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Old 09-07-2012, 04:20 PM   #1 (permalink)
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1996 454 power loss towing.

Hello all.. I'm stumped. I have a 1996 GMC 454 dually. It's been an awesome truck. I tow a large 5th wheel and the last time I towed it the service engine soon light came on and there was a loss of power towing. We were on vacation so I had to take it to a shop. They said it was out of time, retimed it and I was on my way.

The next hill I started to climb the same problem happened. I made it home and after a couple of local drives with out the 5th wheel the light went off. All power is normal, no miss, no over heating, runs awesome. I hooked up the 5th wheel again to tow it, and the first little hill I came up to.. had loss of power, like 35 mph at 35kRPMs.

Does anyone have a clue why this thing will run great with out my heavy 5th wheel on, but dog out while towing? The shop read the code as out of time.. timed it and thought it was fixed. It wasn't. Thanks,
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Old 09-07-2012, 04:33 PM   #2 (permalink)
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The teeth on your distributor gear may be worn out. Its a fairly common problem on the vortec 7.4 motors. The teeth on mine were like razors they were so worn out.
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Old 09-07-2012, 04:37 PM   #3 (permalink)
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The teeth on your distributor gear may be worn out. Its a fairly common problem on the vortec 7.4 motors. The teeth on mine were like razors they were so worn out.
And this will cause loss of power and give an out of time code while under a load? This really makes sense to me. I was thinking fuel pump, or regulator, or even injectors.. but it runs fine with out a load. So I didn't think it was those.

I have to almost remove the manifold to remove the distribute I bet. Wow.. never even consider that maybe the problem. Thank you.
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Old 09-07-2012, 05:15 PM   #4 (permalink)
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I should mention, soon after unhooking the 5th wheel the service engine soon light goes off. Even when it's on it runs fine.. just under power if I'm towing. I will pull the distributor in the morning and see if its worn looking.
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Old 09-07-2012, 05:25 PM   #5 (permalink)
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The teeth on your distributor gear may be worn out. Its a fairly common problem on the vortec 7.4 motors. The teeth on mine were like razors they were so worn out.
X3. Have had this same thing happen on two Vortec BBC's!!! You can diagnose it with a scan tool showing your timing curve. Timing will be moving around erratically if you have the gear issue.
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Old 09-07-2012, 05:36 PM   #6 (permalink)
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X3. Have had this same thing happen on two Vortec BBC's!!! You can diagnose it with a scan tool showing your timing curve. Timing will be moving around erratically if you have the gear issue.
Thank you for the reply. I don't have a scanner, but it looks easy enough to remove it and see if it's worn. After taking it to a shop and paying to have it fixed.. I want to do it right this time and do it myself. (with help from this site that is).
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Old 09-07-2012, 06:46 PM   #7 (permalink)
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better change the shit outta your oil!!! Might even be a good idea to have an oil anaylisis done to see if there is any bearing material in it. The metal missing off of your dizzy gear went somewhere, and unfortunatly it was probably throught the rods and mains. In reality, all you can do is hope the filter caught most of it, and keep running it. But you better keep it in mind, the lifespan of that BBC just got alot shorter.
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Old 09-09-2012, 11:50 AM   #8 (permalink)
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Okay, update.. took off the dist, and in fact the gears were very worn... Got the new one back on, and the first thing I noticed when it started was better oil pressure. I ran it 15 mins, and it runs very smooth, and very well. When I tow my 5th wheel next month that will tell if this fixed it. (fingers crossed)

Uh uh.. I change oil every 4 to 5k miles. I use Quaker state full syn. I agree the metal went some where, but it's been over the course of a couple of years so I hope I caught most of it via the filters. For the price of a gasket I will drop the oil pan and check it.

Thanks again for all the replies.. THANK YOU THANK YOU... I will pas this info on to anybody else that may have this problem.
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Old 09-10-2012, 01:02 PM   #9 (permalink)
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Was wondering why there was no dizzy in the '97 454 I just pulled from the salvage yard.
Gotta wonder if Comp Cams' new carbon-fiber dizzy gear might solve this? If it even fits, that is.
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Old 09-11-2012, 08:40 PM   #10 (permalink)
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Was wondering why there was no dizzy in the '97 454 I just pulled from the salvage yard.
Gotta wonder if Comp Cams' new carbon-fiber dizzy gear might solve this? If it even fits, that is.
Haven't seen it yet, but I would bet they only make it for the .500 shaft, and not the .491 stock diameter.
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