help with my 92 5.7l

[chimp koose]

I thought I had my 92 chev  truck 5.7 L fixed the other day with a new ignition module but it now has a fluctuating idle problem . I took some throttle body cleaner spray and went at it tonight thinking that the IAC was clogged up but after a half can of cleaner I would be optimistic if I noticed much of an improvement .The idle will not fluctuate when idling in park or neutral . It fluctuates less in reverse and more when sitting in drive . When you come to a stop at an intersection it takes about 5 seconds before it starts to fluctuate and it seems to do it at a regular interval. If I push the throttle to even 600 rpm the problem goes away .It appears to be idling at 300 to 400 rpm in gear. When it fluctuates you can see the injectors momentarily pulse the fuel supply . I put a bottle of sea foam in the topped off fuel tank tonight . When I installed the ign module I did not disconnect the battery , I did put all that insulating goo under the module before installing . Whats up ? It ran fine right until it stalled out and died the other day with no signs of a problem . I replaced the module , cap , rotor and a very dirty air filter .

[wayne petty]

throttle body fuel injection???

do you have a scan tool.. get into the live data..

ECT,  engine coolant temp warmed up  187 to 220F...

TPS, throttle position sensor voltage. under 0.99 but usually over 0.5.. a few models may be OK at 0.35 ..  but i like above 0.5 and below 0.75..  crack the throttle a few times..  release.. monitor the minimum TPS voltage..  it should be exactly the same each time.


IAC, look at the idle air counts...  20 to 50 is where i like to see them.


if you get variable TPS minimum voltage readings... pull the air cleaner housing.. engine off.. grab the the throttle lever..  open the throttle part way.. wiggle.. you should not have any play..
(O)... the O being the shaft in the BORE..  if you have an OVAL throttle shaft bore. (O ) ( O)    wow.. that almost looks dirty..   you will have to replace or Rebush the throttle shaft bore..


rebushing the throttle shaft bore is fairly easy for those with a bunch of proper tools..  the hard part is the screws for the throttle blade.. they are M2.5 x .4 or something like that pan head with a big head..

the exposed ends of the threads are also MELTED or DEFORMED.. so you cannot possibly pull them without snapping off the head..

you will want to get the TBI unit torn down far enough to get at the throttle blade screws..   you will want to back them out no more than 1/3 of a turn..  do not try to remove them yet..   grind the exposed threaded end off with a dremel..   once you get down to where the threads are flush.. tighten the screws back up and take that last thread off.. without going flush again..  now try to back the screws out.. if they bind.. tighten them up again and grind a little more..

with the lever off the far end of the shaft.. you can work the shaft out..

you will need to do some shopping first..

a throttle body gasket kit.. look up the parts yourself.. some come with a fuel pressure regulator diaphragm.. that is the one to get..  it will also have wedding ring sized filters and some tiny tiny thimble filters. the thimble filters go in the side of the injectors..

you will want to visit an engine or cylinder head rebuilder.. purchase some 0.375 or 0.376 sized K line valve guide liners...

you will want some 3/8 wooden doweling.

you will need a LETTER Y drill..

if you happen to have a 3/8" valve guide reamer or the sizing tool from an old school 3/8 valve guide knurling tool kit..

the shaft diameter is close to 0.372.. don't tell the engine builder that. .ask for the sizes above..   the letter Y drill is 0.404" the .375 guide liner has 0.015 liner wall thicknesses..  the 0.376 has 0.0145 wall thicknesses..

you can use tiny hose clamps to hold the guide liners to the wooden dowels to make it easy to cut to length with the dremel..

you will also want to jot down these part numbers..
GP Sorenson 800-9214 and 800-9215..  they are the large and small fuel line Orings.. usually less than $3 a box of 10..  they are not included in the gasket kit..  the larger versions fit the GM fuel filters also.  no use turning it into a fiero..

please use some kind of lube on the Orings and housings when reinstalling the fuel injectors.. and use the included long screws to guide the cover down on the fuel pressure regulator..

is this enough instructions..

i was thinking about doing rebushed throttle bodies to run an exchange service with the local professional parts store..  a friend closing his salvage yard had a whole barrel of gm throttle bodies for me.. before i could get there somebody offered him a pile of cash for them..  drat..  i did not even need the injectors.  that is what they wanted.


when resetting.. you have to back the idle stop screw all the way back to allow you to center the throttle blades...  you should peen the tiny amount of extended screws over..

supporting the heads of the screws creatively... with a long extension in a vice..

you will have to reset the idle stop screw at a point about 1/2 turn farther in than the throttle blades stick in the bore..

when you get the TBI reinstalled..  you should set base idle..  stuff towels down into the idle air passage..  to block it completely.. adjust the throttle stop screw so the engine just barely idles.. or around 475 to 525 RPM..

unplug the idle air passage..  slowly take the RPMS up to 2000 and let it stay there for 20 seconds..  this is with the engine up to operating temp...  slowly return to idle.. take 20 seconds to close the throttle.  that should give the computer a chance to relearn idle air position.. if you look at the TPS and the IAC..

again below .098 TPS... 0.5 to 0.70 ..

IAC 20 to 50..  if below 20.. you need to close the throttle farther..  if above 50.. you need to open the throttle farther.  or is that reversed.. i forgot..

[Arnold]

I thought I had my 92 chev  truck 5.7 L fixed the other day with a new ignition module but it now has a fluctuating idle problem . I took some throttle body cleaner spray and went at it tonight thinking that the IAC was clogged up but after a half can of cleaner I would be optimistic if I noticed much of an improvement .The idle will not fluctuate when idling in park or neutral . It fluctuates less in reverse and more when sitting in drive . When you come to a stop at an intersection it takes about 5 seconds before it starts to fluctuate and it seems to do it at a regular interval. If I push the throttle to even 600 rpm the problem goes away .It appears to be idling at 300 to 400 rpm in gear. When it fluctuates you can see the injectors momentarily pulse the fuel supply . I put a bottle of sea foam in the topped off fuel tank tonight . When I installed the ign module I did not disconnect the battery , I did put all that insulating goo under the module before installing . Whats up ? It ran fine right until it stalled out and died the other day with no signs of a problem . I replaced the module , cap , rotor and a very dirty air filter .

 My 01 Focus started to do a similar thing. I took it to a seriously sharp local garage where the owner asked if his son..young..could do this..I said sure. He told his son that was a vacuum leak and keeps throwing the computer off and it will keep trying to adjust it until the leak is fixed. He told him to look for some vacuum elbow that could not be seen..just felt  It was cracked and they changed it..did not want to charge me but I gave them $20..dropped in and left with my car fixed in like 2 seconds..
 My 94 5.7 gave me all kinds of grief..finally it was time to fix the vacuum leak..I never did.
  I think that the map sensor diaphragms crack in those things..as well coolant temps sensors are a problem too
  Wayne sure knows these things..if there is play..me would go to the bone and get another good used one. Change the whole thing. Prolly the dist at the same time.
  As far as vacuum leaks..these 5.7's ran pretty much forever..till they needed intake/oil seals.
  You need good intake vacuum with these later..post carb.... totally unlike early sbc's..
  Have you had the injector out to  check it/clean it.
  It is pretty hard to even clean the gunk in there without taking out the injector.
  Might be the regulator..I think those are in the tbi unit..pressure/rich surging..
  I'ld check the vacuum and then throw some used parts at it.
  These things were pretty simple bullet proof units.

[chimp koose]

Thanks for the replies . This unit has 360,00 km (220,000miles)on it . Rebuilt at 150,000 km but likely untouched fuel system , just long block.I am going to look it over this weekend . I am not that good with electrical test tools . I am the vacuum gage carb guy .Funny thing  , if I even just rest my foot on the throttle when stopped (left foot braker here) there is no idle problem . The engine wants to idle around 300 to 400 rpm and that's where the surging starts