It is not the grid heaters

[BigPapa]

NCA = No Color Associated

 

[petersonj]

what does the NCA mean? also, what are the big blue boxes?

I believe that "NCA" is referring to the wire color - in this case "no color associated". The blue boxes are enclosures representing a component. The wiring inside of a blue box is part of that component.

- John

 

[RTRAM]

The ambient air temp is 40. I was reading the manual and on page 14-90 there was a test for the preheat. The battery voltage was at 12.5. I had the ignition key on and both air intake terminals were at 10.1 volts. The preheat cycled for about 15 seconds and then clicked off. There was a humming that continued, and the battery voltage was at 11.1 volts. The test does not say how to test for the post heat cycle.

I disconnected the grid heaters and started the truck. The alternator went to 15.3 and the battery was at 14.5 volts. It appears that the charging system is working. I have replaced the battery and alternator. The problem with the ignition switch was a fusible link that died during the last battery test.

Sorry this took so long to get back to you but life happened.

 

[BigPapa]

I think what you’re seeing may be normal for a 1st Gen. That’s why the 2nd Gens have two batteries.

 

[RTRAM]

The problem appears to be that the grid heaters don't cycle. The voltage stays very low until the engine temp comes up and then they turn off. I am used to them cycling. Now, they just appear to stay on for 15 miles which is really not good in the dark with the headlights on.

 

[Timd32]

There was a humming that continued, and the battery voltage was at 11.1 volts.

The problem appears to be that the grid heaters don't cycle.

When you are disconnecting are you doing the small wires or large wires?

Kinda sounds like one of the relays might be stuck possibly.

I have fully disassembled new ones to paint the bracket that appeared to be bare metal. They are pretty simply deals. They can get pretty rough after time.

The description of operation says there are 2 modes of postheat depending on the Temps. But does not list those tests or much anything other then it will cycle and or run both as needed.

While in Wait to Start can you try to Crank the truck to see if it cycles them back off? The voltage should pop back up would be my guess. From the 10v to 12v deal.

PREHEAT CYCLE
The air intake preheat cycle will start if the following conditions exist:
^ The ignition switch in in the ON position.
^ The PCM has not received a crank signal.
^ The air intake temperature is at or below 59°F (15°C).

• If the preheat cycle is started, the PCM will illuminate the Wait-To-Start lamp.

• Once the preheat cycle has finished, the Wait-To-Start lamp will go out, and the engine can be started.

• If the PCM receives an engine crank signal while the preheat cycle is running, the air intake relays will be DEENERGIZED causing the preheat cycle to be aborted.

POST-HEAT CYCLE
The air intake post-heat cycle will begin if the following conditions exist:
^ The engine has been started and is running.
^ The air intake temperature is at or below 59°F (15°C) when the ignition switch was turned ON.

The intake air heaters have two different modes of operation depending upon the intake manifold air temperature:

• Either both heaters are ENERGIZED

• Or they are cycled ON and OFF individually (while one is ENERGIZED the other is not and vice versa).

• The amount of time that the air intake heaters remain ENERGIZED depends upon the intake manifold air temperature.

 

[RTRAM]

I disconnect the small wires. I was wondering if the 10.1 volts going to the grid heater was an issue. Both relays are cycling off since the voltage to the grid heater goes to zero. I will try it again to see if I start the engine if they both go to zero volts. Otherwise, it is looking like a sensor issue?

 

[RTRAM]

I am understanding more about this.
Today, the ambient air temp was 35 degree F, the battery voltage was 12.5 volts.
When i turned the key for the pre-heat cycle, the battery went to 10.8 volts and both the front and back were at 10.1 volts. I waited for the cycle to complete and both relays went back to 0 volts.
I started the truck, the battery went to 10.5 volts and both relays were at 9.8 volts. I didn't time it, but it was a couple of minutes and I had not heard either relay click off. The battery was at 9.6 volts, and both relays were at 8.9 volts. After another period of time, the front relay went to 0 volts and the back was at 10.1 volts with the battery voltage at 10.5.
When the post cycle was complete, the alternator was at 14.6 voltage, the battery was 13.9 volts and both relays were at 0 volts.
Does this help? It appears that in the post heat cycle that the one relay does not cycle.

 

[petersonj]

Does this help?

You have provided good information. The grid heater operation seems to be normal with one exception - I believe they are staying on too long between cycles. Also, I think that the grid heaters should stop post cycling as soon as the transmission shifts into a certain gear or road speed reaches around 25 mph. I don't think your grid heaters are turning off under those conditions, according to some of your previous posts. Or, it may be that those features weren't programmed during the era of your truck. I just don't know.

If I were in your shoes, I would skip any more diagnostics and I would wire in a momentary switch in the cab (a place of your choice) and do away with the programmed grid heater operation. To me, there is no value in having a computer control them, when a simple momentary switch on your dash could do a better job.

I installed a switch on the 2001 truck in my signature within a week after I drove it off the lot. I quickly tired of the headlights dimming from the post cycling while driving on the dark winding road that I lived on at the time. And what an unnecessary drain on the alternator! With 370,000 miles on the truck now, I am still using the original alternator with brushes replaced twice and bearings replaced once. Never a failure - just scheduled maintenance.

- John

 

[RTRAM]

This was a long and twisted road to success. There were several issues to resolve on the way.

The first thing was to understand that the battery worked great during the summer, but as it got cooler, it did not have the reserve to handle the grid heater.

Second was understanding that the ignition switch has two battery feeds in. Even though I got the truck started with the first one, I didn't understand that the second one was the issue. That was a bad fusible link. Of the few things on this truck that I don't like, fusible links are #1. They are hard to find and not easy to repair in the field.

Third-When I was testing the grid heater relays, the output going to the grid heater itself was only putting out 10 volts with a 12.5+ on the hot side. I replaced those and now I have 100% voltage through the relay. Also, after 30 years I had never stopped to clean the connections, so maybe that helped a little also.
Fourth - I went to Geno's and got both air intake sensors #3918461 and #4327029. The old ones were 30 years old.

After replacing those parts, I started the truck in 35-40 degree weather. The truck started and the after a short time, the volt gauge in the truck started to cycle like it should. I checked the voltages on the grid relays and they were cycling between the two relays and both had a 12.5+ voltage output. I drove the truck and when it came up to temperature, the voltmeter stopped cycling, just like it should.

Just to be sure, the next day in 40 degree weather, the truck started and the grid heaters cycled correctly. It seems that the heater is working better than I remember but I am old.

So, success. Thank you to everyone who gave advice.