L31 with LT1 bottom end

[Crazydavez28]

If the geometry is good like you say, you don't need shorter pushrods. You need longer rocker studs.


Check the fuel pressure, connect a scan tool to see what the IAC is being commanded to do. Wouldn't hurt to verify that the IAC passage is clear of carbon/varnish/sludge, and the EGR is seating.

I don't know how this could be related to oil pressure since you should have "plenty" of pressure when the engine is cold.

The trunions on these PRW rockers are huge

Never thought about the EGR I will check that out. BUT I used an old intake manifold off the shelf and never swapped the egr valve. The old knocking motor had none of these issues. I did do the throttle body mod and left the rivet holes open. Started and idled great but would push thru the converter at stop signs. I plugged the two holes and this stumbling issue started.

 

[Supercharged111]

Look for vacuum leaks. My stupid evap purge solenoid was always flowing which effectively made it a vacuum leak. Starts and idle smoothed out a bit after I fixed that.

 

[Crazydavez28]

Update: Chinese distributor should be avoided at all costs. Rotor tab was broken off, stem diameter was .005" undersize!!!, and it did not have an oil seal under the cam reluctor and oil was just starting to get thru... Gear looked good though that's the only part I am using in rebuilding one I had one the workbench.

Intake manifold is a disaster, thought I broke the gasket during assembly but in fact the lower manifold cracked on the front ear under the AC compressor. Hoping to get the old lower salvaged and put this thing back together today.

Edit: got it back together and it runs pretty good now I am suspicious I had the wires for 4 and 6 swapped or the broken tab on the rotor was cutting out on number 4. Oil pressure is a good 10-20 psi better on the dash and the fuel pump runs for 5+ seconds when you shut it off.

 

[Crazydavez28]

Look for vacuum leaks. My stupid evap purge solenoid was always flowing which effectively made it a vacuum leak. Starts and idle smoothed out a bit after I fixed that.

I checked my purge solenoid when I switched manifolds and it was working. I'm thinking the problem might be in the tune but I'm still a noob at this black box. It starts good when cold but gets cranky when warmed up.

It seems rich when it stumbles around starting up. I cut the fuel prime pulse a little and was wondering about the stall prevention dumping fuel. I am going to try going the other way with the fuel prime but the weather here today sucks.

I upped the idle speed to 700 and that smoothed out that problem. It has remote start so I want it to fire right up like stock.

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[Schurkey]

Fuel prime has NOTHING to do with rich/lean. The injectors aren't firing during the "prime". If they are firing, it's because the engine is cranking, the injectors are controlling fuel flow into the intake manifold not the fuel pump.

 

[L31MaxExpress]

I checked my purge solenoid when I switched manifolds and it was working. I'm thinking the problem might be in the tune but I'm still a noob at this black box. It starts good when cold but gets cranky when warmed up.

It seems rich when it stumbles around starting up. I cut the fuel prime pulse a little and was wondering about the stall prevention dumping fuel. I am going to try going the other way with the fuel prime but the weather here today sucks.

I upped the idle speed to 700 and that smoothed out that problem. It has remote start so I want it to fire right up like stock.

This truck gets a little attention around town

You must be registered for see images attach

Are you tuning the Black Box? Are you using HP Tuners?

 

[Crazydavez28]

I'm tuning the black box with EFI Live. I did some tuning on my 0411 454 but the Black Box seems pretty bare bones to make a truck run.

I'm talking about the initial fuel pulses not fuel pump prime. I need it to fire up and idle good but it stumbles around for 3-5 seconds and then clears up.

I got a new MPFI spider for this build and I am beginning to wonder if i need to tweak the flow rate any.

 

[L31MaxExpress]

I'm tuning the black box with EFI Live. I did some tuning on my 0411 454 but the Black Box seems pretty bare bones to make a truck run.

I'm talking about the initial fuel pulses not fuel pump prime. I need it to fire up and idle good but it stumbles around for 3-5 seconds and then clears up.

I got a new MPFI spider for this build and I am beginning to wonder if i need to tweak the flow rate any.

Try 22.1 opposed to the 23.1. That is what GM used on the later 4.3s with the factory MFI spiders.

I have VE, MAF and Spark tables I could copy into Excel from the LT1 cam L31 suburban my brother had. It was running long tubes and a ported intake base. Might run a little rich if your setup does not pull as much airflow.

 

[Crazydavez28]

Try 22.1 opposed to the 23.1. That is what GM used on the later 4.3s with the factory MFI spiders.

I have VE, MAF and Spark tables I could copy into Excel from the LT1 cam L31 suburban my brother had. It was running long tubes and a ported intake base. Might run a little rich if your setup does not pull as much airflow.

Those tables would be helpful. I have made some changes to the VE table to try and lower the LTFT. they were maxed out at 12.5 now I see -3>8% but dialing these in will be a learning experience. FYI this is a comp marine cam and should flow better than stock.

 

[Crazydavez28]

Try 22.1 opposed to the 23.1. That is what GM used on the later 4.3s with the factory MFI spiders.

I have VE, MAF and Spark tables I could copy into Excel from the LT1 cam L31 suburban my brother had. It was running long tubes and a ported intake base. Might run a little rich if your setup does not pull as much airflow.

Those tables would be helpful. I have made some changes to the VE table to try and lower the LTFT. they were maxed out at 12.5 now I see -3>8% but dialing these in will be a learning experience. FYI this is a comp marine cam and should flow better than stock.

 

[L31MaxExpress]

Those tables would be helpful. I have made some changes to the VE table to try and lower the LTFT. they were maxed out at 12.5 now I see -3>8% but dialing these in will be a learning experience. FYI this is a comp marine cam and should flow better than stock.

I forgot you had the marine cam. Was thinking it had the LT1 cam. What I had is probably still a better starting point.