98 K2500 electrical gremlins-help needed

[rickpilgrim]

This has been going on and off for 2 yrs and for once I'm at a loss.

First- when you first start the truck the complete(gauge doesn't show it) electrical system seems to "pulse". Lights get brighter/dimmer heater fan faster/slower anything electrical has this problem.
Now I've had 3 new alternators and 2 new sets(dual battery plow truck) of batteries and done numerous electrical checks for shorts, opens grounds and no change. After 10-15 minutes everything stabilizes and acts normal at 13.9v on gauge and multimeter. ECM????
Second- when below 40 degrees if left overnight when you first start it it will be between 8-15 min before you can shift out of park. New shift cable didn't change it, new column from Tahoe no change, 2 -4L80E makes no difference.
Add that to the new fuel spider and regulator that acts just like the leaking one and no check engine light or no codes set even when smoking black under full throttle really make me wonder.
Ideas anyone?

[rickpilgrim]

Bump

[speedygonzales]

With regard to shifting out of park. We all know you have to press the brake to get it to shift. I've never actually looked at the schematic for it but isn't there a switch on the brake that is used to release (maybe a solenoid) to be able to shift it out of park?

Maybe that solenoid (if that's what it is using) is sticking due to the cold weather. If you could find the lock out mechanism and see if it's getting voltage when it's cold and not moving might explain a lot. I'll look though my shop manual when I get home this afternoon for the circuitry.

Can you explain the pulsing of the lights? For example, does the engine rev up and down when it is happening? What happens to the pulsing when you rev the engine to about 2000 RPM's? What is the voltage at the battery while the pulsing is going on? What is the voltage at one of the lights when it pulsing? I think you see where this is going.

[rickpilgrim]

First, you can hold the brakes to the floor and unless it's not warmed up it refuses to shift from park. Right now we have a 97 Tahoe steering column in it and nothing has changed. I haven't seen a solinoid in the column but that would make sense if the OE column and the Tahoe column(complete with all switches and key) didn't act the same.
The electrical "pulsing" goes away 10-15 min after cold start. Engine keeps a steady rpm down to 575rpm at idle. The electrical guage "vibrates" around 14v while this is going on. My digital meter can't follow it accurately, the lcd display keeps shifting between 12.? to 14.? to fast to show the last digit. I thought AC ripple in alternator but Verus says none, and after putting on 3 new(2 paladin and now delco reman) alternators no change.
What's really strange is the ecm never sets any codes, it does communicate with the Verus and Modus but even when you unplug the MAF it registers the change but does not record a code. My to do list is to change PCM but for now I just warm it up for 15min and go after that.

[speedygonzales]

While I do see where you are going with the fact the PCM doesn't register a code when you unhook things. It doesn't account for the pulsing of the fan motor before it's up to temp. Since the PCM doesn't even get into the fan motor control. Or lights for that matter.

If you unplug things, does the SES light come on? Does it come on during prestart check?

[rickpilgrim]

SES on startup yes, otherwise no light when unplugging sensors. I realize the ECM doesn't control lights and fan but it seems strange in any event.

[speedygonzales]

During the pulsing, use your meter and measure from the output post of the alternator to the following points.
Any where on the engine.
Any where on the frame.
Negative post of the battery.
See if there are any differences in the readings.
Just for laughs if you have a set of jumper cables try connecting different things together like frame to case of alternator, or negative terminal of battery to alternator case. See what happens.

[rickpilgrim]

Found the pulsing electrical problem today and feel like an idiot.
Our 98 K2500 is strictly a snow plow truck and when I've taken it to the shop the plow is taken off. Today I was lazy and left it on.
The Western pro plow has a solinoid to activate the 250 amp pump motor and it looks like an old Ford one. It is hung vertically on the core support and either the spring was weak or disk loose as it would "tickle" the pump motor whenever the truck was running. When starting until the alternators fully charged the batteries it was enough load to vary the voltage. New western solinoid cured that problem, now onto the rest.

[speedygonzales]

After leaving the batteries disconnected over night, let us know if the shifting problem still exists or any running issues.

[rickpilgrim]

Originally Posted by speedygonzales

After leaving the batteries disconnected over night, let us know if the shifting problem still exists or any running issues.

Will do after the next snow storm passes through. Thanks

[speedygonzales]

Update?

[rickpilgrim]

Had both batteries unhooked for 2 days - no change whatsoever. Probably going to leave it as is untill summer, my 1998 crew cab 434 Th400 swap and full paint and body needs to be done by April, not much time to do anything else.

Thanks for the help Speedy

[speedygonzales]

I have to post this now cause who knows if I'll remember come the summer.
I dug up the shop manual (4 thick books) book on the column.

The brake transmission shift interlock (BTSI) has a solenoid in the column that is powered up to lock the shifter. Under the correct conditions, it is un-powered to release the shifter.

There is a simple procedure to follow to allow troubleshooting and not have it lock when you don't want it to. It's called the BTSI override.

When your vehicle is finally warmed up and allowing you to shift like it should do this:
Put the ignition switch in the OFF position NOT lock. Remove the #16 (Turn-B/U) fuse. The solenoid should not be engaged to lock the column at this point.

So what should happen is the next morning when you start up, there should be no waiting to shift into D since the lock mechanism will not be active.

I tried this and here's what I did. I turned power on and pressed the brake and shifted to neutral. then turned the power off but did not (could not) turn the key all the way back to lock.

I pulled the fuse and then tried different lock locations. One thing I did find was that the shifter is also mechanically locked by the key switch. You must come out of the lock position before it can move. So I just turned it up one spot from lock to OFF. The shifter would then move without doing anything else. I also started the engine and was able to shift without pressing the brake so I knew the electronic lock was disabled.

I think you could do the same thing when your shifter is working. Then you know the solenoid is working. Then put the shifter in neutral and turn the power off and pull the fuse.

If the next morning, you still have to wait for the shifter, it must be another mechanical issue. If it DOES let you go right away, then you know it's the BTSI.

[speedygonzales]

The BTSI assembly is located just below the column hanger bracket. Should be on the RH side of the column. It has an adjustment procedure.