S-10 4.3 "hunts" at hiway speeds

[Driver43]

2001 S-10 w/4.3L 5 Speed manual trans. Engine "hunts" at hiway speeds. Torque is not constant. I can feel the changes in engine power. Accompanied by a drop in gas mileage from 23 to 20 MPG. Took to Chev Dealer & they installed plugs, ign wires and new dist rotor. No change in symptom. Still bad gas mileage. Vehicle has 155K miles and is one owner-me. Most all driving is hiway. What should I do to get the engine performance back where it was and stop the erratic engine?

[MT-2500]

Originally Posted by Driver43

2001 S-10 w/4.3L 5 Speed manual trans. Engine "hunts" at hiway speeds. Torque is not constant. I can feel the changes in engine power. Accompanied by a drop in gas mileage from 23 to 20 MPG. Took to Chev Dealer & they installed plugs, ign wires and new dist rotor. No change in symptom. Still bad gas mileage. Vehicle has 155K miles and is one owner-me. Most all driving is hiway. What should I do to get the engine performance back where it was and stop the erratic engine?

Check fuel pressure when it is acting up.
Post back fuel pressure readings
Any check engine lights on or flashing?
Any code stored in VCM?

[Driver43]

Thanks......
Will replace fuel filter this weekend and then go back to Chev Dealer next week for analysis.

[Driver43]

You were wise in suggesting a fuel problem. Changing the fuel filter solved the problem. It was filled with a dark jello-like substance. When shaken it came out of the filter in chunks. Thanks for your advice.

[MT-2500]

Originally Posted by Driver43

You were wise in suggesting a fuel problem. Changing the fuel filter solved the problem. It was filled with a dark jello-like substance. When shaken it came out of the filter in chunks. Thanks for your advice.

You are welcome.
And thanks for posting back how it is going.
It would be wise to recheck fuel filter and fuel pressure after driving it some.
Fuel tank may be full of junk or fuel pump going out.
Old dark black stuff can come from a bad fuel pump.
Let us know how it goes.
Good luck

[Driver43]

After driving for about 200 miles, the problem came back. Same as before, constant surging. Now if I floorboard it, it runs without skipping a beat during acceleration, even if I lug it down first. Took it back to dealership but their tech who is best at computer diagnosis was out sick, so maybe next week. Not a happy camper.

[MT-2500]

Originally Posted by Driver43

After driving for about 200 miles, the problem came back. Same as before, constant surging. Now if I floorboard it, it runs without skipping a beat during acceleration, even if I lug it down first. Took it back to dealership but their tech who is best at computer diagnosis was out sick, so maybe next week. Not a happy camper.

Read and Remember what I told you in last post.
Sounds like you may have a fuel tank full of crap.

Pull fuel filter back off and have a look in it.
Computer diagnostic will not tell you if tank is full of crap.
It does not take a computer tech to remove and check fuel filter for crap in it.
Good luck and let us know how it goes

[Driver43]

Took vehicle back to dealership and the tech connected up the diagnostic computer and we went for a drive. Nothing, although the surge symptom was in full cry. They told me they'd like to have my money but it would be like throwing darts. I can't afford that, so since a fuel filter solved the problem for a while, I plan to have another fuel filter installed at somewhere other than a dealership. I can have several replaced at my oil change place for just a fraction of what a filter alone would cost at GM. Film at 11:00 ;-)

[MT-2500]

Originally Posted by Driver43

Took vehicle back to dealership and the tech connected up the diagnostic computer and we went for a drive. Nothing, although the surge symptom was in full cry. They told me they'd like to have my money but it would be like throwing darts. I can't afford that, so since a fuel filter solved the problem for a while, I plan to have another fuel filter installed at somewhere other than a dealership. I can have several replaced at my oil change place for just a fraction of what a filter alone would cost at GM. Film at 11:00 ;-)

A good scanner will show fuel pressure or fuel filter problems.

Also a good fuel pressure test would be in order.

[Driver43]

I had the fuel filter replaced again to see if there was any crap in the tank causing the filter to clog. The filter looked just fine. No chunks or crap as was the case when I had the filter replaced a couple of weeks ago. But I put a new filter on anyway. Since the dealer's computer did not show anything as I drove the tech around I'm about at the end of my rope. I am convinced it is a fuel problem but my knowledge of the fuel system is scant. I bought the Haynes book for my vehicle and maybe I can learn enough to ask the right questions. Meanwhile, I'm still driving around in a herky-jerky pickup. If you have any suggestions, I'd be happy to hear them.

[MT-2500]

Originally Posted by Driver43

I had the fuel filter replaced again to see if there was any crap in the tank causing the filter to clog. The filter looked just fine. No chunks or crap as was the case when I had the filter replaced a couple of weeks ago. But I put a new filter on anyway. Since the dealer's computer did not show anything as I drove the tech around I'm about at the end of my rope. I am convinced it is a fuel problem but my knowledge of the fuel system is scant. I bought the Haynes book for my vehicle and maybe I can learn enough to ask the right questions. Meanwhile, I'm still driving around in a herky-jerky pickup. If you have any suggestions, I'd be happy to hear them.

Sounds like you need to find a dealer that has a factory trained tech that knows hoe to read a scanner.
But You need to.
Run a fuel pressure test.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[avlind]

Hello, I have a94 Chevy S10 V6 4.3 vin Z, 2w, 5 speed manual trans and I have had the same issue in the past. I can't recall if you mention that the check engine light was on or not, but you may want to check the Oxygen Sensor.

If I remember correctly, it is located on the driver side mid way way down the exhaust near the main frame of the the truck.

Good luck,
Aileen

[Driver43]

Thanks for the input. I have not had a chance to take the vehicle to a larger dealership yet for further testing, but I will ASAP. There are no alerts such as Check Engine Light, just a herky jerky drive down the road at legal highway speed.

[Driver43]

Well, you were right about the fuel pressure. Took my pickup to my local dealership and they found that fuel pressures were "marginal". Replaced fuel pump and cleaned gunk off of strainer and so far all is well. It was expensive but worth the $$ as long as the infernal hunting stays gone. Also, I'm getting one to two MPG better. For that I have no explanation. Could be the cooler weather. I dunno.

Thanks much for all who responded to my post especially MT-2500...!

[MT-2500]

Originally Posted by Driver43

Well, you were right about the fuel pressure. Took my pickup to my local dealership and they found that fuel pressures were "marginal". Replaced fuel pump and cleaned gunk off of strainer and so far all is well. It was expensive but worth the $$ as long as the infernal hunting stays gone. Also, I'm getting one to two MPG better. For that I have no explanation. Could be the cooler weather. I dunno.

Thanks much for all who responded to my post especially MT-2500...!

You are welcome and all of use are glad to help.,
Glad you got it fixed.
And thanks for posting back the fix and how it went
The better mileage is engine running right.
Cool weather usualy lowers gas mileage due to long warm up and winter fuel.
Good Luck