I have a 94 bronco 302 EFI E4OD MassAir question. I realize that EECIV has a LF Trim allowance of +/- 100%, my bank 1 LF trim is +25-30%. This is a forced induction (kb) vehicle running 6psi boost. I am posting this because it recently started knocking (detonating) a lot at low boost levels (3-4psi) whenever I go to give it power, I have already ruled out a bad tank of gas. I have the ignition retarding up to 12 degrees under boost and 20 degrees during knock, it is still knocking under power. I am not even really being very aggressive with it, this is maybe giving it 50-60% throttle. I called kb, and they are hell bent on a vacuum leak, they recommended removing the blower, and redoing all the gaskets, that is like 6hrs worth of work on a "maybe". Other problem is it recently started idleing rough during its "low idle" (680rpm). Here is some info: During the "rough low idle" it has 10-12" Hg at the intake manifold (after compressor), during high idle (smooth) it has about 16"Hg at the manifold, cruising on highway, it has about 18-19" Hg at intake manifold. Fuel pressures seem ok, about 30psi on rails at idle, 40psi on rails at 0" MAP, about 60psi under 3.5psi Boost. SF Trim shows hovers around 0, LF trims is at about +25-30%, does this data suggest a vacuum leak, and 6 hours worth of disassembly, I do not have access to an EVAP smoke machine, any other advice???

Thanks
Brian

 

starter fluid sprayed around the intake etc.. will show or give an idea were a leak may be. also have you checked or replaced your O2 sensor. if its reading rich it will lean out the injectors and cause a knock. are you sure about your timing. i thought you needed less timing at boost not more. also check your plug wires for arcing at night . make sure they are not touching each other. also check your plugs to give an idea exactly what cylinder is having the issue. a vacum leak will cause what you discribe. have you pulled codes maybe another sensor is bad like tps or iac

 

No codes, only thing that looks slightly out of whack are the LFtrim values. The ignition system is all brand new from the TFI module to the plugs. I tired spraying it no real reaction. The rough idle is only half the problem, the main problem is the detonation. Even with 20degrees of retard it will not terminate the knock.
Brian

 

and your sure that your timing hasnt slipped. what octane are you running? have you looked at the plugs? what color are they?
also how many o2 sensors do you have ?

 

Ok I relunctantly put this thing on a dyno today, with air/fuel metering, the problem is fuel rail pressure is dropping out on the unit under load, and it is going way lean very early, looks like it might be time for a high output in tank pump. I have traced the rough idle to a vacuum leak at the EGR valve. now I am trying to get it to stop knocking. KB keeps saying their setup should work with a stock fuel pump and their FMU/Boost a pump. The dyno don't lie, boost a pump is maxed out 18 volt output, FMU is engaging, under 4psi boost, rail pressure jumps right up to 60psi, at sustained boost, fuel pressure starts dropping, and once it falls to about 40 under boost, engine knocks. A/F was about 14.4 during the test, way to lean for a s/c setup, Kb says it should be around 10.5-11.5.
Brian

 

could you have a bad injector possibly causing pressure loss? does your bko have a 2 pump system i know some did have one intank and one on the frame rail. ive heard the boost a pump not working after awhile from being over worked or possibly your intake pump is going out in general.