Sluggish/hesitating, especially when cold

[zedbear]

2000 Sierra, 5.3L, 103K miles. Having an ongoing issue, driving me NUTS. Any tips appreciated.

 

I replaced the fuel pump module with a Delphi unit due to a bad sending unit this past March and also replaced the intake/valley pan gaskets/knock sensors and harness, and also valve cover gaskets in April.......

 

A few months ago, I started experiencing some light to moderate pinging on acceleration. Within a day or so, the pinging was gone. Perhaps some bad fuel or something. But I decided to run some sea foam through it anyways just in case. I had done this before with no ill effects. I also cleaned the MAF sensor with the proper cleaner at that time......

 

Within a few days, the truck started behaving a bit strangely. Seemed a bit sluggish on acceleration, especially when warming up. Idle seemed maybe a little low. Shifting characteristics also changed. It seemed slow to downshift when going around a corner and was just acting wierd in general. Also seemed like the truck was slowing down faster when coasting. Thinking I had reinstalled the MAF wrong and/or neglected to tighten something down, I removed it, cleaned it again, and reset the computer. No change. Replaced fuel filter. No change. With the hesitation and crappy shifting, I was POSITIVE I had screwed the MAF up somehow when I had cleaned it........so I bought a new one. No change of course.

 

Thinking about the seafoam, I pulled all the plugs (AC Delco Iridiums), which only had 30K miles on them. They looked alright. Beginning to fall into the trap of throwing parts at it and after some more research, I decided to replace the front O2's, which were original anyways. No change. Bought new plugs. No change. At that point, I stopped the parts changing madness before it got out of hand and haven't done anything since then (couple months now).

 

I also checked the fuel pressure. Was within spec for the bleed down test. Running at idle, it was at just over 50 IIRC, but the needle bounced around/vibrated when I would raise the RPMs. Not sure if that matters or not. No fuel visible in the pressure regulator hose but I think I could smell a very slight trace of fuel odor when sniffing around the hose port. Again, not sure if that matters.

 

It's totally driveable, never misfires or runs rough, no codes, fuel mileage seems unchanged. It's just a PIG. I Certainly not the peppy truck I was used to. With the very cold weather recently, it feels like an old carb engine with a sticky choke when I drive it away in the morning. Colder weather definetlly makes it worse. I highly doubt its the intake gaskets I replaced. I've replaced intake gaskets on various vehicles over the years and never screwed it up. Feels like I'm hauling something all the time.

 

I also notice a very slight hissing or whistle sound under moderate to heavy acceleration. I thought vacuum leak at first but it actually sounds more like air being forced OUT somewhere rather than in. Pehaps I partially clogged the cats when I did the seafoam? IDK, all these symptoms could be a total coincidence and not related to the seafoam.........

 

I'll probably end up taking it to the shop unless you guys have any simple troubleshooting I can try. Thanks.

[Jsdirt]

Throw a vacuum gauge on there. That'll verify if the cats are indeed plugged.

 

I recall this happening to my ol' man's '84 Ram when it only had 30k miles on it. You'd stomp it to the boards, and all you'd hear is intake honk, and what sounded like a blown compressed air hose in the exhaust. REAL loud hiss. The cat was completely plugged solid.

 

If you have low vac at part throttle, that's your problem.

[zedbear]

Throw a vacuum gauge on there. That'll verify if the cats are indeed plugged.

 

I recall this happening to my ol' man's '84 Ram when it only had 30k miles on it. You'd stomp it to the boards, and all you'd hear is intake honk, and what sounded like a blown compressed air hose in the exhaust. REAL loud hiss. The cat was completely plugged solid.

 

If you have low vac at part throttle, that's your problem.

 

 

Thanks for the reply. Been too cold out to mess around with it but I will pick up a gauge and check it out.

 

This thing is being such a PIG, I wish something would just BREAK so I'd know whats wrong lol.

 

Could just be my imagination but the brake pedal feel seems a little different sometimes the last few months. Maybe there is indeed a vacuum issue....

[Jsdirt]

Careful what you wish for ....

 

With the gauge, if your seeing overall low vacuum readings that's usually an indicator of a restriction in the exhaust.

 

Keep in mind though, with computer-controlled-everything nowadays it really could be anything. Since it's been apart for repairs prior .... before buying a gauge, make sure all the vac lines are hooked up, and if they are, make sure they're in the correct spot. If the problem started after the repair, there's probably a 100% chance there's something left open, or not where it's supposed to be.

 

I hear ya on the cold. Was out in the barn today, 20° out there, replacing a timing belt tensioner in a '00 Ford Focus. Can't believe it made it into the barn without jumping time. The tensioner has 4k miles on it ...

[zedbear]

Careful what you wish for ....

 

With the gauge, if your seeing overall low vacuum readings that's usually an indicator of a restriction in the exhaust.

 

Keep in mind though, with computer-controlled-everything nowadays it really could be anything. Since it's been apart for repairs prior .... before buying a gauge, make sure all the vac lines are hooked up, and if they are, make sure they're in the correct spot. If the problem started after the repair, there's probably a 100% chance there's something left open, or not where it's supposed to be.

 

I hear ya on the cold. Was out in the barn today, 20° out there, replacing a timing belt tensioner in a '00 Ford Focus. Can't believe it made it into the barn without jumping time. The tensioner has 4k miles on it ...

 

 

I did the intake gasket job in April. Took it on a 3500 mile round trip from Buffalo to South Carolina to Dallas and back to Buffalo and it ran great. Drove it all summer into early Fall with no issues. Problems seemed to start around the time of the damn Sea foaming in Oct. So I know its not from plugging hoses into the wrong spot or anything like that.

[txab]

Take a fuel pressure reading key on, engine off.

[zedbear]

Take a fuel pressure reading key on, engine off.

 

 

Will do.

 

As far as vacuum readings, what numbers am I looking for?

 

Thanks.

[Jsdirt]

Check this out: http://www.secondcha.../public/186.cfm

 

Scenario 14 is the one that may apply to you.

[zedbear]

Thanks for that link.

 

I checked vacuum readings. Seems to be normal. At idle it's a steady 19 inches. Jumps up and then comes back down like it should when I apply throttle. So maybe the cats are a dead end.

 

Checked fuel pressure again. 56-58 PSI key on, engine off.

 

50 when running at idle.

 

2000 rpm, it drops to about 48......

 

I took some starting fluid and sprayed various areas around the intake and also the inject ports and around the TB. Nothing.

 

Ugh. Thanks for the help so far.

[txab]

Pressure is ok. I believe 55 - 62 psi for your year. So you're at the low end with 56 psi.

 

 

Have you put a scanner on this and pulled any codes?

[txab]

Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggish or Spongy Checks

Action

 

DEFINITION: Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down part way.

 

Preliminary Checks

• Refer to Important Preliminary Checks Before Starting in Symptoms .

 

• Search for bulletins.

 

• Check the PCM grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .

 

• Remove the air filter element and check for dirt or for being restricted. Refer to Air Cleaner Element Replacement and replace as necessary.

 

Fuel System

• Check both injector fuses for being open. An open injector fuse causes four ignition coils and four injectors not to operate. Replace the fuse. Inspect the ignition coil circuits and the injector circuits for an intermittent short to ground.

 

• Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .

 

• Check for a restricted fuel filter. Refer to Fuel System Diagnosis .

 

• Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

 

• Check the fuel injectors. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

 

• Check the items that cause an engine to run rich long term fuel trim near -13 percent. For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .

 

• Check the items that can cause an engine to run lean long term fuel trim near 24 percent For a lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

 

Sensor/System

Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .

 

Ignition System

• Check both injector fuses for being open. An open injector fuse causes four ignition coils and four injectors not to operate. Replace the fuse. Inspect the ignition coil circuit and the injector circuits for an intermittent short to ground.

 

• Wet down the secondary ignition system with water from a spray bottle. Wetting the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as water is applied.

 

• Check for proper ignition voltage output with J 26792 spark tester .

 

• Remove the spark plugs and check for the following:

 

- Correct heat range

 

- Wet plugs

 

- Cracks

 

- Wear

 

- Improper gap

 

- Burned electrodes

 

- Heavy deposits

 

Refer to Spark Plug Visual Diagnosis in Engine Electrical.

 

• An improper spark plug gap will cause a driveability problem. Gap the J 26792 spark plugs using a wire gauge gap too. Refer to Spark Plug Replacement in Engine Electrical.

 

• Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to DTC P0172 Fuel Trim System Rich Bank 1 or DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition. Refer to Spark Plug Visual Diagnosis in Engine Electrical for diagnosis of coolant or oil fouled spark plugs.

 

• Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a cylinder can be located with a misfire, use the DTC P0300 table for diagnosis.

 

• Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

 

Engine Mechanical

• Ensure that the engine coolant temperature is not above 130°C (266°F). This condition causes the PCM to operate in Engine Coolant Over Temperature-Fuel Disabled Mode. While in Engine Coolant Over Temperature-Fuel Disabled Mode, the PCM will disable the fuel injectors to four cylinders at a time to keep engine temperatures from reaching damaging levels. The system perceives the Engine Coolant Over Temperature-Fuel Disabled Mode as a lack of power, miss, or rough idle. If the vehicle operates in Engine Coolant Over Temperature-Fuel Disabled Mode, refer to Engine Overheating in Engine Cooling for diagnosis.

 

• Excessive oil in combustion chamber -- Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

 

• Low cylinder compression -- Refer to Engine Compression Test in Engine Mechanical 4.8L, 5.3L, 6.0L.

 

• For incorrect basic engine parts. Inspect the following:

 

- Camshaft

 

- Cylinder heads

 

- Pistons, etc.

 

Refer to Engine/Engine Mechanical.

 

Additional Checks

• Check the exhaust system for possible restrictions. Check for the following:

 

- Inspect the exhaust system for damaged or collapsed pipes.

 

- Inspect the exhaust manifold for a collapsed inner wall.

 

- Inspect the mufflers for heat distress or possible internal failure.

 

- Inspect for possible plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of engine. Check back pressure by removing AIR check valves near exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust.

 

• Check the transmission torque converter clutch (TCC) for proper operation. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission 4L60E.

[zedbear]

Pressure is ok. I believe 55 - 62 psi for your year. So you're at the low end with 56 psi.

 

 

Have you put a scanner on this and pulled any codes?

 

 

I have a scangauge. There have been no codes.

 

After I checked the above pressures today, I pulled off the air intake to check things over. I noticed that rubber boot where the plastic part of the intake connects to the TB seemed sorta stretched and floppy. When I put it all back together, I tightened the hell out of the hose clamp there. Drove it not long after and I swear it felt like it had more power and that weird whistle under moderate acceleration seemed to be gone! 40 minutes later as I approached my destination, it seemed to be getting more dogish again. A few hours later when I headed home, it felt like a dog again and that slight whistle sound was back. Wonder if I'm on to something here. I gave the whole air intake a quick visual but maybe I need to pull it off again and look closer for cracks. Perhaps replace that rubber boot on the TB.....

[zedbear]

I loosened the air intake and repositioned it slightly. Tightened the clamps. Its back to normal for the most part! I knew it had to be something stupid. I can still hear a slight noise under acceleration so I probably need a new rubber boot at the TB. I blew some money throwing parts at it but not too bad. Oh well, I figured it out and it feels like the responsive truck it always was again.