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'89 350 TBI - Severe hesitation/surging; worse when cold

This is a discussion on '89 350 TBI - Severe hesitation/surging; worse when cold within the Technical / Maintenance forums, part of the General Discussion category; Hello All, I'm working on a friends truck and need some help. It's an '88 Chevy 350/auto TBI w/150,000 miles. ...

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    '89 350 TBI - Severe hesitation/surging; worse when cold


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    Hello All,
    I'm working on a friends truck and need some help. It's an '88 Chevy 350/auto TBI w/150,000 miles. Here's the symptoms:

    SIGNIFICANT hesitation when just taking off normally. Stumbles but doesn't die and will eventually get going.
    If you floor it from dead stop, it will backfires through TBI.
    Runs fine at higher speeds.
    Does the above worse when it's cold. Gets a little better once warmed up. You have to "feather" the pedal when cold or acts like it will die.
    Surges at idle. The longer it idles, the worse it surges.
    Starter has to spin over for a looooong time before it will start whether it's cold or hot. Still slow to start.
    NO check engine light.

    I just changed plugs, wires, cap, rotor, air filter and fuel filter. All of which were in really bad shape. Plugs were white/light tan in color. No oil fouling.
    Found timing WAY too far advanced causing high idle. I reset it back to zero.

    Changing all of the above made NO difference whatsoever to the surging or hesitation or slow starting.

    Any ideas, thoughts or suggestions would be GREATLY appreciated!
    Thanks,
    Drag

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    Registered User BeaSSt's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    This sounds alot like the set-up I was experiencing w/ my freshly rebuild 350ci @ 160K. After we finally got it back on the road. Minus the part of all the parts being in real bad shape. Come to find out, just like you discovered, the timing was advance to like 10* adv. Once we un-plugged the 'puter connection, to re-set the timing back to zero, the hesitation and stumblin/surgin stopped.

    Could the timing chain poss. be in as bad a shape as the other parts you've found???

    Good luck,
    Don
    Silver '02 35th Ann'y A4 Camaro Z28 w/ T-Tops and 16" chorme w/ BFG g-Force T/A KDWS 245-50/16's
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    Registered User JSPERFORMANCE's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    Also, make sure your egr valve is operating properly sometimes the actuator solenoid fails and allows it to open at tip in and causes a similar problem...

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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    Im gonna say the fuel pump. I just had a similar problem with my brother's 1990 silverado. I changed everything that you did, and still the same problems. His was extremely hard to get up to speed, it didn't backfire though. I got so confused because it was injecting gas fine i thought from looking at the Throttle Body, so i changed everythign electrical. Then i finally took it to my mechanic and it turns out it was the fuel pump.

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    Registered User slowrider's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    Could also be that the egr valve is full of carbon not allowing it to close properly. Try cleaning it before you spend the money to replace it.

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    check fuel pressure 9-13 psi, whats it idling at?

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    98 Chevy Silverado TB RACING's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    I have the same problem with my 88. I built the motor and after several (7) times adjusting the timming it finnaly became stable. Due to the ECU control on the truck I still cannot get it perfect. Check all emission control devices, plugs, and TBI settings. I now have it to where it starts fine (hot & cold) but after a few days it will run rough again. I am still troublshooting so maybe we can find something out together and with the help of others.
    1998 Chevy Silverado ext. cab/Short bed, Suspension/body lift ??, 35x12.5xR15 Mud King.

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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    I actually fixed my problem. I posted what I found on my other post about the low fuel pressure. I copied my reply below. Hope your able to find out what's wrong with yours too. This truck is now driving just like it was brand new again.

    Well, I checked the resistance to the fuel pump and I wasn't sure which wires to test and they were very hard to get to (stepside truck - has NO room outside the frame rail) so I randomly checked all three. I got 55ohms on one and only 12ohms on another. I wasn't sure if that was good or bad and since I had already bought a fuel pump, I figured I would just go ahead and change it which I just finished; WOW!! This is like a new truck. I checked the fuel pressure afterwards and it was a constant 12psi which is perfect!

    This completely fixed the stumbling but not the slow start so after reading around the internet and the archives here, I started checking different sensors although I wasn't getting any error codes. When I got to the MAP sensor, the readings were HIGH at over 6 volts constant running or not (I would have expected this to throw a code to the comp). I found the vacuum line from the MAP sensor to the back of the TBI had a VERY SMALL split in it. I replaced it and rechecked the sensor readings; PERFECT! Turn the key and it fires right up!!

    Drove the truck some and everythings perfect again. Just like a new truck!

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    98 Chevy Silverado TB RACING's Avatar
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    Re: '89 350 TBI - Severe hesitation/surging; worse when cold

    Great, thanks that will help me out. I will do that as soon as I get back from Iraq.
    1998 Chevy Silverado ext. cab/Short bed, Suspension/body lift ??, 35x12.5xR15 Mud King.

 

 

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