77 replies to this topic

[Spencer Rutherford]

Bummer of a finish.  Do you know what failed electrically? 

not 100% but thinking maybe something with the kill switch as the data shuts off it  would only happen when i would bottom the car out on a curb like in 7 with the big drop off on the other side of the curb. but then there is another sputtering problem that seems to come late and once off the track while its warm it doesn't want to stay running until it cools off. im going to check the kill switch connections and going to change a connector on the engine harness. 

[38bfast]

Spencer we have had many of the kill switches fail. Yes check the connections but replacing the kill switch is not a bad thing to do as a maintenance item.  

[Spencer Rutherford]

Alright I’ll change it just to be safe

[Tom Sager]

My '01 had a similar episode to Spencer's recently.  Got into some nasty rumbles and the car just shut off.  After cycling the key it re-started.  A credible source said that a main relay under the hood can sometimes temporarily fail causing this.  Anyone else experience this in a VVT car and does changing the relay help or is it an inherent weakness in these cars? 

[Spencer Rutherford]

My '01 had a similar episode to Spencer's recently. Got into some nasty rumbles and the car just shut off. After cycling the key it re-started. A credible source said that a main relay under the hood can sometimes temporarily fail causing this. Anyone else experience this in a VVT car and does changing the relay help or is it an inherent weakness in these cars?

just rough rumbles? Mine seems to only do it when I put two wheels off and the bottom of my car hits the rumbles Chris seemed to think I was hitting the power plant frame on the ground and something about How that causes it to shut off. Not sure but he seems to know a lot about these vvt electrical problems

[Spencer Rutherford]

https://youtu.be/qIBH18zBbgs

[Tom Sager]

https://youtu.be/qIBH18zBbgs

Very very similar to my experience. 

[Spencer Rutherford]

Very very similar to my experience. 

how did you fix yours?

[tynor]

Check your battery tie down.  I had similar problems when running over the gators at T14 at Kershaw.  Turned out to be the battery moving around just enough for the + terminal to short itself against the tie-down strap. 

[Tom Sager]

how did you fix yours?

Haven't.  It happened the last time I was in the car. 

[chris haldeman]

I have multiple cars out there with the main relay bypassed

[Spencer Rutherford]

I have multiple cars out there with the main relay bypassed

so i should i try bypassing it?

[Tom Sager]

I have multiple cars out there with the main relay bypassed

[davew]

I also have several cars with main relays bypassed. Hit a bump and the engine dies. Turn the key to off for a couple seconds (a long time when at speed) and it will restart. If you just go to start without going to off, the car will not restart until everything resets, about 12 seconds.

 

By monitoring various voltages on AIM data, we traced the issue to the main relay shutting down. Jumpering the main relay will stop the problem. BUT, it creates another. The ecu expects certain things to power up in certain orders, leaving the jumper in will change the order and you will get a check engine light with multiple codes. Also the circuits controlled by the relay will remain hot and drain the battery.

 

I believe the issue is actually in the control side of the relay. We tried multiple relays with no help. Jumpering works perfect which tells me the issue is not in the controlled side of the relay. So far I have not traced the wires to find a source.

 

At Gingerman last year, Voytek hit the same pothole at the top of the hill, the car died 2 laps in a row, He left the car in gear as it rolled and after exactly the same time, it restarted. If he avoided the pothole, the car ran fine. By using video to see the dash and AIM data to compare what sensor died, we discovered the main relay failure. Data can be a really cool diagnostic tool some times.

 

Dave

[Tom Sager]

I also have several cars with main relays bypassed. Hit a bump and the engine dies. Turn the key to off for a couple seconds (a long time when at speed) and it will restart. If you just go to start without going to off, the car will not restart until everything resets, about 12 seconds.

 

By monitoring various voltages on AIM data, we traced the issue to the main relay shutting down. Jumpering the main relay will stop the problem. BUT, it creates another. The ecu expects certain things to power up in certain orders, leaving the jumper in will change the order and you will get a check engine light with multiple codes. Also the circuits controlled by the relay will remain hot and drain the battery.

 

I believe the issue is actually in the control side of the relay. We tried multiple relays with no help. Jumpering works perfect which tells me the issue is not in the controlled side of the relay. So far I have not traced the wires to find a source.

 

At Gingerman last year, Voytek hit the same pothole at the top of the hill, the car died 2 laps in a row, He left the car in gear as it rolled and after exactly the same time, it restarted. If he avoided the pothole, the car ran fine. By using video to see the dash and AIM data to compare what sensor died, we discovered the main relay failure. Data can be a really cool diagnostic tool some times.

 

Dave

 

Thanks Dave, this could be very useful info for a lot of people. 

[FTodaro]

Let me ask, Where is the main relay, is it in the fuse block under the hood?

[Jim Drago]

Let me ask, Where is the main relay, is it in the fuse block under the hood?

THE GREEN ONE UNDER HOOD

[Tom Hampton]

I believe the issue is actually in the control side of the relay. We tried multiple relays with no help. Jumpering works perfect which tells me the issue is not in the controlled side of the relay. So far I have not traced the wires to find a source.

Some terminology:

"controlled side of the relay" = contacts
"control side of the relay" = coil
 
I presume by jumpering you mean bypassing the contacts....in other words connecting Vbat to Vswitched. 
 
I've helped with a couple of chris' cars (3 in total maybe?)  2 at the shop, and 1 via telephone/text message.  IIRC both of the ones at the shop were second hand racecars partially built by someone else---and dumped on Chris' to "finish up."  I spend an hour or so on one with a multi-meter, and finally traced to the big connector between the dash harness and the engine harness.  I'd traced the issue to somewhere between those two harnesses, and I unplugged the connector to determine which side of the connector was at-fault.  I didn't find anything "wrong", and when I put it back together everything magically worked.  We decided to bypass that part of the circuit to just avoid the issue at the track on that car. 
 
I agree that on the cars I've dealt with, the issue appears to be with the control wire coming from the ECU to the coil of the Main Relay. I don't recall right now whether that is a +12V signal or a GND. The relay itself is fine, but the wire between the ECU and the Relay is F-ed. I think in the first car I energized the coil and got the relay to switch (proving the relay is fine...just not getting a signal). 

I still don't know what I did with that multimeter.  Its been missing since then.  I know I got it back....but F if I know what I did with it after getting home.
 
I don't recall doing as much diagnosis on the second car....just enough to determine it was another stupid f-ing main relay...and bypassed it again.  And the third car at the track (I was at home doing something lame like mowing the yard), I just confirmed some things on the schematic to verify he could bypass safely. 
 
PS: Chris LOVES electrical work!