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Discussion Starter · #1 ·
I was off to get new tires installed, and another issue came up.

No spark off of either coil pack. Looking at the Infinity datalog, it gets the sync signal so I think that means the cam and crank sensors are working, and that the Infinity is getting power and is on. The injectors are squirting fuel. There's no engine protection flags on the data-log. I swapped the ASD relay with one of the other ones, and also checked it's operation with a meter. No fuses are blown. The battery is charged.

Anything else I should check?

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After 2 revs, the only synch signal is coming from the crank sensor. Time to go into PCM diagnostics.
 

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Will it run on just the JTEC, or does your build require the new PCM?
 

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Yes, the Jeep/TruckEngineController is OE. Wasn't sure if you have a standalone or piggyback. You may have a bad wire or connection, or crank sensor.
 

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If you can monitor crank signal, unplug it and see if it logs a signal. But if you had an oscilloscope, then you can see if it has signal at the sensor and at the input to the ECU. Plus you can see if you are getting trigger to the coils.

I had to buy one for troubleshooting the crank and cam signal, so i bought a cheap build ity
yourself one (i.e. solder, etc). It is one channel but it worked for what i needed it. I had pictures of the traces but i deleted them off my phone. Planning on getting a good multi channel one sometime.
 

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So is it triggering at the ECU? Without the wire to the coils connected to the ECU?

Edit:
Check power and ground at the coil harness.
Check conductivity to the coils from the ECU harness unplugged and shorts to ground.
Back probe the ECU pins for all signals, then remove the coil trigger wire to the coils and check trigger signal on the ECU
 

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The crank sensor gets power, then closes the ground path back to the ECU on the timing notches passing by. The ECU then signals to fire each cylinder coil pair according to the firing order - one spark before TDC on the firing stroke, the other pole sparks on a dead hole. If your crank sensor is swinging from 0-5V as it should, you have to confirm the signal is relayed successfully to the coil packs. You've already confirmed you have sequential fueling, correct? Both use the crank trigger reference. I've read about folks having connector pin issues in the injector and coil connectors.
 

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Discussion Starter · #16 ·
I'm pretty sure the Infinity is the issue. I've checked continuity from the Infinity to the ignitors to the coils. The coils are getting the battery voltage on pin 3, about 9-10V when cranking. The coil outputs from the infinity have no activity on any of them.

I wanted to put the stock PCM back in and see if it can make sparks- that would almost prove that the Infinity is the problem. The Infinity uses different sensors, or the same sensor with a different connector, for the following:

1. Cam sensor
2. Crank sensor
3. MAP- ignored if sensor isn't working, uses TPS and RPM to estimate plenum vacuum.
4. Fuel pressure- not used in the stock PCM
5. Intake air temp- default temperature used if sensor isn't working
6. Knock sensors- not used in the stock PCM(?), and not used during 'start engine'.
7. O2 sensors- not used in 'start engine' mode

The TPS, idle control, and coolant temp sensors are the same in both systems. This leaves the two angle sensors.

Anyone know if this is right??

Unfortunately it still doesn't activate the spark plugs. So either there's at least one sensor that the stock PCM does need but it's seeing, or whatever is preventing getting a spark is common to both the stock PCM and the Infinity and that's what needs to be fixed.

I should add that if the Infinity is the problem, AEM no longer fixes products that are out of warranty. So I'll have to fix it myself or buy, install, and tune a different ECU...:rolleyes::cry:
 

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Dan Lesser is who I would turn to when attempting to diagnose/repair an ECU. I think he worked for Visteon, who were major automotive electronics suppliers and sponsors during the CART-IndyCar days in the early 2000's.
 

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From what I remember without checking, the crank and cam during spark. The engine temp and intake air temp are using to determine the fuel trim/fuel pump run time on start up. If it is cold outside the fuel pump will run longer and you can hear it run longer when you turn the key to the start. If it is warm, the fuel pump runs shorter.

If your scope is dual channel, hook up both the cam and crank signal and see the traces. You should see a bunch of pulses that are the same pulse width and then one with a longer pulse width. I would have to look at the cam and crank gear to determine the number of pulses you should see. I will look in the service manual in see if I can count them there.
 

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Oh and you did check the ASD relay right? As the stock PCM controls that for ignition but not sure if that was removed for your AEM. And the stock PCM controls the ground circuit for the coils.
 

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with the cam signal you are going to get equal pulse widths for the hi and lo signal as the cam gear timing has 1 tooth that is equal in length to the non tooth side. Not sure if it is per rotation as I would need to calculate the gear ratios between the small drive gear and the cam gear. So I am going to assume you should see 1 hi pulse per 2 crank rotation from eyeballing it.

With the crank, you are going to see 10 pulses per rotation. 2 short widths hi pulses, followed by a long wide pulse then 2 short again. I cannot see if the long pulse is going to equal without seeing the complete crank as I all could find online is only a part of the crank. My guess would be 4 are equal width and 1 is not as that is usually how timing gears/slots made but the cam gear in the Viper is not like that so little weird to me with that design.
 
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