I bought a 52mm bbk/edelbrock TB on ebay, supposedly for 88-92 cars. The car is a 91 formula 350. Well I've got the car apart and there are two major differnces between the stock one and the new one

TPS mount is different. The stock has a little arm on the tps that is moved by a corresponding arm on the tb, The new one has a large round indented area with a shaft that narrows down to a thin knifelike piece about 3/8" in width. completely differetn. Besides the two screw holes that mount the tps dont line up

Second, on the backside of the stock tb there is a canal around the 52mm opening on that side that leads to a smalle vacauum (?) fitting on the bottom. No such animal at all on the new one.

Please help, I must have got the wrong tb, althought the cable connections all appear to be more or less the same. I was going to go racing this weekend in a bracket race, but now crap!

 

Is there anyway you can take a picture and upload it?
I bought an 85-88 TB for my 89 and everything appears to match up except for the throttle cable hookup. Does your throttle cable seem to hook up the same with the new one?

The vacuum fitting you are referring to on the stock TB, is it on the right/rear side pointing down when looking at it from the front? This is the same on both of my TBs also. BTW mine is a Lingenfelter 58mm TB.

 

the cables all appear to match up. The problem is the tps mounting and the fitting that you are describing, yes its in the position you say. What the hell is going on here?

 

On my holley TB, I had to file down the arm on the stock TPS. I ground about 1/8" off, then it fit perfectly. The only other problem I had was that the supplied screws were too short, and because it's a different thread pitch than stock, I couldn't reuse the stockers.

 

I think something else is going on here. I had a 58mm HOlley and I decided not to use it, I sold it without putting it on and bought this one. The holley looked the same on the tps interface arm thingy, but this one is completely different. I know I didnt describe it very well. I guess Im going to put the stock one back on now and take some pictures tomorrow. Besides, it doesnt have that small vacuum fitting coming off the bottom on the drive side like the stock one and the Holley did. It must be for another car or ???


Crap, this was supposed to be an easy bolt on, hah!

 

Oh hell, I just looked at the auction where I bought it and it says "LT1, TPI, or LT4". I bet the sob is for LT1 and it doesnt work on this car, oh the joys of ebay
##$%^^&

 

Damn, that sucks. See if the seller is willing to let you return it for a refund. How much did you pay for it?

 

Here are the pics that show the tps mounting and the back without the vacuum fitting on the bottom driver side. I posted this on the Houston F-body website hoping someone can confrim that this is for a LS1 or LT4. Anybody here know? Anybody want to buy it?

 

here is the other pic showing the tps mounting.

 

Thats a LT1 style....

You can make it work, Just slot the screw holes on a LT1 tps sensor and cut and solder the new plug on your harness.

Sloting the holes will giv eyou the room to adjust it.


Or just send it back and buy the right one.

 

Ok, I figured I could get the TPS to work, but what about that vaccum fitting? Normally where there is a vaccuum fitting there is a reason for it right? do you know the one im talking about? It is on the bottom of the TB on the drivers side. I have no idea what it is for. Probably better to either sell this one or try to get the guy to take it back. He did say "TPI" in the auction heading.

So this is defientely for LS1 rigtht? Waht about LT1. I want to know so that when I advertise on Houston fbody site to sell it I can say for sure
thanks

 

The LS1 uses a completely different single-blade throttle body.

The 94+ throttle body sensors are different (not sure about 93), and apparently different enough to require a different throttle body. I think that if you get an LT1 TPS and wire an adapter that you can use it. I suspect that the wiring should be the same, but the connector is different. You might get lucky and find the same wire colors, but if not you'll need to know what wires do what for each setup, then wire up a little adapter for your harness.

 

OK, I appreciate that. Its for an LT1, not LS1. I figured I could do something about the tps, but what about that vacuum fitting? I guess I could try it without it and see if anything explodes

 

That vacuum fitting underneath the old TB goes to the EGR solenoid. LT1s used a different EGR setup, hence no fitting.

It's ported vacuum, so you either have to ditch EGR functionality, or get the right TB, but you can run that TB with a touch of ingenuity.

 

I have no problem with ditching egr functionally as you say. If I understand EGR right it is justa an emission control system that helps lower emissions and wont affect performance. I do need to pass emissions testing, which I just did a month ago. So would it be possible to just leave the fitting off while using this tb and when I need to pass emissions again, put on the stock tb and hook up the egr solenoid vacuum fitting again?

Im sure I can make the tps work

 

If I recall. Wire color was the same....


If you need a LT1 TPS pig tail let me know I belive I still have one around. maybe the TPS also...

e-mail me Chris@cecoatings.com

 

Well it might be worth a try. When you say the wire colors were the same, do you mean the colors going into the pigtail on the 91 would be the same as the colors going into the pigtail not he 94? In thiis case, with a 94 pigtail and tps, I could hook the wires back up to the same position on the pigtail and just plug it in to the tps?
I guess it would be worth a try. Would you sell them, or I just pay shipping or what. I new tps is $20 at the auto zone

 

Hey Larry,

The wire colors are the same for 93 and 94+ and that could be extended to say TPI applications as well but terminal placement does not match since the connector (and subsequent TPS) is of a different design. All of these TPSs serve the same purpose and have the same design with a 5 volt reference, a ground, and a variable signal 'output'. These wires will have the same color on an LT1 as they have on a TPI. On a TPI the reference wire is terminal C (grey), the signal wire is terminal B (blue), and the ground wire is in terminal A (black). So match those to the LT1-style TPS connector by color when you get it. The grey wire will go to terminal A, the black to terminal B, and the blue to terminal C on the LT1 connector. That should get the TPS wired and mounted but the TPS is non-adjustable on an LT1 (that is taken care of in the PCM) so you will need to make sure the TPS ends up reading properly. If it is off you may be able to open up the holes on the TPS and adjust it a little bit.

As for the EGR, I would just run some other vacuum source to it as it will set codes and trip the SES light if it is still flagged as operational in the PROM but not actually operational.

HTH,
Matt

 

wow, thanks a lot matt, that was excellent information. I appreciate it

 

OK, I got a TPS pigtail from a LT1 from a guy and I am going to buy a LT1 TPS and mount it onto the throttle. So I need to cut of the pigtail on the TPI car now, and splice the LT1 Pigtail onto the wires in the car, then just plug it in. I thought I understood what you are saying, but now I am unsure again. The LT1 Pigtail has a grey, blue, and black wire like you said, but apparently the terminals are different. on the lt1 pigtail the its A=grey, b=black, and c=blue. If i understand you correctly I just need to match the colored wires on the LT1 pigtail, to the colored wires on the TPI after I cut off the existing TPI pigtail right? the terminal should take care of themselves no?

thanks again

 

I bought the Lt1 tpd but didnt have time to do the swap tonight. I just disconnecte that EGR vacuum fitting from the stockTB and ran the motor to see what would happen. didn't notice any difference, no engine light, etc. I wonder if its really necessary to connect that somewhere. I didn't see any obvious place to reconnect it

 

You won't get a light just sitting there idling, but you might get one while cruising steadily.

It's gotta be ported vacuum though, not just manifold vacuum.

 

I was looking at the back of the LT1 throttle body here in my office (instead of working), and I notice a channel around the passenger side tb opening that leads to a brass vaccuum fittin on the bottom of the passenger side of the TB (see photo in this thread above). This would be ported vaccuum I guess right? I what about Teeing off this point and connecting the vaccuum fitting for the EGR Solenoid there?

 

Ported vacuum would come a small hole right at the edge of the throttle blade. See if there's one there and follow it.

 

Roger that. You got it.

As for the vacuum fitting, if it gets it's feed from the behind the throttle blades, it will have intake vacuum provided and give you what you need for that EGR vacuum line. Just follow the porting in the TB casting itself and see if it comes from behind the throttle blades or in front of them. I am willing to bet that the fitting you are referring to has vacuum supplied to it.

 

OK, Im confused about ported vacuum vs manifold vacuum. First JZA said I needed ported vacuum for the EGR solenoid vacuum line. Is this correct? Matt seemed to be saying in the last message that manifold vacuum which comes from the back of the TB like this one, would be OK.

Second question, is the line indicated in the picture attached here ported vacuum? I don't think so since it comes from that channel around the tb opening that opens into the back of each tb opening. This fitting has a hose that goes to the charcoal filter canister and this is the one that I was going to tee off of and connect to the EGR Solenoid. I got everything apart at home and will finish it up tonight. I hope it works.

 

Manifold vacuum .should. work, since the solenoid is still controlling the actual opening and closing of the valve. But I always try to get everything as it was from the factory. Go ahead and tee that off and use it.. didn't mean to confuse you, I was just illustrating the original setup. Lemme take a look at my service manual tonight.. I know there's a good reason they do it that way...

 

OK, I appreciate all your help, and everyones, dont get me wrong. I will hook it up that way tonight and see how it runs. I guess you are saying that that fittin is manifold vaccum right? I still don't really understand the difference I guess, but heck, Im learning a lot every day on this stuff. Im going to keep the factory setup, throttel body and fittings, in case I need to hook it back up that way. I kind of like to keep more or less factory too unless there is s good reason to change something (like it goes faster, haha).
thanks again, I will watch for further repsonses here.

One other question, everyone says the LT1 TPS is not adjustable but you can enlarge the mounting holes to make it that way. I was looking at my stock on for the 91 tpi and it doesnt have elongated mounting holes. How does it adjust. Also as one guy said, the stock tps mounting bolts dont work, they are too long, but the diameter and threads seem to be the same. I am going to the hardware strore on the way home to get some shorter ones with the same thread.

 

The SD computers (late TPI, TBI) have non-adjustable TPS sensors. I don't know the exact circumstances that it follows, but the computer basically sets the TPS 0% voltage at what it's sitting at with the TB blades closed. What I mean by the exact circumstances is that when it decides to set that.. I know that if you have the gas mashed to the floor while you're cranking it, that it cuts off fuel (what's called Flood Clear mode).

You won't need to elongate any holes on the LT1 TPS unless it's waaay off the way it sits once you have it mounted. Anywhere from .5 to .7 volts should be okay.

 

OK, I finally got the car back together with the LT1 throttle body. started it and got code 22 and code 42. 22 is "throttel position sensor, low voltage" and 42 is "electronic spark timing". but first let me say that the position of the throttel cable is a little farther foward, so the car idles is way off, 2000 rpm. Is there a way to lengthen the throttle cable short of cutting it a splicing in a shorte piece of cable?
I guess I need to check the tps voltage and may have to adjust it by elongating the holes like we thought I shouldn't have to do. I can check the voltage and do that. But what is the EST code for? Something to do with the high idle or something to do with the vacuum line for the EGR solenoid I moved to the Teed of position like was mentioned earlier in this thread, or ??what.

I'm getting to the point where I am starting to think I just need to sell this TB and get one for the TPI.

 

Well, Im making progress. I "wallered" (as they say here in Texas) the TPS holes and adjusted the TPS to higher voltage and the codes disappeared. The idle is still high tho, about 1200rpm. Doesnt appear to have anything to do with the vacuum. I connected the Charcoal canister filter fitting back to where it was, took of the tee that I had connected to the EGR solenoid, and just left the EGR solenoid fitting off , like before, and it didn't make any difference in the codes or the idle.

Oh by the way, this is all with the Throttel cable completely disconnected so it isnt pulling on the TB at all. So now Im going to somehow lengthen the TB cable so that wont make it idle high, then see if i can adjust the idle down with the adjusting screw. Supposedly you are not supposed to adjust that screw, but maybe on the LT1 it was different.

I would appreciate any comments or suggestions

 

It sounds like all you need to do is set the minimum idle at this point. I'm not sure what the LT1 guys do, but us TPI folk usually have to adjust that minimum idle any time we make changes to the volumetric efficiency of the engine.

It isn't that you aren't supposed to touch that screw, it is just that it usually is within range for the IAC to do its thing and control the idle per the specs in the PROM and shouldn't need to be moved. Jacking it in and out without knowing the whole story will send you chasing your tail. Now in your case, you know the TB is the primary thing that has been changed so it is likely the culprit. It's the guys that all of a sudden have an idle problem and use that screw to adjust it without narrowing down the root cause that are setting themselves up for failure. Heck, even the factory TBs aren't always set perfectly for the factory stock engines.

You want to adjust that minimum idle screw until the IAC reads between 10 and 20 counts. I like to have mine set low so the IAC is doing as little as possible to keep the engine idling when it is totally warmed up.

Basically the IAC system offers a range of idle RPMs that it can control by opening or closing the valve and allowing more or less air into the engine while the TB blades are closed. So if the engine won't idle down and you know the cable isn't pulling the blades open (as in your case with it disconnected), you either have a vacuum leak or the minimum idle is set too high. You can verify which is the case by adjusting that minimum idle screw to close the blades and see how it effects the idle. If you close the blades all the way and it won't idle down, you have a vacuum leak. If not, you just need to set it per the instructions in the tech article on this site or until you see the IAC counts within the 10-20 range.

Once you have the minimum idle set to where you want it/should be, be sure to go back and RE-adjust the TPS so it reads properly.

HTH

 

Thanks again Matt. By the way I looked at your website, very nice car. Looks like you've done a lot of work there.

I havent' set the idle before so I will read the tech article you mentioned on setting it. Frankly im not sure what you mean by 10 to 20 clicks on the IAC, I was just going to adjust it back down to 650 rpm after warmed up, thats where it was before, but I will read that article and figure that out.

By the way, I didn't mention it but one of the two bolts that holds the round TB plate onto the shaft was missing, leaving a small hole there, I plugged it with a piece of rubber just to see how it affected the idle and the idel was still 1200 rpm, of course it was higher without that plug. I've got to get a bolt to plug that, but apparently it is a very unusual size, the same size as the TPS mounting bolts I beleive. Do you know what size those are? I used the bolts from the TPI TB for the TPS mounting, but they were too long, so I was looking for shorter ones. Went to 2 auto parts stores and two hardware stores and coulndt find a match. Finally just bought some spacers and used the same bolts. Why the heck do they have to make things so difficult? haha.

I understand what you are saying about the idle adjustment, it is turned out pretty far on this TB, that's how I got it.

One more thing, you say be sure to test the TPS after I adjust the idle. I just turned it a little last night after elongating the mounting holes inthe direction to increase the at rest voltage, after getting the low voltage code, so I don't know what it is actually reading. To test that you put a probe on the signal wire, and then to ground, then move the throttle? According to the shop manual the low should be at least .2v and the high 4.8 or 4.9 I think it said. Is that how you do it?

Also what about ideas on increasing the length or adjusting the throttel cable. I thought of cutting the cable in that last section where it is open between the TB and the covering at the bracket on the plenum and using some kind of clamps to splice in an extra piece, but I hate to butcher my car like that if there is another easier way. What do guy who put in a TB spacer do? same problem.

thanks again

 

Hey Larry,

I checked my service manual and it does say manifold vacuum for the EGR solenoid. But that's for a 92..

It sounds like you got the TPS problem figured out. Just as long as the voltage goes the right way for the right range.

About those TPS screws: a lot of wire cutters have screw cutters built into them. They just look like several holes of different sizes and threads. You just open the cutter, thread the screw in to the length you need it and squeeze and it cuts a nice clean cut without boogering the threads (assuming you can squeeze the sucker hard enough).

Vader has a good write up on setting your minimum air setting. Check around or ask him for it. Tom Keliher ([former] suspension moderator) also had an article on setting min. air/TPS that was published in Super Chevy (or one of those magazines). (where'd Tom go anyway?)

And like Matt said, you only really ever need to mess with it if you change something major in the motor (usually cam).

Now you just need to hook up a scanner and see what the IAC counts are.

 

Well I jury-rigged the throttle cable to the TB with a piece of wire. It was only about 1/2" short. I wish there was a better way, its really kind of pitiful looking, but works.

I adjusted the idle down with the adjusting bolt, only went down to about 900-1000 rpm. Is there any way to ajust it down further, I don't have a scan tool to check the IAC, I guess that would be a good idea

I cannot find a way to plug that hole I mentioned where the round TB plate bolts to the shaft, so there is quite a vacuum leak through there. I put my finger on it while running and idle went from 1300 rpm to the 900 to 1000 rpm I mentioned. Does anyone have any idea what size and thread that thing is? Its a BBK/Edelbrock 52mm TB for a LT1. I appears to the same thread and diameter as the TPI stock TPS mounting bolts, which I could not find at the hardware store either. Why in the heck don't they make these things a normal size in case you need to replace them. It is between 4mm and 5mm, neither does 6/32, 8/32, 10/64, nor 3/16 fit it. It looks closest to 3/16 but the thread is different. jeeez.

Took it for a drive, runs good. Is there any downside to leaving the idle at around 1000 rpm, besides gas mileage?