At wits end with electrical issues

[Pdxguy77]

I think my ECM is bad....Ive checked and rechecked my grounds, Brand new battery with brand new alternator. Pulled and cleaned IAC. and still have 2+ volt drops when my headlights and heater are on. And when i apply my brakes at a stop light i lose another volt. Now by themselves everything is fine. Headlights and brakes half a volt drop same with my heater and brakes. but put all three togther, then my truck wants to die.


Any ideas?

 

[Andy D]

set your meter for DC amps and measure total draw. Remove fuses one by one until you find one that is drawing so much. Then once you have a ckt under suspicion isolate the trouble by disconnecting stuff til the meter drop[s. Hunting electrical gremlins requires patience , logic and good eyes and nose. -+

 

[Pdxguy77]

set your meter for DC amps and measure total draw. Remove fuses one by one until you find one that is drawing so much. Then once you have a ckt under suspicion isolate the trouble by disconnecting stuff til the meter drop[s. Hunting electrical gremlins requires patience , logic and good eyes and nose. -+

i did that while back..becuase its such a wide range of area (head lights, climate control, brakes) by them selves they arent a problem. but headlights with brakes do it, climate control with brakes do it. and headlights and climate control with brakes do it. and at a stop in park headlights and climate control do it...im wondering becuase it starts doing this after the truck is warmed up which put me down the IAC route

 

[Earl43P]

Sounds like the idle is low.

I say that only if these symptoms occur at idle.
If it happens at higher rpm, then you do have an electrical problem.

Nothing about those symptoms indicates a PCM problem.

Since it is an older truck, take a look at your Bat- cable.
It's proper connection is from Bat - terminal to a grounded clamp on the framerail to the large terminal bolted to the block. If you are missing the connection to the frame rail, simply add one from the block. There are also crucial and often overlooked grounds on the chassis to the frame, PS aft of cab and the all-important ground at the radiator support and from the firewall WS wiper motor bolt to intake manifold.

 

[JC 97]

I have the same problem.My truck is a '97.I have not found the problem yet.I suspect the iac also, cuz it happens after clutch in and engine falling to idle.Always catches itself.I can go days with no problem and then it happens five times in a row or once.It is random.I'll figure it out eventually or not.

 

[Mark_88]

Sounds like the idle is low.

Could well be...when I finally found an idle adjustment screw for my carb and upped the rpms almost all of my stumble disappeared...

I knew I just needed a good screw... this proves it...

 

[MrRangerSir]

I think my ECM is bad....Ive checked and rechecked my grounds, Brand new battery with brand new alternator. Pulled and cleaned IAC. and still have 2+ volt drops when my headlights and heater are on. And when i apply my brakes at a stop light i lose another volt. Now by themselves everything is fine. Headlights and brakes half a volt drop same with my heater and brakes. but put all three togther, then my truck wants to die.


Any ideas?

Well, none of this is a symptom of a failing ECM.

You mention a 2V drop. Measured where and how? If this is a guess from your dashboard voltmeter, confirm it with a reading directly across the battery terminals with a multimeter. These things can be found, but it takes time and patience.

 

[Pdxguy77]

i had a buddy run my electrical while i was at the battery with a multimeter. did each by them selves then together with each other. before i cleaned the IAC it would drop pass 11.9 volts now i got it up to 12.5 to 12.9 volts after cleaning. I did the IAC test and its working and clean. so now on to chasing grounds again........