88 chevy truck popping through tbi

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  #1  
Old 10-16-07, 08:09 PM
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88 chevy truck popping through tbi

88 chevy 1500 5.7 350 5spd
I recently rinsed the motor off as I usually do but this time I must have got something wet after I washed it it was missing and backfired so hard it busted the flowmaster, so I left it alone for about 6months (spare truck) I pulled it out an gave it a tune up plugs,wires, distributor,ign module,pick up coil,cap and rotor, it cranks and runs fine but when I get on , it just boggs until about 5grand then starts poping back through the tbi if I just ease into it its fine till 3/4 throttle, i put the timing light on it, and checked the egr and coil but still no change im thinking it may have bent a pushrod or lifted a rocker stud but it dosnt have any ticking just a slight little miss at idle
 
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  #2  
Old 10-17-07, 04:54 PM
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It's probably in the throttle body assembly. I'd rule out the pushrod/rocker if you're not getting any ticking noise from the upper end.

A backfire would target the throttle body and the central point injectors. I believe that's what you're dealing with in that year. In the days of carburetors I've seen the insides of a Rochester taken out by a backfire.

Hope this helps,

Bob
 
  #3  
Old 10-18-07, 04:16 AM
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if it has a convertor on the exhuast system you might want to get it checked for a restriction.
also double check timing, if its retarded it will backfire through the tbi you will need to disconnect the est connector to check base timing.
if its a steady backfire through the tbi it could be a camshaft lobe or other valvetrain problem but if its just an occasional backfire would be looking at timing and may even check codes it shouldnt really have anything to do with the throttle body as a lean or rich condition does not cause an engine to backfire through the intake.
 
  #4  
Old 10-18-07, 04:33 AM
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Did you disconnect the wire when timing ?
This all started after you washed it ? Kind of eliminates cam lobe, bent push rod, converter or anything mechanical. Does the check engine light come on ? If so what codes does it have ?
 
  #5  
Old 10-18-07, 06:54 PM
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Yes this all hapened after I washed it, it doesnt have a converter, and no check engine is on, yes I disconnected the wire when timing, it isnt really a backfire through the tbi but more of a popping and it only does it under a load after half throttle, it doesnt do it as bad since the tune up
 
  #6  
Old 10-18-07, 07:19 PM
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You might want to check the pressure regulator in the TBI. Our one truck the spring broke and it ran poor after half throttle or so. It had low pressure at idle, we didn't check it at full throttle but it had to be really low I would imagine. You already replaced most of the ignition, and most of the sensors that could have been effected by the backfire should set the check engine light. If you knocked out the O2 or one of the sensors like that it should set the check engine light...
I would throw a pressure gauge on it and see what it has, just to clear that off the list...
Also look for a blown off vacuum hose from the backfire.
 
  #7  
Old 10-18-07, 08:51 PM
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I have checked the vac lines it may be the o2 sensor cause it does seem to be a little rich smelling but ill check the fuel pressures, im just not sure if it was the backfire or the water that messed something up thanks
 
  #8  
Old 10-19-07, 04:03 AM
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if it has a slight miss at idle you may want to do a compression test to see if any cylinders are low.
might also check the distributer shaft for play just remove the cap and grab the rotor and wiggle it side to side if it has alot of slop it can cause a miss and possible backfire problem.
 
  #9  
Old 10-19-07, 02:35 PM
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It has a new distributor and has good compression on all cylinders, i think its gonna be valve train because I was driving it and it seemed to stop doing it so I run it hard to see and it went back to running bad and started ticking, after it idles a few minutes it stops, then once I rev it hard it starts ticking again, may be a bad lifter
 
  #10  
Old 10-19-07, 02:54 PM
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might pull the valve covers and inspect the valve springs and rocker arms and pushrods.
 
  #11  
Old 10-19-07, 09:21 PM
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I pulled the valve cover everything looked and felt good, but it only ticks when run hard or under a load, you think it could be collapsing under load?
 
  #12  
Old 10-19-07, 09:40 PM
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its been setting for 6 months you might run an oil additive like rislone in it for awhile to see if the ticking goes away but a callapsed lifter isnt typically going to cause an engine to bog down or cause a pop through the tbi the only way that I can think of it really affecting performance is if the knock sensor was detecting the noise and the computer retarded the timing wich could cause a loss of power but if it runs bad even when its not making the noise you probably have more than a lifter problem are you sure the valve springs are in good shape did you try to push down and open each valve by hand a broken spring may not be that noticable just looking at it but if you can easily move the valve you should look a little closer at that paticular spring.
 
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