K1500 Dizzy replacement choices

[nemesis_morte]

Ok guys i am looking at trying to push as much MPG out of my 1994 K1500 as i can. Currently im looking at about 11mpg. On the books for replacement are as follows;

changing from 1 wire O2 sensors to 3 wire sensors
Replacing all lights with LEDs
Replacing headlights with Xenon kits
Pre-heating fuel

Now the purpose for the above is to consume less power this less load on the alt. and the O2 sensors are old so they need to go anyway so i figure heated sensors will be good just need to run a 12v and ground.

Now for the big choice here. I have heard that a Vacuum dizzy provides better MPG and throttle response and of course is adjustable. I have a squeaking (very low but still) coming from my dizzy and it is just driving me insane so i have decided to snatch it and replace it. Currently it has an electronic dizzy. So my questions are as follows;

Will a vacuum dizzy profile more MPG?
Will switching to a vac dissy cause a CEL?

 

[ak diesel driver]

dizzy??? does it wobble when you drive it? please explain

 

[nemesis_morte]

Dizzy is short for Distributor.

 

[Turbine Doc]

Nemesis you realize this is mostly a Diesel site ???

So you'll have to speak in specifics when referring to gasser stuff or are you talking about the 5.7 Diesel, I've been around vehicles a long time and never heard of a distributor referred to as a dizzy.

So long as sensors are working your EFI distributor will give more mpg than vac one when combined with the TBI unit you have or do you have a carb instead of a TBI unit on yours?

It is common for low mpg from bad O2 sensors you say you have, how about the cat is it still on the truck, how many miles on the TBI injectors, you are a 94 when was last o/h of the engine, I recently did a o/h after 230 K miles on my 4.3L (little cousin to the 5.7 gasser) 90 GMC and it was pretty gummed up in the intake & EGR which will also hurt the mpg?

Need more historical info on this ride before we can make good recommendations.

 

[3500GMC]

Couple things. Your 94 distributor is totally electronically controlled, initial, curve and max timing. Check initial timing, if it's good the computer does the rest. SES light will activate if the computer doesn't see the proper distributor.

Preheating gasoline is the exact opposite of what one should do. Cooler air/fuel charge is more dense= more power and efficiency.

Save your money on the fancy 'bulbs' and use it for a complete tune-up. Get in on a quality scope. OTC Nemisys/Pegisys, snap-on verus, Launch X431, etc..

 

[THEFERMANATOR]

Unless you want to go carbed, then you are stuck with the stock distributor, no if ands or buts about it. If this is a 94 with an auto it should already have a 3 wire O2 sensor in it as well, if not one is a good investment. Also a set of short tube headers will help. As TD pointed out, new injectors can help espescially if this is a smal block or V-6 as they were low pressure TBI injection(in 94 the 454 went to high pressure injection to help with milage and emissions). A new set of injectors and an adjusteable fuel pressure regulator set up to about 15 PSI along with a 95 TBI pump for a 454 will also help milage out some as well. If you really want to boost the milage though, freshening the engine up and adding in a small EFI cam along with cleaning up the heads will be your best bang for your buck. I've done a couple now and they have all seen a 3 MPG+ improvement in milage, BUT if you port the heads wrong you can easily LOSE that much as well. Do the basics first to it like AC DELCO plugs, premium 8 MM wires, premium brass plated contact distributor cap and rotor, new fuel filter, new air filter, gut the hot air side of the intake so it only gets cold air, set your base timing up to about 4 degrees instead of 0, install a 3 wire O2(hook the positive side of teh O2 to the 12V+ side of the EGR valve solonoid), and replace the timing chain set if it has more than 150K miles and see where you are at. If you stil lwant more milage you will need to pull the engine and freshen her up with new rings and bearings, install a COMP CAMS XE249H hydraulic flat tappet cam indexed in to 2-4 degrees advanced with a COMP 2100 timing chain set, clean up and LIGHTLY port the heads(cut swirl port heads in teh wrong place and they will KILL your power and milage, clean em in teh right places and they will flat out HAUL A$$) and intake along with cut the horn off the throttle body, and go with a free flowing exhaust with some mid length headers.

 

[nemesis_morte]

Just a little history on the truck. The guy i purchased it from said it had a replacement engine dropped in it around 80k miles (unknown if its a 5.7l or 5.0l. Stock was a 5.7 but the replacement engine might very well be a 5.0l) on it the body has about 280k on it. The engine does like it has been replaced but most of the old parts were xfered to the newer engine so those parts were either installed incorrectly or just old so they started having problems. I have replaced almost every pully and part to the front end of the engine (such as tensioner pulley, power steering pump/pulley, alternator, water pump, fan/clutch, A/C compressor i replaced with a bypass, etc. The balancer and smog pump/pulley i havent replaced). It is a throttle body even though its a 94 its an early 94 so uses most all 93 parts such as 1 wire O2 sensors, etc. I have already pulled the TBI and cleaned it well as that was most of my problems (no vacuum) the injectors are pretty clean and spraying very nicely and checks out on the pressure. I already dropped a new fuel filter in as well. Other parts were electronic that has nothing to do with the engine. I am about to brake down the engine on the upper and lower half for replacement of head gaskets (just to be safe) the manifold has a leak on the left side so i am going to drop headers in, the oil pump isnt working that well or the screen is clogged ( reads 40 for a while till the engine heats up then it red lines to almost no pressure). I have pretty much replaced every sensor on that engine other than a few like the knock sensor, engine temp sensor and 02 sensors. New starter, clutch pack, clutch master/slave cylinders, etc also replaced. Pretty much i have replaced everything but the upper and under of the guts of the engine.

Any other ideas let me know ill take a look at all your suggestions are greatly appreciated. Thanks again guys.

 

[Turbine Doc]

On your list of stuff replaced I don't see cap-rotor-wires-plugs listed, I don't think you'll be able to retrofit a vac dist in it as PCM/ECM will probably limp when it doesn't see the electroninc distributor, have you looked into a better program in puter chip for mpg.

Your report of oil pressure drop off does cause concern, you need to verify with a mechanical gage what pressure is, if dropping off is real and not a bad sending unit you may be looking at an engine overhaul.

Before spending too much $$$ on bling stuff you need to investigate health of the engine in depth save the $$$ for bling for engine overhaul a worn out engine can cause poor mpg as well.