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Spending big bucks - still not fixed |
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Written by Richard McCuistian
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Friday, 01 May 2009 |
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What's a customer to do?
I have a 2000 3500 4X4 with a 454 engine. Several years ago the truck broke down in FL and the dealer began replacing parts until it ran to the tune of $2700.00 Immediately after this event the truck developed a misfire issue from 3800-4200 rpm.
Once past that the truck runs like a champ up to the shift point. This only occurs when passing or while towing a load since regular use does not approach this rpm. I have been told everything from low fuel pressure at high demand to a worn camshaft I think ignition issue since we replaced everything from crank sensor ,fuel pump, injector harness, intake gasket, distributor gear, plugs wires cap and rotor, fuel filter, and regulator all at the direction of various dealerships over the past few years.
I read the report on cam sensor and distributor indexing. Does this seem like the issue? Bud
Have somebody with a scan tool check the Cam Retard Offset (see attachment) Let me know what happens...
Richard
I replaced the distributor and cam sensor. Then I had a reputable mechanic set the timing ( indexing ) The problem was still persistent and he suggested maybe flashing the Ecm or possibly replacing it. I took the truck to a local dealer and asked them to re flash the Ecm however they informed me this was not the problem and I would be wasting my money.
They insisted on running their own diagnostics and told me the crank sensor was bad..... They claimed the sensor that was in the truck was an inferior after market part (Installed by a neighboring dealership just a few weeks ago ) and they put a "GM" sensor in.... Guess what? Still have the same problem. Now they are sating the harmonic ring gear has excessive end play. The claim is that there cannot be more than 11 thousandth end play but they are getting 45 when they checked it. When I asked how they checked this they could not provide an answer but told me to fix it I needed to replace the thrust bearing. I find it hard to swallow that one day in Florida this just happened and the truck has been running this way ever since. Correct me if I am wrong but would this cause consistent rpm range failure for over 60,000 miles? This issue has an exact failure point and an exact continuation point. It accelerates strong and smooth up to and at exactly 3800 rpm sputters pops backfires and ends at 4300 rpm and runs strong and smooth up to the shift point. Their claim is that the jerking is from the transmission being worn out.....
Is there a way to attach a meter or scope to the crank sensor to verify that it is actually loosing signal and not an anomaly in the Ecm. In my opinion if it were the end play issue it should occur at varying intervals of load and acceleration. I am sinking more money in poor mechanic expertise and swapping better old parts for good new parts than the truck is worth....Does GM have a tech that can help????
Bud
If somebody really gets serious about that problem they'll check the cam and crank sensor signals with digital storage oscilloscope and see if the crank signal is dropping out - if the thrust bearing is worn and is causing this problem, the o-scope would tell the tale. If they can't tell you how they arrived at their measurement of wear (and they should be able to), then I wouldn't trust them to fix anything. If a customer wants to know how I arrived at a conclusion, I'm more than happy to show them exactly how I made the measurement and I'm also happy to show them the specifications. They should be too.
Their theory carries some weight (I've seen bad aftermarket parts and the other dealer might have picked the sensor up at a local parts store), but I can fully understand your point as well - if this was a worn thrust bearing (and it's remotely possible that it might be) then why did the problem happen all at once.
A sobering question to ask them (without giving them an okay) would be to ask if they'll be willing to absorb the cost of everything they've done if replacing the thrust bearing doesn't fix it. A diagnosis like that should be guaranteed, as Draconian as that may be. I don't think you should okay hundreds of dollars worth of work unless they'll be willing to come clean with you if that doesn't fix it...
And if that isn't the problem, why should you pay any more than you already have to get it fixed? Most shops charge a diagnostic fee, which you may have already paid them. If they charged you for another crank sensor, I'd make them return the part they replaced so you can get a refund from the dealer who installed it. These situations are always really tough; they're not sure what to do about the problem, and like most shops, they want to charge for everything they do to try and fix it, even if nothing they do works.
I understand that they have overhead, but let's get serious - it isn't right to take your money and send you on your way with the same problem you had before you paid the bill. One more question; are you sure the mechanic set the Cam Retard Offset right? I'm still wondering about that adjustment...
Richard
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Last Updated ( Monday, 04 May 2009 )
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