Hi folks, First post. I've lurked for awhile, when registrations appeared to be shut off. Came back recently to scout around and was glad to see everything's still very lively here. I'm chasing down a problem with vapor lock that showed up in my very first highway road trip out to San Diego, about a month ago. A lot of seemingly different things all happened at the same time, and I'm trying to untangle it all and need some objective thoughts on causes and potential remedies. I live in Denver, and I made it over all the mountain passes and into Grand Junction just fine -- some hesitation and chugging on the steep parts of the passes -- I just eased up a bit on the gas and the car found its feet again. In GJ (on the West edge of Colorado, down south, near the Utah line), stopped for gas and a couple tacos and car started anemically, but got out on the road just fine. at just about the Utah line, my fuel gauge went from F to E (looked behind me and saw no trail of gas) but the car was still running fine. Not having a gas gaughe anymore, I figured that I should fill up before that long desert stretch so that I could watch the odometer and be sure I didn't run out of gas. Pulled into Green River, UT and hit the big truck stop in town, went to gas up and when I opened the cap (an aftermarket locking one), I got a PSHHHHHHHT! from high pressure venting that went on for about 5 minutes. I tried to fill up and it would only take about a half gallon -- which does not make sense, because GJ is about 110 miles from Green River -- it shoulda taken about 6 gallons or so. So I grab the laptop and get some free wifi and start reading about plugged charcoal cans as possible causes for high tank pressures (mostly for other engine configurations). I strolled across the street to an auto shop to ask if I can just keep my cap looser and avoid the pressurization problem without difficulty. Guy said that the carcoal can isn't really needed and even if it's cracked or has a leak, it should not cause problems (mine was cracked anyway). So, with this news, and the car a bit cooled off, I filled it up with about 5 gallons and got back out on the road. The gas gauge was working and on F. About 5 miles past the "no services for 100 miles" sign (10 miles outside of Green River), the car sputtered and hesitated like it was running out of gas and I came to a halt on the side of the road. It would not start again. Gas gauge on E again. While I'd never seen it beforehand, vapor lock was just as it had been described to me -- like running out of gas in the heat, when you have a full tank. Knowing that I had many miles to go, and a stop in Vegas with record-setting 118 degree heat on the docket, I ended up renting a car (a hassle that I won't bother telling here, as it's long and painful and full of woe), moving all our stuff into it and continuing on my vacation that way. My car stayed with the only real mechanic in Green River while I went on to my July 4th family reunion. The mechanic in Green River had blown air back into the tank (on the pickup line) to "blow off" a filter-strainer that he felt sure was blocking fuel flow and causing anemic pump performance. He took it on a 45 min test drive afterwards and got the same kind of hesitation that I'd seen, though he didn't come to a stop. So, I had the car shipped back to Denver and it spent awhile in the shop -- I wanted the tank dropped, the fuel filter replaced, my sending unit checked/replaced, all my fuel lines tested & replaced as needed, and the charcoal can replaced. I also asked that any hard lines from the pump to the carb be insulated (we settled on using flexible fuel line (slit down the side) as a "wrapper/insulator" for these). All that work has been done and I've been driving it for the past week here in the city and for short 50-60 mile trips. No problems. ... on to the questions ... Are any of my fuel system problems related to each other? -- that is: tank pressure, fuel temp, sending unit failure, vapor lock When I had the tank dropped last week, they did not replace/remove/service the phone-book-sized rectangular tank behind the back seats (I call it a "vapor condensing tank") -- is this a stone left unturned that will bite me in the biscuits later on? I've heard a number of people describing similar problems to mine, and a range of solutions get talked about, but I'm not sure how to weigh them: - putting in an electric "goose" pump back by the tank that I can switch on when on the high mountain passes or when I get the locking behavior in hot weather - ditching the mechanical pump entirely and running a "fuel loop" with an electric pump, and lines (pickup & return) that are routed as far and away from the engine as I can - finding the 4-row radiator from the 1971 tow package (I think they used the same 4-row radiator for all kinds of GM cars through the early 70s) and throwing that in so that the engine runs a lot cooler overall I take good care of the car, and it's in near-immaculate factory original shape, and I may show it at judged Buick events in the future, but I'm not worried about being docked points over any of these changes. I bought the car (some 15 months ago) to be a driver. Looking forward to thoughts and suggestions. I don't pretend to know everything, so I'm open to learning. Thanks for the time and consideration, -- Randy
What are the elevation changes you dealt with? If the carb is jetted for high elevation it can run bad in low elevation. How old is the fuel pump? My car started hard after sitting because the fuel pump still worked but couldn't produce quite enough pressure to fill the float bowls quickly. A new fuel pump solved that problem. If you're still using the original pump it may be allowing air pockets in the line as it misses pumps. Think about a heart skipping beats and you'll get the idea. Have you checked out the rubber fuel lines at the pump and at the tank? If those are dry rotten they may appear fine but a little wiggle will open up the cracks and allow air into the lines and a loss of pressure. Have you checked for vacuum leaks? A bad pcv gasket or carb gasket or intake gasket can cause a lean condition which could be made worse by elevation changes. It sounds like overall you have a small issue which is going to be a pain in the butt to track down. I went through the same kind of things. I would drive 20 miles without an issue and then the car would just die anytime I hit the gas from a stop. In the end I replaced all the rubber bits (vac lines, fuel lines, gaskets) and it fixed many issues. Then a new fuel pump fixed a bunch more. Ultimately my condition was from worn out fuel parts and a really bad intake gasket leak.
I've had a similar problem--'79 403 Trans Am would act like it was out of gas at 1/4 tank, and when I pulled off the cap it would whoosh and the tank would 'boom' as it expanded back to normal. Apparently the vent function through the canister was not working. I didn't delve deeper into it, I just got into the habit of leaving the cap loose. If your pump is pulling against a sealed tank it might be pulling the top and bottom inward, decreasing capacity, if it didn't pop back like mine would. Patrick Or you could sell it to a flipper who really wants a rock crawler and he'll suggest it's an easy fix, just rewire the dome lights or maybe it's an axle seal.
Between Denver (5200 feet or so) and Green River (~4000 feet) I got up to about 10,000 feet in between, and it ran fine. I expected some chugging on the steeps. I'm jetted for high altitude. I asked my mechanic about how it would run in the thick air before I set out, and he said that it might make it harder to start when I'm out at sea level, but it should run okay. The pump that was in it was about 14 months old. Just had a new one put in. I had most of the lines replaced last year. A couple were not leaking but a bit dried out and cracking. All flexible lines were replaced last week. No vacuum leaks. In the spring time, I went pretty much bananas over what I was sure was a vacuum leak in the climate control system (defrost vents did not throw air), but it turned out to be a stuck vent door. I've had it gone over twice in the past year to make sure it's tight, and it's tighter than ever. Not that I think we are seeing the same problems, but I do think that by taking the "shotgun" approach, I'm (like you did) taking out the zones where the problem -=could=- live. I'm really down to some basic choices in the whole battle between fuel delivery and heat. The biggest problem for both me and my mechanic is that neither one of us feels good about making any changes where we can't tell that the problem has been fixed. It means that I probably need to take a couple more hot weather road trips in the next month before things start cooling off. Anyhow, thanks for chiming in. It's good to hear others reasoning through this stuff. -- Randy
You need to determine exactly what temperature the engine is running at. That takes a good gauge. IMHO, no Buick should be without a good oil pressure and temperature gauge. Higher temperatures make vapor lock more likely. So do the ethanol fuels we use. If your engine is running at more than 210*, it will make things worse. Using more than 50% anti freeze can overheat an engine. IMHO, the stock 3 core radiator is inadequate, and yours could be clogged. Running a 195* thermostat means the engine will never run cooler than 200* Your fuel pump also incorporates a vapor return line. It circulates hot fuel and vapor back to the tank. Is that line clear? That whoosh you heard when you took the cap off means the tank is not venting. A 71 car should have a vented cap. Do you have the right cap? I'd ditch the locking cap and get the right fuel cap. The engine could be running lean because the fuel pump can't supply enough fuel, and that will make it run even hotter.
Good points from Larry. I was hoping to steer you towards quick and easy fixes. Hopefully it's a gas cap issue or a bad vent tube. Those are quick and easy too.
I haven't read anything about the FUEL FILTER, that would have been my first look at, the aftermarket fuel cap next, good luck. Johnny
Hi Larry. Thanks for taking time to read and reply. As for the gauge, the 71 has no temp information on the dash. You get warnings, but nothing else. I'm very much considering getting a temp-pressure-charge trio set of gauges to mount underneath by the ashtray, because the lack of information is disquieting for me, too. My radiator is the stock unit. Had a leak and crud in it when I bought the car, so I had it repaired and rodded out. Totally agree on the cooler things are, the odds of vapor locking go down. I should point out that at -=no time=- did my engine overheat, as far as I'm aware... at least the warning lights didn't come on and I had no venting under the hood. Thermostat is new as of a few months before the road trip -- had the whole cooling system gone through. I'll ask about which thermostat was put in when the cooling system was gone through. I want to get a 4-core radiator, and I want a new one, to be honest. If anyone can shoot me a link to one, I'd be grateful. My radiator is somewhere around 2 5/8 to 2 3/4 inches thick. There are too many options out there for a dimwit like me to decipher. A guy in the club mentioned that they used to make a thicker (like .25 in thick) rubber gasket to go between the carb and manifold, but I've had zero luck finding such an animal. The Q-jet has really small float bowls, and the cooler I can keep those bowls, the better off I'll be. Yeah, had that line totally cleared and the flexible bits replaced. I put the original cap back on. I don't have pesky gas-siphoning kids in the neighborhood, so I don't need the aftermerket locking one, anyway. Anyhow, it sounds like I'm on the right track. Thanks again, Larry. == Randy
