No start after rebuild

[Anchor]

Project I started last year and am finally getting around to finishing. Engine in project truck was ruined by previous owner when brass or bronze dist. gear came apart and went throughout the engine. Got another 5.7 and took apart and hauled off to machine shop. Got it back during winter and assembled it slowly. Finally have it in truck and am having a hell of a time with no start. Only thing I used out of the old engine is roller cam and roller tip rockers. Installed new LS7 lifters. After I had it in place I hooked up timing light and got it I believe pretty close on timing by spinning with starter. When attempting to start it gets strong pulses of fuel from both injectors. I hooked up my induction timing light to both the coil wire and a bunch of plug wires and got nice flashes at all points. Spark and fuel. I assumed it should start. No such luck. I got to thinking that maybe somehow I had set my valves way too tight or something. They are hydraulic. Pulled the plugs today and compression is around 170 on all so is assume that is not the problem. .5 volts at tps, IAC ohms out good. My mighty vac crapped out but I can suck on egr with hose and it moves. I have a friend who lives far away who is a lot smarter than me. I have worn him about out with this and he is at a loss. Can't check vacuum cause it won't start but you can feel vacuum at pcv port on tbi with finger when cranking so I at least have some. All of the sensors worked fine when I pulled the engine last summer or fall but I realize that can change. Any ideas or instructions would be welcome. Thank You

 

[evilunclegrimace]

WHAT YEAR

 

[Schurkey]

First Guess: Timing light shows "correct" timing because the distributor is 180 degrees off. It's sparking on the exhaust stroke.

 

[Anchor]

WHAT YEAR

Sorry, 1992

 

[Road Trip]

When attempting to start it gets strong pulses of fuel from both injectors.

Hello Anchor,

I'm going to assume from the above that we're dealing with a TBI-era truck.

Schurkey beat me to verifying that the spark isn't occurring 180° off. (distributor)

-----------------------------------------------------------------------------------------------------------------------------------------------------
(The following is OPTIONAL reading if Schurkey's suggestion to verify/reset the distributor phasing solves the no start.)

But if the ignition spark timing was correct & still no joy, then please check the following:

IF you have verified that the rotor is pointing to the number #1 plug when it is
at Top Dead Center of the Compression Stroke, and given the 170 psi of Compression,
then I have a couple of fuel questions for you.

#1) How old is the gas in the truck? Fresh fill? Or been in the truck since before the previous
engine met it's demise and the truck was back-burnered by the PO? (Months or even years ago?)

If a sample of the fuel won't run in a lawnmower, same same for your motor.

#2) On the assumption we're dealing with a TBI, the starting Air/Fuel ratio can range
from ~1.5:1 (at an engine coolant temp of 40° below) all the way to 14.7:1. (at ~201°F)

In English, the output of the ECT (Engine Coolant Temp) sensor is critically important to the
computer figuring out exactly what's the optimum air/fuel ratio needed to quickly start your
engine based on multiple tests in the dyno lab.

One of the benefits of the TBI system is that we can watch the fuel delivery, even while
the engine is cranking over. We had a gentleman in here who was having difficulty starting
his engine, and when he showed us a video of it cranking, the fuel was really flowing.

To see what I'm talking about, follow this link, and start watching the video at the ~13:18 mark.
You will see about 12-15 seconds of the 2 shower nozzles sharing too much of a good thing. LINK

IF this is what you are seeing, then the first thing to try is to put your computer into the "Clear Flood"
mode. You do this by flooring the gas pedal while cranking, and this tells the computer to cut the
fuel delivery way back. If this gets your engine to start, then that's a pretty positive indicator.

And the reason why I share this with you is that either your ECT sensor's electrical resistance is no
longer tracking properly to the temperature it's subjected to -or- an open wire/circuit between the
ECT and your computer will give you the same (mis)behavior.

****

For what it's worth. As always, for starting/running we need the proper triad: Spark + Fuel + Compression

PS: In that earlier thread, that forum member's no start was due to a bad sensor, which we verified after
the fact. Just make sure that your ECT sensor wire has continuity all the way back to the computer, and as
always, ensure that the computer <> engine grounds are in shiny, new condition.

Best of luck, and be sure to let us know what you discover.

Cheers --

 

[Anchor]

First Guess: Timing light shows "correct" timing because the distributor is 180 degrees off. It's sparking on the exhaust stroke.

Thank you Shurkey. I was watching the rockers and was pretty sure I had it right for tdc #1. Would it not be popping like crazy if 180 degrees off. I hope your guess is good. Quick fix.

 

[Anchor]

Thank you Shurkey and Roadtrip for your input. Can't believe it but I had the timing 180 off. I put a finger in the #1 plug hole and sure enough the damn thing was 180 off. Instead of confirming compression I just watched the rocker arms and Must have dropped the distributor when both were down not up. Derrrrr. As soon as I redid the distributor it fired on first revolution and purred. You guys have both given me great input in the past and I sincerely appreciate the help. Time has kind of caught up with me and this will probably be my last major project of this sort. I wouldn't be doing it now if I didn't have a pretty good shop with a lift in it. Cheers to you and all of the people here that get us bumblers through.

 

[Sean Buick 76]

I always stick a wine cork in #1 and turn it over by hand till the cork pops. Then you know

 

[Schurkey]

Watching the rockers can be misleading. At TDC-Exhaust (the wrong stroke) both valves should be open...on overlap. So "just barely" open. Add in some lifter leak-down, and the valve may even be closed.

If you're not feeling for REAL compression, you need to watch for the intake valve closing and staying closed as the piston comes up on the compression stroke. If you're seeing the exhaust valve closing...you're one full crank-turn away from where you need to be.

 

[Road Trip]

Can't believe it but I had the timing 180 off. I put a finger in the #1 plug hole and sure enough the damn thing was 180 off. Instead of confirming compression I just watched the rocker arms and Must have dropped the distributor when both were down not up

Hello @Anchor,

Congrats on getting the engine started, and thanks for sharing what it took to get it sorted out.
By sharing the real world fix, this only adds credibility to the abstract 'no start engine theory' shared in this forum
by the folks that actively participate in the remote troubleshooting. Good stuff.

Watching the rockers can be misleading. At TDC-Exhaust (the wrong stroke) both valves should be open...on overlap. So "just barely" open. Add in some lifter leak-down, and the valve may even be closed.

To me, getting the distributor installed correctly phased to the camshaft/crankshaft is almost a rite of motorhead passage
given how many of us have been bitten by this at least once since picking up tools and fixing our own engines. (!)

After helping countless people troubleshoot why their brand new engine was sneezing fire out of the carb instead of starting,
the problem was so common that I got to thinking about how people are somehow not being taught how to properly recognize the
unique valve train timing that is common throughout the 4 stroke world?

And I think part of the root cause of the misunderstanding is the way that 4 stroke theory is always taught verbally (or via the written word) as:
Formal: Intake > Compression > Power > Exhaust ; Power Mechanics textbooks
Informal: Suck > Squish > Bang > Blow ; Mnemonic commonly used by old salt shop teachers to help us marblehead students remember the proper sequence of events. :0)

And we all recite this magic incantation this way when troubleshooting. This is one of those things that, although correct,
can obscure the side by side exhaust<>intake stroke relationship. (With the Intake stroke at the beginning of the phrase
& the exhaust stroke at the other end, it gives the illusion of space between the events when there really isn't any. (!)

So, when I am providing local mentoring for someone on their first engine build, I instead make them recite it the following way:

Compression > Power > EXHAUST > INTAKE > (repeat)

And I always draw the following and have them verify this is what we see when cranking the engine over with a long-handled 1/2" ratchet:

You must be registered for see images attach

Disclaimer: The exhaust & intake curves drawn are 1st-approximation theoretical. The closest cam to this would be a small RV/Towing cam.
And the larger the duration the earlier we open the valves & the later we close them, causing additional overlap > choppy idle.
(And detailed cam theory is a non-goal of this reply.)

At this point in the build, here's the state of the engine:

* As soon as short block was built, the timing pointer to timing tab accuracy was verified via a piston stop.
* The front cover is installed.
* The cylinder heads are installed & torqued.
* Valvetrain installed. The hydraulic lifter preload has been set visually. (Inner plunger just off the retainer plus desired preload.)
* Oil pan installed. Oil pan drain bolt verified tight. Oil filter installed & verified tight. Pour new engine oil into lifter valley. Oil pressure sending unit
..(or mechanical oil pressure gauge) installed.
* Prime oil pump as desired. (No more air hissing out of the rocker arm spit holes.)
* Install/torque intake manifold.

At this point, the distributor and all 8 spark plugs are yet to be installed. Using the #1 cylinder exhaust port & matching exhaust manifold,
I prove to the engine builder that the most forward valve on the #1 cylinder *is* the exhaust valve. And when we crank the engine over in
the normal direction of rotation (clockwise as seen when facing the front of the engine) enough times, we will eventually recognize the pattern
of almost 360° of crank rotation with NO valve activity, followed by the exhaust valve opening & closing, followed immediately with the intake valve
opening & closing.

Once the intake valve closes, the very next time we see the timing mark on the harmonic balancer? THIS is the TDC we want. I have found time
and again that by getting the engine assembler's head sync'd up with the expected cam activity, then the distributor goes in...with confidence.

* Now that the distributor is in, go ahead & install the valve covers.
* And once the valve covers are on, now it's time to install the spark plugs, wires, etc.

****

Here's why we experience misfires when the dizzy goes in 180° (cam degrees) out, no extra charge.

If you look at the red splat above, the firing of the spark plug will ignite the inhaled combustible mixture and push the piston down the power stroke.

But if you look at the purple splat above, the exact setting of the distributor will decide if you are going to create a backfire in the intake -or- out the exhaust.
If the dizzy is a little advanced/BTDC, then the probability will be a backfire out of the exhaust pipe. By the same token, if the dizzy is retarded/ATDC,
then the probability will shift to a backfire through the opening intake valve.

Essentially, exactly where the distributor is set versus the closing of the exhaust valve and/or opening of the intake valve will determine what you experience.
For at cranking speeds my working theory is that a out of sync spark plug firing will also light off whatever is behind whichever valve is still open when this occurs. (!)

And of course the bigger the cam (more the duration + smaller the lobe separation angle) the more the possibility exists for both intake & exhaust valves
to be open during the overlap period. So engines with big aftermarket cams can give you either or even both intake & exhaust backfire symptoms.

...but I digress. With a stockish short duration cam appropriate for a heavy GMT400 vehicle (& especially if the lifters aren't fully pumped up yet) it would
be possible to get the distributor 180° out (cam degrees, 360° out crank degrees) and have steady cranking w/no misfiring.

All of the above is not absolutely necessary. You could just use the wine cork mentioned by @Sean Buick 76 in reply #8.

Or you could rely upon a TDC whistle like the one seen in this short video:

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But if you are leading a son/daughter/grandson/granddaugher/niece/nephew through their first engine build,
try showing them how the valves behave -and- use the cork. Make them predict which valve will open next,
and when the cork will pop. And then show them that because of the curved drive/driven gears that the dizzy
has to be started a little further CCW than the desired final orientation of the distributor rotor to the #1 spark
plug wire tower.

The bottom line is that you can choose to just follow the recipe & cookbook your way through this part of the
engine build, but it's more satisfying to reason your way through and *know* that the distributor is installed
correctly.

****

I know that the OP has already got this all sorted out, but just wanted to append this here in case anyone
else researching a similar no-start might benefit from an explanation of the distributor to crank phasing
from a slightly different perspective.

FWIW --