Just got back from towing my boat (7000 pounds) about 150 miles, and I noticed that I could hardly maintain 60 on the freeway. If there was any hill at all, I would fight to stay above 50. I averaged 9 MPG without the boat, and 5MPG with. The truck always seems to run rich, but no miss and no codes.

I have:

89 350 C6 410 rear end
5.8 roller cam crate engine
all new sensors including O2,
new fuel pump and filter,
new cap, rotor, wires, plugs,
ignition control module,
timing at 20 degrees, no pinging
new air filter, dual exhaust
cat removed, cherry bombs

Maybe I expect too much but my old Pinto had more power than this truck. Anything over half throttle does nothing. The throttle opens, but there is no change in the engine sound at all.

I checked the fuel pressure at an idle and it was good, but I haven't checked to see if the regulator has a leak. I will check that out tomorrow.

Any other ideas would be helpful. Thanks, Kurt

 

vacuum leak? thats what im thinking is wrong with my 300 its got the same thing low power horrible mpg and its running rich so u might want to check that out

 

Recently had drop in mpg and power. Vacuum leak, but mine was in the vapor line coming from rear tank along the frame; totally rotted. This line T's with front tank and then goes up to vapor canister B4 going to intake. Vacuum at idle went from 15 back up to 20 inches with the line repair.

 

I'm running 21 inches at idle. All new hoses

 

"New"= Days,weeks,months,1/2 yr.,almost a year?
What octane?What plugs/gap & how long in? stock or brass cap & rotor? How long running at 20 BTDC? Last time compression tested & basic outcome?How new is O2 do you have 1 or 2? If 1, did it ever have 2? Was the ECT sensor/switch specifically Replaced? When did it last run good & when it lost performance , was it gradual or all at once. Last one How did you go about modding your Base Timing? Similar to method for a 302 ? Here's my 2 cents (adjusted for inflation) Until yhe PCM enters "closed loop function", the engine's air/fuel ratio remains static, in a fuel enriched state. also Timing advance only occures perportionally to RPM. Basicly,the flat line version of a timing advancement curve. If you have a helper and a timing gun. Note timeing at idle and at 500 rpm increases to 4000 rpm before norm.op.temp. is reached (195F) Repeat after temp is reached & compare results. there should be an additional 24BTDC between 1500 RPM & all in by around 3500 RPM.

 

Engine and all attached sensors were replaced in Jan. The sensors and fuel pump were from Ford. The O2 sensor (single) and ICM I installed two weeks ago. I used brass cap/rotor and have been running 20 degrees since I installed the engine. I set the timing warm with the spout removed, then reinstalled and disconnected the battery for 10 minutes. No pinging, and I run regular gas.

The truck has 500 miles since the new engine, and it was dead when I got it, so I have no way to know how it was before. It's been the same since I started using it, I just never pulled anything until now. I can smell that it runs rich, and it has always burned around 10 MPG.

I don't have a tach in the truck, but the timing definitely advances nicely when I give it throttle. I checked the compression when I installed it and it was between 135 and 141 on all.

The temp comes up and stays on the m in normal but I will check it with a real gauge tonight.

 

Have you checked your Vacuum advance at the distributer?

 

Pinging or not, I'd get that timing back to 10º BTDC, then re-assess. Twenty degrees is a whole heckuva lot of advanced base timing.

Not to mention, 7000 lbs. is quite a bit for a 200-horse, 300 ft-lb engine. Like others said, too, I'd check your compression even though it's a new engine. Just because you didn't hear any detonation, doesn't mean it's not happening.

Jason

 

His engine should have computer-controlled timing advance, not vacuum.

Jason

 

FYI... An EFI motor has an electronic distribitor.. not a vacuum advance version.

Kurt:
Have you verified the fuel pressure? It should be about 35psi with vacuum and 43 without.