2000 Chevy Tahoe Z71 5.7l vortec
1. Sluggish.
2. Backfiring through the exhaust originally.
3. Poor fuel efficiency.
4. Smell of fuel in cab intermittently.
5. Exhaust backing up into cab (only happened once though but it was really bad, couldn't get it over 35 that night either.
Parked it to work on it. Been parked since October 20, 2021.
Several on that list could be restricted exhaust/plugged catalyst.
Backfiring through exhaust would more-likely be ignition timing related.
Cam timing could cause a lot of that...but how would the cam timing suddenly alter?
Failed ECM; or failed sensors/outputs could cause some of those symptoms. Scan tool needed.
Failed fuel injection "spider" or pressure regulator could cause some of this. Fuel pressure testing needed.
Parts I have replaced. And work I have done.
1. Changed oil. Running 10/40 full synthetic.
GM hasn't recommended 10W-40 for decades. Next oil change, consider 5W-30.
2. Changed spark plugs ( the spark plugs I took out had alot of carbon build up an were not gapped correctly )
Did you install the correct plugs? Have they fouled since you installed them?
7. Replaced fuel pump ( one of the guys broke the fuel line adapter so I had to replaced the assembly, when I did the fuel pump quit working so I replaced that as well)
8. Replaced the fuel pump relay. ( Reason the fuel pump stopped working)
What is the fuel pressure?
9. Replaced the cam shaft sensor and the crankshaft sensor ( the computer was blowing codes that were related to these sensors so I changed them out)
What does the scan tool show for "cam offset" or "cam retard"? The computer measures the difference in the synchronization between cam sensor signal, and crank sensor signal. They should be within 2 degrees at ~1100 rpm.
10. Oil pressure regulator sensor( because the first person I allowed to help me thought that's where the crankshaft sensor was and ended up breaking the sensor )
Oil pressure sensor. Not a "pressure
regulator sensor".
Now the Tahoe just cranks but I can't get it to turn over.
"Cranking" and "turning over" are the same thing. Your engine cranks, but doesn't run.
There is a back fire in the intake. After a few adjustments the sound changed and now it sounds worse. Several backfires from the intake.
WHAT "adjustments"?
Backfire in intake can be from exhaust valves not opening, plugged/restricted exhaust including plugged catalysts, but more-likely from incorrect ignition timing. Thus the need to use a scan tool to look at that "cam offset" figure.
Connecting a timing light might help--if the timing is not a full 180 degrees off. That would show "correct" when using a timing light, but still cause a non-running, backfiring engine. In fact, I think having the ignition timing ~180-out is very likely.
I think the cats are clogged but I don't think that would be the reason the Tahoe will not turn over.
It is possible for exhaust to be so plugged the engine won't run. But it'll almost certainly fire at least a couple times. Apparently, yours isn't even doing that.
one of my neighbors gave me another Chevy but a trailblazer with the whole top end taken apart needing a head gasket replaced. I jumped on it but that's for another post.
You're gonna love the ('02--'09) Trailblazer once you get it sorted-out. That is a world-class six-popper in a very nice chassis/body.
If this is a much-newer current-production Trailblazer, you've got a rancid lump of scrap metal and plastic.
Anyways I have adjusted the dotributor like 9 times so far trying to find TDC could that be the problem.
Yes. Doesn't matter how many times you've "adjusted" it, if you're not getting it RIGHT.
Also the vacuum lines crumbled in my hand when I went to move it out of my way. Working on trying to get them routed correctly to. Could that be an issue?
Probably not the reason it won't start. Might be a reason it doesn't run properly.
Ps. Someone said something about a lobed cam???? I don't even know what that means or how to check it. ?????
They likely mean that a cam lobe has gone flat from excess wear or a failed roller lifter. Yes, that's possible. No, not real likely. And the other cylinders should run. You'd most likely have an engine that ran poorly and made evil knocking noises.
I would hook up a scanner and see your cam position. If you cant do that then make absolute your not 180 out. Imo sounds like distributor is way off. Any codes?
YES.
You need to verify your distributor installation before you throw any more time and parts at the truck.
YES.
Search for "finding cylinder 1 TDC in a small block Chevy". There are YouTube videos and written instructions on the subject. Verify that the distributor rotor is pointing at the #1 terminal when the engine is at TDC.
TDC
COMPRESSION for #1. NOT TDC
Exhaust for #1.
If you don't already have a scanner that will read live data from the engine (there are several Bluetooth adapters and apps available, or dedicated hardware) get one and find out if you have any active codes. You'll also need to see sensor data, such as coolant temp, air temp, MAF airflow, manifold pressure, and oxygen sensor status. These will help tremendously.
YES. I don't have much faith in the laptop-computer/cell-phone software; but
other folks use that successfully. I'll take a dedicated scan tool, thankyouverymuch.
And regarding the timing, I've had the reluctor wheel shift on the distributor shaft and f___-up the timing, this on my 1995 S10 Blazer 4.3L VIN W. Just keep this in the back of your mind if for some reason you can't get the timing right. You may need to look closely at the distributor.
The reluctor wheel does not alter the timing. It alters the synchronization of the cam sensor signal. With faulty synchronization, the distributor gets turned to "fix" the synchronization, but that screws-up the alignment between the rotor tip and the distributor cap terminals.
Having the reluctor wheel shifted could be a problem, but not for timing.
