Odd intermittent transmission issue
 

Hey folks!
Thanks already for your input. I have gained so much from this forum and I appreciate everything.

I have searched here and elsewhere and I have finally decided to make my own post.

2000 Blazer 2wd 4 door LS.
4.3
169xxx miles

Purchased in December 2019.

Known issues: fuel pressure regulator leaking.

Current problem:
Intermittent loss of power in Overdrive. Vehicle moves, though slowly, and will climb in speed when accelerator is applied. Tach will not rise above approx 2K rpm despite input until 2and gear. Once vehicle shifts into second gear it accelerates normally.

Will accelerate appropriately from dead stop if manually shifted to 2nd gear before letting off brake.

When this anomaly occurs, vehicle will not move in D with foot off brake.

Feels like vehicle is trying to start from 3rd.

Sometimes at a stoplight while in D I will feel a subtle shifting feeling and problem goes away, accelerates normally.

When does this happen?
Randomly. 70% of the time vehicle is 100% fine. This anomaly occurs first thing in the morning, after a short drive, after a long drive--- randomly.

How long has this been going on?
Since February.

Actions taken:
Cursory inspection of wiring harness.
Serviced transmission in December (before problem presented)

Possible contributing factors:
Trans fluid cooler lines have been cut at one point and spliced with rubber tubing and hose clamps.

No MIL light. MEL light works, but I'm not throwing any codes at present.

Thanks!

Did this start to happen right after trans service? If so i would be dropping the pan back down and making sure nothing is out of place.

It started before the trans service.

When it starts it will be intermittently a problem for a few days and then I won't notice it for a week or so.

Update
 

Update since the last post.
Transmission cooler lines are leaking. Pretty significantly. I've been keeping the transmission serviced; checking hot & level, adding as necessary. I don't know enough about how that pump circulates fluid through the cooler to know if a drop in return pressure from a leak would cause something like this. Either way, the lines need to be replaced. I'll update again once that has been done.

Update
 

This seems like it might be germane:
Shift indicator lights don't illuminate in P, N, 3 or 1.

Range switch/neutral safety switch, I imagine. but would that cause the problem I am describing?

Sometimes, rarely but sometimes when I get in at night, before I put the key in, P is just barely glowing.

4/20 update
 

Since last original posting:

Problem went from intermittent to constant.

Replaced a and b solenoids. Had a code for B being stuck.

Found a questionable wire in exterior trans wiring harness and repaired.

Replaced range sensor/ neutral safety switch.

Replaced ignition switch. Security light was on and abs lights were coming, would also randomly die when turning left so I figured it was time.



No change to trans problem. Still starts out in a high gear. I can floor it in D and I won’t get over 1300 rpm. Will slowly gain speed and then shift into a more appropriate gear and off we go, will run more or less normally until I come to a stop again. I can leave a stop in 2nd or 1st and manually shift through. Torque converter locks at highway speed per brake-tap &rpm rise test.

This forum has been very helpful.

I’m still leaning toward a wiring/electrical issue.

This morning I got the following codes:
P0756 Shift Solenoid B Performance / Stuck Off
P0327 Knock Sensor 1 Circuit Low Bank 1 or Single Sensor
P0300, which we all know and love.

The DTC post on here for P0756 looks like it would be super helpful, but the images are not available.
https://blazerforum.com/forum/diagno...plained-28842/

There is an available wiring diagram for P0758 which is also associated with Solenoid B.

I suppose my next step, since I have replaced solenoid B, is to re-examine the wiring harness and use the P0758 wiring diagram to to try to identify faults.
I've looked over the external wiring harness again and didn't see any obvious problems, but that doesn't mean a whole lot.

I've verified bus voltage and a functional CLSTR fuse. It looks like the Terminal E, Pink wire on the external wiring harness connector is the first place to look, and it looks like the VCM provides ground in order to actuate the solenoid. So there should be voltage.

The diagnostic chart for P0756 isn't available currently., sadly

Did all of these codes arrive together or are they unrelated?


George

This has been fixed.

Awesome! Thank you so much.




Hard to say. I was unable to read codes for quite a while due to not having a scanner and local shops avoiding cars due to the Rona. Got my own phone scanner thingy now. The knock sensor hasn't come back since I cleared it.

That said, the engine is running really really poorly now. Misfiring bad enough to cause the CEL to flash/blink after taking off from a stop. I'll get it home and keep it off of the road until I get that taken care of.

I'll carry on with the diagnostic for the solenoid B (P0756) code and report those findings here.

The engine problems have been covered in other threads. I'll do the fuel pressure / compression/ ignition systems checks & inspections and see what comes up.

Thank you for your help.