Who has a good troubleshooting story

qslim

The Man with the Big Yellow Car
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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.
 
Local client with complaint of sputtering, cutting out, going into "limp mode" and loss of power going downhill with a CEL. Runs fine going uphill no CEL. Gets advice from several folks and shops who tell her to replace PCM. New PCM results in no change. Then they tell her the cats are shot and plugged. Replaces mini cats, inspects main cat, no change. They recommend several other things all of which she does with no change.

She contacts me and after explaining the symptoms, I relate that it sounds like the drive gear on the cam and the driven gear on the camshaft synchronizer have some wear along with the timing being right at the edge of what the PCM can compensate for. She brings it in, we toss the scanner on it and it is sitting at 11 degrees. PCM can compensate for about 10 or so. Under acceleration, the slack gets removed, it gets into range, everything is fine. Going downhill decelerating against the motor, slack moves the other way, moves out of time and throws CEL with poor running.

Works perfectly once we set the timing at the camshaft synchronizer.
 
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'87 Dodge Ramcharger 2-wheeld drive with a fuel injected 318 in it. Around town, no issues at all. On the highway for long stretches, however, the rig would just suddenly die. I'd pull over, restart the vehicle, and drive for miles without incident. Then once again, without warning, it would suddenly die. I started researching it, and everything I found leaned toward electrical issues/components, which is definitely not my forte. I thought it was a fuel issue. I needed it to be a fuel issue! So, I dropped the tank, and lo and behold, the pickup tube had a filter that was pressed right up against the bottom of the tank, effectively eliminating that portion of the filter. The remaining 75% of the filter was plugged with a super fine silt. As best I could tell, the filter would eventually plug up enough that it would collapse, cutting off the fuel supply. Once the engine stalled, the filter would relax, and would allow enough fuel to flow that the rig could be driven for miles before collapsing again. I replaced the filter, bent the pickup tube ever so slightly upward off of the floor of the tank, and never encountered another problem with it.
 
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I had a 2011 Cummins that I had installed a delete kit on (remove the egr, plug some coolant return lines, remove the exhaust particulate filter, add a tuner). Afterwards it ran great but in the 1200 to 2700 rpm range it had a really bad vibration sound. I spent months trying to find it. Even took the HVAC box apart thinking a tool, nut or bolt had fallen in. Finally, after changing oil in it I started it up to make sure sure my filter wasn't leaking and saw an AC line way back on the firewall that didn't have a bolt to secure it! Replaced it with a spare and lo and behold the vibration i had for the last 6 months was gone
 
Local client with complaint of sputtering, cutting out, going into "limp mode" and loss of power going downhill with a CEL. Runs fine going uphill no CEL. Gets advice from several folks and shops who tell her to replace PCM. New PCM results in no change. Then they tell her the cats are shot and plugged. Replaces mini cats, inspects main cat, no change. They recommend several other things all of which she does with no change.

She contacts me and after explaining the symptoms, I relate that it sounds like the drive gear on the cam and the driven gear on the camshaft synchronizer have some wear along with the timing being right at the edge of what the PCM can compensate for. She brings it in, we toss the scanner on it and it is sitting at 11 degrees. PCM can compensate for about 10 or so. Under acceleration, the slack gets removed, it gets into range, everything is fine. Going downhill decelerating against the motor, slack moves the other way, moves out of time and throws CEL with poor running.

Works perfectly once we set the timing at the camshaft synchronizer.

How often have you seen that happen? Sounds like you zeroed in on the problem pretty quick.

I started researching it, and everything I found leaned toward electrical issues/components, which is definitely not my forte. I thought it was a fuel issue. I needed it to be a fuel issue!

Haha, yeah I'm the opposite. I always thought wiring/electrical issues were easier to fix because they're typically less nebulous than fuel problems. It's been my experience that wiring/electrical issues are more likely to end up as a hard fail which I much prefer to something that sorta works for the most part but every once in a while doesn't.
 
How often have you seen that happen? Sounds like you zeroed in on the problem pretty quick.



Haha, yeah I'm the opposite. I always thought wiring/electrical issues were easier to fix because they're typically less nebulous than fuel problems. It's been my experience that wiring/electrical issues are more likely to end up as a hard fail which I much prefer to something that sorta works for the most part but every once in a while doesn't. There's nothing more annoying than trying to fix a machine when the symptoms come and go.
 
I had an old Ford pickup truck that developed a noise in the front of the engine near the timing cover. I chased it trying to determine exactly where the noise was coming from. I didnt have time to fix it so off it went to a shop I trusted. They called me back a short time later and said come get your vehicle it's fixed. It turns out I had dropped a small bolt down the front of the engine and it landed and stuck just right and was rubbing on the harmonic balancer. Talk about feeling dumb!!! From that point on if I drop something in the engine compartment it gets found and yes i have spent hours looking until i found it lol
 
Several years ago on a trail run, the Jeep would shut down on obstacles like this where it would get twisted up just right. It was frequent and consistent.
DSC_0921_zpsp1kaqtzw.jpg


Later, I went out and found an easy trail to try and recreate the problem.
20170408_115357.jpg


20170408_160837.jpg


I figured out that if I could stuff the front driver and rear passenger enough to teeter totter the Jeep, I could cause it to shut down. And I could hear the fuel pump start and stop while rocking. This was the kill position.

So, I set this up with a forklift and a pallet jack...
20170408_212226.jpg


This was a very long day of rocking, poking and prodding and chasing wild geese. I learned about how the ASD works and ruled out the fuel pump. Eventually, I discovered that if I poked certain wiring bundle with a stick, the ASD would shut the engine off. I suspected a frayed wire in that bundle.

I began disconnecting the entire front of the main wiring harness back towards the transmission trying to get to the suspected section. I got there and found nothing.

Tired and feeling defeated, I put the wiring back to together and kept rocking and poking. But this time, I couldn't shut the engine down. I kept at it for a while, just to be sure. The engine kept running.

Then I remembered that I had replaced the O2 sensors a couple months earlier. And I had just disconnected and reconnected them a couple hours ago.

My best guess is that one of the O2 plugs wasn't fully seated and would open up when the Jeep was twisted up just right. It's been nearly 3 years, and the problem has never come back.

The troubleshooting feels heavy handed, but I still don't know how else I would have figured this out.
 
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Several years ago on a trail run, the Jeep would shut down on obstacles like this where it would get twisted up just right. It was frequent and consistent.
View attachment 109851

Later, I went out and found an easy trail to try and recreate the problem.
View attachment 109849

View attachment 109852

I figured out that if I could stuff the front driver and rear passenger enough to teeter totter the Jeep, I could cause it to shut down. And I could hear the fuel pump start and stop while rocking. This was the kill position.

So, I set this up with a forklift and a pallet jack...
View attachment 109850

This was a very long day of rocking, poking and prodding and chasing wild geese. I learned about how the ASD works and ruled out the fuel pump. Eventually, I discovered that if I poked certain wiring bundle with a stick, the ASD would shut the engine off. I suspected a frayed wire in that bundle.

I began disconnecting the entire front of the main wiring harness back towards the transmission trying to get to the suspected section. I got there and found nothing.

Tired and feeling defeated, I put the wiring back to together and kept rocking and poking. But this time, I couldn't shut the engine down. I kept at it for a while, just to be sure. The engine kept running.

Then I remembered that I had replaced the O2 sensors a couple months earlier. And I had just disconnected and reconnected them a couple hours ago.

My best guess is that one of the O2 plugs wasn't fully seated and would open up when the Jeep was twisted up just right. It's been nearly 3 years, and the problem has never come back.

The troubleshooting feels heavy handed, but I still don't know how else I would have figured this out.

Mother of God, articulating the TJ w/ a forklift and pallet jack huh?? Most people would have just started throwing parts at it! :LOL:

Talk about feeling dumb!!! From that point on if I drop something in the engine compartment it gets found and yes i have spent hours looking until i found it lol

Reminds me of a moment back when I was active duty installing a gun system on an F-16... It was the middle of the night, we were just wrapping up the installation, and all I had to do was install the two bolts that connect the unit that transfers the rounds from the ammunition drum into the belt. I was literally hand-threading in the last bolt when I said out loud "wouldn't it suck if I dropped this?". Well, I dropped it - inside the drum. We had to take it all back out. Whoops.
 
How often have you seen that happen? Sounds like you zeroed in on the problem pretty quick.
Never seen it before. Never heard of it. The clue was the change in performance going uphill versus downhill and the consistency thereof. That and it is older with quite a few miles which pointed me to that as a possibility.

Sorta related but I read the stuff from folks with OPDA issues and am aware from that there is an issue with cam drive gear wear and the issues that causes.
 
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