Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

what makes a TBI run rich?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 90K5, Mar 22, 2003.

  1. 90K5

    90K5 1/2 ton status

    Joined:
    Jun 1, 2000
    Posts:
    3,719
    Likes Received:
    0
    Location:
    Lubbock, TX
    finally getting a trouble code...O2 sensor says rich exhaust...its a 350 TBI, what causes them to run rich, what can i do to fix? thanks
     
  2. R72K5

    R72K5 Banned

    Joined:
    Mar 5, 2001
    Posts:
    8,905
    Likes Received:
    0
    Location:
    central IL
    probably is oxygen sensor, check and see if it looks old, if you can get it out without too much troubele then see if you cqan find a repair book with testing instructions or find somewhere that will test it, O2 sensor is one of the biggest things that affeect fuel mixture control
     
  3. 90K5

    90K5 1/2 ton status

    Joined:
    Jun 1, 2000
    Posts:
    3,719
    Likes Received:
    0
    Location:
    Lubbock, TX
    O2 sensor brand new this morning
     
  4. R72K5

    R72K5 Banned

    Joined:
    Mar 5, 2001
    Posts:
    8,905
    Likes Received:
    0
    Location:
    central IL
    one thing you could do that only really aaffect idle is to unscrew the big IAC motor from the side of the TBI unit and get can of carb spray cleaner and spray the crap out of the pintle end and spring on the end of the IAC motor assembly and blast it off with compresseed air and measure from mounting flange out to end of the pintle of it and make sure is 1-1/8" or less bwefore reinstalling it, the IAC has the square four pin plug connector, most likely black in color, cant miss it. also clean the linkage at the TPS assembly on pass side of the TBI unit with carb spray too, and blast with air and WD40 it
    check all three mounting screws 1/2" socket make sure are tight, and check all the torx bit screws that hold the injector housing and stuff down, they like to work loose, and check other bigger torx bit screws also, they will be loose probably. unplug and plug the EGR valve vacuum source, make sure EGR valve isnt stuck on hung up, tap with hammer if it is to loosen it up to make it return to closed position
     
  5. jc71355

    jc71355 1/2 ton status

    Joined:
    Jan 13, 2002
    Posts:
    830
    Likes Received:
    0
    Location:
    Port Neches, Texas
    He He I wish I had your problem, I've been fighting lean codes for a year now. Did you check the spray pattern of the injectors? Also, check your temp sensor to make sure that the motor doesn't think it's colder than it actually is.

    BTW, It's funny how much our trucks look alike /forums/images/graemlins/grin.gif
     
  6. Miller

    Miller Registered Member

    Joined:
    Mar 21, 2003
    Posts:
    56
    Likes Received:
    0
    Location:
    Mtn Home Idaho
    how ar eyou guys checking your codes? scanner or paper clip trick. Ive found that the paper clip deal isnt by any means a substitute for a scanner. but that doesnt mean I know how to use scanner very well.

    My rig throws a code 44 think thats the one for lean exhaust, but I think its richined the intake side up to try and compensate for the lean mixture in the ex due to build up of yellow grimmy residue on my rear fender, almost looks like diesel smoke.
    guess thats about all Ive gota say blah , mine will only through the code every ounce inwhile, service engine light comes on at highway speeds, then goes away.
     
  7. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    Have you checked your Vapor canister Purge valve. It may be bad. also if the canister is saturated with gas it will throw a code 45.
    here's other causes of a code 45
    High fuel pressure- Usually not a problem unless you have replaced the stock pump with a high pressure aftermarket one.
    Leaking injector
    MAP sensor. To test- disconect MAP sensor. This should put the ECM in bypass. If the rich A/F mixture goes away replace the map sensor.It really helps to have a scanner to do this test.
    Bad TPS. a bad signal or intermittant signal from the TPS can make the ECM think the engine is accelerating and will richen up the fuel mixture.
    Bad coolant temp sensor as said in previous post.
    if you have a scanner it will tell you exactly what the coolant temp sensor is telling the computer.

    Bad O2 but you said yours is new
    Well thats about all I can think of.
     
  8. 90K5

    90K5 1/2 ton status

    Joined:
    Jun 1, 2000
    Posts:
    3,719
    Likes Received:
    0
    Location:
    Lubbock, TX
    how do i check the vapor canister purge valve?
     
  9. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    Disconnect and plug the vacume line that goes to the vapor canister located in left front of the engine compartment. It is easier to disconnect it at the throttle body.
    If the problem goes away then replace the whole canister/valve.
    If you unpluge the vacome line and fuel comes out of it. replace everything also. Once the canister gets saturated they are no good.(overfiling your tank can cause this or a bad gas cap)
    Not all trucks have a purge or tank pressure relif valve. Most just have a canister. i thionk they used the valve mostly on Calif modles.
    It is usually located next to or on top of the canister.
    *****Edit*****
    I am assuming this post goes along with your other posts about idle problems ect.
    With all the info you gave I think your problem lies in the Coolant temp sensor or possibly the MAP sensor. Both of these sensors can give a rich exhaust signal but not throw their individual codes.
     
  10. 90K5

    90K5 1/2 ton status

    Joined:
    Jun 1, 2000
    Posts:
    3,719
    Likes Received:
    0
    Location:
    Lubbock, TX
    coolant temp sensor replaced, no change. where exactly is the map sensor?
     
  11. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    The MAP sensor is located on a bracket on the passenger side of the throttle body. It is the rectangular "Black Box" with a flat plug with 3 wires going to it. It also has a vacume line that goes to the back of the throttle body.
    FYI There are two other devices on that bracket. The thin square box next to the MAP sensor is the ESC box it works with the knock sensor to retard timing.
    On the bottom of the bracket is the EGR solonoid it also has a vavume line running to it and a line that goes to the EGR. This box opens vacume to the EGR after the engine warms up.
    MAP sensors are kinda expensive (80.00 ?) It really helps to have a scanner when trying to find these kind of troubles.
    An AutoXray scanner available at most parts stores is only around 140 bucks. They work good It not only gives codes it also reads what all the sensors are doing and engine operating paramaters and displayes the output on a small screen. This makes it far easier to find a non operating engine control device. Mine has saved me a lot of money. Its cheaper to buy a scanner in the long run. Than to replace parts till the problem is fixed.
     
  12. MOABDADC22

    MOABDADC22 1/2 ton status

    Joined:
    Jul 24, 2001
    Posts:
    1,348
    Likes Received:
    0
    Location:
    Cheyenne, Wy
    I had a 1990 TBI that was running rich. Turns out the drivers side intake gasket failed and was sucking air. ECM compensated by dumping lots of fuel (To get the perfect 14:1 air/fuel ratio). Check your spark plugs. Mine were almost 90% fouled. Just my two cents based on my experience. /forums/images/graemlins/thumb.gif
     
  13. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    Oh yeah I forgot about gaskets /forums/images/graemlins/thumb.gif The gasket on the bottom of the throttle body can go bad too and cause those problems.
    To Test- With the engine idleing. Get a spray bottle and Spray water around the intake manifols and TB gasket. If the RPMs drop off there is a leak.
     
  14. 90K5

    90K5 1/2 ton status

    Joined:
    Jun 1, 2000
    Posts:
    3,719
    Likes Received:
    0
    Location:
    Lubbock, TX
    Well, i had to leave it back home, school started up again today...left it at a shop to diagnose it. Gonna go and pick it up next weekend, but keep the ideas coming though...thanks everyone
     
  15. Khi5in

    Khi5in Registered Member

    Joined:
    Mar 19, 2002
    Posts:
    46
    Likes Received:
    0
    Location:
    Medford Massachusetts
    Iac motor, intake, all good calls, but any vaccum leak will cause a rich code. If you have access to a scan tool see it would be nice but also if you have a heated o2 sensor see if the ground is broken had that problem on a customers car.
     
  16. YtseJam

    YtseJam 1/2 ton status

    Joined:
    May 19, 2002
    Posts:
    147
    Likes Received:
    0
    Location:
    CT USA
    These use a single lead O2, no pre-heater. Start with the basics. Check all of your ignition componentes. Plugs, cables, cap, rotor, and ignition timing. Set the timing to 0°s BTDC with the timing connector opened. Going on what you've already checked, I would not suspect IAC problem or a vacuum leak @ the throttle body or you would notice erratic idle operation and usually an IAC error code will set. I would also check your fuel pressure. See what your psi is at key on, watch to see if it bleeds down and if it is in spec. If it does bleed down, pinch off the return line and see if it still bleeds down.
     
  17. Miller

    Miller Registered Member

    Joined:
    Mar 21, 2003
    Posts:
    56
    Likes Received:
    0
    Location:
    Mtn Home Idaho
    it doesnt throw a code 44 at all.

    my truck started flickn the service engine light at me this week. and has been smokeing alittle bit, but saying it had a lean exhaust, hmmm. anyways it threw a code 44, and the system was in closed loop, at idle. but at idle it should swap between closed and open loop. guess what it was. the element inside the o2 sensor rattling around.

    I never would have suspected the 02 sensor because I replaced it withn the last year.

    Im now not smoking and no codes are being stored. all that cause the o2. gas seems to last a little longer to.

    Evan
     

Share This Page