TBI and low MPG advice

[lothar863]

I worked it out and I am getting around 4mpg which i think is low.

I was excepting more like 8-9

refresher 1989 r3500 with the 454 FI

I know I have a high idle problem
To sort that I have ordered a new TPS and IACV

I have also read that rebuilding the TBI could help

First question
which ac delco rebuild kit do it need?
I am finding it hard to get a solid answer on which part number which one is it?



Second question
I have ordered a 1 inch swirl TBI spacer Trans-Dapt 2535.
Anyone run a TBI spacer did it do anything for you?



Third question
I am seeing this Fuel injector body spacer and seeing that people are using it instead of or with the gasket to get more air space below the injectors.
Anyone try one of these and what did you see?


Fourth question
I am seeing fuel pressure springs ranging from 12 psi to 28 psi and a different adjustable regulator cap that has a screw and uses the stock spring.
Same thing did anyone use any of these and what were your results?


I am not looking to make MAD POWA. But Increase fuel economy and maybe a bit better power would be nice.

 

[bucket]

My TBI rebuild kits have always come from Napa. I've used the injector pod spacers a couple times, it seemed to increase mpg and improve top end power. Nothing drastic, but seemed noticeable.

4 mpg is absolutely terrible, I get at least double that with my crew cab dually and it's lifted, 4x4 and runs a carb. What is your timing set at? What do your spark plugs look like?

 

[shiftpro]

I would check to see if your parking brake is stuck on.

 

[lothar863]

I would check to see if your parking brake is stuck on.

parking brake releases just fine and the truck will roll freely...although it is a pain in the ass to push it.

My TBI rebuild kits have always come from Napa. I've used the injector pod spacers a couple times, it seemed to increase mpg and improve top end power. Nothing drastic, but seemed noticeable.

4 mpg is absolutely terrible, I get at least double that with my crew cab dually and it's lifted, 4x4 and runs a carb. What is your timing set at? What do your spark plugs look like?

I did finally find the plugs i bought for the truck. I have only pulled one and they are the same ac delco part i ordered. the plugs were older but the plug looked fine. i may just replace them anyways.

Advanced auto said they had a bdw rebuild kit and it should be in later today.

How about the springs?

 

[Camar068]

interested...

 

[shiftpro]

parking brake releases just fine and the truck will roll freely...although it is a pain in the ass to push it.

I was just kidding about the parking brake... you would smell nrake liner if it was. It's just that your mpg are so seriously out of the park.
I wonder of something is up with your transmission to cause this...?

 

[bucket]

I've never messed with the fuel pressure springs before. I've always left the pressure set the way the factory did.

 

[chengny]

This might sound sarcastic but it has happened to me before: check the exhaust system for fur/acorns etc.

If a vehicle sits idle for an extended period of time, it is not unheard of for mice to move in to the exhaust system and cause a restriction to gas flow. That condition can result in poor performance - and a decrease in fuel economy.

 

[Overland Suburban]

I would pull that 454 right outta there and trade me straight across for a good running 350 tbi engine with a rebuilt throttle body and new intake valve cover and pan gaskets! 150 lbs of compression across the board



Tracy

 

[Rusty Nail]

I would check to see if your parking brake is stuck on.

I laughed out loud but only because that was frigging hilarious. My dog looked at me crazy!

4mpg is HALF what it ought to manage.
Don't only consider changing the plugs...a tune-up is in order.
Fuel filter and stuff...**** man all kinds of things are way more important than messing with fuel pressure.
Did you ever chrck to see if the parking brake was stuck on or something like that? Maybe you have some stuff wrapped around your flywheel! Sheesh!

 

[lothar863]

I was just kidding about the parking brake... you would smell nrake liner if it was. It's just that your mpg are so seriously out of the park.
I wonder of something is up with your transmission to cause this...?

Just had a shop rebuild it and a brand new torque converter

 

[lothar863]

I've never messed with the fuel pressure springs before. I've always left the pressure set the way the factory did.

I am not the best at finding info on these engines. But from what I can find it sounds like the bowls the injectors sit in should get 12 psi but from the factory 9-12 was acceptable and the springs may weaken over time. I ordered the 14 psi spring to make sure they are getting enough pressure.

 

[lothar863]

This might sound sarcastic but it has happened to me before: check the exhaust system for fur/acorns etc.

If a vehicle sits idle for an extended period of time, it is not unheard of for mice to move in to the exhaust system and cause a restriction to gas flow. That condition can result in poor performance - and a decrease in fuel economy.

This is possible. I am not seeing anything but i did get some garbage out of the exhaust after first startup. Replacing all of the exhaust is on the todo list. I cleaned the acorns, nests, snake skins and other items off the engine when i started working on it. but i do seem to get a healthy amount of gases out of both tail pipes.

 

[lothar863]

I laughed out loud but only because that was frigging hilarious. My dog looked at me crazy!

4mpg is HALF what it ought to manage.
Don't only consider changing the plugs...a tune-up is in order.
Fuel filter and stuff...**** man all kinds of things are way more important than messing with fuel pressure.
Did you ever chrck to see if the parking brake was stuck on or something like that? Maybe you have some stuff wrapped around your flywheel! Sheesh!

Fuel filter was replaced along with cap, rotor, wires, and coil.
Every time i have put gas in it i have added a bottle of Lucas injection fuel treatment with it.
Nothing is around the flex plate.

I have the plugs i just couldn't locate them when i was doing the tune-up items.
I also havent checked the timing.
I have a timing light somewhere i will just need to find it
It sounds like the timing should be at 4 degrees stock but where is the best place to set the base timing for economy?
Also could someone link me how to get it to where I can set the base timing?

Also where does the ecm pull data for the fuel map on these?

As far as i can see i am not finding an O2 sensor in the exhaust.
Should there be one?

Does it pull from other sensors? RPM? Speed? TPS?
I do not have the speedo cable hooked up because the shop had the connection clocked the wrong way and i haven't got under the truck to rotate it back.

A little background I have always dealt with newer more electronic vehicles so I am a bit out of my element on it but trying to get up to speed.

 

[4WDKC]

Fuel filter was replaced along with cap, rotor, wires, and coil.
Every time i have put gas in it i have added a bottle of Lucas injection fuel treatment with it.
Nothing is around the flex plate.

I have the plugs i just couldn't locate them when i was doing the tune-up items.
I also havent checked the timing.
I have a timing light somewhere i will just need to find it
It sounds like the timing should be at 4 degrees stock but where is the best place to set the base timing for economy?
Also could someone link me how to get it to where I can set the base timing?

Also where does the ecm pull data for the fuel map on these?

As far as i can see i am not finding an O2 sensor in the exhaust.
Should there be one?

Does it pull from other sensors? RPM? Speed? TPS?
I do not have the speedo cable hooked up because the shop had the connection clocked the wrong way and i haven't got under the truck to rotate it back.

A little background I have always dealt with newer more electronic vehicles so I am a bit out of my element on it but trying to get up to speed.

Get a scanner on the truck to make sure all the sensors are functioning, check engine lights only tell you there is a probloem not what the problem is on these older trucks. My guess is the coolant temp sensor for the ecm and yes there should be an o2 near the manifold usually driverside, does this still have all of the stock exhaust on it? At 4mpg timing wont hurt mpg, it gets bad mpg because the truck is big, heavy and the engine is under powered and low on compression. Do all the free tbi mods, make your fpr adjustable and get a new pump for a 91 Camaro 5.7 tpi ep247 (IIRC) or 96+vortec truck ep381 make sure you buy actual AC Delco pumps as others are not equal to these. The stock pump might push 9 psi or 12 psi quality control was terrible for them. The new pump can push more fuel for any future upgrades. Also raising your fp may require at tune...