no cold start. need help

[tobaccogrower]

1993 w250.



above 40* grid heaters cycle like normal. turn on the key, wait to start light comes on, hear the buzz then click and light goes off.



below 40* no light buzz or click. if i gust go ahead and start the truck the wait to start light comes on as soon as it starts the the grids cycle. what gives?



i pulled bolth sensors out of the intake and cleaned them. is there a way to test them? is there any other thing i could check and test? on thing i need to add is when they do come on like normal somtimes i hear a buzz coming out of one of the relays on the inner fender.



thanks in advance on any help!

 

[JLEONARD]

Clean very electrical connection INCLUDING the grounds which means the screws that mount the relays to the fenderwell, the ground strap from the block to the body, etc.

Since I am a mechanical engineer I always to those things for electrical problems.

That said I never bothered to "wait to start" unless the temperature was under 25 F or so.

 

[DVolk]

Are you getting click and no starter action ? id say its bad bround or some bad relays to test the grid heat put a jumper cable up to it for a few seconds then start the truck , i got one grid heater on a conversion hooked to a relay activated by a push button

 

[RSchwarzli]

Did it ever work? Is this a recently developed issue?

 

[tobaccogrower]

160,000 on the rig and they always worked. it was 11* here last night. i started truck up to go to a buddys down the street to play some pool. the wait to start light was on from the time i started the truck to the time i got to his house. (maybe 3 minutes total)



ill check the grounds today. i also heve to replace a transmission mount. yea!



the grids work. just after i start the truck, when its below 40. above 40 the work like they should.

 

[JLEONARD]

the grids work. just after i start the truck, when its below 40. above 40 the work like they should.

Yes I have had grounds become not so grounded in extreme cold (metal contracts, condensation becomes ice then insulates) so I'll stand by my earlier post... . at least until my feet get too cold.

 

[RSchwarzli]

[so I'll stand by my earlier post... . at least until my feet get too cold.

Wise cracker tonight arentcha?

 

[HHhuntitall]

... . you don't want to hear this, but I had a customer's '92 that did that. The PCM was the culprit. I don't know why the temp difference, or how it makes a difference..... does the PCM sense the temp and actuate the heaters longer when it's colder? And now the PCM is failing in the colder sequence, but not in the warmer?

 

[DVolk]

Sounds like a bad relay , i had that happen on my burb when it had a sick. 2 in it

 

[cerberusiam]

The PCM was the culprit. I don't know why the temp difference, or how it makes a difference..... does the PCM sense the temp and actuate the heaters longer when it's colder? And now the PCM is failing in the colder sequence, but not in the warmer?

The PCM bases the cycling off the IAT readings. The problem is it can't if it doesn't get readings.



Cold shrinks the solder joints on the computer board and a cracked one will actually seperate in say 10 degrees, where at 60 degrees it will make contact. Usually, if the temp fluctuations effect the operation its a problem on the electronics board and new computer.



Now when you get a new supposedly good PCM and the same thing happens you really start scratching your head. No fear, send the offending one back and get another and another until it is fixed. The rebuilders don't temp test these things so small cracks in solder will get missed.

 

[rMetzger]

Wow. Sounds like a good excuse to get a pushbutton to manually trip the heater-relays yourself, as needed.

 

[cerberusiam]

Wow. Sounds like a good excuse to get a pushbutton to manually trip the heater-relays yourself, as needed.

So how long do you hold the button down on a cold start? How long on and off so the engine warms correctly? How does that change with the temperature?



Push buttons are great for some things, but, not those that can go POOF and the let the magic smoke out. :-laf