95 chevy running rough, can't find problem!

Have a question or want to start a discussion? Post it! No Registration Necessary.  Now with pictures!

Threaded View


My 95 1/2 ton silverado with 5.7L is running rough, and I can't find the
problem.
 It acts as if it is going to stall when I accelerate and begin to slow
down. Once I stop, it idles good. The check engine light doesn't come
on. I replaced the fuel filter, air filter, distributor cap & rotor, and
ran 2 bottles of fuel injector cleaner thru the system. I also cleaned
the idle control valve. None of these things helped.
 When the truck sits for several hours, like overnight, it doesn't begin
acting up immediately, only after a few minutes of driving.
Any ideas on what could be wrong??








Re: 95 chevy running rough, can't find problem!


My guess is that it is running lean after warm up.  I would put a vacuum
guage on it and check for leaks, broken lines etc.
Quoted text here. Click to load it



Re: 95 chevy running rough, can't find problem!


I may very well be out in space. But my friend's Buick
Station wagon, the throttle position sensor was bad. It was
a PIA to replace, but it made a big difference.

--
Christopher A. Young
Learn more about Jesus
We've slightly trimmed the long signature. Click to see the full one.
Re: 95 chevy running rough, can't find problem!


Jeff wrote:
Quoted text here. Click to load it
   My 90 Sierra with 5.7l was doing the same thing. Do you get a
clicking noise from under the dash when the truck stumbles or runs
rough. In my case I can corroded battery cables. I had to peel back the
insulation on the cables to find the corrosion. And the corrosion was
quite a ways up the cable from the battery connections. Hope this helps.

  Bob

Re: 95 chevy running rough, can't find problem!


Jeff wrote:
Quoted text here. Click to load it
EGR valve?

Re: 95 chevy running rough, can't find problem!--complx


How do I test the EGR valve? Are they expensive to replace?








Re: 95 chevy running rough, can't find problem!--complx


Jeff wrote:
Quoted text here. Click to load it

Most often the valve seat (in the intake manifold), the actuator shaft,
and the pintle become coated with carbon.  Usually, this causes an
extremely rough idle.  There are a couple of bolts mounting the EGR to
the manifold--not fun to get to, but with patience, it's not bad.  If
it's gunked up pretty bad, you can use some carb cleaner to clean it up.
  It's a pricey item.  I think somewhere around $135 or so.

Also, sometimes the EGR mounting bolts will work loose and cause an air
leak.

Good luck.

Re: 95 chevy running rough, can't find problem!


Basically these newer vehicles have a lot of different electrical components
which give input to the engine computer and then a lot of components in the
fuel injection system.

The *new* way to find these problem is to "test" various components to see
if they are operating as they should. Then you would know what is working ok
and does not need to be replaced. Which needless to say can save a ton of
money as opposed to the "guess and replace parts" strategy.

For testing all this stuff, you need a GM Factory Service Manual set for
your year/model vehicle, a multimeter, a fuel pressure gauge (they make one
for GM TBI vehicles), and in some cases an exhaust pressure gauge which
would go into the oxygen sensor hole for testing exhaust back pressure.

Then just find the symptom in the shop manual, then it would have detailed
troubleshooting instructions for the symptom. Sometimes several pages of
things listed to check.

You can order a Factory Service Manual set from helminc.com or from a GM
dealer. They cost about $135, but you get what you pay for. Anyway get the
right tools for the job.

As an example of a test, there is a "coolant temperature sensor" which tells
the engine computer what temperature the engine is running at. Very easy to
test. Place a thermometer in that area, unplug the electrical connector,
place your multimeter on ohms, then read the ohms on the two connectors for
the sensor. Then look up in the shop manual what the resistance (ohms)
should be for that temperature.

If it is reading what it should, then no need to replace. Say that sensor
costs around $25, well you just saved yourself $25! Then on to the next
sensor.

With the shop manuals it is sort of the case of "too much information".
Something like the above coolant temperature sensor may be listed in 4 or 6
different spots in the various manuals (4 different books to set). So may
take a bit of learning of where to find the information you are looking for.
But that is a lot better than not enough information provided...

As to shop manuals, older sets have a general service manual, a fuel and
emissions service manual (engine troubleshooting), an electrical diagrams
manual, and a unit repair manual. Newer sets have this all mixed into a 4
book set with each book about 2 inches thick.



Re: 95 chevy running rough, can't find problem!

Quoted text here. Click to load it