Photo: M Huy Photography/Flickr

Last week, I asked Jalopnik’s wrenchers to tell us about their worst, most embarrassing wrenching misdiagnoses. Here are the most pathetic cases of “Oh crap, that wasn’t actually the problem?”

Any seasoned mechanic will tell you: “Never throw parts at your car.” That doesn’t mean that you literally shouldn’t toss heavy starter motors and alternators at your poor, flimsy sheetmetal (though you really shouldn’t do that either). No, it means you shouldn’t exercise the “guess and check” method to fix your car.

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But cars are complex, and sometimes all symptoms point to just one possible fault. “This isn’t a guess, this is certainly the problem,” you convince yourself. But sometimes, you find out that your “non-guess,” which took you three days to complete, actually ended up being the wrong diagnosis.

Here are a few stories from readers that will make you feel sorry for the poor bastards:

What? A Bowling Ball? (GMo)

Photo: Joonas Tikkanen/Flickr

Not one that is too bad but kinda funny:

Installed new beefier sway bars on my car. A few days later I notice an occasional “clunk” sound coming from the back when taking a slow turn or going over a small bump. Thinking I screwed up the torque or geometry on the endlinks, I jack up the car re-check the torque for all of the bolts, double check the geometry. Nothing shifted, all bolts were at spec. Start getting worried I’ll need to take it into my guy for closer inspection.

After I drop the car back down I go upstairs and grab a beer...a thought strikes me! Go back down to the garage, open the trunk - low and behold my wife’s bowling ball was still in there and was rolling around making the thunk noise. Did a little facepalm at that moment.

That Darn Floor Mat (Bullitt Ride):

Photo: Truck Hardware/Flickr

A friends 1998 Camry 5-spd sat parked at my place during the summer last year. When he said he was going to come pick it up I went out to start it for him and it wouldn’t turn over. I tried boosting it and it still wouldn’t turn over. Suspecting some sort of electrical issue, I then spent a few hours looking at wiring diagrams, probing and jumping relays, eventually determining that the problem must have been in the ignition switch contact block. So I went to the local wreckers to get one, successfully locate and remove one from a car, go home install part... still nothing. Damn it. Look at wiring diagrams some more and then go to inspect switches on clutch pedal. I notice that there’s two switches, one when the clutch is fully up and one when it’s fully down. I try pressing the clutch fully down and notice the pedal arm hits floor mat slightly when fully pressed. I move the floor mat down slightly so that arm does not hit..... car starts....FUUUUU!!! The difference between the car starting and not starting was literally 1/4" of clutch pedal movement. That was a good waste of an afternoon.

The Loose Fuel Hose From Hell (damondrummer7)

The fuel tank and hose above is actually from a ‘96 Jeep Cherokee, but you get the idea.

I crashed my 818R at slow speeds in the wet during a test-and-tune autocross. For about a week after I spent every waking moment figuring out what happened to make it not run right intermittently, trying desperately to get it working by the next weekend when I planned to have my last autox before the homemade car’s inaugural track day.

For starters, I re did every ground rivnut/ground ring terminal. Then I re made about 1/3 of my home made wiring harness. After that didn’t work I replaced every sensor/connector I could get my hands on: MAF, MAP, spark plugs/cables/coil packs, knock detector, temperature sensor, even the injectors.

Friday night I removed the entire firewall and pulled the fuel pump out of the tank out of desperation to find that the hose from the pump to the fuel rails was entirely disconnected. Any fuel the engine was getting was out of either luck or act of god. Tightened the hose clamp and I was good to go.

Took the whole week off of work, spent around 70 hours in the garage and about $300 on sensors for a loose hose.

This One’s Nuts (Straight6PackRacing)

Photo: Sam Schmidt/Flickr

Engine was cutting out under hard cornering on our LeMons car. We convinced ourself it was a bad fuel pump - we dropped the tank, replaces the pump and went back out on track. Same issue. Then did the lift pump. same issue. Then did the fuel filter. Dame problem. Replaced the pressure regulator and redid the vaccume system. Same issue.

As we were rechecking the vac, we noticed a nut that had a bundle of ground leads that was a little loose. Tightened it down with a lock nut and car never cut out again the whole weekend. We replaced dang near the entire fuel system because the coil ground was skipping out when we put it into a corner.

Corrosion Is The Mother Of Misdiagnoses (jip1080)

Car wouldn’t crank reliably. It was old, and British, so that wasn’t too much of a surprise. Must be a flat battery, charged it, fired up. Hmm. A day later, doesn’t crank. Crap. Check battery, appears dead. OK, I’ll throw in a new battery since that one had been a WalMart el-cheapo special. New battery installed, cranks right up. Few weeks later go to start it. Nothing. Crap. Check battery, flat. DANG. Must be alternator. Order new alternator from England (cheaper and quicker than the parts dealer out West after shipping). Install. Charge battery. Cranks fine. Woo hoo! Few weeks later won’t start. Dang. Check battery, it seems fine. Ug, maybe it’s the starter getting tired. Order new starter from England. Install. Doesn’t start. Crap.

Then I checked the battery again. The reading is acting funny. That’s when I saw that the terminal connections on the wires were corroded and needed a good cleaning. Yeah, it’s been fine since. When I’d read the battery as flat I’d had the multimeter leads on the terminal connectors. When it had read full I was on the actual terminal posts. On the plus side I have a fresh starter, a fresh alternator and a fresh battery. I still felt like a moron though.

All Because Of A Few Spark Plug Wires (StaceyS)

Photo: I0Inix/Flickr

Rescued a badly degraded almost not running BMW E21. Cleaned it up and started trying to diagnose a smokey, rough running M10 with no power that wouldn’t idle.

I spent a few hours adjusting the valve train. Very slight improvement.

I cleaned all the spark plugs. No change

I cleaned out the distributor cap (which was brand new). No change.

I checked all the spark plug wires (which were all new). No change.

I then started suspecting that the catalytic converter was clogged, so I dove under the car and started battling rusty exhaust system bolts. Got the mid-pipe section that houses the cat off and tried looking down the pipe to see if it was clogged or falling apart. I did see some white grit coming out the exhaust end, but nothing on the engine side.

I tried blowing the cat out backwards with an air compressor, got a bit of gunk out, put the whole thing back together and the car back on its wheels. No change.

Took the whole thing apart again and decided to bash the cat material out of the pipe, figuring that since it was shot, I’d just try running it without any cat material and then at least it would run ok and I could order new exhaust components (which was my plan eventually anyway). Bashed it all out, and confirmed that the front side of the cat was clogged up with sooty residue (most likely from not being able to run hot enough to burn that crap out).

Put it all back together and anticipated a smooth running, strong(ish) engine. No change at all. Rough running, smoking, no power. Ug.

More internet research and then I discovered this little gem of information about the M10 engines: Somewhere between 1979 and 1980, BMW changed the direction of the distributor rotation.

I went out, swapped 2 spark plug wires and the car ran like a kitten...

...Oh, and I forgot. I also suspected a bad oxygen sensor (this was before bashing the catalytic converter to pieces). I couldn’t get the existing oxygen sensor off the car, and I ended up bashing the crap out of it so badly, I couldn’t get a wrench on it properly, and I couldn’t get any leverage on it from under the car. So I ended up REMOVING THE EXHAUST MANIFOLD just to get that damn thing off. Replaced it with a new O2 sensor and put the whole damn thing back together again. No change.

Replaced An Entire Suspension For Nothing (Nobi)

Photo: Alden Jewell/Flickr

Worst misdiagnosis I’ve done was on my old Grand Prix GTP. It had a clunk in the front end, so I bought the GM Performance Parts W-Body handling kit for it thinking it was the sway bar bushings and links. The kit comes with a bigger sway bar and bushings and a nice beefy strut tower brace. Installed it with some Moog links, and the noise was still there. I figured it must be the strut mounts. Replaced the mounts, and the noise was still there. Replaced the struts, noise was still there. Replaced the springs, noise was still there. Replaced the axles, noise was still there. Finally, in my last moment of living-at-home-without-paying-rent-and-have-more-money-than-brains, I bought some tubular lower front control arms for it thinking if the arms were making the noise, might as well grossly overcompensate so they’d last longer. They had heim joints instead of compliance bushings. I figured they’d ride smoother and last longer than the stock rubber control arm bushings.

It did for a month.

I knew better than to put parts in my car that were meant for dragstrip use and drive it daily. I knew that the heim joints weren’t properly sealed from road grime and debris. I drove it like that anyway, and in a month, the clunk returned with a vengeance. I gave up and threw some amazingly cheap new factory control arms in and not only was the ride improved, but the noise disappeared. Turns out the noise the entire time was from some collapsed compliance bushings in the control arms. I could have replaced both the bushings by themselves if I’d caught that for $30 for the pair.

Did The Noise Occur During Left Or Right Turns? (CaptainWompus)

Front hub(s) on my 05 Saturn Vue Redline.

Knew it was humming, could feel it through the steering wheel and floorboard, and based on sound I was 99.999% sure it was the left front. So I bought a new hub, got a hub socket and rented the slide hammer from Autozone. I was ready for a couple hours worth of work and a quiet(ish.. it’s a Saturn after all) ride again!

3 hours later the goddamn thing hadn’t budged even a little. It took nearly an hour alternating back and forth between an impact gun and a 2 foot long breaker bar to get just the axle nut off. The hub wouldn’t separate after that.

Thanks to Michigan, the iron hub had fused to the aluminum knuckle.

I finally gave up, put everything back together and dropped it off at my mechanic’s the next day. Turns out I spent 3 hours on the wrong fucking side of the thing. It was the right that needed to be replaced!

It also took him and 2 of his other mechanics about 2 hours of wrenching and blow-torching to get the hub out of the knuckle on that side. Apparently these things are super fun to change hubs on, especially in rust-belt states.

The Improperly Routed Subaru Cold Air Intake (ThatOneGuy)

Photo: James Henry/Flickr

I may be a little late in the game to have anyone read this, but it’s a pretty infuriating tale. A couple years ago I bought a 99 Impreza RS coupe. I’d spent about a year trying to buy one before someone else snatched them out from under me, so when I finally made it to look at one that was mostly intact, I hastily snatched it up, and on the drive home I regretted that haste when i noticed that the oil light winked on at idle once the engine was well warmed up.

After facepalming for about a week straight, i resigned myself to rebuilding the engine. It wasn’t too bad, I’d already built quite a few subaru boxers before, so i wasn’t going in blind, but pulling the engine, tearing it down, cleaning everything up, inspecting everything, and putting it back together in my free minutes still took almost a month, and about $1500.

Once everything was back EXACTLY as i found it, and I’d taken it on a few short test runs, i decided it was safe to take it on the 30min commute to work. And then, when I reached the final off ramp from the interstate, and took my foot off the gas, the oil light winked on again, and it was accompanied by a horrible screeching noise. I immediately shut off the key, pulled into an abandoned parking lot, and called the gf for a ride home. I’d imagined the only possible explanation was that I’d gotten a bum oil pump, so I ordered a new one, and as soon as I could i went back and changed the pump, there in the parking lot. Once it was back together, I fired it up and breathed a sigh of relief when there was no ugly noise and no oil light. However, on the way home, at a stop sign a few blocks from my house, I watched the oil light fade on, and heard the same gnarly squeak.

The car probably sat in my garage for like 2 more months, I was disgusted, and about ready to swear off subarus. All i could do was open the hood and glower at the engine for a few minutes every few days. But one of those times I noticed that the goofy cold air intake that was on the thing when i bought it was plumbed weird. there was a matching blue molded silicone hose that went straight from the intake manifold to the crank case vent. and matching caps that clamped over the valve cover vents. thinking i was groping at straws, I went out for a drive and got the engine up to operating temp. soon enough the oil light came on at idle, and the screech came back. I pulled over, popped the hood, and pried off one of the valve cover caps. There was kind of a backwards popping sound, and the screech went away. I looked in the window and sure enough, no oil light.

TL:DR I rebuilt an engine and then replaced an oil pump in a sketchy parking lot because someone had replaced the factory air box with a cheap aftermarket CAI and plumbed the pcv system to pull full engine vacuum on the crank case, confusing the oil pressure sensor, and causing one of the valve cover gaskets to make a super high pitched farting sound.

The Bavarian Milkshake (E30345i)

Photo: FotoSleuth/Flickr

On my first e30 back when I was about 20 years old, I was driving to work one morning when I suddenly noticed the temp gauge was waaayyy above the 3/4 mark. I instantly pulled over and checked the dipstick: milkshake city. At over 200k, I naturally assumed the headgasket was gone. So I got a tow home, and proceeded to tear the head off the next day. Low and behold, the HG was perfect. Huh? Well, the night before the car overheated, I had noticed the throttle body heater (where it cycled coolant from the head through a cavity around the TB to prevent it from freezing or something) started leaking a small amount of coolant into the intake. So I figured the easiest thing to do was to bypass it. Easy, right? Pop both hose ends off of the TB coolant circuit, and connect the hose ends with a barbed hose fitting. Voila. Bypassed. But while I was in there working I also had to disconnect the crankcase breather hose that came from the valve cover (it also tied into the TB to burn off crankcase vapors). In my young and dumb wisdom, I neglected to take any photos or mark which hose was which, and so I ended up hooking one of the coolant hoses up to the breather hose. Which caused coolant to pour into the valve cover and down the oil drains where it mixed with everything else. Somehow this extremely simple and very recent mistake failed to dawn on me until I had my engine half apart... FML.

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