89 suburban TBI - from HELL - dumps fuel, and timing light wont work

Lonnng story short- 89 suburban 5.7L supposed to have newer crate motor, Stock TBI injection. We bought it with a flattened cam. And it still ran pretty good.



Bought a new RV cam and lifters, assembled just like all our other SBCS. Ran good, broke in cam for a couple hours, adjusted timing to get it perfect and it has not ran right since.



We have replaced Every sensor on the throttle body and intake. We replaced the Computer, and the tbi wiring harness. Tuneup, fuel filters, pump, And much much more. I can get it to run (Barely) but it backfires and DUMPS FUEL.



I dont want to put a carburator on because of emissions. Ive been told my RV cam is too big. But after i broke in the cam it ran great for about a week.



Ive redropped the distributor about 20 times, and its good, its not 180 out. (and have had about 5 smart guys try to fix this) ever since it stopped running good, NO timing light will work on this. WTF!!! Ive tried 4 that work fine  

not to be stupid...but can you define "don't work"
the light doesn't flash?
the light flashes but not hitting the timing marks?

if it's the first one, maybe the ignition system should be inspected fully  

If no timing light will work then I would change the sparkplug wires or at least swap #1 with another to see if your timing light will work that way.  

# 1....  ignition rotors on these have burned through..

#2  while you have it off..   take a bright flash light..  look straight down the distributer shaft where the rotor was... see the riveted star shaped device.. thats the reluctor..  under that is a ceramic magnet.. it actually sticks out a bit so you can see the center... look to see if the magnet is cracked..   if it is .. replace the distributer ... reman units have a one piece reluctor that works far better...

why does a cracked magnet effect how it runs...   the spark advance system uses the the previous sine wave to time when the coil fires...  this allows the timing to be computer controlled...  try jumping the A and B connector.. this blocks the advance and it runs with the advance locked...  

i would also inspect the ignition coil... look for power marks around the core close to the external frame.. that would indicate that it is leaking high voltage..

use a coil output voltage tester..   (like  Great Neck/Adjustable ignition spark tester
Part Number: 25069).     one with a gap or use a carefully placed screw driver.. see if it will throw a BRIGHT BLUE spark almost an inch...   orange weak spark.. toss the coil... most replacements can be had for 25 bucks at AZ..

got a digital volt ohm meter....      check the spark plug wires... set meter to 200K OHMs...     measure each wire...   the display should read less than the wire length in inches...  if the wire is good...    so a 24 inch will will read less than 24 on the display at the 200K setting..

while you are crawling up on top of the motor... check the ground wires to the back of the heads...  make sure they are installed and tight..

make sure the ground wires that come out of the ecm harness are installed , tight and properly terminated...( properly terminated.. means a proper Ring terminal, properly crimped to the end of the wires and installed on the stud. with a star washer....)  

did u disconnect the timing bypass wire before u set the timing? b/c if u didnt then the timing mark will be way advanced( under the water pump)and an rv cam is not too big for that motor its just a step up from stock.  

Yep, don't forget the timing bypass wire on the passenger side firewall you have to disconnect. That could be your timing issue.

On the dumping fuel part, check the O2 sensor and make sure it's plugged in, that the wire to the sensor is good, and I'd also recommend pulling the sensor out and checking to make sure it's not clogged up with carbon and junk.  

Wayne's right about the distributor. The shaft bushings wear out and then the pickup teeth touch and blow the ignition module. When you pull the cap off check for side movement in all directions. If you have a scan tool check for a good rpm signal. If all is good check for a good spark from your coil. On these,after you change ANYTHING disconnect the battery and make the ecu relearn. This will keep you from chasing your tail. On chasing your tail, don't forget the bypass wire, the ecu will not accept timing changes without it.  

+1  

Check the Tempeprture sending unit. I had this problem on both of my Suburbans, '90&'91 4x4s. Changed the sensor and cleaned the spark plugs, runs like new. A bad sensor causes the flooding. computer thinks its 30 below 0.  

Are your timing marks lined up properly?