Engine Performance problem
1993 Pontiac Sunbird 4 cyl Front Wheel Drive Manual 89000 miles
Car just started running ruff all of a sudden. Seems to be miss firing in idle can drive the car and in lower gears 1-2 seems ok with intermittent bursts of power however in the upper gears 3-5 it has little power and slows going up hills. Have a code reader and get no error codes. Checked the injectors with an ohm meter all read about 12.8 ohms. Checked the signal with a node light and all are getting a signal. Pulled the DIS module to have it tested but was told they could not because it has the coil and module all in one. Cost of new was 260. Read that maybe the crank sensor may cause this. Any suggestions?
Step 1 - Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If all fuses test ok continue to the next step. How do I check my car fuses?
Step 2 - To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) and the fuses test ok a trouble code scan is needed to identify any system trouble. Use a simple scanner tool to retrieve trouble codes and check if they relate to the specific problem, like an ignition coil failure code. If a trouble code is present but does not pertain to the immediate problem like a EVAP code ignore it until a later time, after the engine is running properly. The reason we repair non-related codes after the engine is running properly is because sometime false codes can be triggered by a rough running engine. Once the engine is running properly the code present might cycle and turn itself off. You might say "if the engine isn't running right shouldn't it have a check engine light and a trouble code?". Sometimes conditions occur that will not be detected by the computer, example: if the intake or exhaust valve operation fails the computer can not detect the failure because the problem is not sensor related, so the engine doesn't run smooth and the computer thinks everything is ok with no codes. If the trouble code retrieved relates to a cylinder misfire like a injector driver or ignition coil failure first these problems and re-test system. If no trouble codes are present proceed to the next step. How do I scan my service engine soon light?
Step 3 - Check for broken or dilapidated vacuum hoses on and around the engine, your car's engine is designed to run on a system that can hold vacuum. Vacuum hose are typically connected to the engine intake manifold and will supply engine vacuum to various accessories like power brakes. On some cars are designed with a larger vacuum transfer hose that connects the intake manifold to the IAC (idle air control) motor. If a broken or dilapidated these vacuum lines can cause the engine to lose vacuum which will allow the engine to run rough and die. Inspect all engine and accessory vacuum lines to look for missing, torn or dilapidated lines and replace as needed. Also have a helper rest their foot on the gas peddle just enough too keep the engine running and double check the engine when it is running to listen for any whistling noise coming from the engine that is not usually present. Follow the noise and inspect vacuum lines in that area, also when the engine is running it will pull inward a broken or weak piece of the hose to create a larger vacuum leak. Check the integrity of all vacuum hoses at each end of the hose, typically this is where a vacuum hose fails. If all vacuum hoses check "ok" proceed to the next step.
Step 4 - A pocket IR thermometer laser temperature reader is handy for detecting a cylinder misfire. If you have visual access to all cylinder exhaust manifold ports you can use a pocket IR thermometer temperature detector to detect a cylinder misfire. Start with the engine cold, then start the engine, take temperature reading on all cylinders, if one cylinder is considerably lower temperature then the other cylinders you have found the cylinder that is malfunctioning. Example: on a four cylinder three of the exhaust ports test at 190 degrees and one is at 81 degrees. The cylinder at 81 degrees is misfiring. Once you have found the cylinder that is misfiring isolate the following tests to that cylinder, if haven't found the misfiring cylinder continue with the following steps in this guide: (the next step can be combined with step 6 and 7)
Step 5 - The spark plugs in your engine can give you valuable information about how the engine is running. The chemical reaction inside the combustion camber will leave deposits on the spark plug that can tell you the condition inside the engine's combustion chambers. For example: if the engine is running rich all of the spark plugs will have a black or grey shoot covering the spark plug electrode. If the engine is running lean all of the spark plugs will be clean and white (check your spark plug condition). If one of the spark plugs looks way different then the remaining spark plug the cylinder the different plug came out of might be having a problem. Before you remove the spark plugs, mark the plug wires to identify their positions in the firing order, this will help to make sure they do not get mixed up. Next, use a spark plug socket to remove the spark plugs, we use a spark plug socket because the inside of the spark plug socket is lined with rubber to help cushion the spark plug insulator, which is made of porcelain and is easily cracked or broken. If a spark plug insulator is cracked or broken the engine will misfire because the ignition spark will travel to the engine block (ground) instead of the spark plug gap (between the electrodes) How do I change my spark plugs?
Step 6 - Engine compression is very important for a smooth running engine. An engine depends on an equal compression reading in each cylinder to run smoothly. If poor compression exits in one or more cylinders it can cause a rough idle condition and low engine power output. A compression test of all cylinders is needed to check for engine wear and internal damage. Remove ignition coil connector or ignition system or fuel pump fuse to disable power to the ignition or fuel system to avoid fire. Compare cylinders compression reading, typical compression readings are between 125 p.s.i. and 160 p.s.i. all cylinder readings should be within about 5% of each other. If low compression exists a cylinder malfunction exits and further inspection is required. Possible causes for a low compression condition are: burned intake or exhaust valve, broken piston or piston ring, broken valve spring or a blown head gasket. If engine compression tests "ok" proceed to the next step.
Step 7 - The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil and that transfers the electrical energy into the secondary ignition system, i.e. coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug.
I did the spark plug test where after taking out each spark plug and grounding the tip, what I found was that plugs 1 & 4 were very weak and sometimes no spark at all. So I suspect the coil assembly is the problem. This car has what is called the DIS, Direct Ignition System It contains 2 coils along with the ignition module. I suspect that the one coil must control plugs 1 & 4. The DIS gets a reference signal from the cam position sensor which then in turn communicates with the ECM or computer control module. From what I''ve read below 400 rpm the DIS controls the timing and above 400 the ECM Regulates timing. So it looks as though I'm going to have to fork out the $260 (OUCH!) For a new module
October, 27, 2008 AT 9:10 PM
Hey, just imagine what you are saving by doing it yourself. If a garage done it you would have most likely put out $500 - $600