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Noise/Backfire/No start

k20

k20

3/4 ton status
Joined
Sep 9, 2001
Posts
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Location
Mineral Springs, NC
Alrighty, time to post this for the 2nd time as the first time ck5 went down as I submitted :mad:

Alright, for the sake of electronics, lets call my truck an 87 TBI 454. Now as for symptoms.

Yesterday went out, drove maybe 2 blocks from my house, and it started spitting and sputtering, idling really low (400rpm) and generally poor. So I checked the computer chip as it has popped loose before and given similar symptoms. After that, it fired up and ran just fine.

So today, I go to leave, get 3 blocks away and it starts makin a noise like an exhaust leak. Sounded like one of those delivery style trucks. Came home, parked it, took my moms jeep to school. Came home to start diagnosing, and the noise isnt exhaust. It was coming from the area of the torque converter/flexplate. Pulled off the inspection cover, and checked the TC bolts and looked over the flywheel as best I could for cracks.

Fired the truck up, didnt hear the noise, so took it for a testdrive. Got about halfway around the neighborhood and the noise started again :crazy: . Got 2 blocks from my house and it started surging, spittin, coughin. Got home, killed it, checked the chip again.

I also changed the ignition module since I had another sittin on the shelf, and Ive had those cause weird issues in the past. Now the damn thing wont even start. It just backfires up through the throttle body when you try to start it. I swapped ign modules back thinkin maybe the new one was bad out of the box, still just backfires through the throttle body.

Does anyone have a clue as to what to check next? Im at wits end with this thing, does anyone have any ideas as to what to check next before I blow this thing up?

Thanks guys. Chris.
 
O yeh, the noise is kind of 'fluttering' it changes with engine rpm. If you blip the gas, it goes up w/ the rpm, and as the engine rpm falls, the noise seems to 'linger' for a second, before it falls.
 
If the flexplate is cracked up by the crankshaft, you won't be able to see it just by pulling the inspection cover.

I had a van that busted the whole center out of the flexplate one time.

Not sure how this would cause it to spit and sputter but it might explain the noise. :dunno:
 
yeh i was lookin up in there the best I could, the non-running diagnosis comes first though.
 
Put the pedal to the floor and then try to crank it over.
 
I mat it, and itll fire for a few seconds, but as its running its spittin back up through the throttle body, have to feather the throttle to keep it runnin, but its spittin, burpin and coughin the whole time.
 
So today I did an ohm check on the pickup coil, it tests good. It is definately getting fuel, and it is getting spark. Just the timing seems to be retarded. The distributor base hasnt moved, the holdown is tight. What could it be.
 
it wouldn't have an effect if it is already bad..... my 91 burb did strange things when the knock sensor went out.... it always threw a code with a quickness if it was related to the knock sensor
 
what Im sayin though, is that if I unplug it entirely, there is no change in the way it tries to start. There are no stored codes, nothing. I know if it is unhooked it will run fine, b/c for about 2 weeks after I put my engine in I didnt have a knock and it was just fine.
 
I just had a light bulb go on, check your exhasut. maybe your cat is breaking up and rattling, and it plugged the pipe. Lower the pipes at the manifold and see if it runs.
 
I doubt its that for 2 reasons, first my cats are fairly far to the rear and the noise was definately near the tc/flexplate area. The other reason is, just before I came in, I pulled the ECMB fuse to kill the FI and cranked it over to clear it out, it actually fired and ran decently for 3 or 4 seconds before it ran out of gas and died. Put the fuse back in and its dead again....so.....its possible it might just be flooding out, though there isnt a heavy odor of gas in the air.

I need to put another set of plugs in I think.
 
I had a somewhat similar problem, turned out to be bad needle seats and float level was WAY off. But since you have TBI, idk...
 
Just for the hell of it, I put on a spare coil I have sittin here, still no change. Now I just need my dad to come home to help me push the 55 outta the way so I can get into the garage attic and get my spare distributors, ESC modules, and other random spare parts to throw at it........
 
Ok, I just confirmed it is drowning in fuel, I had a couple sparkplugs layin on the bench from the last time I changed. Put em in, the truck actually started and ran for about 6 seconds, then it died, I ran around to the front, pulled out the 3 plugs I had just put in and poured gas out of em. :mad: :mad:
 
time for the hourly update

I went out to try it again after reading any and everything on the internet about TBI, and I noticed an anomoly, when I am cranking, the tach is showin 6-700rpm, when the truck tries to catch, it kinda gurgles, the tach starts dancing between 4 & 6k rpm. The tach is hooked to the side of my msd box, and the msd is tied into the factory wiring w/ msd adapters. Argh.

All of this, Im thinkin it might be the pickup coil sending out wacked signals.
 
Can you remove the MSD and try running it that way?

I know others have had failures of the MSD that have caused problems. If the ECM is *thinking* the engine is revving as high as the tach is showing, it will dump fuel that fast.
 
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