PotM GrandMarq.NET - Panther Headquarters Forum Index PotM
GMN Chat Room GMN's STORE!! GMN's Gallery Please!!
Results 1 to 13 of 13

Thread: Low MPG 1988 GM with 302 EFI

  1. #1
    Member Tanner02480's Avatar
    Join Date
    Aug 2018
    Location
    Sherbrooke, QC
    Posts
    51

    Default Low MPG 1988 GM with 302 EFI

    Hi guys,
    I would like to resolve the low MPG problem on my car,
    I have a 87 and 88 grand marquis, the 87 one is ok, it run fine and have a good MPG

    but my 88 is wrost on fuel efficeiently the difference between the two cars is importent (around 40%)

    I did a tune up on it : spark plugs, wiring, distributor cap : new, I did the timing adjustement to 10BTC (was a little bit to high)

    no jammed brakes, bearings rotors, pad and calipers are new,

    No check engine light, no smoke, no strange smells

    What can I check or replace to improve the fuel efficiently on this car ?

    I wonder if the o2 sensor or the map sensor doesen't work properly, the check engine light should turn on ?

    thanks, and please excuse my English
    1987 Colony Park LS wagon
    1988 Grand marquis LS sedan

  2. #2
    Beater gonna beat sly's Avatar
    Join Date
    Mar 2010
    Location
    Lewisville, TX
    Posts
    20,462

    Default

    If the 88 has towing gears, this will probably be the case. Around town driving may be 1 better, but highway driving will be lower. If the rear suspension is sagging and the nose is higher than the tail, it will catch more air under the car when moving down the road and cause more resistance. Check the air filter and snorkel to make sure there's nothing sucked up in it blocking the air. Check the vacuum hose to the MAP sensor. If it's not in top shape, replace it. The only other thing I can think of is to check for fuel leaks with the car running and see if there's a small hole in a fuel line or a leaky seal at the tank. Maybe an injector stuck open? If the oil smells of gas, it could be a bad injector. If the alignment is off, it could kill fuel mileage.

    That's all I can think of right now that you haven't already done or pointed out here.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 88 MGM (SOLD), 93 Vic, 2000 Crown Vic, 2003 Expedition
    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Quote Originally Posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

  3. #3
    I'm an air-conditioned gypsy gadget73's Avatar
    Join Date
    Jan 2005
    Posts
    36,862

    Default

    You've got most of the obvious stuff. Definitely check for vacuum leaks. These things run richer when there is a leak.

    There is no check engine light. Worth scanning for codes though. If the smog pump bypass does not work and it keeps pumping air into the back of the cylinder head, the ECM will read the mixture as lean and add extra fuel.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  4. #4
    I post a lot... knucklehead0202's Avatar
    Join Date
    Apr 2015
    Location
    Southern Commiefornia
    Posts
    2,016

    Default

    Fuel filter is an easy cheap thing to replace so that's worth a shot as well.

  5. #5
    Member EaOutlaw1969's Avatar
    Join Date
    Feb 2018
    Location
    West lake Worth Florida ( Palm Beach County )
    Posts
    304

    Default

    double check your tire air pressure in case you forgot to check them recently
    2000 MGM LS Palm Beach Edition a work in progress

  6. #6
    Member Tanner02480's Avatar
    Join Date
    Aug 2018
    Location
    Sherbrooke, QC
    Posts
    51

    Default

    Quote Originally Posted by sly View Post
    If the 88 has towing gears, this will probably be the case. Around town driving may be 1 better, but highway driving will be lower. If the rear suspension is sagging and the nose is higher than the tail, it will catch more air under the car when moving down the road and cause more resistance. Check the air filter and snorkel to make sure there's nothing sucked up in it blocking the air. Check the vacuum hose to the MAP sensor. If it's not in top shape, replace it. The only other thing I can think of is to check for fuel leaks with the car running and see if there's a small hole in a fuel line or a leaky seal at the tank. Maybe an injector stuck open? If the oil smells of gas, it could be a bad injector. If the alignment is off, it could kill fuel mileage.

    That's all I can think of right now that you haven't already done or pointed out here.
    My 87 and 88 have the same rear axle (3.08), the suspension is ok, the rear is a little bit higher than the front , no fuel leak, I just replaced a broken part of the fuel line, air filter is new, alignment is ok and no fuel in oil, I have to check the vaccum hose to the map sensor, thanks for answer





    Quote Originally Posted by gadget73 View Post
    You've got most of the obvious stuff. Definitely check for vacuum leaks. These things run richer when there is a leak.

    There is no check engine light. Worth scanning for codes though. If the smog pump bypass does not work and it keeps pumping air into the back of the cylinder head, the ECM will read the mixture as lean and add extra fuel.
    How I can check if the smog pump is working ? when I purchased the car, the belt of this pump + AC was missing, and I installed a new one, this is the first thing I did on this car. thanks for answer


    Quote Originally Posted by EaOutlaw1969 View Post
    double check your tire air pressure in case you forgot to check them recently
    Tire pressure is ok, thanks for answer
    1987 Colony Park LS wagon
    1988 Grand marquis LS sedan

  7. #7
    Member Tanner02480's Avatar
    Join Date
    Aug 2018
    Location
    Sherbrooke, QC
    Posts
    51

    Default

    I read somewhere that the Engine Coolant Sensor failure could result in a two rich mixture because ECU think that the engine is still cold
    1987 Colony Park LS wagon
    1988 Grand marquis LS sedan

  8. #8
    I'm an air-conditioned gypsy gadget73's Avatar
    Join Date
    Jan 2005
    Posts
    36,862

    Default

    If the smog pump doesn't work properly, you'll get codes during the engine running self-test. Usually its 44 and 94, but 41 & 91 or 42 & 92 depending whats going on. The smog pump can produce codes for a lot of reasons, often the passages in the head will clog up but if you get an always lean code, it may not be shutting off when it needs to. Remove the belt and see if the always lean code goes away.

    A failed temp sensor that is out of range will also code, but you may need to measure it directly to confirm

    http://www.grandmarq.net/oldfuelinjection/page10.html

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  9. #9
    I post a lot... knucklehead0202's Avatar
    Join Date
    Apr 2015
    Location
    Southern Commiefornia
    Posts
    2,016

    Default

    My first '90 and my current '90, with 3.08 and 3.55 gears respectively, got within 1-2mpg different on the highway. Around town need not apply because i don't bother to count that. 3.08 car ran stronger despite higher mileage so not all rules come into play. Your experience may vary...

  10. #10
    Member Tanner02480's Avatar
    Join Date
    Aug 2018
    Location
    Sherbrooke, QC
    Posts
    51

    Default

    Quote Originally Posted by gadget73 View Post
    If the smog pump doesn't work properly, you'll get codes during the engine running self-test. Usually its 44 and 94, but 41 & 91 or 42 & 92 depending whats going on. The smog pump can produce codes for a lot of reasons, often the passages in the head will clog up but if you get an always lean code, it may not be shutting off when it needs to. Remove the belt and see if the always lean code goes away.

    A failed temp sensor that is out of range will also code, but you may need to measure it directly to confirm

    http://www.grandmarq.net/oldfuelinjection/page10.html
    Okay, Thanks for answer, is it possible to have these codes and don't have the check engine light on ?

    I will proceed with a diagnostic anyway, I located the test connector
    1987 Colony Park LS wagon
    1988 Grand marquis LS sedan

  11. #11
    I'm an air-conditioned gypsy gadget73's Avatar
    Join Date
    Jan 2005
    Posts
    36,862

    Default

    Some late 88's got a check engine light, but not all. Yours may not have a functional one. Definitely possible to have codes without a light. Very few things actually turn that on.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  12. #12
    Member Tanner02480's Avatar
    Join Date
    Aug 2018
    Location
    Sherbrooke, QC
    Posts
    51

    Default

    Quote Originally Posted by gadget73 View Post
    Some late 88's got a check engine light, but not all. Yours may not have a functional one. Definitely possible to have codes without a light. Very few things actually turn that on.
    You right, the check engine light do nothing, it only light during the time I turn the key to START, It's not give me the blinks to tell me the codes, I have no choice to read the codes with a voltmeter, my diagnostic connector is in bad condition ,There is some oxydation on the terminals, I difficultly get codes 21 and 24 but maybe due to the cold temperature this morning, I will take the time to do that in my garage after an engine warm up and diagnostic connector cleanning...
    I will come back with updates next week, Thanks To all
    1987 Colony Park LS wagon
    1988 Grand marquis LS sedan

  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
    Join Date
    Jan 2005
    Posts
    36,862

    Default

    The engine has to be warmed up in order to test it properly, otherwise you'll get at least a code 21. Cold enough and you may get a 24 as well. If the engine is warm and you get one or both, that could definitely explain some of your issues.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
GMN Approved Links!


www.rockauto.com www.adtr.net