I done swapped in this 350 TBI into my 83 Z28 to ditch carburetors all together for a while. The engine and electrical had been sitting for about 4 years doing nothing. Well she runs... but poorly. It has a new cap, rotor, plugs, and wires. I got a new TPS (not tested for the .58v yet) a new MAP sensor, and a new IAC solenoid. Getting that new TPS changed how the engine acted in a big way; before it would have a fluctuating idle, ran rough and would intermittently die if I didnt stay on the gas. I did do the IAC procedure just about as perfect as you can get except testing the TPS. Im trying to get it in time, but the engine has to stay running at an idle first! So its just timed to ear for now. I took it out to drive when I got the TPS, I slapped it on when I bought it, and noticed the difference. When I drove back, it was really sluggish. I think Im gonna buy a coil and pick-up next. I figure the more new parts going on eventually Ill nail this damn thing.
FYI this engine came out of a 1990 G20 van (w/o A.I.R.) Its a beast even tho it runs like crap. Quite possibly has an RV cam, IDK.

Any thoughts?? Anyone ran into a similar problem? I know TBI engines are just about the same in any GM vehicle to a point.

 

I would suggest trying to determine if it is fuel related or spark related before buying any more new parts. I am kind of in the same boat-or car if you will. I put a 350 tbi in a 1983 Buick Regal with Grand National hood and interior-but white. It ran great. On the street, on the freeway to the referee station. Ran clean on the dyno for the smog. Failed because of the gas cap and the evap test. Replaced the seal on the tank sending unit/fuel pump and went back. Passed on the evap but the car would not go over 20 mph on the dyno. Checked it out and it was leaning out throwing a code 44 also-lean. Replaced fuel filter, checked fuel pump pressure-12 @ idle-modified pressure regulator-18 @ idle-replaced map sensor with others I had lying around. Everything reads well on the Snapon scan tool but runs like crap after running well for about 2 miles. I replaced the ecu-1228746-replaced several chips anlu and auml. I am thinking that I may have screwed up the tps. The referee said it was reading close to 1.0 volt at idle and should be closer to .5 so I modified the tps after breaking off one of the frozen screws, drill retap etc. then bending the tang a little and cleaning off the rust. Now reads .75. I feel like I'm chasing my tail. What kills me is that it ran so well the first time going to the referee station. The only thing different I did was reseal the tank and modify the tps, So today maybe a new tps. The engine has surged at idle from the beginning then got worse, but disconnect the map sensor and it idles smooth. I am starting to have second thoughts about TBI.

 

Sounds like both need to be tuned - you can't expect the fuel map and spark map from a 3/4 Ton van or truck to be the same as a car?

 

That may explain the Z28 problems, but not mine. My engine ran GREAT under all conditions and even passed the strict California emissions test under load on a dyno then suddenly started to be starved for fuel.

 

Check the wires going to the MAP sensor for resistance, you could have a bad wire. MAP sensor could be bad.


GanymedeElegy, set your TPS up right and get back at us. .5 volts at idle and I think 4.2-4.3 volts at full throttle.

 

You mentioned the engine sat for 4 years. In the van? Outside? In a garage? Have you checked compression? Do you have a compression gauge? Do you have access to a scope to check ignition firing? Do you have any sort of scan tool? Starting with the basics will help eliminate any variables. Sometimes when engines sit for a while, especially if they have a lot of miles already, the rings can stick on one or more piston, and may take a while to get loose.

I would agree somewhat about the tune. You may want to get a computer from a 90 passenger car with tbi after making sure the engine is sound. Remember that F bodies have the passkey and can cause additional issues.

 

possible MAP problem. Vacuum leak FI cars can be real finnicky sometimes. also check in the coolant temp sensor. If it isnt reading right it could be tricking the computer into thinking the engine is cold, when hot. and vice versa. Which throw's everything off. Good luck

 

Tomorrow Ill be able to jump back into it for a full day.. finally. It sat in the van for about 4 years, and I sprayed carb cleaner in each of the cylinders.. alot of carb cleaner and hand cranked the engine over several times by hand before I dropped it in place. The MAP isnt new, just out of a different vehicle. I noticed an immediate improvement.. but it wasnt enough. I need to check the voltage, cus the TPS is an adjustable one. I still want to get the new pick up for the dizzy just for the hell of it. Even the coil too since its only a $20. I might get a new prom later on with a better fuel curve and to not freak out the ECM about getting a 5 speed. I shouldnt have to change the ECM after getting the 5 speed right?

 

The manuals and automatics use different computers? Im not sure..different prom's definately...What part of the valley are you in?

 

To the original poster:

The first thing I would do if I were you is a fuel pressure check. I bought the adapter fittings off of eBay, and they let you hook up a shrader valve in line with your fuel line. On my TBI cars, I usually get crap for pressure. Over 12 under load is usually good enough to run, but may not be enough to go fast.

I have found that even brand new TBI spec fuel pumps suck. I know it is terrible to drop the tank and change the pump again, but I do it with every 3rd gen I get. I use the 89 TTA pump, which is the same as the late 90's Vortech 350 in tank pump, and I never have a fuel delivery problem again. I am not running super high power engines right now, and it is more than enough to supply any TBI engine. It just takes that out of the equation. It seems to me that your fuel delivery may be in question.

You should also hit up eBay and get the adjustable fuel pressure regulator for your throttle body. You will find a sweet spot between 13 and 20 that gets you tuned in right. A stock new TBI pump may not even give you 13!

For the guy with the Buick, you have a really key clue here that you are not investigating. Your setup was running PERFECT. Then you resealed the tank. Guess what? The blown seal in your tank was acting as a vent, and now you don't have one. Or at least it is no longer adequate for what you are doing.

Our third gens have a separate from the tank, rather large vent for the evap with a vent cap running off on its own near the tank. I bet you're not venting properly, and with that, you are getting the problems you describe. A quick check is to drive it around with the gas cap off. See what that does and then go to the others.

When you have a massive problem coming from nowhere, always go right back to the last change you made. Yours was sealing up the tank sending unit, so it makes sense that whatever got disturbed in the process or the new blockage may be the issue.

 

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that's some pretty sound advice Kris. Good work.

 

Thanks!

I have learned a lot from this forum; if I can spread some more around, I will.

 

Yeah looks like you are doing well

 

Thats my next plan of action. I have a pump, its not new but it was the one in the tank from a 90 Camaro that had 3.1 and I know those have to put out more than 14 psi. Ill re-install the other pump, and I do want to get that fuel pressure reg with the return port and built in gauge. I just went to Autozone.. hate that place but its all that Lindsay has ATM and a Napa, anyways got a new MAP to see what it does... absolutely nothing. I returned it. I got back here, and checked the voltage on the TPS its 0.53, which is about normal without adjusting it, but I adjusted it counter clockwise as far as it would go, and it ran a bit better. Didnt check the voltage yet. I disconnected the tan/black stripe wire for the dist. advance and timed it to 6 degrees. before I started the car, I connected the old MAP cus it would stay running while the tan/black wire was unplugged. It started, stayed running without the fluctuating idle, then I timed it to 6* and plugged the advance back in. So far its running fine, like it never had the problem. Im still untrusting haha. Im letting it cool off so I can change in the right coolant temp sender gauge and pour in some radiator stop leak.. that rad is junk and Ill get one later.

 

BTW UnderCover TBI im in Porterville, Tulare county

 

My transmission is toast. I lost my 3rd and 4th. The trans was smoking good haha. Oh well, Im trying to get this other Maro witha 5 speed. Im gonna drop the tank and put that other pump in. It runs fine at idle now. Just getting on the gas trying to get to speed is the problem. It runs like the plug wires are melted.. no more like a starving carburetor. Ill post the result tomorrow.

 

WOW!

Now the trans is smoked, oh boy. Well, that's life with old cars. Good luck man!

 

YEP it was the fuel pump. I put the other one in, and the car started right the hell up like it never had any problems. Now I need to get a transmission :/

 

one problem after another eh? and cool thanks for answering that.

 

Hello all....

I wanted to ask a question about setting the timing procedure on a 5.7 TPI stock setup. Do you adjust the IAC and TPS FIRST before you set the timing or visa versa?

The engine starts up, but has a slight hesitation when you give it gas.

Thanks for all the help!!

 

Not sure about the TPI. All I know about timing is unplugging the tan/black stripe wire that goes to the distributor so the computer dont try advancing it. And yea, one problem after another its a chain reaction. If one thing goes its a domino effect. New parts are breaking the old parts haha

 

I found a Holley brand TBI. There is no IAC motor for it. There is also a clip for 4 wires to the injector pods. Is this a stand alone aftermarket thing? or is it a replacement? It has an adapter plate for bolting it on a 4bbl carb intake.. and a good carb intake is 3 times better than a stock TBI intake im sure.