Erratic Fuel Pressure

[sk8nSam]

Anybody know what's up with my DB-1/Honda? The engine misses like crazy. The problem got progressively worse as the weekend at NJMP Lightning went on. Data analysis reveals the problem is erratic fuel pressure. An AiM screen print is attached. Anybody else had this problem? How do I fix it?

[chrisH]

The Walbro fuel pumps used in the Honda kits tend to fail, so I would imagine this is your issue. We had the same thing happen awhile back. Although not as erratic as yours, you can see from the attached screenshots how much worse it got from the beginning of a session to the end. Replaced the fuel pump and all was good.

I know some guys have switched to a different fuel pump, but not sure which model. Maybe someone could chime in on that. We don't let fuel sit in the cell overnight, and will probably replace the fuel pump after a few events as a precaution.

[cliff]

To tag on what Chris said...I use a fuel safe pump from Pegasus. I think I have replaced it 2 times in 6 years. You want to pump the fuel out, but running those pumps dry can hurt them. If you don't know the history of the pump I would just replace it. The other thing to check is your electrical connections as heat and vibration as the session progress can make it look like a pump problem.

[racerjon1]

Just went through fuel issues in a DB3/Honda with all of the "OE" Honda pieces.

If you haven't been in there yet, it is made up of this in the tank:

Fuel screen "sock."
Fuel Pump
4-inch (roughly) rubber hose
Fuel pressure regulator - (diaphragm type, nestled in an aluminum block, has o-ring and a clip. It's an odd setup.)

I started seeing low fuel pressure. As a session would go on, it would drop to 10psi under throttle. I did the usual fuel filter inspection. No excessive dirt, no fuel cell foam. (Turns out because of the sock, you're probably not going to see fuel cell foam in the in-line filter.)

In the tank, fuel cell foam looked good, but the sock was black. I believe from fuel cell residue - most likely due to ethanol content in the gas.

Since I was in there and had heard stories, I replaced the Sock, Pump and the diaphragm piece which plugs into the aluminum block. The diaphragm was super hard to seat in the block. I need to do research to see if there might be a different size o-ring.

Put it back together... ran fine for 4 sessions, and then lost fuel pressure - the in-tank hose segment had gotten soft and was collapsing.

Of course.. none of this was erratic, so it may not be any of your issues but since I hadn't seen a lot of into on the system, parts, etc I figured every chance for someone searching helps.

A note: after talking to Honda, they suggest every rubber part the fuel touches gets replaced each year. (Fuel cells every five per FIA..)

[chrisH]

Another option is installing an external regulator instead of the finicky internal diaphragm Jon mentioned. One less piece of the Honda parts puzzle to worry about.

[cliff]

one last thing...if you can find some "non-ethanol" gas to run thru the system, do it after the weekend. That ethanol stuff is pretty wicked.

[Dave Harmison]

A couple of questions from a Kent guy who might consider a Honda some time:

Why are fuel pumps so short lived? Compared to street use and durability, they should last forever.

Do Hondas use EGO sensors? EGO in street cars is traditionally for closed loop cruising fuel control, not WOT. If you don't have an EGO, can't you run 100LL Avgas which would be better for the fuel cell?

[problemchild]

Why are fuel pumps so short lived? Compared to street use and durability, they should last forever.

I expect this is a misconception.

Most of the people who have had issues were converting older cars with older fuel cells. The fuel system and electrical requirements are just plain different and people are focused on the conversion first, and updating the fuel and electrical later. There may be a learning curve for some of us old timers. I have changed several fuel pumps in 3 different cars that I now know was not necessary. As several people have mentioned, the kits come with a economy street car regulator, which can be replaced with an external pressure regulator. The ethanol does not help obviously.

People that have an external regulator, a good baffle around the pickup in the cell, and change the sock regularly should have minimal issues.

[racerjon1]

Do Hondas use EGO sensors? EGO in street cars is traditionally for closed loop cruising fuel control, not WOT. If you don't have an EGO, can't you run 100LL Avgas which would be better for the fuel cell?

We do have an O2 sensor on the cars, and I am guessing it has something to do with the Honda ECU.

As far as avgas and other fuels - I CAN get non-ethanol 93 octane fuel, right until we are required to use the track fuel for events like the runoffs, then we're stuck with whatever the track has.