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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a 2002 Chevy Suburban with an 8.1. My wife has driven

Customer Question

I have a 2002 Chevy Suburban with an 8.1. My wife has driven since new. she is a mother of 4. she has put 139,000 miles on it. Most recently, we had the typical crank sensor problem, where it stalls in the middle of the road. that has been repaired. On the way to doing that, we put in a new fuel pump, cam sensor, a vacuum sensor on top of the intake manifold, new spark plugs, and of course a new crank sensor. It ran great for a short while, and has never stalled in the middle of the road any more. But, for the last 6 months, when it is cold it runs great, when it is hot it runs great. At mid-temperature, it starts cutting out and not developing any power. I believe it is mis-firing in the ignition system. My reason for this is 1) the tachometer drops at the instant there is a mis-fire and works great when the engine is running correctly; 2) There is a backfire once in a while when trying to hurry it. I believe it's dumping fuel into the exhaust then giving spark {I was a mean kid as a teen to make noise}. My most recent mechanic's input was coolant in the combustion chambers by a cracked or warped head. that was a big waste of time. All cylinders were very clean and looked identical. The problem returned immediately after reassembly. I learned what a great engine the 8.1 is internally. There was no ridge at the top of the cylinder walls and the hash marks were still on the cylinder walls. It has a great gasket set in it. Unlike the early 2000 5.7 Chevy's. The question is, where would I look for an ignition-related problem? As each coil is independent for each spark plug. I believe the problems is between the ignition switch and the engine.
JA: Are you certain it's the fuel pressure sensor that's in need of attention? What about the fuel rail? Have you checked it yet?
Customer: That was a quick response without information yet.
JA: Are you fixing your Suburban yourself? What have you tried so far?
Customer: yes
JA: Anything else you want the mechanic to know before I connect you?
Customer: nope
Submitted: 8 months ago.
Category: Chevy
Expert:  Jared D replied 8 months ago.

Good morning,

I am a big fan of the 8.1L also- I have one in my personal truck. That engine is a mean machine.

So, When you are getting the backfire is it at partial throttle, coasting down hills?

When you say the tach drops, does it drop to nothing at all?

Customer: replied 8 months ago.
She says it backfires when giving gas, the drop in the tach is a bounce
Expert:  Jared D replied 8 months ago.

That sort of sounds like a plugged catalytic converter. No trouble codes are set right?

What sort of scan tool do you have access to?

Customer: replied 8 months ago.
The engine light has not come on , the converter is not plugged, It is loosing is spark
Customer: replied 8 months ago.
It,s spark
Expert:  Jared D replied 8 months ago.

Do you have a scan tool?

Do you have a spark tester?

https://www.amazon.com/Thexton-THE404-Spark-Tester/dp/B0002STSBM

Customer: replied 8 months ago.
Scan Tool, Cen Tech CAN OBD 11...... code PO101 MAF or VAF A Circut Range/PERF. No spark tester
Expert:  Jared D replied 8 months ago.

You have the p0101 code currently active?

Will your scan tool monitor live data streams so you can watch the reading from the MAF?