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Username Post: 92 K1500 GIVING ME FITS        (Topic#355148)
texas tough 
Poster
Posts: 1

Reg: 02-07-19
02-07-19 10:57 PM - Post#2759355    

Bought truck as a project with blown head gasket. did top end with fresh rebuilt heads, adjusted valves timed engine, engine started and was idling ok. a few weeks later truck started loping at idle, sputtering, backfire ect. replaced coolant sensor, checked egr valve, rebuilt throttle body. cleaned IAC motor, checked pcv valve, checked for vacuum leaks. tried another ignition module. no change. now truck starts cold, and hunts for a decent idle, sometimes almost dies, then the computer brings it back up, like the computer keeps testing something, and its not happy so it idles it up again, almost like its trying to come off of choke, (it has no choke) and it almost falls on its face and dies, so the computer gives it more fuel or timing or both.. once warmed up some, it wants to idle quite high, I would guess well over 850 rmp. it seems something is malfunctioning intermittently. weve checked for aarcing wires, and found none, the distributor capp is good, wires good, distributor seems good. I took it out and inspected it and it passed all checks. I ohmed the IAC and both circuits passed muster. the only thing I can think of is a possible malfunctioning Iac, a failing ignition coil, a failing fuel pump. theres no codes being thrown by the computer. battery is new. any ideas appreciated. I dont have a pico scope and dont know what to check anyway. if im correct in my understanding that the cooant sensor and the IAC are what control idle exclusively during open loop, then if all else is correct, logically It would indicate I have a intermittent malfunction with the IAC.



 
Guy named Guy 
Poster
Posts: 40
Guy named Guy
Age: 27
Loc: Grand Prairie, TX
Reg: 07-31-13
02-08-19 12:58 AM - Post#2759359    
    In response to texas tough

When it starts hunting, unplug the 02 sensor on the drivers side manifold and see if it quits. I've had a few TBI trucks that would do that until you unplugged the 02. If that doesn't help then try unplugging the timing advance connector located behind the plastic panel under the hood on the firewall, it's a tan wire with a black stripe. when unplugged your computer will revert to base timing with no advance, and IF it idles smooth instantly then that would point to a problem with either the distributor or the ecm.
BTW - your engine light will come on when you unplug the timing connector, it'll go away once you plug it back in and restart the engine.



 
thx1138v2 
Contributor
Posts: 178

Reg: 05-01-14
02-08-19 08:57 AM - Post#2759380    
    In response to texas tough

I had almost the exact same problem. Mine was due to improper throttle body assembly. When I put the injectors back into the body I didn't put the metal sealing rings that go around them in the correct position.

The metal ring goes in first, followed by the injector, then the O-ring, and then the upper most part with the screw holes.

It's simple to test. Just take the injectors out and closely observe the sequence it comes apart.

Don't forget to reset the computer when it's back together. Disconnect the negative battery terminal for 15 minutes and then reconnect it. Start it up and it should be fine. I take mine out for a ride for 15 minutes in stop and go and 15 minutes at highway speeds to get the computer to re-learn its variable settings.





Edited by thx1138v2 on 02-08-19 08:58 AM. Reason for edit: No reason given.

 
bowtie44s 
Valued Contributor
Posts: 4166
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
02-08-19 09:28 AM - Post#2759383    
    In response to texas tough

Check the firing order again. Where is the timing set? Take the valve covers off and watch it idle. Do all rockers look like they're moving the same?

Jeff

'88 Chevy K3500, aluminum head roller cam 511inĀ³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Sabino 
Member
Posts: 62

Reg: 07-16-05
02-08-19 09:42 AM - Post#2759384    
    In response to texas tough

You might want to check fuel pressure and/or replace fuel filter. I had poor idle and checked fuel pressure/ replaced fuel filter it and resolved my problems. I have a 93 c1500

As for the backfire, I had a knock sensor problem causing problems once. I logged the data and saw burst of knocks when engine studdered. I assumed this caused a spark retard. Replaced the knock sensor and it resolved my problems

65 Belair 350
68 Camaro 327
85 Caprice 5.0L
93 Suburban 5.7L TBI


 
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