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1990 GMC low rpm stumble

This is a discussion on 1990 GMC low rpm stumble within the TBI Tuning (87-95 / OBD I) ECM/PCM forums, part of the Performance category; Hey all, I'm looking for some direction on my truck. I am running a somewhat stock 1990 GMC K1500. I ...

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    Question 1990 GMC low rpm stumble


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    Hey all, I'm looking for some direction on my truck. I am running a somewhat stock 1990 GMC K1500. I have headers, K&N filter, and a Crane Compu Cam. I'm not sure of the cam specs off hand, If anyone thinks the cam is in question, I'll dig up the cam card.

    Problem is, There's a low rpm stumble. Sometimes it stalls flat on its face, most times it has a bad stumble under 2000 RPM. I've replaced all spark plugs, wires, cap and rotor. Map sensor, Temp sensors, and the throttle position sensor.

    I'm not sure where else to look.

    Any Ideas?
    Thanks!

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    Wink Re: 1990 GMC low rpm stumble

    It sounds like you are going to need a tune. All or most of the stuff you have added has caused the engine to run leaner now with the stock tune. You might also have a vacuum leak, which I would check for first. Good luck.
    Ignorance can be fixed....STUPID is FOREVER!

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    Registered User tbiparts's Avatar
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    Re: 1990 GMC low rpm stumble

    First step is check your timing. Next step check for vacuum leaks and most importantly you'll probably need a tune on that chip.

    Give Brian Harris a call 1-336-471-2827

    If you need any other parts or advice give me a call or contact me off the site www.tbiparts.com

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    Re: 1990 GMC low rpm stumble

    Unplug the little hose from your EGR valve and put a nail in the hose to plug it.

    I had the same issue. This is what the GM guy did and it fixed it.
    Not sure what this did but it worked.

    He told me to replace the thing the hose was attached to. I did but that didn't fix it so I kept the hose plugged, been like 2 years no issues lol.

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    Registered User romakdaddy's Avatar
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    Re: 1990 GMC low rpm stumble

    Quote Originally Posted by Soah View Post
    Unplug the little hose from your EGR valve and put a nail in the hose to plug it.

    I had the same issue. This is what the GM guy did and it fixed it.
    Not sure what this did but it worked.

    He told me to replace the thing the hose was attached to. I did but that didn't fix it so I kept the hose plugged, been like 2 years no issues lol.
    the egr control solenoid is bad and causing the egr valve to open prematurly.its basically causing a huge vaccum leak through the egr valve.the valve itself could be sticking open.id replace both.

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    Supporting Gold Member GreaseDog's Avatar
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    Re: 1990 GMC low rpm stumble

    i'm getting the same low RPM stumble, and it doesn't matter what gear the trans is in, or engine speed... and my EGR solenoid has been plugged for a year and a half. any ideas?
    77 Chevy K20 - 80 GMC K2500 (in pieces)
    90 Chevy K3500 - 93 Chevy C2500 (in pieces) - 94 Chevy K1500

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    Registered User romakdaddy's Avatar
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    Re: 1990 GMC low rpm stumble

    Quote Originally Posted by GreaseDog View Post
    i'm getting the same low RPM stumble, and it doesn't matter what gear the trans is in, or engine speed... and my EGR solenoid has been plugged for a year and a half. any ideas?
    could be a skip

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    Real 4x4s' Rust ryan_thompson87's Avatar
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    Re: 1990 GMC low rpm stumble

    What's the fuel pressure set at. I had the same problem before turning up the fuel pressure.
    Last edited by ryan_thompson87; 01-31-2010 at 08:59 PM.

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

    07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille


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    Re: 1990 GMC low rpm stumble

    Quote Originally Posted by Soah View Post
    Unplug the little hose from your EGR valve and put a nail in the hose to plug it.

    I had the same issue. This is what the GM guy did and it fixed it.
    Not sure what this did but it worked.

    He told me to replace the thing the hose was attached to. I did but that didn't fix it so I kept the hose plugged, been like 2 years no issues lol.
    Just unplug the egr solenoid......no need to plug the vacuum line
    1986 K10 Suburban
    350,TBI
    CFM-Tech Super Sucker
    Jet AFPR
    TBI heads
    Comp 12-388-4(260H)cam
    3" Walker quietflow SS exhaust

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    Supporting Gold Member GreaseDog's Avatar
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    Re: 1990 GMC low rpm stumble

    Quote Originally Posted by romakdaddy View Post
    could be a skip
    a what? we're talking about a truck, not playing Uno.
    Quote Originally Posted by ryan_thompson87 View Post
    What's the fuel pressure set at. I had the same problem before turning up the fuel pressure.
    14 or 15psi.
    77 Chevy K20 - 80 GMC K2500 (in pieces)
    90 Chevy K3500 - 93 Chevy C2500 (in pieces) - 94 Chevy K1500

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    Real 4x4s' Rust ryan_thompson87's Avatar
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    Re: 1990 GMC low rpm stumble

    You can try turning it up to 18 or so. I Don't specifically remember your setup but your running Vortecs right? And you have the same pump I do?

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

    07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille


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    Supporting Gold Member GreaseDog's Avatar
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    Re: 1990 GMC low rpm stumble

    Quote Originally Posted by ryan_thompson87 View Post
    You can try turning it up to 18 or so. I Don't specifically remember your setup but your running Vortecs right? And you have the same pump I do?
    no, i'm not running the Vortec engine yet, still beating on the L05 relentlessly... the damn thing won't die!

    are you running the EP241 or the EP381?
    77 Chevy K20 - 80 GMC K2500 (in pieces)
    90 Chevy K3500 - 93 Chevy C2500 (in pieces) - 94 Chevy K1500

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    Real 4x4s' Rust ryan_thompson87's Avatar
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    Re: 1990 GMC low rpm stumble

    241. Just for fun, unplug the MAP sensor, (green plug, right by the IAC, I'm sure you know that) It'll force the ECM to go to a default fuel table and dump fuel to it. My stock regulator even made adjustable still couldn't put out the pressure I needed had to go to a XtremeFI unit. In the mean time while I was waiting for the US post office to make it to the Great White North, I just had ran with the MAP unplugged. Normally pig rich but as lean as I was it worked out O.K., I was a little rich at idle sometimes, but at least I could drive it and not get furious at it bogging from every light.

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

    07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille


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    Registered User Jameslleary's Avatar
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    Re: 1990 GMC low rpm stumble

    Not knowing much about your steups, I will throw my $.02...
    *Cam a tooth or so off?
    *Vac Leak through TB shaft?
    *7 and 2 plug wires crossed?
    *some type of exhaust restriction, forcing the EGR valve open uncommanded?
    *bad pulse sensor in Dizzy?
    * Intake Manifold Gasket leak(shoot some propane onto the crankcase)?
    *Compression check?
    *have a buddy drive around while you watch a scanner to see if anything abnormal happens when it stumbles.
    *And, not for nuthin`, but i have been sold a TPS or 2 that were just thrown back on the shelf after someone else returned it as defective.......Murphy`s law, ya know?
    Good luck!
    Last edited by Jameslleary; 02-05-2010 at 10:14 AM.
    1986 K10 Suburban
    350,TBI
    CFM-Tech Super Sucker
    Jet AFPR
    TBI heads
    Comp 12-388-4(260H)cam
    3" Walker quietflow SS exhaust

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    Real 4x4s' Rust ryan_thompson87's Avatar
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    Re: 1990 GMC low rpm stumble

    New engine, and the used parts (sensors and the like) Came from the old engine and were good. But thanks.

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

    07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille


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    Supporting Gold Member GreaseDog's Avatar
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    Re: 1990 GMC low rpm stumble

    eh, it runs, just a little annoying... screw it, its getting 6mpg on a good day. i'll continue beating it into oblivion. as soon as i get my tax check back, i'm buying another truck and taking this one out of comission for a while.
    77 Chevy K20 - 80 GMC K2500 (in pieces)
    90 Chevy K3500 - 93 Chevy C2500 (in pieces) - 94 Chevy K1500

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    Registered User crossy's son's Avatar
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    Re: 1990 GMC low rpm stumble

    The 94 nearly stalls when you floor it but if you're 3/4 pedal or before, its fine.

    but man when you floor it just noses over and acts like its gonna die....
    91 Dodge 4x4 12v Cummins Intercooled/5 speed, D60 & D70 rear w/ 3.55's and a Powr-Lok--- Lots of fuel and some boost-

    SOLD-- 91 Reg. cab shortbed GMC, Black on black, 350tbi crate, 5 speed w/hurst shifter, 3.42 G80--- Over 400,000 miles on body

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    Real 4x4s' Rust ryan_thompson87's Avatar
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    Re: 1990 GMC low rpm stumble

    It's been awhile since I've hooked the scanner up, I'm gonna have to do it and watch my BLMs. Just out of boredom and never having done it yet I got a full rebuild kit for my Throttle body, so I'm gonna play with it a little. I really gotta get working on a chip for this thing however.

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

    07 GMC Sierra Classic - 2" Rough Country Full Leveling Kit/285 Duratracs/Gibson Exhaust/10% Tint/Billet Grille


 

 

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