Tech question

[GrndNatnl]

Turbo Technical Question

Ok, I'm becoming a frequent poster already... but I have a couple more questions.

The first question is about a certain functionality in my car in general. Could someone explain exactly how the turbo functions under the following conditions? When the car is idle, in park (or neutral), and I rev it.. I can not hear the turbo spool. And the boost gauge jumps from the usual idle vac to zero, or maybe 1 or 2 psi of boost. If I rev it and hold it at a higher RPM, it shows a pound or two of boost, but I think it goes right back down.

Now when the car is in gear (under load), I of course.. can hear the turbo, and it builds boost and holds it until I let out and cruise, or if I mash the gas it continues to build.. blah blah blah...

Why does the turbo not respond, or doesnt seem to respond, while out of gear? (Only with load / acceleration) I've heard plenty of cars that whenever revved and RPMs rise, the turbo can be heard spooling, and still creates a little boost? Is that a wastegate function? I'm just curious about how that works. I would think the turbo should spool with any throttle input.

----------------

One more question: I have a switch wired up to the top right & left pins of my ALDL for TCC lockup switch. It was working great... and today I noticed it would not lock up the converter. The other day I used a GM trouble code scanner to check for codes (which there was none but the good 'ole code 12). I hooked the wires back up into the correct ports, and last I drove it today, the switch doesnt lock it up. Should I reset the ECM or something? Could this be a TCC solenoid problem all of the sudden? Should be any problems considering the tranny was rebuilt with a crapload of new parts 20,000 miles ago. Is there good way of testing the automatic lockup on the highway? Traffic is so bad around here, overdrive is rarely reached, and I've noticed it running in 3rd a lot. I let off the gas, it goes down,.. soon as I touch it again, back up.

Thanks for reading. Sorry for the long post. I'm still learning about my car day by day. And I have found no better place then this message board to do so.

 

[Sinful6]

Boost is proportional(derived from) to load.

 

[UNGN]

Re: Turbo Technical Question

Originally posted by GrndNatnl
Ok, I'm becoming a frequent poster already... but I have a couple more questions.

The first question is about a certain functionality in my car in general. Could someone explain exactly how the turbo functions under the following conditions? When the car is idle, in park (or neutral), and I rev it.. I can not hear the turbo spool. And the boost gauge jumps from the usual idle vac to zero, or maybe 1 or 2 psi of boost. If I rev it and hold it at a higher RPM, it shows a pound or two of boost, but I think it goes right back down.

Now when the car is in gear (under load), I of course.. can hear the turbo, and it builds boost and holds it until I let out and cruise, or if I mash the gas it continues to build.. blah blah blah...

A turbo doesn't need "load" to spool. It needs Massflow. Enough high temp air and burnt fuel to spin the turbine and make the compressor do work (compress air and build boost).

Massflow is related to throttle position. If you open the throttle there is a higher massflow than when the throttle is closed. out of gear, the thottle needs to be opened very little to rev up the motor. If you floor the motor out of gear, in seconds it will overrev. Not much massflow and not much time to spool the turbo.

In gear, the load of the torque converter keeps the motor from overrevving so the throttle can be opened wider and for a longer time. If the massflow is high enough the turbo will spool.

Note that the massflow is spooling the turbo and not the load. If load spooled a turbo we'd all launch in 4th gear or buy 1000 RPM stall converters.

Cars with smaller turbos may indeed be spooling out of gear (smaller turbos have a smaller massflow requirement to spool). Blow off valves on some cars can keep the turbo spinning (not building boost however) even while the throttle is partially closed. the blow off valve bleeds off the excess boost.

 

[JToups386]

Well said UNGN! That helped further explain it to me too, as opposed to the "load" theory. Good answer!

 

[GrndNatnl]

Ah!

Ok, that makes sense. I like to have a better understanding of how these things work. Helps to better the car all in all.

I'm only running the stock turbo. I would think that if I brought the engine RPM up to a certain point, while out of gear and held it for longer then just a quick rev, it would spool eventually. Giving it time to spool with -some- massflow. Also considering the fact that its not a monster turbo and shouldnt need much ( Its stock turbo). If I hit the throttle out of gear, the boost gauge will jump from vac, to around zero, then back down to vac. I'm guessing the TR's I hear spooling while revving have a little more in the motor itself. Meaning they're producing more high-temp exhaust and massflow with RPM even out of gear. Am I correct?

 

[UNGN]

People with grand nationals don't "pop the car out of gear" or "push in the clutch" to rev the motor up. If you heard the turbo spool why someone was "reving" their GN, odds are pretty good the car was in gear and the converter was loose enough to allow the motor to rev quickly and high enough that the turbo was spooling. Also, the fact that you heard it means that it would have a low restriction intake and exhaust. It's hard to hear turbo noises with the stock airbox/exhaust still in place. An open K&N makes a lot of noise.

 

[GNVenom]

In order for the converter to lock up, your brake switch must be closed...that is, the switch at the pedal has two connections, one for the brake lights and the other for the lockup. It's the blue connector, and the two wires connect together, completing the lockup circuit, only when the brake pedal is at rest. If the switch is not closed, the converter won't lock. Try this: Turn your lockup switch on at maybe 40MPH, then lift up on the brake pedal with your foot. If it locks up then, you need to adjust your brake switch. If not, pull that blue plug and be sure the pink wire is 12 volts with the key on. If it isn't, you may have a blown fuse.
-John Spina
http://www.casperselectronics.com
Look for the SEPTEMBER SALE items on the web page!

 

[GrndNatnl]

Ok, I'm gonna be foolin with various stuff on the car today, mainly the lockup issue. In the Transmission forum, I re-posted the same question with a followup on this mornings test drive. I'll check the brake switch. But if the switch is open [you mean], meaning I let off the brake and just drive. The converter should be allowed lockup. But I would think.. if its not adjusted right and it wont allow lockup, then my brake lights must not be turning off either...

UNGN, thanks for the explaining. Just one more thing for example. On one of these many TR parts websites I have in my favorite places, is a sound file I listened to for an exhaust system. One of of Jim Testa's car, and another from what counds like a serious strip car. It's started, it idles.. they puch the throttle a couple times and you hear that turbo loud and clear. Another is the video on BuickPower.com where they shoot the GN in the dark with the parking lights running and the engine running. You can hear that one too. I first thought of all this because I made a sound file from that one that plays for my Windows startup on my computer. Check it out and you'll see what I mean. I just want mine to sound like that, LoL.

 

[QuickWE4]

That noise you're hearing from Testa's car isn't the turbo - it's harmonics from that special Testa wing on the trunk

Sorry Jim, had to take a shot at ya - all in good fun

Seriously - I had often wondered the same thing because it does spool at idle. In fact, the file name on that .wav is "spoolatidle".

Mine never did that either, and I've got a THDP, cold air, test pipe to an ATR system.

?
Rich

 

[GrndNatnl]

Uh oh...

Now I got big problems. After fooling with the lockup this morning, I just had it out again, and the trans is seriously acting up. I dunno if fu*king with the lockup over and over caused a problem, which I'm afraid of, or whatever else could have gone wrong. It shifts firm as usual, but when I let off the gas, and tap it again, it has that "clunk" to it where it feels like theres play in the gear. Then when I'm slowing to a stop at a red light, it kinda has a shake, and i hear it going "clink-clink". I can feel it kinda tug or jolt.

Pleeeease, someone tell me what could have went wrong. I'm not looking forward to a trans rebuild which has already been rebuilt not too long ago. Any idea how much its gonna run if I have something seriously wrong? I'm quite upset right now, so I appriciate any and all ideas.

 

[blackbuick87]

Sounds like the convertor is stock in the locked position. I will be fine in first gear but in 2,3, and 4 it will act funny is this is the case. What did you do?

 

[Danster]

Sounds like your TCC solenoid might be broken. Do a search on this subject in this BB and you'll find find a well written procedure for trouble shooting the TCC solenoid. If it turns out to be your problem, the part is not expensive and you should be able to do it yourself. Good luck!


Dannyo

 

[turbo buicks]

the converter is made to unlock when the brake is depressed if you keep it locked when you slow down or let off the gas it will damage it. i heard that from one of the forum memebewrs so i never cared to try locking it on my own. kirbans performance sells a TCC solenoid which locks and unlocks the converter and they said if it malfunctions it feels like coming to a stop in a manual tranny car w/o pressing in the clutch. maybe your converter is shot. i think on gnttype.org it says the converter should last about 200 miles if you keeps it locked. thats a lot of 1/4 mile passes but daily driving can do that in a few days.

 

[GrndNatnl]

It feels funny when it downshifts at crawling speed, while coming to a stop. I dont think it's stuck locked up, since I can still hear it lock and unlock while driving on the highway. I just hear this light clanging when I'm slowing to a stop, and I can feel it jerk a little.

 

[turbo buicks]

i dont know what it is but there i a way to test if the converter is lock/unlocking how its supposed to. get up to 45 slowly just cruising and keep it around there. you should feel the converter lock up and it will feel like a shift at 45 mph. with the gas steadily being applied to keep speed up lightly dfepress the brake but not enough to stop the car. you will hear a increase in RPMs, this is the converter unlocking. it works in my car.

 

[tc86gn]

do you have a scan tool to watch it with?? It sounds like the tcc solenoid to me.

 

[GrndNatnl]

Dont have a scan tool yet. I just have a little GM code scanner that flashes trouble codes. Only thing that shows up is code 12, which is good. Nothing else.

I reset the ECM, and I'm going to take it for another test drive soon as I get the chance. (Busy work weekend ahead) I'll do the 45 mph test and see how it is, and I'll pay attention to the slowing down and see if it still jerks and makes any sounds. Should any clanging be normal in the least when slowing to a stop?

If it continues to do it, I'm going to replace the TCC solenoid, since I need to replace the badly seeping pan gasket anyway. I think the solenoid is older, and a new one only runs around $45 bucks. If it still does it after that, then I'll have to look into some more serious work. It still shifts firm (and chirps second), so it could have been just a temporary thing, based on the fact that it was hot as hell after running it around all morning and screwing with the lockup switch. We'll see as soon as I get to fool with it next.

And yes, I have been keeping a very close eye on the fluid. It's still bright red, fresh, and always at the right amount, so its not like its low on fluid or any of that. Thanks for the help guys. Dunno what I'd do without this website. As well as gnttype.