scooby94

I have a 96 454 Mag efi, that is giving me a code 33. I had replaced the map sensor, cleared the code, and the code still comes back. I have checked all the wiring, and appears to be ok. I also have about 29-30psi at idle and about 32psi at 4000 rpm. Specs is showing me 34-36psi. I disconnected the pressure regulator at idle and it is pushing out 36psi when I do that. All the plugs are black, except for #7, it is half black and half clean. I have check the VST it seems to be ok. Has anyone had this problem before or any ideas of what is could be. I don't have a scan tool and everyone around me has about a two week wait.

mats

The spec shows the fuel pressure with the vacuum hose disconnected so that seem to be OK. Code 33 is among other things triggered by low vacuum at idle. Are the throttle plates closing comletely or do you have some other vacuum leak? Have you checked the MAP output voltage at idle? Can be done with a DVOM.

Dave_N

Sounds like your fuel pressure is ok. What is the vacuum (or MAP) at idle?

Double check that VST. You mentioned that the #7 plug was "half clean". When the VST overflows it drains into the #7 intake runner. That plug may be washed clean from fuel. I think I would start by rebuilding the VST.

Dave

mats

Another thing to check is the wiring from the MAP sensor. If you have an open in the MAP signal it will run very rich. It will basically steam unburnt fuel from the exhaust. A scan tool would help a lot in understanding what inputs the the ECM gets. In lack of a scantool you could measure the MAP output signal on the ECM side of the MAP harness by piercing the insulation.

scooby94

I checked the map voltage drop at an idle, it is 2.45v at 12" of vacuum, and that's at about 600rpm. I did find two problems though, my sea water pump was leaking. So I rebuilt is and found that half of the impeller was missing. Upon doing that when I took off the mechanical fuel pump, I found that the diaphragm had let go and was leaking into the sea water pump oil reservoir. So I went to the auto parts store and matched one up, $55 compared to $140 from merc. I am going to put back together tonight. My other issue is I think the timing is too low. I tried checking it in service mode and the motor just died. But without it being jumpered it is about 8 degrees. The book says 8 degrees, but ain't that in service mode?

Dave_N

If your fuel pump was bad, you may have had fuel going into the vacuum line and up into the plenum, which would cause a rich condition. Did you check the clear yellow vacuum hoses for fuel?

As far as base timing goes, on all the MEFI1 systems, you have to raise the engine speed up to about 1600RPM before you drop it into service mode or, as you found out, it will die.

Just say NO to the automotive fuel pump

Dave

scooby94

What is the difference between the automotive fuel pump. I put it on last night and fired it up and my fuel pressure appears to be good and responsive. The vacuum line coming of the intake to the vst and fuel pump has little or almost no vacuum at idle. I have cleaned it out, and I can blow through it. I cleared the code 33 and it still came back on, that is still puzzling me. So from the amount of timing at idle NOT in service mode is 8 degrees, is that too low and should I try and bump the timing up?

Ted G

iTrader: (1)

An automotive fuel pump should not have the vent tube to attach the overflow line to(that runs up to the manifold) If it does, you're o.k. You cannot rely on timing out of service mode as the ecu will vary it constantly. You need to run it up and then put it in service mode or base will never be correct.

scooby94

I made sure that the pump had the vent tube on it. But I still have almost no vacuum on that hose. The same tube runs to the vst. If there is no vacuum on that line, will it affect the vst system. Or could that be caused by low timing. Because my map sensor is showing 2.45v at idle, which to me mean low vacuum. There is another vacuum line under the T.B. which plugs into were #2 cyl is and goes to behind the T.B. I can't see why it's there or what its' for. If I have too can I plug the VST and fuel pump vacuum hose into those ports.

mats

I am not sure I understand when you say that you have no vacuum on the hoses? Do they leak?. 2.45 V at idle is not unusual and should not trigger code 33. It would be good to check the base timing, if nothing else just to put that to the side.