Ok, I've been doing searches and reading posts about bogging, and not one single post I've read has the same symptoms that I do, so here goes.

First off, no codes. My car has the 4L60E with 3.08 gears. Got the car two months ago, and here's what I've done since I got it: New MSD cap and rotor for the Optispark, Taylor wires, TR55 plugs, new fuel pressure regulator, new IAC valve, new O2 sensors, and rebuilt the transmission. It was doing this also before the trans was rebuilt, so.... anyways, at any temperature, in overdrive, cruising is great. Floor it, it's great. But try to feed into it or just go half-3/4 throttle, and I can slightly feel the car dip, like it got a couple hundred pounds added to it, and the RPM's drop ever so slightly, but noticeable. The engine begins to ping if I continue to press the accelerator, it initially does not increase in speed, but eventually will very slowly. Stomp it, and she goes like all get out, but come back down and try to accelerate mildly, and it don't go nowhere. It almost feels like it wants to downshift, but not fully, like it's applying passing gear but not coming out of 4th, even though I'm not giving it enough throttle to drop into passing gear. Stomping it drops into passing gear like it's supposed to. The lockup converter stays locked in through all of this too. Going back to normal cruise and all seems well.

Also, sometimes after the car has heated up and I've driven around for awhile, I'll kill it, Perhpas go into a store or whatever, then start back up, take off and it pings almost constantly under medium load, gas mileage drops 2-3 MPG, and feels weak. I've ran three tanks of 93 octane through it, and even dropped to 89, just to see, and still the same symptoms, no better, no worse.

Back to the cruise/acceleration thing, If I'm doing over 2500 rpm (about 80 mph), I don't really notice this problem as much, but between 1800 and 2400 (50-70), it's very apparent. The closer I get to 2500 RPM, the less noticeable it is. Has anyone experienced or heard of something like this? I'm almost suspect of the transmission, but it did it before the rebuild and now after as well. HELP!!!

 

[QUOTE=The Vetted Hotness;1578091156]and here's what I've done since I got it: New MSD cap and rotor for the Optispark, Taylor wires, TR55 plugs, new fuel pressure regulator, new IAC valve, new O2 sensors, and rebuilt the transmission.

Why did you do all these mods? Was there a problem with the car before you started? If not I would start with the electronics you changed out and back up from there. Re-install the old cap and rotor, regulator, etc. to see what may have caused the change in negative performance. One thing to remember is do not go lower in octane fuel than recommended. This will cause detonation (Ping) and lower performance.

 

That doesn't necessarily sound right. When you depress the gas pedal 1/2 or 3/4 throttle, the Torque converter should unlock. Did you know that our engines only make about 60-80 HP @ low RPM's. That would be slow acceleration in my book. The don't start waking up until 2000-2500. Are you sure your converter is unlocking? If the converter stayed locked the downshift to 3rd would give the RPM's to get into the power band of our engines.

I know you said it does it at any temperature but have you tried it cold? Transmission fluid below 140. The TC will not be commanded to lock below that temperature.

It should drop more that "ever so slightly" to allow the RPM's to increase to a usable range and have some slip. The throttle position sensor and the Vehicle speed sensor are two things that tell the converter to unlock. There may be more. I'm sure a transmission guy will chime in here shortly and talk about the transmission mechanicals. I'm an electrical kinda guy.

Or it's coming out of 4th and the TC isn't unlocking. It would seem about the same. You would get knock counts and further kill your performance. A scan tool would be handy here but I know most don't have them.

The pinging is not normal. The knock sensor is able to retard the timing about 20 degrees. That's it's limit. It should set a code though though but not always. Same with the TPS. It tells the TQ to unlock. I've seen many fail and not set a code.

BTW, That's a very complete description of the problem. One of the best ever.

 

Couple of questions: Was the tranny rebuilt because it wasn't coming out of lockup and was the torque converter replaced? Have you checked fuel pressure while driving-the pinging/spark knock COULD be from a lean condition. As "1963SS" stated could be TPS, but you'd need a scanner and the ability to read live data to check. You should also be able to see while driving with a scanner whether or the PCM is requesting torque converter lockup (TCC) on/off and see the rpms change accordingly on the scanner.

 

I'll answer questions as best as I can-
1)"Why did you do all these mods?"
Answer: These weren't Mods, they were needed. When I got the car it was missing at higher RPMs, and hard to start. Through many searches and post readings, I determined that the car simply needed a major tune up. I changed the Fuel Pressure Regulator because removing the vaccum line to it would prove a ruptured diaphragm by fuel spewing out the diaphragm canister. It runs much better now, with this one exception of bogging, it was there before and after repairs.

2) "That doesn't necessarily sound right. When you depress the gas pedal 1/2 or 3/4 throttle, the Torque converter should unlock. Are you sure your converter is unlocking? If the converter ........"

Answer: I haven't been able to get the car out immediately on the road and up to highway speed to test that "cold fluid" torque converter lockup. I did misinform you though; it will unlock the TC once I get it hard into passing gear, but the TC does stay locked up until I get the throttle 90-100% open and kick down to passing gear.
I know they don't produce much power at low RPMS, but I have a 98 Accord four-banger that'll outrun this car IF I simply try to mildly accelerate from 50-70, of course stomping it leaves the Accord in the dust. I mean, this thing drags its *** from 50-70 like I'm pulling a trailer house. I wouldn't say that I suspect the TC of locking/unlocking incorrectly though, I've had several GM vehicles with lockup TC's and this one seems like it's not acting any different than my previous ones.

3) "It should drop more that "ever so slightly" to allow the RPM's to increase to a usable range and have some slip."
Answer: I mean, dropping, as in from 2100 to 2000. It's hard to say exactly how much it drops, but it does. If anything, I'd think it should rise slightly due to the added throttle position, until the TC unlocks then it should climb 3-400 RPM, which it will once I get it in passing gear. Maybe my TC is staying locked too long, but why does it drop another 100 rpm when I begin mild acceleration?

4) "Or it's coming out of 4th and the TC isn't unlocking. It would seem about the same. You would get knock counts and further kill your performance. A scan tool would be handy here but I know most don't have them."

Answer: You may be right, I just know it seems like it is binding either in the transmission, or the engine power is getting cut and losing half-3/4 of my power. I can also feel some slight surging, it's hard to tell with how the Corvette rides, but I'm mostly certain it's slightly surging too during this mild acceleration. But I've done some tests on my fuel pressure and TPS already. They both behaved as they should while out driving. My fuel pressure climbed from 35-45 during acceleration as it should, with no noticeable drops. This evening I'm going to disconnect the vaccum line to it and make it maintain 45 psi constantly and see how it behaves, just to eliminate that question. My TPS holds constant while cruising, and climbs/falls correctly with throttle position changes, even while out driving, I tested that with a multimeter a week or so ago, that was my first suspicion, but not the culprit. But I am tempted to change the TPS just to eliminate that question also.

I'm planning to get an ALDL cable and some free scan-ware for my laptop to scan the counts of the O2's, IAC, and anything else I can get, it's just gotta wait for some available money, rebuilding the transmission took a chunk out of my wallet.

5)" Couple of questions: Was the tranny rebuilt....... "

Answer: I've answered some of your questions already through the other answers, so I won't repeat them, unless you want more clarification. I rebuilt the transmission because I've got a heavy foot and 3 and 4 started slipping if I accelerated too hard, and on my way home one evening, it suddenly started slipping badly in first and second. The trans guy said my 1-2 apply servo was cracked badly and the o-ring seals were practically melted, my 2-4 band was burned, and my 1-2 clutches were burnt to a crisp. I saw the parts; they were mostly cooked. It performs good now, better than before, but this same nagging issue as before. He checked my TC, I was going to replace it, but he recommended not to. Now, I kinda wished I'd replaced it, if nothing else but to eliminate that question.

Yeah, I need to get the ALDL cable and check my running conditions. Which program is best for this? I want to get some editing software too, like LT1 Edit. I don't have to change my chip for this, do I? It seems as though it simply overwrites the PCM info.

This morning on my way to work, it didn't do any of this. It accelerated fine, no bogging or dragging-*** like it has in the past, but I was almost to work before I noticed it wasn't doing it like before, and I couldn't test it more, but I will on my way home this evening to see if it is still doing it. When I got to work, it was idling higher than normal, don't know why, about 500 rpm more, right around 1300 RPM. Weird.

 

I read your complete post and once I got to the high idle part--as '1963SS" said i'd question the TPS also. Since the PCM looks at throtlle position for IAC valve control and converter lock up/unlock. Of course you also have the wiring between the TPS and the PCM itself. I've seen theTPS get little "hitches and glitches" in them while movig thru their travel and not set a code. They can however usually be seen with a scope or analog VOM--just sayin'

 

Check the tps with a scanner. Also, check the timing. It sounds as if you might have too much timing. In 4th, as you give it throttle, if the knock sensors pick up detonation, the computer will pull back timing big time and you'll feel a lack of acceleration.

 

[QUOTE=c92vette;1578092607]As the op answered, these aren't mods. They are maintenance procedures that should be done on any used car just purchased.

 

Thanks for all the help and suggestions. This evening it performed as usual, dragging ***. And it is definitely slightly surging under the medium load. No doubt about it. I think I'll bear it for now until I can get the ALDL cable to run some runs and log it all down. Then I'll come back to this and post my findings, probably in a couple weeks. That is, unless someone comes forth with the answer, that'd be great too. Or, I figure it out. I'm really leaning hard that it's more of a transmission issue, as it only does it in OD. If I drop to third, no problems, surging, plenty of power, it's great. ONLY in od does it do this.

 

First thing this morning, I got out on the road as quick as I could to test the car cold before the lockup TC started working. My road is bumpy and noisy, so it was hard to tell, but I don't think I had any pinging or bogging, but once again, hard to tell. Test 1 done as best as I could.

So a couple miles later, and the operating temp is up to 175 deg. I turn onto another road, this one is smoother and quiet, so it's easy to hear and feel the car. It shifts into 2nd, 3rd, and finally 4th at about 38 mph......Pause this here...

From here, let's establish a couple of assumptions; first, that I'm holding a constant throttle position of roughly 30% during acceleration, and when I'm cruising at a constant 60 mph, let's say my throttle position is about 10%. Now, back to going into 4th at 38 mph, throttle is about 30% and accelerating fine and normal..... Un-pause...

Continue accelerating fine, all is well. At 48 MPH, my TC locks up like normal, and the RPMs are now about 1800 rpm. The engine begins pinging immediately, and I no longer see an increase in speed. My engine is bogging, pinging, and I gain about 1 mph in the next 30-40 seconds and I'm not moving the throttle. See what I mean? Dragging ***! I back off the throttle to about 20%, it quits pinging, the car feels like 500 pounds got removed from it, and it begins accelerating to 60MPH. Go back to about 30%, pinging is back, gradually feed up to 70% throttle, all the while again pinging, bogging, surging (surging may be missing, backfire, can't tell for sure) not really gaining speed. I get to about 70% throttle, at roughly 63 mph, it unlocks the TC, I go to passing gear, and off we go like normal now. Test 2 done.

I'm holding a constant 60 mph, about 10% throttle, and drop the shifter to 3rd, my RPMs rise to about 2500. I begin applying more throttle, no ping, no bog, no issues that I can tell. Seems to accelerate fine. shift back to OD, shifts up pretty firm, never came out of lockup as best as I can tell, pings, bogs when I try to accelerate again. Test 3 done.

Now, I would say that it was dependant upon throttle position, but it didn't seem to do it in 3rd or while it was cold. Nor does it act up in 1st or second at those throttle positions. I'm more inclined to say it does it while in TC lockup, because before TC lockup in 4th at about 40-45, I can accelerate fine, no bog, no ping, but as soon as it goes to lockup, BAM! it starts. I could probably get this less noticeable when I tune it with a laptop and ALDL cable by simply changing the lockup speed to something higher, or delay 4th to come in until 60MPH, but that's not fixing it, it's simply covering it up. I need to find the problem and fix it.

Could I have some bad electronics in the Transmission causing this? I'm so lost now, I'm about ready to take it to a shop, and that's bad for me, I never take my vehicles in, I do 99% of my own work. Don't we have som transmission guru's on this website? I need to get their input on this as well. I'm going crazy trying to figure this out-

 

I'm no ones guru---but IMO if you get access to a scanner it will tell you whether or not the PCM which is the trans "brain" is asking for the converter to lock or unlock. If the scanner is showing "TCC off" while driving and you're having the no power/won't accellerate/ pinging and feels like it's staying in lock up problem then yes you may have a internal trans problem--bad converter/lock up solenoid/wiring or valve body.

On the other hand if the scanner shows "TCC on" while you're having these problems then the PCM is keeping lock up engaged which once again IMO could be caused by sensor inputs to the PCM as I said before the TPS comes to mind. I would imagine if you take it to a competent shop they would drive the car with a scanner and check in the above manner. JMO

 

Thanks Twister... I too feel like the lockup is the culprit with each passing test while driving. This morning I did another test... when it began to bog, I tapped the brake lightly to force the TCC to unlock, and Voila! it began performing like I would expect it and the ping stopped. So I'm 99.9% sure it's something to do with it staying in lockup when it shouldn't. Now, the question is; WHY? You pose good points to look at: TCC solenoid, pressure sensors, TPS sensor, etc. Pressing on......