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Old 06-20-2005, 04:15 PM
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96 Silverado Pickup Diagnostic Codes

Hello All, Newbie to the site... hope to absorb huge amounts of knowledge from ya'll
I have a 96 Silverado, 4.3L V6, and a week ago, began having fits with the engine running... low power, no acceleration, almost refuses to shift, pinging badly, overheating. I had the diagnostic codes scanned and it showed a variety of sensors with problems. Everything from the intake air temp (AIT) (Only got the IAT code once) to 3 of the 4 O2 sensors. I pulled all the O2 sensors and cleaned and reinstalled them, cleared the codes and test drove it again, no help. within minutes had the check engine light again, had it scanned, still O2 sensor flags. So I broke down and bought the "upstream" O2 sensors, 1 each side, and replaced those. Cleared the codes and tested again, still no improvement in running. Got a new check engine light. Had it scanned again, showed "Random/Multiple misfires". I installed a complete new set of Platinum plugs, new wires, new cap and rotor. Cleared the codes once again, and retested. It seems to run a tiny bit better, and so far have gotten no check engine light, but the bad acceleration is still there as is the pinging. I have ordered a scanner of my own that I hope to have in my hands by tomorrow so that I can do this a bit more inexpensively. Does anyone have any suggestions as to what I might try with this problem?
I'm an aircraft mechanic with plenty of tools and experience, just not with sensor systems. They're non-existent on aircraft piston engines. This is my first foray into the world of automotive, computerized systems.
Any help would be greatly appreciated.

Dave Danger

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Old 06-20-2005, 04:42 PM
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Most likely problem is the fuel pump (in tank)
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Old 06-20-2005, 06:20 PM
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Quote:
Originally Posted by Bumpstick
Most likely problem is the fuel pump (in tank)
I would agree with Bumpstick, these fuel pumps are the weak link on these trucks. Were the oxygen sensor codes for lean conditions? also the P0300 could be set from a bad fuel pump. You need to test fuel pressure. let us know what the pressure readings are and we could help.

Steve
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Old 06-20-2005, 06:21 PM
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sounds like you have a timing problem... check all the sensors that controls timing. im not sure about the 96 4.3 but you might be able to adjust the timing with the distributor. hook a timing light up to it and check that.
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Old 06-20-2005, 09:55 PM
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Bumpstick & 1931 Steve,
Gawd I hope it's not the in-tank fuel pump again. I pulled the tank and replaced that pump about 2 to 3 years ago. The symptoms I had at that time were much more pronounced.. the engine would either run ok if the pump decided to run, or it would flat shut off a few seconds after the pump did. Very black and white. I will however see if I can tee in a fuel pressure gauge somewhere and determine the idle and running pressure. It can't hurt to eliminate that possibility.
I wondered about the timing myself, but the manual that I have access to (Clymer's) says that the 96 & up has computer controlled ignition timing and it can't be changed manually (They don't even give a degree specification). I will put a light on it tomorrow just to satisfy myself that it's in the ballpark.

Dave Danger
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Old 06-21-2005, 06:09 AM
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Correct on the OBD 2 starting in 96.
http://www.troublecodes.net/
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Old 06-21-2005, 06:31 AM
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Dave there is a fuel pressure test port on the fuel rail on top of the engine.

Steve
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Old 06-28-2005, 06:36 PM
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Alright guys, (Some of this is a repeat to keep MY mind clear)
More info on my problem. None of my initial codes were for lean conditions or fuel pressures. My initial codes were primarily for O2 sensors, and an inlet air temp sensor. I cleared those and replaced the first two O2 sensors (closest to the exhaust manifold each side). After that, the only code I could get was random multiple misfires. I was advised that a tuneup was in order, so I replaced all plugs with new Platinums, a full set of wires, a new cap & rotor and a new inline fuel filter. The misfires went away and I can no longer get any check engine light or codes. The truck however continues to run almost identically... weak acceleration, difficulty shifting, water temp climbs very quickly above 212+ (even sitting at idle). I now have in my possession an Autotap® diagnostic code scanner. It plugs into my M125 Palm Pilot for a readout. It not only will read out codes but will read (while driving), any and all sensors and parameters in the entire system. I Love it. Problem now is that I seem to have almost too much information. I'm seeing all kinds of millivolt readings from various sensors, and varying temperatures from others... So much so that I'm having difficulty understanding what I'm seeing! (Incidentally, I can observe the engine timing as it changes from instant to instant, but still don't know what it ought to be). I don't know when a reading is good or bad. Failing all other advice, can anyone recommend a good manual that will give me not just the code numbers (I can find the codes and brief one-line descriptions), but full explanations of what they mean and how to interpret them?

Last edited by Dave Danger; 06-28-2005 at 06:42 PM. Reason: additional info
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Old 06-29-2005, 07:20 AM
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Did you take a fuel pressure test? If so what was it? By the way it will not set a low fuel pressure code, and the O2 codes would either indicate a lean or rich condition, or a heater failure.

Steve
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Old 06-29-2005, 10:39 AM
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just like steve said. if your fuel pump is failing and your fuel pressure is low then the only code your going to get is a lean condition from the O2 sensors. and it will still run like crap. the reason the misfires stopped when you changed the plugs is because your plugs were all carboned up from the lean condition. runn it long enough with the new plugs in it and you'll get the misfires back.

if you've changed the fuel filter then that only means 1 of 3 possible things. 1) you have a kinked fuel line somewhere and its not letting the correct amount of fuel through
2) your fuel pump is failing and it isnt pushing the fuel through, or
3) the screen on the in-tank pump is blocked with dirt or other sediment.

check the fuel pressure and let us know. good luck!

-Matt
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Old 06-29-2005, 11:08 AM
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Fuel filter been changed? How about a check of the regulator?
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Old 06-29-2005, 11:56 AM
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Possible restricted exhaust.

The GM service manual is the best there is as far as explaining the codes. IMO
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Old 06-29-2005, 12:05 PM
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what did the plugs you took out look like, or the one that are in there now, for that matter? Lean, rich, a lean condition can be caused by improper fuel pressure as stated or a vaccum leak that is going unregulated, ie. after the MAF sensor. Usually where the intake plenum meets the heads. Simple gasket failure.
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Old 06-29-2005, 01:39 PM
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Sorry just looked at you first post again and seen that you have the 4.3 v6. This should be a vin W engine. check the 8th digit of the vin. If it is these engines had a lot of problems with the fuel injection set up. The poppet valve will get sticky and cause all sorts of driveability problems. Also the EGR system can cause these problems. Still a good place to start is with a fuel pressure test. Does the engine overheat to the point of boiling or is it just the temp gauge goes up? What was the first trouble code(s) # set?
The fuel pressure should be= Test with the key on and the engine off = good pressure is 60-66 psi.

Steve
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Old 07-06-2005, 08:57 PM
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Update on the problems...
I broke down and had a leaky radiator repaired. The inlet side (plastic) tank had a small crack that I'd been nursing with JB Weld for quite a long time. Decided that I needed to eliminate that as one factor in my troubleshooting. (I could not believe the WEENIE 5/8" thick radiator core installed in this truck!) I am shopping for a heavy duty as we speak. The temperature does seem to be a bit more stable and not nearly as prone to boil as it was. That said, nothing else has changed. Truck still runs like crap. I have yet to find a fuel pressure gauge that I can tap into my fuel injection system to determine what my fuel pressure looks like. I am leaning that way though with my suspicions. I had several tuneup shops advise me that my catalytic converter was plugged solid. This after putting my truck up on a rack and rapping the converter sharply with their knuckles... "ya hear that clanking?" (I heard nothing more than the heat shield vibrating) "that means that it's all broken up inside.. pieces probably blocking up all kinds of things here...We can replace that converter for a piddl'n $250.00, then we can see what all else is blocked". I nodded my head and asked for my truck back on the floor.
I think that if the exhaust system were anywhere near blocked... I'd not be able to manage to get it up to 65 mph out on the interstate. I can do that.. did it just a few minutes ago. Admitted, it took me almost 4 exits worth of driving to get it to 65, but it will get there. It just has NO acceleration ! That feels like fuel restriction in some manner. As for someone's advice a few posts ago about a lean condition... it's an overly rich condition that will foul plugs, not lean. However, I'm in no condition to argue the finer points of spark plug analysis at this time. My truck's running like a weak sister and all my knowledge ain't making squat difference right now.
I'll post back when I get some fuel pressure readings.
Any other advice, please don't hesitate!

Thanks
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