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89 chevy k15 TBI idle problems

 
huggerOchevy
I love my Chevy Chevette!
Posts: 2
Joined: 01/10
Posted: 01/21/10 08:52 AM

Ok im new so if anybody could help me out id appreciate it..

i just droped a remand jasper 350 in my truck and now the thing dosnt want to idle. some days it runs pretty good some days it runs like crap. i toped the new motor off with a brand new edelbrock preformer man, new distributer, plugs,wires,waterpump,iac valve an entire new fuel sending unit, fuel filter pretty much everything but the TBI its self is new under the hood... i warm it up in the morning, some days the idle is smooth as glass, some days the idle surges up and down to the point where it almost dies. i pull up to a stop light it does the same thing.. i have to keep a little bit of foot in the throttle to keep the idle up 95% of the time. ive shot the entire manifold with starter fluid to find and leaks, nothin, i cant hear the injectors surging, i cant find any vacume leaks and im about to go crazy. i dont know if its the map or what? anbody have any ideas?

thanks
Matt  

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waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 01/21/10 10:21 AM

surging on a TBI is usually fuel pressure problems....     it could also be fuel pressure regulator problems.. that is built into the throttle body... throttle body gasket sets

here is a picture of the contents of the kit..   there are 2 different kits...  both have the pressure regulator..

http://contentinfo.autozone.com/znetcs/product-info/en/US/gps/96-541D/image/8/


i would also like you to first check the grounds.. near the thermostat housing..   remember.. the ecm is only grounded to the motor...    make sure the engine is grounded to the body also.. usually at the back of the heads...   if everything is not grounded properly... you can have all kinds of problems...

do you have access to a scan tool????    you can look at the throttle position sensor voltage...  above 0.35 and less than 0.99...    make sure that when you work the throttle .. that it comes back to the exact same voltage every time....  worn throttle shaft bores will cause havoc...   with the engine off... grab the throttle lever... open it slightly... see if there is any play when you wiggle it around...     why is this important...  the ecm knows that the lowest voltage it sees is when you have the throttle closed...  if that voltage changes.. the ecm goes crazy...

with the scan tool... look at the coolant temp... should be between 195 and 225F...    then with it warmed up... look at the IAC...  (idle air counts.)  this is the counts the ecm has commanded the idle air control motor back from 0...

normal counts is 20 to 50 at idle... with the engine warmed up;....   if the throttle is too far open.. the counts will be below 20... if too far closed.. it will be above 50...

you might also pinch off the vacuum hose to the power brake booster...  if the booster is blown... the ecm will have a problem with the idle ....




back to the throttle shaft bore....  if there is play in the throttle shaft..   most carb shops can rebush the bore...   you can strip the injector case off the top for them do just do the rebush.... and do the orings and regulator your self... with the kit...

be sure to specify that you want the throttle shaft bore rebushed...  i have worked in shops .. that sent complete units in..  they cleaned the injectors  replaced the regulator.. installed new orings... and did not rebush the throttle lever... saying that they had broken off screws before...  so they don't do them any more...    that was 120 bucks out the window...

if you are handy with tools.. i can post instructions on diy.. rebushing.. don't try it without...  

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huggerOchevy
I love my Chevy Chevette!
Posts: 2
Joined: 01/10
Posted: 01/22/10 10:01 AM

Wow thanks boss i really appreciate it. if the weather lets up here in phoenix for five minutes im going to try and run through this stuff this weeknd.. i do all my own work so any instructions or advise you have would be helpful.. the scan tool i could probably get to if it comes down to it but i myself do not own one.

thanks again
ill update you when i get a chance
matt  

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gettnlarge01
Everything in my driveway’s a Chevy
Posts: 545
Joined: 01/10
Posted: 01/22/10 03:47 PM

+1  
luck is when skill and opportunity meet

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firefightercjr
I love my Chevy Chevette!
Posts: 1
Joined: 02/10
Posted: 02/02/10 08:37 PM

im having a problem my self and it boggles my mind.... i have a 84 350 converted to tbi. when trying to time it unpluged..... it seems to run great if the timing mark is strait up and down w the water pump and all the way down atleast 45 degrees to the passenger side. when you try and bring it to the timing mark it runs like crap and most of the time wont run at all there. any ideas.... are the harmonic ballencers the same from cab to tbi?  

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waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 02/02/10 09:27 PM

ok.. 84 harmonic balancers are set up with the 12 o clock timing marks.. not the 2...

does your timing light have adjustable advance???    dial in 30 degrees . or 40 degrees... see if the marks look better then..


mr gasket has a bolt on timing pointer for the 12 o clock timing marks... its like part number 4600

http://www.summitracing.com/parts/MRG-4600

or

http://www.jegs.com/i/Mr.%20Gasket/720/4600/10002/-1?CT=999

according to the second link.. it fits with 7 inch balancers 1977 and up...   take a look at how long it is...  

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55Guy
Administrator
Posts: 1153
Joined: 07/06
Posted: 02/03/10 07:55 AM

The above TBI problem could also be the idle air control valve going bad.  

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waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 02/03/10 12:28 PM

firefightercjr  i have another question...   did you hook up the various connections under the dash board for the later computer...

like the ALDL connector...   the neutral safety switch so the ecm knows when you have it in park or neutral.. it has a different program for the timing...

the check engine light... some of the 84.s might take some modes to make it work... ... as they might have a check engine light driver module...

the timing can also only be set with the tan wire disconnected..  or the ALDL connector ,   A and B terminal jumped.. depending on the year of the ecm...


how about the speed sensor... so the ecm knows how fast the truck is going ... ??????
some are in the transmission.. some are in the speedo...

post the year of the ecm or the ecm number...  if you need info...  

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bobellis51953
I love my Chevy Chevette!
Posts: 1
Joined: 02/10
Posted: 02/12/10 05:49 AM

I have a 88 Chevy C3500  7.4 (454) with TBI. Runs rich a idle till it gets hot. Hunches surges stinks from to much fuel. Check engine light is fuctional & not on. Can anybody give me some help? I have acess to scan tool or anything else I would need, just don't know where to start.  Thanks, Bob  

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waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 02/12/10 07:39 PM

copy and paste this link... then print the chart...

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/6a/large/0900c15280067e6a.gif

it is a chart of what  you should see when you have a scan tool....

i would look at the coolant temp sensors and wiring.. i have had these years with a pig tail on the coolant temp sensor go bad.. i have also found the rare one with insulation that has fallen off the twisted pair for the coolant temp sensor  back far in the harness..   you have to test the voltage at the sensor pig tail..

 make sure there is a 192/195 thermostat.. and that it works properly...  

autozone.com does have a free repair manual online for these. and they do have the wiring diagrams..

the AZ stuff is not complete... but it helps..  

i would also want you to if you have air injection on this truck.. to unplug the air injection hoses at the check valves on the tubes that are screwed into the exhaust manifolds...    plug the check valves so they cannot pull air in.. then start the motor.. see if the smog pump and diverter valve are functioning properly.. that the air flow to the upstream air.. cuts off after about a minute...   why.. when the diverter valves go bad.. or the check valves rot away...  uncommanded air into the upstream exhaust will screw with the fuel ratio as it dilutes the exhaust stream before it passes the oxygen sensor..

it could also be the fuel pressure regulator..  the oxygen sensors..  the throttle position sensor..

you have a scan tool ... so you are way ahead of the game...   print the chart.. post any thing out of range ... and trouble codes.. i have a gm manual at my knee.. covers everything on this system..  

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gettnlarge01
Everything in my driveway’s a Chevy
Posts: 545
Joined: 01/10
Posted: 02/13/10 10:43 AM

+1  
luck is when skill and opportunity meet

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