'79 40-Series Engine "Stutter" (1 Viewer)

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Joined
May 6, 2021
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Hey, all. Just became a proud member of the 40 club, and this is my inaugural post... I posses some basic mechanical knowledge, but still have a lot to learn about the nuances of the Land Cruiser, so please bear with me!

I picked up my new Cruiser in Northern California and subsequently began the long, hot drive back home to Los Angeles, with a stop-over in Yosemite for good measure. The 1979 FJ40 I purchased was originally sold in California, then spent some time in Oregon before returning home to the Golden State with its PO. I am the fourth owner. It had been de-smogged, then re-smogged with its original equipment roughly four years ago. It's a relatively low-mileage rig (less than 70k), and DMV records seem to support that. Engine has never been rebuilt and a recent compression test shows consistently strong numbers (130-140) across all cylinders. There are no significant fluid leaks. This is all for a bit of context...

On the first leg of my trip, after 2-3 hours of driving the engine began to lose power and "stutter," which shook the whole vehicle, and became pronounced unless I took my foot off the gas completely. My top speed on the highway was between 60-65, but there were some back roads mixed in so I wasn't going flat out the whole time. It was in the high 80's/low 90's outside but the engine temp gauge stayed between the 1/3 and 2/3 mark, usually closer to 1/3. I pulled off and let the truck rest a bit, then continued on. The problem re-emerged as I climbed into the mountains and the stutter appeared in 3rd and then 2nd gear. I had to pull off completely on a particularly steep incline.

At this point I spoke to the PO, who reported having a similar issue on occasion, but thought it was the result of the smog equipment. After letting it rest, I made it to a gas station and filled the tank (it was down to 1/4). I started on my way again, and the problem disappeared completely. This led me to believe it was possibly some issue with the tank (which is original) or fuel pump/sender. But, again, I mostly have no idea what I'm talking about.

The truck was driving perfectly after that, making a couple of trips down into Yosemite Valley and back out over the next couple of days. No problems at all. Then, on the last leg of my trip back to LA, the stutter re-emerged a couple of hours into my drive (just in time for the grapevine, of course). I let it rest, filled the tank, had some In-n-out, and made it through the pass. But for the rest of the trip it continued to stutter at around 50 mph, sometimes lower.

What do you all make of this, seasoned Mudders?
 
crud in the fuel tank.

fuel filter clogged

Next time it happens check the fuel level in the sight glass on the carb.
 
If your fuel tank is under the passenger seat you can pull the fuel level sender and take a peek inside.
 
Fellow LA based 40 owner here (pre smog 1971). I had a similar issue pop up earlier this year, which only appeared on longer drives to/from the eastern sierra. My symptoms included backfiring, bucking and loss of power, the latter of which was progressive once it occurred (65, then unable to do much more than 55 without bucking/backfiring every 10mi or so). For what it's worth, this only popped up after a few hours spent in 3rd gear and conveniently far from home. So after replacing the fuel filter and ruling out the fuel pump, I rebuilt the carb (Rochester 2GC) and the issue hasn't reoccurred... yet. Case not closed though as I'm still having fuel delivery issues at the venturi cluster, but no more backfiring/bucking. Food for thought.
 
Fellow LA based 40 owner here (pre smog 1971). I had a similar issue pop up earlier this year, which only appeared on longer drives to/from the eastern sierra. My symptoms included backfiring, bucking and loss of power, the latter of which was progressive once it occurred (65, then unable to do much more than 55 without bucking/backfiring every 10mi or so). For what it's worth, this only popped up after a few hours spent in 3rd gear and conveniently far from home. So after replacing the fuel filter and ruling out the fuel pump, I rebuilt the carb (Rochester 2GC) and the issue hasn't reoccurred... yet. Case not closed though as I'm still having fuel delivery issues at the venturi cluster, but no more backfiring/bucking. Food for thought.
I was wondering if there were any brave LA-based 40 owners regularly making that drive!

Yes, "bucking" perfectly describes the issue. It is interesting that it only occurs after multiple hours of highway driving.

Does seem like there is some kind progressive fuel delivery issue at work here. I will probably investigate the fuel sediment/tank crud issue first, then move on to the carb if that doesn't settle it.
 
Interested to hear what you find. I wondered about crud in the tank, but nothing of note in the fuel filter when I changed mine and sort of assumed that would create an at-all-times issue versus progressive onset hours into an otherwise fine drive. Maybe others will chime in since fuel sediment/tank crud is a common response to similar posts here.
 
Thought I'd close the loop on this thread as we head into the new year, and enter prime desert excursion season here in the People's Republic. Happy to report that I have solved the progressive fuel delivery issue, which seems to have been caused by vapor lock in conjunction with some other issues. Hard to say that one thing in particular solved it, so here's everything I did...

Firstly, I checked the fuel tank for sediment, which is not so easy with the 79+ rear tank set up... No obvious crud or rust issues there. Then I removed all the hard fuel lines between the tank and the carb to inspect and clean them (including the vapor return lines that 78+ owners will be familiar with), and replaced all the soft lines. Also replaced the fuel filter. Then I continued on in the spirit of baselining... Coolant flush. Oil and filter change. I also made sure the vacuum system was all buttoned up. Finally, I got a heat sleeve (summit racing) to wrap the fuel line between the pump and the carb. Does it actually do anything? No idea.

Since completing all of the above, I've driven my Cruiser almost daily and had no recurrence of the vapor lock (or whatever it was). Even found some time to get her a little muddy between recent storms...
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