5 replies to this topic

[Avl_Paul]

Hey,

I suspect, among other things, that my manifold heater might not be working. I measured the resistance with it disconnected from the relay box at 10.2 Ohms at room temp. By blowing a heat gun down the intake, the resistance starting dropping (got it down to 7 Ohms in a few secs). According to one of Sprockets posts, the resistance should go up with temperature (anti-intuitive). Does this mean my manifold heater has gone bad?



Still can't figure out why my car is not running the fuel pump (or manifold heater) when you first key-on. I have a diagnostic tool arriving this week so hopefully that will reveal some of the issues. It won't fire the injector during cranking either. But if I spray gas or starting fluid down the intake, it will start up and then start running the fuel pump and injector. Make any sense to anyone?

Thanks,
Paul

[Ethel]

Sure I've just read somewhere that Mems sensors do drop resistance as they get warm - I'll see if I can find it for you.

http://homepage.swis...0it/ATS_wit.htm

Edited by Ethel, 03 February 2008 - 06:42 PM.

[Sprocket]

http://en.wikipedia....ure_coefficient

http://en.wikipedia....wiki/Thermistor

The Heater is a PTC element so when the temperature rises, so does the resistance.

The Heater in the manifold when the engine is cold will have a low resistance and draw current heating the element and the air/fuel entering the manifold. As the engine temperature rises, the resistance of the heater rises and less current is drawn resulting in less heat. There will be a point at which no current is drawn and no heat given, which i suspect is around about where the ECU switches it off.

I will go and physicaly check a good one now and post up the results later (other things to do in the garage )


Also, are you sure the imobiliser is functioning correctly? Being the 1995 Spi i would think that this may be one of the ECUs that needs a coded signal from the alarm ECU and the alarm ECU a coded signal from the engine ECU. You have to disabel the imobiliser before you turn the key in the ignition. Not having worked with these, I can only speculate that the fuel pump would not prim in this case, Why would it?

[Avl_Paul]

Also, are you sure the imobiliser is functioning correctly? Being the 1995 Spi i would think that this may be one of the ECUs that needs a coded signal from the alarm ECU and the alarm ECU a coded signal from the engine ECU. You have to disabel the imobiliser before you turn the key in the ignition. Not having worked with these, I can only speculate that the fuel pump would not prim in this case, Why would it?

As far as I know, the immbolizer is working correctly. The engine won't crank at all if the immobolizer is "active" and the light is on. When you deactivate the immobolizer, the light goes off and the engine will then crank but does not get primed with fuel and injector doesn't fire. I've confirmed that the circuit works by disconnecting the ECU connector and activating the fuel pump by grounding the appropriate pins on the ECU connector.

I've noticed that the "Main Relay" in the relay box is closed all the time (regardless of key on/key off position). As long as the ECU is plugged in, the main relay is powered. Is this correct? It might explain why my battery is being drawn down overnight. The first time you key off after disconnecting the battery, you hear the fuel pump run for a few seconds. After that, the battery has a constant 0.36 Amp demand even with the key off. Unpluging the stepper motor drops it to 0.26 amps (not that my meter is that accurate).

Thx,
Paul

Edited by Avl_Paul, 03 February 2008 - 08:07 PM.

[Sprocket]

There will be permenant 12v to the main relay, but the ecu will not ground it until the igintion is switched on. you will measure 12v at the concerned pin at the ECU. When the ECU grounds that pin, will then read zero volts.

Have you checked that the ECU ground is connected and in good condition.

when the igntion is swithced on is there 12v on the white wire at the ECU connector? cant remmember the pin

Sounds like the ECU is dead.

Oh and I'll get back to you about the heater resistance, whoopsie, i forgot, got side tracked with something else

[Avl_Paul]

See my measurements for each below. I should have an "loaner" diagnostic unit arriving tomorrow. If the ECU is "dead", how do I determine that for sure with the diagnotic?

There will be permenant 12v to the main relay, but the ecu will not ground it until the igintion is switched on. you will measure 12v at the concerned pin at the ECU. When the ECU grounds that pin, will then read zero volts.

I am seeing 1.3v on the main relay coil from ECU pin (S3 pin per Haynes) regardless of key on or key off position. If I disconnect the battery and reconnect the battery, it will then go to 12v. But the first time I key on, it goes back to 1.3v and stays there regardless of key on/off.

Have you checked that the ECU ground is connected and in good condition.

Yes, I remembered seeing that tip and confirmed this weekend. No measurable resistance from ECU Pin 29 to the engine frame. I also checked and saw that the wire is still connected.

when the igntion is swithced on is there 12v on the white wire at the ECU connector? cant remmember the pin

I assume you mean Pin 11 which comes from the Ignition (and also goes to the Fuel Pump Relay Coil and Purge Valve)

Yes, I see 12v when the key is on. It drops to 0 when key is off.

Sounds like the ECU is dead.

That's what I'm afraid of. I'm holding on to the hope that it is just a strange combination of dead sensors. Given some of the sketchy wiring I have found, it could also be that but I haven't found the mis-wired part yet.

Oh and I'll get back to you about the heater resistance, whoopsie, i forgot, got side tracked with something else

No worries - if you have a chance, that'd be great.