So, this is for anyone with a TPI setup in your car,

What type of gas mileage do you get (list gas mileage, motor, type of driving, driving style, gas type)?

I get about 11 miles to the gallon with my 305 LB9. I drive city (like, I hardly ever go on streets above 40 - maybe once a week), and my driving style could be considered aggressive, I accelerate quick (not to the point of spinning the tires, though in the rain I do that sometimes) and sometimes I just have to gun it for fun (I go to high school, so I'm sure you all understand), and I run regular or mid-grade.

Does 11mpg seem good for what/how I drive (I mean, I have about 98,000 miles on this engine)?

 

no!!!!!

 

when was your last full tune up?

what tire pressure u running?


all the info about my car is in my car domain, but i do mostly stop and go traffic 50 and under all week and some highway. I get about 160-170 miles to the tank before the gauge gets low. On average I can go about 180 before getting real low.

 

I get about 140, less when I'm really driving the car hard - which is usual (I generally fill up about after 120 miles - and generally get 11 gallons into the tank to get it full, so it's not empty).

Tire pressure, I don't know, but the tires are a month and a half old - Falkens.

Umm, last full tuneup.

The plugs/wires/cap/rotor were all replaced in July or August. New O2 was installed about a month ago.

The car isn't completely stock.

I have a BBK 67gph fuel pump, headers, no cat, flo-pro muffler, and I'm pretty sure the cam isn't stock.

 

I have an 88 5.0 tpi 5 speed and get 17-20 mpg never under 200 a tank though, I usually get 260-290 to the tank if it runs until its on fumes.

 

I have a 85 T/A 305 TPI, I get 18mpg around town and 24 highway w/AC
It has over 100,000 miles on it

 

Oh, also, it seems all the smog crap is taken off.

 

1983 G20 Van weighing in at about 5,500 lbs. Daily driven. 305 TPI, ported 187 TBI heads, 10.5:1 compression, PRODUCTION LT4 cam, Doug Thorley Tri-Y headers, TPI setup with all stock parts (modified by porting), with LT1 24# injectors, being run by a 1995 TBI PCM. With a 700r4, 2,600 rpm converter, 3.08 gears, and 28" tall tires, I am getting 22 mpg highway, 16 mpg city. I have a moderately heavy foot and I run 75 mph while on the highway with the cruise set.

 

Well, since it seems that I am getting absolutely horrible mileage compared to what I should be getting, what do you think it could be?

Like I said,

Plugs/Wires were changed late this summer (ACDelco/Taylor Spiral Core 8mm), as was the Cap/Rotor (ACDelco/Summit Racing).
The timing chain and cover was replaced in late June or early July.
The Oil has about 2000 miles on it (5W30 Pennzoil) - is full.
The Belts are new (changed with timing chain) and tight.
K&N Air Filter are in place
New umbrella valve seals were installed in July or August
New Fram Fuel Filter installed in August
New BBK 67gph Fuel Pump installed in August
4 New Falken Tires in September
Belts were retightened, a new O2 sensor was installed, new battery was installed and the throttlebody was de-carbonized all in late september.

 

Also, the car idles at 1200 RPM (stock is supposed to be 500-650?), and the TPS connector seems to have a bent pin in the middle.

 

tps settings must be spot on in order to get proper performance. mabie it all out of wack causing a bad dump of fuel all the time??

 

Not only does it have the bent pin (seems to connect, but it takes some force), but the top bolt is missing (?), so any adjustments I could've made if I could've gotten a reading from the voltmeter would've been worthless.

I adjusted the IAC to try and get the idle RPM down from 1200, and I got the screw moving - it didn't change the idle speed, though.

 

if the pin is bent on the sensor then replace it. and get another bolt too. you would probably get better mileage with the tps unpluged lol. than with a tps giving bad readings.

 

When my 86 TA had the 305, I got 18+ hiway at 60-65. (TPI, 700R4, 3.27 gears) I think with your modified motor, and city only, 11 mpg sounds about right. The 1200 rpm idle is wrong. Look into that. I now have a 406 TPI. With a 2200 stahl I got 20+ mpg at 75, with a 1900 stahl I get 24 mpg at 75-80. That's straight hiway driving on vacation, no city driving at all. I could add 1 mpg by going to larger rear tires, and straight gas is suppose to get better mileage than gasahol. My mileage figures are using gasahol. (Here in Iowa, gasahol at 89 octane is cheaper than regular unleaded 87 octane.)

 

Okay...so, my idle magically dropped to about 800...maybe it's getting used to the IAC screw being back so far...

 

Or you have an intermitten vacuum leak like me haha. Every time I start looking for the bugger, the engine runs fine. Oh well, I'll replace all the vacuum lines when I replace the EGR valve.

Also, check your fuel pressure when you turn the car off. It should hold 40-50psi for quite some time before dropping off (at least 5 minutes, maybe more). If it drops off right away, you could have leaking injectors.

 

Hell, I'm not even sure the EGR is in my car anymore. With all the smog equipment gone, and all the tubes cut off and the holes welded shut on my TES headers, I'm pretty sure there's no EGR, unless I don't know where to look.

 

the egr is under the runners and upper plenum , towards the rear of the engine, it's a round diaphram.

 

All right, I've seen that - it's still in place. Where does it connect to (aka, where are possible vacuum leaks?)

 

I have a 305 TPI LB9 and it gets about 18 in the city, 24 on the highway...so you definantly got a problem! lol

 

Well the EGR system has two vacuum lines. A source vacuum (bottom of throttle body to solenoid, by coil) and the switched vacuum (solenoid to EGR valve). You also have a short line from the plenum then down to a check valve, which Tees off into the cruise (if you have it) and the HVAC source line. There is another HVAC line which goes to the coolant diverter. Brake booster has a huge vacuum line going to it. Thats it for vacuum lines (unless I'm forgetting something). You also have the PCV lines (though they are not for supplying vacuum, they will raise the RPM if they leak) and the canister purge line going to the throttle body. If for some reason you have a MAP sensor, there is a line to that as well.

 

yeah without the vacuum line running to the EGR Valve the car pretty much could have a vacuum leak right at the EGR all the time...

 

Hmm, yeah, I'll have to have a look at all that ****.

Any easy way to test for vacuum leaks?

Also, when I go to check my timing, what is it that I am supposed to unplug so that I get the actual timing (not what the computer is changing it to)?

 

easy way to cheack for vacume leak.... I spray a light mist of brake cleaner around the areas that I think might be leaking and see if the engine stalls. If it does then you have a leak.

As for fuel mileage, I have a 350 TPI 150K miles and I get around 18 city and 24 highway, thats with AC on.
If I really REALLY drive it hard I have gotten 15mpg before.
I have NEVER got less than 230 miles before my fuel gauge got in the red.

 

Where do common leaks occur? I mean, I have no idea where to even begin looking to have an idea of where one might be.

The EST is what gets unplugged for checking base timing, correct? Is it one of those wires that plugs into the distributor?

Also, how do I "check" the injectors? I just want to look at resistance, right?

 

intake manifold base, vacume lines (they run lots of places) and the throttle body gasket. Anything that is under the throttle plate has vacume on it untill it fills the combustion chamber.

 

Well, I checked a few of the injectors today (not all because it got really windy out and I'd rather not have leaves in my engine bay), and they were checking at 10 Ohms of resistance. That's not correct, is it - they're supposed to be like 16, right?

I don't think these injectors look new - they're probably original.

Also - I just reconnected the CCV hose (on the passenger side of the intake manifold) to the valve cover breather (passenger side - where oil goes in), I'm sure that was helping... *rolls eyes*

 

That would deffinitely have a bit to do with the idle, after all it connects to the throttle body.

 

Didn't seem to affect the idle at all - but then again, I barely got to things to connect (since it was dark and I had a mini-flashlight).

But it...seems...to run a little better. We'll see how the mileage is affected.

Then I need to see what is up with these injectors...

 

replace the injectors... if they are ohming out at 10 then they are crap.

replace them all, i wouldnt be suprised if that also cures your fuel economy issue

 

And the ESC wire you have to disconnect to set the timing is a brown wire with a single connector over on the passenger side strut tower.

You'll also have to pull the battery cable when finished because having this disconnected while you check/set the timing will cause a check engine light.

 

Another common problem, especially this time of year as it starts to cool off, is the O2 sensor when you have headers. You almost have to convert to a 3 wire heated O2 sensor with headers or it won't read properly because it doesn't stay hot enough. The 3 wire is heated so this isn't an issue.

 

Yeah - mine's not there. It plugs into the distributor, which connector is it? The one closest to the center?

 

Nevermind on that - I know where it is.

I'm sure the fuel injectors aren't helping, and when I replace those, I'm gonna go ahead and put in an adjustable fuel pressure regulator, since I might as well (maybe).

I was thinking, since I have the hypertech chip, which says you're supposed to run Premium, would that be part of the problem, since I don't run premium?

I'm gonna fill up with premium this time and see what happens.

 

I drove across the USA a few months ago. I tried with A/C, without A/C, at 70 mph constant, at 100 mph constant. Nothing seemed to matter. I filled up my tank 11 times in 2.5 days and got 19 or 20 mpg every time. That's all highway, no traffic jams.

I know my timing is set at 8° when the factory setting is supposed to be 6° and I should probably check the TPS voltage. But other than that, I can't figure out why I can't get the higher mileage.

Synthetic oil, tires pumped up, fresh tune up, cleaned the entire engine spotlessly clean when the head gaskets were changed out. So there is no gunk in there (it was pretty clean anyways). Idles spot on at 650 RPM.

*shrugs and holds up hands*

 

Yup - it's just...weird.

Now, since the MAF is de-screened, can it cause me to get some bad mileage?

I've also read about "checking" the MAF by taking readings of the "A" and "C" pins...umm...where are these?

 

You shouldn't adjust the idle screw like a carb, that's why it didn't change the idle, the ECM changes back by increasing the Idle bypass air (IAC.)

 

Well, I did it like that article said...

 

same problem here, i think....

some time ago i scanned my engine via diacom, and it turned out that my blm&int values rise+fall....
i had about 12MPG (HIGHWAY ; most of the time 70-75mph, some kickdowns to 140mph) ;

so i dediced to fix that problem....
throttlebody, plenum, runners, egr, everything ripped off....
replaced my vacuum lines, replaced the egr gasket, the rings of the injectors, and the other gaskets (throttlebody, plenum->runners ; runners->manifold)

plugged in every vac-line, every connector is plugged in, too....
now my blm value is 160 while idling , while driving ~130-140 ; int while idling 128 (almost static) ; while driving "up and down".....



perhaps the "idle screw" could help me... fixed that blm problem 2 years ago perhaps this time it'll be the same?!

 

The IAC & TPS article is missing a step, the timing set connector must be disconnected before adjusting the idle screw.

 

And that is where... Is that the thing on the firewall that connects to the dizzy?

 

@mp81: it's the brown cable on the firewall at the passengers side!

i'll try this, too...

i think my problems come from a bad o2 sensor.
my cat is empty, perhaps the loss of backpressure is preventing my o2sensor to work properly... perhaps i'll try a heated sensor...

do you have a laptop with aldl cable& diacom?
this should give you more info what's going wrong with your engine!

greets from germany
alex

 

Well, I have a laptop but none of that other crap (anyone got info on that stuff?).

My ESC Seems to be on the drivers side firewall, but whatever.

 

Yes, it's on the passenger side - A qucik disconnect with brown wire, and yes the ESC module on the driver's side.

 

So, what...Just disconnect the ESC while I'm adjusting this?

 

If it has a set timing disconnect then don't disconnect the ESC.

Here's a reply I posted with the steps.
Just don't forget to reconnect when done.
https://www.thirdgen.org/forums/tpi/...ns#post3527297
https://www.thirdgen.org/forums/atta...gconnector.jpg

 

I just tried that...and nothing happed differently.

 

If you unplugged the set timing disconnect on the passenger shock tower (single wire, round connector), then there is no way the timing should not have changed while trying to set it. Should have also turned on the Check Engine light and require a battery disconnect to clear that when done. Sure you unplugged the right wire?

 

Don't mean to steal the thread but i've got a 305 with tbi at 121,000 miles on the enngine and get about 200 miles to the tank. is that normal of above average? cuz it seems i get more to the tank than most of you

 

I wonder if my SES light is burned out. How would I go about checking that?

I'm pretty sure it was the correct wire - it was brown with a round connector. Not on the passenger shock tower - there are no cables there. It was up on the top of the passenger firewall.