Wife and are a looking at a 2008 Suburban Z71 with the 5.3 engine and 175,000 miles. When we first started it up, it had a really bad knock like the engine was going to jump out of truck. It stopped after 20-30 seconds and then ran smooth but had a very faint knock low on the passenger side of the engine. When we drove it it seemed to be lacking power similar to the spark retard our 05 tahoe had with a bad knock sensor so thats what I thought it was. I've done some reading and now I wonder if the dod system is having problems. Am I going in the right direction or is there something else that could be wrong. We haven't bought it yet and the salesman said I could plug my scanner into it tomorrow so is there anything I can do with the scanner to try to narrow down what the knocking issue is/was. Its a very clean, rust free truck otherwise. Thanks
2008 5.3 Hard knock on cold startup
- Thread starter ace16a
- Start date
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kbuskill
***CAUTION*** I do my own stunts!
Hard to diagnose something like this over the internet. It could be something as simple as the torque converter bolts being a little loose causing the knock when it's cold but after it warms up it goes away.
iamdub
Full Access Member
I'd only buy it if the price reflects an engine replacement. If that happens and you find it was just a cracked flex plate or loose converter bolts, score for you. Let us know what codes you get.
You didn't say but I am assuming there were no check engine lights after it started. May not find any codes at all and I think the salesman knows that. Since it is a cold start problem, the salesman needs to allow you to leave at a trusted/qualified shop overnight and let them diagnose the noise. You can also deduct the diagnostic fee off of the asking price if you come to a deal.
tom3
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Could be the DOD going south, or some major piston slap. I wouldn't touch it unless the price is really at a big discount. I was seeing a lot of lease returns - just before the lock down - at really good prices.
I haven’t had time to get back and plug the scanner in yet. There were no check engine or service lights on. I think I’m just going to look for something else with the 6.2 engine on one that’s had the dod removed already. I’ll let you know if I do decide to check with the scanner. I guess if they’d take about $3000 less I’d go for it.
Walk away and don't look back.
Oh yea, always be willing to walk away. If they did take $3000 off, I would be tempted myself. Going after something with the 6.2 engine in it may be the ticket for you though.
iamdub
Full Access Member
You positive it's a knock and not a tick? Could be a $20 set of exhaust manifold gaskets and/or a broken exhaust manifold bolt(s). Dealer doesn't have to know this, though.
swathdiver
Full Access Member
That's an easy -$5000 for a (new used) replacement engine. You need a bi-directional scan tool to test AFM and a good tool to look at each cylinder for misfires and such.
The 6.2s in the wagons did not get AFM until 2010 (L94 engine). Easily found in Denalis and Escalades and very rare in 2010 GMC Yukon XL (no AFM 6.2) and some 2008-2009 LTZ Tahoes.
How much are they asking for that $2000 Suburban anyway?
