No power when accelerating

[Gratiotguy]

1999 Sonoma, 4.3L V6, 2 wheel drive, X engine code, about 92,000 miles.

It doesn't accelerate smoothly. It starts, runs, idles fine. Drives fine at constant speed. The problem comes when during moderate acceleration, either from a stop or when speeding up from a constant speed, ie: passing another car or getting on the freeway.

If I go real easy on the throttle, it runs fine and accelerates ok. But if I give it too much gas, it sputters out, misses, chokes, total loss of power. This happens under normal driving conditions.

The 'check engine' light hasn't come on.

Any ideas?

[MT-2500]

Originally Posted by Gratiotguy

1999 Sonoma, 4.3L V6, 2 wheel drive, X engine code, about 92,000 miles.

It doesn't accelerate smoothly. It starts, runs, idles fine. Drives fine at constant speed. The problem comes when during moderate acceleration, either from a stop or when speeding up from a constant speed, ie: passing another car or getting on the freeway.

If I go real easy on the throttle, it runs fine and accelerates ok. But if I give it too much gas, it sputters out, misses, chokes, total loss of power. This happens under normal driving conditions.

The 'check engine' light hasn't come on.

Any ideas?

How is fuel pressure and fuel filter?
Is exhaust restricted?
Have you done a good ac delco tune up?

[Gratiotguy]

How do I check the fuel pressure and the exhaust system? The truck had a similar problem a couple years ago, check engine light came on, the code was for the MAF sensor. I changed it, problem resolved. At that time I also changed the fuel filter. I replaced the MAF sensor a few days ago, it didn't fix the problem this time.

When it comes to diagnosis issues like this, I'll admit that I'm fairly clueless, but I'm confident when it comes to doing the work.

[MT-2500]

Originally Posted by Gratiotguy

How do I check the fuel pressure and the exhaust system? The truck had a similar problem a couple years ago, check engine light came on, the code was for the MAF sensor. I changed it, problem resolved. At that time I also changed the fuel filter. I replaced the MAF sensor a few days ago, it didn't fix the problem this time.

When it comes to diagnosis issues like this, I'll admit that I'm fairly clueless, but I'm confident when it comes to doing the work.

Diagnostic and good repair manual.is first step on repair.

Get a good repair manual.
And a good fuel pressure gauge and vacumn gauge.

To test fuel pressure you will need a good fuel pressure gauge with a hose long enought to reach outside mirrow or outsie windshield where you can read fuel pressure driving on the road.
Parts laces sell tem and some loan or rent them.
Codes or check engine light on most of your local parts place can read codes for you.
Restricted exhaust can be checked with a vacumn gauge and vacumn gauge readings tells you a lot about engine running.
Like low vacumn burnt valve, vacumn leaks or late timing.
Here is guide lines for 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 85-105 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 85-105 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.
Post back you vacumn gauge readings.
At idle and engine at 2K RPM.
Post bback any code no's you may have.

[Gratiotguy]

good info, thanks for taking the time to post it. I'll get a manual and fuel pressure gauge this weekend and get started on it.

[MT-2500]

Originally Posted by Gratiotguy

good info, thanks for taking the time to post it. I'll get a manual and fuel pressure gauge this weekend and get started on it.

You are welcome and glad to help.

Along with the fuel pressure gauge do not forget a vacumn gauge.

For the 10 bucks for vacumn gauge you get one of the best and oldest testers that will tell you more about engine running and problems than any other tools for the money.
18-20 range is good
Neede flopping = burnt valve or cylinder miss.
Low vacume reading = late timing, egr valve problem, or vacume leak.
Lower vacumn at 2K RPM over idle is restricted exhaust.

[Gratiotguy]

It was the rotor, it had a pretty good size burn mark on it. Changed it along with the dist cap, wireset, and plugs. Runs great now.

[MT-2500]

Originally Posted by Gratiotguy

It was the rotor, it had a pretty good size burn mark on it. Changed it along with the dist cap, wireset, and plugs. Runs great now.

Thanks for posting back how it went and fix.
That answers the question about a good AC Delco tune up.

[Gratiotguy]

The problem is back. Just like before the tune up. It ran fine for about 150 miles, then I noticed that it had a slight loss in power for a short time (a few days), then right back to where I started. I checked all of the connections, everything was ok. The electrode on the rotor still looks new. The electrodes in the distributor cap are clean but they do have a little bit of white discoloration.

I don't drive the truck very often, maybe 250 or 300 miles a month. When I give it gas and it bogs down, I've noticed that the tach will read higher rpm - as it should when I give it more gas - but the engine sounds like it has completely stalled. Then when I ease off the throttle the engine will start firing again.

[MT-2500]

Originally Posted by Gratiotguy

The problem is back. Just like before the tune up. It ran fine for about 150 miles, then I noticed that it had a slight loss in power for a short time (a few days), then right back to where I started. I checked all of the connections, everything was ok. The electrode on the rotor still looks new. The electrodes in the distributor cap are clean but they do have a little bit of white discoloration.

I don't drive the truck very often, maybe 250 or 300 miles a month. When I give it gas and it bogs down, I've noticed that the tach will read higher rpm - as it should when I give it more gas - but the engine sounds like it has completely stalled. Then when I ease off the throttle the engine will start firing again.

Was th tune up good AC-Delco parts?

Any check engine light or codes?

How is fuel pressure and filter?

[Rainey222]

Originally Posted by Gratiotguy

The problem is back. Just like before the tune up. It ran fine for about 150 miles, then I noticed that it had a slight loss in power for a short time (a few days), then right back to where I started. I checked all of the connections, everything was ok. The electrode on the rotor still looks new. The electrodes in the distributor cap are clean but they do have a little bit of white discoloration.

I don't drive the truck very often, maybe 250 or 300 miles a month. When I give it gas and it bogs down, I've noticed that the tach will read higher rpm - as it should when I give it more gas - but the engine sounds like it has completely stalled. Then when I ease off the throttle the engine will start firing again.

I had an old Chev Camaro and it did something that sound very similar to what yours is doing. It turned out i had a broken motor mount. When i gave it lot of gas the engine rocked and the coil wire would rub on the hood. The wire was shorting out where it rubbed and the plugs would stop firing until i let up on the gas. Check the coil wires and the distributor and plug wired. make sure they are not rubbing or shorting out when you rev the engine.