I've got an 86 240 that won't start. Spark plugs spark but are dry. IIRC replaced plugs wires rotor and cap about a year ago. Replaced both fuel pumps, the sending unit and MAF within the last 3 months. FUEL Relay is from 2010, it clicks when I switch to on and when I crank. Bypassing it doesn't change anything. I replaced the 25amp fuse under the hood, check the connection to the battery, the fuse holder is a good condition water proof holder. If I pull the return line off of the fuel pressure regulator I get lots of gas, lots of pressure. Vacuum line to that is about a year old, no sign of gas in there.

After replacing the in tank fuel pump it still wouldn't start so I pulled the plug from the ecu. Noticed some corrosion, cleaned it off and it started up first try. Replaced and cleaned some fuses during all of this as well. Drove it around Sunday and to work today. Then on my way home from work it had trouble starting. It started sputtering and would stall out if I gave it any kind of throttle. Managed to limp home just barely sipping the gas and now it's in my driveway not starting. Given that it ran when I pulled and cleaned the big plug into the ecu I feel like I'm missing some really obvious loose wire, but I can not for.the life of me think of anything else to try other than replacing the ecu.

Any ideas? It's going to rain the next two days really not looking forward to that on my motorcycle

 

ECUs rarely go bad, too often get the blame.
You replaced the fuel pumps? Why? Was the car running before you did it?

The symptoms you describe sound like a bad MAFS. What MAFS is in there now? Just because you changed it doesn't mean it's good! Many aftermarket ones are very shoddy!

 

Well the extended life story is three months ago I ran out of gas(gas gauge and odometer didn't work and it was my girlfriends car previously). Afterwards it ran terribly, I was again in a limp home situation. I replaced the external pump as that was the common wisdom I got from people. That didn't work so in a moment of desperation I unplugged the MAF, and presto it started. Unplugging the MAF right now doesn't change anything. The 'new' one was from a junkyard as I needed the car the next day. Then a few weeks ago it would sometimes stall out when I went from park into drive or reverse. Then it started feeling low on power occasionally, then it sat for a weekend and wouldn't restart.

Fast forward to this weekend I was again trying to fix it. That's when I noticed the dry plugs. Couldn't hear the in tank pump come on so I checked out the in the in tank pump and noticed one of the wires was corroded through, the other was hanging on by a thread. So new pump, new sending unit. I now gather that the broken wire was probably my gas gauge. When that didn't work I checked the fuel pressure regulator which seemed to work. I don't know much about fuel injection but I was satisfied gas was getting to the engine area, just not into the cylinders. So I started looking at electrical things that might be the culprit. Which is when I ended up checking the ecu.

But to summarize: the MAF could well be garbage, but last time it went I was able to just unplug it to diagnose it. Fuel pumps seemed like a good idea at the time, at least I have a gas gauge now.

I do agree with you, it seems weird to me that a bad ecu would fix itself so I'm wondering if I disturbed some other loose wire in the process.

Edit: ha I swear this cars electrical purposely toys with my sanity. I unplugged the maf, the other sensor on the manifold, turn off the headlights, and it started. Plugged in the MAF and it was still running so I took it around the block. Replaced the o2 sensor and it still started, went around the block again. Headlights on and it still starts. So ot would seem none of those things fixed it, but itz running fine. I've got half a mind to rewire this whole damn car next winter.

 

Well, it is an '86 which falls in the years that had biodegradable wiring which causes all kinds of electrical issues. Basically the insulation on the wiring starts to flake off - especially in the engine compartment. This results in shorts between different sensors, etc. and results in all kinds of electrical gremlins.

 

Yeah this is my 3rd 240 I'm unfortunately familiar with their experiment with biodegradable wire sheathing. I think the connection for that o2 sensor is right near where the ecu's loom comes through the fire wall. I'm wondering if I'll find a short in there

 

I am new and I have an 88 740. I have had similar starting problems. Try this is you want. Next time when you turn the ignition and the car begins sputtering, pull fuse #1 and the cars idle should rise, immediately after replace the fuse #1. If you have one hand on the fuse and one hand on the key you could time it just right where the car starts and you would let it idle till warm. This has worked for me in an emergency. I am still looking for the source of this problem.