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2001 4.3 chevy problem kicking my butt, HELP
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 2:35 am    Post subject: 2001 4.3 chevy problem kicking my butt, HELP Reply with quote

Doesnt happen very often, but when it does......... Had a 2001 1500 chevy truck come in with a 4.3 v6 that would run fine sometimes, miss, sometimes, and stall and not start, or run so badly you could not drive it. So I started with anything obvious. Fuel press was at 75psi, so I changed the injector spider to the new updated GM unit which includes the press regulator, also pulled the lower intake and replaced gaskets leaking coolant into oil, and outside the engine(common problem on these engines) No change. Next the AC suction line runs right over the top of the distributor, and drips condensation on it. The cap was hammered with moisture damage and corrosion, so I changed the cap, rotor, plugs, and wires. No change. Next the TSB said the water problem usually ruins the distributor so I changed that! Plus it came with a cap and rotor, so now they have been changed a second time. Drum rolllll, no change. And like I said it will run flawlessly for 10- 15 minutes, or it will be so bad right when you start it that it cant be driven. Next I changed the map sensor because I once had a Bravada that would just crap out and die with no codes, and it turned out to be the map sensor, plus it is a cheap part, so I changed it just for the heck of it. Nada change (getting pretty frustrated now) Changed mass air flow from another car and you guessed it, no change. Changed the ignition module, and it seemed like it was finally fixed, but then after about 20 miles it started to ping and crap in the mid rpm range every time you would accelerate moderate to hard . I need to give this thing back regardless of how much it costs me to find the problem. At this point I dont care about the money , I just want to give it back knowing It is fixed. It does not give any codes, except once it gave a po300 random missfire code, OH GEE DO YA THINK good thing ya told me I didnt notice my face slamming into the dash, and into the back window while driving!!!!!!! Most cars you cant get the stupid light to stay off, and on this one you cant get it to come on, and when it finally did, it was basically worthless. When it is running bad it sounds like the worst cross firing distributor cap that has just been soaked with the hose you have ever seen, even when it stalls and you try to restart it, it cranks like the timing is massively too advanced (cranks real hard) Do you think the knock sensor could be bad? This one has the 2 wire one that is on the rear of the driver side just under the head, rather than the single wire one just above the starter on the pass side of the block. I am wondering if maybe the computer is damaged because it is mounted under the battery tray (genius, battery acid leaks here, lets mount the computer under it!)
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Sun Nov 25, 2012 3:03 am    Post subject: Reply with quote

Any noticable issues with ckp????
coolant temp and iat the same at startup? + or - 9 degrees
Doesnt that motor have 2 knock sensors.....im not assumeing anything there

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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sun Nov 25, 2012 3:12 am    Post subject: Reply with quote

what is your 5V reference doing when this occurs ? thanks to CAN data, all it takes is one module to do something stupid and kill your voltage to your sensors on everything. you may not have a PID for reference voltage (not return/signal voltage) so you may have to hook up a DVOM and watch it.
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 3:45 am    Post subject: Reply with quote

I tried un plugging the coolant temp sensor when it was running bad, it surged for a second, recovered, and kept running bad. I will check and see if I can check the 5v, but in live data, everything looks normal even when it runs bad.
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 3:46 am    Post subject: Reply with quote

Elaborate on the dvom hook up.
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 3:55 am    Post subject: Reply with quote

Keep in mind we are talking the old style 4.3 that they have been making since the 80s the newer generation v6 engines did not come out until later in 01, and this is the early production 01 however they did change the knock sensor location in 2000 from the pass side above the starter, to the driver side rear under the head, and it has 2 wires, only did it I believe for the last two years of the 4.3 production
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clay
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1972 Chevrolet Nova

PostPosted: Sun Nov 25, 2012 11:58 am    Post subject: Reply with quote

About all I can throw out is possible crank postion sensor flaky? I'm trying to remember if it actually uses crank postion so I might be out in left field. Clay
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 2:51 pm    Post subject: Reply with quote

It has a cam and crank sensor. The cam sensor is in the new distributor, so its replaced also, the crank sensor is in the bottom of the timing cover and not expensive either. Seems like it would put the engine light on if it was the problem. Maybe I will pull it tomorrow and see if it is cracked, or hitting the crank trigger wheel. If it looks damaged in any way I will get a new one. One thing that seems off to me is that when you turn the key on, the check eng light does not come on, and then go out in a few seconds after start up, it just stays off the whole time.
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af2
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1933 Willys Coupe

PostPosted: Sun Nov 25, 2012 4:15 pm    Post subject: Reply with quote

My 99 Tahoe did similar to what you are seeing. It turned out to be the crank sensor, after it completely failed I was able to find it to be the problem.
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Knarley Darley
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PostPosted: Sun Nov 25, 2012 5:09 pm    Post subject: Reply with quote

Thanks. I will check it and hopefully it will be obvious when I find it.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sun Nov 25, 2012 10:59 pm    Post subject: Reply with quote

as far as the DVOM (digital volt/ohm meter) you just need to hook it to one of the 5V ref wires and see if it has a drastic change. it should always be at or near 5V. couple more questions.... does it start running bad only after driving ? it has a POS linear EGR valve. those things will sometimes stick after they open and cause a vacuum leak. check actual vs desired position in your data. have you pulled the air intake hoses completely off and looked for obstructions ? i have seen those stupid "turbo" things, that you stick in the air intake, actually move around and turn sideways blocking off the air flow. also might check out the cat. the honeycombs can come loose from the shell and get in a weird position that it intermittently stops up the exhaust. look at vacuum when its acting up (use a mechanical gauge not scan tool data).
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It seems we can look at our magical Balls and come up with a fix?

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Knarley Darley
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PostPosted: Mon Nov 26, 2012 12:14 am    Post subject: Reply with quote

Some times it runs bad right when you start it up, and some times it will go 10 or more miles, and then run a little bad, or really bad, or die. The egr, That is a good call. I hadnt thought of, and I have had problems with them sticking open in the past. I just dont understand why it would crank so hard like the timing is super advanced after it acts up,(only some times on the hard cranking) and when it starts missing, it is not just one cylinder, it is all of them. It starts massively shooting ducks, like a wet dist. cap. Air intake is stock, and the cats are fine. They wont be for much longer if I don't find the problem.
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Mon Nov 26, 2012 1:43 am    Post subject: Reply with quote

go back and re-check the fuel pressure. 75 psi on the old system was really high. ive never seen one of those Vortechs with pressure that high. you might be flooding the cylinders and its actually hydro locking on startup. of course, if the EGR is stuck open, the vacuum will be low and the MAP will tell it to dump fuel.
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Knarley Darley
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PostPosted: Mon Nov 26, 2012 1:14 pm    Post subject: Reply with quote

That is why I changed the whole injector spider and regulator right at the start to correct the high fuel pressure. It runs between 58-63 now. I drive with a manual gauge slapped right against the windshield, under the wiper arm to hold it in place. I am going to drive with the egr unplugged and see what happens
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Mon Nov 26, 2012 1:20 pm    Post subject: Reply with quote

check your desired vs actual position with the scantool. if its stuck open, unplugging it wont help.
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