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88 Horizon Bad Gas Mileage

Discussion in 'L: Horizon/Omni, Rampage, etc' started by cadman777, Jan 3, 2016.

  1. cadman777

    cadman777 Active Member

    Jul 2, 2015
    This is a re-hash of a previous post after I did a lotta work on this car (mostly for free).

    It's an '88 Horizon Americana 2.2L.

    It now runs great, only it still gets bad gas mileage.
    It gets around 18 around town, but not known what it gets on the highway, b/c my neighbor doesn't do any highway driving. From what I read, it should get at least 25 around town.

    It's got around 40k miles on it.

    The main things I can think of that I haven't checked are the cat for clogging.

    Other than that, does anybody have any suggestions?

    Also, can someone tell me a standard test used to determine whether or not the air flow through the cat is okay or is restricted, without having to remove it and do a visual inspection?

    Thanx ... Chris
  2. ImperialCrown

    Level III Supporter

    Jun 8, 2008
    I did re-read the previous 'DRB II' thread to see what might have been missed. Link here:

    The cam timing is very important. You didn't want to take it back apart at the time, but the fuel economy may stay low and it may run exceptionally strong until this is corrected. The cam sprocket hole must be canted towards the rear of the car following the centerline of the engine (blue line in diagram), not true vertical. A tooth or two off (advanced) will affect mpg, even though it seems to run powerfully. This shouldn't take too long to correct and may be your whole problem.

    Then double check the ignition timing. When you said that 'you set it by the book', that means that the 2 wire coolant sensor was disconnected to set timing? You can reconnect it and erase the code afterwards to turn off the 'power loss' light. Sometimes you can bump it to 12° BTDC if the label says 10° BTDC. If you try to set the timing with the coolant sensor connected it will be retarded.

    Were you able to verify that the lock-up torque converter does lock up when warmed and ~ 42-47 mph? The lock-up can gain you 2-3 mpg in overall driving, up to about 4-5 mpg on the highway.

    Does this car see a mixture of driving? Does the customer drive the car gently and not a leadfoot? Does it get to do long trips and not short trip/stop and go? Is idling and warm-up times kept short as possible? Car lightly loaded? Tire pressures 35 all around?

    A cat can usually be tested by thumping it with a rubber mallet and listening for an internal rattle of a broken up ceramic element. The chunks can block the exhaust exit. Sometimes the ceramic element melts into a blob and won't rattle. If it is a bad restriction, exhaust will try to push out upstream like at the EGR or the exhaust front joint donut. Sometimes you can look at the element by disconnecting the pipe at the front. A laparoscope can go around a bend.
    A furnace manometer can measure pressure from a restriction ahead of the cat. There will be some, but not a lot at idle. I have found cat debris blown into the muffler at the rear causing a rattle/restriction there.

    Double check all vacuum line/hose routing. The plastic and rubber hoses behind the valve cover gets the full heat from the exhaust manifold and usually harden, break and leak.

    High idle is usually caused by a vacuum leak.

    Did you ever straighten out the evap system and did it pass the book tests without a replacement SMEC?

    Has the stalling, richness and code 13 gone away? Any rich running will kill fuel economy.
    Doug D likes this.
  3. GLHS60

    GLHS60 Well-Known Member

    Jun 23, 2008
    Along with everything IC says you can check cam timing with a light if desired.

  4. 88horizon5speed

    Aug 12, 2013
    If it helps you any;

    I have an 88 horizon with the 5 speed. I get around 37-38 highway, have gotten up to 39.8. I typically get around 34 country driving. (not sure if I made that up but I think city and "country" driving is different in terms of MPG).

    I check my fuel mileage every time I gas up, when my highway mileage drops significantly it has always meant something was wrong, ex when my head gasket was bad versus fixed. I know that doesn't answer your question but its the same car and mine has no aftermarket parts or changes so it may help you to know what I get. Also, in winter time my mileage drops significantly due to higher idle time for warming up and also I have heard but not confirmed the winter mix fuel lower MPG.
  5. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
    Level 2 Supporter

    Jul 10, 2002
    If you can still get 34-38 mpg highway, there is nothing wrong with the car. If city mileage is so low, either you are locked in stop-and-go traffic a lot, or it is your driving habits.
    Idling to warm up a car is unnecessary and wasteful. You should not be idling it more than about 10-15 seconds, unless you live in Alaska or similar extreme climate. Engines warm up faster if they are driven vs idling. Winter fuel mix will not cut mpg more than about 2 mpg.
  6. 88horizon5speed

    Aug 12, 2013

    Its pretty typical to be 0 or below this time of year where I live; and I wasn't sure if you were talking to me about city mileage being low or not. I don't really know what my stop and go city MPG is because I don't typically drive in stop and go traffic much. For me its either highway or country back roads where the only traffic light you'll hit is blinking yellow. But I think I may not have been clear. I was just stating that when my mileage goes down significantly it has always proved to be something wrong with the car. When all is right with the car the mileage is very consistent at those numbers.

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