Thread: EFI Fuel Rail Pressure

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I had the '33 out for about 75 miles of highway running yesterday and it seemed to be loading up and also seemed to be using more fuel than normal. This is the SBF 347 Stroker running Edelbrock's ProFlo XT EFI system. I also noticed some "flutter" to the right side exhaust, and it was loading up at idle and low rpm, like pulling away from a light. Right side plugs are sooty, more so than the left, but I also smelled some raw fuel in the left. Both baffle pipes are black & sooty, so I'm running rich. I'm pretty sure that my fuel map is dialed in pretty good, so I'm not looking to lean out the air/fuel at this point.

I hit the ignition to check fuel pressure, and it jumped immediately to 40psig as it should. After the pump prime cycle, in the past the pressure would hold constant (engine off) at 40psig for quite a while, at least 1/2 hour if not more. Now as soon as the pump stops the PI needle is falling, going to zero within three to five seconds. Now it could be the pressure regulator, which returns unused fuel to the tank, but I'm thinking that I may have a few injectors partially stuck open, or sticking. Anyone have experience in this arena? Ideas on best approach?

Sounds like an injector or two is dirty! At least that's how the old Hillborn Injector on the sprint car did when an injector was dirty. I'm certainly no EFI expert......

Put a can of Lucas fuel injector cleaner in it and run it for 20 miles or so, it will make a difference. I ran Lucas on my trip to Va. last June, about 2000 miles round trip, in the Dakota and I averaged just under 20 mpg for the trip. That isn't too bad for a 1/2 ton pick up and I was normally 5 mph over the speed limit.

Well, I've got nothing to lose in dumping in a bottle or two of injector cleaner in it and running some gas through it! I was (am) thinking that it was going to be a more invasive "fix" than that, but fingers crossed!

Unless you're running more than a 22 gal tank or so, one bottle will be fine, two would be overkill.

OHM the injectors & see what you get compared to Edelbrock specs?
Lucas is a good idea too.
FPR crossed my mind too.

Originally Posted by t-top havoc

OHM the injectors & see what you get compared to Edelbrock specs?
Lucas is a good idea too.
FPR crossed my mind too.

The FPR was something I thought of when I watched the pressure dropping, but it doesn't explain the running rich. I'm thinking that the charge of fuel was leaking into the cylinders, but I'm not sure....

Can you test the spray pattern yourself?
Just wondering if you could, then you may be able to see leaks // clogs?
Does the pump lose power // prime?
Sorry for the dumb questions, I do realize not a lot of people have injector flow testers.

Originally Posted by t-top havoc

Can you test the spray pattern yourself?
Just wondering if you could, then you may be able to see leaks // clogs?
Does the pump lose power // prime?
Sorry for the dumb questions, I do realize not a lot of people have injector flow testers.

No, I don't have an injector flow tester, but I've seen some explanations on how to build a station to cycle them open/closed for cleaning. If the in tank cleaner doesn't work later today I may be looking at that next, after checking resistance on each one.
No, the pump is fine. The normal operating mode is that the pump is energized for only about three or four seconds to prime the system with "Ignition ON", and then it's interlocked with an "Engine Run" signal. If you turn the ignition "ON" and don't go to "Start" then it primes and the pump stops. It had a full tank of gas (15 gallons), and no reason to think that fuel pressure was low as it ran strong, but fat. My fuel pressure gauge is a little 1" dial on the fuel rail supply.
On Friday coming back towards home (still on the highway) I punched it in fourth, took it up to about 4000rpm and when I let off got a rapid exhaust pop along with what I know would have been a long visible flame had it been at night (lake style headers with baffles, exit just in front of the doors). I dumped a bottle of cleaner in it last night, and this afternoon will take it out for a run to see what it does. I'm not overly optimistic, but hopeful.

Well, it looks like it's not going to be as easy as cleaner. I went up to K10 and ran it in 4th, about 3500rpm and goosed it up and down a few times to 4500 and 5000. When I let off at that engine speed and let it back off I get a "flutter burn" out the right side. Did about fifty miles. It seemed like it was better, but it's not. As I was coming home trying to do about 30 to 35 in third it surges like it normally does on a cold start and you try to go too quick, that herky jerky lope that's common to an overlapped cam when cold.

The fuel pressure is still dropping off as soon as I turn the key off, which seems to me to point to an injector or two not staying seated when powered down. Not sure what that means. If I turn the ignition "ON" pressure goes to 40 and holds, but as soon as the ignition is "OFF" pressure drops to zero within five seconds. Not sure how to trouble shoot this beast. I guess I'll pull all the plugs in the morning and see if I can pinpoint a cylinder, or group of cylinders that are fat.

Sounds like you're on the right track. Read the plugs and try to isolate the offending cylinders. Maybe investigate the value of say, 4 injectors, then the cylinders that are questionable, replace those and see if you were right.

Sometime back, maybe in the summer..??..?? there was some discussion of adding acetone to gas and reportedly it does help clean injectors very well. I think there is/was a couple of videos on U-tube where guys fabbed a simple tester / cleaner setup fwiw...

Originally Posted by 34_40

Sounds like you're on the right track. Read the plugs and try to isolate the offending cylinders. Maybe investigate the value of say, 4 injectors, then the cylinders that are questionable, replace those and see if you were right.

Sometime back, maybe in the summer..??..?? there was some discussion of adding acetone to gas and reportedly it does help clean injectors very well. I think there is/was a couple of videos on U-tube where guys fabbed a simple tester / cleaner setup fwiw...

Yeah, I guess this will be another learning experience. Looking at Summit, the 35# Edelbrock injectors are $57 each, or $336 for eight which is a savings of $15 per injector!! I was a little shocked. As I understand them at this point the injector has a needle valve (pintle) which is closed by spring pressure, and opened by a strong little solenoid coil. That coil has a duty cycle of a few milli-seconds, so if you power them "ON" to "test" them you can burn them out in a heartbeat. I had thought that the pressure was holding with the ignition "ON", but that's not the case. The system primes, pump goes "OFF", and rail pressure falls. Now I'm thinking that if I prime the system and let it bleed down several times, then pull the plugs I'm going to find some wet plugs in the offending cylinders. Hope I'm not over analyzing this....

Again, I think you're on the right track. Pull & dry the plugs, then cycle the pump without firing the motor, pull and inspect the plugs and injectors, search for the wet ones.

I don't agree with the duty cycle thing cause when the motors making 3 to 4 thousand RPM (or more) the pulses are just about constant!

Do you have an exhaust leak causing O2 sensor to read lean and ecm then riching up the system??????????

Originally Posted by jerry clayton

Do you have an exhaust leak causing O2 sensor to read lean and ecm then riching up the system??????????

Nope. Not a bad idea, but not the problem. The issue is that it was doing great, then efficiency seemed to be going south, and then it was very obviously running fat. Problem is I can't say why.....