Howell TBI excessive fuel consumption

[CJKen]

Installed Howell TBI in 2013 in my ‘85 CJ7 AMC 258 i6 / 4.2l . My mpg has fallen to 10 this past year. There is black smoke when I start it and at low idle - so running rich. It doesn’t stall. No codes. It passes CA smog inspection fine. The car is using too much fuel.

Changed: fuel pressure regulator, injectors, throttle position sensor, temp sensor to computer, oxygen sensor, and the computer. Still same problem. Troy at Howell now questions the fuel pressure: incoming and return line. Incoming is 12, which is fine they said. Return line pressure is 8. Howell says I need it to be 5 or less. Wonder why this has become a problem now, after over 5 years of getting 15-20mpg.

I can replace current 1/4” return fuel line with 5/16 or 3/8 as Howell suggests - but it still must connect to 1/4” fitting at gas tank. Seems trying to push more volume into the small fitting would create back pressure, not relieve pressure. I have tried everything Howell has suggested so far, and nothing has changed.

I tried researching this among previous threads/posts over the past few weeks. I just joined the forum tonight to ask for help. Anyone here have any suggestions? Ideas? I’ve got to figure out this fuel consumption problem.

 

[jfmcj7]

It was the worst mod I did on my Jeep. Dit is 3 years ago and between 2 shops they can't get it to work right. I am done. Called Howell several times myself and they are no help. If it was not for CA smog, I would have done an engine swap a long time ago. Good luck. Hope you get it sorted out.

 

[rogerlaredo]

I helped a friend with the same issues. A previous owner had replaced the fuel return line with 1/4" brake line. The AMC 258 i6 / 4.2l ran like . Replaced the return line with 3/8" and it has run perfect since.

 

[Lumpy Grits]

LG

 

[Torxhead]

Yup, there probably is a clog or kink in the 1/4" return line, that is way too much return pressure. Convert to at least 5/16" since you have to change it anyway. You can't do much to the return line size at the tank without major surgery, but swap to 5/16" from the throttle body back. I find it hard to believe you pass CA. smog with all that black smoke, There should have been a code sent, sometimes it takes awhile.

 

[PistolDave]

I have built several of these TBI setups from junkyard 88-95 GM pickup/van parts, same hardware that Howell uses. I have always used an in tank pump setup on mine and have never had any problems as many describe. All of the in tank pump setups I have used have 3/8 supply and 3/8 return fittings, so I have essentially zero return side pressure. TBI setups will not run properly with any significant return pressure. Running larger diameter line all the way back to the tank fitting may solve or at least help your problem even though it still has to pass through a 1/4" opening. There are a lot of frictional losses in long runs of small diameter tubing. To see an illustration of this, pickup a 15 foot piece of 1/4" fuel line and try to blow through it, then blow through a 3" piece, big difference. If you are interested in converting to an in tank pump retrofit system, check these guys out:

http://www.tanksinc.com/index.cfm/page/ptype=product/product_id=84/category_id=61/mode=prod/prd84.htm

PA-TBI is the model for GM TBI setups.

 

[Lumpy Grits]

Allow me to add-Use metal line as much as possible here.
OP-How did you get your Jeep to pass our SMOG test, with the smoke deal??
LG

 

[CJKen]

Thank you to everyone who has responded. I replaced the return fuel line with 3/8 stainless line today. I will let you all know what happens after I run a few tanks of fuel.

I wrote a lengthy post earlier about this, but when I went to submit it, it was erased and said I must post more than 3 characters!!! Frustrated. Went to check out help posts and found this has happened to many others. I asked for answers by using my iPhone to post as this computer seems unable to communicate with this forum. I am trying this one more time...