No start after manifold gaskets replaced

MLBX

MEMBER
2006 GMC YUKON
6.0L
V8
4WD
AUTOMATIC
174,000 MILES

Truck had codes P0171 and P0174 and wouldn’t pick up acceleration. After looking up the codes and common fixes to the problem it led me to the intake manifold gasket which is a common issue. I replaced the gasket yesterday and made sure to put everything back how it was and cleaned out the valley for the gasket to set properly. I put the new gasket on put everything back on truck will crank but will not start when it starts to catch it immediately turns off. I have check fuel pressure it is at 55 PSI right where it’s supposed to be. I am getting spark and compression but something is preventing it to start. Anyone have any ideas or where to check it would be greatly appreciated?

Monday, June 14th, 2021 AT 9:24 AM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

More than likely we are just missing something that basic so let's start running through these things and see what comes back.

https://youtu.be/dCjmRL3p4Cs

Also, can you get a video of what this is doing when it is trying to start? The fact that it tries to start but then cuts off sounds like a timing or air/fuel ratio issue. Based on the fact that you just did the intake gaskets means we may have a vacuum leak still.

Let's use this guide to help look for a leak to rule that out.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If you have spark, fuel, and compression the engine should start so the fact that this is trying to start tells us that we have too much or too little of one of them.

Let's start with this and we can go from there. Thanks

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Tuesday, June 15th, 2021 AT 5:06 PM