Rough idle and spark knock

Tiny
RYOUNG6179
  • 1993 CHEVROLET TRUCK

Engine Performance problem V8 Four Wheel Drive Automatic 206000 miles

93 K1500, rough Idle and spark knock, have done the following, Timing chain & gears, retimed, cap, rotor, plugs, wires, egr valve, egr valve solenoid, fuel filter. It started when I was slowing down from the interstate, noticed spark knock, and a rough idle thought maybe bad gas, put in 104 octane, no difference. Thought maybe knock sensor, but that doesn't account for the rough idle, I think. Is it possible a dead cylinder? There are no codes showing.

There is no knock at idle and it idles rough. I will check out the sensor though. I have retarded the timing to 12 btdc and has reduced the spark knock
under a load but there is no difference in the rough idle. I have checked compression and pulled valve covers and all seems fine. All cylinders are between 90-100 psi

Its a 350 with over 200,000 miles on it, I'm sure it's low with all the wear, but it still had alot of power. I could understand a lot of the problems associated with that many miles. It's just I go to work everything fine, 15 minutes later rough Idle and spark knock, Lends me to believe something has failed.
I wasn't a gradual thing. Spark knock sensor pigtail connector looked bad, ordered another one.

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Sunday, July 12th, 2009 AT 1:02 PM

27 Replies

Tiny
MERLIN2021
  • EXPERT
  • 17,538 POSTS

Actually, if the knock sensor is working, it will retard the timing during knock periods.

DETONATION/SPARK KNOCK Symptom Definition A mild to severe ping, usually worse during acceleration. Engine makes sharp metallic knocks which change with degree of acceleration.

Possible Causes & Corrections: Check for obvious overheating problems. Ensure initial timing is correct. Check TPS adjustment and operation. Check fuel system for low pressure or volume. Also check for induction air leaks. Ensure ESC system is operating properly.

Ensure EGR valve is not always open. Ensure TCC system is operating properly. Remove carbon from engine with top engine cleaner. If excessive carbon exists in combustion chamber, check for excessive oil burning due to leaking valve guide seals.

Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons. Ensure correct PROM is installed in vehicle. Check with dealer for latest application information.

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Sunday, July 12th, 2009 AT 5:31 PM
Tiny
MERLIN2021
  • EXPERT
  • 17,538 POSTS

You might want to read the codes if the service engine light is on...it will point you in the right direction.
Cross these two"A" and "B" terminals as shown, then turn the key on. Count the flashes, a 22 will flash as 2 flashes then a short pause, then 2 flashes, if more than one code is stored, the pause will be longer. The codes will display three times and end with 12. Write them down and post here. This connector is right under the middle of the dash...


http://www.2carpros.com/forum/automotive_pictures/62217_GM_ALDL95_Older_3.jpg

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Sunday, July 12th, 2009 AT 6:33 PM
Tiny
RYOUNG6179
  • MEMBER

I have a code reader and the only time I coded something is when I was testing a component and ran when disconnected. That's why this is so puzzling to me, usually when something non mechanical craps out I pick up a code. I got so frustrated with this truck I turned into a parts replacer, even though I check out the parts and they seemed fine. My manual lists a spark control module mounted next to the tbi But I don't have one there on my truck so that is about the only component I haven't checked, because I can't find it.

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Monday, July 13th, 2009 AT 6:31 AM
Tiny
MERLIN2021
  • EXPERT
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FUEL SYSTEM PRESSURE TEST TBI 1. Turn ignition off for 10 seconds. Turn ignition on, and listen at fuel tank for fuel pump operation. Pump should run 2 seconds (20 seconds on models with fuel module). If fuel pump runs, go to next step. If fuel pump does not run, go to step 7). 2. If fuel pump runs, turn ignition off. Verify fuel tank has fuel. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Remove air cleaner, and plug air cleaner vacuum ports (if equipped). Disconnect fuel line between throttle body and fuel filter. Install Fuel Pressure Gauge (J-29658A) and Adapter (J-2968A-85) between steel fuel line and flexible hose, ahead of in-line fuel filter. 3. Turn ignition on, and note reading on pressure gauge. If fuel pressure is 9-13 psi (.63-.91 kg/cm 2 ), no problems are present. If pressure is less than 9 psi (.63 kg/cm 2 ), go to step 5). If pressure is greater than 13 psi (.91 kg/cm 2 ), turn ignition off, and bleed fuel pressure. Disconnect fuel return line downstream of pressure gauge. Insert return line into a gasoline container. 4. Turn ignition on. If pressure is now 9-13 psi (.63-.91 kg/cm 2 ), correct restriction in fuel return line between disconnected point and fuel tank. If fuel pressure is greater than 13 psi (.91 kg/cm 2 ), check for restricted return line (including fuel filter) downstream of pressure gauge. If no restrictions are present, replace fuel pressure regulator (TBI 700) or fuel meter cover/pressure regulator (TBI 220). 5. Check for restricted line between in-tank fuel pump and pressure regulator. If fuel line is okay, disconnect injector connector. Turn ignition on. Gradually pinch fuel pressure gauge outlet hose. Note pressure. 6. If pressure is greater than 13 psi (.91 kg/cm 2 ), replace fuel pressure regulator (TBI 700) or fuel meter cover/pressure regulator (TBI 220). If pressure is less than 9 psi (.63 kg/cm 2 ), check for faulty fuel pump or incorrect part. Check fuel pump coupling hose and pump inlet filter in fuel tank. On models with dual fuel tanks, check for faulty fuel tank selector valve and meter switch. 7. Apply 12 volts to fuel pump test connector. For fuel pump test connector location, see underhood engine component views under COMPONENT LOCATIONS in SYSTEM/COMPONENT TESTS article in this section. If fuel pump now runs, repair open in fuel pump relay drive or power circuit or repair faulty fuel pump relay. To test relay, see SYSTEM/COMPONENT TESTS article in this section. 8. If fuel pump does not run with 12 volts applied to fuel pump test connector, repair open in fuel WARNING: Begin fuel system trouble shooting and diagnosis with fuel system pressure test. Relieve fuel system pressure before disconnecting any components or installing fuel pressure gauge. CAUTION: DO NOT pinch off fuel return line completely. DO NOT allow fuel pressure build-up to exceed specification, as damage to fuel pressure regulator may occur.
Check for vacuum at PCV, remove PCV frm hose, any vac? If low check for slit hose, or a common problem on high milage vehicles is TBI carboned up at the base. Remove TBI and inspect the bottom, it may be gunked up. You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! If that doesnt do it, you may need a new idle air control valve, it's bolted to the throttlebody
Torque Converter Clutch (TCC) Solenoid Disconnect harness connector to TCC solenoid. Measure resistance between TCC solenoid terminals. SeeFig. 10-Fig. 15 . Solenoid resistance should be greater than 20 ohms.
TIMING CONTROL SYSTEMS (C-4 & C-5) C-4, Electronic Spark Timing (Gasoline Engines) An open or short to ground in Electronic Spark Timing (EST) or by -pass circuit will cause ECM to turn on Malfunction Indicator Light (MIL) and confirm fault causing Code 42 is present. Refer to appropriate TESTS W/CODES article in this section. C-5, Electronic Spark Control (ESC) Circuit (Gasoline Engines Except 2.5L, 4.3L Turbo & Vehicles With 4L60E Transmission) 1. An open or short circuit on ESC wire to ECM will cause a loss of 12-volt ESC controller signal. This will cause ECM to fully retard ignition timing. 2. If a scan tester is available, connect tester to Data Link Connector (DLC). Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tester. 3. If a scan tester is not available, backprobe ECM ESC signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at ECM terminal should drop to zero volts, and return when knock signal ceases. 4. If signal does not respond as described, check knock sensor signal to controller signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. See KNOCK SENSOR under ENGINE SENSORS & SWITCHES.
POSITIVE CRANKCASE VENTILATION Required Service - The PCV system may require service for obstructions if any of the following conditions exist: Rough Idle Stalling or Slow Idle Speed Oil Leaks Oil in Air Cleaner Sludge in Engine A leaking PCV valve or hose could cause: Rough Idle Stalling High Idle Speed If engine idles roughly, check for clogged PCV valve and for plugged or broken PCV hoses BEFORE adjusting idle. Check correct PCV valve application to ensure the correct valve is fitted. Replace PCV valve if required. Checking PCV Valve Function (Except 2.5L) 1. Remove PCV valve from rocker cover. Run engine at idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary. 2. Turn engine off. Remove PCV valve. Shake valve and listen for rattle of check valve inside PCV valve. If a clear rattle is not heard, replace PCV valve. 3. Visually inspect valve for varnish or deposits that may make PCV valve operation sticky, restricted or incompletely seated. Replace if necessary. 4. Engine must be sealed for PCV system to function as designed. If leakage, sludging or dilution of oil is noted and PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly. 5. Since an engine operating without any crankcase ventilation can be damaged, it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.
ELECTRONIC SPARK CONTROL (ESC) MODULE REMOVAL & INSTALLATION Turn ignition off. Remove bracket-to-firewall screws. Rotate bracket to access ESC module. Disconnect ESC module harness connector. Remove ESC mounting screws and remove ESC. To install, reverse removal procedure. NOTE: On models equipped with external ESC module, ESC is located on bracket behind distributor, mounted to firewall. The other thing to check on high mileage trucks is the timing chain, it may have jumped by 1 tooth and this will allow it to run, but real diesely like1 Check timing marks and #1 at TDC, Compression you gave is low...150 or so is the avaerage.


http://www.2carpros.com/forum/automotive_pictures/62217_k1500TCC_1.jpg


Installation 1. To install, reverse removal procedure. To insure correct timing of distributor, install with rotor correctly positioned as it was before distributor was removed. 2. If engine was cranked after distributor was removed, remove No. 1 spark plug. Place finger over No. 1 cylinder spark plug hole. Crank engine slowly until compression is felt. Align timing mark on pulley to "0" on engine timing indicator. Turn rotor to point to cylinder No. 1 spark plug tower on distributor cap. Complete distributor installation. Start engine and check ignition timing.


http://www.2carpros.com/forum/automotive_pictures/62217_dista_1.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_Dist_2.jpg


If it has esc, it's on a brackett behind the distributor, mounted to firewall.

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Monday, July 13th, 2009 AT 7:40 AM
Tiny
MITCHS
  • 1993 CHEVROLET TRUCK

If somebody could please help me I would really appreciate it. Recently I had made a 600 mile roadtrip and the blazer ran fine until I pulled off of the interstate and noticed that when I decelerated the vehicle would shake alot and almost come to a stall when sitting at a stoplight, got horrible gas mileage, and the smell of gas was strong. I popped the hood as soon as I got home and noticed that somehow one of the Plug wires had come off of the distributor. So instantly I replaced it and it ran better but it is still nowhere were it was at before.

It still has a really rough idle but for the most part it seems that the gas smell has mostly gone away. I have only drove it once since it happened once it was up to speed the shaking went away. What do I do. Do I start by replacing all the spark plugs? Or may this be a more serious problem?

Any help will be greatly appreciated.

Thanks in advance.

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Tuesday, May 2nd, 2017 AT 11:27 AM (Merged)
Tiny
LES DANE
  • MEMBER

You may have a leaking fuel supply/return line under the lower intake manifold. Also could be the spaghetti injector tubing under the lower intake as well.

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Tuesday, May 2nd, 2017 AT 11:27 AM (Merged)
Tiny
LAMONSTER
  • 1993 CHEVROLET TRUCK
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 190,000 MILES

I installed the engine in a jeep and modified the air cleaner housing. The piece that had the flap that opens and closes with temp is no longer there. Now the engine doesn't want to idle when cold. The idle goes up and down until it stalls. It also smells rich.

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,248 POSTS

I have to be honest. I'm not sure what all has been done to make this work. If it smells rich, check to make sure the fuel pump pressure is within spec. Also, check the regulator to make sure it is not sucking gas through the vacuum hose. Check the coolant temp sensor too. It determines how rich or lean the mixture is when cold.

Again, I'm not sure what I am dealing with, so it is somewhat difficult to guide you. Also, let me know if O2 sensors are functional, what computer is running the engine, does it run good when it warms up.

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
PAULKING29935
  • 1994 CHEVROLET TRUCK

Engine Performance problem
1994 Chevy Truck V8 Four Wheel Drive Automatic 213000 miles

1994 Chevy K1500 213000 miles on it. The truck has been starting to bounce around when idleing in park and when you are in gear at a light or stop sign. I overhauled the throttle body and tested the o2 sensor it was good. Problem went away for a while now it is getting worse. Was told that the next thing to do would be to check the egr valve. What do you think. Also I have already had the intake off due to leaking antifreeze and when I did I cleaned everything out of the valley.

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

Clean out the idle air control valve and the EGR valve and see what happens-also look for vacuum leaks

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
PAULKING29935
  • MEMBER

I cleaned out the IAC when I did the throttle body still have to d the egr valve what do you think is the best thing to use when cleaning the egr I have a sonic cleaner that I used when I did the throttle body. Also I already checked for vaccum leaks thats all good

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

If it works for you go for it-otherwise carb cleaner or a decarbonizer of such-bore brushes-

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
TOMMYBOY96
  • 1996 CHEVROLET TRUCK

Engine Performance problem
1996 Chevy Truck V8 Two Wheel Drive Automatic 78000 miles

I have a 96 chevy c 1500, 5.7ltr. Auto, 2wd, my check engine light is on and the codes are po300, and po305, it is idleing rough and it has a distinct miss comming out of the right (pass. Side) tailpipe. Any hints as to what this might be?

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

P0300 Random Misfire code usually indicates a vacuum leak or bad fuel

P0305 is a misfire in cylinder no.5 should lead you to check the spark plug, fuel injector and compression.

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.

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Tuesday, May 2nd, 2017 AT 11:28 AM (Merged)
Tiny
FR3AKD1
  • 1995 CHEVROLET TRUCK

Engine Performance problem
1995 Chevy Truck V8 Two Wheel Drive Automatic 153000 miles

The truck runs at speed with no noticeable fluctuation in rpms or idle, however at a stop light or in park it idles rough to the point of dying (which has done a few times). I have checked my timing, replaced the plugs and wires(AC Delco), as well as the Coolant temp sensor, PCV Valve and EGR Valve (Check Engine light flashed and I read OBD1 code). Distributor, cap and rotor are ony 1 1/2 yrs old.

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

Clean out the IACV and test the throttle position and manifold absolute pressure sensor

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)
Tiny
FR3AKD1
  • MEMBER

Edit: tested the map and tps, both tested withing range. Cleaned IACV. Still having issues. Anymore suggestions would be helpful.

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)
Tiny
FR3AKD1
  • MEMBER

Any other suggestions?

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

(Check Engine light flashed and I read OBD1 code). Did you came up with a code?

The truck runs at speed with no noticeable fluctuation in rpms or idle

Now in park and stop lites it idles rough-don't get it-Lets try this last one-EGR pressure sensor on left side of firewall

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)
Tiny
FR3AKD1
  • MEMBER

The code that was produced from OBD1 was bad egr, so that is why it was changed. EGR Pressure sensor? I can't find anything about this part except in a Ford. Could you explain where it would be?

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Tuesday, May 2nd, 2017 AT 11:29 AM (Merged)

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