Gas milage

[Frank718]

Related to poor milage, my 170K mile relatively stock GN was getting very poor mileage. This was a gradual decrease in economy over time. I used to get 30 MPG on 95% highway driving, and 22-26 with mixed.

Eventually (100K miles later) , I was getting 12 MPG with 160 miles per tank, and I quit tracking it and started driving it less thinking my engine was just worn out. Then last year, at smog check time, it would not pass no matter what tuneup I threw at it. After failing 2X, I gave it one more shot and reduced the fuel pressure, or at least, attempted to. I hit a wall around 35 PSI. I could not adjust it lower?!?!

After a lot of head scratching, I determined that coupled with a Walbro high volume fuel pump, the fuel return line was too restrictive, resulting in high rail pressures at idle, 15, and 25 MPH tests. The BL numbers during these tests were in the low 90's.

My "Quick Fix" to get it to pass was to swap in an old low volume fuel pump, lower the line-off pressure, which reduced my high HC numbers to a point that it passed. I never drove it with this setup long enough to get MPG numbers, but the BL numbers were higher, around 105. Still rich, but enough to get it through and registered.

I have since replaced MOST of the return line, including the length up and into the tank with a mix of AN hose and aluminum 3/8 line, and put the good pump back in and returned the FPR adjustment to 43 PSI line off. I am now getting an average of 19 MPG, BL numbers much closer to 118. The one part of the line I have not replaced is the steel piece that runs from the connection near the Pwr Steering gear to the FPR. I figure this part still has some restrictions, but the replacement StSt Hard line I received was so poorly bent, I ended up putting the old one back in.

I still feel I have some restrictions in the 1 line I did not replace, resulting in some erratic BL numbers. For the most part, they are fine. But the intermittant stumble, lean out and over-rich conditions I encounter at various points in my daily 80 mile commute still occure from time to time. My increased mileage confirms this was a part of the problem.

One other thing worth mentioning: I did get an additional 2 MPG increase by fixing 1 vacuum line leak, so before going all out and replacing fuel components, I would make sure all vacuum ports and lines are checked! Some reduction in economy is due to the age/miles on not only the engine, but the car itself. Engines can be rebuilt, but we also need to consider the items that we rarely think about, like the fuel and vacuum lines we tend to "Assume" are OK! (My cracked vac line was inside some black plastic conduit and was overlooked for quite some time!)

Hope this helps!

Some times my car loops so I probaly have some vacum leaks. And I haven't change all the sensors yet,so that going to be my next step. I have a new fuel line from the rail to the filter, so I going to change the rest when I get the chance. Thanks every one for your help.

 

[Gary Wells]

This is a word for word quote from a post that did back in April of this year, and I still feel that it holds true.

I have had 5 turbo Buicks over the last 10 or so years, and did up until the last year or so, keep very accurate mileage logs on each car. On the route that I take to work is 25 miles, each way, about half city and about half freeway. and all of the 5 cars has averaged somewhere between 16.5 to 18.3, or so. All basically stock, a few with ta-49 turbos, minor mods, all stock gearing. A hi-po chip will generally cost about 1-1.3 mpg on the average. The '87 turbo Buick that averaged 16.8 or so was running a chip in it, and the '87 turbo Buick that averaged about 18.3 or so was a 10K mile car. Just for comparasion, my '02 Z06 on the same route will average about 19, basically about 1.3-1.7 or so better mpg. I am really curious about some of the turbo Buick owners claiming 30 mpg & so forth. I am also curious about some of the turbo Buick owners that claim 8-10 mpg.

 

[VadersV6]

6=8,
The return line being too restrictive with a high volume pump, causing your problems seems odd. There are far too many people running Walbros and not having this problem.
Ive replaced or fixed just about everything I can point at, which would contribute to poor mileage. I had a very low BLM problem for a long time. I had to drop the BLM offset on my extender chip down to 0 or 1, just to get them in a workable range. This was with FP at about 38. Mike at fullthrottle hooked me up with a new translator chip, after he said in a post, that the extenders require a new translator chip. It doesnt say this on their site, and I asked why. He mailed me a new 6.22 chip for free, and I still had the same issue. But I cleared the computer and switched the translator over to 3" MAF and suddenly my problems disappeared. I could run my BLM offset at the default 8, and have had great BLM's since. Its weird because I have a 3.5" MAf, but Mike said that well, thats just the way it is on some cars. I appreciate what he did for me, but I cant swallow that. If you have to switch to a completely different calibration for it to work right, then there is something very wrong. Supposedly my extender chip isnt supposed to have MAL codes, but it does. All the ID numbers on the chip, check out as well. Ive always been plagued by a code 45 (rich O2), even though Ive replaced O2 sensors and my BLM's look fine...and replaced all ignition components, which can cause them too. Usually comes after about 500 miles. Deep down there is something not right, and Ive given up on trying to find it. If I suddenly found some deep hidden issue that brought me up into the 20's in mileage, I would be ecstatic! Alot of people have compression in the 120's to 130's. Mine are 150..so my cylinder pressures are high, which would make me think I should be getting even better mileage. Has anyone here ever gotten a code 45 from a clogged exhaust? Thats the only thing I havent replaced. Its got some no name small cat welded in...flanges cut off and all....thanks you half assed dickhole!
By the way, you shouldnt be able to run a stock MAF with the extender chip. Ive done that, with the translator not hooked up, and the car ran GREAT! What the hell is that all about???

 

[Dreamcar86]

The engine has about 20,000 since the last owner rebuilt it.The car also has 36lb blue tops, hi pressure regulator,wabaro 340 with hot wire,210 205 cam, J carter chip.One other thing is the fuel gauge don,t work and I just caculate the mile and the gallons I put in the car.Last time I filled up the tank and got 125 miles and the car ran out of fuel.Thanks for the help.

When was the last time that you gave the car a good tune-up? Always start with the basics and keep it as simple as possible. These are little V6 motors and unless you are constantly under boost should get at least 20 MPG on the highway. Does the car smoke? I am not familiar with Jay Carters chips, does it have the capabilities to adjust fuel or timing? What is your fuel pressure? The more information you can give on what you have done or not done to the car will help track down the problem. Go to Turbo Regal Web Site to the section titled "Spring Cleaning" and make sure these items have been addressed. Then go to the quick reference page and make sure you have a scan tool and see if your parameters are set properly. I think someone already mentioned it but I would check for vacuum leaks. Have you jacked the car up and followed all the fuel lines? On the rear passenger side there are some rubber fuel lines that connect the metal lines. Make sure the fittings are tight and the rubber is not cracked.
Hope this is somewhat helping.

 

[justabuickv6]

I just filled up again this morning. 17.1 MPG mixed driving and that was getting on it a bunch. I always fill up at the same station and same pump to remain accurate.

Go by MPG. Don't go by how many gallons you get before another fill up. For example, I filled up this morning. All it would take was 13.1 gallons. My trip odometer said 225. So, if I would have driven it until it was dry, I could have gone another 66 miles. I could have really gone until the trip was 291. Would I ever do that? No. Although the pump and sock is new, the tank isn't so I am sure there is some trash in the bottom.

Does the tank hold 17 gallons?


105k miles. Stock motor.
PT52, THDP, 60lb injectors, Alky chip 24/19, 3600 9x11, PS intercooler.

 

[madhat]

I've put 17 gallons in before :O it was starting to buck though...

 

[6=8]

VadersV6:

Like I said: Restricted fuel return line was a long shot for Frank718, but for me, it was not odd: It was my problem.

I could not adjust my fuel pressure lower than 38 before I changed the return line, and now that I have, I can adjust it down below 20. These comparissons are using the same pump and same FPR

I always thought it strange after making FPR adjustments, putting the vac line back on never dropped the pressure all that much... a 2-3 PSI drop was all I was getting. The return line, in my case, was preventing pressure regulation.

Frank 718:

Give this a try: Its easy and takes 15 minutes to setup if you do not already have a fuel PSI gage connected: Just see how low you can dial the fuel pressure, line off, assuming you have an adjustable regulator. If you cannot manually adjust it to go below a particular pressure, say 35 vac line-off, you either have a bad FPR, vac leak, or you have found the limit as to how much the return line can take back to the tank. Think about it... What is the fuel pressure supposed to be when you put the line back on? In my case, it was my limit... 38 PSI at idle. NOT good for emissions tests or MPG. If you have a non-adjustable regulator, you will need access to a hand-held (Mighty Vac) vacuum pump to test FPR operation. Simulate a high vacuum (15-20 In Hg) for Idle/no-load and see what the pressure is. This should result in low fuel pressure. No vacuum = Engine under load (Line-off) and should be near 40 PSI.

I'm also attempting to point out that fuel lines, in general, are now suspect in any fuel troubleshooting efforts, and our thinking may need to expand a bit. Our cars are 20 - 21 years old now... The fuel lines are not stainless, and can suffer from corrosion, build-up, even rust! Not so odd anymore.

Long shot as a problem in Frank718's case? Maybe. But, maybe not as long of a shot as it used to be!

PS: My suggestions in changing pressures are for diagnostics only. Please remember to adjust the pressures back to regular settings. Most recommend 43 PSI with the vacuum line off.

 

[justabuickv6]

Thanks for the info 6=8