Car Won't Stay Running

[ilateapex]

My Spec E30 will not stay running. Started doing this at Nationals after a qualifying race. Symptoms are that it will start, idle for a short time and then die. I can also start, idle, rev up and hold and it will still die. It is like it just shuts off. Battery is fairly new and I have replaced FPR, CPS, CTS, plugs, ECU, ICV, O2 sensor, and kill switch. Not all were changed for this issue but I listed them anyway. My AFM was purchased new a few years ago. I have confirmed I have adequate fuel pressure, The alternator is charging after being “excited”. It seemed that I could get through a race without issue but would die when getting to impound. Also, if driving it will cough and then catch again sometimes. I am thinking that with the car moving that whatever is being interrupted is back on line and with the engine rotating it just keeps going. Sometimes I can pump the throttle when it is trying to die and it will stay running for a little longer.

What am I missing? Leaving (hopefully) for a race Friday and need to figure this out. I figured replacing the parts would fix it but no luck so now down to the wire.


Thanks,


Michael

[b*saint]

Loose wire?

[jlevie]

With what you have replaced, intake leaks or a bad engine harness would be my suspicions.

[FLG]

You need to narrow things down, i was searching for a random cutoff issue (though it would catch itself just hiccup while driving and never cutoff when idling) for weeks. Turned out to be the connector near the fuse box, cleaned it up and shes been good since.

Clean all your grounds, the engine ground on the oil pan and the ground on the passenger inner fender (very important as its grounds for the DME), your battery terminals, and your battery ground.

When this happens, does your tach drop off completely or does it slowly decrease with engine speed? If it drops off completely than your loosing singal, this points to the DME, CPS sensor, or bad power/ground/broken wire to the DME. If this is the case, first thing to do is to make sure the DME isnt loosing power

Also before you go crazy with LED's or a multimeter probing the harness (its a dam pain) go in your trunk and follow the smaller gauge wiring coming from the battery, on that wire is a fusible link about 12 inches down from the terminal. This is direct power for the DME. It might look fine, but i had an issue where if it was touched or moved in a certain way the car would shut off. Upon further inspection, it had a small crack in the link...enough that the car would run but if disturbed it would cut power to the dme.




Use a multi meter or LED's and watch the power going to your DME on pins 18 and 37, heres a diagram

http://www.e30tech.com/forum/showthread.php?t=86872&page=2

If the DME isnt loosing power but your tach is dropping off completely, than its either a bad CPS sensor (what does the new one ohm out at?) or bad wiring/connection somewhere on the harness. Also make sure the air gap is correct (im not sure what its supposed to be off hand)


Curious, where are you located??

I literally hours upon hours trying to fix the cutoff issue i had...it left me restless some nights. So i have quite a bit of extra parts and troubleshooting knowledge, if you happen to be local to NYC id be more than willing to help.

[ilateapex]

FLG,

Thanks for the info. I am in Eastern KY so quite far from you.

I have done some more trouble shooting. I changed the coil, cleaned the engine ground and the grounds at the strut tower, Cleaned the big plug near fuse box, and inspected the fuse-able link. I did find a crack in the valve cover and replaced the cover.

I am getting funneled to three possible causes.

1. Alternator, Voltage regulator - Testing shows good but may still be the issue as the batt. light on the dash does not light up. I checked the bulb and it has continuity. I seem to remember that it used to light up with key on and go off after exiter got charging started.

2. Vacuum/Intake leak - Still have slight leak at head plugs in rear so going to pressurize intake and see where else may be leaking.

3. Engine harness - I am having a hard time to grasp this could be it but who knows. The problem is too repeatable to be random.

Michael

[jlevie]

There is information in your thread on SpecE30.com that you haven't posted here. Specifically the voltage difference between the main power and DME supply lead and the lack of illumination of the alternator warning light. Work on those problems first as they may be the cause.

[ilateapex]

Jim,

In the SE30 thread you miss understood the extent of the voltage difference. it was 13.8 to 13.6. Not 12.6. I am lumping that into Item #1. Item #1 is referencing the alternator warning light.

[jlevie]

I saw that error this morning. But with apparently no exciter power to the alternator it may not always be holding the system voltage to +13.5v. That plus a voltage drop on the DME cable might be enough to shut down the DME.

[ilateapex]

GOT IT!!!

Yoda Levie put me on the right track. I double checked the voltage at the ECU and for some reason pin 27 did not sound familar. When it was checked I found that it only had 12.7 V where the other power sources had 13.6 V. Looking at the ETM, this is the green wire that comes from the ignition switch, through the OBC relay and then to the coil and ECU. I found that the plug into the OBC relay was loose and when removed one of the pins was black. I cut the wires from the relay and shorted them and then pluged it back into the C104 plug similar to the way it would be in a non OBC car basically bypassing the OBC relay. Now she purrs like before and is rock solid. Basically the coil was seeing less then optimal voltage and the combination of that and the low voltage to the ECU was causing the issue.

Thanks so much for all the help.

Michael