Hesitation under acceleration

[Bioscache2]

I have a 2001 Coupe, manual with approx 120k miles on it. Recently it has been experiencing hesitation, which could be even described as a shuddering, under moderate to heavy acceleration. It doesn't happen all the time, as its most prominent in lower rpms, 1.5k and below, all but disappearing as I hit 2k and it also is more noticeable in higher gears which suggests to me low power high load situations, (like trying to accelerate while cruising).

The only recent work I've done is I changed my air filter on my vararam but that was over a month ago and this has been recent (only within a week or so). Also recently my coolant temps were getting higher (240's) but adding some coolant fixed that and it didn't last long.

It's not always prevalent, some days are worse than others(on it's worse days it has had trouble 'catching the idle' meaning if, while not in gear, I rev it up to 2.5k or so, as it comes back down it will drop below idle (500) and then return to idle, where ideally it should be a controlled descent with it stopping at idle) and some days its hardly there at all. I suspected the MAF and checked for leaks behind it but could find none. I do have one code but no warning light

10 PCM 0100

My guess is still something with the MAF but not sure what, maybe a bad connection I'm thinking I might have to take it to a dealer or other shop but I'm new to the area, College Park MD, near DC and don't know any places except to punt to the dealer. Suggestions?

 

[Patrick]

Ryan,
I can tell you from experience with my old Z06 that the MAF, when it came loose, gave off a Service Engine Soon light and threw codes regarding running "too lean". If you aren't getting any of those, I'd say the problem my lie elsewhere.

Let's start with the obvious, and then I'll let GM Junkie chime in with his thoughts. What type of fuel are you using? Is it a "Top Tier" fuel? And when was the last time you put in a bottle of Techron?

-Patrick

 

[catbert]

Easy things first. Try a spray can of CRC mass airflow sensor cleaner. Don't use anything stronger or you will probably ruin it. Techron and a top tier gas are good ideas, especially if you drive in town a lot. Another thing to consider is Stabil or something like it, if you go a month between fill-ups.

 

[gmjunkie]

There is no code P0100 !
But from your symptom,I think you have a vacuum leak!

Look at the hose where the PCV valve connects to the TB!! There bad to crack and sometimes even whistle!

 

[Bioscache2]

Thanks for the replies guys I do appreciate it. The only fuel I've used recently is Exxon since it's near my place but I was surpised to see that it's not on the Top Tier list, so maybe I will try changing that and add a bottle of Techron. Also I looked at the MAF and it seemed clean but it couldn't hurt to spray the cleaner. What are the rules after spraying, I'm guessing its gotta air dry before use again?

Junkie, I was definitely thinking vaccum leak as well but did not check that spot, I will be certain to check back and report. As for the code, I know it's not on the website list but I could have sworn that was it. I know it was in that first section and know it was 01xx, just can't be positive of the last two numbers. I checked this morning but the code was gone (eliminated by the computer, I didn't reset it). I will check it again next time I drive as I only drive about once or twice a week now with walking to school.

Thanks again guys!

 

[gmjunkie]

Thanks for the replies guys I do appreciate it. The only fuel I've used recently is Exxon since it's near my place but I was surpised to see that it's not on the Top Tier list, so maybe I will try changing that and add a bottle of Techron. Also I looked at the MAF and it seemed clean but it couldn't hurt to spray the cleaner. What are the rules after spraying, I'm guessing its gotta air dry before use again?

Junkie, I was definitely thinking vaccum leak as well but did not check that spot, I will be certain to check back and report. As for the code, I know it's not on the website list but I could have sworn that was it. I know it was in that first section and know it was 01xx, just can't be positive of the last two numbers. I checked this morning but the code was gone (eliminated by the computer, I didn't reset it). I will check it again next time I drive as I only drive about once or twice a week now with walking to school.

Thanks again guys!

I didn't look on the web site Patrick posted 2-3 years ago,I checked it in my GM SI Service Program!

 

[Bioscache2]

So even before I could put new gas in it or blast it with cleaner the problem seems to have disappeared. The last thing I did was make the sure the connection to the MAF was in good and tight. I also checked for the leak were you posted Junk but it's in tact there. I'll keep an eye out as most things don't just get better on their own. Thanks for the help.

 

[Bioscache2]

Update:

Now have, what I think is a related problem but can't be sure. When I started up the car (it was cold out, about 40*). The car was very rough, rougher then it has ever been and the engine check light came on, blinking actually. I immediately shut her down and pulled the code, 10 ACM 0300 (Engine Misfire), and you could hear it occassionally out the tailpipes. Unfortunately I did not have the option of just canceling today so I started the car back up and noticed it was a little better, as the engine warmed up, things returned to normal and the check engine light stayed on, but stopped blinking. I drove to work and everything was fine. Once I got there I checked the codes again and saw the code now had an H next to it. When I went to lunch the car was a little rough at start but again, as soon as it started to warm up, it returned to normal. It followed this pattern throughout the day, but it was never as bad as it was this morning (then again it was never that cold again). I can also hear a ticking (not unlike a sound from a spark) when it's rough and then disappears after it's warm as well. Not sure what the deal is but I'm spooked enough that she's going to the shop first thing tomorrow morning and I will inform you all of what they find.

 

[Toms007]

Ryan, the LSx series engines have a known issue (for lack of better term) with piston slap (probably that ticking you hear) when the engine is cold and then goes away after warm up. So I'd almost bet that is the ticking sound, even my 5.3 Silverado does it (same engine design). As for the rough running, I'll wait for Jesse (GMJunkie) to come back on.

 

[gmjunkie]

Man this will be tough on line!!:W:W:W
I'd remove the engine covers and inspect every vacuum line you see!
I'd double check that short hose at the PCV Valve,Remove and look at it good!! I've had to replace 2 on my 03 in 65,000 miles!Just did it a couple months ago!!
Has it ever had the Spark Plugs changed?Has it ever had the SP Wires changed? Have you ever ran any Techron threw it??(If not maybe you should! How bout the fuel filter??

I'll post this,but it probly won't do any good unless you have a scanner and some other things!! But it may give you some sort of idea!If you don't find any vacuum leaks,you should probly take it to somebody to check it out!!

DTC P0300

System Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the three-way catalytic converter (TWC). The malfunction indicator lamp (MIL) will flash if converter damage conditions are present.
Conditions for Running the DTC

• DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1120, P1220, P1221, or P1258 are not set.
• The engine speed is between 425-3000 RPM.
• The ignition voltage is between 10-18 volts.
• The engine coolant temperature (ECT) is between -7°C-130°C (+19°F-266°F).
• The fuel level is more than 10 percent.
• The throttle angle is steady within 1 percent.
• The anti-lock break system (ABS) and the traction control are not active.
• The transmission is not changing gears.
• The secondary air injection (AIR) diagnostic test is not in progress.
• The A/C clutch is in a steady state.
• The engine is not in fuel shut-off or in decel fuel cut-off.
• The antilock brake system (ABS) signals are not exceeding the rough road thresholds.

Conditions for Setting the DTC

• The PCM determines that an emission type misfire is present.
• The PCM determines that a catalyst-damaging misfire is present.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids


Important

• Before you service the PCM and the throttle actuator control (TAC), remove any debris from the module connector surfaces. Inspect the module connector gaskets when you diagnose or replace the modules. Ensure that the gaskets are correctly installed. The gaskets prevent contaminate intrusion into the modules.
• For any test that requires probing the PCM or probing a component harness connector, use the J 35616-A connector test adapter kit . Using this kit prevents damage to the harness and component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

• Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTC P0461 and DTC P1431 also set.
• A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis .
• A misfire that only occurs during certain conditions may be difficult to locate. Observe the Freeze Frame and the Failure Records in order to determine when the DTC set.
• Excessive vibration from sources other than the engine could cause a misfire DTC. Possible sources of vibration are listed below:
  • Variable thickness in the brake rotor
  • An unbalanced propeller shaft
  • Certain rough road conditions
• If more than 1 cylinder is misfiring, the scan tool may only display 1 misfiring cylinder. This condition is not apparent until the repair is completed. Also, if an ignition coil or module ground circuit is open for 1 side of the engine, the scan tool may only display 2 or 3 misfiring cylinders. Inspect the ground circuit for the ignition coil and for the modules on the cylinder bank of the engine that has more than one misfiring cylinder.
• A misfire may not be apparent at idle. The misfire may only occur above idle during a load. Road-test the vehicle, and monitor the misfire current counters.
• For an intermittent condition, refer to Intermittent Conditions .

Test Description




The numbers below refer to the step numbers on the diagnostic table.

1. The Misfire Current Counters will not increment if certain DTCs set at the same time or after DTC P0300 sets.
   If more than 1 cylinder is misfiring, the Misfire Current Counters may increment for only one cylinder. For example, Cylinders 1 and Cylinder 8 are both misfiring, but only Cylinder 8 increments on the Misfire Current Counter.
   If one of the injector fuses is open, only 2 or 3 Misfire Current Counters may increment for the corresponding side of the engine.
   Wetting down the secondary ignition system with water from a spray bottle may help to locate damaged or deteriorated components. When you apply the water, look and listen for arcing or for misfiring.
   If the Misfire Current Counters are incrementing and there is no apparent misfire, an erratic crankshaft position (CKP) sensor signal could be the cause. Perform the diagnostic that are listed on the table for DTC P0335 first if you suspect this condition.
   If a misfire is present and you suspect a fuel control concern, force the fuel system into Open Loop using the scan tool, and allow the engine to run for a few minutes. If this procedure eliminates the misfire, refer to any fuel control-related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.
   The cylinder with the more significant misfire may cause another cylinder's counter to increment by a small amount.
   If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
   An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, for collapsed lifters, or for worn camshaft lobes.
   
2. If the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.

DTC P0300 - Engine Misfire Detected

Step
Action
Values
Yes
No
1
Did you perform Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2

Important

If any DTCs other than P0135 and P0155 are set, refer to those DTCs before proceeding with this diagnostic.

1. Install the scan tool. Start the engine.
2. Use a scan tool in order to monitor all the Misfire Current Counters on the Misfire Data List. There are a total of 8 counters, with 1 counter per cylinder.

Are any of the Misfire Current Counters incrementing?
--
Go to Step 4
Go to Step 3



3

1. Turn ON the ignition, leaving the engine OFF. Review the Freeze Frame and the Failure Records data for this DTC, and observe the parameters. Turn OFF the ignition for 15 seconds. Start the engine. Operate the vehicle within the conditions required for this diagnostic to run, and as close as possible to the conditions that the Freeze Frame and Failure Records recorded. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
2. Select the DTC option and the Specific DTC option, and then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?
--
Go to Step 4
Go to Diagnostic Aids
4
Is only one Misfire counter incrementing?
--
Go to Step 6
Go to Step 5
5



Inspect for the following conditions:

• Inspect the accessory drive belt and the pulleys for damage or for misalignment. Refer to Drive Belt Vibration Diagnosis in Engine Mechanical.
• Inspect the vacuum hoses for splits, for kinks, and for proper connections.
• Inspect the throttle body and the intake manifold for vacuum leaks.
• Inspect the crankcase ventilation valve and system for vacuum leaks.
• Inspect the PCM grounds for being clean and secure. Refer to Testing for Intermittent and Poor Connections in Wiring Systems .
• Verify that all injector harness connectors are connected to the proper injector or cylinder.
• Inspect the injector and the ignition control fuses for an open. If you find an open fuse, locate and repair the shorted circuit. Refer to Wiring Repairs in Wiring Systems.
• Test for low fuel pressure or for restricted fuel flow. Refer to Fuel System Diagnosis .
• Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust.
• Inspect the fuel for poor fuel quality. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did any of the above inspections isolate a condition requiring a repair?
--
Go to Step 17
Go to Step 6



6

1. Turn OFF the ignition.Disconnect the injector that corresponds to the Misfire Current Counters that was incrementing. Connect the injector test lamp J 34730-2C to the injector electrical connector.
2. Start the engine.

Is the injector test lamp flashing?
--
Go to Step 7
Go to DTC P0200



7

1. Turn OFF the ignition. Reconnect the injector harness electrical connector. Disconnect the ignition wires from the spark plug that corresponds to the Misfire Current Counters that was incrementing. Install spark tester J 26792 to a ground.
2. Start the engine.

Does the spark jump the tester gap, and is the spark consistent?
--
Go to Step 9
Go to Step 8



8

1. Remove the ignition wire for the cylinder that is misfiring.
2. Use a DMM in order to measure the resistance of the ignition wire.

Is the ignition wire resistance less than the specified resistance?
700 ohms
Go to Electronic Ignition (EI) System Diagnosis
Go to Step 16



9

1. Remove the spark plugs from the cylinder that indicated a misfire.
2. Inspect the spark plugs. Refer to Spark Plug Replacement .

Does the spark plug appear OK?
--
Go to Step 10
Go to Step 11
10

Important

If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.

1. Swap the suspected spark plug with another cylinder that is operating properly.
2. Operate the vehicle under the same conditions in which the misfire occurred.

Did the misfire move with the spark plug?
--
Go to Step 15
Go to Fuel Injector Coil Test
11
Are the spark plugs oil or coolant fouled?
--
Go to Base Engine Misfire without Internal Engine Noises in Engine Mechanical
Go to Step 12
12

Important

If the Fuel System Diagnosis does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.

Are the spark plugs gas fouled?
--
Go to Fuel System Diagnosis
Go to Step 13
13
Important

If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.

Do the spark plugs show any signs of being cracked, worn, or improperly gapped?
--
Go to Step 14
Go to Fuel Injector Coil Test
14
Replace or re-gap spark plugs. If you find an improper gap, use a wire-type gauge in order to re-gap spark plugs. Refer to Spark Plug Replacement .
Did you complete the replacement?
--
Go to Step 17
--
15
Replace the faulty spark plugs. Refer to Spark Plug Replacement .
Did you complete the replacement?
--
Go to Step 17
--
16
Replace the faulty ignition wires. Refer to Spark Plug Wire Replacement .
Did you complete the replacement?
--
Go to Step 17
--
17
Was the MIL flashing?
--
Go to DTC P0420 or P0430
Go to Step 18



18

1. Use a scan tool in order to clear the DTCs. Turn OFF the ignition for 30 seconds. Start the engine.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?
--
Go to Step 19
Go to Step 2
19
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK

 

[Bioscache2]

So went to Sport Chevrolet in Silver Spring, MD and was pretty impressed with their operation. Talked to a service manager Mike who scheduled my appointment, and kept it, and listened to my description. A little bit later met their corvette expert Frank. He seemed very knowledgeable and took me into the shop to show me what was up. He said the MAF and it's wires were fine. The culprit was a corroded spark plug wire and coil. He also recommended the rest of the spark plugs and the wire set be changed, which really it is time with 116k on the odometer.

Some other things he recommended were a brake flush (the fluid was black and it's been about 50k miles since the last) and I requested a coolant flush (same time frame and I had added water when it was low so wanted a fresh start given the temp problems I had earlier).

The last thing he recommended was clutch fluid changed out. He recommended changing it every 2 years but this was new info to me. Anyone hear anything about this?

He said there is a local Corvette group that runs a shop night out of the shop and their tech Frank is usually on hand to help and game the group discount. After everything and the discount I expect all work to come in just under a grand. All in all seems like a respectable shop and the pricing didn't seem bad for a dealership. They expect to have the car done by this afternoon, which impressed me as well since I only brought it in this morning.

Just wanted to give an update and feel free to comment on anything, experiences with this dealership, reasonableness of price for all things, etc; as I always welcome an outside opinion.

Also thanks to all for their suggestions and a big thanks to Junk for his expertise, you nailed it with the spark plugs.

 

[Bioscache2]

Ok another update. I got the car back and the improvement is vast but I still think something is wrong and.....it's probably connected to the above.

Major Symptoms are:
- Worse fule economy on highway cruising (used to be 28-29, now 24-25)
- Very slight hesitation when in low rpm's at high gear. Much less noticable then before and more intermitent now, but still there
- When the engine is unloaded during shifting the rpm's jump, as expected, but then on the way down they fall below the idle point and the engine is forced to give it gas to prevent it from stalling
- Idle seems to vary a little but not always, can't pin down under what conditions

To summerize what has been done on the car (some will not be related but I will list anyway)

- New plugs and wires, a coil was replaced (Mechanic who did work seemed compentent so I'd be willing to bet he checked the other coils but will ask him when I get back)
- Flushed brake fluid, coolant, and clutch fluid
- Cleaned the MAF
- Did a smoke test to check for vacuum leaks

I got two suggestions to try changing the fuel filter (it's overdue anyway) and a fuel injector cleaning. No warning lights or codes. Thoughts?