[Hercules2221]

I just finished rebuilding my first 454! AND I havent had the engine explode and shoot a rod through my thigh. Runs like a top, but here is the question: after putting a couple extra performance parts on the engine, it seems to want to run way advanced. Sounds like it is going to die if I put it where the manual suggests at 4 BTDC. Right now, it is off the charts. I cant even tell what my timing is because the mark is showing up before it even hits the timing shield on the timing cover where I get my readings. If I had to guess, it is probably around 20 BTDC at idle. It runs awesome, but I would like to find a way to fine tune this thing. Any ideas on how to get the timing right to get the most out of this engine? My other concern was that I was off a tooth on my line up of the timing chain when I put that together, but wouldnt I be having other issues if that were the case? Like I said, it seems to run fine.
Just FYI, Yes, I unhooked the brown and black wire under the dash to eliminate the computer's interference before I checked the timing. And no, I dont have access to any fancy equipment or dyno. I wish I did.

Here is what I have done to the engine:
New bearings all around
New Lunati Cam & Lifters 60200LK 207 213 .495 .515 112-LSA
New double roller chain
New Speed Pro 10cc dome pistons
New piston rings that I filed to fit. All bores were in really great shape. I just honed them all and tightened up the ring gap a little.
I did clean up all the ports and did some bowl blending to get as much as I can out of the peanut heads.
I put an adjustable fuel regulator on the TBI to adjust the fuel pressure.
Everything else is pretty much stock.

1995 K2500 Suburban
Gen V 454 (TBI)
4.56 Gears
35" Tires
4l80E Trans

 

[chasracer]

If you didn't already, verify where TDC is and then consider putting a timing tape on the dampener. You will probably end up with a bit more initial timing that stock to satisfy the camshaft.

 

[johnsongrass1]

What I would do is get ya some good masking tape, 1" wide.
Calculate the degree's and mark those on the tape. Apply the tape on the damper. Mark the damper for reference. The tape will eventually come off but you'll have the marks for later
reference. I use finger nail polish. Bright orange. It's somewhat reflective and easy to see with the disco gun. A paint pen works too.

 

[ericnova72]

Without a chip retune or replacement, I suspect the TBI is never going to play nice with that cam spec and the computer is going to be wonky with the timing.

I'd guess when you try to turn the timning down then the TBI pre-programmed fuel table just can't get the fueling right. The over advanced timing covers up for that.

It is going to take more than just jacking the fuel pressure up with a adjust regulator to get it right.

 

[Hercules2221]

The tape is a really good idea. And I have been going back and forth with the idea of throwing a carb on this thing instead of the TBI. I need to do some more homework on the best carb, but for now, any ideas on how to get a better idea of where to put the timing until I can get a carb? The only thing I have done at this point is timed it based on listening to the engine. It's frustrating not knowing if I am getting the most out of this engine simply by turning the dist a little

 

[Hercules2221]

How would I chip this thing to run better using the TBI? The more I look into a carb, the more I don't really want to keep the TBI.

 

[BogiesAnnex1]

How would I chip this thing to run better using the TBI? The more I look into a carb, the more I don't really want to keep the TBI.

Back in the day there were a lot of people blowing PROM chips for these, today you’ll have to go to the web to see if anybody’s left. The last engines that got these chips for OBD1 systems was 25 years ago.

OBD1 TBI does not allow for much change to the engine before it hits it’s limits. The system basically looks to the ratios of throttle angle to manifold vacuum to RPM as the engine was designed by the factory. These combinations for operating circumstances are mapped into a PROM chip. When you start changing camshaft or any other things that affect these relationships the integration of a number (called an address) that represents the fuel and ignition settings for a given condition are no longer correct for the situation. Thus the modified engine runs like crap without a reprogrammed chip.

To modify to a carburetor is complicated by the 4L80E automatic as that transmission is operated by the computer so for shift points the computer is looking for engine RPM and throttle position. So before we even get to fuel system mods for the carburetor you have to adapt the carburetor you select to it mounts the throttle position sensor. You can also convert to a standard HEI but you have to supply a tach signal to the computer. It might also still need the vacuum signal from the MAP sensor, been a long awhile since I did one of these and my memory isn’t for sure on that point.

The TBI uses an electric medium pressure pump that is located in the fuel tank. It delivers about 15 to 20psi which is too much for a carb. You will need a bypassing regulator to take the pressure down to the 5 to 7 suitable for a carb. The bypassing regulator is necessary to revert burning out the pump as these are designed to use fuel flow to cool them, so these cannot survive a simple deadhead regulator. Your TBI has a built in bypassing regulator and the plumbing for this system is already in the truck. Now this gets tricky as the computer starts a count down when cranking the engine it is looking either for oil pressure or a tach signal to tell the computer the engine is running otherwise in a few seconds it shuts off the pump and you have to go back through the start sequence from switch off back to cranking.
This circuit can be retired to just drop the computer out of controlling the fuel pump relay, but this comes with the danger that in an upset accident there is no shut-off control on the fuel pump.p, so unlike a carburetor that sees internal fuel spillage that most generally stall the engine stopping the mechanical pump, but in this case without the built in safety features in the factory configuration the electric pump keeps in feeding fuel.

So it’s not that you can’t swap to a carburetor but it is a lot more complicated than meets the eye.

All of this is the big negative about these 87 through 95 trucks, they are not easy to modify whether looking at blowing custom chips or throwing the TBI out for a carburetor. It’s easier if you were starting with a manual gearbox or with a 350 ahead of a 4L60E as for the swap cost of a tranny controller you can just put a 700R4 in these things and get rid of the computer entirely when going to a carb and HEI.

Bogie

 

[Hercules2221]

I realized the same thing when I posted my last 2 posts. I think moving to a carb is going to require way more money than I want to throw into it. By the way, my 4l80e is brand new so I'm not about to just swap that thing out. New intake, New carb, New tranny controller, New distributor, New fuel pump, etc.... I think I will try and hunt down someone that can help me with a chip. If I'm lucky, someone knows someone that has one or still does chips

 

[BogiesAnnex1]

Try this link Mr. Harris may still be at it, he’s done this a long time.

TBI CHIPS Home

TBI CHIPS Home

harristuning.com

Bogie

 

[Hercules2221]

I did see the Harris chips and put in my trucks info to see what he says. By the way, I tried lowering the timing closer to where it should be today. I made it to about 12 BTDC and it sounded great, but as soon as I plugged the little brown and black wire under the dash back in, the computer kicked it back out to around 30 BTDC 🥴😒. It worries me a little because we are trying to take the boat out next week. I'm not sure how that's going to go.

 

[BogiesAnnex1]

There are no simple cheap ways of dealing with engines built since 1987 to the present. They are not intended to be maintained by the general public. The manufactures are designing ever increasingly complicated systems with ever higher levels of cross system integrations that make it very difficult for anyone but a factory trained technician to work on, forcing the buyer to be dependent upon the dealerships for maintenance. This has and is wiping out the independent garage and putting that money into the OEM’s.

I wouldn’t purchase anything newer than 1986 as pickups go. Even these have some computers but they are adjuncts rather than in line processing so they are easy to eliminate.

That said the 87 through 95s can be retro’ed with some mechanical effort. The cost of going to a carb while more than a chip needs to be considered with the fact that chips are often a hunt for the right combination, they frequently are not satisfactory on the initial attempts.

In your case you don’t need a transmission controller you can use what you have already by simply adding a throttle position sensor to the carb. These can mount in a manner similar to an electric choke or can be found in remote mount kits. With a conventional distributor you just need to tap the tach signal from the module to the computer. Obviously you need a fairly detail wire diagram for your truck. The other option is just don’t feed that data to the computer, the transmission will default to shifting at rev peaks and unmodulated does the shifts are generally late and abrupt.

There is also the possibility that your cam timing at installation is off as may be the distributor installation. Off by 20 degrees is close to a distributor gear tooth off. When you connect the black/tan wire the computer will try to get back to what it thinks is TDC. The problem is that OBD1 does not use a cam or crank position sensor so this is being done on some programmed assumptions about the position of the crank to cam to distributor.

Bogie

 

[lmsport]

call these guys Home - Howell EFI Conversion & Wiring Harness Experts

no one knows more about tuning TBI GM Products. I first used them 25 years ago for TBI conversions on Jeeps.

 

[ericnova72]

I did see the Harris chips and put in my trucks info to see what he says. By the way, I tried lowering the timing closer to where it should be today. I made it to about 12 BTDC and it sounded great, but as soon as I plugged the little brown and black wire under the dash back in, the computer kicked it back out to around 30 BTDC 🥴😒. It worries me a little because we are trying to take the boat out next week. I'm not sure how that's going to go.

That's normal, the computer is advancing it way up at idle for fuel economy and low emissions. The fact the computer does this is why you have to pull that interrupt connector out to set the base timing with a light.....otherwise, with it still plugged in, the computer tries to counter your every move.

The computer will drop that high timing as soon as it reads throttle opening from the Throttle Position Sensor(TPS) and decreased vacuum from the Manifold Air Pressure Sensor(MAP) of a engine placed under load and applying power.
The computer is basically doing what a vacuum advance used to do ....remember how you always had to disconnect and plug that to set timing in the old days?

 

[Hercules2221]

Okay, this is probably a dumb question, but can I run the truck With the brown and black computer timing wire disconnected? I am all for keeping emissions low and all, but.... Sometimes a guy has to sacrifice emissions for more horsepower. Sorry to all the environmentalists on the forum! 😁