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1995 Silverado, no power, strange idle

 
gofast777
I love my Chevy Chevette!
Posts: 4
Joined: 10/11
Posted: 10/08/11 05:12 AM

Confused Good Morning,
Recently got a '95 Silverado,350 tbi,K2500,4x4. Truck starts and runs great, until it gets warm, if I restart it while it is warm, the idle is very jumpy, it'll die sometimes. However, what makes this strange is that after 15-20 seconds of babying it, everthing calms down, idles smooth, and runs just fine. No more problems, till it needs to be restarted.  I've owned many a Chevy truck over the years and never encountered anything like this.
Second issue is the serious lack of power. The truck is stock and original at this point and has only 135k miles. I've replaced the tps, fuel and air filter. Checked wires (which were replaced with 8mm) plugs,cap and rotor. All appear good, but I'm going to replace anyway.
Any suggestions on checking injectors? What else should I be looking at?
I live in Denver, and when I get into the hills here, the best I can do is 55mph,in third gear.  Getting passed by a honda with a trailer in just not acceptable.
The truck did pass emissions with no problems....I'm confused...
Any advice or suggestions would be greatly appriciated.
Thank you in advance for all your help!!!  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/08/11 07:05 AM

a few things...    

first... do you own a digital volt meter..

start the engine.. turn on the headlights..    set meter to 20 volt dc scale..

1.  test positive battery to negative battery bolts..   14.1 to 14.8 volts is acceptable..

2.  test negative battery bolt to the engine block..    0.04 volts is expected..

3. test negative battery bolt to the body...                0.02 volts is expected..

4. test engine block to body                                        0.02 volts is expected.

if you got 0.00 on the last 3 tests.. change the meter setting to 2 volt dc and retest..  confirm.. the small readings.. post what you get..

next.. take off the distributer cap..    pull the rotor..  look straight down the shaft at the second layer of material .. its a magnet under the riveted steel reluctor..  if you see cracks.. replace the distributer..    find one at like an az store.. 99 bucks or so.. it will have a different shape reluctor.. and pick up coil.. and usually a transpo module.. this is a far better design..

easy to change..     with the cap off..    bump engine around till the rotor is pointing toward the number one position..   bring the harmonic damper to the base timing on the sticker.. without going past..  in normal direction of rotation so you don't end up with any timing chain slack..     the tips or the reluctor should now line up with the tips of the pick up coil..   if not move the crank until they do..  note where the crank timing marks are..  so you can duplicate the location..

now.. you can swap out the distributer..   you will have to preset the oil pump shaft..  so you can drop the distributer all the way in..   then turn the housing to line up the reluctor tips and the pick up coil tips..  this is where it will fire the coil on start up..    before the electronic timing takes over..  

this is what the new distributer will look like.. this is a six cylinder model. yours will have 8 teeth.


4Pointthreetbidistributer

i will try to find the other picture of the failed distributer magnet tonight .. and repost..  

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gofast777
I love my Chevy Chevette!
Posts: 4
Joined: 10/11
Posted: 10/08/11 09:00 AM

Alright!!
Yes I do have a voltage meter and will start checking when I get home tonight.
Are the symptoms I described common to a cracked dist?  I have no idea what a cracked distributor will cause, so I've never looked at it.
I'll repost my electrical test results later.
Thanks again for the input!!
~G~  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/08/11 01:26 PM

Smallcapheicracks  

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Navyet
I love my Chevy Chevette!
Posts: 4
Joined: 10/11
Posted: 10/11/11 10:16 AM

So I have a 73 nova with a 350 and have almost the same thing going on it idles really low and might shut down after giving a quick burst of aloe of gas. It's stock and rebuilt I guess idk if what they said is true but it has like no power and is so slow and always smells like way to much gas when it's on idk if it's burning or what but I don't see any leaks..  

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gofast777
I love my Chevy Chevette!
Posts: 4
Joined: 10/11
Posted: 10/12/11 05:04 PM

Ok Wayne,
I finally got a chance to get to my truck, sorry it took so long. I know you are trying to help, and I really appriciate it.
The electrical readings you asked for are as follows:
Positive to negative bolts.............  14.35
Neg bolt to block......................    .02
Neg bolt to body.......................    .02
Block to body..........................    .04

I pulled the distributor cap and rotor....cracks, several as a matter of fact.
They are not as big as the ones in your picture, but present none the less.
I'll be getting a new distributor asap.
Can you tell me what exactly these cracks do that causes such chaos with my engine?
Thanks again, I'll post more as soon as I can get the dist put in.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/12/11 07:53 PM

sure...

under the reluctor is the pick up coil....

it makes alternating voltage as the reluctor spins .. as the teeth of the reluctor approach the teeth of the pick up coil.. the voltage goes above 0...   as the teeth line up perfectly.. it drops to 0...   as the teeth pass each other.. the voltage drops below 0...

this voltage is used by the ignition module to control the power  transistor that turns the ground side of the coil on and off...

the pick up coil needs to create about 1.0 volt AC...

in electronics.. voltage is measured from 0...  so it needs to make .5 volts positive and .5 volt negative..

the power transistor turns On at +.3 volts above 0..   as the pick up coil signal drops to 0.. the power transistor opens the circuit discharging the coil....

this is how a conventional electronic ignition works...

but this has computer spark control... since your base timing is set at anywhere from 0 to 15 BTDC.. depending on your application..   the computer uses a trick... it uses the ac wave  which is a nice steady signal dependent on engine rpms and starts a timer ..  this is where the cracked magnets come into effect..

the computer holds back the transistor opening by a calculated amount..  so it can advance the timing..   it uses the previous signal to trigger the timer...  

when the reluctor is cracked...  Ghost waves are created out of time with the regular spark timing signals from the reluctor...

this causes the computer to start a random count down..  random sparks are created.. this causes the detonation sensor to trigger the retard also sometimes..

the new style pickup coil and the reluctor create a far cleaner wave form.. ..

~~~~~~~~~~~~~~~~~~~~~~~~~~~
before taking anything apart.. i normally have a GOOD friend start the motor while i climb under the truck and use a wire brush to clean the spinning damper outer ring.. this is dangerous...  but it works really well...

to ease installation... preset the motor...

take off the cap.. use a 15/16 socket on the alternator pulley bolt.. to advance the motor till the rotor is pointing at the #1 wire position on the cap...

looking at the emissions label. it should give you the base timing .. 0..  10, 15 BTDC...

turn the crank in normal direction of rotation and look at the reluctor teeth.. when they line up perfectly with the pick up coil teeth.. stop...   if you go past.. go back and come forward again...   once lined up...  look at the timing mark on the damper...  it should be at base timing if the timing was correct..   make note of where its at..    then move the crank back and bring it forward to the timing mark as described on the emissions label..  see where the reluctor tips line up again..

where the tips line up.. is where the base timing should be..

just make sure that you are moving backwards with the crank far enough to take out the timing chain slack...

...

you can now.. with the motor preset.. remove the distributer...    

you may have to preposition the oil pump shaft in the block to align with the distributer when you drop it in.. .

once you have the distributer in and down..  with the rotor pointing in the correct direction.. .  you can turn the housing to line up the pick up coil and the reluctor teeth .. lock the distributer down..  put it back together and it should start on the first try..  without the need to turn the housing to get it running..

i love doing this in the shop.. i can preset the motor ... yank the distributer..  work on it..   shove it back in.. lock it down .. reach through the window and turn the key and the engine starts on the first try...  

people think i am amazing..  perhaps they just don't know any better..  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/12/11 08:00 PM

oh.. test 4 is acceptable at that small voltage..

i personally would like to see you install at some point soon.. and additional 12 or 10 gauge ground wire between the back of one of the heads.. usually the one with with alternator mounted on the front and the firewall..  this will shorten the path the electrons have to go to get to the body.. .  this will also drop your #4 test back closer to the expected 0.02..

if you used a full battery cable.. you could get it probably to 0.00.. but that is not needed..

try your other cars.. .  remember the voltage drop test.. it will save you days of changing parts and hundreds if not thousands of dollars..  as all the new cars have everything electronic..

the most important thing.. electrons flow from NEGATIVE to POSITIVE..  if you don't have a good ground.. you won't have enough electrons to operate the circuit properly..

ever tried to water your lawn with a kink in the garden hose????  that is the mechanical version of a voltage drop..  it only shows up when the water is flowing..   when the nozzle is closed. you will have the same pressure at both ends.. open the valve.. the pressure drops at the nozzle end as there is a kink before it gets to you...  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/12/11 10:40 PM

Sounds like a dirty or sticking I.A.C. idle air control valve. It's a stepper motor. I would mark it for a reference point before you remove it. When you take it out it has pintle valve, and seat. Some time and being a 1995 it has miles on it. Anyway when you take it out be careful with it. There are cleaners on the market that won't hurt sensitive parts. Clean that and also the seat that it goes into. Look for carbon or just dirt any where in that IAC area. Good luck..........  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 10/12/11 10:44 PM

Wayne how you doing?

Have you seen any post's from Ron? I emailed him to. Redneck Joe and TUFFNUFF haven't seen any posts from him. We all hope he's OK.

Thanks
Bob  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 10/13/11 12:13 AM

pepsi1.. got a note from ron just the other day.. he has just been buzy...  

he is lurking  around..  

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gofast777
I love my Chevy Chevette!
Posts: 4
Joined: 10/11
Posted: 11/09/11 04:05 AM

Good Morning,
Thanks again for all your help in my quest to boost power in my silverado.
So far I have replaced,
Fuel and air filters,
Distributor(with new, not reman), cap, wires, plugs,coil
Throttle position sensor,
Idle air control valve,
I've run a can of 44k through it,
and reset the timing. And yes, I did unplug the electronic advance wire to set it.
yet I've got no increase in power that is noticable.
The iac valve did seem to help the idle situation but it stills appears at least once a day, but not all the time.
If the cat is clogged or restricted, is there any good way to check that, short of pulling the it out completely?
I apologize for taking so long to get back to you all,work is very busy and the days keep getting shorter.
Any other suggestions or ideas would be greatly appriciated.
Thanks again  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 11/09/11 02:12 PM

testing for restricted exhaust..

hook a vacuum gauge to a intake manifold vacuum source...

start the engine...

you should have around 15 inches of vacuum..  perhaps more...

slowly raise the engine speed..    the vacuum reading should NOT decrease...  it should say the same or increase..

i would really really like you to try something...

engine off...  reach up and grab the throttle lever on the throttle body......

open the throttle slightly...    see if it wiggles around in the throttle shaft bore....

if you have wear...  what happens..    the throttle position sensor at the far end of the shaft sends a variable voltage to the PCM...

if the throttle shaft bore is worn..   it may be worn enough that when releasing the throttle.. the TPS voltage drops to a different voltage each time.. or sometimes..

the TPS voltage has to return to the EXACT same minimum voltage..  every time...

when the throttle shaft bore wears.. the throttle blades catch on the housing bore and stop the throttle from closing all the way.. even a fraction of a degree..  

the change in minimum voltage will tell the computer that you have your foot on the gas as you start.. so it will be really rich or in clear flood mode until the heated oxygen sensors warm up and start sending signals to the ECM as to what the air fuel ratio actually is...

warning.. DO NOT TRY TO REMOVE THE THROTTLE BLADE SCREWS without grinding the exposed threads off...  they will break off in the throttle shaft and ruin your day..  the screws are 2.5 MM x .45 thread probably 6 to 8 mm long.. not something easily found...   i use thin wall valve guide liners for a 3/8 valve stem.. 0.375"    a letter Y drill at 0.404" and grease the shaft when i work it back in..  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 11/09/11 02:49 PM

if you can find somebody with a scan tool that will actually read live data on this...  94/95 is a trouble year.. obd 1.5..

look at the TPS voltage as you work the gas pedal multiple times.. engine off .. and engine running.. it should always return to the same under 1.0 volt setting.. NOT changing at all...

with the engine running..   warmed up...  look at the engine coolant temp on the scan tool.. 190 to 215F..

then look at the IAC  idle air counts.. 20 to 50...  

please post results..

and finding a scan tool that will show live data is hard on that model.. .  you might have to find a professional model..

OTC   snap on...  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 11/09/11 03:10 PM

Good to hear Wayne.

Thanks
Bob Cool  

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