Fuel Delivery Problems

[mike23109]

I'm running a rather basic Edelbrock Pro Flow on my SBC. It's worked great for about 3-4 years. Recenty, I've experienced fuel pressure problems. I'll be driving along and the fuel pressure will unexpectedly drop, causing the engine to go lean and backfire. I figured the pump was going bad and replaced it. I decided to go for the next larger pump Edelbrock makes. I also changed the fuel filter while I was at it. I was driving around Reno the past week (at Hot August Nights) and again experienced a drop in fuel pressure. This time the engine stalled and would not restart for over an hour. The new pump was only a week old. I called Edelbrock and they warrantied me a new pump. I picked it up at Summit and installed it. Since it is pretty hot in Reno this week I also decided to wrap the pump in some heat insulator material from DEI. The next day I experience the same problem while cruising on I80, from Reno to Truckee. No fuel pressure, engine stalled. Not fun! I know I could not have had three bad fuel pumps. The problem almost seems like vapor lock but I've not experienced the problem until recently. Could my fuel pump relay be bad. This is an intermitant problem and I'm thinking it could be electrical but don't know where to begin. Any ideas?

[camcojb]

did you change gas tank caps when this started? If there isn't a vent on the tank (or if it's plugged up) and you run a non-vented cap it will cause a vacuum in the tank as the level drops and the pump will not be able to pick up fuel. You can usually tell if this is the issue by removing the gas cap slowly after this happens and hearing the "whoosh" sound of air being sucked back into the tank when the cap loosens. Bottom line, the tank either needs a separate functioning vent, or a vented cap.

The other thing that could kill the pumps is a restrictive filter before the pump; I run a 100 micron before the pump then the normal 10 micron or whatever after; electric pumps cannot suck through a restrictive filter, but it isn't an issue to push through it (after the pump). Your pump isn't mounted next to the exhaust or similar, and getting cooked, right?

Your problem sounds like a tank vent issue to me though.

Jody

[mike23109]

I have not replaced my gas cap. I've had a vented cap all along. I also have a dedicated vent for the tank. I have not checked to see if it is clogged. You do bring up an interesting point though. I've recently had some tank work done: I had the fuel pickup changed so it draws fuel from the bottom of the tank (the tank was cleaned and resealed) and baffles were added around the new pickup. I don't know if any of this could be part of the problem.

As far as filters go, on the original Pro Flow they did not have a filter prior to the pump, only one after the pump. With the new pump I did add a filter, but like you said, I added small one to prevent problems drawing fuel.

My new pump is installed in essentially the same place as the old one. The original Pro Flow pump was mounted inside the frame rail (passenger side) in my 1970 Chevelle. The new pump is quite a bit larger. I had to mount it outside the frame rail. As I mentioned in my original post, I did not wrap the second pump with any heat wrap. It's about a foot or so away from the exhaust pipe. The current pump is completely wrapped and I also shielded the exhaust pipe where it is closest to the pump. On the road the pump should get quite a bit of cooling air since it is now outside the frame rail. However, the last stall I experienced was while I was on the freeway, going about 65, with an ambient temp of about 75-80.

[Mike Norris]

Jody brings up a viable point with the pre-filter, If it is too fine the pump will strain and over heat. Most are 100 micron inlet filters and I have used as small as 35 micron (Earls). You mentioned:

"With the new pump I did add a filter, but like you said, I added small one to prevent problems drawing fuel." When you mean small do you mean physical size or the size of the media? Do you know what micron size the media is? If you can not figure out the micron size, it may be worth while to remove it and see what happens, though I would not run without some kind of pre filter.

Hope this helps.

Mike Norris

[camcojb]

the smaller the number the finer (i.e. more restrictive) it is. I don't use anything smaller than a 100 micron as a pre-filter.

Jody

[mike23109]

Jody/Mike,

Thanks for the info. The second pump I installed, an Edelbrock 1790, I did not have a pre-filter. It seemed to get real hot, then turned off. The third one, also and Edelbrock 1790, I did install a pre-filter, I beleive it is 60 micron, as recommended by Edelbrock.

As Jody said in his initial post, I think the problem may be with the tank, and not the pump. I'm going to pull it again and have it checked out. Thanks for all of your input and help.

Mike