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Newbie here, need help with 87 burban loss of power high fuel consumption

Discussion in 'GM Powertrain' started by slimyguts, Oct 17, 2010.

  1. slimyguts

    slimyguts New Member

    So here it is:
    1987 Suburban 1/2 ton 4wd 350 auto
    At about 355,000 miles on the engine (and about 530,000 on the truck) I finally blew the head gaskets. Removed, repaired and reassembled top end. Fired on the first try. NEVER had timing marks on the engine, always set by ear. INstalled timing marks and set to 0 as spec states. Engine runs soother than ever at idle. Sounds great. But has HUGE hesitation / surge at midrange rpm. smooths out at higher rpm but never quite feels like rpms reaching their potential. Got engine light and had a code for O2 sensor. Figured that was because all the coolant down the pipes so I replaced it. Now I get a code for Lean Exhaust and burns TONS of fuel. was getting about 16 - 18 when the gaskets blew. Now getting about maybe 8.
    Love workin on cars but dont like all the electronics. Not stupid, have built cars that run in the 10's on the dragstrip without juice but cant get my own truck to run right. Tired of this and need some help.

    Thanks,
    Slimyguts

    Update: Tried to retard timing by 4 degrees, no change. Returned timing to 0. Checked for codes again. Got code 13 - O2 sensor (but its brand new) code 24 - Vehicle speed sensor and code 44 - Lean Exhaust. With the symptoms and these codes I am leaning towards a faulty TPS (throttle position sensor) Dont like to just throw parts at it, want to figure it out. What ya think?
    Last edited: Oct 17, 2010
  2. stephan

    stephan New Member 1000 Posts

    LOL "Slimey Guts" funny name..
    It sounds like you could use a little more timing advance. Key clues are: the hesitation, the poor mileage, & the rpm's not reaching their potential"
    Whether it's your initial setting, or the computer not being able to controll the distributor I can't say. Maybe it's a bit of both, but I would address this first.
    355,000 miles is good service from a 5.7. you must be doing smth right :)

    edit***
    SlimeyGuts says: -->Now I get a code for Lean Exhaust and burns TONS of fuel. <<--
    Not sure why you would get lean code, since you can see you are burning way too much fuel. I would believe your eyes & ears before you believe that particular code.
    You are disconnecting the ecu/distributor wire when you are setting the timeing ..yes?
    Last edited: Oct 17, 2010
  3. Sam_A

    Sam_A New Member

    Welcome to the club!
  4. slimyguts

    slimyguts New Member

    Name is cause I really enjoy fishin and huntin. belong to a site like this for fishin, cleaning fish and deer you play with slimy guts. Only thing I would rather do onther that hunt and fish is be a member of NHRA pit crew. I can hunt and fish right now, too old to get started in a new career unless the heavens parted and a miracle happened. LOL (funny, I is in Oregon too.....McMinnville area....you?)

    Yes, disconnecting the ecu wire prior to setting timeing. Now that you mention the computer not being able to control the dist. advance, I checked timing again. This time with a helper. With the ecu disconnected or connected, when slowly bringing RPM up, using timing light to watch marks, the timing does not advance smoothly, it bounces and jumps up. Not sure if that is normal. ALSO, it runs perfect when in park / netural but has issues when under a load.

    But what bothers me is that prior to the headgaskets blowin out it ran fine. I mean you could tell somethin was gettin ready to go but it had power all thru the rpm range.
  5. stephan

    stephan New Member 1000 Posts

    Hey SlimeyGuts lol,
    I was lmao so much at your name I didn't notice you were from McMinnville. I've been to McMinnville, beautiful town. Yes I'm in southern Ore. NW of Grants Pass. You said you've drag raced. Do you recognize the tower in my signature pic? Do the Livingstons still own that place?

    The timing jumping with the ecu connected is understandable if it is compensating for something irregular, but not being smooth when disconnected is not. It could be too much shaft end play, cam gear to dist. gear play, or timing chain play. Still, since these are the same as before your head gasket repair I don't think they are the immediate problem.
    I think you just need some more advance. If you have a dial back timing light, see what your total adv is. If no dial back light, try puting another 5 degrees in it. If it helps try another 3 to 5 after that. No worries, as the knock sensor will compensate for "too much" providing the ecu is actually controlling the dist adv.
    Also make sure that the ecu is actually controlling the timing, because if it isn't then the only advance you will have is the initial that you are setting it at and it will be a dog.

    edit** if it turns out your distributor is belly up, don't go buy one. I have one I'll give you. It's from my '88, & had 95,000 miles on it when I switched over to a carb. I know a guy that makes the north run about every month or so & can get him to deliver it close to McMinnville.
    Last edited: Oct 18, 2010
  6. 2COR517

    2COR517 New Member 1000 Posts

    I would suspect a defective/incorrect O2 sensor. The lean code correlates to the excessive fuel consumption. Because the O2 sensor is "detecting" a lean (even though it's not) condition, the PCM is dumping more fuel to try and correct. It is also possible that the wiring is damaged from the O2 sensor to the PCM.
  7. slimyguts

    slimyguts New Member

    Just looked at your pic. Is that southern oregon dragway? My buddy that I used to crew cheif for ran there some the last few years. I built and tuned a 66 Barracuda. Called "Fish Fry" Its now painted red and white. That ******* livingston still owns woodburn. Will till he dies I think.

    Will check the O2 again also. But its irratating me!!!
  8. stephan

    stephan New Member 1000 Posts

    No, it's the old timing tower @ Woodburn D.S. Glad to hear the Livingstons' still own it. They were always the most efficient D.S in the Pacific North West. The only owners dedicated enough to run a race between rain showers & they did it well.
    Just try a little more timing advance in stages. It could be the 02 sensor like 2cor says, but I can't think of how you could have hurt it when doing head gaskets.
  9. slimyguts

    slimyguts New Member

    Yes, they do a good job at woodburn. But Jim is quite the ass but his wife and son Jay are good people. O well, I try to stay clear and all is well.

    Have replaced the O2 sensor. How would one go about testing the signal from the O2 just to double check it? And for that matter the TPS? Hate to throw parts at a problem without knowing they are bad.
  10. stephan

    stephan New Member 1000 Posts

    I would give a shout out to murdog or silveradotrailblazer. They have the code sheets & are up on that stuff. There are others on here who also have the knowledge but their names escape me right now. If you start another thread asking about 02 sensor they will answer.

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