: Full Tune-Up Advice for low mpg



tbcaddy18
07-29-09, 04:10 PM
Just curious if anyone has any good ideas and advice about tuning or checking things for helping with low mpg.

I have a 1986 Fleetwood Brougham (RWD) with the 307 Olds engine. I usually get a 50/50 average of 14.5-15 mpg...my highest on the freeway was 18.3 mpg.

Is this normal or should it be higher for this model?...I've heard of others with this same engine achieving 23 or better on the highway.

Thanks for your advice(s)/insight(s)!

csbuckn
07-29-09, 04:32 PM
You can get a little better. The carb probably needs cleaning, decent oil and a tune up should do you some good. Your fuel filter probably needs changing. Its in the carb behind the gas inlet. My mileage is terrible but my carb is garbage. Or you can take about a thousand pounds out of your car somehow.

sven914
07-29-09, 06:13 PM
You could also use a fuel system cleaner. I recommend Gumout with Regane (http://www.carbuyersnotebook.com/wp-content/uploads/2009/05/gumout-regane.jpg). I use it about every three months.

If your car has rough idle, then you may have some vacuum leaks. I would go through the hoses and replace any that look brittle, and I would check to see if the routing is correct.

carnut
07-29-09, 06:17 PM
This is a electronic feedback carb. The solenoid inside the carb fuel bowl that controls the idle metering jets needs to be confirmed that it is set at a 30 degree dwell period, much like setting points to a specific dwell. Low dwell setting will keep the metering rods extended too far and affect mileage badly. Too much dwell will cause a general lack of performance, running too lean. Hardest part is finding a mechanic older than the car to check and adjust the dwell. A fuel filter, plugged, will cause a lower top speed because the fuel will not flow quickly enough as you give it more throttle.

tbcaddy18
07-30-09, 01:31 AM
Thanks for your posts.

I recently changed about 80% of my vacuum lines, the rest were fine. I also just changed my distributor cap and rotor. Im also gonna give the gumout regane a try.

I do clean my carb with a carb cleaner once in a while, but how exactly are you supposed to do it and for how long should you keep spraying the inside?..can too much of the carb cleaner damage something inside the carb/engine?

How often should the fuel filter be changed?...I replaced it about 3-4 years ago...

csbuckn
07-30-09, 08:34 AM
Your carb has some sensors on it so I wouldnt spray for more than a few seconds at a time. Have you did the plugs and wires recently? Some people say that the filter should be replaced every couple of years but I think you should be alright unless your tank has a lot of rust on it. As long as you know its been replaced.

tbcaddy18
07-30-09, 11:39 AM
Yes, I replace my plugs about 3 or 4 years ago with bosch platinum series and I replaced my wires about 1-2 years ago.

Should I keep spraying into the carb (few second intervals) until the can is empty?..or just a few sprays?

carnut
07-30-09, 04:55 PM
I think you might find that mileage will improve with regular AC plugs RATHER THAN BOSCH PLATINUMS. Personally have not had good luck on this old of a car with this new of a plug. Fuel filters are changed by mileage rather than time. Rule of thumb 25,000 mile intervals. spraying the carb should be done around the choke and fast idle linkage, waste of time anywhere else.

jayoldschool
07-30-09, 07:08 PM
I replace my plugs about 3 or 4 years ago with bosch platinum series

Well, there's your problem! Get those Bosch craptinums out of there!

jayoldschool
07-30-09, 07:08 PM
I replace my plugs about 3 or 4 years ago with bosch platinum series

Well, there's your problem! Get those Bosch craptinums out of there!

dirt_cheap_fleetwood
07-30-09, 07:12 PM
Pull the Bosch plugs out. Bosch are meant to be installed in European cars with differently designed engines. Use the ACDelco ones and I guarantee you will see an improvement.

Angry Matt
07-30-09, 08:41 PM
I don't know anything about plugs myself, but AC Delco are obviously the favorite here. Is everybody recommending the fancy ones or just plain? I'm in need of new ones soon.

jayoldschool
07-30-09, 09:38 PM
Regular cheap AC. Stock heat, double check the gap before install.

Stingroo
07-30-09, 10:28 PM
Why is it that the Bosch plugs are bad? I've heard this from a bunch of people, but never really heard a reason for it. :s

sven914
07-31-09, 01:46 AM
Why is it that the Bosch plugs are bad? I've heard this from a bunch of people, but never really heard a reason for it. :s

Bosch plugs aren't bad. Spark plugs are designed to work a specific way in a specific series of vehicles. Take Motorcraft for instance; they were designed for Ford engines and work flawlessly in Ford. Installed in a GM, the engine will run horrible.

Bosch plugs were designed for Volkswagen, BMW, Porsche, and Mercedes. They are made to run effectively at certain RPM bands and fuel mixtures that American cars do not produce, especially Cadillacs.

limo
07-31-09, 12:29 PM
Hi, I drove my 88 RWD with the Olds engine 10 years ago, now hes conserved in my garage, but my mileage was for many years about 19.5 city / 24.5 highway @ 75 mph max. As I bought the car, I started with 13mpg and was frustrated. Then I changed booth the spark plugs and wires for stock AC Delco, cleaned the carb (got new fuel filter and gasket between the carb and the intake), checked&cleaned&replaced all vacuum lines, drained the radiator and checked the proper function of thermostat, checked all fuses (not only the main, but there are a hidden pair of fuses under the dash in the middle of the car), new engine oil&filter, new trans oil&filter and a auxiliary trans cooler... Look at the tire pressure, clean the distributor and check them, brush carefully all contacts, check the OBD self-diagnostic... Check the sensors for proper function and voltage - TPS, MAP, temperature, maybe EGR and PCV valve will be claened... There many things to doo, any will give you some % of mileage, all together will improve it massive. No clogget cat? Leaks in the exhaust? I fixed all the details, and the car still runs better as new.

dirt_cheap_fleetwood
07-31-09, 04:32 PM
Why is it that the Bosch plugs are bad? I've heard this from a bunch of people, but never really heard a reason for it. :s

Sven got it, they are designed differently. There is actually a lot of info to know about spark plugs. They all have different spark patterns, firing voltages, durations, and heat temperatures. Putting ones in that were not designed to be in the engine causes adverse effects.

Angry Matt
07-31-09, 06:45 PM
While we're at it, what plugs do you guys think for a slightly modded '70 472? It has HEI from a 425, cam, intake and some other bolt on stuff. The last guy that worked on the thing put "cooler" plugs in it (I'm not sure the brand), but I'm due anyway. I have the gap at 40. Stock calls for 35, but I figure with the distributor it probably needs more gap, right? Should I use better plugs on this application?

tbcaddy18
08-02-09, 06:46 PM
I will definitely change to AC Delco's ASAP! Does anyone recommend the AC Delco Iridium spark plugs?

tbcaddy18
08-02-09, 06:54 PM
Hi, I drove my 88 RWD with the Olds engine 10 years ago, now hes conserved in my garage, but my mileage was for many years about 19.5 city / 24.5 highway @ 75 mph max. As I bought the car, I started with 13mpg and was frustrated. Then I changed booth the spark plugs and wires for stock AC Delco, cleaned the carb (got new fuel filter and gasket between the carb and the intake), checked&cleaned&replaced all vacuum lines, drained the radiator and checked the proper function of thermostat, checked all fuses (not only the main, but there are a hidden pair of fuses under the dash in the middle of the car), new engine oil&filter, new trans oil&filter and a auxiliary trans cooler... Look at the tire pressure, clean the distributor and check them, brush carefully all contacts, check the OBD self-diagnostic... Check the sensors for proper function and voltage - TPS, MAP, temperature, maybe EGR and PCV valve will be claened... There many things to doo, any will give you some % of mileage, all together will improve it massive. No clogget cat? Leaks in the exhaust? I fixed all the details, and the car still runs better as new.

This is very helpful, I will def take a look at these things in mine. I used to get the same average of 13mpg when I purchased the car as well, then I switch over to Amsoil 5w-30 synthetic then to Amsoil 0w-30 pure sythetic the time after and it jumped it to what im getting now which is 15-16mpg on average with 18mpg on straight freeway. Luckily the synthetic hasn't caused the side-effects suck as leaks and engine damage as what others have said it would do with older cars.