My wife and I are in a very ambitious road trip from Flagstaff AZ in my 93 240 wagon and we’ve run into a problem.

Background: stage 0 was completed just a few thousand miles ago. The car has 200000 miles.

So this car has been plagued since I got it with some sort of fuel (I think) issue at random times. Sometimes it didn’t happen for a month sometimes it happened a few times in a few hours. Usually after some highway driving it would start to miss and sputter a little and would gradually get worse and worse until I was on the side of the road with an engine that couldn’t even idle. If I let it sit for about 15 minutes it would run again just fine for anywhere from 10 to 100 miles. I thought it was the in tank pump, as every time it started at a half a tank of gas. After replacing it with a new pump it’s been great for over 1000 miles from flagstaff to Yellowstone and suddenly in the park, it started happening again. Let it sit for a while, 20 miles, dead again, sit for a while, 20 miles, dead again. We limped about 70 miles out of the park like that. While it still idled a little bit, I noticed that with the pedal to the floor and transmission in neutral, it would rev up and down at a steady pace. Any load and it would die. If I unplugged the maf it would idle a little high but at least smooth for a minute or so but it still couldn’t drive. I swapped it for my spare maf and we made it 50 miles without issue, then it happened again. Unplugging the maf didn’t help and neither did swapping it back. Let it sit for a while and it only made it a mile before we had to pull over again. Now I’ve finally found that my main pump (#4) fuse is blown and when I replace it, it blows the moment I turn the key every time. I swapped the relay with my known good spare and it did the exact same.

Any ideas? I’m thinking a short but to be honest I’m pretty handicapped when it comes to electrical diagnosis so any advice would be appreciated. If anyone is in Southern Montana I’d love some help as well

 

A blowing fuel pump fuse is certainly the way to start to look for the reason of your troubles--the pump itself may be shorted out. I don't think there is anything else on that fuse... So, I new fuel pump? It shouldn't be too hard to find even in southern Montana.

 

My theory right now is a clogged fuel filter causing the intermittent stalling. Maybe the strain on the main pump made it seize and the increased resistance is blowing fuses?

 

Disconnect the main pump and replace the fuse. Check voltage at the pump connector when you turn the key on. Oh if the fuse blows with the pump wire disconnected then you have a different issue. If you have 12V then replace the pump and filter. My 2 cents here.

 

Bad news update: no voltage to meter and it blows fuses even without the pump being connected. The lambda system is on the same fuse so I disconnected that and same deal. Not sure where to go from here apart from tracing the wires to the pump looking for a break.

 

More confusion. There’s no continuity between the two wires to the pump, the positive pump wire to ground, or the positive o2 wire to ground. Doesn’t this mean it’s none of those wires causing the short?

 

If you are stranded in the middle of nowhere and have no diagram to follow - you could always purchase a spool of wire and a fuse/fuse holder. (no more than 20 amp fuse) - connect a fused wire directly to the fuel pump feed under the rear seat (yes looped through the interior of the car) - from a switched or unswitched positive source either under the hood or preferably from the fusebox. That should get you moving to somewhere you can solve the real problem.

 

Alright so I figured out that disconnecting the fuel pump relay stops the fuse from blowing. I checked the relay plug and the top (side with the chamfered corners) middle is ground with 6 ohms resistance. None of the other pins are grounded at all. I don’t know if this is right but this is as far as I’ve gotten so far

 

Finally figured things out yesterday and got it sorted today. I misunderstood on the fuse panel and falsely assumed that “main pump” was the inline high pressure pump. Finally when I realized pulling the relay stopped the fuse from blowing I learned that fuse 4, the main pump, is the in tank pumps. Turns out when I had replaced the in tank pump there was a small spot of bare wire that had bounced around and started grounding on the sending unit body, blowing the fuse. It got to where it didn’t run at all because, as I learned once I replaced the inline pump and filter, they were both completely clogged with sediment and silt. Not only the filter but the old, original, 200,000 mile pump was packed full. It still worked, but only intermittently. Eventually it just couldn’t keep pushing gas without the in tank pump and that’s what left us stranded. Now with a new set of pumps and a new filter it runs better than it ever had in the 5000 miles that I’ve been driving it. My mystery idle stutter ever 30-60 seconds is even totally gone.