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  #16 (permalink)  
Old 08-27-2019, 12:52 PM
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Update.

I have a HEI unit from amazon. The icm crapped out after a few weeks of use. Still running the chinese(I'm assuming) ignition coil and cap rotor pickup. Will be replacing these soon. Yes I'm running a freshly rebuilt by me 700r4 with upgrades. I have not messed with the avs adjuster but I will be soon. Another thing you guys mentioned is reducing the gap to 0.30?? Right now I'm running the stock gap for vortecs which is 0.60 or 045. I also do have a fuel pressure gauge and it reads 6.5 -5.5 and fluctuates a lot. Not sure what might be causing the fluctuation. But it runs good in all conditions except when I mash the pedal all the way down. It does accelarate at a good rate with the whooooooooo noise but doesn't seem right. I also have not checked ALL my plugs to see how it's been running. Will be getting to it this weekend. Will be looking into messing with the avs. So do you guys think I should decrease or increase the avs opening? I can smell gas when I WOT. I will record a clip so you guys can see. Also the dizzy rotor has a bit of up n down play.

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Old 08-28-2019, 05:14 AM
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I've only had two occasions where this happened, and may be quite unrelated to your problem, however I'll mention them anyway.

Both were in boats, which are always under load compared to a car.

My Mercruiser 350 suddenly decided not to rev over 2400. After a lot of fiddling with the fuel system, it turned out to be the plugs. They were those ones with wire as the center electrode. As the gap widened through use, it became to large and acted like a rev limiter. New (regular) plugs stopped the problem.

A friend had a similar engine in a speedboat which had just been rebuilt. His wouldn't rev past 3000 rpm. We discovered the timing chain had been installed two teeth out.
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Old 08-28-2019, 10:29 AM
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Quote:
Originally Posted by Argess View Post
I've only had two occasions where this happened, and may be quite unrelated to your problem, however I'll mention them anyway.

Both were in boats, which are always under load compared to a car.

My Mercruiser 350 suddenly decided not to rev over 2400. After a lot of fiddling with the fuel system, it turned out to be the plugs. They were those ones with wire as the center electrode. As the gap widened through use, it became to large and acted like a rev limiter. New (regular) plugs stopped the problem.

A friend had a similar engine in a speedboat which had just been rebuilt. His wouldn't rev past 3000 rpm. We discovered the timing chain had been installed two teeth out.


Mine revs up all the way in neutral. Just not in drive. Could it be a trans governor problem ?
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Old 08-29-2019, 10:02 AM
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Check to make sure you are not using a short distributor rotor. A short one will be a gap between it and the distributor contacts of greater than .030” or more like a 060”. In the “old days” this gap was close to insure good ignition at higher RPM’s.

Even modern GM rotors are short yielding big gaps. Definitely NG.
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Old 09-12-2019, 10:23 AM
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Gap

So I haven't had much time to do my tune-up but I removed the number 1 and 2 spark plugs and sure enough I put them in right out of the box gapped at .60. Too wide of a gap I take it for the HEI?
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Old 09-12-2019, 10:32 AM
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.035 is plenty, bigger Gap and lean mixture makes the coil ans module work harder
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Old 09-13-2019, 12:16 AM
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Quote:
Originally Posted by boneste624 View Post
.... Another thing you guys mentioned is reducing the gap to 0.30?? Right now I'm running the stock gap for vortecs which is 0.60 or 045. I also do have a fuel pressure gauge and it reads 6.5 -5.5 and fluctuates a lot. Not sure what might be causing the fluctuation....

The Vortec engine came with sequential fuel injection and an ECM managed distributor. You have none of this stuff the Vortec engine spark plug gap does not apply. For a carburetor and ignition not using a discharge capacitor box you need to run a tighter plug gap, I use .030 to .035 that's for these electronically triggered analog ignitions. There really is little to be gained by wide gaps, it's mostly an emissions trick on modern lean running injected engines.



If you have an engine driven fuel pump the pressure will vary as the pumps diaphragm is worked up and down. You're seeing the end result of intake and pressure strokes of the pump. An electric diaphragm or solenoid piston pump will show the same thing, a turbo pump most likely would not show this depending on how well it's bypass is doing.



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Old 09-17-2019, 03:46 PM
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Update

So I bought a msd cap and rotor but could only use the cap because the rotor made contact with the weight's I think. It wouldn't spring back when I would twist it so I reused the one that came with my amazon dizzy. Also replaced coil. I removed all my plugs and gapped them to 0.30 to 0.35 Roughly. All of them were at 0.60 . I also switched vacuum source from ported vacuum to manifolf vacuum but it was idleing a little high so I switched it back. Do I have to set the idle screws again in order to run off full manifold vacuum? But anyways the car sounds a lot stronger at idle and picks up speed quick. But I still cant rev past 3000 in gear for some reason. Also have another issue now.... When I WOT it chokes, no backfires no noises just cuts off like no spark or fuel. I can give it half maybe 75 percent throttle and everything good but when I stab the pedal it does that. Heres pics of my spark plugs.
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Old 09-17-2019, 06:13 PM
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Lifters are pumping up and floating the valves. You need to install the so called “anti pump up “ lifters with a piddle valve under the pushrod seat. Those type lifters prevents pumping up at high RPM and floating the valves. Anti pump up lifters add 500 RPM before the standard weak valve springs begin to float the valves.

GM introduced anti pump up piddle valve lifters in 1967. However, standard lifters were installed in new GM engines until the early seventies or until the GM Plant inventory of those lifters ran out.

Standard lifters are installed in most aftermarket rebuilt engines today.

I wish I could have given you a easy solution to the problem of premature valve float. You will have to replace the cam, lifters and maybe the valve springs to solve that problem.
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Old 09-17-2019, 06:41 PM
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If pumping up is the problem, setting your lifters at zero lash would temporarily solve it. If mousfink is correct, that is.

A free try would be to adjust your lifters just at zero lash or even a tick loose, and see if it clears up. If it does, mousefink is probably right. If it doesn’t your problem is elsewhere.

How is the lash set now?
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Old 09-17-2019, 07:21 PM
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Quote:
Originally Posted by lmsport View Post
.035 is plenty, bigger Gap and lean mixture makes the coil ans module work harder

Hmm, trying to picture them "work harder". The module. It powers up the coil (tries to saturate it) the exact same no matter how wide the spark plug gap is. And the coil, it's in it's field collapsing cycle and nothing is going to make that field harder to collapse. Maybe a solar flare or something? Oh and no the lean mixture doesn't effect them either.
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Old 09-17-2019, 07:29 PM
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If pumping up is the problem, setting your lifters at zero lash would temporarily solve it. If mousfink is correct, that is.

A free try would be to adjust your lifters just at zero lash or even a tick loose, and see if it clears up. If it does, mousefink is probably right. If it doesn’t your problem is elsewhere.

How is the lash set now?

Purchased a L31 crate engine from gm so I never touched the valve lash. Revs up past 3000 in neutral just fine so I'm not really sure why not in gear.




Capable of 255 horsepower, the GM Goodwrench long block 350 engine was created as a drop-in replacement for 1996-2002 Chevy/GMC 1/2-ton and 3/4-ton applications. Its Vortec cylinder heads feature a swirl port design. Specifications
  • 2-Bolt Main Block (1-Piece Seal)
  • Nodular Iron Crankshaft
  • Powdered Metal Connecting Rods
  • Dished Hypereutectic Pistons
  • Compression Ratio: 9.4 to 1
  • Hydraulic Roller Camshaft
  • Lift: .414'' Intake, .428'' Exhaust
  • Duration at .050'': 191° Intake, 196° Exhaust
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Old 09-17-2019, 11:54 PM
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Quote:
Originally Posted by boneste624 View Post
So I bought a msd cap and rotor but could only use the cap because the rotor made contact with the weight's I think. It wouldn't spring back when I would twist it so I reused the one that came with my amazon dizzy. Also replaced coil. I removed all my plugs and gapped them to 0.30 to 0.35 Roughly. All of them were at 0.60 . I also switched vacuum source from ported vacuum to manifolf vacuum but it was idleing a little high so I switched it back. Do I have to set the idle screws again in order to run off full manifold vacuum? But anyways the car sounds a lot stronger at idle and picks up speed quick. But I still cant rev past 3000 in gear for some reason. Also have another issue now.... When I WOT it chokes, no backfires no noises just cuts off like no spark or fuel. I can give it half maybe 75 percent throttle and everything good but when I stab the pedal it does that. Heres pics of my spark plugs.

Your spark plugs look pretty close to typical.



The L31 you have uses a roller cam and lifters with self guiding rockers.


Switching the vacuum source may require resetting the base advance. The cam you have in there is the stock 250 hp SAE net test engine with fuel injection. It's pretty mild and shouldn't be a test for the lifters at 3000 rpm, but one can't rule out manufacturing errors. The valve springs are pretty moderate also, but they could be under spec and loosing control early on.


I really suspected plug gap with that distributor combo, I've used this on a several builds (including one of my own) an ran into that problem. The engines ran nice and pulled like gang busters right up to 3000 then nada. As the RPM's fell back the motors would come on again. A fresh set of plugs which were Accel shorty header plugs gapped at .030 and we're back to scalded ape when I stick the pedal to the floor. Another thing about that distributor is it takes the ProComp/Speedmaster 92mm cap and rotor, there is a nearly identical cap and rotor that I think is 90 or 91mm so if you get that rotor with the 92mm cap there is a lot of distance between rotor and cap.


One also can't rule out that the module isn't good without running a known good distributor in it. Module failures often follow this same profile. The module uses a unique set of contacts which might be vibration or moisture sensitive, I haven't experienced this but based on observation of this arrangement and the lack of a tight fit of the doghouse to the housing I suspect these could be problems with this distributor.


Another worry is that the supplied gear is not compatible with a roller cam and will result in excess wear of the gears. The proper solution is either the ProComp/Speedmaster bronze gear or a modified GM Melonized gear. I tend to shy away from bronze gears on the street as they wear fairly fast. This ProComp/Speedmaster distributor uses a GM sized .491 inch shaft but a larger diameter retention pin, so the GM Melonized gear needs to have the pin hole drilled oversize to accept the ProComp/Speedmaster pin (not difficult to do) otherwise the pin that fits this gear is loose in the shaft and will affect timing even if it doesn't break due to snap loads.



With the engine shutting off at 3000 without a lean backfire leads my suspicions to an electrical or valve spring problem rather than fuel supply. But as always I'm open to surprises.



Bogie
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Old 09-18-2019, 08:37 AM
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Hmm, trying to picture them "work harder". The module. It powers up the coil (tries to saturate it) the exact same no matter how wide the spark plug gap is. And the coil, it's in it's field collapsing cycle and nothing is going to make that field harder to collapse. Maybe a solar flare or something? Oh and no the lean mixture doesn't effect them either.
Lean mixtures are harder to ignite, you just learned something new.

Most HEI modules are current limiting, all GM built ones are, but some aftermarket ones are not so they are affected by the coil resistance, as voltage requirements increase, the coil and module have to disperse more energy.
Get a designer to explain it further, I worked with some guys from Chrysler designing fuel injection and spark control computers for the aftermarket back in the 1980's, I'm just a wrench puller though, they went on to work for multiple FI companies to this day.
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Old 09-18-2019, 10:02 AM
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Quote:
Originally Posted by lmsport View Post
Lean mixtures are harder to ignite, you just learned something new.

Most HEI modules are current limiting, all GM built ones are, but some aftermarket ones are not so they are affected by the coil resistance, as voltage requirements increase, the coil and module have to disperse more energy.
Get a designer to explain it further, I worked with some guys from Chrysler designing fuel injection and spark control computers for the aftermarket back in the 1980's, I'm just a wrench puller though, they went on to work for multiple FI companies to this day.

No, didn't learn anything new yet. I knew lean is harder to ignite.


Current limiting ... how in the world is that linked to spark plug gap? The module has NO way of knowing if the gap is small or wide or if the mixture is rich or lean. We are not in a thread about a computer controlled engine. This is a carbureted engine we are discussing. What does EFI have to do with it?
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