Topic: Renix - No Spark (was:FAQs)

[87cherokee2wd]

Hi I am new here, I recently purchased an 87 cherokee 2wd 2.5l tbi with a 5 speed.  And am trying to get it running but can get a spark, I have been told this site has a lot of info on this renix system in the faq but i dont see an faq anywhere.

[Jeffy]

Most tech is here:  http://4bangerjp.com/forums/index.php/board,11.0.html

It's been a while since we talked about renix.  I know chardrc was the renix guy so it would be one of his threads.  So what's the problem and what have you checked?

[87cherokee2wd]

The entire fuel system is new and i have a good injector pulse but no fire causing a no start.  I have done the c101 clean up have new plugs new wires new distrib new rotor and now new coil but still no output from the coil

[Jeffy]

IGNITION SYSTEM - 2.5L W/RENIX ELECTRONIC IGNITION

1988 Jeep Cherokee

Distributors & Ignition Systems JEEP RENIX ELECTRONIC IGNITION

2 . 5L TBI: Cherokee, Comanche, Wagoneer, Wrangler

DESCRIPTION

The Renix electronic ignition system consists of a solid-state Ignition Control Module (ICM), a distributor, a Top Dead Center (TDC) sensor, and an Electronic Control Unit (ECU).

OPERATION

IGNITION CONTROL MODULE (ICM)

The ignition control module is located in engine compartment, just left of battery. The ICM consists of a solid-state ignition circuit and an integrated ignition coil that can be removed and serviced separately.

Electronic signals from the electronic control unit to the ICM determine the amount of ignition timing or retard needed to meet various engine requirements. The electronic control unit provides an input signal to the ICM. The ICM has only 2 outputs: a tach signal to the tachometer and diagnostic connector, and a high voltage signal from the coil to the distributor cap.

TDC SENSOR

The TDC sensor senses TDC and BDC crankshaft positions as well as engine RPM. Sensor is located on left rear side of engine and is not adjustable. Sensor is secured by special shouldered bolts to flywheel/drive plate housing.

TESTING

1) Disconnect ignition coil wire from center tower of

distributor cap. Using insulated pliers, hold coil wire about 1/2" (13 mm) away from engine block. Crank engine and check for spark between wire and engine block.

[LIST=1]

• If spark occurs, reconnect coil wire to distributor cap.Remove spark plug wire from one spark plug. Using insulated pliers,

hold wire about 1/2" (13 mm) away from engine block.

• Crank engine and check for spark between wire and engine

block. If spark occurs, check fuel system for problems. If no spark
occurs, check for a defective rotor, distributor cap, or spark plug
wires. Replace parts as necessary.

• If rotor, cap and wires are okay, check for loose or

corroded connections at coil terminals. If necessary, clean terminals
and wires. Ensure wires are properly seated on coil terminals and not
wedged between coil body and terminal. If okay, go to next step.

• Check for loose connectors at ICM or ECU. Verify that wire

connectors are firmly plugged into ICM and ECU. Also check for loose
ICM or ECU ground wire connections at oil dipstick bracket. Clean and
tighten if necessary.

• Load test battery to ensure battery is fully charged.Replace battery if necessary. If battery is okay, check voltagebetween terminals "A" and "B" of ICM connector while cranking engine.See Fig. 1.
• Minimum voltage reading should be 9.5 volts. If voltage isokay, go to next step. If voltage is low, check continuity of ICM andECU ground wires. Repair or replace as necessary.
• Using an ohmmeter, check ignition coil resistance.Resistance on primary winding should be .4-.8 ohms. Secondaryresistance should be 2500-4000 ohms. If correct, go to next step. Ifnot, replace ignition coil.
• Check ECU and ICM with Tester (MS 1700) . Replace ICM orECU if either fails MS 1700 test sequence.

Fig. 1: 2.5L TBI ICM Connector Terminals Courtesy of American Motors/Jeep Corp.

OVERHAUL

NOTE: The 2.5L TBI distributor contains no electrical components other than the rotor and distributor cap. If any other distributor part is defective, the entire distributor assembly must be replaced.

[chardrc]

I do not think I had a thread about the ignition system as both Renix vehicles I worked in always had spark (the injector(s) not firing was the more common result when something went wrong (also had a 1990 xj with the Renix 4.0l mpfi)).

If I am understanding you correctly the fuel injector is firing but you have no spark from the coil. If that is the case I would not expect the crank position sensor to be the issue since IIRC the ECU will not fire the injector without a speed signal (may also effect injector timing). Did the Jeep work fine before the no spark issue (any other symptoms leading up to the no start issue)?

Start with everything Jeffy posted. The items below are essentially the same information explained differently except for item 5.

1. Have you been able to verify that the ICM is getting power and is grounded? voltage between the "A" and "B" (power and ground) terminals of the ICM should be above 9.5 volt when cranking the engine (12v with no load)
2. The coil primary resistance should be 0.4 to 0.8 ohms max, the coil secondary resistance should be 2500-4000 ohms max (shouldn't be the problem since you said you got a new coil).
3. The signal from the ECU to the ICM is a 5 volt square wave so it is unlikely that you will be able to read it. I would recommend checking the continuity of that wire. This is the wire from the "B" terminal of connector number "2" of the ICM (left wire of the two wire plug in the middle of the ICM as depicted in Jeffy's post). The wire goes to Pin 27 of the ECM.
4. I could be wrong about it not being the crank position sensor, the FSM says the resistance across terminals a and B of the cps should be 200+/-75 ohms (Jeffy's post refers to this as the "TDC" sensor)
5. You could technically try to send 5v to the "B" terminal of connector 2 of the ICM to eliminate the ecu from the equation. When the leading edge of the 5v square wave reaches the ICM, the ICM charges the coil primary winding. When coil saturation occurs, the module circuitry opens the primary windings to collapse the magnetic field in the windings. This results in a high voltage in the secondary winding to create spark.   AKA if you disconnect the 2 wire connector ( to prevent back feeding the ECU) and apply 5 volts to terminal B there should be a spark from the coil. Only attempt this part at your own risk (hardest part is getting a 5 volt power source). I would only connect the 5 volt source for a short amount of time as I am sure this isn't a normal diagnostic procedure they had in mind when designing the ICM.

good luck

[87cherokee2wd]

I just replaced the cps and still no spark.  The injector is firing just fine just nothing from the coil.  I have check between the yellow of the icm and ground and have 12v and black is made to ground so between the yellow and black i have 12v but using the test lead ports between the coil and icm i am not getting a ground to give me spark.

[87cherokee2wd]

Its alive and running strong, it was the ignition control module.  Now the only thing is the tach is showing too high, it seems to be idling around 900 or so but the tach shows almost 2000...