FAST EZ-EFI Poor Fuel Mileage

rawkinbones13 · #1 (**permalink**) 08-13-2012, 08:52 AM

I installed the FAST EZ-EFI on my 1958 Chevrolet Apache 3100 truck which has a small block Chevrolet 350 and a late model 5 speed transmission with an overdrive. It's a standard small block no bells or whistles, no boring, and no wild cam. I'm using standard plugs, standard plug wires, an MSD 6AL Ignition box, and a very nice MSD distributor. All new equipment. Stock exhaust manifolds and dual exhaust. Before I installed this system I was running a pretty basic quadrajet carburetor. Normally my overall fuel mileage was around 16 or 17 mpg. Since I have installed the EZ-EFI I am averaging 10mpg, I say again 10 MPG!

I drive this truck daily which was the main reason I decided to spend $2000 on a fuel delivery system. When I did my first base tune, my truck ran great, throttle response was excellent. Almost zero vibration in the engine and overall I was excited to get started with this EFI system.

As the days went by and the more I drove the truck the worse things started to get, it started idling rough. If the engine was cold it would cut off when I came to a stop. I noticed I had a bad spark plug wire and a I replaced it and the plug that was in the particular cylinder. I also had a small exhaust leak as well. ( A few problems I thought may happen after rebuilding an engine) After that I reset my engine to the base tune, and overall the truck still runs OK. Occasionally, the truck will back fire with me and it doesn't idle like a truck that has an EFI system installed. The system also seems kinda temperamental (I can take it on the interstate for an extended period and when I hit and exit the truck will run at a faster idle speed for some reason.) but the main thing that has really let me down is the crappy fuel mileage.

I would really like to get this problem resolved.I have spoke to the guys on the phone and they always seemed rushed. One guy in the tech department told me to lower the PSI on my fuel regulator to around 35 PSI and maintain the normal PSI (45 PSI) in the computer. Which didn't help at all. Another suggested I probably had an exhaust leak which I have checked numerous times without being able to find a single leak. I have retraced every wire I have on this unit to make sure nothing was cut or frayed. I have good ground connections either straight to the battery or to a good ground on the frame. Also, it's been a few months since I have tried to start over with a new base tune but when I look at my computer it still shows AL which I thought meant Auto Learn. Would the computer still be trying to self tune after months of running on a daily basis? Overall the fuel mileage is ruining my first EFI experience. I was really hoping to pull better MPG then what I was getting with my 40 year old carburetor.

Does anyone have any ideas what my problem could be? Or is there anywhere I can take this system to that could troubleshoot it for me? Like a certified technician? I have been beating my head against the wall trying to increase my fuel economy and getting back extremely thin marginal increases. I've tried different plugs, different plug wires, different fuel grades, fuel additives, and non-ethanol fuel. I may get a point (.) something increase. But not enough to justify the extra cost of a fuel additive, or a higher grade or God forbid non-ethanol fuel. It's getting to a point where I am thinking about just removing the system all together and going back to a carburetor. I hate to give up on something I spent so much money on. On top of that, I get ribbed by all my friends and especially my dad for getting "suckered" into paying so much for a system that gives me such poor fuel economy. It not only sucks for me but it also sucks for FAST considering most the the guys who are poking fun at me were considering buying a system for themselves at one point.

I'm off my soapbox now, and open to suggestions. Someone help me out please before I give up.

Frankenbean · #2 (**permalink**) 08-13-2012, 11:27 AM

The psi at the fuel system needs to match the psi set in the ECU. How is the regulator set up? Is it vacuum referenced to manifold?

It actually sounds like an exhaust leak somewhere near the O2, gives it a leaner reading that actual....so the O2 may show 13.5 when it's actually 12.5 or worse.

What do the plugs look like?

TurboNova · #3 (**permalink**) 08-13-2012, 12:50 PM

Start with the basics,

absolutly no exhaust leaks, no slip joints and no way for air to get into the exhaust stream.

Fuel pressure set to 43psi, lowering it does really nothing for fuel flow, also this is what the ecu is set at.

Fuel regulator is vac referenced to the intake manifold.

How is your fuel system routed? to the fuel rail then the regulator after on its way back to the tank. It can't be fed to the regulator first like a carb.

If all of that checked out the, what is your target A/F ratios? and are your plugs black? Or what do they look like?

rawkinbones13 · #4 (**permalink**) 08-26-2012, 09:34 AM

I didn't realize that anyone has actually replied to my thread. I was waiting on an email should have just been watching the board I guess.

I have checked and rechecked my exhaust leaks. Even went so far as to take it down the the exhaust shop and have them personally inspect everything to make sure there was nothing I was missing. As I had said before everything checked out fine.

I changed my fuel pressure setting on my fuel regulator back to what it was showing on my computer settings. I actually adjusted that back a few tanks after I was told to change it, I know nothing about EFI and logically it makes zero sense telling someone to do this.

All of my fuel lines are ran precisely the way it shows in the instructions, I have an in-tank fuel pump that is routed to the fuel rail, the exit port feeds to the regulator and the regulator feeds to the return line on my fuel sending unit.

I have checked my plugs and they all look great. I did have a problem a few months ago with cylinder 1. The plug was completely black and had tons of buildup on it, I took the plug wire off and replaced it and now it burns fine. It's still a little blacker than the rest but no residual buildup like before. Do you think that this can be a timing issue.

I didn't change any of my target A/F settings, they are the standard out of the box settings. The instructions doesn't go into adjusting any of these settings so I never would have thought to adjust them anyways. This is my first EFI ever. I willingly admit I don't know a thing about them. I just tried to follow the instructions the best I could.

Pantera Dave · #5 (**permalink**) 08-26-2012, 11:33 AM

Check for intake manifold leaks. You might just have to pull it and re-seal it.

I had rough running and backfiring, and after changing exhaust gaskets, plugs and plug wires, it turns out my problem was a leaky intake. Could also explain why your #1 is black.

rawkinbones13 · #6 (**permalink**) 08-26-2012, 06:00 PM

Pulling the intake manifold doesn't sound like fun, but if it worked for you I guess I'm going to have to give it a try. I just about exhausted all of my other efforts.

I finally have an O2 sensor error pop up on my system. Any ideas what this can mean? I've actually been waiting and hoping that some sort of error would pop up and maybe it would lead me to the culprit. I just didn't think it would take 8000 miles for it to happen. I see they have a new one for sale on FAST's website. Aren't these parts supposed to be interchangeable with most GM throttle bodies. Where I can go to Adanced or Oreillys and pick one up at the counter?

Pantera Dave · #7 (**permalink**) 08-26-2012, 06:14 PM

Originally Posted by rawkinbones13

.... Where I can go to Adanced or Oreillys and pick one up at the counter?

OEM O2 sensor is same as 2006 Cadillac SRX with the V8. Part number 17205.

An O2 sensor error could be a variety of things. It might be intermittent, and go away, or the sensor might be faulty. Hard to say. It is always good to have a spare in your parts box.

rawkinbones13 · #8 (**permalink**) 08-26-2012, 06:25 PM

Thank you Pantera Dave. I doubt this is going to solve my overall problem but it may help. Still don't want to pull that intake manifold but I guess it must be done.

Anyone have any thoughts about the updated driver for this system? I installed mine last year around late October.

rawkinbones13 · #9 (**permalink**) 08-26-2012, 06:28 PM

Not the driver update but the EFI system.

Caprimaniac · #10 (**permalink**) 08-26-2012, 06:34 PM

On the intake; wouldn't pull it..... Check that the bolts are still torqed to spec. You could check for leaks by using start- spray. It would make your idle increase it any leaks. (spray around the ports/ head area.)

I'd change the target AF's to 14 at idle & crusie and give that a try.