Heat Start problem, points to ECU?

325iconverted · 08-10-2004, 08:56 AM

Hello All,

This is my first post to this board, I've been posting to other sites but just found this one. Hi!

I've got an 87 325ic with a Motronic 1.1 (173) ECU. Ever since summer started, I've had this problem where the car will not start if it heats up in the sun too much. It's NOT engine heat but ambient temperature that will prevent it from starting. When it does not start, I get NO power across the ignition coil and NO power at the fuel injectors. In other words, the main relay is not closing. I will post all the information I have gathered so far, and if you have any advice, please please let me know. All this testing has led me to believe that it could be my ECU that is not grounding properly when it gets very hot. However yesterday I put it in the freezer for 30 minutes, and still it did not work. Today, I've got it inside with me all day and we'll see what happens.

I've done:
replace main relay
replace ignition coil
OK: tested main relay ground, continuity between main relay ground terminal and ECU harness connecter terminal.
OK: tested 4 ECU harness connecter ground terminals.
OK: tested crank pulse sensor resistance at sensor harness and ECU harness.
OK: thoroughly cleaned main ECU ground on right shock tower.

Known problems:
Throttle not adjusted properly (does not always activate "throttle closed" switch at idle)

Usually, I go outside after work around 5 pm to start the car, and it does not start. I then poke around and repeat many of the above tests several times, grounding the main relay. Usually, at some point while reconnecting the main relay or the ECU harness connecter, the ICV flips on (starts whirring), and this means the main relay has closed, and wham, the car starts. I'm not sure if the ECU is just cooling off around this time, or, if my fiddling is causing some ground circuit to complete which allows the ECU to work properly.

Any info is greatly appreciated!!!!!

Thanks,
Dave

7hills · 08-11-2004, 06:41 PM

Dave,

Not sure if this will help, and you may have already thought of it, but I have chased an erratic idle for two weeks. Just like you, I tested and re-tested only to find that I couldn't find the gremlin. This afternoon I was checking the TPS sensor for the 3rd time and happened to push the connector while the car was running and this re-created my erratic idle.

To solve the problem I cleaned all of the connections with contact cleaner and then put dielectric grease in the connections as I put them back together. The idle is now stable and it only cost $1.00!

I hope this might help you find the continuity to solve your problem.

Rance

325iconverted · 08-12-2004, 07:07 AM

Rance,

Thanks. I'm going to adjust my throttle sensor and switch this weekend, and clean all the contacts on it and on my relays, the pulse sensor, and anything else I can find

. What is dielectric grease, and where can I get it?

7hills · 08-12-2004, 04:52 PM

You should be able to pick up dielectric grease at any parts store. It will probably be near the gasket sealers and other chemicals. It is a grease designed to promote conductivity and to seal out moisture from the connection. You may have found it if you have changed the bulbs on a newer car, some of the stores will market it as "Bulb Socket Grease".

The electric contact cleaner should be close by as well. Don't let the guys at the parts store talk you into using carb cleaner on the electronics. Carb cleaner can leave a film on the metal and can deteriorate the rubber seals on the connectors.

I hope it helps with your problem, but it can't hurt to have the connections cleaned and sealed. Good luck!