# 95 chevy 1500 running rough



## leonardjudy (Jan 20, 2008)

i have a 95 chevy pickup running rough ,4.3 i changed plugs,wires,rotor button,cap,pcv valve,converter and oxy sensor, when i get on the highway the check engin light comes on and throws the oxy code but i changed it twice so that aint it,could somebody give some advise. thank alot


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## mack1 (Nov 27, 2007)

Hi Leonardjudy
I was hoping someone more qualified (had a similar problem) would offer help, but at this point, I see none. I have a 4.3 engine in a 96 s10 blazer. Probably almost the same as yours that had a fuel injection problem so I got the opertunity to look into the fuel systems further than I wanted to. I bought and read a Haynes Repair Manual. In doing so, I found that the system has probably 5 sensors related to the air and fuel ratio. The computer looks at throttle position and engine timing to know when to inject fuel. It looks at other sensors to know how much to inject. If it isn't right, an oxygen sensor in one of the exhaust pipes will complain about it. (the check engine lamp) The error code will tell you which oxygen sensor is complaining, but won't tell you what the problem is. If you intend to fix the problem yourself, I would suggest you get a repair manual, volt/ohm meter, and fuel pressure guage. For the engine to run smoothly, you will need about 60 psi on the fuel pressure. The meter will help you track down sensor problems. 
Be sure the air filter is clean. 
Wish I could be of more help.


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## leonardjudy (Jan 20, 2008)

thanks for the info mack1. if you could tell me the 5 sensors related to the air fuel ratio i would appreciate it


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## jeepinboy70 (Jan 6, 2008)

You have a 95, the 96 is a vortec motor. The 95 is still a throttle body set up. (15 lbs fuel pressure) And there should be only one o2 sensor. I suggest that if you already replaced the sensor, then. I would look into the wiring going to it. It is 13 years old now, never know what you'll find inside the wiring loom.


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## leonardjudy (Jan 20, 2008)

thank you ill check those wires , but mine is a votec motor unless someone put valve covers that say vortec on it , and it is throtle body


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## qldit (Mar 26, 2007)

Good Morning leonardjudy, from your description it would appear you suspect ignition is the problem, that would also be my suspicion, however, as mack1 suggests, things may not be as they appear.

I also would suggest getting a Haynes type manual and some means of checking the fuel pressure. 
Be careful and ensure decent adapters are used to couple to the fuel rail.

I am a great believer in giving the fuel tank a shot of injector cleaner and running for a period with decent fuel to see if that has any effect before getting too involved with parts changing.

A O2 sensor code may not be an actual O2 problem, consider it as just a pointer that combustion sensing is improper or that the resistance of that circuit may be outside tolerances.
Normally a small voltage is generated by the presence of O2 in the hot gases passing that sensor, so that wiring integrity is important.

When this voltage is apparent the scheme is to add more fuel and modulate engine speed for proper burning efficiency dependent on throttle position. This effect is maintained very quickly and is continuous.

If there is a lot of garbage apparent in the exhaust when the erratic running is happening with correct fuel pressure having been checked, I would be looking at the ignition system more closely.

Defectve leads and massively set plug gaps or running the engine with a plug lead disconnected can reflect into the coil driving circuit and damage the driving system, so spark becomes erratic.

Sometimes this erraticity can be heard on a simple portable AM radio tuned to the low end of the band. (clicking noise is erratic)

Any of this kind of discrepant ignition firing effect is generally more evident under accelleration conditions, especially with low engine speed.
(hesitation)

Others will have different ideas.

Cheers, qldit.


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## leonardjudy (Jan 20, 2008)

thanks for the tips, i've been stump by the whole thing. it runs rough at idle ,like its missing,,just check fuel pressure and the harrness, so far that all checks out,,its gettin crazy ,,lol


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## island auto (Oct 5, 2007)

also check the egr valve remove it and check for carbon buildup holding the egr open


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## qldit (Mar 26, 2007)

Good Evening leonardjudy, these kinds of problems can be a real pain.

It may be an idea to go back to basics and also consider doing a compression check, it can sometimes cause upset if there is a compression loss enough to cause misfiring and this can affect the whole loop.

My gut feeling is that the problem is ignition but gummy or sticking injectors can produce a similar effect.

Does that vehicle have separate coilpacks?

Have you double-checked the firing order and spark-plug leads are definitely correct?

Others will have different ideas.

Cheers, qldit.


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