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Question
duntovlives
this is a new "updated" thread of a previous post. if anyone want to catch up here is a link to the previous thread:
http://www.gm-trucks.com/forums/index.php?showtopic=109531
quick summary:
2003 Silverado, auto trans, 4wd w/ 5.3
Intermittent crank no start will continue until you get it started, then it will run like a top and start every time for the rest of the day. according to the owner, as long as you stick with it and crank and crank and crank some more, sometimes 10 min, sometimes an hour, it will start. initially, the starter will only stay engaged for about 3 seconds at a time. it wont allow anymore (seems like this is by design, is it?). but, eventually, you can throw a jumper box/cables on it and it will allow you to keep the starter spinning until your fingers hurt. and, about the time you think the starter is going to melt down, it starts. (evidently this starter is bullet proof)
and periodically the problem has disappeared for months at a time and it runs like a top.
A number of techs have worked on it in the last 18 months or so. independent techs as well as gm techs.
replaced with GM parts:
2 PCMs (thought the first one was defective, so tried it again)
crank sensor
fuel pump
ignition switch
passkey module
replaced with oe equivalent:
battery
maf
codes that set on a regular basis: P0335-ckp sen A ckt prob & P0336-ckp sen A out of range>> i initally figured these were "false" codes set by extended cranking, but found low voltage supply to sensor, and sometimes, not always they set within a couple of failed attempts to start. currently there are no codes present. even though crank/no start, no spark, no pulse and no cranking rpms present.
codes that set periodically: U1026-loss class 2 communication with atc/trans & U1041-loss of ebcm/ebtcm communications.
in the past it set a code P1626 a few times (only once on my watch), might be the reason a gm tech replace the theft module.
Currently: crank, no start. no codes present. no spark. no pulse. no cranking rpms.
When this occurs, the crankshaft position sensor looses power from the ecm. when/if it does eventually start, the ckp sensor only has about 3.2 volts. when i scoped the signal, it looks normal, just short/low in voltage, but width appears normal and consistent in pattern. and, during this time the truck runs fine. best i can tell, it should have 12v supply from ecm. voltage at ecm pin is equivalent to what is viewed at the ckp sensor. and, voltage remains at 3.2v even when checked with ckp sensor disconnected.
I am assuming this low voltage was the reason for the new ignition switch (just guessing).
all the grounds on the engine (r&l rear of heads) have been checked and verified by all.
all power supply connections have been verified at distribution center, battery and so on.
many an hour have been spent executing the ole' "wiggle test" on anything in reach.
one of the gm techs that worked on it is a friend of mine, and he stated that every test he performed, all diagnosis charts he followed, as well as when he called into the gm techline, all pointed towards ecm failure, thus the second ecm. they also requested me replace the ckp sensor for good measure. but no luck. shortly there after, (next day) out of the blue, it started running fine, no codes, no long cranks times or any other symptoms, so he cut it loose and it did not have any problems for a few weeks.
the fuel pump was replaced as a "shotgun" attempt requested by the owner of the truck early in the game. this was during a period when the truck was running fine, but he felt it was a good guess and the techs couldnt replicate the complaint and the only history codes present were ckp related, they figured they were set due to extended cranking.
and evidently, another tech replaced the maf (another "shotgun" attempt best i can tell)... by this point the owner was numb and was willing to agree to anything anyone suggested.
the owner replaced the battery, as it seemed to him that when it wouldnt start, it didnt take long to drain the battery. he would hook up jumper cables, crank a little more and it would start. seems logical enough.
for the most part, i seem to have traveled down the same path as those before me. although, just in case, i disconnected any and all non oem components. stereo amp, goofy "air horn", brake controller and so on with no luck. all the same, i will leave them disconnected until im done.
i can see no signs of previous damage of any type, from a wreck or such. it is apparent that the hood has been removed and replaced, unclear why. engine and such look unscathed. the dealer checked the vehicle repair history with nothing remotely close to anything having to do with running/starting or drivablity issues or electrical problems. they also ran a carfax on it, in an attempt to uncover any useful info that might point them in a particular direction. no luck.
i noticed the oil pressure gauge was completely maxed out, beyond scale and quivering. and that the odometer was dim. he (the owner) commented that he couldnt necessary recall the when dim odometer started, but did seem to think that the oil pressure gauge wigged out simultaneously with this no start problem. he seems fairly confident actually. this somewhat intrigues me. could these problems be related? im in the process of researching the possibility. at this point, nothing would surprise me.
as you can guess, he has literally spent hundreds upon hundreds of dollars tryin to get this fixed.
he finally decided he would just cut his losses, and has made arrangements to trade it off, running or not, with a local dealer. when he told me he was giving up, i told him id check it out for him. work is a little slow, shop had an empty bay, so i figured why not. maybe help a friend out and figured he doesnt have much to loose.
after a google search or two for related symptoms this evening, i ran across a couple of TSB's that caught my eye:
TSB #3001 NHTSA ID#10008900, no date, no communication with any module, multiple U diagnostic codes.
TSB #3087 jan 01,04 - no cranking RPMs, no spark, no pulse.
my modis/software is updated to 08, but doesnt show either one. and i would assume the dealer would have stumbled upon these if they were relevant. but, still yet, i would like to see them. anyone know anything about them?
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