Good Ol' 3800!

Discussion in 'GM' started by 99LeCouch, Feb 27, 2009.

  1. jkp1187

    jkp1187 Well-Known Member

  2. jkp1187

    jkp1187 Well-Known Member

    Not so good ol' 3800:

  3. timtona

    timtona Member

    hello everyone im new here. i have a 90 olds toronado with the 3800, it runs great but is only getting 13.6 mpg any ideas? its got fresh fluids and a tune should really be doing better than that i think
  4. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    Welcome to CleanMPG!

    First step - Read

    The '90 Toronado is a heavy car, and all the comments and advice you read in this thread apply to your car. Keep it rolling. Easy on the accelerator and coax it to top gear and keep it there. Keep the engine rpm under 2000 on acceleration and under 1500 on the highway.

    For car setup - consider setting tire pressure closer to the number shown on the sidewall. Check that there are no stuck calipers or worn wheel bearings that are causing drag. Check tire tread for odd wear that could suggest misalignment. Your car should feel like it's freewheeling when coasting. If it feels like it's being dragged down, as if downshifted, look for the cause of the drag.

    Your car is not OBD-II compliant so a ScanGage won't work. But I had a '90 Olds Cutlass Int'l that had both average and instant FE in the trip computer. Your Toro may have the same. If it does, use it as a guide.

    And ask questions here. We're happy to help!
  5. timtona

    timtona Member

    i have all the tires at 37psi, there are no stuck calipers, although i do need an alignment. since it does only have a 1 wire oxygen sensor could i run a rheostat on it to adjust my air fuel ratio?
  6. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    13.6 mpg means there is something WRONG with the car. Don't try anything "special" until you get it fixed. I'd recommend against messing with the o2 sensor at all. Many pitfalls and little to gain, especially with a poorly running engine.
  7. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    Your '90 Toro is rated at 16 city / 24 highway / 19 combined under the '08 EPA. Old ratings were 18/21/27. Your stated MPG is about right if you are driving mostly around town, although there is much room for improvement.

    Where are you located and what does your daily commute entail?

    I would recommend against fiddling with the O2 sensor, as changing the value won't do much more than switch the CEL on. The O2 sensor should be changed if a diagnostic test shows that it is getting lazy (long swings between rich/lean). Also, your automatic trans is the old 440T4, and it uses a throttle cable to control shift points. Be sure this throttle cable is properly adjusted so that upshifts happen promptly. A very slight misadjustment of that cable can cause delayed upshifts and lower fuel economy.

    Be sure you aren't carrying extra cargo in the car, keep upshifts at or below 2000rpm by using a gentle foot on the throttle, and keep the car rolling whenever possible. Your car should shift to 4th gear at or above 45mph. Consider planning routes that will take you on roads with few lights or other stops and where this speed is legal and practical.

    My '90 Olds Cutlass had the same transmission, but the Chevy 3.1 engine. A bit lighter and about the same aero drag. And I was able to get 44mpg on the instant FE at 44mph - the lowest speed it would hold onto 4th gear. So there is certainly room for better FE in the car and its powertrain.
  8. timtona

    timtona Member

    thats exactly what i dont understand... it runs great,idles great. but once ina while, while starting it will backfire then miss for a couple cycles untill it straightens out. could i have a bad injector?
  9. timtona

    timtona Member

    i have removed over 300 pounds of accessories, sound deadener, a/c,air ride,spare tire and jack. etc. it also has a cold air intake, free flowing exhaust and oversize plug wires so i think my stats should definately be higher than stock. most of my driving is city, stop- and go though. would a bad iat sensor give me bad mileage? mine looks a little corroded
  10. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    The cold air intake and custom exhaust system are designed and intended for more power, which is the opposite of increased fuel efficiency. Both lead to denser air and more airflow through the engine, and then engine will add a pound of gas for every 14.7 pounds of cold air it can pump through. The IAT sensor, if it's bad enough, can cause a problem with air/fuel ratio calculation.

    Remember that auto manufacturers don't add any extra parts to the engine management as doing so adds cost to manufacturing and also repair or warranty work. So everything included as stock on the car is necessary if you want to reach or exceed the EPA estimates, and the computer that controls spark and fuel is programmed to work in concert with the stock parts. Depending on what is replaced or enhanced, fuel economy will almost certainly suffer to some degree, and worn or defective parts will compound the condition. You can mitigate the loss by using hypermiling techniques, but the tank averages won't really impress until the car is running as the manufacturer intended.

    The cough on startup could be a worn timing chain that skipped a tooth. How many miles are on the engine?

    If you read the posts from 99LeCouch, he's getting "teens around town". It's tough to get much more out of an almost-two-ton car with a pushrod V6 and slushy automatic with the extreme low first gear. But read the "Beating the EPA" article and look up the terms DWB and DWL by clicking on the question mark next to each. For those of us with big GM V6 engines, these two techniques are our closest friends.
  11. timtona

    timtona Member

    hey all i havent been here in a while but heres a follow up on my mpg issues, i was getting 13.6 back in 2009 first i found my ignition module was going bad, so i upgraded to delco type 2 module and coil packs gas mileage went to 14.7,then found an open plug wire,15.3,cleaned the map sensor with rubbing alcohol and a q-tip.,16.4, indexed the spark plugs, 16.6, finally replaced the stretched timing chain, added new gears and tensioner and disabled cam driven the balance shaft by taking the gear off. currently getting 20.4 city, if anyone has an older 3800 with over 100,000 miles i suggest changing the timing gears, chain and tensioner, at 145,000 mine was so badly stretched it barely sat on the gears and the plastic tensioner was worn down to the metal backing plate. for the old 3800 who says you cant teach an old dog new tricks?
  12. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Nice work!!! :thumbs_up:
  13. FSUspectra

    FSUspectra Practicing true conservatism!

    Well it sounds like you're bringing that old dog back into shape! ;)
  14. Phantom

    Phantom Member

    I love the 3800 I have owned several over the years with both tall and short gearing on both the Series I and Series II, even have used the upper intake from the Series III.

    Coolant in the to be taken care of now keep an eye on the coolant level to make sure it is not dropping. Replacing the gasket is not hard it just takes some time look at for a walkthrough.

    Changing the back spark plugs on the 3800 can be difficult but is easier on the GrandPrix if the front dogbone motor mount bolts are removed and a tiedown is used on the bracket to the fraim there are a few holes the hook can be placed. Now slowly bring the engine forward by clicking the straps tighter, hook the straps on before removing the bolts (there is only one on each side). That will give you a few extra inches to get to it.

Share This Page