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No Start, Technical Tips: 1986-88 5000TQ, 1989-90 200TQ, 1989-91 200T FWD
These tests DO NOT apply to the 1989-91 Audi 100/Q, or to the 1991 200TQ with the 20V Turbo engine
These tests DO NOT apply to the 1991 200TQ with the 20V Turbo engine.
Initial Checks, Engine Cranking? Ignition sparking? Fuel Pumping?
If you are having trouble cranking the engine over:
The battery connections should be checked and must be clean and tight with no corrosion. Check the ground strap connection from the battery negative to the body. The Battery voltage and specific gravity should be checked.
The Main Battery positive cable is spliced with a welded connection just before it exits the passenger compartment and goes down to the starter, make sure the starter is getting full battery voltage and current.
On the later 100/200 vehicles with the factory Alarm system, make sure the Anti-Theft relay #8 in the main fuse box under the hood isn't preventing the starter solenoid from working. After removing the relay, you can jumper across terminals 38 and 36 to bypass it.
The first thing to do if your car won't start but cranks over ok, is to make sure you have enough good, "clean" fuel in the gas tank. Make sure a broken fuel gauge is not the reason the car died and won't re-start. Sometimes you can pick up a bad batch of fuel which has water/crud in it and this can cause the fuel filter element to swell up and restrict fuel flow. I usually avoid getting fuel from the local gas station if the tanker truck is there dumping their load. Rumor has it that this fuel dumping can stir up any stuff on the bottom of the station tanks.
Another basic thing to check, is to see if there is any spark being produced while the engine is cranked over. Remove the center coil wire from the distributor and position it so that it is within 1/8 inch from a grounding point and have an assistant crank over the engine. Make sure the gear selector is in neutral or park (automatic transmission). Don't hold this coil wire with your hand as you may get shocked during this test.
On the turbocharged engines, the fuel pump should "only" be running when you crank over the engine, usually you can hear the pump run for a moment after releasing the key from the start position. The fuel pump fuse #13 in the main fuse box should be checked if the fuel pump is not running.
There have been cases of the fuel pump relay having problems with the internal contacts that cause intermittent no start conditions, and problems with supplying the correct +12V to the engine solenoids when the engine is cranking/running.
The fuel pump socket terminals can be tested for the correct voltages after removing the fuel pump relay. The socket terminals are numbered on the fuse box area. With the ignition on, connect a Multimeter across terminals 46 and 50, and then across terminals 48 and 50, approximately +12V should be measured. Connect Multimeter across terminals 46 and 47, then crank over the engine using the starter, you should read at least 9.5 volts. Terminal 47 gets a ground from the ECU pin 21 to allow the fuel pump relay to turn on during cranking and running.
The fuel pump relay can be removed from the fuse box and a jumper connected across the two large fuse box connectors to bypass the relay operation and turn on the fuel pump for testing the fuel pressure. The fuel pump delivery rate (liters/min) should be checked as well, don't overlook a possible clogged fuel filter as the cause of low flow.
Hard starting from a loss of residual fuel system pressure, can be caused by leaky injectors, a bad fuel pump check valve, a leak in the warm up regulator or from a leaky cold start valve. The pressure regulator valve in the fuel distributor can also be leaking on the 1986-88 5000TQ (early 1989 200TQ) and this will cause a loss of residual pressure. The later 1989-90 200TQ which uses the external pressure regulator may be leaking as well.
Go to the Fuel Injection CIS section for details on checking the fuel system pressure, the control pressure and the residual pressure. If the engine won't start and you have ignition spark and the fuel pump is running and you have the correct fuel pressure and delivery, you should check for a major vacuum leak and check the engine mechanical condition outlined at the bottom of this page.
Hard Starting can be caused by a large vacuum leak from one of the breather hoses, the main breather hose on the side of the engine is a likely culprit, as well as the tee vacuum fitting at the valve cover above the main breather hose. The Accordion hose from the intercooler to the intake manifold is another possibility.
One other place to look, is the large rubber intake boot that is mounted on top of the fuel distributor with a large screw hose clamp. Make sure the boot has not come loose or is not cracked.
Hard starting when the engine is cold, can be caused by a lean idle mixture setting from Vacuum leaks or an incorrectly adjusted fuel distributor.
Go to theTroubleshooting section to check for any Intake vacuum leaks and to check the Fuel Injection section to check and adjust this idle mixture.
You should then see if any fault codes are recorded when you crank
the engine over for 5 seconds.
Ignition Switch Check, ECU and Ignition Coil +12V
If you are not getting any spark, you should verify that the ignition switch and the wiring to the ECU and Ignition coil is ok.
To verify that the ignition switch is working, check that the ECU pin 35 has +12V with the ignition key on, measure between pin 35 and pin 18 (ECU ground, pin 9 on the ECU should also be ground). Pin 18 on the ECU is the one furthest forward, next to the body mount (Right/front), Pin 35 is the pin opposite Pin 18, 1/2 step back in the connector. More details on the ECU pin out can be found at ECU Pin Out
If you don't get +12V at the ECU pins mentioned above, you should check that the ECU is grounded correctly by connecting the + DMM lead to the battery + terminal and then connect the other DMM COM connection to pins 9 and 18 on the ECU. If there is a poor ground, check the ground wire that is bolted to the top of the intake manifold towards the rear section of the manifold. Also check that the main Engine grounding strap connections from the drivers side engine mount bracket and body are clean and tight.
The ignition coil "connection block" push on or screw terminal designated as track 15 in the wiring diagram should have +12V with the ignition key on as well. This is the main supply (+12V) from the ignition switch. When cranking the engine over, you should have at least 9.6 volts at the ECU and ignition coil.
Ignition Coil Transistor Driver Module
You should also check the ignition coil "transistor driver module" mounting and connections and test whether the ECU is trying to turn the module on/off correctly. This transistor driver module is also referred to as the "Power Stage" in some texts and this Module then controls the ignition coil terminal 1 connection and subsequently switches the ignition coil on and off to provide the ignition spark. It is mounted on the same bracket next to the ignition coil. There was a service bulletin that mentions the transistor driver module can burn up if the mounting comes loose. (no more heat sink). There is also a ground wire that runs from this firewall bracket to the valve cover to ensure good engine grounding. Make sure this braided ground wire is clean and tight on both ends.
NOTE: Keep in mind, that the ECU will NOT try to switch the Transistor Driver Module on and off to then switch the ignition coil on/off to make a spark, IF it is not receiving the correct signal from the Flywheel RPM sensor, AND the correct signal from the Flywheel TDC sensor (both mounted on the engine near the transmission bell housing), AND the correct signal from the Hall Effect sensor inside the distributor.
TESTING THE TRANSISTOR DRIVER MODULE
On the later 89-90 200TQ with the MAC14 ECU, remove the three terminal connector from this transistor driver module and check between pin 3 (Brown/Blue wire) and engine ground for a good low resistance connection. Then check the voltage between pin 1 and engine ground and then from pin 1 to pin 3 (Black wire), these last two tests should show approximately 11-12V with the ignition key on, and a minimum of 9.6 volts during engine cranking. Pin 1 (Black wire) is the +12V supply (Terminal 15) from the ignition switch.
Check between pin 2 (Green/White wire) and pin 3 when cranking the engine, the "minimum" voltage measured should be ~0.2 volts as detailed in the Bentley, but a better test is to make up a "low voltage" LED test light (LED with 120 ohm resistor in series) and connect the positive (+) side of the LED test light to terminal 2 (Green/White wire) and the negative (-) side of the LED test light to terminal 3 (Brown/Blue) of the transistor driver module. The low voltage LED test light should flicker on/off when you crank the engine over during starting.
The MAC14 ECU pin #22 supplies this switching low voltage to pin 2 of the driver module and this is the connection that switches the transistor driver module on and off.
If the LED test light is not flickering on/off during engine cranking, then the ECU is not switching the transistor driver module on/off. There could be a wiring problem, OR the ECU may not be receiving the correct signals from the RPM, TDC, Hall Effect Sensors, OR there may be a defective drive transistor inside the ECU.
On the 1986-88 5000TQ and early 1989 200TQ with the MAC11 ECU, this ignition Coil transistor Driver module may use a two pin connector with a Brown/White wire on terminal 2, and a Green/White wire on terminal 1. The BR/W wire is the return ground connection which comes from pin 2 on the Mac11 ECU. The G/W wire is the switching wire from pin #22 on the MAC11 ECU. The output from this transistor driver module grounds terminal 1 on the ignition coil on and off to create the ignition spark.
Check between pins 1 and 2 of the transistor driver module connector when cranking the engine. The "minimum" voltage measured should be ~0.2 volts as detailed in the Bentley, but a better test is to make up a "low voltage" LED test light (LED with 120 ohm resistor in series) and connect it across the two pin electrical connector of the transistor driver module. Connect the positive (+) side of the LED test light to terminal 1 (G/W wire) of the connector, and the negative (-) side of the LED test light to terminal 2 (BR/W) of the connector. The low voltage LED test light should flicker on/off when you crank the engine over during starting.
If the LED test light is not flickering on/off during engine cranking, then the ECU is not switching the transistor driver module on/off. There could be a wiring problem, OR the ECU may not be receiving the correct signals from the RPM, TDC, Hall Effect Sensors, OR there may be a defective drive transistor inside the ECU.
Tips on making an LED test light can be found at LED Test Light. This low voltage LED test light will work when testing voltages from 2.5V to 5.0V
On all models, also check for any loose electrical terminals on the connection block between the Ignition Coil transistor driver module and the actual ignition coil. The early connection block has push on spade terminals, two of the push on terminals are usually connected to Track #1. One is for the coil switching on and off (negative) and the other #1 wire connection goes to the tachometer in the instrument panel. The third connections is designated Terminal 15 (+12V) from the ignition switch. You should see +12V at this Terminal 15 connection with the ignition switch turned on, and a minimum of 9.6V here when cranking the engine over.
You can use a Digital volt meter, or a regular test light .
The later connection block has two screw terminals, one for terminal 1 (coil switching, negative) and one for terminal 15 (+12V). The connection into the bottom of the ignition coil should also be checked if a connector is used.
You can connect a regular 12V LED test light, across the Ignition Coil, Terminal 15 (+12V) and Terminal 1, to see if the LED test light blinks on/off while cranking the engine. If it does blink on/off, the Ignition Coil Transistor Driver Module is working and is switching the Ignition Coil on/off.
Distributor Hall Effect Sensor and connector (10V MC Engine)
Remove the three terminal connector from the distributor for the hall effect sensor, using a DMM check for ~12VDC, (at least 9 Volts) between terminals 1 (Red/Black wire) and 3 (Brown/Red), the two outer connector pins with the ignition key on. Pin 1 is the first terminal on the left with the spring release clip wire towards the top. The 10V Engine ECU supplies ~+12V to this hall effect connector at pins 1 and 3.
NOTE: The 20V 3B engine Hall Effect sensor will only have 4.5 to 5.5 volts between Pin 1 and 3 as the Motronic ECU only supplies approx. 5VDC to the Hall Effect Sensor
Check the connection in the plug from the hall sender on the distributor. In some cases the female contacts may be loose and are not making a good connection. Use a small dental pick to push the terminals together to ensure a good tight connection. Re-install this connector onto the distributor connection.
Use a DMM and check for low (<1.0 ohm) resistance between pin 1 and engine ground, in one case, resistance between this terminal and the ECU caused a no start condition, even though 12V was measured across pins 1 and 3.
Peel back the rubber boot on this hall sensor connector and connect a DMM to terminals 1 and 2 with the ignition key on. The voltage measured across pins 1 and 2 will be ~4 volts when the distributor hall sensor is shielded by the metal cover (hat) on the distributor shaft. The voltage should be between 0-0.5 volts when the hall sensor is not shielded by the metal hat. You can remove the distributor cap, and slowly rotate the engine around while you watch the voltage measured at pins 1 and 2.
A better test for the Hall Effect Sensor, is to make up a "low voltage" LED test light (LED with 120 ohm resistor in series) and connect the positive (+) side of the LED test light to terminal 1 (Red/Black wire) and the negative (-) side of the LED test light to terminal 2 (Green Wire) of the hall effect connector. This test is done with the connector plugged on to the distributor connector, and by pulling the rubber boot back off the connector to allow back probing the connector terminals.
The low voltage LED test light should flicker on/off when you crank the engine over during starting to indicate the hall effect sensor inside the distributor is working correctly.
Tips on making an LED test light can be found at LED Test Light. This low voltage LED test light will work when testing voltages from 2.5V to 5.0V
Ignition Coil and High Voltage Wire Resistance Check
Check the resistance across the coil per Bentley. Secondary resistance between large center coil terminal and terminal 1 is spec'd at 5000-9000 ohms. Between terminal 1 and terminal 15 (+12V) the resistance should be 0.5 to 1.5 ohms.
(NOTE: some inexpensive ohm meters may have trouble reading a low resistance like this very accurately)
Check for bad broken high voltage coil wire going into the distributor.
Ohm it out, it should have 2,000 +/-800 ohms) resistance.
Spark Plug Wires, the stock replacement wires have a resistive spark plug connector (5,000 +/- 1,000 ohms), the wire is stranded copper wire, the distributor cap end is resistive also (1,000 +/- 400 ohms)
Check distributor, cap and rotor. Sometimes the distributor rotor will break apart. It also will occasionally burn up the 1K ohm resistor that connects between the rotor center terminal and the rotor tip. Check this resistance, it should be 1,000 ohms (+/- 400 ohms)
It is possible that the timing belt might have broken, so check that the distributor rotor is spinning when the engine is cranked over.
Check the alignment of the distributor hall effect sensor by locating the engine at top dead center on Cyl. #1, check the flywheel mark, the cam gear mark and that the distributor rotor is pointing toward the notch on the rim of the distributor.
As mentioned previously, you can crank the engine over for 5 seconds and leave the ignition turned on, and then check for any stored fault codes. This can help verify the timing sensors are ok if no fault codes are stored. If you get a stored fault code for one of these timing sensors, check the RPM and Timing Sensor connections at the firewall bracket.
Other possibilities: You lost the rpm or timing reference sensor. The TDC reference pin is gone or damaged. The flywheel teeth are damaged.
You may want to remove the two sensors and make sure the clutch has not come apart which may have somehow damaged the timing sensors or flywheel.
Do a compression check to verify that each cylinder has the correct compression. Verify the crank pulley (vibration damper), cam pulley and distributor rotor are turning when the engine is cranked over. Check the timing relationship between the TDC flywheel timing mark, camshaft mark and distributor #1 cylinder mark. In some cases, the crankshaft woodruff key can be sheared off if the crank pulley bolt gets loose and this will radically disrupt the timing and possibly damage the valves.
Check cold start valve operation, go to Engine Control Unit, Output Tests section at Engine Control Unit Fault codes for details on performing this check.
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