[tspargo]

About a month ago I was on the freeway, with no warning it lost power. Like if I'd turned the key off but the dash was still light and working. Pulled over, wouldn't start- wouldn't even try. As if there's no gas or no spark. Waited maybe 5 minutes, then it starts. This has happened 3 times now. I've checked the fuel pressure and it is the same whether it's a cold start or recovering from this issue. So I suspected electrical/spark issues. The last time it occurred I was data-logging, graphs below.

What jumps out at me are the MAP and throttle readings- the coolant temperature too but it recovers. I checked and the readings correspond to 4V being read from the sensors. I thought maybe if a sensor ground somewhere was loose or failing somehow that might cause this, but that should make it go to 5V, not 4. I checked the power and ground connections to the ECU (Infinity 7) and they are all good. Not surprising; if it is a sensor ground issue I think that is inside the Infinity.

Any thoughts? Other parameters I can plot to help figure this out?

1st datalog screen:

Zoom in:

2nd datalog screen:

 

[8.0L>1.8T]

ASD

 

[GTS Dean]

How closely together are the MAP and Temp leads on the ECU connector? The sensors on the engine are not physically close, but I would suspect maybe you have a splice or a pin connector issue. Engine voltage starts a bit low, but then comes up to a normal range. I wonder if the voltage regulator section is causing some weird daisy chain problems.

 

[tspargo]

I'll try swapping the ASD with one the fog light relay. I tried heating up the ASD while monitoring the continuity and it didn't fail but it could easily still be bad.

The v-reg is external, the one on the stock ECU doesn't work and I'm told the Infinity one tends to fail as well so I'm using an eternal regulator. I don't know why it starts out so low.
I'll take a look at those connectors too.

 

[GRCFORCE327]

I'm using an eternal regulator.

You have a link where you got it? Many would be interested in one that lasts for eternity.

 

[tspargo]

I found that the intake air temp sensor wires were barely holding together, when I removed the connector from the sensor one wire broke completely. However I don't see how this sensor being open could affect the throttle, MAP and coolant sensor readings. So I think this was a lucky incidental find. Am I right or clueless?

I'll try to find the P/N of the external reg.

 

[GTS Dean]

It's a Speed/Density system, so the air temperature along with the MAP and TPS readings are crucial to calculating air density. If one of the inputs goes bad, the JTEC uses stored values in the engine map to back-calculate approximate readings for the lost sensor.

 

[RobV]

Like Dean said. If sensor fails, a default value is used so the car can continue to run but that is on OE ECUs. I would think aftermarket would be programmed the same.

 

[tspargo]

That's all true, but the plots are the scaled inputs from the sensors- the AIT sensor reading shouldn't affect the TPS reading. I tried unplugging it while running and the engine didn't even stumble- as has been said, it goes to a default or the last known good temperature. So that wasn't the problem. Nice to have it connected again though.

I couldn't find a point where the TPS and MAP have a common ground splice.

I couldn't find the exact part number match for the external regulator I use. It's TRANSPO-CN C8313-0326-12V. I found ones that are close on eBay- External Voltage Regulator.

 

[tspargo]

It wasn't the ASD relay. Still quits. I did verify that it's because there's no spark though. The Infinity uses two ignitors with 4 channels each- so 3 from one and 2 from the other are used. Since it just quits (if one ignitor died I'd think it would still run, just roughly or run for a few seconds, then die) I think this is pointing to the Infinity itself.

I'm going to try putting the stock ECU back in.

 

[GRCFORCE327]

To quote a person from history (Patrick Henry)... Give me Motec, or give me death. Ran it on the gen1. Tossed the aem in favor of an M150 on the gen3.

 

[tspargo]

Is there anything else I should check? The plugs are grounded through the block right? Is that through a harness or a ground strap?

 

[RobV]

Are the coils getting the trigger signal from the ECU?

 

[tspargo]

That's a good question Rob. Those connectors to the coils are hard to reach, much less hook up a DMM to. I'm going to get under the car and see if they can be accessed easier from there. I did verify that the correct voltage is at the output of the ASD relay. Pretty much all that's left is the connection from the ASD to the coils, and the coils themselves.

 

[GTS Dean]

The damned coil packs are about as hard to get to as one could imagine. You would have an easier time just buying a set of gaskets and pulling the intake manifold. Then again, the fuel line disconnect is a bitch to reach too.

 

[tspargo]

I checked the connectors and they look fine, the wires are in good shape. I measured the resistance between there and the output side of the ASD relay and it's good, even when moving the harnesses around. I did find that one of them didn't have the lock on the clip engaged but no smoking gun. It really is looking like it's the Infinity. For whatever reason now it won't start at all now- the intermittent behavior is gone which should make it easier to fix.

 

[tspargo]

How about if the cam or crank sensor went bad? Actually that can't be the problem- the ASD is getting energized but there's no spark, so it has to be something in the ignition system.

 

[RobV]

The crank or cam sensors will stop it from starting because no signal no spark.

 

[b3rndtt0ast]

How about if the cam or crank sensor went bad? Actually that can't be the problem- the ASD is getting energized but there's no spark, so it has to be something in the ignition system.

how is the inifinty controlling the ASD relay? is it just on a output that it grounds its once the key is turned on? if so you could have no crank / cam sync. if they dont sync, you will not get spark or fuel.
in infinity tuner, the default layout has a start probability on it on the "Start" tab.

 

[tspargo]

I got some help from AEM. I sent them data logs of it quitting. What's happening is that when the MAP sensor, TPS and coolant temp sensor readings go bonkers, the Infinity turns off the injectors and spark go protect the engine (the MAP sensor reading goes to 35 psi- definitely in need of protection!). So now I know why there's no spark. b I still need to figure out why the sensors readings are going wild. I'm back to what Dean suggested- that a sensor ground is going bad. When it occ

I was wrong when I stated that there's no common point for the TPS and MAP sensor grounds- connector C105 and a splice as well. However I haven't found the issue. The harness from C105 to the PCM runs under the brake booster, right above where one of the turbos sits. So I thought maybe some insulation is melted and shorting out to something once the engine and turbos get hot. So I removed the wrapping that surrounds the harness but haven't found any smoking gun. It will still quit randomly but I can move the harness around, pull and tug on it and it and I can't make it quit. I'm thinking that maybe the issue is in the Infinity- a solder joint that opens up once it gets hot or an IC that fails when hot.