1992 Chevy 4.3

[348tripower]

My friend has truck he is having a problem with. It idles very rough and sometimes looses power at speed. He has replaced the map sensor, idle air control, egr valve  and cleaned out the converter. He says that when he unhooks the map sensor the engine temp climbs to 210 and it runs fine. When he hooks it back up the temp drops to 150 and the problems return. Suggestions?

[tomslik]

vortec?
if so, if you've got a scanner available (not a code reader) see what the egr position is at idle or even with the key on engine off, anything but 0 is an issue

not uncommon to have a chunk of carbon holding the valve open.
you'll have low vaccum and really crappy brakes (unless it's hydroboost)

[348tripower]

I don't think it is the vortec but I will ask when he gives me a call back. Thanks.

[wayne petty]

a few things to check...

examine the ignition coil for high voltage leaks...




then yank the distributer cap and rotor look inside...   are there any carbon deposits inside the cap.... or on top of the rotor...  

while the cap and rotor is off.. shine a bright flashlight down the distributer shaft.. look at the gap between the top layer of the reluctor and the shaft.. the second layer is a ceramic magnet...  when this magnets cracks and they almost  all do eventually..  it puts out weird out of phase wave forms from the pick up coil.. this messes with the electronic spark control..

as when the system keeps track of the waveform from the pickup coil is used with a timer to control the next spark event..   the module delays the spark generation to allow the timing to be advanced essentually forward of the base timing...    when these ghost signals appear .. the countdown gets thrown off.. so random sparks are generated... causing the engine to run rough...

i have also found the distributer shafts really loose in the distributer..

so loose on one.. that there was a weird clicking sound when the engine was running.. it was the teeth of the reluctor hitting the pickup coil teeth...

this is a reman distributer from AZ  other stores have them also .. but look for this improved design reluctor..   it creates so much better wave form.. you won't believe how much better the truck will run...

[wayne petty]

i knew i had a picture of it someplace..

[348tripower]

Thanks. I will get him over here this week and tear into this.

[wayne petty]

i forgot the most important thing...

this only takes a minute to do.. can save a lot of time..  and make you look like a genus...

when changing the distributers...

pull the cap.....    figure out where the number one wire is... bump the crank around till the rotor is pointing toward the number one....

use small inputs or  a socket on the alternator nut... to bring the distributer shaft forward until the reluctor teeth line up perfectly with the pick up coil teeth...   be sure that you are rotating the motor in a forward direction when doing this.. if you go past... back the motor up enough that when you start moving it in the forward direction that the slack is gone from the timing chain..   when it is perfectly lined up... >< thats where the distributer is going to fire the spark when cranking..

note the timing mark location on the balancer.....

now... you can preset any motor...  know exactly where the distributer housing lines up with the shaft...  so you can yank it out.. stuff another in... line it up.. lock it down.. reach through the window and crank it... and it will start and run perfect on the first try....


oh.. and what about the oil pump shaft.. you have to choices... preset it.. or lift the distributer just high enough to clear the gear.. sometimes you can get it to work around...

i have been doing this long enough.. that i can drop the distributer in..  use my remote starter to bump the engine around 2 times so the rotor is pointing at the proper angle.. reset the crank with my socket on the alternator nut again... then turn the housing to line up the >< and lock it..

sorry for the long and drawn out explanation..  next time i have a motor on a stand .. i plan on doing a video  on this..

[348tripower]

Thanks again!