Thanks for the input, boost valve, forward accumulator and abuse valve is what I'm thinking currently. Hoping it's not the actual pump that's taking a dirt nap.

 

Im trying to locate the pumps boost valve. Im guessing its above that connector for the turbine speed sensor in the upper right corner next to the rooster, and I have the model that doesnt have access to the boost valve....am I correct in that, or is there a work around?

 

Did the line pressure test, when I'm not having the problem, never goes below about 60ish psi, meets the 55psi minimum. When I'm having the problem, it hits about 45psi in D, then I have to tap the gas just a hair and it rapidly goes to around 65psi.

I unfortunately have the model where the turbine speed sensor seems to be in the way of the boost valve, at least in my photo, the pigtail is in the way. Any work around, or does the pump need to come out/transmission removed from engine?

Also, is that the likely culprit? Seems to be the common denominator in the thread. How about the pressure regulator valve that resides in the same hole? Anyone had to replace the entire pump cover because the hole was bored out?

Probably some questions as I go, trying to get my ducks in a row before tearing this thing apart.

 

seems the white connector is in the way of the boost valve.

 

Try unplugging the big round wire connector going into the trans on the passenger's side of the trans. Once unplug read the line pressure again at idle. With the connector unplugged the line pressure should increase. Once you are done with the test you will need to clear the check engine light.

 

looking at the pics I took, the idle in gear when not having the issue is about 75, maybe 70.

I'm sure there is one, but what is the purpose of unplugging that connector and retesting? Is that to deactivate the solenoids? First time I opened it up I replaced the solenoids for 1-2 and 2-3, did nothing. This time I'm trying to be near certain before opening it up again.

 

Unplugging the connecter will stop the EPC solenoid from controlling line pressure and the pressure should max out for that RPM. If the pressure goes up, then you will know that mechanically the transmission can produce the proper pressure and that the ECM is telling the EPC to lower the pressure or the EPC is defective and is lowering the pressure too low. If the pressure does not increase when the connector is unplugged, then there is a mechanical issue.

With your pressures up and down with the same RMP and load, has me thinking you had an electronic problem. May be MAF, TPS, MAP sensors or a defective EPC solenoid.

 

Pressure is pretty steady up until it warms and I encounter the issue. Then it's steady when it happens, at about 46psi.

If I do that test, where should the pressure be at?

Also, I had it on a computer that was showing ecm to epc was showing the same values. This was before it was warmed up and having the issues though.

 

You're seeing that at least on the surface, it's the same problem as the previous posters right?

 

That is what the ECM is commanding the ECP to do, it is not actual pressure. You need to hook up a gauge to actually know what the pressure is.

Your pressure should be higher than 75 and not fall the 45 when hot.

Pressure is not steady when it goes from 70 cold to 45 hot.

 

The only thing I'm saying is you need to do more test or just blindly start replacing parts.

 

Like I said, I don't want to do that. Where should should idle pressure be w brake depressed? That's where most of my tests were done at. Then id let go n it might go up a bit idling for a second or two. Also when the problem happens, seems like pressure is around 45 or so, then id let off the brake n it'd go up n I wouldnt physically notice the delayed engagement, n then sometimes i let go of the brake, n pressure would stay at 45 n thats when id notice the issue n have to tap the gas.

 

ok so unplug the harness to have it in 3rd gear n R. Limp mode essentially to see if mechanically it'll provide adequate pressure to 3rd gear in idle when warmed up. If it does, then some sort of computer issue. If not, then mechanical pressure issue. One thing with that, when I start in second, and issue is present in 1st, the pressure seems to drop w brake pedal depressed, then come up as i let go of brake pedal. Then i hit gas n it seems pretty seamless, although maybe it's because it's so low torque there isn't a bump felt. Or maybe it's not as bad in 2, yet. Any thoughts on that?


Also, assuming I can just remove the "tcm" fuse under the hood, right?

 

You take the pressure reading in park. You can try pulling the fuse if you want, I'm not sure if that will disable the EPC but you can try it. If you have good pressure with the EPC disabled, I'm not saying it is a computer issue. It could be a sensor or the EPC.

 

yeah i mean something electric related within those parts. So dont put it in D, just do a park reading? In park ive never had the issue. Steady
70-75 like when the transmission is cold in any gear(1,2,3,d,r).

 

well hell. So I pulled the transmission, and saw a worn pr valve. Worn to the bone and had little chips of aluminum in the bore. Rest of the pump looked fine. I did not remove the drums at all. However the teflon seals on the drum shaft looked good. I replaced every other seal from that part forward with original gm parts.

I had a lot of parts because I didn't want tog back in, so I replaced the pump cover completely, pump body w an alleged good used one, looked machined. The rotor, veins, guide, slide, pin and springs. Rebushed the pump body that was used I bought. I was a little suspect of the pump body, seemed like the rotor and veins didn't quite move freely. Maybe should've went with the devil I knew......

Anyway so back together and seemed to run well for a couple days. Now, the main issue where I'd have to tap the gas to engage 1st gear, and there would be a bump felt, that issue issue is gone. But, I still get a low rpm, when shifting into gear. It'll go from a normal 620ish in P or N, down to 420, then bounce up to 520, then down 450, then finally settle in at maybe 500, and really feel like it's bogging down. Condition almost seems worse than before, as far as the temp doesn't need to be completely warmed up anymore (although it was starting to happen at lower temps, like say 140, even before the repair, and was rapidly getting lower by the week). But when it's bogging, if I tap the gas, it'll run and is in gear, no bump felt. This doesn't happen nearly as pronounced in gear, and say at a stop light now, even warmed up, but I can make it happen easily by putting it in P or N for maybe 5 to 10 seconds, and then going into D again. Happens shifting in reverse too, really any gear. I suppose it seems more pronounced because before the PR valve was catching and so the rpms would stay low, and then I'd tap it and it would run freely with that little bump into gear. One thing to note is that before repair, when I had the issue, the line pressure would go all the way down to 46psi, bump gas and it'd grab and recover. Now, same bog issue, bump since the pr valve is replaced (entire pump cover), the psi stays right at 64 withe the issue or not, but I still have to tap the gas to feel like a normal idle.

Before repair idle- I had 70psi in D, P, N when no issue present. Not sure about R o r2, but they may be close to the after results, could be a bit different though.
After repair idle- 64psi in D, P, N. Reverse is like 83, 2nd is 70. All pressure stays the same weather issue is present or not.
after repair- I also pulled the trans fuse, and psi is at 195 to 200 w the a/c off in park.

So I lost 6psi....Maybe the pump body being shoddy and slightly leaking? Could be warped and eating the rotor veins, especially when first engaged in D? I'm going to drop the pan tomorrow and see if there is any shrapnel, if it is sheering itself in there.

Further, I cleaned the throttle body, maf, map and tps. No difference and no codes on that front. Doesn't mean there isn't anything to it, but since this has been a transmission issue, and at least was based on temp, I'm still leaning either TC or that pump body being compromised going in.

If anybody has anything they can suggest to try, I'm open to anything. Like the first time, I want to pull the transmission, if I'm sure about the part I'm to be replacing. Outside chance of an engine issue, I'm looking at that too.