Engine/Transmission (1994 - 1998) Help: Wait To Start - Staying On

[Cooker]

I have a problem that I am looking for a little friendly TDR help with.



My father's 1998 12v is acting up on him. After work, truck unplugged all day, his wait to start light will not go off during the preheat stage before starting the engine. He turned the key off and back on again and he thought the light was staying on to long so he decided to fire it up. He said batteries acted weak so I am inclined to think the grid heaters did not disengage.



He stated this same situation happend the other day after work also, but that time the wait to start light started to flash at him after it had been on a while. Maybe he didn't wait as long today?



In the morning, after the truck has been plugged in, he does not have any problems. My guess is the heater has warmed up the under hood air enough to not need the heaters.



I am thinking there is something wrong with the Intake Air Temp sensor. I will check it for proper resistance and see if that is the culprit. I wanted to throw it out here to see if I am missing something or if anyone else has any ideas.



Thanks again for all the help,

Ryan

 

[JohnE]

Oh boy;



Ryan, there is a lot of electronics involved in the grid heater circuit.



The IAT (as you mentioned) is a place to start. It is simply a temperature variable impedance path which the Powertrain Control Module (PCM) uses to measure intake air temperature and then follow a prescribed heating cycle. IAT sensors are know to get carbon fouled from EGR or exhaust brakes but are generally pretty stout.



The WTS light is not an indication of the heater grids cycling. It is the PCM saying the grid heaters are cycling. The voltemeter is a better indicator.



Relays usually fail open not closed, but (there is always the BUT)...



Check the batteries first. I just replaced the pos Exide replacement batteries with Diehards. Much better starting and the volt meter is back to normal after slowly climbing to the upper line.



Good luck

 

[Cooker]

Thanks John.



I haven't had an opportunity to check it out yet, I hopw to do that this evening. The more I am thinking and reading, I am leaning toward the IAT. I hope it is that simple. I will test that first and go from there.

 

[Cooker]

Still need some help...

Well after a little more investigation my father's truck is still having an issue with the wait to start light.



When the truck is plugged in the wait to start light will go off normally. Without being plugged in it still will not go off in a reasonable amount of time (he counts to 15 and just starts it now). Please note in the last couple weeks temps haven't been below 25 degrees.



We replaced the IAT, after I was certain that was the problem , and still no change.



Now I am thinking a few things:

-Bad wiring somewhere between the PCM and the sensor?

-He has the original batteries in his 1998 and they are getting tired. Do you think it could be an issue with weak tired batteries? (I know replacing a tired battery with a new one has fixed some wierd issues for me on gassers)

-Perhaps a PCM reflas would help?

-Possibly a bad PCM? This is my last resort.



I am open to all suggestions. I apprecaite all the help.



Thanks,

Ryan

 

[Rams-n-Hogs]

If the truck is turning over a little slower, I might consider new batteries. When mine went, I had absolutely no warning. Was leaving on a trip, and went out to start the truck, and it said, "NOT. " Delayed me for about 2 hours while I went to walmart. That was about 2 years ago, and I've got a 96, so you might be in the right time range for a 98. Good luck.



Jim