Tbi to carb.

[Jims86]

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.

I wrote a lengthy reply earlier, but I guess I didnt hit submit.
Anyways, its possible that you have an intake leak under the manifold. Plug the breather and pcv lines, and introduce propane into the crank case via the dipstick tube(After the engine is warmed up, of course) and see if it smooths out.

 

[72chevy2door]

Would I do that while it's running? I've never heard of doing that before so I want to be sure before I go out and possibly make a bomb lol. It shouldn't blow but if It does that means I had some serious blow by. Jims86 you seem to be the tbi guru here have you ever heard or seen a tbi do the things my truck is doing?

 

[HAZZARDJOHN]

I just don't see how switching to a Carb can be cheaper or better than fixing the TBI. I have had a lot of TBI 350's and it is probably the simplest engine made to diagnose and fix. I would be shocked if the cost to fix whatever is wrong would be more than all that is entailed in a Carb swap and you lose all the benefits of Fuel injection. I wouldn't have bought my suburban if it was Carbed, I have carbed vehicles but they are unreliable, get poor gas mileage and are cold blooded half the time to start. Just my opinion.

 

[Jims86]

Would I do that while it's running? I've never heard of doing that before so I want to be sure before I go out and possibly make a bomb lol. It shouldn't blow but if It does that means I had some serious blow by. Jims86 you seem to be the tbi guru here have you ever heard or seen a tbi do the things my truck is doing?

Yup, while its running, at operating temp.
Yes, I have seen, and dealt with these types of things. Some things will drive you nuts looking for the cause. Two that I always keep in mind are the hose between the fuel pump, and sender(in tank) that will deteriorate, and caus low/ no fuel pressure, and some istances where injector drivers in the ECm have gone bad.
Dirty injectors can drive you nutz
EGR valves will sometimes get carboned up, and prevent the valve from closing all the way, and sealing up.
The best thing any TBI owner can do, is get an ALDL cable, and a freeware datalogging program to see exactly what the ECM sees.....and even if you dont understand the info, there is always someone who does, and is willing to help.
Considering your non efi experience, I assume you have a Vac gauge, and a compression tester, and a digital volt meter? A TBI EFI fiel pressure gauge can usually be rented from a parts store.

 

[72chevy2door]

@Jims86, I haven't been by the shop to look at it. Weather here is crap the past two days hopefully it will clear up this weekend. I do have a vacuum gauge and I have a Autometer pro-comp fuel pressure gauge I can use to T-off the fuel line to get the pressures. I also have a compression test gauge. A friend of mine also has a thing(don't know what it's called) that hooks up to my radiator and pressurizes it while the motor is off and it has a gauge to tell you if it leaks. I'm going to use that also to see if any leaks in the coolant system. Might as well check since it's free. Lol. @Hazzardjohn, it would be fairly cheap for me to do the swap because my father has an old HEI distributor and an old Edlebrock carb that I could get for cheap if not nothing. Most I'll spend is whatever the intake gaskets are. I'm wanting to retain the tbi because it was nice while it worked but IF and only IF I can't get this system working right I will do carbureted. I've always had good luck with carb systems I've even done a handful of tunnel-rams before with homemade progressive linkage I'm just wanting to refrain from having to do anymore work than necessary.

 

[Jims86]

@Jims86, I haven't been by the shop to look at it. Weather here is crap the past two days hopefully it will clear up this weekend. I do have a vacuum gauge and I have a Autometer pro-comp fuel pressure gauge I can use to T-off the fuel line to get the pressures. I also have a compression test gauge. A friend of mine also has a thing(don't know what it's called) that hooks up to my radiator and pressurizes it while the motor is off and it has a gauge to tell you if it leaks. I'm going to use that also to see if any leaks in the coolant system. Might as well check since it's free. Lol. @Hazzardjohn, it would be fairly cheap for me to do the swap because my father has an old HEI distributor and an old Edlebrock carb that I could get for cheap if not nothing. Most I'll spend is whatever the intake gaskets are. I'm wanting to retain the tbi because it was nice while it worked but IF and only IF I can't get this system working right I will do carbureted. I've always had good luck with carb systems I've even done a handful of tunnel-rams before with homemade progressive linkage I'm just wanting to refrain from having to do anymore work than necessary.

I know what you mean about the weather...My Cousin's house has about 5 inches of standing water inside.
Your looking at a whole new set of issues if you throw that Edelbrock carb on.
The fuel pressure gauge needs to read EFI pressures. TBI is 9-13 psi. You can also hook it directly to the filter, and it should read betwix 18-20.

 

[72chevy2door]

Ouch that's not good... Unless your a fish. Lol the gauge only reads up to 15PSI. I was going to snag it off a tunnelrammed motor(avatar pic) but you said it has to read efi pressures? Ain't fuel pressure all the same? That's how I always knew it. The only problems I expect to have with the edlebrock is the geometry kit for the 700r4 but local oriellys sells it for like $5 I think. Then the trans lockup kit that you where talking about which it a hundred. Back to the gauge thing if I hook up this Autometer gauge will it mess it up or something? It's an expensive gauge so I don't want to mess her up or anything.

 

[72chevy2door]

I got to play with the truck today and I was testing the egr valve. The solenoid has 37.8 ohms so that's good and it holds vacuum on it but the egr won't hold a vacuum. I used a mityvac and it won't pull vacuum on it. It just leaks down right away as if nothing is hooked to it. I pulled the egr valve off to check for carbon and nothing is there. I am able to push the little pin thing in with ease not sure it's that's good or bad on this truck. I tried pulling vacuum while it's off and I can hear is sucking through the valve so I'm sure it's trashed. Maybe that's been my problem with it surging idle.

 

[Jims86]

I got to play with the truck today and I was testing the egr valve. The solenoid has 37.8 ohms so that's good and it holds vacuum on it but the egr won't hold a vacuum. I used a mityvac and it won't pull vacuum on it. It just leaks down right away as if nothing is hooked to it. I pulled the egr valve off to check for carbon and nothing is there. I am able to push the little pin thing in with ease not sure it's that's good or bad on this truck. I tried pulling vacuum while it's off and I can hear is sucking through the valve so I'm sure it's trashed. Maybe that's been my problem with it surging idle.

That EGR might be the type that opens based on exhaust pressure. When you start the truck, and it warms up, watch the valve while you blip the throttle...should jump open real quick... you can also apply vac with mityvac to see if it opens too, but the truck has to be running.
15 psi gauge should be ok, if you T it in at the Throttle body inlet, which is the drivers side line. most factory readings. i have seen, end up being about 11 psi.
Have you looked inside your distributor to make sure nothing is movin around inside? Sometimes the magnetic pickup coils get corroded, lossen up from th mounting points...raises all kindza hell.

 

[burbboysgc]

When is the last time your timing chain was changed? A sloppy chain can cause all kind of problems. There's a few easy ways to tell with out removing the cover. You tube has alot of videos that show how to. Good luck gettin her goin.

 

[72chevy2door]

@jims86, I haven't opened the distributor yet to check the magnet thing yet. I'm talking to my brother about snagging the egr off his old suburban motor (same year and same model of truck) it's just a spare motor that's sitting around cause he's got a 40 over 350 in it. So I'm going to try his in it. It's free so no money is wasted I suppose. @burbboy, it's a fresh motor. I personally rebuilt the entire engine the timing chain is a cloyes double roller and is brandnew so I'm good in that and both crank gear and camshaft gear are new. The truck seems to run fairly well other than the surging idle every now and then. Sometimes it will surge and sometimes it won't.

 

[Jims86]

@jims86, I haven't opened the distributor yet to check the magnet thing yet. I'm talking to my brother about snagging the egr off his old suburban motor (same year and same model of truck) it's just a spare motor that's sitting around cause he's got a 40 over 350 in it. So I'm going to try his in it. It's free so no money is wasted I suppose. @burbboy, it's a fresh motor. I personally rebuilt the entire engine the timing chain is a cloyes double roller and is brandnew so I'm good in that and both crank gear and camshaft gear are new. The truck seems to run fairly well other than the surging idle every now and then. Sometimes it will surge and sometimes it won't.

Apply vac to that egr valve while running before changing it. there is a small valve inside some of those EGr valves that closes the vac chamber when there is exhaust pressure.
did you put a stock replacement cam back in? Thes systems dont like cam changes too much.

 

[72chevy2door]

Ok I'll put the egr back on and test it while it's runny I never heard of it so no biggy I'll give it a shot. And it's not a stock cam but it is a stock rv style camshaft. I got it off of northern auto it's for the "k" series truck the website said it is computer compatible

 

[Jims86]

Ok I'll put the egr back on and test it while it's runny I never heard of it so no biggy I'll give it a shot. And it's not a stock cam but it is a stock rv style camshaft. I got it off of northern auto it's for the "k" series truck the website said it is computer compatible

Hmmm...I had this problem with my Comp cam, which was problem free in my Tuned Port setup. I ended up sick of the programming of chips, so I just set the minimum idle setting to 50 more rpm than recommended.

 

[72chevy2door]

You think turning up the idle will fix the idle surging problem? It's not an all the time thing. It's only every now and then it will do it.