Multiple Electric Issues? Coincidence or Not?

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Tpok454

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To start off, here is my truck in concern I will list the specs as well as some recent work that I have done.

92 K2500 454 ECLB 4L80E ≈280,000 miles
New Alternator
Battery Tests good
Recently rebuilt transmission by local shop
New brake switch
New IAC and relearned.
Swapped Gauge Cluster
New distributor assembly including cap/rotor.

I am currently having an issue with the transmission locking and unlocking at inappropriate times. The torque converter will unlock, then lock, unlock and lock while driving down the road at 55-60 MPH.
When I go to slow down, around 48-50 MPH the torque converter will try to engage which results in revving up the engine by 1500-1800 RPM that is how it can be noticed, it can also be felt. It will rise, then fall, rise then fall until I am out of that speed range. It will then act normal as I continue to slow down.

I took this truck back to the transmission shop as it is still under warranty. They had the truck for 2 weeks and could not diagnose and solve the issues. At all other times the transmission holds, shifts and runs great. It does not slip or have any "weak characteristics".

At the same time the truck has a high idle issue, initially idling in park at 1500 RPM replacing the IAC valve brought it down to 1,000-1,100 RPM in park and when fully warmed up it will sometimes idle around 700-800. Relearning/ replacing the IAC seemed to help the shifting. Both the transmission shop, and I believe the issue with the trans is related to the high idle. I.E. because the idle is so high the trans think there is higher rpm or load wanting to be applied, therefore it tries to engage the trans while slowing down. However, could this also cause the issue with the torque converter locking and unlocking while at cruising speeds?

Lastly, it seems that the truck acts up the most when there is a weird electrical issue involving my gauge cluster, the rpm and speedometer will bounce around and also "blink" when my turn signal is on. The blower motor (new) will slow down when I come to a stop and sometimes the speakers for the radio will slightly cut in/out when this happens.

All in all there is a lot going on with it and I have a gut feeling it is something simple such as a ground or bad battery. I am going to replace the battery this evening with a known good one to see if that helps. The idle is still a little high so I think I am going to try and relearn the IAC and set it even lower as well as try to relearn the TPS.

Some advice would be greatly appreciated, thanks!

Here's a pic of the rig in question.

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termite

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I changed the heater core in a 99 dakota that did all kinds of strange stuff afterwards. Randomly locking/unlocking, instrument cluster in and out, lights flickering, and overall driving like it had been ragged hard in a derby. Turned out i missed a ground reinstalling the dash, rushing in the dark and cold trying to heat working again. Reconnected ground, problems vanished.

Almost like anew truck aside from being a POS to start with.
 

Schurkey

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I am currently having an issue with the transmission locking and unlocking at inappropriate times. The torque converter will unlock, then lock, unlock and lock while driving down the road at 55-60 MPH.
When I go to slow down, around 48-50 MPH the torque converter will try to engage which results in revving up the engine by 1500-1800 RPM that is how it can be noticed,
I don't understand how a torque converter clutch can affect engine speed by 1500--1800 rpm. And if the TCC engages, the rpm should DROP, not increase.

1800 rpm increase is more like a gear change--or two. Not TCC disengaging. I'd expect the TCC engagement/disengagement to affect engine speed by something like 300-ish RPM.

Lastly, it seems that the truck acts up the most when there is a weird electrical issue involving my gauge cluster, the rpm and speedometer will bounce around and also "blink" when my turn signal is on. The blower motor (new) will slow down when I come to a stop and sometimes the speakers for the radio will slightly cut in/out when this happens.
What is the system voltage when this happens? Is the instrument cluster properly grounded?

What is the NO LOAD voltage at the battery with the engine off? Better be 12.6--12.7 volts. If it's less than that...you need to fully-charge the battery.

The idle is still a little high so I think I am going to try and relearn the IAC and set it even lower as well as try to relearn the T
Have you ever messed with the base-idle screw? That sounds like the sort of problem when folks don't follow the proper procedure for setting the base idle speed.

Connect a scan tool. What, if any, codes are stored? What is the computer showing for voltage? RPM? Throttle position sensor voltage at idle? Coolant temp?
 

454cid

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If you have a scanner graph the voltage on the tps and see if it's doing anything wonky while the truck is acting up. My volvo had transmission issues that were actually the tps shorting to 5volts. The ecm thought I was going wot and downshifting the transmission.
 

Tpok454

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Thanks for the helpful advise. I adjusted the IAC valve once again I had to set the idle pretty low before plugging the IAC back in. The truck will sometimes idle at around 700 but most of the time it still wants to idle at 1,000.

Schurkey
I don't understand how a torque converter clutch can affect engine speed by 1500--1800 rpm. And if the TCC engages, the rpm should DROP, not increase.
1800 rpm increase is more like a gear change--or two. Not TCC disengaging. I'd expect the TCC engagement/disengagement to affect engine speed by something like 300-ish RPM.
My bad, I meant to say what you did, it will go from 1,500 up to 1,800 rpm (therefore around a 300 rpm increase.

As of this weekend and driving it multiple times I believe I have corrected the faulty electrical issues. I had a belt that very squeaky. The trans shop replaced it when it was there for the transmission but it continued to squeak and I believed it to be a pulley issue. After some tinkering I decided to replace the belt myself, Comparing the old one to the new, the one the shop had put on was almost 1.5" longer than the one from the parts store! After installing the new belt the squeaking went away completely, I believe there was some slipping going on cause the alternator to not be able to keep up with the power demands.

The transmission now behaves correctly when I let off the gas and slow down, the TCC does not try to engage. However after correcting the other issues, the TCC still unlocks and locks a few times while driving around 55 MPH. This does not happen every time I drive it or even every time I am at that speed during a driving (as in shutting it off and turning it on doesn't seem to have any correlation). I would say it occurs 25% of the time while driving in OD it does not do this in any other gear.

There is a check engine light that comes on after about 20 minutes of driving particular if I've been driving in OD for a while.

Can anyone recommend a good OBD1 scanner?
 
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