Item Posts    Sort Order

350 TBI timing issues?!?!?

I love my Chevy Chevette!
Posts: 1
Joined: 12/11
Posted: 12/16/11 12:49 PM

Hello All,
I am new to this club, and look forward to any help You all can provide, Thanks in advance!
I have a 1990 (chevy of course) 4x4 stepside, 5.7 TBI, that I am restoring. When I bought the truck, the motor needed rebuilt. I took it to a reputable performance shop, and the following done: bored 30 over, 10.5 to 1 pistons, rotating assembly balanced, new crank(gm), comp cam(extreme energy, the largest i could go without any modifications to heads or transmission), heads redone(stock,completely new valves, rocker arms, etc..).
Everything inside the motor is new,plus plugs and wires. highest octane gas also..

The truck fired right up, and runs fine, however, when trying to time it(disconnecting tan wire with a black stripe to the esc, etc..) I am having some issues. When the timing is set "where it should be", (0 degrees with esc disconnected, and changing drastically when i reconnect it to the positive, somewhere in what I would assume to be around 18 or so to the positive) the motor dies when i turn the wheel, or put it in gear. With the esc disconnected however, the truck seems to run fine other than a check engine light being on.
  I have adjusted the timing up to 16 btdc (tan wire disconnected) and still the same problem..Will this cause any damage to the truck if I drive it with the esc unplugged until I figure out the issue?
Any thoughts? Vacuum? Distributer? Thanks!!!

Post Reply
V-6 Camaros rule!
Posts: 56
Joined: 12/11
Posted: 12/16/11 01:07 PM

is it the HEI Distributor with vacuum advance?

also... i saw this on another forum...

"Base timing with the wire unplugged is 0 or top dead center. Next shut the truck down, disconnect the battery terminal for over a minute. Reconnect timing wire, reconnect battery terminal and start. The computer will next set up the timing scale. Disconnecting the battery makes the computer dump the former timing so it can set it up new again."  

Post Reply
Big Block power for the win
Posts: 940
Joined: 03/11
Posted: 12/16/11 01:41 PM

Welcome aboard:

Are you going to race the truck?

Thats one hell of a stick for the street!!

Have you checked to see if the damper has move or the timing mark hasn't changed.

A cam that size when set up correctly could see 40 degrees of advavnce.

Is this the XE 12-254-3 with .519 .523 that you installed?

If it is the ECM probably can't compesate for that, and feed enough of advance or proably fuel to your engine. That is one big stick for the street. You made no mention of a torque convertor change. I think when you turn the steering wheel yout taking all vacuum from the engine and the engine reponse (BY PASSING GAS)..LOL.. and just dieing. Even if you have a HYDR-BOOST system it will become even worse.

The same thing happens when you put it in gear. It's idling so high it hit the stall of the stock torque convertor.

You have to get a stall convertor between 2200-2500RPM STALL.

Then you have to rework that TBI system with after market Electronics.

Or you will wind up either changing the cam to somthing tamer.

Or put a carb,and intake with a vacuum advance timing.

You should have asked us for some advice before you put put such a large cam in the TBI it's just not going to work with the stock parts..............GOOD LUCK.....  

Post Reply
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 12/16/11 06:50 PM

pepsi is really right on the money with this.. too much for a factory adjustment...

i have a few things to try... as i know the TBI systems (stock not highly modified) and there are some things to ***

can you pull the cap and rotor.. look at picture below..

if you have cracks in the magnet.. the pickup coil will create out of phase and it will really give you problems..

AZ and other stores sell Reman distributers for these small cap HEIs for just over 100 bucks with a totally different pick up coil and way different reluctor.. you won't believe how much better it runs with the reman unit.. if the module says transpo.. its a good one..

set the crank to 0.. TDC.. turn the housing to align the tips of the reluctor and the tips of the pick up coil  then lock the housing down.. after you have verified that its properly seated...


next...   engine off..  grab the throttle lever.. open the throttle slightly.. does the throttle shaft wobble around in the housing.. it should NOT..  this is usually a front to rear motion..  if you have movement.. you might need to get the throttle shaft bore rebushed.. i can give you instructions on how to do it in your shop..  takes a few days of parts gathering..   warning.. DO NOT remove the throttle plate screws without grinding the exposed threads off first..  they will break off in the shaft.. ruining your day..

if your throttle shaft bore is not worn..

you are going to need to set base idle... this is usually done with a funny shaped rubber plug tool in the idle air passage on the passenger side top of the throttle body..  it goes down to where the idle air control motor moves it tapered plug in and out of to control idle speed..  i just use a screw driver to pack a grease rag into the cavity to set base idle..  this stops any air leak while doing the base idle adjustment..

base idle is done by turning the idle stop screw with a T15 tool...  there is a tamper proof plug at the front..   this adjustment is usually done to as low as the engine will run at idle in park..

now that you have either backed off or increased the throttle plate stop.. test the throttle that it is NOT binding as you first open it...

at this point.. you should be able to remove the rag.. the engine will rev up for a second. then hopefully settle in..

you might want to open the throttle slowly. to about 2500 RPMs.. then allow it to close slowly..  this lets the computer know where the settings are...


i would also like you to check the various ground wires attached to the engine...   they are probably on the back of the passenger side cylinder head..    did that pair as i recall of ring terminals get reinstalled...  there might also be one on the back of the drivers side cylinder head..  perhaps on on the intake behind the thermostat housing..


if you have an OBD1 scan tool.. i would like you to plug it in..   access the live data stream..

the ECT.. engine coolant temp sensor should be about 190F to 215F warmed up.. this stock system needs to have a 192F thermostat..  unless you have changed the PROM with a custom prom...

the TPS throttle position sensor needs to be below 1.0 volt...  and each time you work the throttle.. it should drop back to the EXACT same minimum voltage..   if it comes back to a slightly different voltage.. you have problems with the throttle shaft bore... and this change is minimum voltage each time or randomly.. will really screw with the computer program...

when the engine is warmed up and idling.. i like to see on the scan tool.. 20 to 50 idle air counts...  this gives the computer the ability to control the idle speed...


you can.. fool the computer into backing the idle air control motor out..  by letting the system idle..  then blocking more and more of the idle air passage.. at some point when the idle air valve is retracted.. you can reach down and unplug the connector.. this lets the engine idle at a faster idle.. uncontrolled by the ECM...    you can try this..

i would also like you to try this.. with the REAR wheels up in the air.. free to spin..  drop it in gear..  from neutral..  without your foot on the brake..  you can now.. step lightly on the brake.. see if you can stop the wheels without stalling the engine..  

this shows the torque converter clutch is NOT being activated and bringing the motor to a stop..

you might be able with the wheels spinning to plug the idle air control motor back in.. let it idle for a minute with the wheels spinning.. then slow the rear tires down with the brakes.. see if the engine still stalls..


the manifold pressure sensor is plugged into a vacuum hose on the back of the throttle body.. that hose has to be in good shape.. not clogged..

if you have a scan tool...  i have a list of sensor data readings that you need to compare...  

Post Reply