Diagnosing miss at high RPMs for VP 7.4GL with EST electronic distributor

[SpineyNole]

So my Volvo Penta 7.4GL with an EST electronic distributor was missing at over 3000 RPM. The engine runs fine at lower RPMs. This is a relatively new GM gen VI engine. The mechanical aspects of the engine are excellent with compression values of 195 to 200 PSI on all cylinders. I was originally running with regular grade gasoline (86 octane). I have taken the following steps to attempt to diagnose the problem:
1) I checked and adjusted the timing (I have an earlier thread on this). Once I re-timed the engine I get good performance (no miss) until I reach 3800 RPM.
2) I verified that I have over 12 volts going to the ignition coil and ignition module, at idle and while running at high RPM.
3) Even though my ignition coil tested good, I installed a brand-new high quality ignition coil. This did not fix the problem.
4) I replace the off-engine and on-engine fuel filters. This had no effect.
5) I used a portable fuel tank with new mid-grade fuel (89 octane) and temporarily hooked it into the fuel system. This had no effect.
6) I replaced the distributor cap and rotor with new ones. This had no effect.
The spark plug wires are United Marine marine spark plug wires with 240 hours on them. I wouldn't think that the spark plug wires would cause this. The spark plugs are new. At this point, I am starting to believe that the ignition module or pick-up coil in the distributor may be bad. Only other thing I can think of is that I might be running lean at high RPMs. Does anyone have any other ideas or can identify something that I have missed? Thanks for your help.

 

[SpineyNole]

My ignition timing exercise is here:
https://forums.iboats.com/threads/timing-curve-for-vp-7-4-with-est-ignition.755756/#post-5762735

 

[Scott Danforth]

If you have 195 to 200 psi on all cylinders, your gauge is off by 50 psi. New motor is 150 psi

What is your base timing set to?

 

[SpineyNole]

If you have 195 to 200 psi on all cylinders, your gauge is off by 50 psi. New motor is 150 psi

What is your base timing set to?

Nope, 2 sets of gauges show the same. This Gen VI engine has 200 psi compression. Base timing is now set to 2 deg. BTDC, was originally 10 deg. BTDC before the issue showed up.

 

[Scott Danforth]

Nope, 2 sets of gauges show the same. This Gen VI engine has 200 psi compression. Base timing is now set to 2 deg. BTDC, was originally 10 deg. BTDC before the issue showed up.

To get to 200 psi, that is 14:1 compression. Merc spec is 150psi cranking

The. Stock Gen VI is. 9.4:1 motor

Set your timing to 10 BTDC

Check the quality of your fuel

 

[SpineyNole]

Your numbers are wrong. Also, you obviously are not reading the posts, I already used fresh 89 octane fuel. There is nothing wrong with the fuel.

 

[Scott Danforth]

https://pubs.volvopenta.com/publications/7740288

 

[dubs283]

We can absolutely rely on OPs numbers, they have been verified. Are they okay according to spec? Proven by intergoogle searches. Yes.....or no.

The main factor is there is consistent readings from all cylinders, we can now rule out compression/engine lower mechanical issues.

Based on info provided and suggestions, I would tell OP to look at the fueling system from tank to intake, all aspects. If all is sound, verify timing advance. IME most 7.4 BBC can handle up to 44ish degrees of advance, naturally aspirated

 

[Scott Danforth]

We can absolutely rely on OPs numbers

If the OPs numbers are right, he has a diesel.

Spec for a stock Gen VI 7.4 GL (L29) is 9.1:1 compression, 330hp and 150psi cranking compression numbers

 

[Tail_Gunner]

More than probably your harmonic balancer has slipped, 2 degrees base timing is pathetic for a 454 vortec.

Or the balancer was misaligned on this new engine..Or the distributor installation?

Rich mixtures requires less timing
Lean mixtures require more timing.

This is all about flame propagation, rich mixtures are densely packed. Flame travel is reduced to total combustion known as detonation. Lean mixtures are loosely packed it takes more time for the burn to complete.
Overly simplistic...Yes it is... So let us use a complex reasoning process.

Understanding Ignition Timing: Making Maximum Power Means Knowing the Science - Engine Builder Magazine

In a spark ignition internal combustion engine, the purpose of advancing the timing of the engine spark is to get past ignition delay. Ignition delay occurs during the time that it takes to fully ignite the mixture with a spark plug.

www.enginebuildermag.com

 

[Tail_Gunner]

Nope, 2 sets of gauges show the same. This Gen VI engine has 200 psi compression. Base timing is now set to 2 deg. BTDC, was originally 10 deg. BTDC before the issue showed up.

That cylinder pressure would get a compression ratio of about 10.5 something. Meaning you would be using a engine that has been hotroded a smidge, also known as slightly tinkered.

 

[Scott Danforth]

That cylinder pressure would get a compression ratio of about 10.5 something. Meaning you would be using a engine that has been hotroded a smidge, also known as slightly tinkered.

Closer to 13.5:1