1990 chevy suburban engine swap problems

i am biulding a hunting rig and the old gm 350 gave it up. i took it out and had a 350 vortec built for it instead. the engine shop stroked it to a 383 but other than that, it is a new vortec with an air gap intake manifold with an adaptor plate for the TBI to bolt to. The problem is the thing runs like crap. After many machanics have looked at it, they are saying that it is running to lean and because the dynamics of the motor have changed so much that the computer doesnt know what to do. I know this is a pretty rough description of the problem. I am thinking of scaping the whole TBI and going to a 650 edelbrock off road carb. I like the idea of fuel injection but sick of spending money with no results. Anyone have any thoughts.  

i dont know where to get this done, bbut i believe you can have the computer recalibrated, and i think a 650 would be small for a 383  

i was also thinking of puting the TBI off of the 454 on it and seeing if that made a differance but will i still have to change the computer. i dont know the lingo but they say it has a simple computer that cant be alter or changed in it. it was the later models that had the more complex computer in it.  

I have got an original stock 454 tbi and computer with harness from a 90 suburban. I would sell it if you want it.

as far as I know the prom chips can be changed in all those computers.  

Your TBI will work fine for the ammount of fuel you will need since it's not a race rig. The computer chip will have to be re programmed though, it's pretty simple just do a search on your computer for someone in your area who does it. There are places you can send the computer for the work too. (look in the back of Chevy Hiperformance magazine for a vendor) Good luck.  

thanks guys, I will try sending off the computer before i put any more money into big changes.  

i would think that swapping to larger injectors would really help...

there are several steps to go through first..

let me see if i can find the chart of TBI injector flow...

or you might contact jim linder services he might be easily able to help you with injector size changes..

i ran into this when swapping up from 4100 caddys to 4500 and 4900..   went to a larger injector in the original throttle body worked great....

you might want to go to the sizes i marked in bold.... its a lot easier than reprogramming the computer.. you will also want to make sure that the system is going into closed loop.. and running off the oxygen sensors...    you are going to need access to some kind of scan tool to verify the system is working properly..


TBI throttle body and injector information

These injectors are rated at the pressure used by the factory, about 13 PSI

Application Throttle bore size Injector color code Flow rate Part #

2.8l v6 1-3/8" Black/White 35 lb/hr GM 5235430 *RPD

4.3L 1-13/16" Yellow/Blue 45 lb/hr GM 5235203 *RPD

5.0L 1-13/16" Green/White 40 lb/hr GM 5235279 *RPD

5.7L pickup 1-13/16" Orange/Black 55 lb/hr GM 5235206 *RPD

5.7L Cop Car 1-13/16" Yellow/Brown 65 lb/hr 17084327-ACR

Late big block pickup 2" Blue/Black 80 lb/hr GM 1708430 *RPD

big block pickup 2" Dark Red/Dark Blue 90 lb/hr GM 5235231 *RPD



during open loop... like when the engine is warming up.. or you are accelerating moderately hard..  the computer reverts to preprogrammed fuel control.. so your system will act lean....

during closed loop...  when the system runs off feed back from the oxygen sensors.. the fuel ratio can be controlled by the ECM.. but its hard for it to go richer.. its much easier for it to be leaner..  

you might want to print this chart so you know what the data stream should be at..




there are a lot of different scan tools available on a certain list thats popular..  check both the tools and the auto parts sections.. for  scan....    scanner...   scantool ....    OTC....    actron...   autoxray     monitor....

these can be had for under 100 bucks


these are also under 100 bucks



these are under 400 most of the time... be sure that it has the proper cables and cartridges.. they are very expensive..


these can be had for 50 bucks...  again make sure they have the proper cartridges and cables for your application. the 2000 models only have one or two lines of data on the display..



there are several variations of this... 4000, 4000E..  monitor extended...   enhanced monitor..   the enhanced was the last and best...  they can be had for about 300 bucks with cables and cartridges..  again.. make sure that you get cables and cartridges for your application


  there are a LOT of variations in this NEVER been cheep unit..  

A guy i know that teaches the mechanics class at the local collage here took the TBI off and altered some spring in it to give the injectors more psi and then he put a spacer under the injectors to lift them up to let more air flow by. that was the best the motor has ran but it was short lived. it worked great up in the mountains for a week but i still felt the motor wasnt producing the hp that the engine biulder said it would have. after it sat for a while during the winter i started it up just to take it to town and i noticed that when you go from foot off of the throttle to full throttle, it falls on its face. I let it sit for a while longer and then started it up to get it ready for the hunting season but this time it wont even hardly run at all. its like the computer is all out of wack. its the second computer i have put in it. why am i fighting this motor so much? what is changing in it to make it get worse over time. I replaced the motor, transmission, rear end, hubs, and all the accesories on the moter. would love for some more info. i will try the bigger injectors next. Thank you guys for the info  

Hi I know this is an old thread but I just wanted to see if there was any conclusion here.  So I have a 1990 suburban and it had pretty much the same engine switch, i didn't do the engine switch, i bought it like this.  Plus the entire drive train was rebuilt.  It idles nice once in a while but it eventually goes into this pulsating mode where it continually lunges for power and the lights kind of dim and it almost dies out and the idle pulses with it.  And then it will continue doing this for quite a while even when its fully warmed up.  So this new engine is slightly more power rated at the 383 like yours (sorry i'm bad with engine lingo)  So I probably need to get a new computer or calibration of some sort.  I just wanted to know if you figured it out before i start ripping things apart.   Thanks for any help  

jwmm7:
Hi I know this is an old thread but I just wanted to see if there was any conclusion here.  So I have a 1990 suburban and it had pretty much the same engine switch, i didn't do the engine switch, i bought it like this.  Plus the entire drive train was rebuilt.  It idles nice once in a while but it eventually goes into this pulsating mode where it continually lunges for power and the lights kind of dim and it almost dies out and the idle pulses with it.  And then it will continue doing this for quite a while even when its fully warmed up.  So this new engine is slightly more power rated at the 383 like yours (sorry i'm bad with engine lingo)  So I probably need to get a new computer or calibration of some sort.  I just wanted to know if you figured it out before i start ripping things apart.   Thanks for any help

first..    please verify the grounds are properly installed ...

do you have a digital volt meter...  if not they are cheep

start the engine.. turn on the headlights

set digital volt meter to 20 volt scale..

1.   test across the battery.. positive to negative.. is the power stable.. 14.1 to 14.7 volts DC?????

2.    test from the Negative battery post to the engine block..    0.04 volts MAX...

3.   test from the negative battery post to the body...              0.02 volt MAX

4.   test from the engine block to the firewall..                    0.02 volts MAX..

if you get 0.00 on the last 3 tests.. change the volt meter setting to 2 volts DC and retest.. 2, 3, 4

please post results by number..   1. 2, 3, 4..  

there is a ground.. usually 2 ground wires at the back of the cylinder heads..    these can get left off during engine work.. they are VITALLY important..  

there should also be a ground wire to the firewall from the engine..

please do the test..  takes less than 4 minutes including the time to open the hood..

more info to come after results..

why am i asking you to do this..    it sounds like you have a missing ground connection..

remember..  the ground side of the circuit in a car or truck is HALF the circuit..    leave a ground off..    might as well leave stuff unplugged..  

the computer IS ONLY GROUNDED TO THE ENGINE..

if you have a missing or loose or corroded ground connection..   you may not have enough electrons to power the circuit..

i bet that your oil pressure and engine temp gauges are also wacky..

you are going to have to trust me on this one..  i have been doing this for 30 years..  

So this problem escalated to making the suburban undrivable it is at my mechanics now.  So what happens now is when you try and start it, it misfires and still does that sort of lunge thing but to a new level where it can't maintain and very loud misfiring.  

When we disconnect the plug that puts the suburban into bypass mode (turning off the electronic spark, and bypassing the part of the computer that moves the timing forward I believe) it runs fine and we set the timing right in this mode but as soon as you connect the module it doesn't work again.  

So we've tried swapping out one part of the computer module so far but not the computer yet because we don't have one but really the computer should be fine.  

There was carbon build up in the distrubutor so he changed the cover and brush (i believe) but kind of thinking it might be the little module not working in the distributor cap.  But usually when that doesn't work the vehicle will just not run.

We checked all the engine grounds like you asked and the came back all good, sorry I don't have the exact numbers but he used a volt meter and checked them.

He went over most of the sensors also

Also changed the starter (probably unrelated)

And just recently changed the water pump (unrelated also)

Were basically at a dead end and reaching, have no idea.  

trust me, 650 is plenty for a 383. I've run a 700 on a 383 with 11:1 compression and it runs ridiculously rich. If you would like any gas mileage run no more than 650.  

I would put a 650 Carb and a decent intake manifold on it. I agree a 650 CFM carb is plenty for what your use will be.

you will be happier with it for what your doing. The gas mileage may even get better.

Take the computer and fuel  rails etc. and sell them at a swap meet, to off-set your cost.      

So what your saying is ditch the tbi I guess hey.  Well were switching out the little module in the distributor today to see if that is the problem.  I really didn't want to spend a ton of money on this fing truck but its turning out that way.  I've read a lot of mixed feelings about switching to carb.  Would you have a particular brand you'd recommend.  Thx