...

Go Back   Lateral-g Forums > Technical Discussions > EFI and Forced Induction
User Name
Password



Reply
 
Thread Tools Display Modes
  #1  
Old 09-07-2007, 06:27 PM
undertaker undertaker is offline
Junior Member
 
Join Date: Jul 2005
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default 502 ramjet fuel pressure

well my 502 is being moody again and I'm just trying to trouble shoot everything....whats proper fuel pressure supposed to be again? I have 48 with the vacuum line disconnected and bout 42 with it connected at idle.

still have a high idle, no intake leaks, throttle is closing, new cap/rotor/plugs/wires etc. and I also have a very bouncy tach......which I can't figure out a reason for.

Gonna check power and grounds and clean those up but I'm running out of ideas now

truck was trapping 89 mph 2 months ago when I had it at teh track vs. its usual 95 through the traps, didn't even want to go near the bottle.

Of course its time to sell the truck and I at least want it running right to sell itself on its own merits.
Reply With Quote
  #2  
Old 11-10-2007, 10:21 AM
Matty B Matty B is offline
Junior Member
 
Join Date: Nov 2007
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
Default

Your fuel pressure is fine well within spec, however with only that much drop when the vaccum is hooked up ~6 psi that means you only have about 6 in vaccuum at idle. I higghly suspect you have a vaccuum leak of some sort from the sounds of it. Id say go through it again and recheck it. IIRC the MAP sensor is underneath the plenum and if it it hooked up with a hose thats a possible spot for a leak and also why the motor could be running wrong ie down on hp and such. Id check there and report back, I saw this happen on a 210 with this motor at the shop and once we put a new piece of tubing on it, it ran perfectly. hope this helps.
Reply With Quote
  #3  
Old 11-10-2007, 11:38 AM
camcojb's Avatar
camcojb camcojb is online now
Administrator
 
Join Date: Jul 2004
Location: Wilton, CA.
Posts: 12,579
Thanks: 4,186
Thanked 1,443 Times in 625 Posts
Default

Quote:
Originally Posted by Matty B
Your fuel pressure is fine well within spec, however with only that much drop when the vaccum is hooked up ~6 psi that means you only have about 6 in vaccuum at idle. I higghly suspect you have a vaccuum leak of some sort from the sounds of it. Id say go through it again and recheck it. IIRC the MAP sensor is underneath the plenum and if it it hooked up with a hose thats a possible spot for a leak and also why the motor could be running wrong ie down on hp and such. Id check there and report back, I saw this happen on a 210 with this motor at the shop and once we put a new piece of tubing on it, it ran perfectly. hope this helps.
pressure looks good. I've never seen pressure drop in psi equal to your vacuum. In other words, if he had 18" of vacuum there will not be an 18# difference in fuel pressure with the vacuum reference attached. PSI is not the same as vacuum.

If there is not a vacuum leak, and if the throttle blade is set properly and closing then the next thing I'd look at is the idle air control motor. I think you're running the stock Ramjet computer with no end-user tuning which is unfortunate. There are a couple things to try if you can adjust the computer, but don't help if you cannot.

You might try removing the IAC and cleaning it as they do sometimes stick. Possibly plugging it off if possible just to start it and see if the idle drops, then at least you'd know you are dealing with the right issue.


Jody
__________________
Jody

PAST CAR PROJECTS

Like Lateral-G on Facebook!

Follow Lateral-G on Instagram!

SPECIAL THANKS TO:
Jacob Ehlers and Amsoil for the lubricants and degreasers for my 70 Chevelle project
Shannon at Modo Innovations for the cool billet DBW bracket
Roadster Shop for their Chevelle SPEC Chassis
Dakota Digital for their Chevelle HDX Gauge Package
Painless Performance for their wiring harness

Ron Davis Radiators for their radiator and fan assembly.
Baer Brakes for their front and rear brakes

Texas Speed and Performance for their 427 LS Stroker
American Powertrain for their ProFit Magnum T56 kit
Currie Enterprises for their 9" Third Member
Forgeline for their GF3 Wheels
McLeod Racing for their RXT street twin clutch
Ididit for their steering column
Holley for their EFI and engine parts
Lokar and Clayton Machine for their pedals and door and window handles
Morris Classic Concepts for their 3 point belts and side mirrors
Thermotec for their heat sleeve and sound deadening products
Restomod Air for their Tru Mod A/C kit
Mightymouse Solutions for their catch can
Magnaflow for their 3" exhaust system
Aeromotive for their dual Phantom fuel system
Vintage Air for their new Mid Mount LS front drive
Hydratech Braking for their hydroboost system
Borgeson for their stainless steering shaft and u joints
Eddie Motorsports for their hood and trunk hinges and misc parts
TMI Products for their seats, door panels, and dash pad
Rock Valley Antique Auto Parts for their stainless fuel tank

Last edited by camcojb; 11-10-2007 at 11:44 AM.
Reply With Quote
  #4  
Old 11-10-2007, 03:02 PM
Matty B Matty B is offline
Junior Member
 
Join Date: Nov 2007
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
Default

well most vaccumm referenced FPR Ive seen and dealt with typically run 1:1 psi drop per inHg. So typically youll see around ~35 psi at the rail during idle and will rise back to static pressure at WOT and if boosted should rise proportionally to boost.***NOTE FOR THIS ISSUE ID LIKE TO KNOW THE IDLE RPM AT THIS POINT CAUSE THE FUEL SYSTEM COULD BE FUNCTIONING FINE AND ITS JUST THAT THE HIGH IDLE IS CAUSING THIS**** Reason for this is that under vaccum in the plenum there is less resistance to fuel coming out of the injectors and as vaccum drops to atmospheric, atmo pressure puts more resistance on the fuel coming out of the injector so pressure rises to compensate. This function is required in a port fuel injection setup to maintain a consistant pressure vs vaccum. The only times this is not tthe case is with TBI which sprays in atmosperic pressure always so the pressure is set at a static number and also in rising rate fuel pressure regulators which add non proportional pressure to the rail in IMO slopped together forced induction systems.. Im thinking MAP for one reason and thats the huge drop in horsepower as shown by his 1/4 mile trap speeds. If he was complaining of only a high idle id look at the idle air motor as well and it very well could be screwed up as well BUT the additional air introduced by that staying open would be compensated for in this speed density system. The only time youd see a huge horsepower loss would be when the map sensor was no longer refrencing plenum vaccuum correctly. SO Id recommend this..
1) disconnect the IAC, if the idle changes substantially we can at this point assume that it is not stuck, if it doesnt then pull it clean it or replace it and retest.
2) Check MAP voltage, it should be ~1.5-2 volts at idle what we dont wanna see is 0 or 5 volts.
3) Check your static timing with EST unplugged, if it somehow got too advanced it would idle high and would cause pinging which would cause the computer to pull timing out by a bunch causing HP loss.
If none of this fixes any problems id say get back to us.
Reply With Quote
  #5  
Old 11-10-2007, 03:20 PM
camcojb's Avatar
camcojb camcojb is online now
Administrator
 
Join Date: Jul 2004
Location: Wilton, CA.
Posts: 12,579
Thanks: 4,186
Thanked 1,443 Times in 625 Posts
Default

good list of things to try. All I was saying is that one inch of vacuum does not equal one pound of boost. On my stock Vette the fuel pressure was 50 psi or so with the vacuum reference disconnected and 43 psi with it connected. That car had 19-20" of vacuum yet the fuel pressure only changed 7 psi or so, and that is normal.

On boost reference you are correct, one psi of boost should give one psi of additional fuel pressure, but vacuum doesn't work the same way. I don't think his fuel pressure appears an issue, at least with the info he gave. He needs to start looking at the other things mentioned.

Jody
__________________
Jody

PAST CAR PROJECTS

Like Lateral-G on Facebook!

Follow Lateral-G on Instagram!

SPECIAL THANKS TO:
Jacob Ehlers and Amsoil for the lubricants and degreasers for my 70 Chevelle project
Shannon at Modo Innovations for the cool billet DBW bracket
Roadster Shop for their Chevelle SPEC Chassis
Dakota Digital for their Chevelle HDX Gauge Package
Painless Performance for their wiring harness

Ron Davis Radiators for their radiator and fan assembly.
Baer Brakes for their front and rear brakes

Texas Speed and Performance for their 427 LS Stroker
American Powertrain for their ProFit Magnum T56 kit
Currie Enterprises for their 9" Third Member
Forgeline for their GF3 Wheels
McLeod Racing for their RXT street twin clutch
Ididit for their steering column
Holley for their EFI and engine parts
Lokar and Clayton Machine for their pedals and door and window handles
Morris Classic Concepts for their 3 point belts and side mirrors
Thermotec for their heat sleeve and sound deadening products
Restomod Air for their Tru Mod A/C kit
Mightymouse Solutions for their catch can
Magnaflow for their 3" exhaust system
Aeromotive for their dual Phantom fuel system
Vintage Air for their new Mid Mount LS front drive
Hydratech Braking for their hydroboost system
Borgeson for their stainless steering shaft and u joints
Eddie Motorsports for their hood and trunk hinges and misc parts
TMI Products for their seats, door panels, and dash pad
Rock Valley Antique Auto Parts for their stainless fuel tank
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 04:10 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright Lateral-g.net