View Full Version : Pressure dropping under acccel.


fauslpss
02-03-2010, 12:08 AM
Ok have a cammed 2001 SS. When I did the cam I also threw in a hot wire kit and 255 walbro. When I had it tuned the tuner Jeremy said that he had to put in some large values to get the a/f right. At the time I didnt think it was a pump issue but I just installed a fuel pressure gauge and it takes a serious dip after 3000. Idle it shows a touch over 50 psi I would say 52. After 3 it drops quick its down to around 30psi by 5500.

I have no idea where to start. So some input would be well recieved here just need to know what to eliminate first. New hot wire and new pump so go from there.

Ground
Pump
Filter- New filter so not the problem
Voltage
Regulator


Thanks for your input, Eric

Old Geezer
02-03-2010, 08:06 AM
A leak at the pump outlet side? I think it's time to take a look in the tank...

fauslpss
02-03-2010, 02:00 PM
Ill be sure to look in the bucket. Also today in the light I noticed it drops when I rev it not on a load.

Any more help would be appreciated.

Thanks Eric

NSSANE02
02-04-2010, 12:57 PM
My car has been doing this exact same thing for the last few months. Even posted a thread on it a while back http://www.ls1tech.com/forums/fueling-injection/1197103-big-fuel-pressure-drop-wot.html
I've checked and replaced everything but the FPR and that should get here tomorrow so I'll know by tomorrow night if that's the issue. I'll let you know what I find.

fauslpss
02-04-2010, 01:56 PM
Thanks Man please do that would be a big help if saves me from having to do what you did.

Eric

MeentSS02
02-04-2010, 02:19 PM
Even your base pressure is too low (it should be around 58 psi) - you'll need to get in the tank sooner or later. I'd check the internal connections first - the regulator is a pretty low tech piece of equipment in the tank, so the chances of it failing I'd say aren't quite as good.

HUNTER02SS
02-04-2010, 02:23 PM
Replace your fuel filter as well.

NSSANE02
02-04-2010, 03:14 PM
Even your base pressure is too low (it should be around 58 psi) - you'll need to get in the tank sooner or later. I'd check the internal connections first - the regulator is a pretty low tech piece of equipment in the tank, so the chances of it failing I'd say aren't quite as good.
I looked for leaks or damaged lines in the tank before I replaced the pump and didn't see anything, maybe he can check that as well.
Replace your fuel filter as well.
Both have new filters.

fauslpss
02-05-2010, 10:44 AM
Thanks for the input guys.

Eric

Jim Craig
02-05-2010, 11:16 AM
Your symptoms indicate (one of a few reasons) too small a fuel pump -- as engine's consumption (and possibly fuel pressure, if boosted) rise there is not enough fuel in the system and this causes the fuel pressure to drop. The pump in its present configuration cannot keep up with the demand of the engine.

NSSANE02
02-05-2010, 12:18 PM
Your symptoms indicate (one of a few reasons) too small a fuel pump -- as engine's consumption (and possibly fuel pressure, if boosted) rise there is not enough fuel in the system and this causes the fuel pressure to drop. The pump in its present configuration cannot keep up with the demand of the engine.

No... these pumps are capable of pumping MUCH more fuel than either of our cars can drink.

Jim Craig
02-05-2010, 12:28 PM
Really, have you flowed one at the pressures you guys are operating at?

NSSANE02
02-05-2010, 12:57 PM
The pupms themselves will produce over 70 psi and are used in a ton of cars making a lot more power than us.

Lonnies Performance
02-05-2010, 05:55 PM
Yes, a single 255 will support way more than a typical heads/cam car will require. Typically in excess of 550rwhp at a 58psi delivery pressure.

If you have a serious pressure drop at 3000rpm, there is no way your engine needs this much fuel at this rpm/power level.

If you have 50-52 at idle you have a problem. Stock pump should have about 58psi, a good 255 should show approx 62psi at idle.

Typical problems are:
An internal fuel line leak (rubber lines are often the cause)
A bad regulator or a piece of dirt in it caused during pump replacement.
A loose connection at the hose connection in the tank.

A bad pump usually just stops working, but also can be the cause of this problem. I would look at the other items first.

The lack of pressure at idle is a very good indication of another problem as the car consumes almost no fuel at idle.. like 5hp worth of fuel. It is likely bleeding fuel off somewhere.

NSSANE02
02-05-2010, 07:07 PM
Just got my new regulator in, I'll start on it in a few minutes and let you know what happens.

BTW Lonnie, did you get my PM about the reg?

NSSANE02
02-05-2010, 11:53 PM
Just got the regulator in and the pressure is much better than it was. It now idles at 58 and stays above 55 while driving normally but it still drops down to as low as 44 psi at wot. I'm not sure what's going on with that but it's much better than the 30 or lower it was at and it's good enough now that I'm able to tune it to get the afr spot on.

fauslpss
02-06-2010, 02:44 PM
Lonnie you have a PM

It seems the regulator helped some... I heard some people were have issuses with new walbros, that may be some of the problem.

Lonnies Performance
02-08-2010, 09:45 AM
Been without power & internet for a few days...

Call me if you want to discuss in detail.

1969caprice
02-11-2010, 12:27 PM
i got a 2002 silverado doing the same. mine was idling@30 psi and dropping as low as 20. i put new fuel pressure regulator and was idling at 45psi then dropped after like 3 min to 20. while driving, it wont let me rev to 3000rpm. idling i can rev to 5500 but pressure drops to like 15. im going to pull out old pump and install new one. this should eliminate problem??

NSSANE02
02-11-2010, 09:27 PM
GOT IT! (post from my thread)-

Found the problem... kinda. Tonight I capped the return line and hooked up a mech. gauge to the T fitting where the return was. This way I can start the car and check actual pump pressure at the same time.

Both gauges showed a steady 82 psi at idle so the problem is somewhere in the stock regulator housing or the return tubing inside the sending unit. Luckily I ordered a complete fuel system with new feed/return lines and an adjustable regulator last night so my fuel issues should be solved once and for all!

I want to thank everyone for their help and advice through all this, it was without a doubt the most frustrating problem I've dealt with so far.

1969caprice
02-14-2010, 01:56 PM
replaced my fuel pump and fixed problem...

NSSANE02
02-24-2010, 12:21 PM
Did you ever resolve your issue?