Never Ending Electrical Problems

Picked myself up a 1992 Mitsubishi Mighty Max with the 4G63 engine, running but in need of some love. Had some skipping issues when I bought it. Put brand new plugs, wires, cap and rotor, EGR valve, coolant sensor, coolant sender, thermostat, heater and coolant hoses, oxygen sensor, air filter, fuel filter on it. This seemed to fix many problems but it still was at times hard to start and smokes heavily but is not burning oil, a darker white color like it was running rich and would not stay idling. At random points of throttle the CEL would light and cut off, it would cut off if I pressed the throttle to the floor. From this I deduced that it was a throttle position sensor, I could not know for sure because the light would not stay on. I removed the faulty unit and found out why it went bad, the beginning resistance was out of spec, needing to be around 80 ohms and it was over 300. I first tried to replace the TPS with an Eclipse one that started at 150 ohms and this seemed to work for a while but then started acting like the first bad one. I noticed a frayed wire on the connector so I went to the junkyard and found a good connector and a good TPS that started at 80 ohms from a Plymouth laser. I soldered the new connection on and calibrated the TPS to start at 0.5V with a voltmeter at the soldered connections before insulating them. I started my truck up and the CEL is still on. I hooked up an analog meter and it is dumping more codes, starting with 2 codes and going up to as many as 3 or 4 codes at a time between resets. The motor position sensor, the barometric (MAP) sensor, and the coolant sender are all being reported as bad. Since I have recently replaced the coolant temp sender brand new I unplugged it at thermostat open temp (around 180 F) and it read correctly per FSM, just under 300 ohms. From this I deduced that the ECU may have bad/leaky caps, so I took it out and opened it up. It had a funny spell but the caps were not bulging or leaking at all. I hooked the ECU back up and had one hell of a time getting the truck to start afterwards. I was wondering if anyone could point me in the right direction as to what might be wrong? I regrounded all the grounds in the engine bay, going as far as removing every connector and mount point and sanding them to bare metal and cleaning them to make sure good contact is made. This still did not fix the issue. One thing I may be missing, the positive wire coming from the fuse box feeding the horn had shorted to the chassis somehow, I ran a new wire for it. The only thing I can think of is, something else might be shorted? If anyone could give some insight I would appreciate it, I am about to give up on this truck. Thanks!

Or you have a wire that is getting hard somewhere and it has high resistance in it. This will make it think things are out of spec. Just what wire it is,,, well IDK.. I'm sure a second gen guru will jump in and point you in a direction. Don't give up you will probably find it's something dumb that you over looked.

Any chance of swapping a known good ECU just to be sure? What did the plugs look like when you replaced them? Their condition can sometimes point you in the right direction. The cause of the smoking would be my first concern. You aren't using any excess oil or coolant? You might also want to check the timing and condition of the timing belt. How many miles are on it? Have you checked for gasket leaks? Keep us posted with your progress!

Model is 1992 Mighty Max with 208,000 miles. I bought it about 400 miles or less ago so not sure of timing belt or timing. I do not remember what the plugs looked like, could I remove the new ones and be able to tell from them? No excess oil or coolant, checked both yesterday. Have a small oil leak around the exhaust manifold somewhere but it is inconsequential. Could the timing being off cause the motor position sensor to show as faulty? Thanks for the help to both of you.

It wouldn't hurt to pull a spark plug and post a picture. If it is running really rich, it could be fouling your plugs making it hard to start as well as running poorly.

Motor position sensor has to do with the distributor, not sure if it being off(timing) will make the CEL come on for the mps or not. Map is you MAF(air) sensor

for MAP It reads out the code for "Barometric Pressure Sensor", I am going to look into what might be shorted tonight at work in the FSM to see what might be causing malfunction. I will talk to my buddy about timing it this weekend too, won't hurt anything to make sure it's in time. The FSM says that the motor position sensor is on the other side of the throttle body, is it connected to the distributor? The FSM says that the motor position sensor code might be caused by a faulty TPS, but I have installed a known good working TPS. Thanks to all of you for your help, I will pull a plug tomorrow and post a picture for further diagnosis.

Thanks for all your help guys. Here is a video of the engine running, including the color of the smoke and a photo of the spark plug closest to the grill. Thanks again for all your help.

http://youtu.be/M_yfd9VUJvQ

There is a YouTube video called "Chevy TBI running rich problem solving" that you should view, it answers a lot of your issues.

Here is a video http://www.youtube.com/watch?v=M_yfd9VUJvQ

Thanks for the help, I tried to post a youtube video of my problems but I keep getting flagged for mod approval. The video title is "1992 Mitsubishi Mighty Max Woes"

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Originally Posted by stampede_dude

Thanks for the help, I tried to post a youtube video of my problems but I keep getting flagged for mod approval. The video title is "1992 Mitsubishi Mighty Max Woes"

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Thats the spam-o-matic doing it's job. Once you hit X # of posts it won't do it any more. If it mod's any of your post just let us know in the shout box on the main page and we will validate it. But looking at your post count you are nearly there.

Sounds good, thanks! I appreciate it. Any ideas what may be wrong?

I think droppedmitsu and lush are more qualified in these are. I don't have a FI truck. I'm old school carb. But I think they are on the correct path with the piston sensor.

That is a lot of smoke! Did you happen to watch the Chevy video? Also, what codes are you pulling now?

Same codes. Haven't had time to troubleshoot as much lately. Crunk it up today to drive, was initially hard to start like it was getting too much fuel maybe? Had the same smoke, tons more of it, and did the same for about a mile up the road before stopping. Ran fine afterwards, this is really puzzling.

I just watched the Scannerdanner video on a dirty MAF sensor which caused the vehicle to run rich at idle but lean under a load at higher rpms. He removed it and cleaned the carbon out with non residue brake or carb cleaner, although he did say there is a specific MAF cleaner available . This really looks like it might be your answer, at least looking at it from across the country!

Thank you for all your help. I have cleaned the MAF Sensor with CRC MAF cleaner and it did not fix the issue. I referenced my Dodge Ram 50 Electrical FSM and referenced the wiring diagram for my engine. Turns out the coolant temp sensor, the throttle position sensor, the motor position sensor, and the mass air flow sensor all have one of their wires tied into the same line on the ECU of my truck. With that being said, and after the problems I have had, it is almost 100 percent evident that this wire is either loose or broken. I will be investigating this weekend, thanks!! The wires they tie into are B*2 and B*4 on the ECU for reference.

That makes sense, hopefully you'll have a smooth running truck shortly!