<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CDOCUME%7E1%5CPhil%5CLOCALS%7E1%5CTemp%5Cmsoht ml1%5C01%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.0in 1.0in 1.0in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> 1988 Chevy 1500, 4.3L, 375 Transmission (3 speed auto), 235K miles
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Father, brother and I are all decent mechanics/parts changers, but this truck has us stumped.
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It hesitates during acceleration whenever engine is under any stress. Less noticeable after closed loop. Significant lack of power below 2000 RPM. At take-off, while still in open loop, hesitation is huge, but disappears when I flutter the gas. This also usually results in what I would consider normal power for motor and truck size. Take-off on slight downhill also seems to be more like normal, and more than caused simply by the slight downhill.
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Have had this truck 10 years. Installed ACDelco long block at 165K miles, rebuilt tran at 220K, have replaced every sensor, valve, controller, etc. at least once, replaced distributor, rebuilt throttle body. Had it in shop at one time, they claim to have replaced computer. Installed Schrader valve, fuel pressure at rear of TBI held consistently at 11 PSI while driving, even uphill. TPS and MAP sensor voltages read appropriately, even while driving. Some of these changes have improved overall performance, but none has affected this particular issue. Any suggestions?

 

Welcome to the forum

 

something stupid, my 88 S-10 did about the same thing. it turned out someone that replaced the fuel lines switched the pressure and return to the TB under the truck somehwere. how it even ran half right like that i dont know, maybe something to look at?
are the o2 volts reading right? losing ground through the rusty exhaust ( rust between the head, bolts or anywhere else) i have seen cause problems rarely, but it happens.
i had one truck with a burnt / bad leaking intake valve (more like 5) run that way also.
just a few things to maybe check over.

 

My 1998 z71 did the same thing and i only had 8k miles on a brand new Fuel pump... but the fuel pump was bad spent like 2k on other things cause i didn't believe the pump was bad so soon. might be worth checking out