454 Suburban starting issue....

partiallycommittedracing

partiallycommittedracing

Well-Known Member
Joined
Sep 8, 2005
Location
Huntersville, NC
Truck:

1996 2500 Suburban; 2wd; 454 big block, 4L80E transmission; 225,000 miles.

Long background of problem:

For a while the truck would sometimes not start on the first try. You would get the single “click” of the starter solenoid much like you are not getting full power to the starter. You pop the hood and jiggle the battery wires (thought to be a bad/corroded connection of the wires there) and it would start up.
Last weekend, this occurs more frequently, almost every time we tried to start it…the last time we tried it, jiggling the cables did nothing. We pulled the cables and cut fresh ends off and put them in new battery terminals so we would have good connection. We hooked them back up to the battery and would still get the click but no start. Moved on to the starter….pulled it off the truck and cleaned the terminals on the solenoid. Put it back in the truck and turned the key. We got a much stronger crank than it would put out before (after jiggling the wires), but then the truck would not turn over (it would just crank and crank).

I checked for fuel at the rail, and am getting no pressure….so I checked the fuel pump relay and used a jumper wire to bypass the relay. I would get plenty of fuel pressure this way (enough to shoot fuel 3 feet past the front bumper of the truck). I tried to crank it again (with the jumper wire in place)…still not turning over (no spark?).

I am getting power at all of the fuses under the hood (all fuses are also good); I am obviously getting power at the starter. The computer will get warm with the key in the “on” position, so I assume it is getting power too.
What could be the issue here? Crank sensor? Ignition module? Could we have shorted something in the starter swap/battery cable cleanup? Just coincidence that one problem led to another like that (or was the “click, no start-jiggle cables-start” actually not related to the battery cables, related to something else)?

Thanks for the help…
 
it loves its ree-ums.

i think i figured it out...all the tests that i did, pointed to the ICM. So i got one on order and will find out first thing next week.
 
well....back to the top.

Piece of shit is still not working. Replaced the ICM becuase the testing that I followed here: http://easyautodiagnostics.com/gm_icm_test/gm_icm_diagnostic_1.php pointed to it (failed test 4). Still no change. Cranks fine and strong, wont start.

Anyone have any other ideas?

I've about had it with this stupid hobby...
 
fuel pump? spray some carb cleaner in the intake and try starting it then see if it will run if so then its the fuel pump
 
So, you have isolated it to a no spark issue? or no?
 
well i have no fuel and no spark...

If i jump the fuel pump relay with a cheater wire i can get fuel at the nipple on the rail (yea c'mon :flipoff2: ) but still wont turn over.

You cannot hear the fuel pump when the key is turned to "on", but I dont recall if you could before when it worked either.
 
I'm going to try a crank positioning sensor since the symptoms are the same for both and see what that gets me.

after that...i think the rag in the gas tank is the best way to fix it.
 
will try starting fluid next time i am out there.

other options:
-PCM
-Bad coil (this wouldnt cause a no fuel condition, would it?)
-Cam position sensor?
 
thanks for the help. I got it figured out. the PCM itself was fried.

I tossed my buggy (4.3) spare computer in there and it fired right up. Ran like hell obviously, but it served its purpose. Ordering a new computer today and should be back in business.

Thanks again everyone.
 
Sweet! :beer:
 
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