1990 Suburban running poorly, need advice

Discussion in 'General Chevy & GM Tech Questions' started by gilland, Feb 9, 2009.

  1. gilland

    gilland New Member

    I have a 1990 Suburban (156k miles, 350, automatic, 4X4) that hesitates and stalls when under a load.

    When it is in park or in neutral, it runs very well and is responsive to the gas pedal. However, whenever there is an engine load (like when holding the brakes or accellerating rapidly) it looses power and acts like it is choking out. I have an intermittent check engine light which reads a code 44 (lean exhaust). We changed the oxygen sensor, plugs, wires, distributor cap, fuel filter, and also put a new gasket between the carb and air filter ring. Both the throttle position sensor and MAP sensor check out OK. What should I check next? Any help would be greatly appreciated, thanks!
  2. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    How is the fuel pressure? Compression? What about fuel parts, any replaced? Any pings, ticks, loud noises from the motor? Was the O2 sensor OE or did you use the Universal fit? Hows the EGR valve, responding and or blackened? Have you removed it and checked it as well?

  3. gilland

    gilland New Member

    Fuel parts are all original, however the fuel pressure appears to be good. The throttle body injectors don't sputter or choke when I rev the engine. The motor sounds good with no pings or knocks. The only sound change noticed is when there is a load on the engine. In that case, it just sounds like the engine is being flooded and then starts slowing down. The O2 sensor was OEM. I don't know about the compression or the EGR valve. I will take a look at the valve tonight, but dont know how to check compression. I will keep you posted on what I find. Thanks for your help :)
  4. hunter541

    hunter541 New Member

    these are still pretty simple so dont throw every part at this thing make sure you have good fuel pressure minimum of 9lbs and make sure you look at the distributor close i seen one that the pickup part was cracked really bad acted very simular and make sure the exhaust isn't plugged good luck
  5. gilland

    gilland New Member

    How exactly does the EGR valve work? I disconnected the vaccuum line on the top of the unit expecting the engine to perform differently but I couldn't tell that anything changed. I can't feel suction or any movement of air through the hose. Am I suppose to? The hose from the top of the EGR connects to a small module on the side of the engine and then is routed back through another vaccuum line that leads into the base of the carb. There doesn't appear to be any leaks in any of these lines.

    Hunter - The exhaust appears to have more than adequate flow at the tailpipe. I will check fuel pressures tomorrow after work. I assume pressure is good because I don't see it sputter at the injectors when I romp on it and you can visibly see an increase in fuel delivery, however, I haven't actually calibrated the pressure so I can't rule out the possiblity.

    Thanks for the advice guys!
  6. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    Leave the vaccuum hose connect to the EGR and while the truck is running, push up on the diaphram under the inside of the EGR itself. If the engine stalls, then it still functioning, if not the valve is usually bad at any RPM range. Also, you can use a vaccum tester gauge(hand held) to test the EGR. Compression also with a gauge, remove plug, insert gauge in hole for plug and have someone crank engine while you check pressure on the gauge, test all and see chart for the compression range for your year, engine size. There will be a range for what should be and should not be.....Could also be a vaccuum leak somewhee, do you hear any noise around the carb base? How's the carb base gasket?

  7. route66paul

    route66paul Member

    could the cat be clogged up? these show their problems under load.
  8. gilland

    gilland New Member

    EGR Tests out fine, if I press the valve and it kills the engine. I don't hear any vaccuum leak "hissing" although it is hard to tell over the noise of the engine fan, etc. I pulled the four carb vaccum lines (one at a time) and plugged them while under load but I didn't really notice much change in the engine compared to when they are left open. I was told to try spraying carb cleaner around the base to check for a gasket leak since that will supposibly make the engine run rough when it gets sucked through a leak, but that didn't change anything either. I will have to take it in to test the compression since I don't have any tools for that. Thanks for the advice guys, I will let you know if there are any breakthroughs!
  9. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    Well, I would still say that it could also be fuel realted, it may be fluctuating pressure if the pump is weak when its a full flow and drops off. Is this a electric fuel pump? Have you test this also before the compression? Did you also check the convertor as mentioned, I know the exhaust is probabaly on there rusted, any means to open up and see if its blackened badly in the honey combs?

  10. jlsparky7

    jlsparky7 Rockstar

    One thing that could help eliminate dirty carb/plugged cat probs is some seafoam. Put 1/2 a can in the gas tank and 1/2 in a vacuum line.

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