Help! '99 Tahoe doesn't start...

[Osteoblast]

Update

Checked everything again.

So took apart the exhaust.
Shame on me. Wanted it to be OK, because it looked good but I found this

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Will continue tomorrow and try disconnecting the downpipe from the exhaust manifold.
Maybe it will start.

 

[stutaeng]

Update

Checked everything again.

So took apart the exhaust.
Shame on me. Wanted it to be OK, because it looked good but I found this

You must be registered for see images attach

You must be registered for see images attach

Will continue tomorrow and try disconnecting the downpipe from the exhaust manifold.
Maybe it will start.

Yikes! What is that?

 

[Osteoblast]

Ceramics from the catalytic converter.
Somehow the cat got spit out and clogged the exhaust.
So exhaust pressure too high, no start.

 

[Schurkey]

You need:

1. A burnable air/fuel mixture
2. Adequate compression. GM spec at one time was 100+ psi cranking pressure.
3. A spark ACROSS THE PLUG GAP, AT THE RIGHT TIME.
4. Adequately non-restrictive exhaust. When the exhaust is restricted, the engine will often pop or run for a short time, then stall. The exhaust is unlikely to be so plugged that the engine won't even pop.

I was wrong.

 

[Osteoblast]

Update

I took off the exhaust bit still not running.

 

[Schurkey]

Update

I took off the exhaust bit still not running.

I was wrong.

...or maybe not.

Are the plugs fouled from too much cranking?

The four things I posted previously still apply--
1. A burnable air/fuel mixture
2. Adequate compression. GM spec at one time was 100+ psi cranking pressure.
3. A spark ACROSS THE PLUG GAP, AT THE RIGHT TIME.
4. Adequately non-restrictive exhaust.

Which one(s) don't you have?

 

[Osteoblast]

Maybe the engine sucked up ceramics, particles from the catalytic converter?

Plan is to probe the injectors, visually check the cylinders for damage and do a compression test.
I want to try another PCM. I thought I could try swappimg the '98 Tahoe PCM into the'99 Tahoe.

How can I test the spark at the right time?

 

[Schurkey]

Connect a timing light to #1, have someone crank the engine while you shine the light on the timing pointer. I'd expect the damper mark to be somewhere on the pointer/indicator. I don't know what the timing is supposed to be, and if it's working properly, there's no adjustment for it. But verifying the timing would also verify that it's working properly, at least at cranking speed. And if it's working properly at cranking speed, that's not the reason the engine won't start.

Do you have a spark tester?

There's many styles, this is my favorite kind:
www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&psc=1&ref_=lv_ov_lig_dp_it

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You'll find out in a hurry if there's a defective ignition coil, defective cap 'n' rotor, or failed plug wires. Remove each plug wire in turn, connect it to that spark tester. Ground the spark tester in such a way that the firing end faces the driver's seat. Crank engine, look for sparks.

 

[Osteoblast]

I have this tester

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And I get a spark at least in the tester and the spark plugs are new.

Will do the timing test.

Will try renting the tools.

-compression tester
-timing light
-endoscope

 

[Schurkey]

I have this tester

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And I get a spark at least in the tester and the spark plugs are new.

Define "new".

Thirty seconds of cranking could foul the plugs.