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My 1991 164 will turn over but won't start. I don't have power to the fuel pump and I don't have any spark to the plugs. I've checked the fuss panel and all looks go. Any ideas?
Oz
 

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Group 04 Motronic Ignition and Fuel System Troubleshooting

Reference: 1991-93 Alfa 164 V6 12v USA shop manuals.

Problem: Engine will not start

Did you check for power at Engine Services 15A F22 fuse in main fuse box G1 with the key on using a test lamp or meter?

Another way to check for power through fuse without a meter or test lamp is to open hood and check that RED STRIPE Motronic Relay S12b clicks when somebody turns on the key for you (KEY just on, not to start position). This relay S12b is located under black plastic cover closest to bottom end of ignition coil.

Also under that SAME cover is fuel pump relay S12a.

To check if Motronic relay w/diode S12b "red stripe" is sending power to Motronic computer S11 (ECU) and also to fuel pump relay pull fuel pump relay and with meter or test lamp see if with red strip clicked on you have power to fuel pump S12a relay holding socket slot 86 (red wire from S12b) Note: Power with key on and off with key off.

If you have power turning on red stripe relay and getting to pin 86 of fuel pump relay you should have power to green-black wire going to terminal 15 on coil A8 but this is a non fused wire from same terminal Pin 2 igntion switch B1 but same so another way to check for power.

Report your findings.
 

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Another possibility is that the ECU is not getting the Crank Angle Sensor (CAS) or RPM sensor signal. Check the wire and connector that come up from the front side of the crank pulley, between the thermostat and the alternator.
 

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What is happening with this issue?
 

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Discussion Starter #6
Sorry,got sidetracked working on my Alfetta.
the relays 12b is clicking and feeding power to s12a. How do I test the crank sensor? Can I disconnect it at the connector and test it with a meter while turning over the motor?
 

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No not really, you can disconnect it at connector and check resistance between center pin and side pins. One side pin will give no reading and other will give about .6 Kohm. Inspect wiring harness from connnector to crank pulley mounting area for evidence of chaffing/damaged wiring if it got next to alternator or a/c belts.
 

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Steve, I've also seen certain parts of that harness chafe between the rear cam gear and the dogbone mount on the strut tower. It's worth looking at. That's a place that can get tight when replacing a right front motor mount, for instance.
 

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How do I test the crank sensor? Can I disconnect it at the connector and test it with a meter while turning over the motor?
The crank sensor is basically a coil inside. First inspect the wiring and connector to see whether there's any damage. You can measure the coil with an ohmmeter and you should get some low resistance value and not high resistance or open circuit. Next, check the gap between the sensor and teeth of the crank pulley, the gap should be between 0.5 to 1.0 mm. The signal from the CAS is of the form of sine (sinusoidal) wave when the teeth pass through the sensor interrupting the magnetic field. There is a longer signal interruption per revolution when the sensor passes over the two missing teeth area of the crank pulley. Normally, one should use a oscilloscope to look at the pattern of the signal. But you can use a voltmeter and set it to AC volts (~5 volts range if needed). You should get some AC voltage when the crank pulley turns. The page from 24V manual below has some additional information. It said you should get about 0.5V to 100V (page is fuzzy and I believe it makes more sense to be 1.00V). You can measure at the sensor connector but if you measure at the ECU connector (pins 23 and 25) you can also determine whether the wires all the way to the ECU is any good.
 

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Alfa 164 RPM/Timing Sensor S31 Testing info

Reference: Auto Force Tester Diagnosis Manual section on 1991 Alfa 164 Motronic ML 4.1 Diagnosis (March 1990)

Since most people don't have Auto Force EFI-8400 Tester and EFI 8827 ML 4.1 Interface Adapter and an Oscilloscope to test system, they will have to make do with a multimeter.

According to manual RPM AND TIMING SENSOR TEST 1 pages 83-88:

Continuity Check between center pin of S31 connector in engine bay and one of the outer pins is >400 Ohms but < 600 Ohms (.4-.6 Kohm) This is pin 23 black wire and pin 25 yellow wire in ECU S11 connector but if using multimeter (ohm setting) in engine bay on just sensor wiring disconnect connector and test between center and outer pins of sensor end only as a quick test of just sensor first.

Dynamic Check Use oscilloscope to probe pin 23 and pin 25 of interface adapter, crank engine and check for AC wave form from sensor.
OR use multimeter with low AC voltage capability. Low AC voltage observed during cranking test should be 2.0-4.0 VAC. Without interface adapter pin out box you would have to probe wires carefully

Circuit Wiring Check With S11 connector disconnected from Motronic ECU and S31 connector to sensor disconnected in engine bay check for continuity with ohm meter between yellow wire pin terminal 25 in S11 connector and yellow wire (one of side terminals) of S11 connector harness (chassis end). Resistance should be <3 ohms. Repeat test with pin 23 black wire S11 connector and center pin black wire S31 connector (chassis end). Resistance should be <3 ohms.

Note: There are 35 pin sockets opening in ECU S11 cable connector but not all sockets have pin socket terminals however, to locate a pin socket number start at cable end of connector and count 1-18 in top row and 19-35 in shorter bottom row.

Isolation Test With sensor S31 connectors hooked together in engine bay and S11 ECU connector disconnected from Motronic ECU S11 under center dash console area check black wire pin 23 in connecter for a short to chassis/battery ground point using multimeter set to ohm setting. Resistance should be infinite (open aka infinity).
 

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Discussion Starter #11
OK, continuity cked fine, 562 ohms. when turning over I.ve got 1.6 VAC,a little low but I,m just useing a cheap digital meter. No damage to wireing but the insolation is dry rotted and falling off. Whats the bust way to gain access to the ECU?
 

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Remove side carpet from center tunnel under glove box area, remove middle ABS computer and locate motronic computer. It is top most one in stack.

As for insulation on sensor wiring I would flake off what you can and rewrap cable with electrical tape to keep to protect shiny looking cellophane wrapping and EMI braided wire shielding intact.

Have you pulled dizzy cap and checked condition of rotor button and checked resistance of it? Also check wear on spring loaded carbon rotor button in inside center of cap.
 

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Discussion Starter #13
I,ve got the ECU in my hand. Do I need to disconnect the batt. before I remove the cannon plug( conector) The disributor cap looks good.
Oz
 

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YES most Definitively as keep alive pin is always hot with battery hooked up even with key off.
 

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My 92 164 L had the same problem, ( turned over would not start), the distributor was toast and on replacing it car runs fine.

I should say I had some warning, with the car being difficult to start and dying unexpectedly ( usually starting off from a intersection with 50 cars behind me at rush hour). Anyway, check out the distributor.
 

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Dizzy may not need to be replaced but check inside dizzy cap for burned center spring loaded carbon button and rotor condition. Also check terminals for each cylinder inside cap for corrosion.

Use 8mm or 5/16" socket to remove three bolts holding cap to dizzy.
 
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