89 350 TBI problem

Discussion in 'Troubleshooting & Diagnosis' started by Chuck78, Jan 6, 2007.

  1. Chuck78

    Chuck78 Veteran Member

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    Oct 22, 2000
    Columbus, OH, USA
    Checked out most things I know to check other then the fuel pressure. Still no luck. Definitely not the EGR, comp. check came back with all 8 around 150psi, can't seem to locate any real vacuum leaks, although there may be a slight leak around the throttle shaft where it goes through the side of the unit/ TBI base gasket replaced, no fix there. I have good spark, new rotor and cap, new fuel filter. replaced wires a few months ago, but I did slightly burn one due to broken looms, replaced with an old wire, still the same problem. Plugs look good.

    Problem seems to be getting worse, so I am leaning towards the fuel pump going out. Still not 100% certain. It really struggles to climb a steep hill from a stop. It's almost not driveable now.

    Problem does seem for some reason to be more driveable in this cold winter weather until the truck gets good and warmed up.


    Where do I get one of these tools to take the place of the fuel filter? I might just break loose the fittings in the line where it transitions to a 20" stainless flex line from the frame rail up to the back of the engine block, and see if I can just make up a 3/8" tee with the male and female fittings I need.

    We're supposed to get some arctic weather starting this weekend, so I hope to figure this fuel pressure thing out asap or else it may have to wait!

    Any other ideas? Is there a specific procedure I needed to follow to make sure I didn't have a burnt valve? I just cranked them all over 4 times, and checked the gauge, watched if for 20-30 seconds to see if it bled down, and went on to the next. Would a burnt valve not build that kind of pressure to begin with?
    Thanks.
     
  2. Knuckle Dragger

    Knuckle Dragger Moderator Staff Member Lifetime Gold Member

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    Nov 2, 2002
    Waddell AZ
    Chuck, is there a local shop that you can have check the fuel pressure? At this point I think it may be worth the it to have someone run a diagnostic on it unless you already have the equipment to test the fuel pressure.
     
  3. cold Z28

    cold Z28 Veteran Member

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    Sep 12, 2001
    Anchorage,AK USA

    Knuckle is right the fuel pressure is evreything on these trucks. Testing it will eliminate about 80% of "what could be wrong". Pressure should be 9-13 psi at the TB. If the pump checks out then my next notion would be the distributor/pick up coil. They like to go out after alot of milage and you qualify for that. The normal faliure stuff that I know of are :

    1. fuel pump
    2. ignition module
    3. dirtributor
    4. IAC valve(more has to do with idle)
    5. TPS
    These are pretty much the common problems in order of frequency. Ususally for the most part they still run forever and are easy to fix.
     
  4. Knuckle Dragger

    Knuckle Dragger Moderator Staff Member Lifetime Gold Member

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    That's good, I forgot about the wierd problems the ignition modules used to throw at us.
     
  5. Chuck78

    Chuck78 Veteran Member

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    Oct 22, 2000
    Columbus, OH, USA
    ignition module is good. what's the IAC valve?
     
  6. Knuckle Dragger

    Knuckle Dragger Moderator Staff Member Lifetime Gold Member

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    Nov 2, 2002
    Waddell AZ
    Idle Air Control, very doubtful it's your problem. How was the module checked?


    Fuel presure is a must do at this point.
     
  7. danbrennan

    danbrennan Veteran Member Lifetime Gold Member

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    Mar 13, 1999
    Brighton, MI
    I didn't read through all the replies, so maybe this was already covered. I put 160,000 miles on my 1988 TBI full size Blazer before I turned it into a snow plow truck, so I had to fix a few things. Your initial description sounds similar to when my throttle position sensor(TPS) went bad. Injection fuel is calculated by a speed density algorithm, no Mass Airflow Sensor(at least not on my '88), so when I had drivability problems I checked the MAP sensor and TPS. Disconnecting the MAP sensor didn't have much effect, but disconnecting the TPS dramatically worsened my tip-in drivability. I think they're calculating fuel enrichment from a delta signal from the TPS, and when that sensor goes, the engine goes real lean during tip-ins. Anyway, a new TPS solved my problem.

    When the EGR valve failed, the effects were not nearly so dramatic. Mostly it had no effect, except when I was(for example) waiting in line at a fast food resturant. If I tried to inch forward by quickly tapping the pedal, the engine would rev, but then die when it tried to return to idle. In my case, at least, I think the EGR valve got "lazy", and couldn't close fast enough, so the engine was getting EGR flow with the throttle closed, which is definitely an inducement to stall.
     
  8. Chuck78

    Chuck78 Veteran Member

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    Oct 22, 2000
    Columbus, OH, USA
    I'll try disconnecting a few sensors while running and see what happens. Fuel pressure check is definitely a must I would say as well.
     
  9. Chuck78

    Chuck78 Veteran Member

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    Oct 22, 2000
    Columbus, OH, USA
    Checked out everything on engine again while visiting my dad (old timer mechanic until early 80's), did fuel pressure last unfortunately... For $40, you can get the Actron brand fuel pressure gauge for TBI that has a male/female fitting with a shraeder valve out the side, and a 60psi gauge. ($36 gets you a 100psi guage for fuel rail injection systems, same but minus special inline tee fitting)
    Broke loose the flex line from the hard line where it goes from frame rail and up to back of block (to hard line again), inserted gauge there, reading is 5PSI on ign. pos. and running. the 87-95 Haynes truck manual states it should be 9-13 psi, just as someone here said.

    Since the 'burbs changed body style to the new generation 5 years later than the rest of the trucks, my "73-87 truck/91 suburban" manual doesn't show nearly enough on the 89-91 TBI engines, but luckily my dad has an 87-95 truck manual for his buddies 93 Suburban, and that actually had a lot more useful info on wiring diagrams and fuel systems than the other manual had. The older manual has more useful chassis info, but now after seeing this later one, I think I need both manuals to work on my truck! The troubleshooting is much better for a TBI engine as well.

    I'll repost with my success!

    Thanks for all the help, esp. knuckle and mary.
     
  10. Chuck78

    Chuck78 Veteran Member

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    Oct 22, 2000
    Columbus, OH, USA
    No success to be found here! 2 month old filter, new pressure gauge, new fuel pump reads the exact same - 5psi, and exact same problem!!!!!!

    O2 Sensor didn't do anything either. Have to look into how to test the TPS. My dad seems to think that the symptoms spell out vacuum leak, but we haven't found one so far. He was able to tell me that it was running lean just from a test drive, it took me having a scanner hooked to it to deduce that. He hasn't worked as a mechanic for 25 years, but I'll trust his instincts. Computerized stuff is throwing both of us for a loop. His second notion was that since the compression test came back okay, that maybe an intake valve was stuck closed? All ignition components seem alright, athough we were wondering if this lead we found was in fact a tach lead, since it just pegged the meter when we hooked it up. The 92+ Suburban Haynes manual shows all the correct colors of wires and shows this extra wire as a tach lead, but we didn't get a tach reading from it.
    He also said that if it had a vacuum leak, it would typically just stumble to get going, and then take off once it got going. Now it used to take off after maybe 25mph, but it runs much worse at the moment than when it would do that.
     
    Last edited: Feb 3, 2007

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