I love troubleshooting problems on machines. Since I started changing oil at a Honda dealership in the 90's I always loved the process of fixing (not maintaining, maintenance is boring) machines, so I thought I'd make a thread to hear about some interesting/perplexing scenarios that other gearheads have come across in their travels. Here's one of my own that resulted in me kicking and cursing myself loudly in the end:
I've kept this gigantic '77 Grand Marquis in my garage for a long time (pictured in my avatar). About a decade ago or so I took it to a shop in FL to have some new exhaust welded up because I'm not a good fabricator. About 6 months later I noticed that during certain times the Mercury would begin to sputter. Sometimes it would die completely, sometimes it would just get low on power. It seemed to happen reliably on this one gentle grade but only in the afternoon when it was hot. Everything I've describing happened over a period of months because it isn't a car I drive much and at the time we had a little baby and another on the way.
It definitely felt like a fuel issue to me so I ordered a new fuel pump, replaced the soft fuel line in the engine, and took fuel samples to no avail. The thing would still randomly (except for that one hill on hot days) drop in power and sometimes stall. I still had the stock late-70's Ford carb on it, so I decided to replace it w/ a rebuilt Ebay unit out of Canada. Got the new carb installed, no change! At this point I think it was close to 8 months or so with this problem.
The rebuilt carb from Canada wasn't behaving well either. I was having a hell of time getting a good setting on it, so I decided to ditch that one too in favor of a reliable Edelbrock. The Edelbrock dialed right in, but the power loss and sputtering continued.
At this point I decided to get a clear plastic in-line fuel filter so I could see the fuel. I installed it and fired it up in the driveway and was able to see the fuel filling the bowl and flowing into the carb. It took a few drives for the problem to pop up again, but when it did I pulled over and popped the hood to see the little plastic bowl barely full! Fuel was sputtering from the fuel pump so I knew the problem had to be upstream. My approach at this point was to just get it over with a drop the tank. Maybe it was rusted, maybe the pickup sock in there was covered in junk, who knows. Of course with two little kids this project took a backseat.
Now at the 1 year mark I found a weekend to get the Merc up on jacks and drop that tank. I slid under, found the strap bolts, went to pull the soft line coming from the tank when I found it bent around a bolt on the spring perch! Turns out that the guy who welded up my exhaust over a year ago pushed the hose up on the lower spring perch so it was out of the way while he worked and forgot to put it back! The hose between the tank and the hard line on the frame was bent just right so that it wasn't completely kinked, just restricted. When temps got hot the rubber relaxed and restricted itself by bending around the bolt. When it cooled off it opened itself up enough for the engine to run normally.
It was a damn year of me pecking away at this problem. I pushed the rubber hose off the spring perch and have been driving it without issue ever since.
I've kept this gigantic '77 Grand Marquis in my garage for a long time (pictured in my avatar). About a decade ago or so I took it to a shop in FL to have some new exhaust welded up because I'm not a good fabricator. About 6 months later I noticed that during certain times the Mercury would begin to sputter. Sometimes it would die completely, sometimes it would just get low on power. It seemed to happen reliably on this one gentle grade but only in the afternoon when it was hot. Everything I've describing happened over a period of months because it isn't a car I drive much and at the time we had a little baby and another on the way.
It definitely felt like a fuel issue to me so I ordered a new fuel pump, replaced the soft fuel line in the engine, and took fuel samples to no avail. The thing would still randomly (except for that one hill on hot days) drop in power and sometimes stall. I still had the stock late-70's Ford carb on it, so I decided to replace it w/ a rebuilt Ebay unit out of Canada. Got the new carb installed, no change! At this point I think it was close to 8 months or so with this problem.
The rebuilt carb from Canada wasn't behaving well either. I was having a hell of time getting a good setting on it, so I decided to ditch that one too in favor of a reliable Edelbrock. The Edelbrock dialed right in, but the power loss and sputtering continued.
At this point I decided to get a clear plastic in-line fuel filter so I could see the fuel. I installed it and fired it up in the driveway and was able to see the fuel filling the bowl and flowing into the carb. It took a few drives for the problem to pop up again, but when it did I pulled over and popped the hood to see the little plastic bowl barely full! Fuel was sputtering from the fuel pump so I knew the problem had to be upstream. My approach at this point was to just get it over with a drop the tank. Maybe it was rusted, maybe the pickup sock in there was covered in junk, who knows. Of course with two little kids this project took a backseat.
Now at the 1 year mark I found a weekend to get the Merc up on jacks and drop that tank. I slid under, found the strap bolts, went to pull the soft line coming from the tank when I found it bent around a bolt on the spring perch! Turns out that the guy who welded up my exhaust over a year ago pushed the hose up on the lower spring perch so it was out of the way while he worked and forgot to put it back! The hose between the tank and the hard line on the frame was bent just right so that it wasn't completely kinked, just restricted. When temps got hot the rubber relaxed and restricted itself by bending around the bolt. When it cooled off it opened itself up enough for the engine to run normally.
It was a damn year of me pecking away at this problem. I pushed the rubber hose off the spring perch and have been driving it without issue ever since.