Tell me what to do, car will not idle or run

[blueman803]

Ok, my car simply will not run. I had the car running fine, slight idle surge, mpi relay clicked, and had some massive exhaust leaks, but the car ran fine other than that. I hit 7 psi in 3rd gear and then my car would want to die everytime I came to a stop. I thought it was a vacuum leak, so I pressure tested it, and of course I had blown a line off. Fixed that and pressure tested again, held pressure great.

So I take the car for a test run, about halfway up the hill it decides it doesn't want to run. The car sounded like it was misfiring horribly and the car will not idle. I disconnected an injector and the car idled around 1000 while misfiring, so I don't know how to explain that. What could this be? The ECU has a burnt spot and smells like fish, but are these problems typical of a dead ecu, or could I have another problem somewhere else?

 

[ddavisaf]

Your ECU is dead. Get'er fixed.

 

[blueman803]

I tried putting another ECU in and it shorted out, any idea what could cause that? The ECU in it still ran when I tried replacing it, but the new one wouldn't run and had a burn spot on it.

 

[ddavisaf]

http://www.tmo.com/howto/ecu1g/caps.htm
You've got the nonturbo 4G63 or the 1.8?

 

[blueman803]

Non-turbo 4g63 converted to turbo

 

[ddavisaf]

Yeah that's what I figured.
Go and replaced the caps and put the ECU back in. PM steve with any ECU questions. He's the local expert on anything ECU

 

[Julia]

forgetting about the ECU for a second, what would other causes of those symptoms be. That sounds EXACTLY like what is going on with our '93 N/T. Just curious.
Julia

 

[ddavisaf]

Your ECU could have a problem as well.
It's really the only cause for the car to just randomly shut off with no other symptoms. Unless you've got your positive battery terminal open to the world and it's arcing on the hood or strut tower brace. Just put the vinyl cover back over the terminal.

 

[blueman803]

I also noticed the check engine light never comes on even when I start the car. Is this another sign of a dead ecu? Anyway for me to light it up without using the ECU? I really don't feel like taking the gauges out to look and make sure the bulb is there and working.

 

[ddavisaf]

Yes, that indicates a bad ECU. I would still pull out the cluster and check the bulbs though.

 

[wolf20043]

Your ECU could have a problem as well.
It's really the only cause for the car to just randomly shut off with no other symptoms. Unless you've got your positive battery terminal open to the world and it's arcing on the hood or strut tower brace. Just put the vinyl cover back over the terminal.

Put a new ECU in the 93 Julia and I have and it fixed the exact same symptoms.
Mike

 

[ddavisaf]

Huh?

 

[wolf20043]

Huh?

Julias post ^^^^up there. Said the '93 had the same symptoms. Just clarifying that the ECU was the fix.
Mike

 

[ddavisaf]

Oh

 

[blueman803]

I definitely agree it could be the ECU, I just don't want to spend 300 dollars and have it shorted out cause it is something else, can I get a pinout so I can check 12 volts grounds and such? Any suggestions on how to actually troubleshoot the wiring harness

 

[ddavisaf]

I wish someone would post up steve's website.... *hint, hint*

Check the Tech Guide for the article on howto find a short for the wiring harness
Check the vfaq for the ECU pinout.

 

[blueman803]

I have 12V on pins 51, 52, 60, 61, 63, 66, 103 when the car is not on. Are any of these not supposed to have 12V? The pins 61 and 63 barely lit my bulb, so it seemed like there wasn't that much current flow

 

[blueman803]

I have 12V on pins 51, 52, 60, 61, 63, 66, 103 when the car is not on. Are any of these not supposed to have 12V? The pins 61 and 63 barely lit my bulb, so it seemed like there wasn't that much current flow

 

[blueman803]

I have 12V on pins 51, 52, 60, 61, 63, 66, 103 when the car is not on. Are any of these not supposed to have 12V? The pins 61 and 63 barely lit my bulb, so it seemed like there wasn't that much current flow

 

[steve]

Do not under any circumstance use a test light on the ECU pins. Get yourself a cheap multimeter and use it to measure the voltages so that you don't damage anything.

Go look at the pinouts on the VFAQ site and you'll see that 51, 52, 60, 61 are the ECU side of the injectors so you should see close to battery voltage there when the ignition is on.

63 and 66 are the ECU side of the MPI relay coil and with the ignition switch on shouldn't be at battery voltage. Those are the pins the ECU pulls to ground to turn on the MPI relay when you turn the key to RUN or START. The fact that they are high would explain why your ECU isn't powering up.

103 is the backup power supply used my the ECU to retain it's memory when the ECU is off. You should always have battery voltage here or your ECU will forget it's fuel trims and such each time you turn the car off.


It's far more effective to tell us where it's burned.

Steve

 

[blueman803]

It was burned severly were the 47 uF capacitor should be. The ecu was actually missing this capacitor, yet the car was still able to run. Whenever a new ecu was put in, it would burn the ecu out in close to the same spot.

So pins 63 and 66 should not have 12 v when the car is in the off position? I had the ecu removed and was probing the harness. Could this indicate a bad mpi relay?

 

[steve]

It was burned severly were the 47 uF capacitor should be. The ecu was actually missing this capacitor, yet the car was still able to run. Whenever a new ecu was put in, it would burn the ecu out in close to the same spot.

So pins 63 and 66 should not have 12v when the car is in the off position? I had the ecu removed and was probing the harness. Could this indicate a bad mpi relay?

Under that capacitor is where one of the ISC traces run between the two legs of the capacitor. Is this what burned up? Measure the ISC coil resistances just to be sure.

Pins 63 and 66 will have 12v on them with the car off. As soon as the ignition switch is turned to RUN the ECU should pull them close to ground to activate the MPI relay and turn the power on to the ECU and half of the stuff in the engine bay. This may be failing because of whatever is burning up your ECUs and not the problem in it's own right.

Steve

 

[blueman803]

The ISC coils all had 30 ohms, I will try and get a good picture of it.