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Daves71
Daves71, ASE Certified Technician
Category: Chevy
Satisfied Customers: 719
Experience:  35+years experience in automotive repair
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1995 Chevy: 000 miles..Surges and sputters..accelerating..runs rough

Customer Question

1995 Chevy C10 1500 5.7 350 engine 183,000 miles. Surges and sputters when accelerating at low speeds, 20 -35 mph, runs rough as if it is missing at low speeds.
Replaced:
1) Replaced the coolant temperature sensor
2) Replaced MAP sensor
3) Checked the throttle sensor response is as required
4) Checked the O2 sensor via propane torch test, checked fine
5) Replaced the Fuel Filter
6) Checked the EGR valve, seems fine, pushing up on it stalls the truck at idle so doesn't seem stuck.
7) There are no Check Engine Lights and no trouble codes via the paper clip method on the OBD1.
8) Rotor, plugs and wires are new as of 4 months ago.

Running out of all the basic things to check or replace. (It seems that if the O2 sensor where the issue it would not have these symptoms on startup when still in open loop, is that a correct assumption?)

This started suddenly as if something had a hard failure, prior it was running fine.
Submitted: 4 years ago.
Category: Chevy
Expert:  Daves71 replied 4 years ago.

Hi Franchini,have you checked the catalytic converter to see if the honeycomb has broken apart and restricting exhaust flow?Also is this a TBI or MPFI fuel set up.Let me know and we can go from there,thanks,

Dave

Customer: replied 4 years ago.
Dave,

I believe it is TBI, kind of looks like a carburetor right?

I have not checked the catalytic covnerter, although it has been on my mind a a possibility. How does one check it since it is enclosed?

Thought I'd better mention that if you put the truck in neutral or drive and turn off the AC to effectively reduce all load, the truck seems to idle fairly well. You can rev up the RPMs and there are no noticeable symptoms at all sounds smooth, as soon as you put it in gear it begins to sputter, and surge, and attempts to stall. Take it back out of gear and it is fine.
Expert:  Daves71 replied 4 years ago.
The easiest way I have found to check the cat is by removing 1 of the oxygen sensors and see if the problem gets better.The TBI does resemble a carb.I would also recheck the distributor rotor to make sure its ok(i know its not old but have had problems before).
Customer: replied 4 years ago.
I have disconnected the O2 sensor and run it with the problem the same. There is only 1 O2 sensor on this model and it is before the catalytic converter.

Any thoughts on the load vs. no load scenario, why would it only show under load.

I will check the rotor.
Expert:  Daves71 replied 4 years ago.
On the o2 sensor,I ment remove it from the pipe.The problem under load usually is spark related(coil,wires,etc) and on this model usually won't set a code.
Customer: replied 4 years ago.

I have combed through hundreds of forum discussions on similar symptom descriptions and none have provided a solution only unresolved questions with the same symptoms I have described. I have paid this site already once for ideas as well. Is there a methodical guide through process of elimination to get to the bottom of a problem with just layman diagnostics tools. Solving this seems to require some sort of extra knowledge of the engineered vehicals of today which is based on engineered control alorithims in the ECM. Based on what I have tried already and provided above and below, is there a way to methodically eliminate the causes including the ECM itself. First knowing if it is a closed loop or open loop problem. I have had engine misses before and understand that when you power brake under load the miss is easily detectable. Sensor failures should be indicative of closed loop symptoms and problems it seems to me. The problem I am having exists both in open loop and closed loop.

 

At times at idle it will run fine for 10 minutes and then begins to suck air through the throttle control valve to the point where the sucking sound is very loud and noticeable and it begins to sputter and stall unplugging the temperature sensor seems to save it from stalling. Restarting after a stall no problem as if it hadn't been struggling to run before.

 

Above idle when in gear it is a struggle to get it going with the temperature sensor plugged in or unplugged, during acceleration from 20 - 35 MPH causing the truck to sputter and surge really bad until above 35 MPH. Once above 50 to 60 not as noticeable, but the power is not there when you punch it. Engine light only comes on briefly when running at highway speed, with a code 44, for oxygen sensor lean indicated. (OBD1 system)

 

The injectors look to have a good evan cone of fuel spraying from them.

The rotor and cap look in good working condition and are fairly new.

The tailpipe has a good burst of pressure after gunning the engine.

Spraying carburator cleaner around the throttle body gasket does not improve or decline the idle symptoms.

 

Would a timing problem not reveal itself by reving the RPMs in neutral or drive and then wreak havoc when in gear?

 

This is my last gasp for help on the site, I am about to throw in the towel and take to the dealer Monday.

 

Expert:  Daves71 replied 4 years ago.

I went back and re read all the conversations we have had as well as looking at GM tsb's that could cause your problem.I want to see if there is a prom update for your truck but I will need the vin# XXXXX do so.The next thing I noticed that we really did not look at the distributor itself for shaft play,side to side and up and down.I normally would hook up a scan tool and look at all the sensor values at start up and then watch them when the engine is put under load and when it reaches operating temps.I would also hook up a timing light while working with a scan tool to see what the spark and timing does,does timing start to bounce around,does spark get weaker.If the distributor module and pole pickup have problems it can cause the problems you have.Please let me know your thoughts on this,thanks,

Dave

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