95maxrider

iTrader: (32)

Please bear with me, this may get complicated.

The basics:
I have a JWT ECU from a 97 Maxima in my 96 I30. I keep the stock I30 ECU to use to pass emissions as the Maxima ECU throws a bunch of meaningless EVAP codes and the like that can't be fixed/removed.

What happened:
Around October I switched out my JWT ECU for the stock one to pass emissions. I then put the JWT back in after I passed. Then a few weeks later my car started acting REALLY weird all of a sudden. Out of the blue it stalled while I was driving. The engine cut off as did all the electrical systems. I started the car right back up as I was still coasting with no problem. Over the next 24 hours this happened a few more times so I checked my codes and got one for the cam sensor. I replaced the sensor and the problem persisted.

I had my mechanic ride along with me while he had his Snap On scan tool hooked up monitoring my systems. He said that the scan tool lost contact with the computer and then the car immediately stalled. All dash lights went off with the engine, so I completely lost power to all systems in the car. The car proceeded to start right back up. These intermittent stalls seemed to happen more when I went over bumps, but not always.

I decided to take out the JWT ECU and put the stock one back in. It ran perfectly for two months or so, but race season starts soon, so two days ago I put the JWT ECU back in. I should mention the JWT ECU has the nitrous daughterboard installed so there are a few extra wires coming out the back of it. To eliminate those wires as a potential problem source I cut and wrapped them up. I did notice that the nitrous ground coming out of the ECU that grounds to its case was pretty loose, so I tightened it up even though the wires weren't connected to anything.

Driving around with the JWT ECU went fine for 24 hours until I was coming home yesterday. I was going around a hard left hand turn that is extremely bumpy and the car stalled/lost all power. I proceeded to put the stock ECU back in, and within a mile or so the car would buck and jump when accelerating from a stop similar to what it feels like when the car is out of gas. Once going, the car drove fine. This morning driving to work the car did that bucking while going around a left hand turn with mild bumps but didn't stall.

I work at a garage, so when I got to work I did the "shake test" with the ECU/harness. No amount of wiggling wires on the harness could get the car to buck or stall out. I checked the three wires that had been spliced into the main harness for RPM switch, etc to see if they had come apart but they were soldered solid. There is kind of a rats nest of wires behind my center console where the ECU is supposed to rest, so I zip tied some together to make room for the ECU as it has spent quite a bit of time just resting on the passenger side floor. I secured the ECU as best I could and drove home without incident. I have a small scan tool with me to check codes immediately after it stalls next time, but I'm running out of ideas.

At first we thought it was a problem with the JWT ECU, but now that similar problems have manifested with the stock ECU, I'm thinking that with all my swapping of ECUs some of the wires on the harness have been messed up. I should note that while using the JWT ECU the car both bucked AND stalled, while the stock ECU has only bucked so far and has not stalled.

So great minds of All Motor....where do I begin to look for problems? Have you ever seen something like this before?

EDIT: I just went out with the scan tool and got the cam position sensor code again....maybe it's trying to tell me something......

Aaron92SE

iTrader: (128)

That's a doozy you got there!

Have you popped the cover of the JWT ECU? I'm not sure if the daughterboard is socketed like most other 3rd gen ECUs I've messed with. But make sure the daugherboard is plugged all the way into the socket that's on the motherboard. I once had a ton of issues when my experimental daughterboard started coming unplugged.

Other than that, when you say bucking, the idea of a faulty MAF comes to mind. Try swapping out that with a known good unit to see if the problem changes.

Also, I had a very intermittent electrical gremlin with my 92 Maxima with VE30DE engine and harness. Out of the blue while cruising, the car would lose 100% of power. No cylinders would fire. I'd back out of the throttle and 1 second later, I could get back into it and the engine would start running fine again. I swapped out every single sensor in the engine bay with known good units. And I also tested every crucial wire in my engine control harness. I found a lot of weird looking connections along the way, so I repaired them. The problem persisted. The problem continued on up to the day that my VE engine took a dump at 203K miles. I swapped in a VQ35 engine along with 02 Maxima harness and ECU and that solved my problem. Time for a VQ35 swap?

ajm8127

iTrader: (8)

The fact that you notice it more when the car is going over bumps sounds to me like you are having intermittent connection problems. If you got the cam position sensor code twice, even after you replaced the sensor, I'd look at that circuit for loose connections. Make sure your grounds are good too.

njmaxseltd

iTrader: (19)

Being your losing power to EVERYTHING, I wouldn't think the ECU is the cause.
I'd be looking at the ignition switch to start.

95maxrider

iTrader: (32)

Funny you mention that Tom (IIRC?). We were tracking down a voltage loss from the battery to the 8/16 pin OBD harness and ended up checking out the ignition switch. Both bolts were loose, so we tightened them up and for the last 2 weeks the car has been perfect (knock on wood). I still have the cam position sensor code though, even though it was replaced with a new part.....not quite sure what's going on there.