All this work to get it right and it's still a work in progress....What's next?

[Dajain]

Hey guys and gals!
OK, I have done so much to this truck and she still has a miss, problem shifting and really lacking power.
1991 454 TBI meshed with 4L80e transmission

The motor:
I'll start at the top.
New AC Delco injectors
New IAC
TBI rebuild kit
New vacuum hoses for the entire TBI set up
New MAP sensor
New cap, rotor, spark plugs, and wires
Eliminated the dreaded antifreeze coupler in the intake. Yes, it broke off. lol
Timing while operating temp is 4° BTDC
Cold, dry, WOT compression test showed 112 - 130 PSI on all the cylinders. I'm sure the numbers would be better warmed and a wet compression.
New O2 sensor
New starter
New 2.5" exhaust

Transmission:
New shift solenoids and manifold
New fluid
New wiring harness
still has the old speed sensors on it.

The problems....

The miss.
It really seems to have a hard miss under acceleration. Idle does have a slight miss
With the new injectors and ignition system, I would think the power would be greater than what it is. It is really doggish.
But, I wonder if my shift issue is connected.

The shifting:
Goes thru all the gears but takes forever to get up to 60 mph.
Starting out from a stop, it wants to stay in 1st gear. Let off the throttle and it shifts to second, but apply just a little throttle and she kicks back down into 1st gear.
Once in 3rd, don't even feel it shift from 2nd or into 4th. Shifts are very smooth.
I didn't replace the TPS. That could be the issue.
Maybe the speed sensors in the transmission are not reading properly?

I would really like to get this running the best she can. Does anyone have any new ideas what the problem could be.
Thanks in advance!

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[Schurkey]

The universal three recommendations:

1. Verify fuel pressure at prime, and under load.

2. You've already handled the usual "tune-up" items--distributor cap, rotor, plug wires, spark plugs. Verify PCV, EGR, and Evap/charcoal canister systems. Is your initial timing 4 degrees advanced WITH THE TIMING CONNECTOR DISCONNECTED? Does the electronic spark advance work? Verify the knock sensor system. Check for plugged catalytic converter(s). Check for brake drag, and low tire pressure.

3. Connect a scan tool, verify EVERY sensor and computer output. Check fuel trims when the engine is acting up/poor power.

 

[GoToGuy]

In this truck, a tow dually? What model engine? Stock 91 454 ? Big block uses higher fuel pressure than small block TBI.
What year is the 4L80E ? For a stock engine your already carrying a lot of weight. Should do a warm compression check just to see where it's at.

 

[Dajain]

The universal three recommendations:

1. Verify fuel pressure at prime, and under load.

2. You've already handled the usual "tune-up" items--distributor cap, rotor, plug wires, spark plugs. Verify PCV, EGR, and Evap/charcoal canister systems. Is your initial timing 4 degrees advanced WITH THE TIMING CONNECTOR DISCONNECTED? Does the electronic spark advance work? Verify the knock sensor system. Check for plugged catalytic converter(s). Check for brake drag, and low tire pressure.

3. Connect a scan tool, verify EVERY sensor and computer output. Check fuel trims when the engine is acting up/poor power.

1. The fuel pump is new and is putting out 36 psi at any given point. This makes me question the pressure regulator. Maybe it is faulty?

2. I did verify the PCV, but have not vacuum tested the EGR yet.
The timing was done at operating temp, the timing connector was disconnected.
I do have a new knock sensor which hasn't been installed.
Catalytic converter is no longer an option as a fault point. It has been removed
3. Scan tool is my next step. I have the MODIS and should be able to tap into all the info she's willing to provide. I'm not getting a check engine at all, so fault codes may not be present.

In this truck, a tow dually? What model engine? Stock 91 454 ? Big block uses higher fuel pressure than small block TBI.
What year is the 4L80E ? For a stock engine your already carrying a lot of weight. Should do a warm compression check just to see where it's at.

Yes, it is a dually.
It is a 454 Gen V. Yes, it is stock.
Fuel pump is putting out 36 psi.
It is a 1991 (Stock) 4L80e. RPO code shows it was stock in 1991. Probably not the original, but no way to prove either way.
I'm not sure another compression test would be as helpful as a bleed down test. Since the original milage is completely unknown, I think a bleed down might be more beneficial.

Rest of this is not in response to anyone. Just more info.

I also haven't given the motor the steam treatment and then followed with a seafoam treatment.

 

[1998_K1500_Sub]

I’d be very interested to see what the ECU is reading from the TPS. The odd shifting and unremarkable engine performance may be telltale.

Get that scan tool pronto, verify every sensor (TPS, O2, temp,…) and actuator (IAC,…) you possibly can

It’s a nice looking truck.

 

[1998_K1500_Sub]

Eliminated the dreaded antifreeze coupler in the intake. Yes, it broke off. lol

Please explain… all that comes to mind is little that hose in front of the engine that big blocks often sport.

Timing while operating temp is 4° BTDC

At idle, connectors opened at the ECU, it should be 0deg. On my 1995 S10 that’s how it works, I expect yours is the same.

Under same conditions, timing should increase 20deg when engine RPM is raised. This is a function of the ignition control module, not the ECU. Watch for this behavior.

Measured how, timing light? Does a ‘91 have timing marks that show more than simply TDC / 0deg?

Reconnect the ECU connection, watch the timing. Check this against what the ECU reports on the scanner.



You mentioned a “miss”. Do you feel it in the seat or simply hear it? Exhaust manifold leaks come to mind.

 

[Dajain]

Please explain… all that comes to mind is little that hose in front of the engine that big blocks often sport.




At idle, connectors opened at the ECU, it should be 0deg. On my 1995 S10 that’s how it works, I expect yours is the same.

Under same conditions, timing should increase 20deg when engine RPM is raised. This is a function of the ignition control module, not the ECU. Watch for this behavior.

Measured how, timing light? Does a ‘91 have timing marks that show more than simply TDC / 0deg?

Reconnect the ECU connection, watch the timing. Check this against what the ECU reports on the scanner.



You mentioned a “miss”. Do you feel it in the seat or simply hear it? Exhaust manifold leaks come to mind.

You must be one of the lucky ones where the coolant hasn't started to leak yet. lol
The connection I'm talking about is the coolant quick disconnect on the intake manifold, directly in front of the distributor which goes from the quick connect , to a metal line, to a rubber line. Do a YouTube search for this connector and you'll see many people that say it is virtually impossible to remove without the threads breaking off in the manifold. The connector is paper thin between the threads and the main body. It's actually a surprise they could tighten it up without it breaking. lol

And you are wrong about the 0 degrees. If it was any other engine, you would be correct but the base timing on a 454 is 4° BTDC at idle with the timing advance disconnected. Even says so in the repair manual.

Ummm, every Chevy motor I've ever seen where timing is adjustable (and this age) has timing marks that show more than just zero degrees. It's the little "sawtooth" marks on the timing chain cover. I think it covers all the way up to 10-12° BTDC. Not exactly sure what motor you have which has a single 0° timing mark and nothing else

The exhaust is 100% new for the engine block back. No leaks

This is a whole different beast than your S-10 apparently. Thanks for the input though

 

[GoToGuy]

You have total compression test high pressures. Then you have differential compression test to identify worn out areas, rings, valve's, head gasket, and such.
With intake off, changed the QD to a hose fitting,modified aluminum tube to hose bump tube, short piece of gates hose, no more QD.

 

[Dajain]

You have total compression test high pressures. Then you have differential compression test to identify worn out areas, rings, valve's, head gasket, and such.
With intake off, changed the QD to a hose fitting,modified aluminum tube to hose bump tube, short piece of gates hose, no more QD.

I haven't done a bleed down test yet and I'm not planning on pulling the heads or the intake unless I have to. With mileage unknown, We shall see.
I'll be tinkering with it a little today and I'll give it the steam treatment and do a full seafoam treatment and we'll see what kind of carbon comes out of the exhaust.

But, changing out the QD doesn't require the intake to be pulled. Granted, it would be easier to get the broken QD out of the intake that way, but the removal of the intake would make the entire job just that more time consuming. I had the broken part out in about 15 minutes with a little heat and an easy out.

 

[Scooterwrench]

Is the QD actually in the intake or does yours have the spreadbore adapter/riser under the TB?