Lockup issues?

[PlayingWithTBI]

I think with a custom tune but im not sure.

Yes, that's what I meant. Sorry for the confusion.

 

[1998_K1500_Sub]

So i was underneath it poking around and found this red 2 wire plug and i have no idea wheee it goes. Cant find a home for it anywhere. (Yes im aware the front mains leaking ill get to it) anyone know what that pigtails for?

Did you mean to post a picture with this? I sure seems like you did.

 

[letitsnow]

Ive never had one repeatedly go in and out at a steady speed before. When its goin in and out of lockup over and over i can hear the rpm and see it come out of lockup and go up about 200 rpm and back in dropping about 200 rpm and it doesnt stop as long as im holding a steady speed. But i did notice this morning it didnt do it at all until the truck was completely warmed up miles down the road.

They typically don't go into lock up until the motor reaches a certain temp...

 

[tpass]

I had the same issue in my 1996 Tahoe and sorry i cant be more specific, but it was something in the valve body that was worn out. I had the transmission rebuilt, it was 18 years or so ago so I cant be more specific than that.

 

[1998_K1500_Sub]

Ive never had one repeatedly go in and out at a steady speed before. When its goin in and out of lockup over and over i can hear the rpm and see it come out of lockup and go up about 200 rpm and back in dropping about 200 rpm and it doesnt stop as long as im holding a steady speed. But i did notice this morning it didnt do it at all until the truck was completely warmed up miles down the road.

Funny, a similar thing happened to my Suburban this December over the span of perhaps three consecutive days... with engine warm, at road speed (55MPH or so), I noticed TCC unlocking, and then (re)locking, or sometimes unlocking and staying unlocked. It seemed intermittent, in that it might (say) unlock for no reason and then, after a bit (say, after coming to a stoplight and then resuming speed) it would lock and remain locked as it should.

I thought at first it might be a bad brake light switch (flicking the brake lights on inappropriately and triggering TCC unlock) but I checked for that immediately (I monitored the behavior of the taillights) and all seemed normal.

I also checked the coolant temp via the gauge thinking, because it was December and getting cold, perhaps a bad thermostat was allowing the coolant temp to drop and trigger the ECU to unlock TCC. But no, the coolant temps were stable.

So I paid close attention to this behavior over time and I noticed that it *seemed* to only happen when I was driving after dark (headlights & taillights on). In the daylight (driving to work), it never didi it. In the dark (the return trip home), it would.

So I got thinking "Is this related to the 12v power draw of the headlights / taillights / etc., in some way?" I've seen similar problems in other vehicles when the headlights were on due to bad grounds (the 1994-1997 Impala / Roadmaster / Caddy Fleetwood 4dr cars had an issue like this... a bad ground which was shared by the fuel pump and the rear taillights, so when the taillights were on during the night and then braking, the fuel pump voltage would drop, and so the fuel pressure would drop and the engine would die).

So I started looking around under the hood of my Suburban and I noticed the ground straps (passenger's side, back side of the engine, one from engine to frame, one from frame to body) weren't looking too good on account of corrosion over the years (I'm in Illinois and the truck has seen some salt over the years, although I usually don't drive it in the winter). I toyed with the straps - wiggled them around - to check their integrity (they didn't fray or fall apart so...). I made a mental note to get some replacements sometime in the future.

I also crawled under the truck and pulled the connector into the transmission and inspected it for "green" connectors. I found no corrosion. Everything looked clean and good.

What's funny is that, after toying with the ground straps and the transmission connector, the lockup problem hasn't happened since.

So what did I do to make the problem abate? I don't know. Was it the ground straps? Perhaps, perhaps not, as I don't think the transmission control circuits share any electrical paths that include the ground straps. But this is what happened, just as I described.

I'll still keep watching for odd TCC behavior, but I'm also planning on replacing the ground straps ASAP.

 

[Yngwytprik]

Did you mean to post a picture with this? I sure seems like you did.

Oops yes i did. Here it is.

 

[1998_K1500_Sub]

Oops yes i did. Here it is.

That connector looks like the one that normally goes to the EVO on the power steering pump.

See this thread for both useful and useless related information.

1998 to 1996 Vortec 5.7 power steering pump swap

Can I remove the EVO electric plug on a 98 power steering pump and just replace it with a high pressure line in order to install it on a 96 that does not have the EVO? I have a 98 parts truck and a 96 I am fixing up. I didn't realize the power steering pumps were different.

www.gmt400.com

 

[Yngwytprik]

I looked all over the pa pump too and didnt see a spot for it ill look again. Appreciate it

 

[1998_K1500_Sub]

I looked all over the pa pump too and didnt see a spot for it ill look again. Appreciate it

Someone may have removed the EVO from the pump (which is common). In that case, you won't find anyplace for that connector to "plug in"... because it usually plugs directly into the EVO

 

[1998_K1500_Sub]

Oops yes i did. Here it is.

Have you got an engine oil cooler on that truck? If so, keep an eye on those oil lines to / from the cooler, they like to leak.