Engine/Transmission (1994 - 1998) More on grid heaters

[John R]

On my '96 truck, the grid heaters no longer cycle after start uip. During the "WAIT TO START" time I observe the voltage drop. But after start it no longer cycles as it did in prior cold weather. What is defective, and how do I fix it so the heaters continue to cycle while idling cold?

 

[Missouri Mule]

What is the tempature outside?



You can try cleaning off the Intake Air Temp sensor (IAT) tip off with rubbing alcohol.



The PCM is acting up. I doubt the relays are causing problems because they activate the grids before start up but you can check them out.

 

[John R]

The outside temperatures are 25-30F.

 

[Skydiver]

Please allow me to ask you a question John R. Are you sure they are not remaining energized? My grid heaters stopped cyclying years ago. The solenoids were sticking closed & remaining on. I just pulled one wire off each solenoid to disable them until temps drop below 30F. I live in a very rural area and have no neighbors for all the cold smoke to upset.

I place a stick between the drivers seat and fuel pedal to hold 900 rpms for faster warm up. The power seat is great for regulating engine idle speed. LOL

This is the first time I have heard of your type of cycling problem where they work one time then quit during warm up.

 

[John R]

I believe they are not remaining energized because the volt meter does not pull down as it does while the WAIT TO START light is on. Also there is more smoke, and the engine seems to stumble during warm up idle than previously.

 

[John R]

Would someone please describe the architecture of the grid heater system and why two solenoids are required. A previous series of posts described how to change the two solenoids, but it did not describe the control circuit or the logic sequence.

 

[Newf Limo]

John, I won't be too much help, but in part I believe that there are two layers of grid, inner woven so to speak, hence two relays and two leads that go to the Drivers side battery post. Just finished fixing my grid problem yesterday. (corrosion in terminals at battery, not energizing relays, hence no grid heat, no start at 12 degrees)



That is as far as i can go without guessing. That guess would be (and feel ffree to skip this)

Intake air temp sensor reads below 56degress, Engine controle Mod signals relays to energize grids via timer. After engine start, timer circuit continues off and on until a minimum necessary engine temp, or possibly spee, as i think my headlights quit dimming around 20 mph.



This probably doesn't really help you though.

 

[CToney]

Grid heaters are for cold start assistance and to lessen emmissions on warmup. You should have your truck plugged in so that they don't cycle. Having them cycle is hard on batteries and alternators. My grid relays in my '97 had to be changed when I bought my truck. I put a switch on the ground so once I had oil pressure the grid wouldn't work. They operate by two trigger wires and two grounds. The computer will adjust the length of time they are on and how many are on based on the IAT. This is my experience and opinion. On my old '92 I leave them unplugged and will hook the triggers up if I need them. The '92 starts better than the '97 due to the cold start advance.

 

[Ol'TrailDog]

Whilst we are on the topic of grid heaters, I have the blinking wait to start that won't quit syndrome. Following the advice on here abouts, I cleaned the corroded connection with contact cleaner. It worked fine... for a short while. I re-cleaned and used a dentist pick to scratch around and more contact cleaner. Worked fine for a short period then back to the blinking wait to start. It will stop after I've stopped and restarted the truck. But usually I don't need to stop until I get to work so I've just been ignoring it. Any other suggestions?