Automotive noob owner of 88 Shadow

[Aaron_01]

Greetings recently I have become interested in doing my own auto repair.
I have started buying tools and gathering information for different jobs that I can do myself. I enjoy the forums and have perused many of them for some time.

I have a Dodge Shadow 88 2.2 non turbo and have replaced the head gasket, the timing belt, water pump, 02 sensor, various hoses, etc..

My question is can anyone point me to some information about how exactly these engines work? I understand about cams and pistons etc..
What I don't undertsand is compression, rings, among other things.

I hear of rings and valve jobs but nowhere do I see what that would consist of. The how to pages concerning the timing and gaskets are invaluable and saved me time and money. The tip about winching the head up 2" was a lifesaver.

So, what are the tools I need and where can I learn more without being employed in a garage?

I currently own a 88 Shadow as I said and a 93 Caravan with the 3.3.
The van was a great auto and I have replaced the starter, alternator,rear shocks and front struts but I broke some bolts in trying to replace the waterpump. Going to wait till the Shadow is right before going any further on that.

The Shadow is bogging down on low RPMs and I believe it is the MAPS Sensor which I am picking up today.
It stalls in drive or when stopping. At high RPMs it runs fine except that it gets bad MPG.

Any and all tips or advice is appreciated
Thanks
Aaron

[Aaron_01]

I now have a Shadow book which helps explain some things.

MAPS is in but still sluggish on low RPMs, put a baffle in between the vent hose from valve cover to the air intake to keep oil from coating and burning inside.

Idles fine in park or nuetral but drops when put in drive.

I am hoping my MPG improves and the next thing I will try is replacing the speed/distance sensor.

Going to go read my book.

[Aaron_01]

How can I test the main computer on the 88 Shadow?

[Aaron_01]

Cleaned the connections on pins on main computer, only engine code I am getting now is Voltage to high or low on MAPS sensor.

Running much better, idle matches stopped in drive now at 850, although does not respond quickly when gas pedal is depressed. Thinking this is fuel filter and am replacing that in a minute.

Any ideas on what is the cause of MAPS code?

[yogi_123rd]

Replace your bad MAP sensor.

I've included a small writeup on the basics of modern engines and how the computer drives the engine.

Read the section on "computer controlled fuel systems" which explains why a failed MAP sensor causes poor performance.



Understanding Modern Automobile Engine Systems


Back 30 years ago, engines were relatively simple for a backyard mechanic to tinker with and diagnose problems. Poor performance usually meant changing the points and the plugs. A car that wouldn't start usually meant no gas or spark. Today, when a problem occurs, the onboard computer usually sets a "check engine" light. The car may or may not run normally or with poor performance. The novice mechanic then tries a hit or miss method of trying to get the light out and resolve a poor performance problem. This is usually because he wants to avoid taking the vehicle a service station to "put it on the computer" for diagnosis.

Cars manufactured before 1996: (before the ODBII standardization) most autos have a diagonostic mode built into the onboard computer to display what the problem is. It does not require a complicated method or special tool to extract them. These codes were either one or two digits and are output to the user by flashing the "check engine" light. With Chrysler cars, one needs only to turn the ignition switch three times off-on to with the ignition on to get the computer codes. With GM and a number of Japanese model cars, a ground wire is jumped into a specific connector pinout to put the computer into that diagnostic mode. Fords require a scan tool to extract them.

Cars manufactured 1996 or later: The US adoped a standardized interface and standardized codes called ODBII. These codes are one letter and 4 digits. Engine codes begin with the letter "P", with other letters for transmission and body related malfunction codes. For most autos, An ODBII scan tool reader is needed to get these codes. Some manufacturers (Chryslers for one) still have the functionality in the onboard computer to map the four digit code to a two digit equivilent and output it in the pre 1996 format.
In these later year models, the procedure to extract the two digit codes may be still be present, but the method to extract them may have changed from the pre-1996 procedure.


The ignition systems in pre-computer days:

A distributor was used that had two functions. It controlled spark to the plugs and advancement of the ignition timing at high speed engine operation. It used Breaker Points (an electrical switch) within the distributor that rode on raised cam lobes on the shaft of the distributor. Normally the points are unopened allowing an electric connection in the primary ignition circuit. As the points rode on the high point of the cam lobe, the points opened a gap breaking the primary circuit and signalling the secondary ignition circuit to send spark to the plugs. The ignition is wired in parallel to a high voltage coil to one side of the points in the distributor. Electricity will always flow in the path of least resistance. Hence, while the points are grounded, the ignition circuit is grounded thru the points. When the points are open, electricity takes the higher resistant path of going thru the coil, jumping air gaps in the distributor, and to the spark plugs. In this system, over time, the points, distributor, rotor, and spark plugs would build up wear deposits from electrical arcing. This causes higher resistance in the ignition circuit leading to weaker spark and poorer performance.

The second function of the distributor is advancing the timing as the engine speed increases. Gasoline burns relatively slow as far it being an explosive. At higher RPMs, the ignition's timing must be advanced to detonate the gas a bit sooner. In the distributors of old, the breaker points were mounted on a spring loaded plate connected to an actuator run on engine vacuum. At idle, the engine vacuum is greatest. The vacuum actuator overcomes the springs and rotates the plate a certain number of degrees. As the engine rpms increases, vacuum will decrease. The springs in the plate overcome the lesser vacuum tension and the plate rotates back based on the current vacuum level causing timing advancement.

In the mid 70's, with the adoption of the clean air act, the catalitic converter became a required standard on all cars. The catalitic converter requires a relatively hot exhaust temperature to opperate properly. Gasoline also had to be free from octane boosting additives (i.e. no-lead) as combustion residues would foul the converter. This impacted the ignition timing on autos. Advancing an engine's timing causes increased performance, but the drawback is lower exhaust temperatures. Consequently, simular engines manufactured in during this pre-computerized period had lower horsepower ratings over their earlier counterparts. Their ignition timing and timing advancement mechanisms were retarded so as to run hotter.

Computer controlled inition systems:

In the modern engine, the spark to each cylinder is controlled bythe computer. All systems use a Crankshaft Position Sensor (CPS). This is used as a timing signal for number one cylinder and used in determining the engine speed (rpms). A second timing signal is generated from either a Hall Effect distributor or a Camshaft Position Sensor (electronic ignitions system). The computer must see both signals in order to send a signal to the coil (or coil pack module) in order to send spark to the cyclinder. Typically in this case, the computer sets a catch-all malfunction code of "no timing" when there is a problem in either sensor.

A Hall Effect distributor has a lobes with magnetized tips instead of cam lobes. As the lobes pass a stationary magnetic pickup sensor, a timing signal is produced that the computer senses. These systems typically use a single high voltage coil for all cylinders.
With an electronic ignition module, the timing signal usually comes from a camshaft position sensor. These systems typically have a multi coil pack in the ignition unit. Each coil in the pack is wired to two opposing cylinders (one on a compression stroke, the opposing one on an exhaust stroke). In many electronic ignition systems, a single computer signal is used to run these two cyclinders. When the coil discharges, electricity will take the path of least resistance. The cylinder on the upstroke with the compressed air-fuel mixture fires rather than the cyclinder on the upstroke exhaust cycle.

The timing advance function is controlled by the computer. It always tries to get the best performance, but is controlled by the oxygen sensors and a knock sensor. If there are incomplete burns of gasoline (running rich) in the exhaust, the computer would retard the engine timing. There is also a knock sensor mounted on the engine block to sense vibrations. If engine timing is advanced to far forward, the gasoline will pre-ignite and cause pinging. A signal from the knock sensor tells the computer to retard the timing. Also, most computers have a "limp mode" built into them. A "Check Engine Light" (CEL) is an indication of a problem and may put the computer into this recovery mode. The purpose of this mode is to just keep the engine running with safe guesses so it can be brought in to repair the real problem. In this mode, the computer may deliberately not advance engine timing. Sluggish performance and poor mpg result. It does this because if the computer can't read one of it's sensors, it can't be expected to manage the air quality of the exhaust.


The fuel system in pre-computer days:

The fuel was delivered to the engine primarily using a carberator. It's a simple device that as air enters the barrel, fuel will also be drawn and mixed in. It's functions were to regulate idle speed, the air-fuel mix going into the engine, the flow of air going into the engine, and provide a choke mechanism to cold weather starting. The fuel was regulated using two seperate needle valves. One for idle speed and one for air-fuel mixture. It also had a few set screws adjusters to adjust choke and idle speeds. Air flow was controlled by a butterfly value connected to the gas pedal. More air going in meant more gas added. Most carberaters had an automatic choke mechanism. These used a second butterfly valve, actuated by a temperature sensitive spring, to contrict air flow. This results in the engine running gas-rich at lower temperatures until engine heat warmed the spring.


Computer controlled fuel systems:

Most fuel systems today use a fuel injection system. The computer will sends a signal for a fixed lenght of time to the fuel injector so as to send the correct amount of fuel that the engine requires for the conditions. The computer attempts to provide the optimum ratio of 14.7 parts air to 1 part fuel in all driving environments. In this way, all fuel should combust into carbon dioxide and water. Ratio's other than optimum produce partial burn pollution byproducts of carbon monoxide and nitrous oxide.

For the computer to know how much fuel to have the injectors send, it needs to know the volume of air in the maniforld/pellium, the rate the air is enterring the throttle body and the air temperature. The volume of air in the manifold/pellium is a known quantity. A Throttle Position Sensor (TPS) , which is attached to the end of the throttle body's butterfly valve arm, is used to measure the rate air is enterring the engine. The car's gas pedal is attached to this arm.. This sensor is a variable rheostat type of sensor which sends the computer a signal by varying voltage. As the gas pedal is depressed, more air is allowed to enter the throttle body, and a higher voltage reading of this sensor is sent to the computer. The computer also uses a Manifold Air Pressure sensor (MAP) or Mass Air Flow sensor (MAF) to measure engine vacuum in the manifold. Vacuum is highest at idle, and drops as engine speed increases. A sensor reading of the amount of vacuum tells the computer how fast the air-fuel is enterring the cylinders. Thirdly, the computer needs to know the density of the incoming air. An Input Air Temperature (IAT) sensor does this. This sensor is usually mounted in the air filter box. With these three sensors, the computer computes how long (timewise) to pulse the fuel injectors. The exact amount of fuel for an optimum burn is sent to the cylinder. The mechanical choke function in the carberated system has been intergrated into the computer. The throttle body also has mounted on it an Idle Air Control (IAC) motor. At idle, the TPS butterfly air valve for speed control is fully closed. Air is diverted thru a small side bypass hole in the throttle body. An IAC motor is a small moveable electro-mechanical air valve. The computer maintains idle by sending signals to the IAC to move the valve and control airflow passing thru the bypass hole.
After providing the correct amount of fuel for an optimum burn based on the conditions, the computer verifies that the fuel was actually burnt. Oxygen sensors in the exhaust system tell the computer of a lean or rich burn. The computer may adjust gas flow or engine timing to get the fuel to burn cleanly.

Sensor Problems: The computer see a problem in these sensors when the voltage returned from the sensor is out of range. The usual range is .5 volts to 5.0 volts. An out of range value is a shorted sensor (spiking) or a cut wire (zero volts). In this case, the CEL malfunction indicator is set and the computer attempts to keep the engine running. It goes into "limp mode" and tries to use "safe" values possibly based on the other working sensors. Ignition timing may not be advanced at higher engine speeds. The computer is making an educated guess rather than shutting down the engine. Performance is usually gone gas usuage increases.

[Aaron_01]

Thank you that helps a great deal in understanding.

I replaced the fuel filter and of course it wasn't that. Is it common to get new MAPS that are bad? Heading out to check if I don't have a leak in a vacuum line.

[yogi_123rd]

I have never seen MAP sensors bad out of the box. However, the MAP sensors in the Chrysler K-cars tend to have a higher failure rate than other cars (go bad every two-three years or so).

I assume: The CES light is on with the MAP sensor code, and you did clear your computer codes (via disconnecting the battery) prior to retrieving the codes. Old codes can be saved as history.

[Aaron_01]

DOH!! I will do that. I must have cleared them when I cleaned the pins and it wasn't till after I finished with that that I plugged in the new MAPS.

Basically it runs fine, starts right up first try. It just seems to shift early.
It is an automatic and it shifts between 1-2000 RPMs. I find that if I depress the gas more I don't get anything more in fact it accelerates (slowly) through 1st and 2nd better if I lightly tough the pedal.

Could this be a throttle sensor?

[yogi_123rd]

I believe you have the 3-speed transmission.
To answer your question - NO. The TPS controls the engine only. The PCM controls shift speeds. The 3-speed transmission has a throttle cable (connected to gas pedal??) to know how fast the engine is going (downshifting??). This cable does affect the shifting speeds, but it usually causes the shift to occur too late rather than too soon which sets a code 37.

These Codes set the CES light:

11, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26, 27, 31, 32, 33, 39, 41, 42, 43, 44

These codes do not set the CES light, but are retained as history.

12, 19, 28, 29, 37, 38, 45, 46