Base Timing Mode Woes - Falling Fuel Pressure
06-28-2004, 12:54 PM
#1
Guest
Posts: n/a
Base Timing Mode Woes - Falling Fuel Pressure
Falling Fuel Pressure - Gen. VI MAG EFI setup
I recently developed a problem on one of myGen. VI 502 MAG EFI motors. Last week, both motors started up just fine in the driveway before the first water test of the season. After a quick ride around the lake, I came back to the boat launch noticing that one engine was running at a rather high idle (1200 rpm).
The next day, I checked all the throttle linkage to make sure nothing was keeping the throttle body cracked opened. Nothing. Next, I checked all the vacuum fittings and ports for any major leaks. Nadda. Finally, I made an attempt to set the base timing thinking that the timing might be too far advance.
This is where things get weird…
I borrowed a MerCruiser diagnostics / service tool from a local marina. I scrolled through the menu's and selected the option that would allow me to set the base timing. What was supposed to happen, was engine rpm's increase to 1200 - 1300 rpm's and the timing to back down to a lesser value (20 - 30 degrees down to 5 - 8). What actually happened was… nothing! The engine behaved no differently. The scan tool was reading like it had successfully entered base timing mode, but nothing had changed.
I tried the second engine, and it's behavior was what I had expected: idled around 800 rpm, timing floating around between 15 and 25 degrees, base timing idle goes up to 1200 rpm's, timing stabilizes around 8 degrees. I am almost suspicious that the first (bad) engine was stuck in base timing mode. However, the high idle caused by base timing mode on the good engine was fluctuating more than the steady 1200 rpm idle of the bad engine.
Thinking something might have been jacked in the ECU, I switched the ECU's between the two engines. Nope, engine still had the same previous high idle.
The next problem I noticed was the falling fuel pressure. When I would first turn on the ignition, the fuel pressure gauge would read about 35 - 40 psi but then quickly drop to nothing once the (electric) fuel pump was shut off. When the engine was running, I had no problems maintaining fuel pressure (about 30 - 35 psi at idle) but the pressure was not holding on "primer" startup. The second (good) engine was holding pressure just fine. I could turn the ignition to ON, watch the fuel pressure build, hear the fuel pump shut off, then watch the fuel pressure stay steady at about 35 psi for minutes at a time.
What could be causing the fuel pressure to leak like that? That same day, I noticed (smelled) a fuel injector leaking gas. The entire upper intake manifold was removed (with blower, intercooler and 2100 CFM throttle body… uhg!) and I replaced a ripped up O-ring on one of the injectors that got damaged from the sharp painted edge of the fuel rail. Once I put the fuel rail back into place, I checked for any new leaks and found everything to be sealing tight. However, the fuel pressure still wasn't holding.
Next, I disconnected all the fuel injector to make sure the ECU wasn't holding one of the injectors open. Nope, pressure still dropping faster than the panties on the prom queen.
At this point, I threw a few tools across the yard, said some colorful words, went inside and pounded a few beers. I am stumped, I have no clue! I have a sneaking feeling that the fuel pressure leak is coming from the regulator somewhere, but I'm not 100% convinced yet. Also, would this be the source of my high idle speed? I don't see why it would be!!!
Please help, I'm very tired, very frustrated, and very broke… all from working on this project.
-B
I recently developed a problem on one of myGen. VI 502 MAG EFI motors. Last week, both motors started up just fine in the driveway before the first water test of the season. After a quick ride around the lake, I came back to the boat launch noticing that one engine was running at a rather high idle (1200 rpm).
The next day, I checked all the throttle linkage to make sure nothing was keeping the throttle body cracked opened. Nothing. Next, I checked all the vacuum fittings and ports for any major leaks. Nadda. Finally, I made an attempt to set the base timing thinking that the timing might be too far advance.
This is where things get weird…
I borrowed a MerCruiser diagnostics / service tool from a local marina. I scrolled through the menu's and selected the option that would allow me to set the base timing. What was supposed to happen, was engine rpm's increase to 1200 - 1300 rpm's and the timing to back down to a lesser value (20 - 30 degrees down to 5 - 8). What actually happened was… nothing! The engine behaved no differently. The scan tool was reading like it had successfully entered base timing mode, but nothing had changed.
I tried the second engine, and it's behavior was what I had expected: idled around 800 rpm, timing floating around between 15 and 25 degrees, base timing idle goes up to 1200 rpm's, timing stabilizes around 8 degrees. I am almost suspicious that the first (bad) engine was stuck in base timing mode. However, the high idle caused by base timing mode on the good engine was fluctuating more than the steady 1200 rpm idle of the bad engine.
Thinking something might have been jacked in the ECU, I switched the ECU's between the two engines. Nope, engine still had the same previous high idle.
The next problem I noticed was the falling fuel pressure. When I would first turn on the ignition, the fuel pressure gauge would read about 35 - 40 psi but then quickly drop to nothing once the (electric) fuel pump was shut off. When the engine was running, I had no problems maintaining fuel pressure (about 30 - 35 psi at idle) but the pressure was not holding on "primer" startup. The second (good) engine was holding pressure just fine. I could turn the ignition to ON, watch the fuel pressure build, hear the fuel pump shut off, then watch the fuel pressure stay steady at about 35 psi for minutes at a time.
What could be causing the fuel pressure to leak like that? That same day, I noticed (smelled) a fuel injector leaking gas. The entire upper intake manifold was removed (with blower, intercooler and 2100 CFM throttle body… uhg!) and I replaced a ripped up O-ring on one of the injectors that got damaged from the sharp painted edge of the fuel rail. Once I put the fuel rail back into place, I checked for any new leaks and found everything to be sealing tight. However, the fuel pressure still wasn't holding.
Next, I disconnected all the fuel injector to make sure the ECU wasn't holding one of the injectors open. Nope, pressure still dropping faster than the panties on the prom queen.
At this point, I threw a few tools across the yard, said some colorful words, went inside and pounded a few beers. I am stumped, I have no clue! I have a sneaking feeling that the fuel pressure leak is coming from the regulator somewhere, but I'm not 100% convinced yet. Also, would this be the source of my high idle speed? I don't see why it would be!!!
Please help, I'm very tired, very frustrated, and very broke… all from working on this project.
-B
Platinum Member
06-28-2004, 03:11 PM
#5
Guest
Posts: n/a
Re: Base Timing Mode Woes - Falling Fuel Pressure
I checked the IAC, and it appears to be working. I did a "reset" IAC from the scan tool and it kills the engine, like I had expected. However, I can't think of anything else that would modify the idle quite so much. 800 rpm to 1200 rpm is a HUGE jump. I have a difficult time believing a simple vacuum leak could do that. He||, even when I unplug the vacuum line behind the throttle body for the PCV hose, it only raises the idle 50 - 100 rpm's.
Might try swapping out the IAC's next weekend and seeing if that makes a difference. Anyoen got a P/N or perhaps an automotive alternative (i.e. CHEAPER than Merc's)?
Kanook, I got the post... working on a response myself.
Might try swapping out the IAC's next weekend and seeing if that makes a difference. Anyoen got a P/N or perhaps an automotive alternative (i.e. CHEAPER than Merc's)?
Kanook, I got the post... working on a response myself.
