Vapor Lock
 

My 89 EB has been experiencing some vapor lock issues. It has the 5.8 and a C-6 with 125,000 miles on it. The vapor lock only occurs when it's hot out (90 or more) and I'm towing my camper (Trailite Bantam). It has happened twice, the first time after I shut it off for a short period it started up fine and stalled out in a block. I checked the fuel rail and the gas was foamy and had low to no pressure. After about 45 minutes the pressure was back and it fired right up and ran great. The second time it died while going down a steep curvy <st1:state><st1 ="">Montana</st1> </st1:state>hill and would not restart. The wife didn't like me going down the hill without any power steering or power brakes. When I got to the bottom, I checked and had the same thing at the fuel rail. This time I kept cycling the key to the run position to run the fuel pumps and bleeding the fuel and pressure off. This time it only took about 15 minutes to regain fuel pressure. The Bronco ran great the rest of the weekend and had no problems driving back home today.

The Bronco is stock except for a set of Pacesetter shorty headers and a Flowmaster muffler. Both fuel pumps cycled on every time I turned the key to the run position. I replaced the fuel filter after the first time. Does this sound like a pump problem or could it be caused by the headers? I taking a trip to Canada in two weeks and I need to figure this out before I go. Has anyone else had this problem?

sounds like a bad fuel pressure regulator. if you pull the vacum line and it smells like gas then the fpr is bad. are any of your fuel lines close the the exhaust at all? whats your underhood temp like when towing and such. you are running a fan shroud on your radiator correct

This is an old trick, and it works! Believe it or not, wrap your fuel line(s) under the hood with aluminum foil! I am not kidding! It reflects the heat away from the lines! My father had a 77 F150, that would do it EVERY TIME you tryed to pull anything in the summer. After we wrapped the lines, it never did it again!!

How would a pressure regulator cause this problem? The bronco has the fan shroud and the temp gauge reads normal, the motor's not running hot. I think it's a combo of the header heat and extra transmission heat from towing. The bronco has a towing package with the factory tranny cooler. I'm going to wrap the fuel filter and lines near the exhaust and see if that helps. I'm heading on a 180 mile trip towing my camper to Coaldale Alberta for a hockey camp for my son next weekend, so I don't want to have any problems.

the fuel lines on you 89 shouldnt be anywere close to the exhaust. its pretty rare for an efi motor to have vapor lock. thats why i think you need to do some more trouble shooting to diagnose your issue.

I have never seen an efi truck get vapor lock, I have had it happen on my 82 carbed.
I'm with kemicalburns on checking the FPR, it's easy.

I didn't think it was possible to "Vapor Lock" when you have EFI? I would think it would be either an old, swollen fuel line that is closing off internally or a pump issue.

Am I wrong on the EFI part?

or, check for a loose electrical connection at the fuel pump. It's mostly unlikely, but your fuel line could be colapsing somewhere... I had that happen on my 79, and a buddy of mine had it happen on his 85 Chevy as well.

I'll check the Fuel Pressure Regulator. Both times that it happened, while releasing pressure at the schrader valve on the fuel rail, the gas was comming out foamy at first, then I had no gas coming out but air pressure was bleeding off. The engine was running a normal temp but the underhood temp was higher than normal. That what makes me think it's a vapor lock condition.

I am not sure how stupid this sounds but.. my dad has a '55 Ford p/u that I used a few summers back while my Bronco was being worked on. I drove it for about 3 days without a problem. On the last day it reached about 100 and the thing died. I called Dad and after about half hour he showed and tried starting the truck. Which of course fired right up and ran fine making me look stupid. (Daddy to the rescue). On the way home, with him following me, it died again. 10 minutes later after it just sitting it started again and we drove it home. He took it to a mechanic friend who check the fuel lines and everything else. He finally called and said that the gas cap was bad and not venting properly causing a vapor lock. So next time your truck dies try removing the cap and see if it will start. Might sound stupid but an $8 gas cap is one of the cheapest fixes you'll find on a ford. Good luck.

i have heard of something similar to that. always worth a shot

what did you find out with your problem? I just picked up an 89 set up just like yours for my wife and it's doing the same thing. It does act like it is vapor locked. I get the foam and big periods of straight air out of the rails. It's Happened 5 times now in 3 weeks. I do not want her driving it anymore till it's fixed.

Personally I would lean towards the simple things first and try the replacement cap idea. The cap is essentially a check valve with a filter built into it. If the filter becomes clogged with dust and road crud then air cannot move into the tank to maintain atmoshperic pressure inside the tank. Hence the fuel pump(s) work overtime creating negative pressure in the tank which effectively reduces fuel pressure through the system. If the check valve fails, the pressure in the tank can rise under hot atmospheric conditions forcing the in-tank pump to draw in warm fuel which will try to contract again once drawn into the cooler fuel line. When the fuel contracts it leaves a less-than-full fuel line.... air replaces volume that the warmer fuel once occupied. There's your vapor lock recipe.

I think mine was/is caused by the tranny running too hot while towing. I did a fluid and filter change, put in an RV/Towing shift kit and a bigger transmission cooler. I towed the camper to <st1 =""><st1 ="">Glacier</st1> <st1 ="">National Park</st1> </st1>over Labor Day weekend without any problems, but the temperature was cooler out than when I had problems before.

The Bronco ran great all the way to <st1:country-region><st1 ="">Canada</st1> f</st1:country-region>or my son’s hockey camp in mid August. It was warmer when I came home a week later and ended up on the side of the road bleeding air from the fuel system and letting it cool down 4 times!!! While checking things under the Bronco, I noticed that the front driveshaft was too warm to keep my hand on it. That trip home really sucked and took an extra four hours. Once the sun went down and it cooled off outside I didn't have any more problems. I tried loosening the gas cap and didn't see any change, I was back on the side of the road once again. I really hate when cars fly by on the interstate without changing lanes, especially when I'm laying under driver's side of the Bronco!!!!!

Vapor lock is an oft-misdiagnosed issue that rarely, if ever, happens to electronically fuel injected vehicles. I would look elsewhere for the problem, and at the regulator first if it has one.

Wrapping the fuel lines in heat shield never hurt anything though, and can help with fuel mileage. If you are having a borderline issue, that might cure it.