'92 K2500 5.7 TBI - Crank for days and no start after intake gaskets...

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Random thoughts from your post...


winALDL is old school, try TunerPro RT v5 instead.

Thanks Desert! Will do when cable arrives.

Did you follow this procedure?
http://www.gmcmidwestclassics.org/Web pages/Tuning the TBI.pdf

To a tee! The problem is now we can't start the motor and get it up to operating temp to recheck base idle setting. It raced when trying to set it prior to IM gasket job.

What brand distributor, what about your coil?

Bought the reman GM one from O'Riellys. Again, started and ran prior to the gasket job. Only has about 50 miles on it. Coil is also new... Not sure on the brand... Definitely not original AC

Check all of your ground connections including the back of the head and at the T-Stat snorkel.
Just a thought. Did you put rags in the intake ports while cleaning the heads to keep debris out of the intake ports and forget to remove them? I've seen it happen.

Thought of this! Actually cleaned all the ports by hand and then with a vacuum. All clear prior to setting manifold.

Check your fuel pressure at key on, no crank s/b 11 -13 (factory says 9 - 13)

Will do this again. Checked at fuel filter change. Had 11psi at the filter.
 

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Thanks! No. Only did intake manifold gaskets at this time. Did not go deeper into motor as no other symptoms were present.

Timing light is dead on the mark and does not jump around at all... Ran great right up until the problems described here, before the gasket job.

Thoughts??

When dealing with an unknown engine I like to get a base line to make sure I'm not fighting a mechanical issue. Good compression No weak valve sealing etc.

This could also be something stupid like a coil that ohms out ok, shows spark at cranking rpms, but just can't keep up at rpms above that.
 
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with the plugs all looking a little different, I'm sure the age of the motor would indicate that there are some inconsistencies with valve seats etc.

I have not done a compression test as someone walked off with our compression tester.

Again, except for the conditions of intake manifold gasket which were sudden and severe a while ago, The engine run great and would even start right up either hot or cold prior to the gasket job.
 

454cid

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How about swapping in the ICM from the old distributor? It's in the distributor on the TBI trucks, right? The cranking/backfiring reminds me of the behavior of my Vortec when the ICM goes out.
 

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Setting the timing and when the spark event occurs has little to do with if the cam is in the correct position and the valve events are happening at the correct time in relation to TDC.

I've had them jump a tooth or two and keep running, but vacuum will be down, power will be down, they can choke and spit and sputter out either the intake or exhaust, and act as if they won't take throttle and accelerate. A quick check is to pop the cap and rotate the engine back and forth via the harmonic balancer bolt and make sure the rotor is moving in relation to crank rotation. It only takes a few minutes to eliminate as a variable.

They always run good until they don't. How it ran before doesn't eliminate a new or different issue. This could be any number of things from, as said, plugs, coil, etc to a mechanical issue. Where the valves have been adjusted along the way cams going flat are not always a catastrophic event. The distributor wore slam out and falling apart is enough for me to want to verify the engine is of sound condition before the parts throwing and tail chasing begins. Eliminate as many variables as you can. We also live in an age where new out of the box doesn't always work correctly either. Lots of substandard ignition modules and electrical parts out there.

I'm not an efi/ecm kinda guy but the other guys make good suggestions.
 
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Hipster

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How about swapping in the ICM from the old distributor? It's in the distributor on the TBI trucks, right? The cranking/backfiring reminds me of the behavior of my Vortec when the ICM goes out.
one of my thoughts as well
 

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So is it this??????

Again, except for the conditions of intake manifold gasket which were sudden and severe a while ago, The engine run great and would even start right up either hot or cold prior to the gasket job.[/QUOTE]



or from your original post below?????

FORMER ISSUE: Began running rough/low power/poor fuel economy with intermittent check engine light at speed. The loss of power and backfiring at speed finally got so bad we began tearing into it.

We updated/replaced/performed the following with NO CHANGE to the original symptoms before finally diagnosing leaking intake manifold gaskets.

Did the gaskets and now no start.


It either ran fine before or it didn't. But it sounds like you drove it with a problem until it just wouldn't go no more and it hasn't run since this "severe and sudden event"
 
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Schurkey

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NOTE: Old plugs had about 12K miles on them and were mostly tan/brown and a just little "burnt" at the electrode tip when we replaced them. Nothing unusual or noteworthy. Even the ancient plugs we took out when we bought it didn't look bad after God-knows-how-long they were in there, which gave us confidence in the overall health of the old 5.7.
At 12K miles, I'd expect new-looking white porcelains. Modern fuel doesn't color the porcelains like leaded fuel did. Sometimes you get some orange or some green from additives in the fuel, but typically it's very light and takes a long time to show up.

Tan/brown and burnt at the end at 12K is telling you something. I don't know what, but you'll likely find out once you get it running reliably. Oil burning most likely.

That's exactly the style I use--one calibrated for HEI, one calibrated for points, like that one. The folks in the link want $26 which is crazy. Should be able to find similar on Amazon for about half that price. And, again, preferably one calibrated for HEI which will have a recessed center electrode to make for a longer gap that the spark has to jump.
For example,
You must be registered for see images attach

https://www.amazon.com/OTC-6589-Ele...+Spark+tester&qid=1562529520&s=gateway&sr=8-2

So is it this??????

Again, except for the conditions of intake manifold gasket which were sudden and severe a while ago, The engine run great and would even start right up either hot or cold prior to the gasket job.



or from your original post below?????

FORMER ISSUE: Began running rough/low power/poor fuel economy with intermittent check engine light at speed. The loss of power and backfiring at speed finally got so bad we began tearing into it.

We updated/replaced/performed the following with NO CHANGE to the original symptoms before finally diagnosing leaking intake manifold gaskets.

Did the gaskets and now no start.


It either ran fine before or it didn't. But it sounds like you drove it with a problem until it just wouldn't go no more and it hasn't run since this "severe and sudden event"
I am making the assumption that the engine started reliably, but ran poorly under load.

Changing the intake manifold gaskets didn't change the cam timing, didn't change the compression, didn't change the exhaust system. The distributor is "new" but still throws sparks, which mostly but not completely eliminates the ignition pickup coil, ignition coil, and module. Ignition timing is correct. Fuel is spraying.

There could be a "coincidental" failure that just happened to occur at the same time as the intake job. Possible, not hugely likely.

I'm still going with fouled plugs--but I'm very suspicious of fuel pressure. Also, if the intake manifold gaskets were leaking air into the ports, the computer will have reduced the idle air bypass opening to maintain a proper idle despite the air leaks. So the computer is likely going to have to re-learn what the proper position of the IAC pintle is now that the air leaks are gone.

Any chance the OP dicked with the throttle blade "minimum idle" position screw?
 

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For example,
You must be registered for see images attach

https://www.amazon.com/OTC-6589-Ele...+Spark+tester&qid=1562529520&s=gateway&sr=8-2






I am making the assumption that the engine started reliably, but ran poorly under load.

Changing the intake manifold gaskets didn't change the cam timing, didn't change the compression, didn't change the exhaust system. The distributor is "new" but still throws sparks, which mostly but not completely eliminates the ignition pickup coil, ignition coil, and module. Ignition timing is correct. Fuel is spraying.



There could be a "coincidental" failure that just happened to occur at the same time as the intake job. Possible, not hugely likely.

I'm still going with fouled plugs--but I'm very suspicious of fuel pressure. Also, if the intake manifold gaskets were leaking air into the ports, the computer will have reduced the idle air bypass opening to maintain a proper idle despite the air leaks. So the computer is likely going to have to re-learn what the proper position of the IAC pintle is now that the air leaks are gone.

Any chance the OP dicked with the throttle blade "minimum idle" position screw?

I haven't discounted anything anyone has said or that it could be something simple or something someone else has suggested, or that he is fighting multiple issues. He been up, down , and sideways all over this. His presentation is somewhat confusing to me and seems somewhat contradictory. He put a distributor in and a couple line items later he's readjusting it 4 degrees. His original is pretty clear he's been fighting this from the beginning of the problems all the way up to pulling the intake. To me starting and idling would be a great step in the right direction but not really an indicator that it's running great. They can jump one tooth start and idle great but have issues under load and run for months until it jumps again . Spring pressure and follower drag will keep tension on one side of a chain so the timing mark not jumping at idle would be no big surprise and is not conclusive. One tooth is about 6 degrees on a timing ight. The check is free and easy and less then five minutes time

The symptoms described could be a multitude of things. Agree with the comment on ignition it should at least hit like it's trying to fire up. Fuel pump or pressure, yeah, I don't see that on his list. And agree with intake leaks affecting things, but what exactly is sudden and severe? Did it fill the pan with coolant? Another symptom of the same ongoing issue? IDK

Everybody has made suggestions of things to do or check. All good from where I'm sitting but some definitive process whether it be the live data and/or mechanical testing needs to happen.
 
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Big E

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I haven't discounted anything anyone has said or that it could be something simple or something someone else has suggested, or that he is fighting multiple issues. He been up, down , and sideways all over this. His presentation is somewhat confusing to me and seems somewhat contradictory. He put a distributor in and a couple line items later he's readjusting it 4 degrees. His original is pretty clear he's been fighting this from the beginning of the problems all the way up to pulling the intake. To me starting and idling would be a great step in the right direction but not really an indicator that it's running great. They can jump one tooth start and idle great but have issues under load and run for months until it jumps again . Spring pressure and follower drag will keep tension on one side of a chain so the timing mark not jumping at idle would be no big surprise and is not conclusive. One tooth is about 6 degrees on a timing ight. The check is free and easy and less then five minutes time

The symptoms described could be a multitude of things. Agree with the comment on ignition it should at least hit like it's trying to fire up. Fuel pump or pressure, yeah, I don't see that on his list. And agree with intake leaks affecting things, but what exactly is sudden and severe? Did it fill the pan with coolant? Another symptom of the same ongoing issue? IDK

Everybody has made suggestions of things to do or check. All good from where I'm sitting but some definitive process whether it be the live data and/or mechanical testing needs to happen.
I have never "seen" one "Jump" timing with the stock timing set. If you look at a TBI trucks timing chain and gears, it would take a huge amount of slack to be able to jump timing. It would be running very poorly long before it could possibly jump teeth. I've disassembled TBI motors with well over 200K miles, and while they had slack, it was far from being able to jump a tooth! If you've ever looked at a stock TBI timing set with the cover off, jumping a tooth "ain't happening"!
 
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