96 Tacoma 2.7 L 4 x 4 M/T ; NO SPARK

I have read through many threads for "NO SPARK" condition on 96 Tacoma and various relative years to this same problem, does not seem to have follow through with what actually corrected the fault. So, I am going to start a new thread and I hope we can keep it clean, to the point without too much static (outside this issue interference).

I ran through the test chart for a P1300 code (Ignition Circuit Malfunction), which the ECU is clean by way of codes, the diagnostic tree within the FSM is where I started since I have no spark.

Just to clarify, I can make coil spark manually:

Everything connected, key to on position, back pinned Ignition Control Module (IGM) at "IGT" signal wire pin 2 (B-L: color code), with engine at top dead center for #1 cylinder, plug out and grounded, I can take a test light supplied from battery positive and tap probe on back pin at "IGM" pin 2, strong spark (to me I just verified a working IGM and distributor).

After conducting this test, I move on to testing continuity between IGM and ECU (IGF and IGT wires), IGM and Distributor (IGF relative signal B-W), ECU and Distributor (Cam pickup coil, located in distributor on this model truck, also tested air gap and signal generation), Crank sensor and ECU (Red and Green wires, also tested sensor), Tested ECU battery power and grounds, along with all fuses and body grounds, with multimeter. Tested continuity between Ignition switch, Coil, IGM and ECU, all good, also looked at power being supplied to these points as well with key on, good. One last thing I tried, although I do not own an O-scope, is I tested for the IGT signal at IGM pin 2 with a test light while cranking, no flutter or any illumination.

Purchased an ECU from a salvage yard, no change. Purchased an IGM from ebay, no change. I know these are not reliable sources for parts, but is it likely the ECU from the salvage yard has the same fault?

An ECU is expensive for this particular truck for some reason and I would like to be absolute the ECU is causing this fault, there is no way for me to directly test the ECU. If anyone knows of a shop that has the capability to plug in the ECU and run diagnostics at a reasonable price, please share.

I would like confirmation that I have indeed exhausted all testing options or perhaps there is something I have overlooked?

Nick

 

I keep retyping this response haha.

So you have 0.1-4.5V at pin 1 of IGM, 5v at pin 2, and 12v at pin 3. This tells me the ECU is likely ok.

Does the tach move while cranking?

Can you get voltage at the NE+- and G+- signals at the ECU terminal while cranking? As you said an OScope would really help here. Sometimes I just hook up a volt meter, (analog is really good) to see if getting any kind of signal.

It seems like the IGM is giving no feed back to the ecu and this is preventing the ECU from allowing ignition.

BUT! these older trucks show codes sometimes that are not entirely responsible for the no-start/no-spark. This could very well be a bad signal from the CKP or CMP sensors causing failure.

Sorry for your luck, I'll try to shoot you some ideas if I can beyond these.

 

Bishop,

I have nothing at IGM pin 2 when I T-pin and check with test light while cranking (here is where I need an O-scope)... This is the same pin I apply power to simulate the IGT signal and I can make spark. The ECU is suppose to generate a pulse 5v into IGM pin 2, which I am not getting.

The feedback from the IGM to ECU is the IGF signal, which will not generate until system sparks. Its a signal generated from the ignition coil from magnetic flux collapse and without it the ECU cuts fuel pump from functioning.

 

Fiddlesticks, even if the ECM doesnt get signal it should still send 5v to the IGM pin 2. But I may be wrong, I'm helping with a keyboard! haha

This is where it can get hard, you may have something else pulling the 5v reference down, lets try to see if the ECM is producing 5v at another sensor. Pin 1 of the TPS gets a constant 5v reference.


If it doesn't have 5v, it's a ECM problem or ECM power/ground issue. If it does have 5v then its unrelated and I just wasted your time

 

Bishop,

I have been awaiting the chance to get a new battery, now that one is installed, I checked the 5v signal at the TPS connector, 5v exactly is present!

 

Check timing chain?

 

Tony,

The timing chain has been replaced with a complete kit, but not by me, in fact the cam was 3-4 teeth out when it arrived to me. The mechanic said it went through a phase of hard starting and erratic running before it lost spark, had to use throttle to maintain running (without throttle engine would shut down). my idea here is something burned out (perhaps within the ECU) while trying to electronically control proper timing, since the cam was 3-4 teeth out, the system of course could not compensate the difference.

I am curious, what is your speculation that the timing chain would be a reason for no spark condition?

 

Bishop,

I am curious about these output readings. What should the waveform look like and what is the voltage range? do you have a test procedure to follow?

I've only performed an OHM check by back pinning ECU connector and rotated engine by hand to see fluctuation in resistance for both crank and cam sensor.

 

ECU Technologies <jeff@ecutech.co>

248-293-3267

when I was futzing with a CLK430 a few weeks back I thought I had an PCM/ECU issue and I spoke with Jeff... VERY knowledgeable guy. Remember it does not hurt to ask him anything IF you have your facts down cold. Voltages at pins etc etc.

 

I know this is old thread , but I'm having exact same problem right now on 95 2.7 and its driving me crazy. Did this issue ever get resolved ?