". Think of it as a ground comparison for the PCM.
I was curious after checking all if it was a ground or something. So all "low references" should be checked like a ground correct?
1996 GMC extended cab, 2003 5.3/auto
Pretty much.
what defines system voltage?
is that simply the number you get when you ground the positive side of the battery?
cause he got 12.4V
Voltage from cam sensor = 11.49
voltage at crank = 11.48
if that is the case, then he was definitely off .5v and it would seem somehow the cam and crank 12v is grounded but I dont know how, as that is all new wiring/harness. as far as resistance across each wire from sensor to pcm, it checks out fine.
as far as the coil packs. when the engine is cranked, there should be bursts of voltage at the IC circuit correct? 5v or closer to 12v? as that is how the coil pack knows to send fire.
Last edited by LSXmyford; 08-22-2008 at 07:02 AM.
LSX conversions, so easy a caveman can do it.
Originally Posted by LSXmyford
System voltage should be near 12.5 or a little more everywhere in the harness that has B+. Although you're down 1V (which is a small problem), it should run (have spark) at 11.5V if everything else was OK. Obviously it's not OK.
If you have access to a logic probe you could check to see if the ic circuit at the coils is pulsing. You would also be able to tell if the cam or crank sensors are sending any pulse signals to the ecm as well.
System voltage should be close to what you check across the battery. Assuming good connections in everything.
Your low voltage readings on the CKP and Cam Sensor are a problem according to the manual.
____________________________________
Only thing I've found for testing the CKP wiring .Is the difference in the voltage more than the specified value?
- Turn ON the ignition, with the engine OFF.
- Disconnect the crankshaft position (CKP) sensor.
- Measure the voltage from the CKP sensor 12-volt reference circuit and a good ground with the DMM.
- Compare the measured voltage with the system voltage.
0.5 V
__________________________________________________ ___
From above the next steps are tracing all wiring through the system checking for good ground and wiring to PCM.
03 Chevy ECSB, Z71, 6.0L(LQ4), Maggie @ 9PSI, 4l80E, PI Vig 2800, Detroit True-Trac, 4.10, 90mm LS2 TB, Meth Injection, HSW Dry N20, LPE GT7 Cam, 918 springs, Dynatech LT's, Hi Flow cats, custom stainless exhaust, DMH cutouts, DJM Suspension Drop, E-Fans, AirAid, HPT 2Bar SD Tuned, 11.68 @ 114.2
I agree it's out of spec I just doubt 11.5V would keep it from running. The issue does need repaired though.
according to what my bro tested, as far as crank sensor and engine crank, by the fluctuating end numbers...something is happening.
if he set his multimeter on the IC for the coils, shouldnt he see burst of measurable voltage as the engine cranks?
if he set a simple test light from a 12v constant, to the fuel injector ground wire, should he see a flashing light as the engine cranks?
if he cleans the contact surface and reattaches his harness grounds and this things fires...Im gonna flip...
LSX conversions, so easy a caveman can do it.
Usually not. Depends on the test light. The noid lights used for this injector test have the same impedance as the injector coils. Most test lights have improper resistance to light with a stock PCM injector driver.
You might be able to use a test light on the ground control wire of a coil (purple wire at coil #1) hooked to B+ to determine if the coil is being pulsed by the PCM while cranking.
I do not remember from previous posts and topics but have you checked for spark with a spark tester in place of a spark plug?
The coils (each bank) have a ground that is not the same as the PCM grounds. The main ground for all driver side bank coils is terminal A in C148 (8-way connector that connects coils to engine harness). Make sure it's a good ground by test lighting it to B+ with it unplugged (engine harness side) key on, engine not cranking.
Do the same for the low reference circuit (grounds through PCM) in C148 terminal E (brown).
Also check B+ at C148 terminal H (pink, 12V) by test lighting it to battery ground. Terminal D is not used and the remaining 4 circuits are control (on/off ground) circuits for the coils from the PCM.
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