Gas Cap affect Fuel Pressure?

Absolutely.

Not yet. What I did do is did a pressure test while driving which I didn't do before. I was at 30 pounds at idle but when I drove it the results were way below HESCO's recommended pressure at drive time. HESCO recommends around 40 to 41 pounds on acceleration which should remain and not drop off. I could hardly get 35 pounds going uphill stomping on it. So, HESCO recommends dropping the tank and checking the fuel sock thinking there's a restriction keeping the fuel from flowing freely. They also recommend replacing the fuel filter even though it's new it could have filled up with crap from the sock.

Someone at work mentioned the fuel cap but I asked the owner of a parts store who said no and you seem to agree, the cap wouldn't make a difference.

So I plan to drop the tank this weekend and see if I can get that fuel pressure up.

Bill

On Fri, 17 Oct 2003 20:00:02 GMT, the following appeared in rec.autos.makers.jeep+willys, posted by "Cherokee-LTD" :

...but only the pressure in the tank.

I'm also going to check the timing chain this weekend for slack.

I'm going to eliminate as many things as I can before I take my jeep to JRU next weekend.

bill

That's not entorely true Bill. The electric fuel pump is sensitive to a plugged vent in the gas cap. The test would be to open the cap and see if the pump works better.

Not on a CJ7 unless your charcoal canister is crapped out.

There is an air filter on the bottom of the canister that can get dirty which will put a vacuum on the gas tank.

A CJ tank is supposed to be at atmospheric pressure.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

William Oliveri wrote:

Not so, in my case. My Father had an '89 Trans Am GTA and it started running rough. He had it in for service, they did whatever they did to it and told him all was well. Within 20 minutes of leaving the shop it started acting up again... back to the shop. They did some more work to it, said it was ready... 20 minutes later it was acting up... back to the shop. My Father told them he wasn't coming back for it- fix and deliver or keep it (company lease). They ended up delivering it a day or two later and were very apologetic... the car was just months old and they hadn't though of the gas cap. I don't know how much they spent on it (leasing company got the bills) but I would have loved to see the expression on the SM's face when they figured out it was a gas cap.

I had an '80 Monza... same problem except it wouldn't run at all. I went to change the fuel pump, pulled the line off and heard a whoooosh. Put the line back on, pulled the gas cap off and it ran well after a few cranks.

Depending on the capacity of the tank and venting/return lines you can get pressure changes on both sides of the fuel pump. I'm not sure what Bill's symptoms (or make/model) were but when he asks if a gas cap can effect fuel pressure, I say absolutely.

-Brian

: : -- : : Bob C. : : Reply to Bob-Casanova @ worldnet.att.net : (without the spaces, of course) : : "The most exciting phrase to hear in science, : the one that heralds new discoveries, is not : 'Eureka!' but 'That's funny...'" : - Isaac Asimov

Well, a new gas cap is 11.00 plus change. A cheap replacement to be sure.

bill

On Fri, 17 Oct 2003 22:12:05 GMT, the following appeared in rec.autos.makers.jeep+willys, posted by "Cherokee-LTD" :

Thanks for the info. This is the first time I've heard of this problem.