Chugging on 1-2 shift
 

OK guys, I need some help here. Lately while driving if I hit the gas less than half throttle from a stop light, around 2K-2500 RPMs or so, my truck will buck and hesitate a bit before shifting to second. I can literally watch my tachometer jump instead of rising smoothly. However, if I hit the gas more than half throttle, it runs just fine. I can take a video of this if it's unclear too.

What can cause this?

For reference here is what I have replaced lately:

Transmission
fuel pump/filter
plugs/wires/cap/rotor

Anyone?

Assuming there are no codes, I'd next look at the live data stream as well as transmission line pressure.

Line pressure should vary depending on throttle position & MAP values so you may have a sticking valve that works fine under higher line pressure (higher throttle angles - lower MAP values), but sticks and doesn't smoothly engage 2nd under lower line pressure (lower throttle angles - higher MAP values).

Does the RPM shoot up or down? A video would likely help.

RPMs don't shoot, per se. They jump, I guess is the best word. They'll stick at 2200 for a second, then jump to 2500, then 2700 etc, then it'll shift and be fine.

The trans was just rebuilt less than 3000 miles ago, is it possible it could be sticking already?

I'll take a video on my lunch break and put it up here.

Doesn't look as bad as it feels in the videos, but hopefully this helps:

1-2 shift chugging video 1 with commentary - YouTube

1-2 shift chugging video 2 - YouTube

1-2 shift chugging video 3 with commentary - YouTube

Hopefully those help a bit.

It really looks like a transmission problem. Since it was rebuilt so recently, I'd take it to them and have them diagnose it.

If this trans is going bad too, I'm seriously going to cause some crap...

Anything else you think it could be that I can check out on my own? I don't really have the cash or time to take the truck all the way back up there yet again.

When they rebuilt it, did they replace the servo pins & pistons? A leaking 1-2 servo could cause this problem.

It really looks like a lack of apply pressure to the clutch during the 1-2 shift causing chatter in the shift. It can lead to premature wear/failure if left unrepaired.

Yes, new upgraded servo, clutches, etc, after I blew up their stock rebuild in 2 weeks.

I should also mention that I had this problem before and my spark plug on the drivers side front of the motor was really loose. I tightened it up and the problem went away for a couple days. Could just be a coincidence, but it could be relevant.

I don't see how the two could be related.

What servo did they install? Did they install a new pin? Which pin did they install? If it was the aftermarket longer pin, was it adjusted to maintain proper travel?

To check any of this, you'll have to open up the transmission in one way or another which could be further reason for them to leech money out of your pocket.

From your previous dealings with this place, they sound like a bunch of 4L60E illiterates. As I said in your other thread, a stock rebuild should not have blown up with what you were doing to it. They screwed it up and then made you pay for it. Worse yet, you did pay for it and now have further problems... :icon_doh:

IMO, I would find another, more reputable 4L60E shop and have them diagnose the problem then take the findings to the DA for your area and discuss a law suit.

My sister in law is a lawyer, but I'd rather not go that route if I can avoid it. Looks like it's time to go to another trans shop and hope for "good" news.

SEL came on on my way home tonight, so to Autozone I go tomorrow, and hope they can tell me what the issue is.

i have a similar problem but mine just hesitates between 1-2 would this be a similar isssue or is this caused by something else?

That's exactly where mine hesitates. Could be similar. We don't know for sure it's my trans yet, I'm going to autozone in a little while to have them scan my code and see what's going on.

Autozone says my code is the dreaded P0300 random cylinder misfire.

I doubt that the P0300 code is causing a shift problem, but it could be another symptom of the underlying problem. Go through the diagnosis and you just might fix both. There are a host of problems that can cause the P0300 code. For instance, a skewed MAP sensor could cause both a misfire & a trans line pressure issue.

Do you have access to a full feature scan tool capable of displaying live data? It really would help to isolate the problem.

I do not, but have considered purchasing one. Any suggestions on a reasonably priced one?

The more I think about it, I think a misfire makes more sense than the trans. I have noticed the ride seemed more bouncy lately, but may have simply misinterpreted a bouncy ride as the engine hesitating while maintaining speed if that makes any sense.

I'm not sure I agree... With the RPM jump at the shift, that to me says that something isn't happening properly in the trans that wouldn't be attributed to a misfire. As I said, the misfire & the shift problem are likely two different symptoms possibly caused by the same problem.

As far as scanners capable of displaying live data... I haven't gotten too into hand held scanners, but I can do some looking. Post up some ideas if you find them and I'll take a look.

*Not arguing, just discussing*

From what I recall of my several trans issues over the year *sigh* if the trans was slipping, the RPMs would jump without the vehicle moving, right? In this case, the RPMs stop moving, then jump up. When the RPMs jump, so does the vehicle.

Ok, that is a bit different than I had inferred from your videos & descriptions. So there is a noticeable lull in acceleration, then a surge in acceleration, and then the shift?

Yes. Sometimes several lull/surges before the shift.

If that is so, then run through the P0300 OBD2 code listing, including the linked thread and work through everything methodically until the misfire condition is cured. You should also be able to look at the misfire counters for each cylinder to see if you can narrow it down to a specific bank or cylinder.

Ugh... I hate vehicles, lol

Time to go start ruling things out, I suppose. I've been doing research and have a few things that could be going bad.

distributor may have play in it
plugs
wires
cap/rotor
injector
blocked cat
coil

I replaced the plugs/wires/cap/rotor a few months ago but unless I'm mistaken, I used the cheap aftermarket stuff, so I'll start there if a fuel pressure test looks good.

Aftermarket caps & rotors have been known to be problematic on these engines for sure. What kind of plugs did you put in? Did you check the gap before installing them?

I have also run into this situation more than once... Plug wires pushing off of the terminals on the cap due to trapped air. This can happen more so when dielectric grease is used and the trapped air isn't allowed to escape while sliding the boot onto the terminal.

Plugs are Autolite I believe, I did check the gap, and pulled them all back out a few weeks ago to double check that I had them gapped right.

I have never run grease on the plugs, personally. Never really understood what it's for and my dad always told me not to use it.

Dielectric grease in the boots helps to allow them to be disassembled easier later on down the road. If you never intend on doing the plugs/wires again, then it isn't really necessary, but it is something I always do regardless.

The plugs might be your problem. The AC Delco Double Platinum plug is by far the most preferred plug in these engines.

Alright. Money is tight currently, would you recommend replacing plugs, wires or cap/rotor first? I can't afford to redo it all (at over 100 bucks for the cheap stuff) right now.

Do you still have the old parts? If so, how did they look. Wires really shouldn't be affecting things, but the cap/rotor/plugs definitely can be contributing. If the old cap & rotor look good, try swapping them back in. The same for the plugs if they were AC Delco double platinums.

Nope, tossed all of the old parts.

Damn. Might want to think about keeping parts, especially if replacement was preventative maintenance. They still might have life left in them to use in a pinch.

Here are the prices & PNs from RockAuto.com:
AC Delco Cap - D328A - $26.79
AC Delco Rotor - D465 - $8.34
AC Delco Dbl Plat - 41-993 - $5.58ea x 6 = $33.48
AC Delco Iridium - 41-101 - $5.56ea x 6 = $33.36
Total Dbl Plat = $68.61
Total Iridium = $68.49 <-- What I would do

Iridium is a better plug than the Double Platinum?

Finer center electrode with the same platinum tipped ground = more consistent spark and same long life. I'm running the AC Delco Iridium plugs in my Tahoe and had them in my Rainier as well. This was before the price was lower than the Dbl Plat.

I do like consistency. I'm not seeing it listed for my vehicle though.

I'm pretty sure that the 41-101 is a direct replacement for the 41-932/41-993 (41-993 has superseded 41-932). Doesn't come up even on the AC Delco parts finder though...

The 41-993 is listed for the Blazers, 41-101 is in a bunch of other GM vehicles, but not listed for a Blazer.

You could cross-reference the applications and see if there is overlap. If there is, then the plug will work. If in doubt, just fall back to the dbl plats.

I'll stick with what I know will work, haha.

Just ran prices and including shipping, rockauto is 15 bucks cheaper than the local advance... so looks like I'm waiting on parts to get here.

hey sean did you order yet ? did ya use the 5 % discount code ?

Don't know about any discount code, but no I haven't ordered yet. I realized my friend works at an advance auto or something similar, so I'm waiting on him to get me pricing too.

theres a thread on here i made with rock auto discounts

let me find it for ya

edit: https://blazerforum.com/forum/genera...-august-61956/

there ya go
theres updated ones in there

its 5 % but its still something