Electrical Troubleshooting: Temperature, fans, fuel level, reverse lockout

Problem Statement:  Fuel gauge reads high out of sight.

Background:  A new fuel pump and level sender (and basket) was installed just prior to the V8 swap, and was working fantastically.

Research:  The large connector by the brake booster has the resistance lead coming from the fuel level sender.

Troubleshooting:  None yet.

Solution:  None yet.


Problem Statement:  Temperature gauge never leaves pegged low.

Research:  Dark green wire at large connector over brake booster is the resistive measurement source.  One lead to the temp sender in the head, grounded back through the block.  Only goes to the instrument cluster.

Troubleshooting:  Gauge, when grounded on console side of connector, deflects full value.  That’s good.  Same wire, voltage to ground, is +Batt.  Also good.  Conclusion:  the gauge & instrument wiring is good.

Resistance from pin of large connector to wire just before the sender reads <1.0 ohms.  That’s good.  Resistance from wire at the same location to the block is an open (infinite).  That’s bad.  Remove connector at sender, measure from block to the pin on the sender:  3.7KOhm.  That’s right about 58F, which is correct.  I checked connectivity from the brass threads on the sender through the aluminum heads to the -Batt, and all those were good.  I tried several different combinations of lead, connector, and the block, and kept getting an open.

Conclusion:  the connector to sender electrical connection is bad.

Next step:  I tested a spare sender I have lying around, even with the harness connected, and it read perfectly in all conditions.  I will probably try to install this sender, even though it reads about 3.2KOhm at 58F, which is lower than it should be (higher indicated temp).  Maybe I’ll buy an autometer gauge and sender.  The problem with swapping the sender is that it means you loose all the coolant down to halfway down the heads–that’s a pain in the rear.


Problem Statement:  Fans don’t come on.

Research: First, PCM gets temperature from temp sender in water pump.

Troubleshooting:  I measured the resistance (two conductor resistive bridge for this) at PCM (Black pin 6, clear or grey pin 25, black & yellow), and got an open.  On my harness, they wired two temp senders, which is apparently required for LSx motors.  I swapped to the other one, and the reading became 3.7KOhm.  PERFECT!  But I’m pretty sure that during the original testing, I did this as well, and didn’t get fan activation.  I walked away and worked on the temp gauge problem for awhile, and came back to this.

Let’s look at the fans.  Power comes from +Batt->Starter (as a distribution center)->fuse->fan supply->fan return->relay (power side)->ground.  The relay ground was good, the fan->relay connection was good.  +Batt to fan was 0V or open resistance.  I crawled under there, and low and behold, the OTHER problem (first was the wrong connection to water pump temp sender):  when I was installing the starter, I broke a wiring terminal during harness installation.  I assumed this was +Batt->Starter, so I put my own cable (0 gauge) on.  NOPE…this was Starter->Fans.  I’ll pick up a big ring terminal tomorrow, pull the starter, and install it.

Problem Statement:  Transmission is hard to get into reverse.

Research:  Apparently the lockout solenoid only prevents the shifter from getting past the 5th/6th gear pair and over to the R area; I can get over there and up to R, but sometimes it wouldn’t stay there.

Solution:  None yet.  Might be common to the T56, from what I’ve read anecdotally.


Other things:  still have to install O2 sensors, new carpet, wire up the exhaust cutouts, install new stereo amp (and speaker RCA wires, and a power distribution block and amp turn-on for this amp, and run speakerwire back to the speakers).

Upside:  If I can get the fans to work and the O2s in, I can get it emissions tested!  Well, probably dyno tuned first.


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