Tbi to carb.

[72chevy2door]

Hi guys I need a little help on this. I own a 1988 GMC 1500 Sierra Classic suburban with a 350tbi 700-R4 transmission 2wd. I am having problems with the distributor throttle body coil something I don't know but it's causing me tons of stress and I'm broke so I just can't throw parts at it and hope it works. I want to keep the tbi but the way it's going it seems I can't. I have another thread in the engines and performance section labeled Tbi backfire. Had a couple great guys help me but just seems I'm not doing something right and old school carbs are my thing not this computerized stuff. I'd like to know how hard it is to do the conversion from tbi to a carburetor. I have an intake I got at a junkyard, lucked out it's one of them professional products intakes designed for the center bolt valve cover heads for $25. I know I need carburetor and distributor but what else and how hard will it be to do it all?

 

[Jims86]

Hi guys I need a little help on this. I own a 1988 GMC 1500 Sierra Classic suburban with a 350tbi 700-R4 transmission 2wd. I am having problems with the distributor throttle body coil something I don't know but it's causing me tons of stress and I'm broke so I just can't throw parts at it and hope it works. I want to keep the tbi but the way it's going it seems I can't. I have another thread in the engines and performance section labeled Tbi backfire. Had a couple great guys help me but just seems I'm not doing something right and old school carbs are my thing not this computerized stuff. I'd like to know how hard it is to do the conversion from tbi to a carburetor. I have an intake I got at a junkyard, lucked out it's one of them professional products intakes designed for the center bolt valve cover heads for $25. I know I need carburetor and distributor but what else and how hard will it be to do it all?

Fuel pressure regulator reduce the pressure to about 7 psi., Proper throttle brackets, and a geometry kit for the TV cable, if using other than a Q jet. TCI trans lockup kit for 700 R4.

 

[MrMarty51]

If You do not get that backfire fixed before doing the conversion, I`ll put money on it that the backfire will still be there after the conversion.
IF You want it to run good after the conversion then it better be running good before.

Do You have an intake valve hanging up ????

 

[Jims86]

Yup, I agree with Marty. I think you have fuel pressure dropping off, and even going to carb, wont fix the problem. Checking the parts doesnt cost anything...hell, you may pop the dist cap, and find some moisture, or carbon tracing.

 

[72chevy2door]

Hey guys sorry I thought I had responded to this post I guess I didn't. Well I got the backfire thing done and gone but she surges every now and again and stumbles. No vacuum leaks or over loading of fuel. I think it's the throttle body. It was my brothers old one and had 230000 miles on it. I'm still strongly considering going carbureted because it doesn't like to start and will sometimes act like timing is way out of wack.

 

[Jims86]

Honestly, going to carb will be more headach/exspense. Have you taken the IDle air motor off and cleaned it? They get gummed up now and then, due to PCV.
Also, wiggle the throttle shaft to check for excessive play.
Is there still a metal plug where the throttle(idle) stop screw is? If not, someone may have dicked with it.
Does your check engine light work?

 

[72chevy2door]

The idle is factory cause it still has the plug in it. The idle air sensor is the one in the back passenger side of the throttle body right? If so I know it's fine because I had a spare and I swapped it and the tps sensor and it continues to surge. It's as if there is a vacuum leak but there is none. I checked with starting spray and no leaks. The throttle shaft is fairly tight as in not too much play side to side. About what I would expect for it to open smoothly. I know it's a clean tbi unit because I did a minor cleaning and it didn't change anything. My brother has the same Burban as me and he converted over to carb when he put a punched out 350 in it. He said it was easy just time consuming. With hiding and seep rating the charging wires from the ecu wires. He said he had to run a fuel pressure regulator which I figured but he never did do a tci lock up kit. But I'd love to keep the tbi as long as it stops costing me more money! Lol

 

[VAL]

A couple of years ago, I had the same problem with the surging. I'd be driving down the street and the engine would rev up on its own then back down, and stumble when at a stop light. I changed the injectors, new fuel pump, fuel filter etc., everything that had anything to do with the fuel. I finally figured it out, after I spent like $600, that it was a ******* little $40 sensor on the intake, that's right next to the upper water hose outlet. I believe its called an intake air temperature sensor. It had gone bad, and it was making my computer do all kinds of crazy **** with the air/fuel mix.
here's a pic of where and what it looks like.

You must be registered for see images attach

 

[72chevy2door]

I put a new one in just to see if that could fix my problem and it didn't. It has a new knock sensor and both oil pressure sensors are new also. The only old sensors on this motor is the ones on the bracket next to the throttle body

 

[89_3&3]

Egr valve ?

 

[72chevy2door]

No I haven't done the egr valve. But that shouldn't really matter on this would it? My smog pump hasent been on it in a few years. I bought the truck without it.

 

[72chevy2door]

I know the egr is for exhaust gas recirculating or whatever but that shouldn't cause it to surge. I never known one to cause that before. This tbi system is a bad design in my opinion. I wish my truck didn't have it cause I like carbs way better.

 

[89Suburban]

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

You must be registered for see images

 

[Swims350]

I had issues with my tbi and going carb fixed them, until the lifters wiped out(my fault)

I could not refire mine once warm when it was tbi, carb fixed it.

I had this bad miss, or pop like trying to give it too much gas, and that went away too. I had to advance my stock tbi dist. alot to get anything out of mine, so might as well do carb, since I usually run them advanced a good bit when carb'd.

 

[72chevy2door]

I'm thinking that's what I'm going to have to do. Thanks 89suburban for the info I'll try to see if any of that will work when I get the chance. It's the most confusion I've ever had with a motor. I've built tons of motors from Hondas to fords to a whole bunch of small block Chevys but this is the first tbi small block I've done and it's gave me more headaches than what it's worth I think honestly. Before I rebuilt the motor it didn't have to many problems burned oil and had a slight miss that never went away. Tore it down and surprised I didn't find a diamond in the crankcase it was so badly carboned up. The machinist told me he didn't think the motor would've lasted 20000 more miles cause the buildup. But anyhow there really is no performance things done to it so I shouldn't have problems. I have absolutely no money so I can't throw a carb and stuff on her and let her eat. I do have an intake that will work on this motor however so I guess I'm partway there.